Symposium Organizers
Dinesh Katti, North Dakota State University
Christian Hellmich, TU Wien - Vienna University of Technology
Ko Okumura, Ochanomizu University
Peter Pivonka, University of Melbourne
BM01.01: Session I
Session Chairs
Christian Hellmich
Dinesh Katti
Kalpana Katti
Monday PM, November 27, 2017
Sheraton, 2nd Floor, Constitution B
8:30 AM - *BM01.01.01
Cell Biomechanics and Human Diseases—Multiscale Experiments and Computations
Subra Suresh 1 , Ming Dao 2
1 , Nanyang Technological University, Singapore Singapore, 2 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractIn this presentation, we provide experimental results coupled with multi-scale computational simulations of the connections between the mechanobiology of cells and human diseases. In particular, we examine recent experimental findings of how alterations to the normal shape, size, biorheology, and mechanics of cells influence the onset and progression of human diseases. Single cell mechanobiology experiments integrated with optical, acoustic and microfluidic techniques of cell populations are used to establish connections between cell mechanics and pathological states of cells linked to human diseases, with examples shown for infectious diseases, hereditary blood disorders and different types of cancers. The presentation will also address the potential role of cell mechanics in facilitating better outcomes for disease diagnostics, therapeutics and drug efficacy assays.
9:00 AM - BM01.01.02
Tissue Engineering Approaches to Evaluate Prostate and Breast Cancer Metastasis to Bone
Kalpana Katti 1 , MD Shahjahan Molla 1 , Sumanta Kar 1 , Dinesh Katti 1
1 , North Dakota State University, Fargo, North Dakota, United States
Show AbstractCurrent literature indicates that tissue engineering shows much promise for regenerative medicine applications in particular for non-union bone defects. Bone is also a common site for colonization of cancer cells in metastasis stage from several primary site cancers including prostate and breast. Bone is the preferred site of metastasis for prostate cancer and approximately 80% deaths suffered by prostate cancer patients, occurred from skeletal metastases. Approximately 70% breast cancer patients also eventually develop bone metastasis. Drug treatments are often ineffective at this stage. In vitro studies on cancer primary designed to evaluate drug efficacies and targeting are done on 3D environments that can mimic the primary site of cancer but do not emulate the metastasis to bone, when drug treatments are ineffective. We have designed an engineered test-bed of bone metastasis through use of nanoclay-hydroxyapatite(HAP) based nanocomposite polycaprolactone (PCL) scaffolds through a unique sequential culture (SC) procedure. Human mesenchymal stem (hMSCs) cells are seeded onto these scaffolds and after generation of extracellular matrix and initiation of bone mineralization on the scaffolds, they are seeded with human prostate and breast cancer cells. Our experiments indicate that MSCs+cancer cells SC in PCL/ HAPClay scaffolds closely mimics early stage of osteoblastic cancer colonization by developing tight junction tumoroids and inducing mesenchymal to epithelial transition (MET). The gene expression data are indicative of inhibited EMT, enhanced MET, increased angiogenesis by hypoxia when cancer cells were sequentially cultured with MSCs in PCL/ HAPClay scaffolds. Nanomechanical experiments are conducted on the test-beds to study evolution of cancer mechanics. The MSCs+cancer cells SC in PCL/ HAPClay platform, could be used for studying cancer cell biology in the early stage cell colonization and metastasis and in vitro testing of anticancer drugs in a humanoid environment. Therefore, the SC based tumor model can be applied to recapitulate more consistent osteotropic cancer cell behavior in understanding tumor biology. This test-bed also can be implemented for drug screening and evaluations to target colonization stage of cancer cells in the bone microenvironment.
9:15 AM - BM01.01.03
Effect of Cytotoxicity of Ag Nanoparticles on Cytoskeletal Structure and Mechanical Behavior of Red Blood Cells
Kuan-Ting Chou 1 , Ruei-Yi Tsai 1 , Shou-Yi Chang 1
1 , National Tsing Hua University, Hsinchu Taiwan
Show AbstractNanoparticles (NPs, e.g. Ag) have been applied to biomedical fields for use as anti-bacteria products and drug carriers, etc. However, as the probability of human contact with NPs increases, the cytotoxicity of NPs and its effect on the morphology, structure and behavior of biological cells (e.g. red blood cells, RBCs) are of great importance to be investigated. Hence in this study, the morphology and cytoskeletal structure of RBCs under the influence of Ag NPs (50-200 μg/mL, for 0-24 h) were observed using a fluorescence microscope, a scanning electron microscope (SEM), a transmission electron microscope (TEM) and a biological atomic force microscope (Bio-AFM). The stiffness and deformation behavior of RBCs were characterized using micropippte aspiration, nanoindentation and Bio-AFM. The correlation between the change in cytoskeletal structure and the difference in mechanical behavior was examined. Ag NPs were found to cause an earlier hemolysis and a higher malondialdehyde concentration, and the Ag-NP-affected RBCs became echinocyte-like. Microscopic observations indicated that the endocytosis of NPs caused a non-uniform agglomeration of actin/spectrin, and that the size and crosslinking density of cytoskeleton increased. Compared to normal RBCs, the Ag-NP-affected RBCs had an increased elastic modulus, in either a fixed/dehydrated state measured by nanoindentation or a live state measured by Bio-AFM. The micropipette experiment revealed that the NP-affected RBCs exhibited a shorter aspiration length (under the same aspiration time), a longer aspiration time (to pass through the micropipette) and a higher elastic modulus. During aspiration, the actin in normal RBCs compliantly deformed, whereas the actin in Ag-NP-affected RBCs hardly moved. In summary, under the influence of Ag NPs, the stiffness of RBCs increases and the deformability decreases in consequence of cytoskeleton aggregation and thickening.
9:30 AM - *BM01.01.04
A Macro-Micro Modeling Approach to Determine In Situ Heart Valve Interstitial Cell Contractile Behaviors in Native and Synthetic Environments
Michael Sacks 1
1 , University of Texas at Austin, Austin, Texas, United States
Show AbstractMechanical forces are known to regulate valve interstitial cell (VIC) functional state by modulating their biosynthetic activity, translating to differences in tissue composition and structure, and potentially leading to valve dysfunction. VICs can change phenotype dynamically; in diseased valves VICs switch to a myofibroblast-like phenotype and become contractile. Activated VICs display prominent SMA stress fibers and an increase in ECM remodeling. Yet, while advances have been made toward the understanding of VIC behavior ex-situ, the VIC biomechanical state in its native extracellular matrix (ECM) remains largely unknown. We hypothesize that improved descriptions of VIC biomechanical state in-situ, obtained using a macro-micro modeling approach, will provide deeper insight into AVIC interactions with the surrounding ECM, revealing important changes resulting from pathological state, and possibly informing pharmaceutical therapies. To achieve this, a novel integrated numerical-experimental framework to estimate VIC mechanobiological state in-situ was developed. Flexural deformation of intact valve leaflets was used to quantify the effects of VIC stiffness and contraction at the tissue level. In addition to being a relevant deformation mode of the cardiac cycle, flexure is highly sensitive to layer-specific changes in VIC biomechanics. As a first step, a tissue-level bilayer model that accurately captures the bidirectional flexural response of AV intact layers was developed. Next, tissue micromorphology was incorporated in a macro-micro scale framework to simulate layer-specific VIC-ECM interactions. The macro-micro AV model enabled the estimation of changes in effective VIC stiffness and contraction in-situ that are otherwise grossly inaccessible through experimental approaches alone. While the use of native tissues provided much insight, we also utilized 3-D hydrogel encapsulation, which is an increasingly popular technique for studying VICs. Specifically, we employed poly(ethylene glycol) (PEG) gels to encapsulate VICs and study their mechanical response to the surrounding hydrogel stiffness and to varying levels of adhesion availability. Cell contraction was elicited through chemical treatments and the resulting mechanical properties of the constructs were measured through end-loading flexural deformation testing. We applied the downscale model, which was improved by 3D stress fiber visualization. The resulting cell force levels were comparable to native in-situ results. Overall, the developed numerical-experimental methodology can be used to obtain VIC properties in-situ. Most importantly, this approach can lead to further understanding of AVIC-ECM mechanical coupling under various pathophysiological conditions and the investigation of possible treatment strategies targeting the myofibroblast phenotype characteristic of early signs of valvular disease.
10:30 AM - *BM01.01.05
Tuning Mechanical Properties of Marine Biopolymers
Maneesh Gupta 1 , Patrick Dennis 1 , Rajesh Naik 1
1 , Air Force Research Laboratory, Wpafb, Ohio, United States
Show AbstractInvertebrate cutting and piercing structures are highlighted by their lightweight construction, robust mechanical properties, and novel hardening mechanisms. The mechanical properties of these structures often surpass those of synthetic polymers and can be comparable to mineralized composite tissues found in higher organisms, underscoring their potential as models for advanced polymer systems. Our group has in particular investigated proteins isolated from the jaw structures of the marine worm, Neries virens (Nvjp-1) and the giant squid sucker ring teeth assembly (suckerin-12). We have achieved gram scale expression and column-less purification of these proteins enabling investigation of the effects of hierarchical ion exposure on the structure and mechanical properties of these proteins.
With Nvjp-1, it was found that a hierarchical sequence of ion treatments was capable of modulating the mechanical properties of the hydrogels. The sequential exposure of Nvjp-1 hydrogels to certain anions and cations was found to yield dramatic increases (>100 fold) in elastic modulus through the formation of coordinate crosslinks with metal cations. While the metal cations played a central role in the formation of these dative crosslinks, the anions also were essential in enabling and modulating the coordinate interaction between the metal cation and the Nvjp-1 protein. As with Nvjp-1 hydrogels, exposure of the suckerin-12 hydrogels to salt solutions induced a significant increase in elastic modulus. Interestingly, the mechanical properties of the protein hydrogels were greatly dependent on the type of anion present in the salt. The differences observed in the mechanical properties of suckerin-12 hydrogels did not seem to be explained by changes in secondary structure or an increase in crystallinity, but correlated with the presence or absence of microstructures as measured by SEM. Therefore, the ability to dramatically tailor the mechanical properties of polymers through the incorporation of an ionic “dopant” allows for the potential to create structures and materials with graded and reconfigurable mechanical properties.
11:00 AM - BM01.01.06
Engineering Mechanics in Medicine and Biology—Muliscale Elastoplasticity and News on the Cement Line in Osteonal Bone
Christian Hellmich 1 , Viktoria Vass 1 , Claire Morin 2
1 , TU Wien - Vienna University of Technology, Vienna Austria, 2 , Ecole des Mines de Saint-Etienne, Saint-Etienne France
Show AbstractSince its advent in the 1960s, elastoplastic micromechanics has been confronted by
continuous challenges, as the classical incremental elastoplastic tangents are known to
deliver unrealistically stiff material responses. As a complement to the various “secant”
approximations targeting this challenge, we here develop a theoretical framework based
on an extension of Dvorak's transformation field analysis, comprising the derivation of
concentration and influence tensors. We thereby overcome the problem of actually nonhomogeneous
stress distributions across finite (often spherical) material phases, through
consideration of infinitely many (non-spherical) solid phases oriented in all space directions,
arriving at a micro-elastoplasticity theory of porous polycrystals. The resulting
governing equations are discretized in time and space, and then solved in the framework
of a new return mapping algorithm, the realization of which we exemplify by means of
Mohr-Coulomb plasticity at the solid phase level. The corresponding homogenized material
law is finally shown to satisfactorily represent the behavior of the porous hydroxyapatite
polycrystals making up the so-called cement lines in osteonal bone. This is
experimentally validated through strength and ultrasonic tests on hydroxyapatite, as well
as through mass density, light microscopy, chemical composition, and osteon pushout tests
on bone.
11:15 AM - BM01.01.07
Influence of the Mutation on Chemo-Mechanical properties of Osteogenesis Imperfecta Children Bones
Agathe Ogier 1 , Jean-Charles Aurégan 2 , Mathilde Doyard 4 , Caroline Michot 3 4 , Perrine Brunnelle 3 , Zagorka Pejin-Arroyo 2 , Thierry Hoc 1
1 , Ecole Centrale de Lyon- LTDS, Ecully France, 2 Département d'Orthopédie, Hôpital Necker Enfants Malades AP-HP, Paris France, 4 Imagine - Institut des maladies génétiques, INSERM UMR 1163, Paris France, 3 Laboratoire de Génétique Moléculaire, Hôpital Necker Enfants-Malades AP-HP, Paris France
Show AbstractBone mechanical properties are mainly due to its composite microstructre composed by mineral and collagen, enabeling bone to endure repetitive shocks. Nevertheless, an impaired bone metabolism often leads to weaker mechanical properties. For example, a deficient collagen production, associated with gene mutations involved osteogenesis imperfecta (OI)1, and bone becomes more prone to fracture2. The aim of this study was to investigate the consequences of those different mutations on chemo-mechanical properties, as they are diminished in cases of OI compared to healthy bones3.
Bone specimens were collected at Necker hospital from pediatric patient suffering from OI, and from healthy children (CT). Clinically, the OI children were diagnosed as OI type III, ie severe but not lethal OI. Genetically, the mutations causing clinical OI type III were classified as types VI, VII, VIII, XI or direct mutations of the gene COL1A1 or COL1A2. Small bones samples from several patients were cut and polished. Porosity was calculated with a nano-scanner device. Mechanical properties (Young’s modulus, hardness) of bone tissue were assessed using nano-indentation technique. In parallel the chemical properties were obtained with Raman spectroscopy, giving crystal and collagen quality.
Comparison between OI and CT samples emphasizes significantly higher porosity, lower Young’s modulus and crystallinity3. However, genetic types VI and XI of OI bones for the same clinical type III show clear differences. For type VI, a Young’s modulus close to CT was observed, correlated in the same time with a significantly higher mineral to matrix ratio4. For type XI, the carbonate to phosphate substitution ratio was significantly increased in OI type XI compared to CT and other OI genetic types, which can be linked to inefficient remodeling due to impaired osteoblasts producing defective collagen chaperone5.
To conclude, for the same clinical grade genetic type affects different microstructure compounds opening the ability to adapt treatment for each patient.
1. Kang, H., Aryal A.C., S. & Marini, J. C. Transl. Res.181,27-48 (2016).
2. Imbert, L., Aurégan, J.-C., Pernelle, K. & Hoc, T. J. Mech. Behav. Biomed. Mater. 46, 261–270 (2015).
3. Imbert, L., Auregan, J. C., Pernelle, K. & Hoc, T. Bone 65, 18–24 (2014).
4. Bogan, R. et al.. J. Bone Miner. Res. 28, 1531–1536 (2013).
5. Barnes, A. M. et al.. Hum. Mutat. 33, 1589–1598 (2012).
11:30 AM - BM01.01.08
A Structural-Based Computational Model of Tendon-to-Bone Insertion
Sergey Kuznetsov 1 , Shadow Huang 1
1 Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractTendon-to-bone insertion provides a gradual transition from soft tendon to hard bone tissue, functioning to alleviate stress concentration at the junction of these tissues [1]. Specifically, dense and highly aligned collagen fibers are characteristics of the tendon side of the junction, and a high density of the mineral hydroxyapatite with randomly distributed collagen fibers are characteristics at the bone side. Inhomogeneity and discontinuities in tissue-level properties at the insertion manifest in the unique, stress concentration-reducing material behavior at the macro-scale level. Tendon-to-bone insertions may be considered as functionally-graded connective tissues whose anisotropic biomechanical functions depend intimately on the regional biochemical composition and microstructure [2].
To better understand how tendon-to-bone insertion performs, we developed a structural-based computational model of tendon-to-bone insertion using ABAQUS. We adopted Gasser-Ogden-Holzapfel hyperelastic model [3] to describe spatial gradations of mineralization, collagen fibers preferred orientations, and directional collagen fiber dispersions. We started from in-silico elastic model mimicking in-situ biaxial tension test and used our experimental data of porcine attachment site to identify material parameters. Importantly, the specimen is explicitly assumed to be inhomogeneous. A python script was developed to introduce structural grading of preferred fiber orientation which may be rather complex as experiments suggested from our Fast Fourier Transform analyses. A linear interpolation of collagen fiber dispersion was first used to describe the graded material property within the insertion region. A linear variation of mineralization level is also confirmed by our previous Time-of-flight secondary ion mass spectrometry analyses.
Stress distributions are obtained and compared for spatially graded and various piece-wise materials properties. It was observed that spatial grading results in more smooth stress distributions and significantly reduces maximum stresses. The geometry of the tissue model could be optimized by minimizing the peak stress to mimic in-vivo tissue remodeling. This model will be useful for understanding how tendon-to-bone insertion functions and may be also useful for surgical interventions and developing orthopedic implants.
