Henry Hess, Columbia University
Walter Paxton, Sandia National Laboratories
Samuel Sanchez, Max Planck Institute for Intelligent Systems
Symposium Support APL Materials
IEEE Transactions on NanoBioscience
Integrated Design Tools Inc.
Sandia National Laboratories
L2: Artificial Nano/Micromachines in Fluids II
Tuesday PM, April 07, 2015
Moscone West, Level 2, Room 2006
2:30 AM - *L2.01
Advances in Nanomachines for Biomedical Applications
Joseph Wang 1
1UCSD La Jolla United StatesShow Abstract
Recent advances have created synthetic nanoscale machines that mimic the function of natural nanomotors. This presentation will discuss new multi-functional ultrasound-driven nanomotors or catalytic nanomotors that swim in body fluids including undiluted whole blood. The new nanomotors possess numerous attractive properties, including biocompatibility, biodegradability, high loading capacity, and autonomous ‘on-the-fly&’ release of payloads. The increased capabilities and sophistication of these tiny motors hold considerable promise for variety of biomedical applications ranging from drug delivery to target isolation.
3:00 AM - L2.02
Electrospun Polymeric Microtubes Decorated with Nanoparticles as Biodegradable Micro-Rockets
Amit Sitt 1 Jana Soukupova 2 David Miller 1 Joerg Lahann 3 Henry Hess 1
1Columbia University New York United States2Regional Centre of Advanced Technologies and Materials Olomouc Czech Republic3University of Michigan Ann Arbor United StatesShow Abstract
Autonomous motion of micrometer scale objects through a fluid environment has long been a challenge. One method for propelling microsystems is through bubble ejection, where movement is obtained through expelling gas bubbles formed by decomposition of fuels such as hydrogen peroxide inside tube-shaped particles. Such systems are usually referred to as “micro-rockets” because of the resemblance of their propulsion mechanism to that of macroscale rockets.
In this work we present a novel type of micro-rockets which are based on polymer microtubes fabricated using electro-spinning. Throughout the fabrication process, the chemistry of both the interior and exterior of the tubes can be defined and controlled, allowing the transformation of the tubes into micro-rockets by selective deposition of inorganic nanoparticles in the interior. The ability to alternate the interior&’s chemistry allows adsorption of different nanoparticles including metals, semiconductors and metal-semiconductor hybrids inside the tubes, and enables utilizing different fuels for propulsion. The micro-rockets themselves are bio-compatible and bio degradable, and can be further modified by other chemical species, making them potent for drug delivery applications. Furthermore, under external stimulus these particles can shape-shift into crescent-like form, leading to new modes of movement including circular and seesaw motion. The combination of simple fabrication, high control over the dimensions, biocompatibility and chemical modification make these micro-rockets attractive for a large range of biological and industrial applications.
3:15 AM - L2.03
Autonomous Micromotors Powered by Biofluids: Toward in vivo Biomedical Applications
Wei Gao 2 1 Allen Pei 2 Sirilak Sattayasamitsathit 2 Joseph Wang 2
1University of California, Berkeley Berkeley United States2University of California, San Diego La Jolla United StatesShow Abstract
The propulsion of synthetic nanomachines represents a great challenge and opportunity. Unfortunately, the requirement of the toxic chemical fuels (such as H2O2) greatly impedes the practical biomedical applications of such chemically-propelled micro/nanoscale motors. We describe here the use of different biofluids such as water or gastric acid as fuels to propel the new generations of micromachine. For example, the water driven micromotors, which utilize macrogalvanic corrosion and chloride pitting corrosion processes, can be fabricated by using biodegradable magnesium microparticles and a gold patch. Integrating functional self-propelled acid driven zinc micromotors are created by coupling electrodeposition with hard dual-templating synthesis. The fully-loaded micromotors concurrently possess four robust functions including a remarkably high loading capacity, combinatorial delivery of cargoes, autonomous release of encapsulated payloads, and self-destruction. This concept could be expanded to simultaneous encapsulation of various payloads for different functionalities such as therapy, diagnostics, and imaging. In addition, based on the zinc micromotors, we report the first in vivo study of artificial micromotors in a living organism using a mouse model. Such in vivo evaluation examines the distribution, retention, cargo delivery and acute toxicity profile of synthetic motors in mouse stomach via oral administration. These works are anticipated to significantly advance the emerging field of nano/micromotors and to open the door to in vivo evaluation and clinical applications of these synthetic motors.
3:30 AM - L2.04
Bioinspired Chemically Powered Micro- and Nanomotors
Samuel Sanchez 1 Lluis Soler 1 2 Xing Ma 1 Jaideep Katuri 1 Jemish Parmar 1
1Max Planck Institute for Intelligent Systems Stuttgart Germany2Universitat Politegrave;cnica de Catalunya Barcelona SpainShow Abstract
Self-powered micro-motors are currently subject of a growing interest due to their visionary but also potential applications in robotics, biosensing, nanomedicine, microfluidics, and environmental field. These micromotors are autonomous since they do not need external sources of energy in order to move. Instead, self-powered microrobots propel by decomposition of the fuel where they swim. Those artificial nanomotors act collectively  reacting to external stimuli like chemotactic behaviour  and are capable to clean polluted water .
Future operations of autonomous intelligent multi-functional nanomachines will combine the sensing of hazardous chemicals using bio-inspired chemotactic search strategies. With continuous innovations we expect that man-made nano/microscale motors will have profound impact upon in several fields such as biosensing and environmental remediation , among other visions.