References
[1] Y. Liu et al, Mechanisms of Bimaterial Attachment at the Interface of Tendon to Bone (2011), J. Eng. Mater. Technol., Vol.133, 011006
[2] G. M. Genin et al, Functional Grading of Mineral and Collagen in the Attachment of Tendon to Bone (2009), Biophysical Journal, Vol.97, 976-986
[3] T. C. Gasser et al, Hyperelastic Modeling of Arterial Layers with Distributed Collagen Fibre Orientations (2006), J. R. Soc. Interface, Vol.3, 15-35
11:45 AM - BM01.01.09
Structural, Tribological, and Mechanical Properties of the Hind Leg Joint of a Jumping Insect—Using Katydids to Inform Bioinspired Lubrication Systems
Jun Kyun Oh 1 , Mustafa Akbulut 1
1 , Texas A&M University, College Station, Texas, United States
Show AbstractThis study investigates the structural properties of the hind leg femur-tibia joint in adult katydids (Orthoptera: Tettigoniidae), including its tribological and mechanical properties. It is of particular interest because the orthopteran (e.g., grasshoppers, crickets, and katydids) hind leg is highly specialized for jumping. We show that the katydid hind leg femur-tibia joint had unique surfaces and textures, with a friction coefficient (μ) at its coupling surface of 0.053 ± 0.001. Importantly, the sheared surfaces at this joint showed no sign of wear or damage, even though it had undergone thousands of external shearing cycles. We attribute its resiliency to a synergistic interaction between the hierarchical surface texture/pattern on the femoral surfaces, a nanograded internal nanostructure of articulating joints, and the presence of lubricating lipids on the surface at the joint interface. The micro/nanopatterned surface of the katydid hind leg femur-tibia joint enables a reduction in the total contact area, and this significantly reduces the adhesive forces between the coupling surfaces. In our katydids, the femur and tibia joint surfaces had a maximum effective elastic modulus (Eeff) value of 2.6 GPa and 3.9 GPa, respectively. Presumably, the decreased adhesion through the reduction of van der Waals forces prevented adhesive wear, while the contact between the softer textured surface and harder smooth surface avoided abrasive wear. The results from our bioinspired study offer valuable insights that can inform the development of innovative coatings and lubrication systems that are both energy efficient and durable.
BM01.02: Session II
Session Chairs
Christian Hellmich
Dinesh Katti
Kalpana Katti
Ulrike Wegst
Monday PM, November 27, 2017
Sheraton, 2nd Floor, Constitution B
2:00 PM - BM01.02.02
3D Printed Polyurethane Nanocomposite and Biocompatible Materials and Their Thermo-Mechanical Properties
Rigoberto Advincula 1
1 , Case Western Reserve University, Cleveland, Ohio, United States
Show AbstractThe application of thermoplastic polyurethanes (TPUs) in a number of biomedical device applications has multiplied through the years with its excellent hard-soft segment macromolecular composition control and the ability to prepare various injection molded and thermo-formed processing shapes. This means that their thermo-mechanical properties can be tuned towards more mechanically compatible properties to the human body including elastomeric properties. Hence they have been used in a number of prosthesis devices including artificial nose, ear, breast implants, etc. 3D printing is emerging to be an alternative for additive manufacturing with its rapid-prototyping advantage and the ability to incorporated new polymer and nanocomposite in processing methods such as fused deposition modeling (FDM), stereo lithographic apparatus (SLA) and viscous solution printing (VSP). It should be a viable method for the limited and specific production of biomedical devices that is fit for personalized medicine. This talk will highlight our work on 3D printed TPU to form basic structures with compositions of thermoplastic Polurethanes/polylactic acid/ graphene oxide or TPU/PLA/GO. Structure property relationships correlated with the formation of improved modulus and flexural strength with increasing amounts of GO. Exposure to mammalian cells showed proliferation consistent with non-toxic behavior making them suitable for implant devices.
2:15 PM - BM01.02.03
Three-Dimensional Computational Model of Self-Reinforcing Polymer Gels Containing Biomimetic Cryptic Bonds
Santidan Biswas 1 , Victor Yashin 1 , Anna Balazs 1
1 , University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractWe utilize the gel lattice-spring approach to develop the 3D computational model of polymer gels that become stronger and tougher in response to a mechanical deformation. The polymer chains are assumed to incorporate the folded domains that encompass the reactive functional groups (cryptic sites). Under deformation, the domains unfold and expose the cryptic sites, which can then form labile bonds with the linker chains grafted to the network. Once the deformation is removed, the linkers detach from the cryptic sites, and unfolded domains go back to the folded configuration thus hiding the cryptic sites. The gel behavior under applied force is described by the equations of elasticity of the polymer network coupled to the kinetic equations for the folding and binding transitions. The model equations take into account the effects of finite chain extensibility on the gel elasticity and mechanosensitive reaction rates. Elasticity of the transient network is described using Flory’s model. We demonstrate that by patterned placement of gel elements containing polymer loops, a desired shape transformation can be induced in the gel. These shape changes are reversible and once the stimulus (temperature or applied force) is removed, the gel recovers its initial configuration. The developed 3D computational model could be used for designing novel polymer gel-based materials that exhibit self-strengthening under deformation.
2:30 PM - BM01.02.04
Fluidic Non-Hydrogel Scaffolds for Cell Aggregates Formation
Masashi Maruyama 1 , Yasuhiko Tada 1
1 , Hitachi Ltd, Hitachi Japan
Show AbstractSoft materials scaffolds attract great attentions in mechanobiology. Among soft materials, fluidic materials are expected to offer unique effects deriving from the high movability of the scaffold. However, they are far less studied compared with conventional hydrogels because of the difficulties in the scaffold preparation. In this study, we developed a simple and facile strategy for fabrication of fluidic scaffolds and spontaneous cell aggregation on fluidic scaffolds was investigated aiming at formation of functional organoids. In order for realization of fluidic scaffolds suitable for spontaneous cell aggregation, fluidic materials must be stable under culture conditions and have appropriate viscosity. However, because the densities of fluidic materials are very often smaller than that of water, preparation of stable fluidic scaffolds against the buoyant forces and surface tensions has been quite limited. Thus, we developed thin-layer fluidic scaffolds with engineered surface energy to reduce the influences from buoyant force and surface tension. Culture of hMSCs on the thin-layer fluidic scaffolds was demonstrated and spontaneous cell aggregation accompanying slides of the fluidic layers was observed for scaffolds with appropriate viscosity. The details of scaffold preparation, cell culture, and potential applications will be discussed in the presentation.
2:45 PM - BM01.02.05
Interfacial Shear Strength and Adhesive Behavior of Layer-by-Layer (LbL) Silk Ionomer Microcapsules
Sunghan Kim 1 , Ren Geryak 1 , Shuaidi Zhang 1 , Ruilong MA 1 , Rossella Calabrese 2 , David Kaplan 2 , Vladimir Tsukruk 1 , Volodymyr Korolovych 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States, 2 , Tufts University, Medford, Massachusetts, United States
Show AbstractThe interfacial interaction between adjacent layers is a critical property to determine the robustness of layered structures. The interfacial shear strength between two different layers, specifically, in layered structure-based microcapsules is a critical mechanical property, which should be determined for ensuring the robustness of microcapsules. In order to prevent unexpected interfacial failure of layer-by-layer (LbL) fabricated microcapsules, the interfacial shear strength of layered structures must be characterized. In this work, the interfacial shear strength of silk fibroin (SF)-poly-L-glutamic acid (Glu)/ SF- poly-L-lysine (Lys) and SF-Glu/SF-Lys[poly(ethylene glycol) (PEG)] have been investigated by analysis of friction behavior between silk ionomers through an atomic force microscopy (AFM) based sliding test using functionalized AFM tips. The interfacial shear strength of silk ionomers determined in nanoscale with a functionalized sharp AFM tip is close to the interfacial shear strength determined in microscale with a functionalized colloidal AFM tip. Results show that both approaches have the consistency for analyzing the interfacial shear strength of silk ionomers at different spatial scales of contact mechanics. We found that chemical bonding interactions and surface morphology are critical factors to determine interfacial shear strength of silk ionomers. This work proposes a critical approach to understand the transfer of shear load between adjoining surfaces, and provides a better mechanical model governed by molecular interactions to design mechanically robust and durable microcapsules based on layered structure.
3:30 PM - *BM01.02.06
Freeze Casting, a Review—Structure-Property-Processing Correlations of Self-Assembled Polymers, Ceramics, Metals and Hybrid Materials with Complex, Hierarchical Architectures from the Nano- to the Macroscale
Ulrike Wegst 1
1 , Dartmouth College, Hanover, New Hampshire, United States
Show AbstractThe skilled use of biological materials and their striking mechanical efficiency, such as unique combinations of strength and toughness, have played a key role in the development of mankind and technology, and the course of history. The considerable advantage that we have over our ancestors, today, is that we cannot only successfully apply and use biological materials in their "native" state, but that we have tools to investigate and test them at almost all levels of their structural hierarchy to identify structure-property correlations and principles of function and optimization. Important challenges that persist are both the design of synthetic materials that mimic the performance-defining features of their natural counterparts and their fabrication in bulk with a fast and easy production process. One manufacturing process that shows promise is freeze casting, the directional solidification of water-based solutions and slurries; it offers a relatively fast route for self-assembled structures with complex architectures, whose hierarchical structures span dimensions from the nano- to the macroscale. Reviewed in this presentation will be common design motifs and the mechanical performance of a range of natural structural materials, resulting design requirements for biomaterials, and opportunities and challenges associated with the freeze casting process and its application to the large range of polymer, ceramic, metal and hybrid materials that can be manufactured with it to mimic the attractive structural and mechanical characteristics of their natural counterparts. Described will be the different mechanisms that drive structure formation during processing by directional solidification and how these can be employed in the material’s structural and property optimization for applications that range from tissue scaffolds to energy generation and storage.
4:00 PM - BM01.02.07
Measuring Viscoelastic Mechanical Properties of Highly Compliant Materials by Impact Indentation
Aleksandar Mijailovic 1 , Bo Qing 1 , Daniel Fortunato 2 , Krystyn Van Vliet 1
1 , Massachusetts Institute of Technology, Newton, Massachusetts, United States, 2 , Harvard University, Cambridge, Massachusetts, United States
Show Abstract
As material stiffness decreases, precise and accurate measurement of viscoelastic properties becomes increasingly difficult, often due to inaccurate contact detection between sample and probe surfaces. Impact indentation is an experimental technique based on instrumented indentation that can overcome these challenges, and measures viscoelastic response of highly compliant materials with the advantage of accurate contact detection and improved temporal resolution. We present a novel method grounded in analytic contact mechanics to analyze the data from such experiments, providing facile measurement of viscoelastic moduli and relaxation time constants of the material that are typically reported via oscillatory shear rheometry, creep compliance, or stress relaxation. We validate the applied theory against shear rheology experiments using compliant polydimethylsiloxane (PDMS) with shear relaxation moduli ranging 102 - 104 Pa. Using a standard linear solid material model, we find good agreement of viscoelastic moduli and relaxation time between rheology and impact indentation measurements. Next, we demonstrate applicability for fully hydrated biological soft tissues including murine heart and liver and porcine brain, reporting instantaneous and relaxation shear moduli and relaxation time. This new yet straightforward method offers the potential to measure local viscoelastic mechanical properties with millimeter scale spatial resolution, minimizing complications due to sample geometric constraints and inaccuracies of contact detection otherwise limiting mechanical characterization of soft tissues and engineered scaffolds.
4:15 PM - BM01.02.08
Promoting Proliferation and Elongation of Bone Marrow-Derived Stem Cells via Nano-Grain Deposited Periodic Nanostructures
Mayuko Shiozawa 1 , Yousuke Akiba 2 , Katsumi Uoshima 3 2 , Kaori Eguchi 2 , Hiroyuki Kuwae 1 , Weixin Fu 1 , Shuichi Shoji 1 , Jun Mizuno 1
1 , Waseda University, Tokyo Japan, 2 , Niigata University Medical and Dental Hospital, Niigata Japan, 3 , Graduate School of Medical and Dental Sciences, Niigata, Niigata, Japan
Show AbstractTi nano-grains deposited periodic nanostructure was confirmed to promote bone marrow-derived stem cells (BMSCs) proliferation and elongation. BMSCs on nanoscale line and space (L&S) patterned substrates with rough-grained surface were remarkably elongated in the direction of lines. Furthermore, cell proliferation amount on the substrate with rough-grained surface was about twice of that with fine-grained surface. These results provide a great step for understanding into mechanism of osseointegration.
Osseointegration is a phenomenon that bone and implant connect directly on nanoscale. A lack of osseointegration leads to bacterial growth which causes inflammation around implant. In order to ensure sufficient osseointegration, a better understanding of mechanism is required. Previous studies indicated implants with microstructures enhanced bone formation [1]. Nanotopography on flat substrate such as nanoscale grains and porous was reported to affect cell responses[2]. However, effects of nanotopography on nanostructure in cell responses were unclarified. In this work, we studied BMSCs culture on a Ti nano-grains deposited nanoscale L&S structure. The studied structure was expected to promote BMSCs proliferation and elongation, and thus help further clarify the mechanism. Furthermore, it is the first time that periodic nanostructures are applied in BMSCs culture to the best of our knowledge.
The deposited nano-grains material was Ti which has been widely applied as artificial tooth roots. 100 nm/100 nm L&S patterned substrates with rough-grained (grain size: 30~100 nm) and fine-grained (grain size: less than 1 nm) surfaces were designed to culture BMSCs. The substrates were fabricated by nanoimprint lithography, etching and Ti deposition. Scanning electron microscope observation showed that the substrates with rough-grained and fine-grained surfaces were successfully fabricated. BMSCs were cultured on the substrates for evaluations of cell proliferation amount and the states of cell elongation. Optical microscope observation showed cell proliferation amounts per 1 after 1-day-culture, 19 cells proliferated on the substrate with rough-grained surface while 16 cells proliferated on the substrate with fine-grained surface. Those after 3-day-culture, 199 cells proliferated on the substrate with rough-grained surface while 98 cells proliferated on the substrate with fine-grained surface. Live imaging and optical microscope observation showed almost all BMSCs on the substrates with rough-grained surface elongated in L&S direction. On the other hand, almost all BMSCs on the substrates with fine-grained surface elongated in random direction. Ti nano-grains deposited L&S nanostructure promotes BMSC proliferation and elongation. The results have considerable potential for understanding mechanism of osseointegration.
[1] Steven E., et al. ORALMAXILLOFACIAL IMPLANTS. 30, 754-760(2015)
[2] Cristian Covarrubias, et al. Appl.Surf.Sci. 363, 286-295(2016)
4:30 PM - BM01.02.09
Understanding Artificial Touch—Modeling Friction for a Novel Classification of Surfaces in Haptic Devices
Charles Dhong 1 , Cody Carpenter 1 , Darren Lipomi 1
1 , University of California, San Diego, La Jolla, California, United States
Show AbstractWe have found that human subjects can differentiate between two silicon wafers that differ in surface energy alone. The two types of silicon wafers were coated with a hydrophobic, low surface energy silane and the other was exposed to a plasma treatment, which created a hydrophilic, high surface energy surface. Despite their differences in friction coefficients, we do not always observe in our experiments that the hydrophilic and hydrophobic surfaces would generate differentiable forces. We explain the frictional basis for haptic discrimination of surfaces by sliding a patterned, PDMS-elastomer block and measuring the force as it slides on the different surfaces and mathematically modeling this interaction using an elastic rate-and-state friction model. We present these results in terms of a novel “discriminability matrix” which highlights conditions under which the high-energy surface and low energy-surface would exhibit frictional differences. The rate-and-state model recreates Schallamach waves and suggests spatiotemporal regions of compression and tension on the finger, which could be a novel and relevant method to categorize surfaces for human perception.
4:45 PM - BM01.02.10
The Investigation of Bacteria—Hydrogel Interactions During Different Mechanical Stimuli
Nehir Kandemir 1 , Waldemar Vollmer 2 , Nicholas Jakubovics 3 , Jinju Chen 1
1 School of Mechanical and Systems Engineering, Newcastle University, Newcastle upon Tyne United Kingdom, 2 The Centre for Bacterial Cell Biology, Newcastle University, Newcastle upon Tyne United Kingdom, 3 School of Dental Sciences, Newcastle University, Newcastle upon Tyne United Kingdom
Show AbstractThere has been a higher demand for implants and medical devices due to increased life expectancy. Although some of the inserted implants or medical devices coated with polymeric hydrogels showed no complications after insertion, a part of them can get severely affected by biofilm associated infections which can lead to complete implant removal. The use of antibiotics to treat the infections can provide a short-term solution but it also increases the possibility of antibiotic resistance which is a current and emerging problem. Therefore, to avoid the need of antibiotics in such cases and to inhibit bacteria growth in hydrogels, the relationship between the bacteria and their growth microenvironment must be characterised. This study aims to investigate how physical factors (i.e. stiffness) and chemical factors (i.e. chemical composition of growth environment) would affect bacteria-hydrogel interactions and bacteria cell mechanics. A combined experimental, numerical and a theoretical approach is adopted to extract the mechanical properties of Escherichia coli and Staphylococcus epidermidis embedded in various concentrations of hydrogels prepared with different bacteria growth media consisting of different nutrients, and a buffer. Various mechanical property characterisation techniques including rheology and compression tests have been employed to study how the materials encapsulated with cells behave subjected to different types of loading. This study has revealed that bacteria cells may decrease or enhance the mechanical integrity of hydrogels depending on the nutrients supplied and the loading type. These findings will contribute to the understanding of cell-materials interactions.
BM01.03: Poster Session
Session Chairs
Christian Hellmich
Dinesh Katti
Tuesday AM, November 28, 2017
Hynes, Level 1, Hall B
8:00 PM - BM01.03.02
Effects of Misfit Strain on Energy States of Zinc-Blende Spherical Core/Shell Quantum Dots
Youjung Seo 1 , Y. Eugene Pak 1 , Dhaneshwar Mishra 1 , S.-H Park 2
1 , Advanced Institutes of Convergence Technology, Suwon Korea (the Republic of), 2 Electronic and Electrical Engineering, Catholic University of Daegu, Gyeongsan-si Korea (the Republic of)
Show AbstractStudies on core/shell heterostructured QDs have reported the enhanced optical properties for intensified optical functions such as enhanced photoluminiscence (PL) and luminescence quantum efficiency (QE). These properties can be altered by changing the core/shell lattice and physical dimensions which leads to mechanical strains in the heterostructure. Lattice distortions induced by the structural lattice mismatch between the core and the shell give rise to an internal potential effect. This leads to a shift of the conduction and valence subband energies in QD core/shell assembly by changing the interatomic distances, which alters the energy levels of the bonding electrons.
As a result, QD core/shell nanostructure can exhibit a large change in the emission properties because of the instrinsic strain fields. However, quantifying the strain effects that depend on the shell thickness as well as the lattice mismatch between the core and the shell have not yet been theoretically analyzed in detail.
In this work, we developed the spherically-symmetric analytical model incorporating deformation potentials in the Hamilitonian to quantify the effects of strain on the binding energy of light exciton confined in type I II-VI group semiconductors with spherical QDs core/shell structure. To calculate the conduction, valence subbands and the ground-state energies to obtaine the binding energy that includes the strain effects in QD core/shell, we used 1s hydrogenic like wavefunctions the variational method and the effective-mass approximation (EMA). Parametric studies on the ground-state subband and binding energies considering the variations in the hydrostatic strains are also presented. Here, we used the finite confinement potentials taking into account the parameters such as the QD radius and the shell thickness. Since the strains used in the analysis take into account of both QD size and shell thickness, this work can be useful in designing functional improvements by optimizing the geometries of the QD nanostructure.
8:00 PM - BM01.03.03
Computational Study of Selective Adsorption of Peptides on MoS2 Surface with Biomining Applications
Maral Aminpour 1 2 , Sibel Cetinel 1 2 , Niloofar Nayebi 1 2 , Carlo Montemagno 1 2 3
1 Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada, 2 , Ingenuity Lab, Edmonton, Alberta, Canada, 3 , National Institute of Nanotechnology, Edmonton, Alberta, Canada
Show AbstractOne of the most pressing challenges of our time is the extraction and recycling of valuable rare metals from mixtures in mines and consumer wastes in a more cost-effective and environmentally friendly way. In this study, we aimed to separate out valuable rare metals from the mixtures by designing the peptides with specific recognition ability to bind to individual metals as smart biomaterials. Phage display combinational technology is used to engineer materials by selecting a highly competitive peptide binder among a population of billions. The positive output of our experimental work motivated us to investigate and study the microscopic mechanism of binding of experimentally selected adhesion peptides on MoS2 surfaces by means of molecular dynamics (MD) calculations, paving the way to engineering peptide sequences with enhanced affinity to a given surface. For each surface-peptide combination, peptide interactions with the surface, peptide conformations in solution, binding geometrics and adsorption energy on the basis of NPT and NVT calculations will be calculated. The analysis involves the visual inspection of molecular conformations over the entire simulation time and the distance of individual residues of the peptides from the surface. To our knowledge, the presented work reveals for the first time the interactions of the peptide with Molybdenum disulfide surface and can play an important role to gain insight in to the interaction mechanism between peptide and the surface to finely tune the biomolecule specificity toward a desired binder.
8:00 PM - BM01.03.04
Towards Plant-Inspired Tactile Sensors—Biomechanics of the Tactile Blep
Afroditi Astreinidi Blandin 1 2 , Massimo Totaro 1 , Irene Bernardeschi 1 , Jurgen Engelberth 3 , Lucia Beccai 1
1 Center for Micro-BioRobotics, Istituto Italiano di Tecnologia, Pontedera, Pisa, Italy, 2 The BioRobotics, Scuola Superiore Sant'Anna, Pontedera, Pisa, Italy, 3 Department of Biology, University of Texas, San Antonio, Texas, United States
Show AbstractAt first sight, plants might seem simple compared to other organisms like humans or animals. If so, how do they manage to survive and achieve a complexity of tasks with a simple system level structure? And if they are not so simple, are there complex organizations, even organs still undiscovered? In both cases, we have a lot to learn from them [1]. One of their astonishing capabilities involves the perception of mechanical stimuli, namely ‘mechanoperception’ [2], also through specialized sensory organs like in the case of the Dionaea muscipula trigger hairs [3].
Intriguing protruding hemispherical structures have been reported on the surface of some plants [4–6]. In Pisum sativum they are present in all phases of the tendril development [7]. The tactile bleps of Bryonia dioica Jacq. tendrils are even hypothesized to be one of the specialized sensory organs. Another hypothesis is that they display augmented shear force sensitivity with respect to normal force.
Their architectural model is surprisingly complex [4]. Different components can be observed, each one presenting a particular shape. In addition, the materials involved span over a wide range of elastic moduli. Among others, the blep is composed by a soft inner cytoplasm (in the Pa range), surrounded by a callose (in the kPa range) and a cellulose (in the MPa range) ring, and the outer cell wall (in the GPa range). Inspired by that, we have previously modeled a soft bio-inspired artificial dome-shaped bilayer structure, which demonstrates tunable shear and normal sensitivity under different mechanical conditions and structural compositions [8].
The aim of our work is to investigate the mechanical behavior of the natural blep structure. We aspire at shedding light on the factors influencing its mechanical behavior (i.e. geometry, material properties), and at testing the hypothesis of an augmented sensitivity to shear force. To this purpose, 2D and 3D finite element analyses are performed with COMSOL Multiphysics®, in particular subjecting the model to side and normal force to evaluate stress distributions and deformations. Finally, following a biomimetic approach we extract working principles for a new generation of plant-inspired tactile sensors.
References
1. Mazzolai, B. et al.; Front. Bioeng. Biotechnol. 2014, 2, 2.
2. Monshausen, G.B. et al.; J. Exp. Bot. 2013, 64, 4663–4680.
3. Guo, Q. et al.; J. R. Soc. Interface. 2015, 12, 20150598.
4. Engelberth, J. et al.; Planta. 1995, 196, 539-550.
5. Junker, S.; New Phytol. 1977, 78, 607–610.
6. Cota-Sánchez, J.H. et al.; Flora 2013, 208, 381–389.
7. Gerrath, J.M. et al.; Int. J. Plant Sci. 1999, 160, 261–274.
8. Astreinidi Blandin, A. et al.; Living Machines 2017 proceedings, in press.
8:00 PM - BM01.03.05
Electromechanical Fatigue Behavior of Human Red Blood Cells
Sarah Du 1 , Yuhao Qiang 1
1 , Florida Atlantic University, Boca Raton, Florida, United States
Show AbstractA red blood cell is typically envisioned as a dielectric particle in that its cell membrane acts as an insulating shell that envelops the conducting cytoplasm. Such dielectric properties of red blood cells allow us to induce electromechanical deformation of freely suspended cells, using weak alternating current electric fields. The electric force exerted on cell membranes, known as dielectrophoresis, is determined by the polarizability of cell and surrounding medium, as well as electrical frequency and field strength. Using the dielectrophoresis and Kelvin-Voigt solid models, we perform a comprehensive analysis of the electromechanical behavior of single red blood cells in response to electric field. By varying the field strength, we characterize the nonlinear viscoelasticity of cell membranes. By using amplitude shift keying method, we further investigate the electromechanical fatigue behavior of red blood cells under a dielectrophoresis-controlled cyclic loading condition. Hysteresis is observed in the stress–strain curve of cell membranes. As the number of load cycles increases, the maximum extension ratio of cell membranes decreases and the characteristic time of extensional recovery increases.
8:00 PM - BM01.03.06
Intracranial Shock Wave Interactions with Nanofibrillar Implants
Virginia Ayres 1 , Haozhi Dong 1
1 , Michigan State University, East Lansing, Michigan, United States
Show AbstractRecent work has been reported that indicates that a biomaterial-based intervention could eventually contribute new options for the treatment of perforating/penetrating central nervous system (CNS) injuries. This is an extremely challenging problem, with limited treatment options and, in the case of brain injury, low survival rates. In first minutes of brain injury survival, the CNS soft tissue environment is further compromised by mechanical shock, which is acute in cases of high speed projectiles. In present investigations, the interactions of shock waves with nanoporous scaffold implants embedded in soft tissue are modelled using finite element analysis. Elasticities are realistically modeled based on previous investigations [1,2]. The goal of the present investigation is to provide information on whether immediate or delayed implant insertion is preferable as a therapeutic intervention.
[1] VM Tiryaki, VM Ayres, I Ahmed, DI Shreiber. Differentiation of reactive-like astrocytes cultured on nanofibrillar and comparative culture surfaces. Nanomedicine, 2015 10(4): 529–545.
[2] VM Tiryaki, VM Ayres, AA Khan, I Ahmed, DI Shreiber, S Meiners. Nanofibrillar scaffolds induce preferential activation of Rho GTPases in cerebral cortical astrocytes. Int. J. Nanomedicine. 2012 7:3891-3905.
8:00 PM - BM01.03.07
Evaluation of Mechanical Property of Intermediate Filament Related with Stiffness of Breast Cancer Cell by Use of Nanoneedle and AFM
Ayana Yamagishi 1 2 , Moe Susaki 2 , Yuta Takano 2 , Masumi Iijima 3 , Shun’ichi Kuroda 3 , Tomoko Okada 1 , Akira Nagasaki 1 , Chikashi Nakamura 1 2
1 Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology, Ibaraki, Tsukuba, Japan, 2 Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Tokyo, Koganei, Japan, 3 The Institute of Scientific and Industrial Research, Osaka University, Osaka Japan
Show AbstractCytoskeleton consisting of actin, microtubule and intermediate filament binds to one another and forms three-dimensional network structure. This cytoskeletal structure plays an important role for maintaining cell shape and stiffness. Intermediate filament nestin is suggested to be involved in metastaticity of cancer cells. Previously, we have established nestin knockout cell (KO cell) by using highly metastatic mouse breast cancer cell FP10SC2 (SC2) (1). Since the elastic modulus of KO cell was significantly higher than that of SC2, nestin is considered to soften cell body. However, this finding contradicts a general role of cytoskeletal proteins that provide mechanical support for the cells. Nestin has an extremely long tail domain at C-terminus and co-polymerizes with vimentin which is one of the intermediate filament. Because vimentin is reported to interact with actin filament via its tail domain (2), we predicted that long nestin tail domain inhibits the binding between actin and vimentin and could affect mechanical property of the cytoskeleton.
In this study, we analyzed mechanical property of cytoskeletal structure by tensile test of vimentin filament in a living cell using atomic force microscopy (AFM) and nanoneedle which was fabricated from an AFM tip (3). When an anti-vimentin-antibody-immobilized nanoneedle was inserted into and retracted from a cell, a force to rupture bindings between vimentin filaments and antibodies could be observed as a negative force curve (4). The negative force curves from SC2 and KO cells showed obviously different feature in this tensile test, suggesting that extensibility of the cytoskeletal structure is different between SC2 and KO cells. Additionally, proximity ligation assay showed that the number of binding site between vimentin and actin filament decreased in SC2 cells in compared with that in KO cell. The nestin’s long tail domain might hinder the vimentin binding to actin filament. These results suggest that reduction in the binding site between vimentin and actin filament increases the extensibility of the cytoskeleton and contributes to a decrease in cell stiffness.
(1) Okada et al., BioMed Res. Intl., 8494286, 2017
(2) Esue et al., J. Biol. Chem., 281, 30393-30399, 2006
(3) Obataya et al., Nano Lett., 5, 27-30, 2005
(4) Mieda et al., Biosens. Bioelectron, 31, 3293-329, 2012
Symposium Organizers
Dinesh Katti, North Dakota State University
Christian Hellmich, TU Wien - Vienna University of Technology
Ko Okumura, Ochanomizu University
Peter Pivonka, University of Melbourne
BM01.04: Session III
Session Chairs
Nora de Leeuw
Christian Hellmich
Kalpana Katti
Hannes Schniepp
Tuesday AM, November 28, 2017
Sheraton, 2nd Floor, Constitution B
8:45 AM - *BM01.04.01
The Effect of Crosslinks from Advanced Glycation End-Products on the Mechanical Properties of Collagen Type I
Nora de Leeuw 1 2 , Thomas Collier 2 3 , Anthony Nash 2
1 School of Chemistry, Cardiff University, Cardiff United Kingdom, 2 Department of Chemistry, University College London, London United Kingdom, 3 , Massey University, Taranaki New Zealand
Show AbstractNon-enzymatic glycation of collagen molecules has been hypothesised to result in significant changes to the mechanical properties of the connective tissues within the body, potentially resulting in a number of age-related diseases. We have investigated the effect of a cross-link on the tensile and lateral moduli of the collagen molecule through the use of a steered molecular dynamics approach, using identified preferential formation sites. Our results show that the presence of intra-molecular AGEs results in an increase in the tensile and lateral Young’s moduli in the low strain domain, with little effect exhibited at higher strains.
9:15 AM - BM01.04.02
The Biomechanical Impact of Keratin Dispersants on Human Stratum Corneum
Jacob Bow 1 , Yoshihiko Sonoki 2 , Masayuki Uchiyama 2 , Reinhold Dauskardt 1
1 , Stanford University, Stanford, California, United States, 2 Skin Care Products Laboratory, Kao Corporation, Tokyo Japan
Show AbstractThe stratum corneum (SC) is the outermost tissue layer in human skin. This multifunctional material performs its many biomechanical roles via a complex multi-scale composite structure which includes large cornified cells (corneocytes), rigid intracellular keratin bundles, bound and mobile intercellular lipids, and cell binding protein junctions known as corneodesmosomes (CDs). Changes in SC hydration impact the visual and tactile perception of our skin, the SC’s barrier function, and overall skin health, all through alterations to the biomechanical properties of the tissue.
Here we apply a suite of biomechanical and biochemical experiments to evaluate the effects of two keratin dispersing compounds, 1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid (ectoine) and 2-[2-(guanidine)ethoxy]ethanol (GEE), on the biomechanical response and perception of SC. Studies were conducted on normal, lipid-extracted, and lipid plus natural moisturizing factor (NMF) extracted SC in order to probe specific lipid and keratin interactions. Both compounds are found to improve the dispersity and hydration of keratin bundles in corneocytes to a higher degree than water hydration alone. This change in keratin dispersity is found to improve the mobility of water through the tissue, increasing the rate at which mechanical stresses in the SC develop when exposed to a dry environment from ~ 2 to ~ 3.3 MPa/hr. Further, changes of up to ~ 4 J/m2 are seen in corneocyte cohesion after ectoine treatments, suggesting that ectoine interacts with the corneodesmosome binding proteins of the SC. In particular, cohesion is decreased in solvent-dehydrated tissue and increased in hydrated tissue. These effects are attributed to competition between ectoine interactions with keratin and CDs. Finally, these effects are correlated with a better perception of skin dryness and tightness in drying environments during clinical studies, as well as improved skin appearance and reduced roughness.
9:30 AM - BM01.04.03
Toughness-Enhancing Looped Nanoribbon Silk of the Recluse Spider
Sean Koebley 1 , Hannes Schniepp 1
1 , College of William & Mary, Williamsburg, Virginia, United States
Show AbstractThe brown recluse spider makes a silk featuring a morphology unique amongst all spiders: it is a nanoribbon with a thickness of less than 50 nm and a width of 6–8 μm. We recently discovered that the recluse spider has a unique external spinning postprocessing apparatus that "sews" microloops into this ribbon silk at a speed of about 15 loops per second. Using a highly sensitive tensile tester we discovered that this looped metastructure represents a unique toughness enhancing mechanism. Our mathematical models show that it is feasible to increase toughness of elastic materials by 1000% and more via addition of such loops. Our generalized model successfully explains toughness enhancements in hidden-length systems from the molecular scale to the macroscale. Proof-of-principle experiments on synthetic, macroscopic looped structures confirmed the functionality of this bioinspired mechanism and was in excellent agreement with the predictions of our model.
9:45 AM - BM01.04.05
Synovial Fluid as a Biomarker of Meniscus Alteration in an ACLT Rabbit Model
Catherine Bosser 1 , Caroline Boulocher 2 , Aurélie Levillain 1 , Camille Douillet 1 , Adeline Decambron 3 , Cécile Nouguier 1 , Thierry Hoc 1
1 , Ecole Centrale de Lyon, Ecully France, 2 , VetAgro Sup, Marcy l'Etoile France, 3 , B2OA, Maisons-Alfort France
Show AbstractKnee osteoarthritis (OA) is a major public health issue, affecting 10% to 15% of adults over 60. This joint disease often leads to meniscal degradation, especially in the medial compartment, impairing meniscus biomechanical and functional properties (load-bearing, load distribution and shock absorption [1]. Similarly, during OA, synovial fluid (SF) properties are modified and can be used as biomarkers of OA on-set and progression. The purpose of this study was (i) to assess the efficacy of viscosupplemention therapy on the viscoelastic properties of rabbit knee menisci and (ii) to correlate the mechanical changes of menisci with SF properties.
Anterior Cruciate Ligament Transection (ACLT) was performed in twenty four adult male New-Zealand White rabbits on the right knee joint. Half of them (n=12) was treated with a single intra-articular injection of a commercial high molecular weight hyaluronic acid (HA). Six additional healthy rabbits were used as non-operated not treated controls. Right medial menisci were removed two weeks (n=12) and six weeks (n=12) after ACLT and were graded macroscopically. Indentation-relaxation tests were performed in the anterior and posterior regions of the menisci. For all operated joints, SF was retrieved and analyzed by Raman microspectroscopy to characterize SF chemical and structural changes. SF viscosity and proteins content were also analyzed using an original tribological approach.