 Solovev, A. A. et al., Nanoscale, 5, 1284 (2013)
 Baraban, L. et al., Angew. Chem. Int. Ed., 52, 5552. (2013), b) S. Saha, et.al., Phys. Rev. E 2014, 89, 062316, c) Y. Hong, N. M. K. et al, Phys. Rev. Lett. 2007, 99, 178103
 Soler, Ll. et al., ACS Nano, 7, 9611 (2013), b) J. Orozco, et al Angew. Chem., Int. Ed. 2013, 52, 13276-13279;
 (a) Gao, W. and Wang, J., ACS Nano, 8, 3170 (2014). (b) Soler, L. and Sanchez, S. Nanoscale, 6, 7175 (2014)
3:45 AM - L2.05
On the Mechanics of an Engineered Living 1D Swimmer at Low Reynolds Number from Cardiomyocytes
Brian Williams 1 Sandeep Anand 1 Taher Saif 1
1University of Illinois at Urbana-Champaign Urbana United StatesShow Abstract
There is a rich diversity of flagellar swimmers in nature. In general, they use a long tail, known as flagellum or celia, to propel themselves in fluids. Due to their small size, the fluid around them appears as viscous, resulting in low Reynolds number dynamics. Thus, there is no inertial component in the propulsion. Until to date, there is no engineered low Reynolds number swimmer that can propel itself autonomously. Earlier efforts resulted in swimmers that are driven by external magnetic fields. Here we present a swimmer that propels itself autonomously by using live rat cardiomyocytes. The swimmer consists of a flexible tail and a rigid head. Cardiomyocytes are plated on the tail near the head. The cells self-organize themselves by interacting with the flexible tail substrate, and with each other, and emerge as a group all beating in synchrony. The cell forces bend and deform the tail with time against the viscous drag of the fluid. This fluid-structure interaction results in a bending wave that travels from head to the tail end giving rise to a time irreversible dynamics. Such motion results in a net propulsive force on the swimmer. The swimmer moves forward by overcoming the longitudinal viscous drag. The swimmer dynamics is modeled within the framework of slender body hydrodynamics. The model predictions match within 10 percent of the experimental observation. The future potentials of such biological machines will be discussed.
4:30 AM - *L2.06
Light-Induced Reconfiguration and Directed Motion of Chemo-Responsive Gels
Olga Kuksenok 1 Anna C. Balazs 1
1University of Pittsburgh Pittsburgh United StatesShow Abstract
A remarkable feature of certain biological organisms is their ability to alter their shape and functionality in response to environmental cues. Polymer gels undergoing the Belousov-Zhabotinsky (BZ) reaction are unique self-oscillating materials that can be used to design a variety of soft materials with biomimetic functionality. We focus on chemically-mediated communication between multiple pieces of BZ gels. We show that the system exhibits autochemotaxis, which results in a spontaneous self-aggregation of the pieces. We also find that the aggregated structure can undergo spontaneous, autonomous rotation. Moreover, the gels&’ coordinated motion can be controlled by light, allowing us to achieve selective self-aggregation and control over the shape and motion of the aggregates. We then focus on novel polymer gels that combine two distinct functionalities. First, these gels contain spirobenzopyran (SP) chromophores grafted onto the polymer matrix; the SP moieties are hydrophilic in the dark in an acidic aqueous solution, but become hydrophobic under illumination with blue light. Hence, incorporation of these chromophores into the gel allows us to remotely control the gel's swelling or shrinking. Second, these gels also contain a Ru catalyst that is grafted onto the polymer chains. When placed into a solution containing all the reagents needed for the Belousov-Zhabotinsky (BZ) reaction, these SP-BZ gels undergo self-oscillations. We show that these systems undergo large scale shape changes, with an initially flat sheet morphing into a variety of complicated 3D forms. Moreover, these SP-BZ gels undergo self-propelled motion, with the mode of motion being controlled by external light. Our results point to a novel class of active self-oscillating materials and to a robust method for controllably re-configuring their 3D shapes and their self-propelled motion. These gels constitute idea materials for creating small-scale soft robots that undergo autonomous and controlled movement.
5:00 AM - L2.07
Actuation-Navigation-Sensory Capability in Cancer-Fighting Nanorobotic Agents
Sylvain Martel 1
1Polytechnique Montreacute;al Montreacute;al CanadaShow Abstract
Robotics can enhance the therapeutic efficacy in cancer therapy beyond what is possible with the manipulation of molecular structures alone which has been the main focus of the pharmaceutical industry. Such robotic enhancement could rely on the implementation of advanced functionalities in each agent designed to transport a therapeutic payload to specific tumor sites that would yield optimized effects. Such functionalities would include navigation capability towards the sites of treatment in order to avoid systemic circulation, self-actuation providing a propelling force sufficient to penetrate the tumor volume beyond the diffusion limits of larger drug molecules, and sensory capability to target regions such as the hypoxic zones that would lead to the best treatment outcomes. Although the field of biomimetics has given rise to new technologies inspired by biological solutions at the macro- and nano-scales, an artificial solution supporting such an embedded capability level is still far beyond present technological feasibility. But methods relying on biology can also be inspired by far-reaching technological concepts. It is shown how such “reverse-biomimetic” approach can be used to implement medical nanorobotic agents having functionalities only envisioned for future medical nanorobots and which are still far beyond present technological feasibility at such a scale.
5:15 AM - L2.08
Fabrication of Flexible and Location Traceable Hydrogel Micro-Motor
Kyoung Duck Seo 2 Byung Kook Kwak 3 Samuel Sanchez 1 Dong Sung Kim 2
1Max Planck Institute for Intelligent Systems Stuttgart Germany2Pohang University of Science and Technology (POSTECH) Pohang, Gyeongbuk Korea (the Republic of)3Chung-Ang University College of Medicine Seoul Korea (the Republic of)Show Abstract
Artificial self-propelled nano- and micro-motors, which are inspired by natural biomotors, were recently engineered with a rich variety of architectures, such as nanowires, microtubes, spherical particles, helical structures, and more. Those autonomous micro-motors offer great possibilities for research from fundamental mechanisms of motion at the micro- and nanoscale to potential biomedical and/or environmental applications. However, typical artificial micro-motors are commonly formed by rigid structures and/or based on inorganic materials though micro-motors based on polymeric materials were rarely reported. Furthermore, a shortcoming of developed micro-motors is that they are difficult to trace and monitor changes in their location when they are introduced into human body for in vivo biomedical applications.
Here, we describe the fabrication of flexible and location traceable micro-motor, named organo-motor, assisted by microfluidic devices and with high throughput. The organo-motors are composed of organic hydrogel material, poly (ethylene glycol) diacrylate (PEGDA), which can provide high degree of flexibility to their structure in contrast to inorganic rigid materials. For spatial and temporal traceability of the organo-motor under magnetic resonance imaging (MRI), superparamagnetic iron oxide nanoparticles (SPION; Fe3O4) were incorporated into the PEGDA microhydrogels. Furthermore, a thin layer of platinum (Pt) was deposited onto one side of the SPION-PEGDA microhydrogels for achieving self-propulsion in aqueous fluids containing hydrogen peroxide solution, H2O2. Furthermore, the motion of the organo-motor was controlled by small external magnet enabled by the presence of SPION in the motor architecture.
In conclusion, developed organo-motors enabled us to give the possibility of developing biocompatible and flexible micro-motors compared to the conventional rigid micro-motor. In addition, outer surface of the organo-motor can be easily functionalized with proteins or bioactive material through acrylate group of PEGDA.