At both endpoints, viscosupplementation significantly improved the macroscopic appearance of the medial menisci compared to the operated non treated group (p = 0.002). Viscosupplementation also enhanced glycosaminoglycans content in the anterior region of the menisci. Medial menisci viscoelastic properties and SF Raman spectral fingerprints were not significantly different following viscosupplementation compared with the operated not treated groups. Meniscal viscoelastic properties were significantly lower six weeks than two weeks after ACLT for both operated groups. A clear modification of Raman fingerprint was also measured with a large modification of proteins content between these two endpoints.
To conclude, SF tribological and physicochemical modifications were correlated with the alterations of medial menisci viscoelastic properties and matrix structure following ACLT in rabbits. Such a characterization of SF could provide a surrogate biomarker of OA prognostic and participate to the identification of predictive factors of response to treatment, in order to improve OA care and therapy.
1. Levillain A et al.,J Mech Behav Biomed Mater. 2017 Jan;65:1–10.
2. Bosser et al. Patent "Method for the detection of joint diseases".
10:30 AM - *BM01.04.06
Poroelastic Properties of Biomimetic Cartilage-Like Scaffolds
Michelle Oyen 1 , Giovanni Offeddu 2
1 , University of Cambridge, Cambridge United Kingdom, 2 Biological Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractCartilage is a structural tissue with unique mechanical properties deriving from its electrically-charged porous structure. Here, cartilage-mimicking materials are fabricated using polyelectrolyte hydrogels based on polyvinyl alcohol and polyacrylic acid. The mechanical response, as measured via indentation, of physically-crosslinked cryogels are compared to those of heat-treated chemical gels made from the same polymers, as a result of pH-dependent swelling. Indentation measurements are analyzed within a poroelastic framework to decouple elastic modulus and fluid flow response. In contrast to the heat-treated chemically-crosslinked gels, the elastic modulus of the physical cryogels was found to increase with charge activation and swelling. The permeability of both materials to fluid flow was impaired by the presence of electric charges. This cartilage-like mechanical behavior displayed by responsive cryogels can be reproduced in other polyelectrolyte hydrogel systems to fabricate biomimetic scaffolds for tissue engineering and repair.
11:00 AM - BM01.04.07
Finite Element Modeling and Simulations of Cancer Cell Behavior under Mechanical Loading
Dinesh Katti 1 , Kalpana Katti 1
1 , North Dakota State University, Fargo, North Dakota, United States
Show AbstractCellular mechanics as a potential biomarker for cancer progression is of great interest to researchers and clinicians. It has been experimentally found that the mechanics of cells change as cells grow and proliferate. In recent years, it is reported that many diseases have mechanobiological manifestations. Understanding the mechanisms of cancer progression, the severity of the disease and progress during metastasis stage, when cancer cells migrate to distant organs leading to patient death is critical for the development of drugs and drug delivery systems. Prostate and breast cancer cells migrate from the primary tumor site to distant organs, in particular to the bone. We have designed in vitro test-beds to study cancer metastasis using biomimetic nanoclay-in situ hydroxyapatite-polymer nanocomposite scaffolds that regenerate bone, mimicking the remote bone location. Prostate cancer cells are seeded on the bone-mimetic scaffolds using an innovative sequential culture process. The test-beds successfully create cancer tumors observed in the physiological environment. Nanoindentation experiments have been used to evaluate the mechanics of live cells. In the current work, a detailed finite element model of a cancer cell is constructed. The cell comprises of all the important structural elements of a cell including the cytoskeletal elements such as microtubules, intermediate filaments, actin filaments, cell membrane, cytoplasm and the nucleus. Finite element simulations of nanoindentation experiments on cells are conducted. The simulations are conducted for a cell with various levels of degradation of the cytoskeletal elements. Simulations of nanoindentation experiments on cells placed on various substrates to evaluate the role of substrate stiffness on the nanomechanical response of the cell are also conducted. The simulations provide an insight into the key mechanisms that influence the nanomechanical response of cells. These studies help move forward the investigation of the mechanical behavior of cancer cells as biomarkers for disease progression.
11:15 AM - BM01.04.08
Cytoskeletal Dynamics of Neurons Measured by Combined Fluorescence and Atomic Force Microscopy
Cristian Staii 1
1 Physics and Astronomy, Tufts University, Medford, Massachusetts, United States
Show AbstractDetailed knowledge of mechanical parameters such as cell elasticity, stiffness of the growth substrate, or traction stresses generated during axonal extensions is essential for understanding the mechanisms that control neuronal growth. Here I present experimental results which combine atomic force microscopy and fluorescence microscopy measurements to produce systematic, high-resolution elasticity maps for different types of live neuronal cells cultured on glass or biopolymer-based substrates. We measure how the stiffness of neurons changes both during neurite outgrowth and upon chemical modification (disruption of the cytoskeleton) of the cell. We find a reversible local stiffening of the cell during growth, and show that the increase in local elastic modulus is primarily due to the formation of microtubules in the cell soma. We also report a reversible shift in the elastic modulus of the cortical neurons cytoskeleton with temperature, and demonstrate that the dominant mechanism by which the elasticity of the neuronal soma changes in response to temperature is the contractile stiffening of the cytoskeleton induced by the change in myosin II activity. These results present a potential method to reversibly control the mechanical properties and the myosin activity in cortical neurons, through variations in temperature without requiring additional chemical modifications.
11:30 AM - BM01.04.09
Investigation of Viscoelastic Properties of Malignant Human Breast Cells Using a Shear Assay Technique
Jingjie Hu 1 , Yuxiao Zhou 2 , John Obayemi 3 , Jing Du 2 , Winston Soboyejo 1 3
1 Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States, 2 Department of Mechanical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 3 Department of Mechanical Engineering, Worcester Polytechnic Institute (WPI), Worcester, Massachusetts, United States
Show AbstractThe changes that occur in the viscoelastic properties of cancer cells are proposed as markers for the detection of the different stages and aggressiveness of breast cancer. In this study, the viscoelastic properties (Young’s moduli, shear moduli and viscosities) for both nuclei and cytoplasm of human breast cells are studied through a combination of shear assay approach and digital image correlation (DIC) technique. The non-cancerous breast cells (MCF-10A), less metastatic breast cancer cells (MDA-MB-468) and highly metastatic breast cancer cells (MDA-MB-231), respectively, are subjected to constant shear stress exerted by the fluid flow in a parallel-plate fluid chamber. Cell deformation and detachment are observed in situ. Local displacement and strain are mapped on each cell by applying DIC on the recorded images. Generalized viscoelastic Maxwell model is then applied to characterize the observed creep behaviors for nuclei and cytoplasm, respectively. The moduli and viscosities are consistent with those reported in literatures. The results show that the modulus of the nuclei is much higher than that of the cytoplasm for all three different cell lines. Furthermore, the moduli for the noncancerous breast cells are found to be twice as high as less metastatic breast cancer cells and almost eight times higher than highly metastatic breast cancer cells. Similar trends are also observed in viscosities. The decrease in cell stiffness in malignant breast cells is mainly attributed to the reduction of actin filaments when cells evolve from healthy to cancerous state that are observed via immunofluorescence staining. The clinical implications of this study are discussed for using cell viscoelasticity as biomarker for detection of metastatic potential of breast cancer cells.
11:45 AM - BM01.04.10
Stimulation of Cell Adhesion by Mechanosensing—From Single Molecules to 3D Materials
Laith Kadem 1 , Katharina Siemsen 1 , Sören Gutekunst 1 , Grace Suana 1 , Wei Wang 1 , Rainer Herges 1 , Christine Selhuber-Unkel 1
1 , University of Kiel, Kiel Germany
Show AbstractCells can feel the mechanical properties of their surroundings and actively respond to applied external forces in a process called mechanosensing. This mechanism has far-reaching impacts on biological functions, ranging from proliferation to stem cell differentiation.
There are numerous approaches to control cellular mechanosensing using biomaterials. For instance, soft polymers could be employed to define the Young’s modulus of the cellular environment. We here present a three-dimensional porous hydrogel that was exploited for controlling both cellular growth and mechanosensing. Likewise, cellular mechanosensing could also be activated by applying “tickling” forces onto cells using biofunctional molecules. The molecules we employed in this work are RGD-conjugated push-pull substituted azobenzenes that oscillate upon light exposure and thus exert forces onto cellular integrin binding sites. We have seen that the oscillation of RGD-push-pull azobenzenes leads to strengthening of cell detachment forces at a timescale of seconds. Furthermore, at timescales from several minutes to hours we observed enhanced expression levels of adhesion-associated proteins such as vinculin, talin, zyxin, and paxillin. This result suggests that the cells reinforce their adhesion in response to “molecular tickling” and also activate larger-scale signaling cascades.
In general, the development of novel approaches to control cellular mechanosensing provides a stepping stone toward exploiting mechanosening in biomaterial applications, particularly for regenerative medicine.
Reference:
L. F. Kadem, K. G. Suana, M. Holz, W. Wang, H. Westerhaus, R. Herges, C. Selhuber-Unkel (2017): High Frequency Mechanostimulation of Cell Adhesion. Angewandte Chemie International Edition, 56: 225-229.
BM01.05: Panel Discussion
Session Chairs
Christian Hellmich
Dinesh Katti
Tuesday PM, November 28, 2017
Sheraton, 2nd Floor, Constitution B
1:30 PM - BM01.05.01
BM01.05.01: Panel Discussion moderated by Christian Hellmich | Panelists: Ming Dao, Massachusetts Institute of Technology; Nora De Leeuw, Cardiff University; Michelle Oyen, Cambridge University; Kalpana Katti, North Dakota State University; Markus Buehler, Massachusetts Institute of Technology
Christian Hellmich 1
1 , TU Wien - Vienna University of Technology, Vienna Austria
Show AbstractPanel Discussion moderated by Christian Hellmich
Panelists:
Ming Dao, Massachusetts Institute of Technology
Nora De Leeuw, Cardiff University
Michelle Oyen, Cambridge University
Kalpana Katti, North Dakota State University
Markus Buehler, Massachusetts Institute of Technology
BM01.06: Session IV
Session Chairs
Tuesday PM, November 28, 2017
Sheraton, 2nd Floor, Constitution B
3:30 PM - BM01.06.01
Protein-mediated Diffuse Damage Formation and Nanoscale Energy Dissipation in Bone
Zehai Wang 1 , Deepak Vashishth 1 , Catalin Picu 1
1 , Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractBone, as well as other structural biomaterials, exhibits hierarchical organization from the nano- to the macroscale. It has been shown that accumulation of submicron diffuse damage and formation of nanoscale dilatational bands enhances the macroscale inelastic deformation and toughness in bone. However, the mechanical origin and quantification of such enhancement are still lacking. Here, we use X-Ray Diffractometry to characterize the nanoscale mineral structure and create a three-dimensional mineralized collagen fibrils model with stochastic structure representing the extrafibrillar mineral organization. We propose a mechanism for the formation of diffuse damage based on non-collageneous protein denaturation and predict the total energy dissipated associated with this mechanism in the vicinity of a major crack tip. We compare this result with the specific energy dissipation measured in bone creep/recovery tests. This study provides insight into the nanoscale toughening mechanisms in bone and provides guidance for the development of bio-inspired composites with enhanced toughness.
3:45 PM - BM01.06.02
Multiscale Characteristics of Bone Toughness
Sabah Nobakhti 1 , Sandra Shefelbine 1
1 , Northeastern University, Boston, Massachusetts, United States
Show AbstractAt nanoscale, bone is a composite of collagen molecules and hydroxyapatite mineral crystals. Alterations in quantity/quality of the collagen and mineral affects other properties such as porosity, tissue mineral density and matrix elasticity at micro-scale and consequently, strength and toughness at the whole bone level. Toughness in bone is obtained through structural hierarchy and various toughening mechanisms acting at different length scales. Previous studies on bovine [1] and human [2] bone have proposed that bone’s toughness is mainly derived from its mechanical heterogeneity. It is generally believed that the elastic modulus is positively correlated to the amount of mineral in bone [3] and therefore, fracture toughness should be primarily affected by bone mineral content and distribution. Genetically altered mouse models of bone pathology allow us to examine how molecular defects alter the bone mineral and derive whole bone toughness across length-scales.
We generated whole bone crack resistance curves in notched three-point bending experiments on the femur for mouse models of bone pathology. In this configuration, crack initiation toughness, propagation toughness and fracture toughness is characterized for each bone. We measured the degree of mineralization with quantitative backscattered scanning electron microscopy and the elastic modulus with nanoindentation of the tibia. Mineral to matrix ratio was measured in humerus by thermogravimetric analysis and collagen fibril to tissue strain is quantified on ulnae by small angle x-ray scattering. Crystal size was measured on humerus with wide angle x-ray diffraction and the mineral composition was quantified on tibia by Fourier transform spectroscopy.
We found that the degree of mineralization, the elastic modulus, and fracture toughness varied significantly across mouse models. Toughness is generally lower in highly mineralized bone, bone lacking anisotropic arrangement of the collagen fibrils, and porous highly-vascularized bone. Modulus is not correlated to the amount of mineral between and within the groups. Crystal size is not correlated to the degree of mineralization nor the tissue elastic modulus. Mineral to matrix ratio is however positively correlated to bone mineral density. This project allow us to better understand the critical contributors to toughness by examining a wide range of pathologic mice spanning the spectrums of strength and ductility.
References:
[1] Tai, et al., Nature materials, 2007.
[2] Katsamenis, et al., Bone, 2015.
[3] Currey, Journal of Biomechanics, 1988.
4:00 PM - BM01.06.03
Wear Modeling of HDPE/CNF Nanocomposites under Lubricated Conditions
Songbo Xu 1 , Annie Tangpong 2
1 , Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi'An China, 2 , North Dakota State University, Fargo, North Dakota, United States
Show Abstract
One of the difficulties in tribological studies of the polyethylene component in total joint replacements is that their wear test under lubricated conditions very long time duration to obtain a detectable wear loss, because of their low wear rates. In this paper, a theoretical wear model which couples elastohydrodynamic lubrication theory and Reye’s wear model was proposed to predict the long term wear of high density polyethylene (HDPE) and HDPE/CNF nanocomposites under lubricated conditions. The Newton-Raphson method was used to solve the contact lubrication problem with a high convergence rate. Various factors on wear are considered including lubricants’ property (viscosity), material properties (Young’s modulus, asperity height, specific wear volume, and coefficient of friction), and operating parameters (normal load and sliding speed) was coupled into the construction of the wear model. In addition, to validate the theoretical wear modeling a pin-on-disk (a stainless steel cylinder sliding against a polyethylene component disk) wear test is performed under 95% glycerol/water lubricated conditions. It was found that the wear of HDPE and HDPE/CNF nanocomposites were increased with the increasing of the sliding speed and normal load, but decreased with the increasing of the asperity height and lubricant’s viscosity. The computational modeling showed the good consistence with the experiment results. The model may significantly reduce the time consumption of the long term wear test and provide a helpful support for the biomedical application of the new polyethylene based nanocomposites.
4:15 PM - *BM01.06.04
Clinical Significance of 3D Printing in Treatment of Bone Disorders
Susmita Bose 1
1 , Washington State University, Pullman, Washington, United States
Show AbstractCurrent clinical approaches treating bone defects involve the use of bone transplantation or synthetic materials to repair and restore functionality. There are an estimated one million bone grafting procedures performed annually in the U.S. and a few million worldwide to repair fractures, cysts, bone defects, tumors, as well as hip and knee replacements. Increase in the number of procedures is strongly tied to the increase in musculoskeletal disorder, aging population segment and sports related injuries. In some cases, patients with special anatomical needs or concerns related to specific defect size complexity, patient matched devices are necessary. Role of 3D printing or additive manufacturing (AM) is becoming important in those cases of patient matched implants due to lower cost and shorter lead time to manufacture. 3D printing or additive manufacturing technologies are currently being used in both dental and orthopedic applications. In 2016, since FDA has already approved additively manufactured devices, thousands of AM devices are already being used in human. However, additively manufactured components are still questioned for their reproducibility, machine to machine part quality variations and process specific material properties. Establishing process property relationships for different AM techniques are vital towards successful implementation of these manufacturing practices in biomedical devices.
Hard biomaterials, e.g., calcium phosphate (CaP) ceramics being compositionally similar to the inorganic part of bone, show significant promise towards bone implant applications, in both 3D printed tissue engineering scaffolds and in surface modified hip and knee implant devices. We have used CaP scaffolds, fabricated using 3D printing technology, for bone tissue engineering. Dopant chemistry in CaPs plays a vital role in controlling their resorption or degradation kinetics as scaffolds’ mechanical strength and biological properties of these resorbable CaPs. 3D interconnected channels in CaP scaffolds provide pathways for micronutrients, improved cell-material interactions, and increased surface area allows improved mechanical interlocking between scaffolds and surrounding bone. In vivo studies show improved osteogenesis, angiogenesis and drug delivery using these 3D printed scaffolds. An additional coating of polymer can help improve mechanical and biological properties as well as control the drug release kinetics. CaP coated metallic orthopedic devices can be clinically significant for revision surgeries as well as infection control, in orthopedic and bone tissue engineering applications while improving their current performance. The presentation will include recent scientific and technological challenges towards developing next generation bone tissue engineering scaffolds and implants using 3D printing with enhanced osteogenic and angiogenic properties, while improving mechanical reliability.
Symposium Organizers
Dinesh Katti, North Dakota State University
Christian Hellmich, TU Wien - Vienna University of Technology
Ko Okumura, Ochanomizu University
Peter Pivonka, University of Melbourne
BM01.07: Session V
Session Chairs
Christian Hellmich
Dinesh Katti
Kalpana Katti
Candan Tamerler
Wednesday AM, November 29, 2017
Sheraton, 2nd Floor, Constitution B
8:30 AM - *BM01.07.01
Multiscale Smart Materials by Design—Connecting Simulation, Design, Synthesis across Multiple Scales
Markus Buehler 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show Abstract
What if we could design materials that integrate powerful concepts of living organisms – self-organization, the ability to self-heal, tunability, and an amazing flexibility to create astounding material properties from abundant and inexpensive raw materials? This talk will present a review of bottom-up analysis and design of materials for various purposes – as structural materials such as bone in our body or for lightweight composites, for applications as coatings, and as multifunctional sensors to measure small changes in humidity, temperature or stress. These new materials are designed from the bottom up and through a close coupling of experiment and powerful computation as we assemble structures, atom by atom. Materiomics investigates the material properties of natural and synthetic materials by examining fundamental links between processes, structures and properties at multiple scales, from nano to macro, by using systematic experimental, theoretical or computational methods. We review case studies of joint experimental-computational work of biomimetic materials design, manufacturing and testing for the development of strong, tough and smart mutable materials for applications as protective coatings, cables and structural materials. We outline challenges and opportunities for technological innovation for biomaterials and beyond, exploiting novel concepts of mathematics based on category theory, which leads to a new way to organize hierarchical structure-property information. Altogether, the use of a new paradigm to design materials from the bottom up plays a critical role in advanced manufacturing, providing flexibility, tailorability and efficiency.
9:00 AM - BM01.07.02
Nacre-Inspired Alumina with a Nickel Compliant-Phase Fabricated Using Spark Plasma Sintering
Amy Wat 1 2 , Claudio Ferraro 3 , Xu Deng 4 , Eduardo Gutierrez 3 , Antoni Tomsia 1 , Robert Ritchie 1 2
1 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 3 Department of Materials, Imperial College London, London United Kingdom, 4 , University of Electronic Science and Technology of China, Chengdu China
Show AbstractModern engineering ceramics are lightweight and have high strength, but these materials are rarely utilized as a structural material due to their low toughness. Natural materials provide inspiration for tough ceramics by utilizing hierarchical microstructures and gradients that enable toughening mechanisms that are rarely found in synthetic materials. In this study, we use nacre model material to create bioinspired, high toughness, structural ceramics. Nacre is the mother-of-pearl portion of abalone shells that displays three orders of magnitude increase of fracture toughness (in energy terms) compared to the toughness of its constituents. This dramatic elevation in toughness is a direct result of its brick-and-mortar microstructure. We replicate this structure by coating alumina platelets with nickel through heterogenous precipitation. These platelets are cast and aligned using slip casting before getting sintered using spark plasma sintering. The final materials illustrate the need to account how the composition of the slurry and sintering conditions can affect the strength and fracture toughness of the bulk ceramic materials.
9:15 AM - BM01.07.03
The Achilles Heel of Nacre
Ting Tan 1
1 , Univ of Vermont, Burlington, Vermont, United States
Show AbstractNacre possesses superior strength and toughness. Here, we show that nacreous sections can exhibit complete brittle fracture along the tablet interfaces at the proportional limit under pure shear stresses of torsion, and quantitatively separate the initial tablet sliding primarily resisted by nanoscale aragonite pillars from the following sliding resisted by various microscale toughening mechanisms. We postulate that the ductility of nacre can be limited by eliminating tablet interactions during crack propagations.
9:30 AM - BM01.07.04
Smart Architectural Design Identified in Biological Nanocomposites
Vesna Srot 1 , Birgit Bussmann 1 , Miloš Vittori 2 , Julia Deuschle 1 , Boštjan Pokorny 3 4 , Peter Van Aken 1
1 , Max Planck Institute for Solid State Research, Stuttgart Germany, 2 , Biotechnical Faculty, Ljubljana Slovenia, 3 , Environmental Protection College, Velenje Slovenia, 4 , Slovenian Forestry Institute, Ljubljana Slovenia
Show AbstractOptimally tuned nanoarchitectures reflecting functionality have been often recognized in biominerals produced by living organisms. These biominerals consist of closely intertwined inorganic and organic components. Mechanical properties of such constituent phases with insignificant characteristics are amplified when arranged into biological complex composites. Their outstanding performance optimized for various functions in animal bodies has been an inspiration for engineering similar materials. Since functional composite properties are often regulated on the nanoscale, advanced analytical and imaging transmission electron microscopy (TEM) techniques combined with measurements of mechanical properties have been employed in our work.
We studied the uncommon yet remarkable microstructural and compositional adaptations in (i) incisors of coypu (Myocastor coypus Molina) [1] and (ii) claws of terrestrial crustacean (Porcellio scaber) [2].
(i) Continuously growing incisors of coypu are a superb example of a smartly constructed self-sharpening functional device enduring heavy gnawing loads [3]. They consist of natural complex composite, with the front of the incisor covered by hard and resistant enamel, whereas the softer bulk dentin is being gradually removed while gnawing. Chemical analysis using energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy has uncovered an Fe-rich and chemically diverse amorphous surface layer (Fe-SL) that is covering pigmented enamel (Fe-EN). The Fe-L2,3 energy-loss near-edge structure (ELNES) proves that Fe in the Fe-SL is in predominantly 3+ valence state, while the O-K ELNES displays three main Fe concentration-associated spectral shapes. Three vaguely separated phases and their intermixtures, namely ferrihydrite, (Fe, Ca)-phosphate and (Ca, Fe)-phosphate, were determined within the Fe-SL. In the outer Fe-EN, elongated hydroxyapatite (HA) crystals are surrounded by ferrihydrite pockets. Comparison between pigmented and non-pigmented enamel showed close connection between the microstructure and mechanical properties. Pigmented enamel, consisting of soft amorphous ferrihydrite in the spaces between HA crystals, appears to be a highly advanced composite compared to the non-pigmented enamel.
(ii) Claws of the walking legs in the terrestrial crustacean are thin structures supporting the entire body and are evolutionary optimized for withstanding unidirectional loads. We determined the predominant mineral component of the claw cuticle to be amorphous calcium phosphate (ACP), while other exoskeleton regions are mineralized with calcium carbonate. The brominated claw exocuticule and the structurally anisotropic endocuticle consisting of axially oriented chitin-protein fibers interwoven with ACP particles, form a durable fracture and wear resistant composite material.
[1] V Srot et al., ACS Nano 11(1) (2017), 239
[2] M Vittori et al., J Struct Biol 195 (2016), 227
[3] PY Chen et al., Prog Mater Sci 57 (2012), 1492
9:45 AM - BM01.07.05
Mechanics and Toughening Mechanisms of Nacreous Materials
Sina Askarinejad 1 , Nima Rahbar 1
1 , Worcester Polytechnic Institute, Worcester, Massachusetts, United States
Show AbstractStudying naturally growing composites such as nacre give us a fantastic vision to design and fabricate tough, stiff while strong composites. Nacre is a great example of natural ceramic-based composites with high strength and toughness. Previous studies on mechanical performance of these structural materials show that their outstanding properties are direct results of the nano-scale features and the optimized arrangement of the elements. In our preliminary study we used a physics-based finite-element model to investigate the deformation and toughening mechanisms of nacreous structure. The effects of all the structural features such as mineral bridges, asperities as well as mechanical properties of constituents were discussed in that study. In the next phase of the research, freeze-casting method was employed to fabricate nacre-inspired multilayered materials. Mechanical and fracture properties of these man-made composites were also discussed and a theoretical model was proposed to describe the deformation mechanisms. In that study, our results pronounced the effect of interface properties on the mechanical response of multilayered composites. Hence, we were led to investigate the effect of interfaces in nacre. In order to provide the outstanding mechanical functions, nature has evolved complex and effective functionally graded interfaces. Particularly in nacre, organic-inorganic interface in which the proteins behave stiffer and stronger in proximity of calcium carbonate minerals provide an impressive role in structural integrity and mechanical deformation of the natural composite. In this study, a micromechanical analysis of the mechanical response of “Brick-Mortar” and “Brick-Bridge-Mortar” composites is presented considering interface properties. The results solve the important mysteries about nacre and emphasize on the role of organic-inorganic interface properties. The effect of mineral bridges is also studied. Our results show that the properties of proteins in mineral bridges proximity are also significant especially in increasing the elastic modulus of the structural composite. In the last phase of our study, we focused on the platelets’ waviness in the structure of nacre and using numerical and experimental techniques we were able to find the optimum range of waviness angle in order to gain the largest tensile toughness for the same volume fraction of constituents. More studies are needed to consider all the structural details in order to find the optimum design of multilayered composites.
10:30 AM - *BM01.07.06
Guided Engineering of Bio-Nano Interfaces by Biomolecular Self-Assembly
Candan Tamerler 1 2
1 Mechanical Engineering and Bioengineering, University of Kansas, Lawrence, Kansas, United States, 2 Institute for Bioengineering Research, University of Kansas, Lawrence, Kansas, United States
Show AbstractTo date, the scope of biomolecular self-assembly has been widely expanded with the realization of vast possibilities in supramolecular strategies offering infinite opportunities for fabricating next generation biomaterials. With their ubiquity and importance, proteins play an essential role in biological systems. Proteins are the performers of directing or maintaining the cellular dynamic interactions, providing major components of structural scaffoldings as well as controlling nucleation, growth and assembly of biological tissues at nano-, meso- and macroscales. Manipulating protein building blocks as functional self-assemblies in designing hybrid materials will enable novel materials and systems with versatile functions. By offering a controlled self-organization at a molecular level, these functional self-assemblies can be tailored to provide guided interactions at the biological and solid interfaces. Inspired by Nature’s biomolecular building blocks, we explore smaller protein domains, i.e. peptides as the key fundamental molecules and mimic their precise molecular recognition mechanisms as the basis of molecular scale interactions. With the modularity of the peptides, our group in the recent years has focused on designing chimeric molecular constructs that contains both ability to self-assemble on solid substrates and to display additional functionalities such as bioactive or antimicrobial property. We also expanded this approach by genetically incorporating them into functional proteins and enzyme constructs. These multi-component-multi-functional units may be fine-tuned for a variety of directed self-assembly applications. Binding kinetics and thermodynamic parameters drive the fine-tuning of these multifunctional units. Such fine tuning may allow the engineering the competitive binding ability of the solid binding peptides over a wide range of biomolecular interactions towards creating a functional molecular interface. The focus of this presentation will be on how these bioenabled peptide based interactions can be designed and developed by providing specific examples on biomedical applications. Guiding biomolecular and cellular interactions at the bio-materials interfaces will be provided for the metallic implants as well as mineralized coatings for restoration of tissues. The integration of biological building blocks may allow harnessing the extraordinary diversity and protein functions to generate smart bio-hybrid materials for wide range of applications including sensing and tissue engineering applications. Acknowledgement: National Institute of Dental and Craniofacial Research. Grant Number: DE025476 and National Institute of Arthritis and Musculoskeletal and Skin Disease, Grant Number: AR062249.
11:00 AM - BM01.07.07
The Effects of Materials on the Development of Long-Term Implants with High Fracture Resistance
Fatma Bayata 1
1 , Istanbul Bilgi University, Istanbul Turkey
Show AbstractThe failure of dental implant is frequently occurred due to the biomechanical complications occurred during chewing process. Stress transformation from implant material to bone tissue, the integrity of implant material to the bone tissue and the mechanical behavior of implant material are the most important concerns in the development of long-term implants. This study aims to avoid the biomechanical problems in implantation technology by means of decreasing the stress concentration around the implant. For this purpose, the design parameters were optimized and a new implant model was developed. Then different materials were assigned to the implant model and the biomechanical properties were tested under real biting forces using Finite Element Analysis (FEA) according to ISO 14801. Hence, the effects of implant materials and design parameters on the stress state, fatigue life of implants and bone interactions were investigated. The developed implant design displayed high fracture resistance and satisfy the recommended life (5 x 106 cycles) for dental implants under actual cyclic biting forces. Besides, implant-bone interaction was enhanced and smoother stress transmission was achieved from the implant to the bone tissues under biting forces.
11:15 AM - BM01.07.08
Cancer Progression in Prostate Cancer Metastasis to Bone
MD Shahjahan Molla 1 , Dinesh Katti 1 , Kalpana Katti 1
1 , North Dakota State University, Fargo, North Dakota, United States
Show AbstractProstate cancer (PCa) is the second most frequently diagnosed form of cancer in the United States, and sixth leading cause of cancer originated deaths among men worldwide. Cancer metastasis, or the colonization of cancer cells away from primary site, is a complex process requiring dramatic remodeling of the cell cytoskeleton, actin (microfilaments), microtubules (MTs) and intermediate filaments, an interconnected network of filamentous polymers and regulatory proteins. Recent work has demonstrated that during cancer metastasis physical forces act through the cytoskeleton to affect local nanomechanical properties of cancer cells. Nanomechanical properties such as stiffness and elastic modulus have been found to be crucially connected to cancer cell attachment, viability, differentiation, and migration. Moreover, some anticancer drugs act on the cell cytoskeleton and thus have a significant effect on cellular nanomechanics. Herein, we investigated the relationships between cancer nanomechanics and cytoskeletal changes during cancer progression. We investigated the interconnection between nanomechanical properties and cytoskeletal changes during prostate cancer progression using the novel 3D tumor model. Two prostate cancer cell lines MDA-PCa-2b and PC-3 are sequentially cultured with human mesenchymal stem cells (MSCs) to mimic the MET (mesenchymal to epithelial transformation) stage of prostate cancer bone metastasis using PCL/nanoclay scaffolds. A unique cell culture technique termed as ‘sequential culture’ has been applied to create a bone-mimetic niche for colonization of prostate cancer cells. Human MSCs were seeded on the bone-mimicking PCL/nanoclay scaffolds, where they differentiated into bone cells and then formed a mineralized bone matrix. Then, human prostate cancer cells were seeded on the MSCs seeded scaffolds. Sequentially cultured PCa cells with MSCs formed self-organized multicellular tumoroids with distinct tight cellular junctions and hypoxic core regions. Nanomechanical properties of prostate cancer cells have been evaluated using nanoindentation technique using 10-micron conospherical diamond indenter. An in situ displacement-controlled nanoindentation technique (using Hysitron Triboscope) has been designed to perform nanoindentation experiments on living cells (human prostate cancer cells) and under physiological conditions (cell culture medium; 37 °C). Immunofluorescence confocal microscopy has been performed to investigate the cytoskeletal changes in cancer cells. Cytoskeletal components actin, tubulin, vimentin, and cytokeratin are stained using immunocytochemistry. Changes in fluorescence intensity during the different period has been observed. qRT-PCR experiments have been conducted to study the key genes related to the cytoskeleton (N-WASP, stat 3/5, cofilin, cortactin, α-actinin, filaminA, myotubularin, destrin, gelsolin, thymosinβ4, paxillin).
11:30 AM - *BM01.07.09
Analyzing Composition-Property Linkages in Bone Using Nanoindentation and Raman Spectroscopy
Shraddha Vachhani 2 , Siddhartha Pathak 3 , Surya Kalidindi 1
2 , Bruker Nano Surfaces, Santa Barbara, California, United States, 3 , University of Nevada, Reno, Reno, Nevada, United States, 1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractIn this work, we utilize novel quasi-static and dynamic nanoindentation techniques to characterize bone’s mechanical behavior in both dry and hydrated states, and its linkages to bone’s composition at the lamellar level. Two sets of samples – ‘wet’ (hydrated) and ‘dry’ (dehydrated-embedded) – were prepared from femora from two inbred mouse strains, known to differ in their whole-bone mechanical properties (A/J, and C57BL/6J [B6], each 16 wks of age, 4-6 individuals per group). Wet samples were sectioned and surface polished to 0.25µm, and tested using fluid tips with spherical probes of 1 and 20 µm radii. Samples remained moist throughout all preparation and testing steps. Dry samples were embedded in PMMA, sectioned transversely below the third-trochanter and surface polished to 0.05µm.
Raman spectroscopy (RS) was used to assess compositional details over an area of 60 x 60 μm ROI at 2µm intervals, across the antero-medial (AM) cortex of each sample. Specifically, the mineral to matrix ratio was calculated within a 60 x 60 μm ROI at 2µm intervals to measure the degree of mineralization of the bone matrix. Nanoindentations were carried out across this same cortex with a 13.5 µm radius spherical diamond tip. Indentation stress strain (ISS) curves, obtained from the nanoindentation generated load-displacement curves, were used in combination with the RS ratios to study property-composition relationships across the AM cortex of the two strains.
Our ‘dry’ sample results demonstrate that the new bone close to the bone-edge had a lower mineral-to-matrix (phosphate-to-CH2 wag) ratio, lower mineral maturity (phosphate-to-monohydrogen phosphate ratio) and higher degree of carbonate substitution (phosphate-to-carbonate ratio) in the mineral. There was a significant difference in the mineral-to-matrix ratio of the two strains of mice, with the A/J mice showing an overall higher mineral-to-matrix ratio and lower carbonate substitution in the mineral. While newer bone appeared to show evidence of difference in the mineral-to-matrix ratio (p < 0.03) between the mouse strains, the differences in composition appear to be far less significant as the bones matured (p > 0.05). Local mineral-to-matrix ratio appears to be a good indicator of the local mechanical properties and correlated well with the elastic modulus and indentation yield strength. Intra-strain differences in both bone composition and relationship between composition and local mechanical properties were found to be statistically insignificant.