5:30 AM - L2.09
Water-Responsive Actuation in Nanaporous Metals
Ye Xinglong 1 Liu Lingzhi 1 Jin Haijun 1
1Institute of Metal Research, Chinese Academy of Sciences Shenyang ChinaShow Abstract
Many biological materials use water to modulate their volume and mechanical properties to achieve actuation and other functions. For example, spider silk contracts in response to environmental humidity which is essential for maintaining tension in the web after prey-capture [Liu Y et al., Nature Mater., 2005]. Inspired by the nature, some water-responsive synthetic materials, such as hydrogels and polymers, have been explored for actuation. But these actuators typically work under low loads, because these are compliant materials and/or the actuation strain diminishes rapidly at increasing loads. Here we report that metals can also be water-responsive when they gain a nanoporous structure. The water-capillarity in the nanopores drives the metal to expand and contract reversibly, leading to actuation with reversible strain up to ~ 1.3%, the largest stress-generation reaching ~23 MPa and a strain energy density as large as ~ 0.15 MJ/m3. These figures are comparable to that of the best-performance water-responsive polymer actuators [Ma MM et al., Science, 2013]. Furthermore, the nanoporous metals can bear high loads. And for water-responsive nanoporous metal actuator, the actuation strain and stress-generation are inherently insensitive to the external load. These features render them as promising candidates as “artificial muscles” in future to drive the microrobots which no longer require an external power.
5:45 AM - L2.10
Glucose Powered ldquo;Organic Enginerdquo; (Chemo-Mechanical Machine) with Artificial Active Transportation for Autonomous Drug Release System (Novel Artificial Pancreas)
Munkhbayar Munkhjargal 1 Koji Toma 1 Takahiro Arakawa 1 Kohji Mitsubayashi 1
1Tokyo Medical and Dental University Tokyo JapanShow Abstract
Many glucose sensors have been developed for monitoring blood sugar level in diabetic in order to control the blood sugar level by an insulin injection by hand or electric power. On the other hand, we have reported a novel chemo-mechanical energy conversion device “Organic Engine” using artifical active transportation, which detected glucose and converted its chemical energy to mechanical power for autonomous drug release. But the system required 100 mmol/l glucose (10 times higher in blood). In this study, the performance of the organic engine was improved by a multi-enzymatic oxidation, thus successfully applying for the self-regulation system (artificial pancreas) in blood sugar level.
The artificial pancreas consisted of chemo-mechanical decompression unit and periodic drug release unit. In the decompression unit, a glucose oxidizing enzyme membrane functioned as a separating diaphragm between liquid and gas cells. The enzyme oxidation reaction with glucose in the liquid cell would induce the oxygen consumption, thus resulting in the decompression in the gas cell. After decompressing by enzymatic reaction, the pressure would return periodically to the atmosphere level by a pressure regulator, and the drug simultaneously release to glucose solution. In order to improve the decompression performance, the oxidation activity of the enzymes (glucose oxidase (GOD), pyranose oxidase (POX), alcohol oxidase (AOX), galactose oxidase (GAO)) for glucose and/or glucono-1.5-lactone were compared.
REUSLTS and DISCUSSION
By comparing the oxidation behaviours, POX+GOD co-immobilized enzyme indicated the highest activity than that of others because POX oxidizes both glucose and its product D-glucono-1.5-lactone. As a result, the GOD+POX decompression rate was indicated 3 times higher than that of only GOD, and necessary decompression rate of 7.4 Pabull;cm3/sec was obtained at 10 mmol/L glucose (blood sugar level). The autonomous drug release system with the multi-enzymatic unit showed the self-regulation function of glucose level such as pancreas organ.
L1: Artificial Nano/Micromachines in Fluids I
Tuesday AM, April 07, 2015
Moscone West, Level 2, Room 2006
9:30 AM - *L1.01
Designing Self-Powered Nanomotors and Pumps
Ayusman Sen 1
1Pennsylvania State University University Park United StatesShow Abstract
Self-powered nano and microscale moving systems are currently the subject of intense interest due in part to their potential applications in nanomachinery, nanoscale assembly, robotics, fluidics, and chemical/biochemical sensing. We will demonstrate that one can build autonomous nanomotors over a wide range of length-scales “from scratch” that mimic biological motors by using catalytic reactions to create forces based on chemical gradients. These motors are autonomous in that they do not require external electric, magnetic, or optical fields as energy sources. Instead, the input energy is supplied locally and chemically. These "bots" can be directed by information in the form of chemical and light gradients. Further, we have developed systems in which chemical secretions from the translating nano/micromotors initiate long-range, collective interactions among themselves and neighboring inert particles. This behavior is reminiscent of quorum sensing organisms that swarm in response to a minimum threshold concentration of a signaling chemical. In addition, an object that moves by generating a continuous surface force in a fluid can, in principle, be used to pump the fluid by the same catalytic mechanism. Thus, by immobilizing the nano/micromotors, we have developed nano/microfluidic pumps that transduce energy catalytically. These non-mechanical pumps provide precise control over flow rate without the aid of an external power source and are capable of turning on in response to specific analytes in solution.
10:00 AM - L1.02
Enzyme-Driven Chemotactic Synthetic Vesicles
Claudia Contini 1 Denis Cecchin 1 Adrian Steve Joseph 1 Sophie Nyberg 1 Giuseppe Battaglia 1
1UCL London United KingdomShow Abstract
Directional locomotion or taxis is possibly one of the most important evolutionary milestones, since it has allowed many living organisms to outperform their non-motile competitors. In particular, chemotaxis is one of the most elaborated targeting process present in Nature. By sensing a chemical gradient, uni- or multicellular organisms are able to move toward or away from favourable/unfavourable stimuli, adapting to changes in environmental conditions. This phenomenon normally involves the presence of a specific chemical gradient of signalling molecules that guides cells in their orientation and movement. Chemotaxis is therefore a potent long-range directional process, extending over length scales that are several orders of magnitude larger than the motile system itself. Creating an artificial self-propelled object, similar to many biological micro and nano- motors present in Nature, is one of the main challenges in nanotechnology. The chemotaxis applied to an artificial nanovector could used for a wide range of applications, including drug delivery systems and nanoreactors. Combining natural enzymes with synthetic vesicles, we propose an efficient chemotactic nano-system driven by enzymatic conversion of small water-soluble molecules. We achieve this by encapsulating enzymes into nanoscopic polymer vesicles (known as polymersomes) whose membranes are designed to contain permeable domains within an impermeable matrix. The asymmetric distribution of the permeable domains enables the localised expulsion of the entrapped enzyme reaction products. This in turn allows propulsion in a specific direction that is controlled by the signalling molecule concentration. We demonstrate this concept, using physiologically- relevant hydrogen peroxide and glucose coupled with catalase, glucose peroxidase and their combination loaded within asymmetric polymersomes. We show that the combination of membrane topology and enzyme encapsulation produces propulsion and chemotaxis without requiring chemical modification, at very low signalling molecule concentrations. Finally, we propose a new diffusion mechanism whereby selective permeability across nanoscopic membrane compartments is exploited to generate locomotion.