Dynamic nanoindentation experiments on our ‘wet’ samples show that newly formed bone along the endosteal edge of the AM cortex (with a higher collagen content or a lower mineral-to-matrix ratio) demonstrates a trend towards a higher viscoelastic response. When normalized for anatomical location relative to biological growth patterns in the antero-medial (AM) cortex, bone tissue from B6 femora exhibits a higher viscoelastic response compared to A/J tissue.
BM01.08: Session VI
Session Chairs
Mohan Edirisinghe
Christian Hellmich
Kalpana Katti
Ko Okumura
Wednesday PM, November 29, 2017
Sheraton, 2nd Floor, Constitution B
1:30 PM - *BM01.08.01
Hierarchical Integration of Repeating Units Toughens Enamel Bioceramic Composite
Malcolm Snead 1
1 , University of Southern California, Los Angeles, California, United States
Show AbstractTeeth are covered by enamel, a bioceramic composite that forms the hardest tissue in the vertebrate body. The repeating fundamental unit is defined by a discrete bundle of hydroxyapatite (HAP) nanocrystallites fabricated by single cell that are woven together to yield a tough-, functional-, chewing surface essential for nutrition. Enamel starts as a self-assembled mixture of extracellular matrix proteins: some proteins appear to guide the crystallite habit of the HAP mineral phase in the repeating units while other proteins serve to hierarchically organize the repeating units into a continuum. Amelogenin is the most abundant enamel protein and is believed to control largely HAP crystallite habit. Multiple amelogenin protein monomers self-assemble into nanospheres that influence crystallite habit. Self-assembly is dependent upon two specific domains, one located in the amino terminus and the other in the carboxyl terminus. Elimination of amelogenin reduces the thickness of the enamel in genetically engineered knockout mice. In vitro produced recombinant amelogenin undergoes self-assembly and amelogenin engineered to eliminate either domain suffer from self-assembly defects that can be measured by AFM and dynamic light scattering. Similarly, animals genetically modified to lack either or both self-assembly domains also demonstrate characteristic defects in enamel formation. Humans have been identified with genetic mutations in these self-assembly domains and their enamel reveals defects similar to those seen in genetically engineered mice, suggesting the phenotypes share a common molecular pathogenesis. Ameloblastin is the second most abundant matrix protein and its distribution during enamel formation is initially found across the entire secretory surface of the enamel-forming cell. However, its distribution is quickly altered to one that is circumferential, outlining the cell but also unifying the perimeter of forming enamel into a continuum of HAP nanocrystallites. Genetic engineered mice have been created in which its human counterpart replaces the mouse ameloblastin gene and this broadens the distribution of ameloblastin and results in a slightly altered hierarchical organization of the mineral phase. These in vitro and in vivo manipulations permit identification of the minimal protein components for enamel formation. The elucidation of the engineering specification of biological replacement of diseased tissue offers realization of a biological repair for enamel. This could be a major breakthrough towards replacing metal or polymer based dental restorations.
2:00 PM - BM01.08.02
Tracing the Nanoscale Chemical Mapping of Enamel-Crystallite through Human Tooth Decay
Fan Yun 1 2 3 , Rongkun Zheng 1 2 3
1 School of Physics, The University of Sydney, Sydney, New South Wales, Australia, 2 Australian Institute for Nanoscale Science and Technology, The University of Sydney, Sydney, New South Wales, Australia, 3 Australian Center for Microscopy and Microanalysis, The University of Sydney, Sydney, New South Wales, Australia
Show AbstractTooth decay, or dental caries, is the most frequent infectious disease among humans world-widely. The outermost and hardest highly-mineralized layer of tooth known as enamel is the first target of caries by chemical dissolution and commonly begins with the demineralization of enamel hydroxyapatite crystallites by acids produced by oral bacteria. However, despite decades of research on dental caries, the complex nanoscale structure and chemistry of the tissue is still not fully understood, in particular, the nature of the inter-crystalline space. Crystal dissolution of enamel HAP in nanoscale is thought to occur in two types: dissolution from the periphery or from the center. In the former, removal of unit cells triggers from the Mg-rich ACP intergranular phases. While in the latter type which is also called center perforation, the crystal periphery remains almost normal and demineralization occurs from a fine planar structure named central dark line (CDL). Neither a dislocation nor a lattice twin boundary, the stacking structure and chemical composition of CDL still remained a great challenge to model accurately, hampering our understanding of caries etiology at the mechanistic level.
We report here on the application of atom probe tomography in combination with transmission electron microscopy (TEM) to characterize central dark line in sound enamel apatite and a naturally decayed lesion in early stages of caries. By reconstructing the 3D chemical crystalline structure we find evidence that CDL can be found along the center of the crystal, parallel to the c-axis and bisecting the crystal thickness. The obviously higher composition of trace elements like Mg and Na are responsible for the preferential dissolution and provide pathways for ions exchange during demineralization and remineralization. These observations can also connect CDL to the ribbon-like organic-rich precursor in amelogenesis during the early formation of human tooth enamel.
2:15 PM - BM01.08.03
Nature’s Multiscale Design Strategies and Smart Manufacturing
Xiaodong Li 1
1 , University of Virginia, Charlottesville, Virginia, United States
Show AbstractRecent discoveries in seashells unveil that nature uses multiscale design strategies to achieve exceptional mechanical properties which are still beyond the reach of many engineering materials. The multiscale hierarchical structure, ranging from micro lamellae down to nanoparticles, renders seashells multilevel strengthening and toughening mechanisms such as crack deflection, interlocking, lamellae’s deformability, biopolymer’s viscosity, nanoparticle rotation, deformation twining in nanoparticles, and amorphization, jointly contributing to seashell’s ultra-high mechanical robustness. To realize nature’s performance in engineering materials, we need to intelligently design and select materials. This talk will present several case studies in which nature’s multiscale design strategies and materials selection principles are applied through smart manufacturing.
3:30 PM - *BM01.08.04
Innovative Manufacturing Research to Enable Biomechanical Engineering
Mohan Edirisinghe 1
1 , University College of London, London United Kingdom
Show AbstractMore recently, a new frontier that very significantly enhances the use of biomechanical engineering has emerged; these are finer biomaterial entities such as microbubbles, nanovesicles, porous and solid particles at all scales, different types of capsules and smart nanofibers. These products are increasingly playing a crucial role in the application of engineering in medicine and for which there is a significant industrial demand. But a striking limitation has been the lack of commercially viable methods to reproducibly generate such structures with adequate process control. This talk will focus on novel methods and devices created by exploiting the well-known principles of phenomena such as electrohydrodynamics, microfluidics and gyration to prepare such fine entities containing the desired contents including active pharmaceutical ingredients, with clear possibilities of controlled mass production.
4:00 PM - BM01.08.05
Forces and Interfaces—Structural Damage to Biomolecules During Droplet Generation
Susannah Evans 1 , Ronan Daly 1
1 , University of Cambridge, Cambridge United Kingdom
Show AbstractPrecise and reliable microdroplet generation is highly desirable for studying solutions containing biological materials such as cells and enzymes, for creating functional coatings and also for continuous manufacturing and late-stage customisation of pharmaceuticals [1]. Inkjet printing is one technology capable of handling fluids in such a manner but during the printing process these, often delicate, molecules are frequently impaired and are seen to lose activity. However the precise mechanism of this damage is poorly understood. This research examines how the shear and extensional forces and changing interfaces experienced by the biological ink throughout the printing process impact on the retained activity of the example biomolecule, Horse Radish Peroxidase (HRP).
An inkjet system imparts large stresses and strains to the working fluid, for instance due to pressure variation within the print head for droplet generation and elongating flow upon droplet ejection. Concurrently, the ink is exposed to a variety of interfaces within the print head, ancillary equipment or upon ejection and impact with the substrate. A previous study demonstrated loss of activity up to 70% when printing HRP with losses experienced once compression rates exceed 2.5µm3/µs [2]. We report on the structural changes induced to HRP, a predominantly alpha-helical protein pervasively used within biochemistry, due to inkjet printing through an activity study. The influence of the moving air-liquid interface experienced by ejected droplets is investigated by comparison to printing with the nozzle submerged in different fluids.
It is anticipated that through a better understanding of the damage caused to proteins during the inkjet printing process, the technology can be more easily translated into large-scale bio-printing and enable molecules with higher printability to be clearly identified based on their structural and physical properties. Furthermore, as interest in using bio-macromolecules as drug candidates has increased due to their favourable properties, which include fewer side effects and higher efficacy than small molecule drugs, this research demonstrates a clear application within the pharmaceuticals industry.
[1] R. Daly, T. S. Harrington, G. D. Martin, and I. M. Hutchings, “Inkjet printing for pharmaceutics - A review of research and manufacturing,” Int. J. Pharm., 2015.
[2] G. M. Nishioka, A. A. Markey, and C. K. Holloway, “Protein damage in drop-on-demand printers,” J. Am. Chem. Soc., vol. 126, no. 50, pp. 16320–16321, 2004.
4:15 PM - BM01.08.06
Monitoring the Stiffness Distribution of Engineered Tissues—A Preliminary Study
Sevan Goenezen 1
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractSignificant progress has been made in tissue engineering in the last few decades, wherein cells are planted into a biodegradable polymer or other scaffold substrates and regenerate native tissue, while the polymer degrades. One of the major challenges is to coordinate polymer degradation time with extracellular matrix (ECM) production through cells. In particular, if the polymer degrades faster than native tissue is produced, 1) structural stability may not be ensured, 2) cells may negatively respond to changes in their stiffness environment. Currently, there is no straightforward approach to monitor the stiffness distribution non-destructively in three dimensional space (3D) and time, while the engineered tissue is continuously growing and remodeling. Uniaxial compression tests will provide bulk properties, but the actual stiffness will likely vary throughout the engineered tissue. More recent methods rely on solving inverse problems for the stiffness distribution from measured full field displacements using ultrasound, magnetic resonance imaging (MRI), or optical coherence tomography (OCT). These techniques were mainly utilized to measure full field displacements in two dimensional space (2D) and application to 3D requires highly expensive equipment extensions. For example ultrasound based methods usually acquire displacements in 2D with linear array transducers and would be required to be replaced by two dimensional array transducers. Three dimensional displacement data collection may also require drastically increased imaging time, for example with MRI scanning in the third dimension.
In this talk, we will present a novel approach to map the stiffness distribution in 3D, relying on inverse algorithms based on finite element techniques, 2 digital cameras, a digital image correlation system, and force sensors. A set of 2 digital images of the specimen’s surface are recorded before and after applying a force to deform it. From these images, a digital image correlation system will determine surface displacements that are essential in the inverse solution process. A great advantage of this method is the low acquisition cost, since it requires basic force sensors and regular digital cameras used with a digital image correlation software that are relatively low cost. Finally, the proposed approach is conveniently scalable to various specimen sizes and various surface geometries, in other words the surface geometry can be complex and does not necessarily need to be flat.
4:30 PM - BM01.08.07
Long-Term Imaging of Cellular Forces with High Precision by Elastic Resonator Interference Stress Microscopy (ERISM)
Nils Kronenberg 1 , Philipp Liehm 1 , Elena Delaka 1 , Andrew Meek 1 , Malte Gather 1
1 , University of St Andrews, St Andrews United Kingdom
Show AbstractThe ability to monitor mechanical forces applied by cells is crucial to advance our understanding of a range of fundamental biological processes.1 Today, various biophysical techniques exist to investigate different types of interactions between cells and the substratum they adhere to (e.g. Traction Force Microscopy2), each having a specific set of advantages and limitations.
With Elastic Resonator Interference Stress (ERISM),3 we present a robust approach to measure mechanical cell-substrate interactions in diverse biological systems by interferometrically detecting deformations of an elastic micro-cavity. ERISM yields stress maps with exceptional precision and large dynamic range (2 nm displacement resolution over a >1 μm range, translating into 1 pN force sensitivity). This enables investigation of minute vertical stresses (<1 Pa) involved in podosome or invadopodium protrusion, protein specific cell-substrate interaction and amoeboid migration through spatial confinement in real time. ERISM requires no zero-force reference and avoids phototoxic effects, which facilitates force monitoring over multiple days and at high frame rates and eliminates the need to detach cells after measurements. This, and the excellent long-term stability of the elastic micro-cavities, allows observation of slow cellular processes, like differentiation, or force monitoring during prolonged disease states (e.g. during podocyte damage,4 a pivotal event underlying the pathogenesis of multiple glomerular diseases), as well as further investigation of cells, e.g. by immunostaining.
In this presentation, we explain the working principle of ERISM and quantify its stress sensitivity and lateral resolution via Atomic Force Microscopy indentation measurements. We demonstrate the high accuracy and long-term, time-lapse capability of ERISM and also show applications to cell-culture level disease models of kidney injury and cancer invasion.
1. Bao, G. & Suresh, S., Cell and molecular mechanics of biological materials. Nat. Mater. 2, 715–725 (2003).
2. Kraning-Rush, C. M., Carey, S. P., Califano, J. P. & Reinhart-King, C. A., Quantifying traction
stresses in adherent cells, Methods Cell Biol. 110, 139–178 (2012).
3. Kronenberg, N.M., Liehm, P., Steude, A., Knipper, J.A., Borger, J.G., Scarcelli, G., Franze, K., Powis, S.P., Gather, M.C., Long-term imaging of cellular forces with high precision by elastic resonator interference stress microscopy, Nat. Cell Biol. (2017). DOI: 10.1038/ncb3561
4. Kronenberg, N.M., Haley, K. E., Liehm, P., Harrison, D.J., Gather, M.C., Reynolds, P.A., Podocyte Injury Elicits Loss and Recovery of Podocyte Cellular Forces Monitored by Time-Lapse Elastic Resonator Interference Stress Microscopy, submitted
4:45 PM - BM01.08.08
Scaling Views on the Strength and Toughness of Bio-Composites Consisting of Soft and Hard Elements
Ko Okumura 1
1 , Ochanomizu University, Tokyo Japan
Show Abstract
In this presentation, we would like to share our simple views on several topics in soft matter physics, which may be useful for understanding mechanical properties of complex hierarchical structures found in nature. In particular, we will emphasise topics related to mechanical aspects of biological composite comprising soft and hard elements, such as nacre, a shining layer found on the surface of pearls.
Firstly, we briefly discuss several topics to introduce our strategy to extract simple views. The topics will include coalescence of liquid drops [1], the drag friction in a granular medium [2], and high stretchability of “Kirigami” (paper with many cuts) [3].
Secondly, we discuss static aspects of fracture by taking as examples three biological materials: nacre, spider webs, and the exoskeleton of lobsters [4]. In the layer of nacre, hard plates are glued together with soft biological polymers. We show scaling laws from the exact solution to a simple model, which are in good agreement with finite-element model calculations. We thereby reveal mitigation of stress concentration at crack tips and its mechanism. On the basis of our simple views on nacre, we provide insight into the toughness of the exoskeleton of lobsters. We further discuss a possible mechanical adaptability of spiders to living environment by using a simple model of spider webs. For this problem, we focus on the maximum stress appearing on the web under a pretension and regard the stress as a measure of the strength of the web.
Thirdly, we discuss dynamic aspects of crack propagation, focusing on the following unresolved phenomenon: the velocity of crack propagation exhibits a jump as a function of initially applied load. We tackle with this problem by using a simple simulation model [5] and another simpler model [6]. For the latter, we find an exact solution for the dynamical problem. By the two approaches, we elucidate the physics of the dynamical features of crack propagation.
References
[1] Maria Yokota and Ko Okumura, Proc. Nat. Acad. Sci. (USA), 108 (2011) 6395–6398.
[2] Yuka Takehara and Ko Okumura, Phys. Rev. Lett. 112 (2014) 148001.
[3] Midori Isobe and Ko Okumura, Sci. Rep. 6 (2016) 24758.
[4] Ko Okumura, MRS Bulletin, 40 [04] (2015) 333-339.
[5] Yuko Aoyanagi and Ko Okumura, Polymer 120 (2017) 94-99.
[6] Naoyuki Sakumichi and Ko Okumura, https://arxiv.org/abs/1611.04269 (under revison).
Symposium Organizers
Dinesh Katti, North Dakota State University
Christian Hellmich, TU Wien - Vienna University of Technology
Ko Okumura, Ochanomizu University
Peter Pivonka, University of Melbourne
BM01.09: Session VII
Session Chairs
Elisa Budyn
Christian Hellmich
Roger Narayan
Ko Okumura
Thursday AM, November 30, 2017
Sheraton, 2nd Floor, Constitution B
8:30 AM - *BM01.09.01
Mechanical Properties of 3D Printed Structures
Roger Narayan 1
1 , North Carolina State University, Raleigh, North Carolina, United States
Show AbstractAdditive manufacturing, also known as 3D printing, is an approach that is being considered for fabrication of individualized medical devices. In additive manufacturing, fabrication of three-dimensional objects is performed via selective joining of solids, liquids, or powders in a layer-by-layer manner. Microscale and sub-microscale features may be incorporated within these customized medical devices to promote appropriate cell-medical device interactions. Two photon polymerization is an additive manufacturing approach that involves use of ultrashort laser pulses to selectively polymerize photosensitive materials at small length scales. In the two photon polymerization process, multiphoton absorption of photons initiates chemical reactions between photoinitiator molecules and monomers in a transparent matrix. The quadratic character of the two photon absorption probability and the well-defined polymerization threshold of this approach allow one to overcome the diffraction limit and create medical devices containing features below one micrometer. The use of biocompatible materials for two photon polymerization will be described. Mechanical evaluation of two photon polymerization-processed materials using nanoindentation will also be discussed. Our results indicate that additive manufacturing approaches such as two photon polymerization provide unique benefits for processing medical implants and prostheses with appropriate mechanical properties and unique medical functionalities.
9:00 AM - BM01.09.02
Dynamic Interaction between Cultivated Cells and Liquid on Cell Differentiation
Nobuyuki Tanaka 1 , Junko Takahara 1 , Akane Awazu 1 , Yoshihide Haruzono 2 , Hiromitsu Nasu 2 , Yo Tanaka 1
1 , RIKEN, Suita Japan, 2 , Kitagawa Iron Works Co., Ltd., Fuchu Japan
Show AbstractWe have proposed a method for jet-flow based wettability assessment and applied to in-liquid assessment of cultivated mucosal epithelial cells (N. Tanaka et al., Biomaterials, 34, 9082-9088, 2013). The previous study has revealed the correlation between mucous formation and surface wettability and the importance of wettability assessment on cellular surfaces.
Surface wettability is one of the most important properties expressing physico-chemical interactions between liquids and materials. The wettability normally depends on both surface morphologies and chemical properties of materials. High wettability surfaces tend to spread a small volume of liquid to large area on the surfaces. On the other hand, low ones can form liquid into droplets, resulting in liquid repelling. Contact angle is a common index of wettability, where and low and high contact angles indicate low and high wettability, respectively. However, the contact angle on cellular surfaces is hardly measured because of its high wettability and in-liquid measurement.
The principle of proposed wettability assessment method is based on the behavior of liquid covering a material in a container during or after the application of jet-flow pressure from the nozzle equipped on the system. The main indexes of proposed method are (1) liquid squeezed size during jet-flow application and (2) liquid recovery speed after the cease of application. The liquid squeeze size and recovery speed in case of high wettability surface are smaller and quicker than those in low case, respectively.
Recently, we newly found out the difference of liquid recovery speed between myogenic differentiated and undifferentiated cells in vitro. In this time, we discuss the possibility of non-invasive assessment of cell differentiation via the surface wettability of cells.
9:15 AM - BM01.09.03
Mechanotargeting of Nanoparticles
Sulin Zhang 1 3 , Qiong Wei 1 , Changjin Huang 2 , Peter Butler 3
1 Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, Pennsylvania, United States, 3 Department of Biomedical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractTargeted delivery of nanoparticle (NP)-based therapeutic agents to malignant cells and tissues has exclusively relied on chemotargeting, wherein ligands coated on nanoparticle surface specifically target the receptors overexpressed on malignant cells. Here we first show from a fundamental biophysics that cellular uptake can also be biased to malignant cells based on altered cell surface mechanics, suggesting mechanotargeting. To assess the efficiency of mechanotargeting, we direct the cells (HeLa and HCT-8) into different mechanical states and promote their metastatic potential by seeding cells on hydrogels of varying stiffness. In vitro delivery reveals that cells on stiff gels are mechanically more stressed and expose a larger surface area accessible to NPs, presenting two competing factors on cellular uptake. Prolonged culture on stiff hydrogels drives cohesive HCT-8 cell colonies into dispersed, individual malignant cells, featuring a metastatic-like phenotypic change. The dispersed cells are soft and adopt an unspread, 3D morphology, resulting in several-fold higher uptake than the pre-dispersed counterparts. Our study opens a new paradigm in harnessing mechanics for future nanomedicine
9:30 AM - BM01.09.04
Angiogenicity, Invasiveness and Chemoresistance of Breast Cancer—An In Vitro Engineering Test Bed
Sumanta Kar 1 , Dinesh Katti 1 , Kalpana Katti 1
1 , North Dakota State University, Fargo, North Dakota, United States
Show AbstractBreast cancer (BrCa) has the propensity to spread to other organs and bone is the most common site of breast cancer metastases. Approximately 70% breast cancer patients eventually develop bone metastasis. The interaction between cancer cells and the host microenvironment has been considered to be responsible for the establishment of metastatic lesions. To study bone metastasis, numerous 2D models and in vivo animal models have been developed. Nevertheless, 2D models suffer from severe limitations in terms of mimicking in vivo cell morphology as well as cellular interactions whereas animal models are expensive and time-consuming. Therefore, the goal of this study is to engineer bone-mimetic 3D in vitro model to study breast cancer mediated bone metastasis. Here we report the development of a novel PCL/in situ HAPclay 3D in vitro bone model for breast cancer bone metastasis. In this study, we have sequentially cultured (SC) breast cancer cells (HBCCs) with mesenchymal stem cells (MSCs) on PCL/in situ HAPclay scaffolds to recreate bone-mimetic environment conducive for the growth of cancer cells. Cell viability (WST-1), Alkaline Phosphatase (ALP) assay, and SEM imaging were performed on scaffold constructs at days 28, 33 and 38. We quantified mRNA levels of genes responsible for epithelial-mesenchymal transition (EMT) (Twist, Vimentin), angiogenesis (VEGF, IL8), and chemoresistance (MTDH) using qRT-PCR. Confocal studies were also carried out to detect protein levels of various genes. Cell viability (WST-1) assay results indicated that both MSCs and HBCCs have been able to thrive and proliferate on scaffolds. MSCs showed significantly low cell viability as compared to both HBBCs and SC at indicated time. Insignificant changes were observed in SC constructs at day 33 and day 38, and HBCCs showed overall good cell viability. Inconsequential levels of ALP activity was observed in MSCs and SC constructs, which is consistent with our previous study on prostate cancer. Nanomechanical evaluations are conducted on the breast cancer test-bed. FTIR spectroscopic evaluation is also conducted on the in vitro tumors. Also, scanning electron micrographs revealed the formation of tumors when breast cancer cells were sequentially cultured with mesenchymal stem cells. Gene expression studies have confirmed enhancement of metastatic properties of cancer cells upon sequentially culturing them with mesenchymal stem cells. Drug studies using Doxorubicin followed by gene expression showed downregulation of gene associated with chemoresistance (metadherin). Together, a novel bone-mimetic 3D cancer model has been developed that could be used as a test-bed for drug studies.
9:45 AM - BM01.09.05
Solitary Waves in Morphogenesis—Determination Fronts as Strain-Cued Strain Transformations
Brian Cox 1
1 , Arachne Consulting, Sherman Oaks, California, United States
Show AbstractWe consider cells exhibiting two properties: 1) cells undergo a one-time strain transformation (i.e., a discontinuous change in their state of strain) when they sense a sufficiently large strain stimulus imposed by a contacting neighbor; and 2) cells migrate continually to maintain a preferred local cell density (number of cells per unit area). In a homogeneous population of such cells, a strain pulse can be initiated by stimulus at a single point and then propagate very stably with constant amplitude in a self-sustaining manner across the population. Such a pulse could serve as a reliable trigger for a “determination front”, i.e., as the timing signal for sequential maturation of cells into a different state. We consider three different cell actions for generating the strain transformation: a sudden change in the preferred area density of cells; the onset of proliferation; and the commencement of a growth process that changes the overall geometry of the population. We demonstrate that the wave problems in all three cases are isomorphic. Thus biological systems in which two or three of the mechanisms occur simultaneously will generate the same type of stable strain pulse. Analytical results, including closed form approximations, are derived for the amplitude of the strain in the pulse, which is independent of the length of the time interval over which the strain transformation is completed once triggered and of the details of the time history of a cell’s strain while it is undergoing the strain transformation.
10:30 AM - *BM01.09.06
Human Stem Cell Derived Osteocytes in Bone-on-Chip
Elisa Budyn 1 2 , Nabila Gaci 1 , Samantha Sanders 1 , Morad Bensidhoum 4 , Eric Schmidt 3 , Bertrand Cinquin 5 , Patrick Tauc 5 , Herve Petite 4
1 Mechanical Engineering - LMT, Ecole Normale Superieure Cachan, Cachan France, 2 Mechanical Engineering, Oral Medicine and Diagnostic Sciences, University of Illinois at Chicago, Chicago, Illinois, United States, 4 Biology - B2OA, University Paris Diderot, Paris France, 3 Mechanical Engineering, University of Illinois at Chicago, Chicago, Illinois, United States, 5 Biology - LBPA, Ecole Normale Superieure Cachan, Cachan France
Show AbstractLarge bone defects cannot repair. Such pathologies carry $10 billion financial burden on the U.S. healthcare system. Successful techniques promoting good quality tissue regeneration is complex and requires the addition of functional materials. Bone repair called remodeling is orchestrated by osteocytes that derive from mesenchymal stem cells in the bone marrow. Osteocyte in situ mechanical microenvironment is difficult to precisely quantify due to the cell dentritic complex shape and the ECM (Extra Cellular Matrix) highly hierarchical structure. The dentritic cell morphology is characteristic of their full differentiation and is key to enable their mechano-sensitivity. It is essential to quantify the relationship between in situ mechanical stimulation and the cell biological response to design successful regenerative therapies.
Dual experiment and 3D multi-cellular multi-scale modeling investigates stem cell derived osteocyte mechanobiology in bone-on-chip composed of MSCs differentiating into osteocytes reseeded on human bone. Osteocytes with their cytoplasmic processes and attached to their PCM (peri cellular matrix) to sense mechanical stimulations in the mineralized ECM were explicitly modeled from segmentation of confocal microscopy images. The ECM multi-scale local constitutive damage and heterogeneity were implemented around the cell. The multi-scale image-based FEM model was subjected to the experimental boundary conditions and validated by the experiment. Close cooperation between mature osteocytes and their progenitors exists to detect defects and initiate remodeling. The in situ calcium response of the cells at different differentiation stages to in situ mechanical loads were measured in vitro by the released chemical concentration variations under mechanical load in confocal microscopy. The differentiation stages were assessed by in situ immunohistochemistry and by histochemistry of fixed samples .
The live systems mechanically behaved as fresh human bone at the macro scale and the FEM model measured the local stress field. The cells reorganized in vitro as they would in vivo at the different stage of differentiation and produced a mineralizing collagen I fibrous ECM at 109 days of which the strength was a quarter of native bone. Histochemistry of fixed samples showed calcium minerals and collagen type I at 39 days. In situ immunochemistry revealed the production of E11 and sclerostin by early and mature stem cell derives osteocytes at 640 days.
The calcium membrane transport seemed to adapt to the expected in situ mechanical load at successive stages of differentiation. The cells reorganized in network at 256 days and released chracteristic osteocyte proteins.
E. Budyn, M. Bensidhoum, S. Sanders, E. Schmidt, P. Tauc, E. Deprez, H. Petite, Bone-on-chip to study osteocyte mechanotransduction and ECM formation, European Cell and Materials, (2016) v. 32, Suppl. 4, p. 32.
With the support from NSF CMMI BMMB 1214816, the Farman Institute.
11:00 AM - BM01.09.07
Damage Accumulation and Failure in Tissue
Sai Deogekar 1 , Catalin Picu 1
1 , Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractBiological tissues have complex fibrillar structure with the main component being collagen. Studying the mechanics, damage accumulation and failure of fiber networks leads to an understanding of the macroscopic failure of soft tissues. Failure in such fibrous networks can occur either due to failure of the fibers or due to failure of the inter-fiber bonds. A number of studies can be found in the literature which study both these failure mechanisms for networks subjected to small deformations. However, fibrous networks exhibit a number of peculiar behaviors (such as increasingly anisotropic behavior and high Poisson’s ratios) in the large deformation regime which may affect their strength. In this work, we study the deformation and failure mechanisms of collagen-based tissues under large deformation. We identify the key structural and material parameters of the fibrous networks which have an impact on the overall strength. The study elucidates aspects of the failure of biological tissues, and provides guidelines for the design of superior materials for tissue engineering and other applications.
11:15 AM - BM01.09.08
Influence of Donor Age on Stem Cell-Based Tissue-Engineered Cartilage
Ophelie Pollet 4 1 , Caroline Boulocher 1 , Christel Henrionnet 3 , Astrid Pinzano 3 , Morad Bensidhoum 2 , Thierry Hoc 4
4 LTDS UMR 5513, Ecole Centrale de Lyon, Ecully France, 1 Campus Veterinaire, VetAgro Sup, Marcy L'Etoile France, 3 , IMoPA UMR 7365, Vandoeuvre les Nancy France, 2 , B2OA UMR7052, Paris France
Show AbstractThe annual incidence of articular cartilage injuries worldwide is around 30 million cases of knee osteoarthritis (OA) and 1.2 million cases of focal cartilage defects. Tissue-engineered products offer great hope for the treatment of OA through developing biomimetic tissue substitutes. However the impact of donor age on stem cell-based tissue-engineered cartilage (TEC) has been underinvestigated while aging is known to influence mesenchymental stem cells (MSCs) metabolism and function [1,2]. The objective of the present study was to evaluate TEC architectural and mechanical properties depending on the MSC donor age using in vitro and in vivo models.
For the in vitro study, collagen sponges were seeded with MSCs from young (<20 yo) or old donors (>60 yo) during 28 days in a chondrogenic medium. Indentation-relaxation tests and biphotonic microcopy were performed to study TEC viscoelastic properties and microarchitecture, respectively. Histology was used to investigate cartilage extracellular matrix (ECM) content. For the in vivo study, an osteochondral defect was created on the weight bearing portion of the right medial femoral condyle in twelve adult male nude rats. The defect was repaired with TEC from young donors in six rats and from old donors in six rats. Four weeks postsurgery, the repair tissue area was evaluated as above.
In vitro, MSC from young donors were more “active” with a more intense multiplication compared to MSC from old donors. The quantity of ECM, especially type II collagen and glycosaminoglycans, was significantly higher in TEC from old donors. No differences in TEC mechanical properties were observed suggesting a difference in collagen quality. In vivo, inflammatory reaction and bone degradation were observed in the joints implanted with TEC from young donors. The mechanical properties of repair tissue were significantly higher in rats with TEC from old donors associated which were associated with a strong microarchitectural difference in term of collagen fibers and chondron size. However, in both cases, mechanical properties of the repair tissue were lower compared to native articular cartilage.
To conclude, in the in vitro model, a higher amount of collagen was synthetized by the chondrocytes derived from the MSCs from old donors. In the in vivo model, TEC from old donors resulted in a repair tissue with a greater instantaneous modulus than TEC from young donors but smaller than native articular cartilage. In the near future, the influence of knee joint microenvironment during the in vitro process could be investigated to improve the mechanical properties of TEC.
[1] M. N. Starodubtseva, Mechanical properties of cells and ageing. Ageing Research Reviews, Vol. 10, pp. 16-25, 2011.
[2] M. Zaim et al., Donor age and long-term culture affect differentiation and proliferation of human bone marrow mesenchymal stem cells. Annals of Hematology, Vol.91, pp. 1175-1186, 2012
11:30 AM - BM01.09.09
Janus-Like Behavior and Charge Inversion in Negatively Charged Semi-Permeable Plasma Membrane
Shayandev Sinha 1 , Haoyuan Jing 1 , Siddhartha Das 1
1 , University of Maryland, College Park, Maryland, United States
Show AbstractThe role of semi-permeable membranes like lipid bilayer is ubiquitous in a myriad of physiological and pathological phenomena. Typically, lipid membranes are impermeable to ions and solutes; however, protein channels embedded in the membrane allow the passage of selective, small ions across the membrane enabling the membrane to adopt a semi-permeable nature. This semi-permeability, in turn, leads to electrostatic potential jump across the membrane, leading to effects such as regulation of intracellular calcium, extracellular-vesicle-membrane interactions, etc. The negative charge of the plasma membrane (PM) severely affects the nature of the moieties that may enter or leave the cells as well as a large number of ion-interactions-mediated intracellular and extracellular events. In this study, we theoretically demonstrate that this semi-permeable nature may trigger the most remarkable charge inversion (CI) phenomenon in the cytosol-side of the negatively-charged lipid bilayer membrane that are selectively permeable to only positive ions of a given salt. This CI is manifested as the changing of the sign of the electrostatic potential from negative to positive from the membrane-cytosol interface to deep within the cytosol. We also report our discovery of a most fascinating scenario, where the negatively charged PM behaves as a “janus-like" membrane, where one interface (e.g.,membrane-cytosol interface) shows a positive surface (or zeta) potential, while the other interface (e.g., membrane-electrolyte interface) still shows a negative zeta potential. Therefore, we encounter a completely unexpected situation where an interface (e.g., membrane-cytosol interface) that has negative surface charge density demonstrates a positive zeta potential. We establish that such a behavior of the membrane can be ascribed to an interplay of the nature of the membrane semipermeability and the electrostatics of the electric double layer (or EDL) established on either sides of the charged membrane. We also study the impact of the parameters such as the concentration of this salt with selectively permeable ions as well as the concentration of an external salt in the development of this CI phenomenon. We anticipate such CI will profoundly influence the interaction of membrane and intra-cellular moieties (e.g., exosome or multi-cellular vesicles) having implications for a host of biophysical processes.
11:45 AM - BM01.09.10
Molecular Muscle Based on pH-Driven Stretching-Shrinking of Peptides
Grazia Messina 1 , Marta De Zotti 2 , Giovanni Marletta 1
1 Chemical Sciences, University of Catania, Catania Italy, 2 , University of Padova, Padova Italy
Show AbstractMaterials that change structure and properties in response to different local stimuli are increasingly being studied in view of their potential application in the wide fields of nanosensors, molecular machines and/or bio-inspired nanotechnology. A particularly challenging application, in this context, concerns their potential as nanometric switches, taking profit of the stimuli-driven structure modification to be applied as molecular muscle or molecular spring.