10:15 AM - L1.03
Realising Autonomous Transport for Janus Particle Catalytic Swimming Devices to Enable Biosensing
Stephen Ebbens 1 Andrew Campbell 1 Richard Archer 1
1University of Sheffield Sheffield United KingdomShow Abstract
Janus colloidal swimmers produce motion by asymmetrically decomposing dissolved fuel molecules around their surfaces. The goal for Janus swimming devices is to allow the delivery of drugs within the body, or transport of analytes in a microfluidic device. Here we survey the steps taken towards autonomous transport for these devices within our research group and highlight the challenges that still remain.
The key to controlling Janus particle device trajectory is to influence rotational diffusion rate. If left to undergo unrestricted Brownian rotational motion, swimmer trajectories are rapidly randomised; because their direction of travel is determined by the Janus particles orientation. Consequently, without control, the propulsion force manifests as super-diffusion at time scales beyond the rotational diffusion constant, rather than the more useful directed motion required for applications. So we describe and compare the wide range of methods we have investigated to modify and control rotational diffusion; including stimulus responsive size change, magnetic quenching, self-assembly, gravitational bias, control of catalyst patch symmetry, and topographical and surface chemistry patterning.
In particular we consider these guidance mechanisms with reference to harnessing Janus colloids to perform analyte transport to a detector patch within a static solution biosensor device. In contrast to protein motor systems that have been proposed to perform a similar function in 2D, we show that synthetic motors have the significant advantage of moving in 3D, which can allow super diffusive binding of an analyte throughout a sample volume. Having gathered cargo, the colloids can autonomously accumulate at an interface and then be guided by surface structures to become localised at a detector region. This mechanism could enable traces amounts of analyte to be concentrated for analysis. Finally we discuss the remaining challenges to apply this approach to concentrate analytes in biological solutions, which concern limitations of current propulsion producing mechanisms and surface catalytic reactions.
10:30 AM - L1.04
Microscale Actuation of Colloidal Fibers of Self-Assembled Janus Ellipsoids
Aayush Shah 1 Benjamin Schultz 1 Wenjia Zhang 1 Sharon Glotzer 1 Michael Solomon 1
1University of Michigan Ann Arbor United StatesShow Abstract
We produce fibers of Janus ellipsoids by self-assembly and show that their length can be configured on demand by application of an electric field. Assemblies of colloids are useful for forming soft matter that can reconfigure its shape or structure so as to perform a microscopic function such as sensing, transduction, or actuation. Here we investigate how two kinds of particle anisotropy - ellipsoidal shape and Janus interactions - combine to yield unusual structure and function by means of self-assembly. The particles, Janus ellipsoids, are produced by stretching latex spheres into ellipsoids, followed by evaporative deposition of a layer of gold onto one-half of the particle. In aqueous solution, addition of electrolyte controls the relative binding of the two Janus faces of the ellipsoids. Equilibrium self-assemblies include clusters and one-dimensional chains. Confocal microscopy experiments and computer simulations show that the fibrillar assemblies can be actuated on application of an external alternating-current electric field. The actuation occurs by a sliding mechanism that permits rapid and reversible expansion and contraction in a way that is potentially useful for microscale actuation and force transduction.
10:45 AM - L1.05
3D Navigation of Individual Self-Propelled Janus Microspheres in Solution by Controlling Their Swim-and-Tumble Motions
Utsab Khadka 1 Frank Cichos 2 Haw Yang 1
1Princeton University Princeton United States2University of Leipzig Leipzig GermanyShow Abstract
A key challenge in the artificial nano-/micro-swimmers field is to be able to study them in solution free of the influence of the container walls: When a swimmer is close to a container wall such as the bottom window of a microscopy sample chamber, the flow field is inevitably influenced by the liquid-wall interface. The problem is exacerbated for smaller swimmers where thermal fluctuations play an increasingly prominent role.
Here we report driving, in 3D, photophoretic gold-polystyrene Janus microspheres in solution. Our experiment goes beyond solving the 3D observation problem and controlling the swimmer. Taking inspiration from the run-and-tumble motion of micron-sized bacteria such as Escherichia coli for effective directed transport in low-Reynolds number environments, our scheme utilizes both self-propulsion and rotational random walk for maneuvering the artificial micro-swimmer. The particle is “photon nudged” by the use of adaptively delivered weak light pulses to arbitrary 3D targets in the solution. We will describe the experimental challenges associated with the measurement of the particle that is mobile in 3D and also those associated with driving it.
The ability to navigate individual miniaturized swimmers in solution will facilitate diverse immediate applications including: fundamental tests of non-equilibrium statistical mechanics, principal studies of fluctuating hydrodynamics at interfaces, single-particle sorting, and bottoms-up material assembly, to name only a few.
11:30 AM - *L1.06
Nanoparticles, Nanomachines, and Nanopropellers in Biological Fluids
Peer Fischer 1 2
1Max Planck Institute for Intelligent Systems Stuttgart Germany2University of Stuttgart Stuttgart GermanyShow Abstract
Nanomachinery that locomotes through fluids at small length scales is the realm of low Reynolds number hydrodynamics, which is characterized by instantaneous and time-reversible flows that are described by the time-independent Stokes equation. Any time-dependence is only present through the boundary conditions and this means that micro- and nano-machines are subject to kinematic reversibility, the consequence of which is generally summed up by the ‘scallop theorem&’: A micro-organism or swimmer operating at low Reynolds numbers cannot propel if it executes reciprocal geometrical strokes that are a sequence of shape changes that are identical when reversed, if the fluid is incompressible and Newtonian. In Purcell&’s own words, ‘Fast, or slow, it exactly retraces its trajectory, and it&’s back where it started&’. This significantly complicates the demands placed on the design of artificially engineered micro and nanomachinery, as reversibility has to be broken either by realizing complicated time-asymmetric actuators or by fabricating anisotropic micro- and nanostructures. Here, solutions will be presented that allow micro- and nanomachinery to operate under these constraints. I describe a fabrication methodology that we have recently developed that permits us to grow engineered nanomaterials that break symmetry, such as hybrid Janus-like structures. These are powered by self-catalytic chemical reactions, and can be grown and operate in the size range from about 30 nm to several microns. The method is general and allows the fast parallel wafer-scale fabrication of uniform hybrid nanostructures with complex three-dimensional architectures. Potential applications of these nanomaterials are presented.
I will also discuss the complexity that is found in the rheology of biological media, where efficient locomotion in biomedically relevant systems calls for special nanoparticles. Nanoparticles are promising for drug delivery, localized sensing, and the stimulation of individual cells. Active propulsion of nanostructures would permit the efficient, targeted delivery of such particles. However, transport in biological media is complicated by the presence of macromolecules and polymers, such as glycoproteins and polysaccharides, which form an interconnected network that results in gel-like structures that are characterized by a nanometric meshlike structure. These gels form a natural barrier for bacteria and viruses. However, nanopropellers with a diameter of 70 nm can actively and efficiently move through such gels, as I will show. These structures open up new possibilities in the controlled motion in extra- and potentially intracellular matrices. Finally, the non-Newtonian character of these biological media also allows much simpler machinery to be operated than what is possible in water. In particular, a shear-rate dependent actuator that swims at low Reynolds number will be discussed.
12:00 PM - L1.07
Wood as Inspiration for High Specific Torque Micro-Actuators
Joseph Jakes 1 Nayomi Plaza 2 1 Xavier Arzola 2 Samuel Zelinka 1 Rod Lakes 3 Don Stone 4
1USDA Forest Service, Forest Products Laboratory Madison United States2University of Wisconsin-Madison Madison United States3University of Wisconsin-Madison Madison United States4University of Wisconsin-Madison Madison United StatesShow Abstract
Thin slivers of wood composed of a few intact wood cells are moisture-activated high specific torque micro-actuators with shape memory capabilities. We find the wood slivers twist multiple revolutions per cm length when wetted and untwist when dried. A simple torque sensor with 10-8 N#8729;m sensitivity was built using a 63.5 µm diameter tungsten wire. The slivers produced specific torques as high as 25 N#8729;m/kg, which is about three times higher than electric motors and recently reported carbon nanotube yarn torsional actuators. A further advantage of wood slivers over the carbon nanotube yarn torsional actuators is that they produce high specific torques during both twisting and untwisting. In contrast, carbon nanotube yarn torsional actuators require return springs to untwist. The wood slivers also exhibit a shape memory twist effect. The majority of twist from wetting can be locked in by drying under constraint, and then the locked-in twist can be recovered by rewetting the bundle.
The wood sliver behavior derives from its cell wall nanostructure, which could be mimicked to make bioinspired micro-actuators. A wood cell is basically a hollow tube with nanofiber-reinforced composite walls. The nanofibers are stiff semi-crystalline cellulose microfibrils that are wound helically around the cell and embedded in a matrix of hemicelluloses and lignin. The matrix swells during water uptake and the helical microfibril constraints causes the cell to twist. We propose that the properties and spatial distribution of hemicelluloses and lignin within the matrix lead to the shape memory effects and high specific torque during untwisting. Hemicelluloses are branched amorphous polysaccharides and lignin is an amorphous aromatic polymer. From a solubility parameter viewpoint, lignin and cellulose are incompatible. Wood overcomes the incompatibility by using the hemicelluloses to coat the microfibrils and bridge the cellulose and lignin. During wetting, the hemicelluloses pass through a moisture-induced glass transition and hemicellulose chains are able to slide past one another. In contrast, the lignin does not pass through a glass transition and remains in its rigid glassy state during wetting. If the wood sliver is constrained and dried in the twisted state, the softened hemicelluloses vitrify in a new configuration and lock in the majority of the sliver twist. Additionally, the vitrified hemicelluloses lock a strain in the lignin. Upon rewetting, the hemicelluloses soften and the lignin, remembering its original configuration, provides the recovery forces to cause the sliver to untwist to its original configuration during drying.
12:15 PM - L1.08
Dynamic Coupling at the Nanoscale
Krishna Kanti Dey 1 Frances Ying Pong 1 Selva Jeganathan 2 Peter J. Butler 2 Ubaldo M. Cordova-Figueroa 3 Ayusman Sen 1
1Pennsylvania State University University Park United States2Pennsylvania State University University Park United States3University of Puerto Rico-Mayaguuml;ez Mayaguuml;ez United StatesShow Abstract
Understanding collective and emergent behaviors of active colloidal assemblies provides useful insights into the statistical physics of out-of-equilibrium systems, thereby enabling researchers to better engineer and utilize many body dynamics at the submicroscopic regime. Recently, there has been a surge in the development of model systems to investigate controlled transfer of energy from self-propelled microswimmers - such as bacteria, algae, and inorganic catalysts to their immediate surroundings. Herein with a series of experiments, we demonstrate that nanoscale catalytic swimmers also can distribute momentum around their vicinity, significantly influencing the motion of nearby passive tracers. We measured diffusion of polymer tracers during enzymatic catalysis using various analytical techniques such as dynamic light scattering, fluorescence correlation spectroscopy, and diffusion nuclear magnetic resonance spectroscopy. In all the measurements, the diffusion of tracers was found to enhance substantially during enzymatic turnover of substrates. The increase in tracer diffusion was found not only to depend on the tracer size but also on the total rate of reaction, which is similar to the observations reported for particles near active micron-scale swimmers.
12:30 PM - L1.09
Catalytic Pumps for Colloid Manipulation and Patterning Processes
Maria Jose Esplandiu 1 Ali Afshar Farniya 1 Adrian Bachtold 2
1ICN2, Instituto Catalan de Nanociencia y Nanotecnologia Campus UAB, Bellaterra Spain2ICFO, Institut Ciencies Fotoniques Mediterranean Technology Park, Castelldefels SpainShow Abstract
Catalytic motors and pumps have become a very attractive research topic. They comprise novel and autonomous synthetic machines which can self-generate their required power to actuate and perform specialized tasks. In this way they become promising candidates to mimic the extraordinary biological machinery.