Peptides are ideally suited for this purpose because of the range of useful structural and chemical amino acid properties. This variety of properties allows to take profit of non-covalent interactions, including electrostatic (acidic and basic amino acids), hydrophobic, p-stacking (aromatic amino acids), hydrogen bonding (polar amino acids) as well as covalent (disulfide) bonds as well as steric contributions, directing the amino acid assembling. Each of these interactions in turn can be managed by tuning simple chemical parameters as ionic strength, pH and temperature.
In this communication we show the shrinking-stretching cycling behavior of Trichogin GA IV (TRIC), a peptide belonging to the family of peptaibiotics, i.e., antimicrobial peptides rich in the helix-inducer α-aminoisobutyric acid (Aib) residue, and its analog in which four positively charged Lysine residues have been introduced (LysTRIC). Both peptides were anchored to polycrystalline gold surfaces through a N-terminal lipoic acid moiety. The loading and the conformational properties of the surface-bound peptides were investigated by means of Quartz Crystal Microbalance with Dissipation monitoring and Localized Surface Plasmon Resonance and Force Spectroscopy measurements. We have found that only yhe analog of Trichogin GA IV (i.e., LysTRIC) underwent repeatable cycles of chain shrinking and stretching in response to pH cycling, producing a small but measureable nanomechanical response. This behavior has been explained in terms of the reversible switch of its structure between the two, well-defined, different helical conformations: 310-helix and α-helix. The effect has been found to double when the dimer is tested in similar conditions. Overall, the LysTRIC and its dimer can be used as biomolecular device able to shrink and stretch its thickness in response to pH variations
BM01.10: Session VIII
Session Chairs
Amit Bandyopadhyay
Dinesh Katti
Jeffry Nyman
Alex Robling
Thursday PM, November 30, 2017
Sheraton, 2nd Floor, Constitution B
1:30 PM - *BM01.10.01
Assessing the Matrix Quality of Human Cortical Bone
Jeffry Nyman 1
1 , Vanderbilt University Medical Center, Nashville, Tennessee, United States
Show AbstractThe fracture resistance of bone arises from each level of its hierarchical organization. With aging and the onset of certain disease such as diabetes, deleterious changes occur at multiple length scales: thinning of the cortex (macro-level), increasing intra-cortical porosity (micro-level), and accumulating advanced glycation end-products (nano-level). There are now imaging techniques that assess the structure of cortical bone and the micro-architecture of trabecular bone in vivo. Ongoing research is translating several matrix-sensitive techniques to the clinical assessment of bone matrix quality. Specifically, being sensitive to physiochemical properties of materials, Raman spectroscopy (RS) can be done directly on bone or done transcutaneously using spatially offset probes. To determine whether RS could potentially report on the fracture resistance of human cortical bone, we analyzed single edge notched beam (SENB) specimens. The specimens were extracted from the lateral quadrant of the mid-shaft of cadaveric femurs (female and male donors spanning 20 to 100 years of age). With the osteonal axis aligned parallel to the polarization axis, Raman spectra were acquired from multiple spots using a confocal Raman microscope with a 20X objective and a 785 nm laser for each donor (N=58). The peak ratio of the intensities at 1670 cm-1 and at 1640 cm-1 significantly correlated with the J-integral (crack propagated normal to the osteonal axis). Moreover, when age and apparent volumetric BMD (vBMD) from micro-computed tomography of the notched region were included in general linear models, the Amide I sub-peak ratio of 1670/1640 (cm-1) significantly explained 50.5% and 46.6% of the variance in crack initiation toughness and in the J-integral, respectively. Next, after identifying the origins of proton signals within human cortical bone using nuclear magnetic resonance (1H NMR) relaxometry, we found that matrix-bound water correlates with the material strength of human cortical bone, explaining 64% of the age-related variance, and that loosely bound water detected by NMR contributes to bone toughness. Perhaps relevant to diabetes, we also recently showed that bound water also correlated with the ability of human cortical bone to resist crack growth as determined by the aforementioned fracture toughness testing and that the linear combination of bound water (positive) and pore water (negative) explained 47% of the variance in crack initiation toughness when age was included as a covariate. Using ultra-short echo-time magnetic resonance imaging (MRI) with magnetization preparations to null either the pore water or bound water, MRI-derived bound and pore water concentrations, together as significant covariates, explained 63% of the variance in the strength of cadaveric radii from elderly donors. Thus, emerging tools have the potential to assess the matrix quality of bone in vivo, thereby improving the prediction of fracture risk.
2:00 PM - BM01.10.02
Atomistic Study of Wet-Heat Resistance of Calcium Dipicolinate (Ca-DPA) in the Core of Spores
Ankit Mishra 1 , Pankaj Rajak 1 , Subodh Tiwari 1 , Chunyang Sheng 1 , Aravind Krishnamoorthy 1 , Aiichiro Nakano 1 , Rajiv Kalia 1 , Priya Vashishta 1
1 , University of Southern California, Los Angeles, California, United States
Show AbstractThe extreme heat resistance of dormant bacterial spores strongly depends on the extent of protoplast dehydration and the concentration of dipicolinic acid (DPA) and its associated calcium salts (Ca-DPA) in the spore core. Recent experiments have suggested that this heat resistance depends on the properties of confined water molecules in the hydrated Ca-DPA-rich protoplasm, but atomistic details have not been elucidated. In this study, we used reactive molecular dynamics (RMD) simulations to model the dynamics of water in hydrated DPA and Ca-DPA as a function of temperature. The RMD simulations indicate two distinct solid-liquid and liquid-gel transitions for the spore core. Simulation results reveal monotonically decreasing solid-gel-liquid transition temperatures with increasing hydration. Additional calculations on the specific heat and free energy of water molecules in the spore core further confirm the higher heat resistance of dehydrated spores. These results provide an insight into the experimental trend of moist-heat resistance of bacterial spores and reconciles previous conflicting experimental findings on the state of water in bacterial spores.
This research was supported by the Defense Threat Reduction Agency Grant # HDTRA 1-14-1-0074. We thank Dr. Douglas Allen Dalton for his encouragement and continued support throughout this investigation. The computations were performed at the Centre for High Performance Computing of the University of Southern California.
2:15 PM - *BM01.10.03
3D Printed Porous Metals for Load-Bearing Implants
Amit Bandyopadhyay 1 , Anish Shivaram 1 , Indranath Mitra 1 , Susmita Bose 1
1 , Washington State University, Pullman, Washington, United States
Show AbstractThough non-cemented implants are becoming popular among both traditional and younger patients, a key challenge still remains with these implants i.e., early stage osseointegration. Porous metal coated implants take longer time to bond with the surrounding bone tissue than cemented implants. Moreover, current manufacturing practices for porous metal coating results in a weak interface between the coating and the implant. We have used laser based 3D printing to enable location or design specific coating deposition ability with designed pore size and volume fraction porosity.
In this work, porous titanium and tantalum implants, with varying volume% porosity, were manufactured using Laser Engineered Net Shaping (LENS™) to measure the influence of porosity towards bone tissue integration in vivo. Surfaces of LENS™ processed porous implants were further modified with TiO2 nanotubes to improve cytocompatibility of these implants. We hypothesize that surface modified 3D printed porous Ta or Ti coatings on Ti can enhance early stage in vivo bone tissue integration ability in load-bearing implants. To test our hypothesis, in vivo experiments using a distal femur model of male Sprague-Dawley rats were performed for a period of 12 weeks. In vivo samples were characterized via micro-computed tomography (CT), histological imaging, scanning electron microscopy, and mechanical push-out tests. Our results indicate that porosity played the most important role for Ti based coatings to establish early stage osseointegration forming strong interfacial bonding between the porous implants and the surrounding tissue, with or without surface modification, compared to dense Ti implants used as a control. However, when compositional variations were included, adding Ta with Ti, both porosity and composition played a significant role towards in vivo bone tissue integration. We have also measured the role of porosity towards mechanical degradation under cyclic loading. Increased pore volume lowered fatigue life of these implants.
The presentation will focus on processing as well as physical, mechanical and biological characterization of 3D printed porous metal implants.
3:15 PM - *BM01.10.04
The Biology of Wnt-Regulated Mechanical Signaling in Bone Tissue
Alex Robling 1 2
1 , Indiana University School of Medicine, Indianapolis, Indiana, United States, 2 , Roudebush VAMC, Indianapolis, Indiana, United States
Show AbstractThe search for pathways involved in load-induced bone formation was advanced considerably several years ago, when genetic mapping studies among families with osteoporosis pseudoglioma (OPPG) revealed that the low density lipoprotein receptor related protein 5 (LRP5) had important functions in the mammalian skeleton. Mice engineered with a loss-of-function mutation in Lrp5 exhibit low bone mass, but the weight-bearing portions of the skeleton bear a greater deficit in bone mass than the non weight-bearing portions. Those observations led us to test the hypothesis that Lrp5 is important in mechanical signaling. When subjected to in vivo ulnar loading, Lrp5-/- mice exhibit a severe reduction in load-induced bone formation, compared to wild-type controls. Shortly after the discovery of families harboring loss-of-function mutations in LRP5, other investigators identified a series of missense mutations in LRP5 that result in abnormally high bone mass (HBM) among the patients that possess those alleles. In light of the strong effects of Lrp5 loss-of-function mutations on mechanotransduction, we investigated whether the Lrp5 gain-of-function (HBM) alleles might also alter mechanoresponsiveness in the bone tissue. Specifically, we asked whether normal expression of one of two different Lrp5 HBM mutations would enhance load-induced bone gain and/or prevent disuse-induced bone loss. To this end, we knocked in two of the human missense mutations into mice, and conducted axial tibial loading experiments. These mice were more sensitive to mechanical loading than WT mice. The question of how Lrp5 participates in mechanotransduction under normal conditions emerged as a particularly relevant gap in our understanding of this pathway. We looked at several secreted inhibitors of the Wnt/Lrp5 pathway and found that the osteocyte product sclerostin was dramatically regulated by mechanical loading. More importantly, when we prevented sclerostin from being regulated by the mechanical environment, using a transgenesis approach, we found a nearly complete lack of response to stimulation. Work on the recently identified sclerostin co-receptor Lrp4 also suggests that this protein might participate in the sclerostin-driven mediation of mechanotransduction. To address this issue, we have generated both floxed loss-of-function and knock-in gain-of-function mouse models to elucidate the role of Lrp4 in mechanical signaling. Taken together, the data suggest that the Wnt pathway is a crucial cascade in bone’s response to mechanical loading. Therapeutic targeting of this pathway holds great promise for augmenting bone mass.
3:45 PM - BM01.10.05
Microstructural Origins of Creep and Fatigue Behaviour of Arundo Donax L Using Nanoindentation, XRD and Internal Friction Measurements
Connor Kemp 1 2 , Gary Scavone 1 2
1 , McGill University, Montreal, Quebec, Canada, 2 , Centre for Interdisciplinary Research in Music Media and Technology, Montreal, Quebec, Canada
Show AbstractWoodwind instruments are played using a natural cane reeds manufactured from the culm of Arundo donax L (ADL), a bamboo-like material that is regarded as a hierarchical composite with orthotropic elastic symmetry. These reeds are extremely variable in terms of stiffness and vibrational performance and are known to degrade with time, making it difficult to identify and maintain reeds that will perform adequately and consistently. In this study, nanoindentation, XRD and other chemical analysis methods are used to identify the changing behaviour of reed material with time and exposure to moisture. Nanoindentation testing of the fiber cell wall (average diameter of 5 to 20 microns) structure was performed to quantify the viscoelastic behaviour of the fiber microstructure through analysis of creep parameters using strain rate - stress relationships and comparisons with more complex creep models (specifically, considering the viscoelastic response under a Berkovich tip). The use of nanoindentation can identify the source of stiffness degradation to see if it manifests in changes in fiber modulus and/or hardness, or if this effect is more matrix dominated. Results indicate that degradation due to moisture is not confined to the matrix of the microstructure, as is evidenced by changes in measured creep parameters. The effects of creep become more important with increased exposure to moisture, and may indicate a way that manufacturers can use to screen raw material for producing less variable reeds.Macro-scale testing of damping using internal friction (frequency dependent, stress-strain hysteresis) measurements is also completed to elucidate the effects of these changing microstructural properties on vibrational performance.
4:00 PM - BM01.10.06
Self-Organized Structural Calcites, Aragonites and Organic Networks within the White-Pearl Oyster and Its Dynamic Fracture Behaviors
Guowei Chen 1 , Hongyun Luo 1
1 School of Material Science and Engineering, Beihang University, Beijing China
Show AbstractBiological evolution has produced natural materials with exceptional fracture resistance and structural capabilities. Structural calcites, aragonites, and the bonding organics decide the growth, microstructures and mechanical properties of the oyster shell. The crystallographic orientation and structures were characterized and observed by XRD and TEM. The micro hardness and the induced crack propagations were tested and observed by micro hardness tester and SEM. Here, it was found out that the calcite prisms together with the coated organics not only construct another kind of ‘brick and mortar’ structure similar to the aragonite tablets, but also constitute a typical Murray networks. The calcite layer can be divided into three sublayers and direct evidences show that the calcite prisms are produced by two oriental methods, nucleation and growing in the first sublayer or fusing from the aragonites. The dynamic process and the micro mechanical behaviors of the aragonite tablets in the tensile tests were detected by acoustic emission (AE), which gave the interpretation of the dynamic mechanical behaviors during the fracture processes: fracture of the organics and friction of the minerals at the first two stages; wear and fracture of the minerals at the third stage. These mechanical behaviors and the corresponding AE events showed several critical features, such as the power-law distributions of the avalanche sizes and interval, which suggested that the underlying fracture dynamics during the fracture process of the nacre displayed a self-organized criticality (SOC). The results also implied that the disorder and long-range correlation between local micro-fracture behaviors may play important roles in the nacre’s deformation and fracture process. Calcites and aragonites are combined and working together, like two layers of vertically oriented ‘brick and mortar’s, ensuring the stable mechanical properties of the whole shell.
4:15 PM - BM01.10.07
Multimodal Surface Instabilities in Curved Film-Substrate Structures
Ruike Zhao 1 , Xuanhe Zhao 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractStructures of thin films bonded on thick substrates are abundant in biological systems and engineering applications. Mismatch strains due to expansion of the films or shrinkage of the substrates can induce various modes of surface instabilities such as wrinkling, creasing, period doubling, folding, ridging and delamination. In many cases, the film-substrate structures are not flat but curved. While it is known that the surface instabilities can be controlled by film-substrate mechanical properties, adhesion and mismatch strain, effects of the structures’ curvature on multiple modes of instabilities have not been well understood. In this paper, we provide a systematic study on the formation of multimodal surface instabilities on film-substrate tubular structures with different curvatures through combined theoretical analysis and numerical simulation. We first introduce a method to quantitatively categorize various instability patterns by analyzing their wave frequencies using Fast Fourier Transform. We show that the curved film-substrate structures delay the critical mismatch strain for wrinkling when the system modulus ratio between the film and substrate is relatively large, compared with flat ones with otherwise the same properties. In addition, concave structures promote creasing and folding, and suppress ridging. On the contrary, convex structures promote ridging and suppress creasing and folding. A set of phase diagrams are calculated to guide future design and analysis of multimodal surface instabilities in curved structures.
4:30 PM - BM01.10.08
Mechanically Interfacing with Biology Using Piezoelectric Poly-l-lactic Acid Nanowires
Michael Smith 1 , Yonatan Calahorra 1 , Qingshen Jing 1 , Yeonsik Choi 1 , Chess Boughey 1 , Sohini Kar-Narayan 1
1 , University of Cambridge, Cambridge United Kingdom
Show AbstractCollectively, cells can perform incredibly complex tasks. Their function allows us to interact with the world, fight disease and repair the materials that make us. The ability to control this behaviour could lead to significant advances in areas such as regenerative medicine, tissue engineering and bio-mimetic materials.
The emerging field of mechanobiology hints that this behaviour could be influenced by regulating the mechanical environment of the biological system. Currently this is achieved by varying the physical properties of the substrate or scaffold material. However, the use of functional materials could lead to so-called ‘smart’ scaffolds, capable of in situ control of the local mechanical environment. Piezoelectric materials are ideal candidates to perform such a task, especially when nanostructured, given their ability to both detect and apply small forces. This work describes the production and characterisation of piezoelectric poly-l-lactic acid nanowires and their implementation into a device which allows for local mechanical stimulation to be applied to a cell culture as it is growing – towards a piezoelectric ‘lab-on-a-chip’ for mechanobiology.
Poly-l-lactic acid is a biologically derived polymer that exhibits shear piezoelectricity. Here, nanowires of this polymer have been produced using a template wetting method, and their piezoelectric properties characterised using Piezoresponse Force Microscopy (PFM) [1] - the first observation of shear piezoelectricity in this material at the nanoscale. The combination of shear piezoelectricity in high aspect ratio nanostructures yielded very sensitive force transducers, and these structures were then implemented into a device using Aerosol Jet Printing [2]. Human Dermal Fibroblast (HDF) cells were cultured on these devices, and through the indirect piezoelectric effect, the nanowires were used to apply local mechanical stimulation to the cells as they were growing. The effect of this stimulation on the behaviour of the cells was then observed.
[1] M. Smith, Y. Calahorra, Q. Jing, and S. Kar-Narayan, “Direct observation of shear piezoelectricity in poly-l-lactic acid nanowires,” APL Mater., vol. 5, no. 7, p. 74105, Jul. 2017.
[2] M. Smith, Y. S. Choi, C. Boughey, and S. Kar-Narayan, “Controlling and assessing the quality of aerosol jet printed features for large area and flexible electronics,” Flex. Print. Electron., vol. 2, no. 1, p. 15004, Mar. 2017.