Catalytic pumps made of bimetallic structures rely on the self-generation of electrohydrodynamic forces triggered by the electrochemical decomposition of a chemical fuel at the metallic surfaces. The chemical reaction together with the forces produced at the surface of a catalytic pump can be used to manipulate charged colloids in a novel way .
In this work we will show that a Au-Pt pump can be used to tailor colloidal patterning at certain locations of the sample through a series of sequential steps and in an autonomous fashion . The studies will be also extended to other bimetallic combinations and to semiconductor/metallic structures to evaluate their potentialities in the manipulation and local self-assembly of colloidal systems.
In this way guided self-assembly mediated by catalytic pumps becomes a novel alternative to the more conventional colloidal self-assembly triggered by external fields. The autonomous fashion and precise location of a colloidal patterning on a surface can have a very important impact on a wide range of fields. These active systems can become a very versatile tool to approach technological important challenges in nanofabrication and also stimulate research groups interested in smart nanostructured surfaces for sensing, catalysis, photonics, corrosion or self-healing systems.
 A. Afshar Farniya, M.J. Esplandiu, D. Reguera, A. Bachtold, Phys. Rev. Lett. 2013, 111, 168301.
 A. Afshar Farniya, M.J. Esplandiu, A. Bachtold, Langmuir 2014, 30, 11841minus;11845
Henry Hess, Columbia University
Walter Paxton, Sandia National Laboratories
Samuel Sanchez, Max Planck Institute for Intelligent Systems
Symposium Support APL Materials
IEEE Transactions on NanoBioscience
Integrated Design Tools Inc.
Sandia National Laboratories
L4: Bio- and Molecular Machines II
Wednesday PM, April 08, 2015
Moscone West, Level 2, Room 2006
2:30 AM - *L4.01
Design of Self-Oscillating Polymer Gels toward Bioinspired Autonomous Micro- and Nanomachines
Ryo Yoshida 1
1The University of Tokyo Tokyo JapanShow Abstract
We have developed “self-oscillating” gels that undergo spontaneous cyclic swelling-deswelling changes without any on-off switching of external stimuli, as with heart muscle. The self-oscillating gels were designed by utilizing the Belousov-Zhabotinsky (BZ) reaction, an oscillating reaction, as a chemical model of the TCA cycle. We have systematically studied these polymer gels since they were first reported in 1996. Potential applications of the self-oscillating polymers and gels include several kinds of functional material systems, such as biomimetic actuators, mass transport systems and functional fluids. For example, it was demonstrated that an object was autonomously transported in the tubular self-oscillating gel by the peristaltic pumping motion similar to an intestine. Further, it is possible to create a new dynamic interface by immobilizing the self-oscillating polymer. We prepared a self-oscillating polymer brush surface and evaluated its dynamic behavior. Besides, autonomous viscosity oscillation was realized via metallo-supramolecular terpyridine chemistry, etc. Self-oscillation between unimer/micellar or unimer/vesicle structures was also realized for a synthetic block copolymer. And recently, novel comb-type self-oscillating gels were designed. Our studies have created new concepts of functional gels and expanded their potentials. In the presentation, our recent progress on self-oscillating polymer gels will be summarized, mainly focused on designing artificial autonomous micro- and nanomachines.
3:00 AM - L4.02
Exploiting Janus Particles in Biomedicine - From Asymmetric Capsosomes to Self-Propelled Swimmers
Philipp Sebastian Schattling 1 Cindy Dreier 1 Brigitte Staedler 2
1Aarhus University Aarhus Denmark2Aarhus University Aarhus C DenmarkShow Abstract
Particles featuring a break in their symmetry are of considerable interest in material science, since they impart drastically different properties within one single particle. Thanks to their intrinsic heterogeneity, these so-called Janus particles find manifold application as stabilizer in Pickering emulsions, modulated optical nanoprobes, or self-propelled nano-/ microparticles. However, in a biomedical context Janus particle still hold a niche existence and are always evaluated in direct comparison to their symmetric analogue, which are much easier to synthesize. In an effort to address this issue, we present two concepts, which rely on the Janus characteristic of the fabricated particle.
Capsosomes are well-recognized as simple cell-mimics and are identified as subcompartmentalized hollow polymer vesicles, which contain liposomes as subunits. Among others, these subunits were equipped with different sets of enzymes and thus were able to perform enzymatic cascade reactions. In this context the efficacy of this cascade reaction were particularly depended on the proximity of the interchanging enzyme pairs. We present a strategy towards a new generation of capsosomes, featuring a spatially confined allocation of two sets of liposome subunits within a polymer hydrogel shell. The Janus characteristic was implied to the assembly, by an immobilization method of template silica particles at a water/wax interface in a Pickering Emulsion approach. This allowed modifying the two hemispheres separately by a layer-by-layer deposition procedure. The choice of the utilized materials to activate and inactive each hemisphere were chosen in a manner, that the following hydrogel shell could be assembled around the particle, while maintain the structural integrity of the subunits.
In a similar manner, we introduce the fabrication of self-propelled Janus shaped microswimmer. The design of these Janus particles consisted of a silica particle decorated on one hemisphere with two different enzymes. On the second hemisphere a hydrogel was formed in a grafting-from method. The propulsion or enhanced diffusion respectively of the particle based on the collaboration of the two enzymes and was initiated by the addition of glucose.
We believe that both introduced concepts will broaden the application of Janus particle, particular in the context of biomaterial science.
 Loget, G.; Kuhn, A., Journal of Materials Chemistry 2012,22, 15457-15474.
 Walther, A.; Müller, A. H. E., Chemical Reviews 2013,113, 5194-5261.
 Teo, B. M.; Hosta-Rigau, L.; Lynge, M. E.; Städler, B., Nanoscale 2014,6, 6426-6433.
 Hosta-Rigau, L.; York-Duran, M. J.; Zhang, Y.; Goldie, K. N.; Städler, B., ACS applied materials & interfaces 2014, 10.1021/am502743z.
 Schattling, P.; Dreier, C.; Städler, B., submitted.
3:15 AM - L4.03
Emergent Structures in Suspensions of Self-Phoretic Colloids
Ignacio Pagonabarraga 1
1University of Barcelona Barcelona SpainShow Abstract
The dynamics of self-propelled micron-size particles is affected by the fluid in which they are suspended, since it interferes with the internal mechanisms which generate their propulsion. These active objects also modify the properties of the fluid they are embedded in due to the generation of active stresses. Since these liquids are intrinsically out of equilibrium, a dynamical study of the mesoscopic structures these materials develop is required.
I will discuss a simplified computational approach which resolves individual self-propelled motion. I will analyze the dynamic cooperativity in suspensions of self-phoretic colloids in (quasi)-2D configurations.
I will consider how the the phoretic mobility, which accounts effectively for the
colloid-solute interactions, determines the emergent phases in such suspensions, leading from a cluster phase to a jammed state. The computational study shows that the cluster size distribution follows an exponential behaviour, with a characteristic size growing linearly with the colloid activity, while the density fluctuations grow as a power-law with an exponent depending on the cluster fractal dimension.
The study singles out the role of hydrodynamic interactions in the development of such structures, showing that their effect is to work against cluster formation.
3:30 AM - L4.04
Self-Propulsion of a Catalytically Active Particle in Confinement and External Fields
William Eric Uspal 1 2 Mihail Nicolae Popescu 1 2 3 Siegfried Dietrich 1 2 Mykola Tasinkevych 1 2
1Max-Planck-Institut fuuml;r Intelligente Systeme Stuttgart Germany2Universitauml;t Stuttgart Stuttgart Germany3University of South Australia Adelaide AustraliaShow Abstract
Micron-sized particles moving through solution in response to self-generated chemical gradients serve as model systems for studying active matter. Their far-reaching potential applications will require the particles to sense and respond to their local environment in a robust manner. The self-generated hydrodynamic and chemical fields, which induce particle motion, probe and are modified by that very environment, including confining boundaries. Focusing on a catalytically active Janus particle as a paradigmatic example, we investigate the motion of the particle near a hard planar wall. We find that, for certain surface chemistries, the particle can be trapped by the surface, and, at definite height and orientation, either “slide” along the wall, or “hover” above it without motion. Building on this foundation, we subsequently consider the effects of external fields (e.g. gravity and shear flow) and chemically and geometrically patterned boundaries. We find that “sliders” and “hoverers” can exhibit robust response to these environmental cues, such as rheotaxis (stable upstream swimming) in shear flow.
3:45 AM - L4.05
Overcoming Characterization Challenges of Bio-Inspired Nanomaterials
Brandon Vaughn Slaughter 2 Patrick Fleig 2 Andrew Gomez 2 Claire Melo 2 Gabriel Garcia 3 Scott Reed 2 Caroline Bouvie 3 Matthew Jackson 2 Trevin Heisey 2 Chris Lino 2 Marissa R. Anderson 2 C. Jeffrey Brinker 1 Carlee Ashley 2 Eric Carnes 2
1Sandia National Labs Albuquerque United States2Sandia National Laboratories Albuquerque United States3University of New Mexico Albuquerque United StatesShow Abstract
The standard suite of materials characterization approaches used in describing the morphology of nanoparticles and other nanomaterials is replete with challenges that confound experimental interpretation, and otherwise preclude carrying out a comprehensive materials analysis. In particular, describing size, polydispersity, shape, and porosity often relies on methods such as dynamic light scattering (DLS) and transmission electron microscopy (TEM). With these techniques, factors including sample concentration, purity, thermodynamic stability, overreliance on assumptions, and/or extensive sample preparation often render a meaningful analysis of the true materials properties inadequate for further system development, especially when working toward preclinical and clinical translation. Furthermore, even when seemingly trustworthy results are provided by one of these techniques, there is often poor correlation to other standard characterization approaches.
In this work, we describe a multi-faceted approach to morphological analysis of a composite nanoparticle system. This system is comprised of mesoporous silica nanoparticles (MSNPs), which are enveloped by a fused lipid bilayer to form a therapeutic nanoparticle system known as a ‘protocell&’. The MSNP component of the system is synthesized using a well-known aerosol generation technique that typically yields a polydisperse mesoporous nanoparticle population ranging in size between roughly 10 - 1000 nanometers. These MSNPs are then calcined to remove organics and fused with lipids to form protocells. Following synthesis, these particles can be solute-loaded for therapeutic applications, and/or surface-modified to facilitate targeting and influence biodistribution and stability. To fully characterize these nanoparticles, we employed a host of characterization techniques for both MSNPs and protocells, including DLS, TEM, scanning mobility particle sizing (SMPS), optical particle sizing (OPS), nanoparticle tracking analysis (NTA), and zeta potential analysis (zeta). This multifaceted approach was then correlated to in vitro and in vivo results to determine how nanoparticle morphology from each analysis technique related to biological interactions. Additionally, several synthesis and post-synthesis processing steps were studied using this suite of analysis techniques, including MSNP aerosol generation, liposome fusion, sonication, storage, filtration, and fractionation.
By using a comprehensive analysis suite, variations between techniques became apparent, and as a result we are better able to predict behavior and interactions with biological systems for similar nanoparticle types in terms of size and surface characteristics.
4:30 AM - *L4.06
Which Tool in the Toolbox? Functional Diversity across the Kinesin Superfamily
William O. Hancock 1
1Penn State University University Park United StatesShow Abstract
Different nanoscale transport and actuation applications require different motor properties, and insights into fundamental molecular mechanisms can be gained by studying the natural diversity found in nature. Kinesin motors have evolved to carry out diverse transport processes in cells, and thus they provide a valuable toolbox of motors that move at different speeds, have different abilities to generate sustained forces, and possess different affinities for their microtubule tracks. I will discuss work in my lab to understand the specific adaptations of transport (kinesin-1,2 and 3 family) and mitotic (kinesin-5 and 7 family) kinesins, and will describe nanoscale tracking experiments we are carrying out to understand the nanoscale dynamics of each motor domain as it walks along the microtubule. Understanding this diversity across the kinesin superfamily both aids in choosing optimal motors for optimal applications, as well as helping to understand how the activities of many motors can (or cansup1;t) sum to achieve maximal performance.
5:00 AM - L4.07
Directional Control of Microtubules by Designing Their Biophysical Properties
Ryuji Yokokawa 1 Naoto Isozaki 1 Suguru Ando 1 Hidetoshi Kotera 1
1Kyoto University Kyoto JapanShow Abstract
A kinesin-microtubule system playing an important role in intracellular transport has been studied for potential applications as in vitro nanoactuators. A challenge toward a molecular sorter/concentrator is to control microtubule gliding directions in an inverted molecular configuration to allow microtubules to glide on a kinesin-coated surface. Although several methods have been proposed, none of them has controlled microtubules to multiple directions in a given static environment. Here, we propose a method to control gliding directions by designing biophysical properties of free end of microtubules such as surface charge density, flexural rigidity, and distance of kinesin molecules. The negatively charged-surface of microtubules was further charged by conjugating DNA molecules. As biotin and streptavidin molecules have neutral charges, we started with microtubules biotinylated at their minus end (seed), which were prepared by a standard protocol for polarity-marked microtubules. After adding streptavidin molecules, 20-bp or 50-bp dsDNA molecules were conjugated. Electrophoretic mobilities were measured for non-labeled seed, biotinylated seed, streptavidin-labeled seed, 20-bp DNA-labeled seed, and 50-bp DNA-labeled seed, resulting in significantly higher values for DNA-labeled ones. The result enabled us to predict sharp turns of DNA-labeled ones in a given electric field (7 kV mminus;1). We further elongated those microtubule seeds to have long polymerized plus ends and assayed. It revealed three different curvatures in the order of 50-bp, 20-bp, and non-labeled microtubules according to their electrophoretic mobilities. The other property, flexural rigidity, was designed by modifying microtubule polymerizing buffer conditions. When microtubules are polymerized in the presence of GMPCPP (GMPCPP-MTs), flexural rigidity is 3.2-fold higher than that of microtubules polymerized with GTP (GTP-MTs). Although curvatures are theoretically proportional to flexural rigidity, our measurement in the same electric field resulted in ~2-fold difference in curvature. Other than designing microtubules, we also attempted to change distance between kinesin molecules coated on a glass surface. It is inversely proportional to the curvature, we expect to obtain further parameters to control gliding direction of microtubules. In summary, we propose three parameters to control microtubule gliding directions on a kinesin-coated glass surface under a given electric field. This rational engineering design opens a way to establish a nanomachines based on the kinesin-microtubule system.
5:15 AM - L4.08
Optimal Combination of Power Stroke and Diffusional Stepping in Molecular Motors
Regina Katharina Schmitt 1 Jonas Johansson 1 Juan MR Parrondo 2 Heiner Linke 1
1Lund University Lund Sweden2Universidad Complutense de Madrid Madrid SpainShow Abstract
The development of machinery on a nanometer scale is often inspired by molecular motors, which impress with very high efficiencies. Two main mechanisms for translational motors are commonly being discussed: first, the power stroke mechanism, where the ATP consumption is thought to lead to a strong conformational change of the protein, pushing the motor actively forward . Second, a rectification process of thermal fluctuations through feedback, which can extract energy from the thermal bath at the expense of information processing. The latter is sometimes referred to as a “Brownian ratchet”, suggested as early as 1957 by Huxley .
We have developed a generic theoretical model that can describe both mechanisms and their interaction. We are specifically interested in the theoretical limits of efficiency for the two mechanisms and find that the highest efficiency can be achieved by a combination of power stroke and rectification process.
The model consists of a particle diffusing freely in a piecewise linear potential coupled to a feedback control system. Depending on the particles position, potential barriers are set up at specific predetermined positions. Both the positions and shape of the barriers can be varied. Thus the model allows to gradually explore the interplay of power stroke on the one hand, and work extracted from the heat bath using information about the particles position on the other hand. The system is investigated both analytically and with dynamical simulations. We conclude that the interplay of power stroke and information leads to maximum efficiency and moreover increases the robustness of the process. The gained knowledge on these energy conversion processes may not only lead to a better understanding of the functionality of molecular motors, but is also useful in the design of future, efficient synthetic molecular motors and nanomachines.
 J. Howard, Protein power strokes, Curr. Biol. 16 (2006), 517-9
 A.F. Huxley, Muscle structure and theories of contraction, Prog. Biophys. 7 (1957) 255
5:30 AM - L4.09
Self-Running Micro-Droplets of Liquid Metal with Record Speed on a Race Track
Mohammed G Mohammed 1 Michael Dickey 1
1NC State University Raleigh United StatesShow Abstract
We describe a new approach to self-running micro-scale droplets of liquid metal that results in velocities ~20 cm/s, which is higher than any reported velocity for liquid metals. The technique works by first depositing and patterning metal films on glass slides. These films serve as the ‘race track&’ onto which liquid metal droplets run. Droplets of eutectic gallium indium (EGaIn) in acidic solutions spontaneously wet these films, resulting in capillary forces. The solid films dissolve into the liquid metal and the droplets run rapidly along the surface due to the capillary forces. The capillary forces are sufficient to delaminate the films. Our results suggest this delamination process is critical for the incredibly large velocities. The liquid metal drop runs with velocities up to 20 cm/sec which is orders of magnitude higher than any reported velocity of metal drops, and the kinetic energy of our liquid metal drops is orders of magnitude higher than that of any running liquid drops. This system is easy to prepare, does not require special surface treatment, and works effectively in ambient temperature and pressure.
5:45 AM - L4.10
Chemically Active Colloids under Spatial Confinement
Paolo Malgaretti 1 Alvaro Dominguez 2 Mihail Nicolae Popescu 1 Siegfried Dietrich 1
1Max Planck Institute for Intelligent Systems Stuttgart Germany2University of Seville Seville SpainShow Abstract
Chemically active colloids, capable of self-motility via promoting catalytically activated chemical reactions in the surrounding solution [1,2], induce hydrodynamic and chemical fields that decay with the distance from the particle in a similar manner . Therefore, when the active colloids are in the vicinity of walls, other particles, or fluid-fluid interfaces, a rich, complex behavior, emerges from the interplay of the two fields (see, e.g., Ref. ). Focusing on a simple model of chemically active colloids , here we discuss examples of motility driven by effective interactions with various physically relevant types of bounding surfaces.
 R.F. Ismagilov et al, Angew. Chem. Int. Ed. 2002, 41, 652.
 W.F. Paxton et al, JACS 2004, 126, 13424.
 R. Golestanian et al, New J. Phys. 2007, 9, 126.
 W.E. Uspal et al, Soft Matter, Soft Matter 2015, 11, 434.
L5: Poster Session
Wednesday PM, April 08, 2015
Marriott Marquis, Yerba Buena Level, Salon 7/8/9
9:00 AM - L5.01
Biomechanical Investigation of Femur-Tibia Articulation of Lubber Grasshopper
Jun Kyun Oh 1 Mustafa Akbulut 1
1Texas Aamp;M University College Station United StatesShow Abstract
This study focuses on the tribological properties of femur-tibia articulation of grasshopper (Romalea guttata) leg joints. It was found that the coefficient of friction for the articulation was very low, 0.052 ± 0.001 and 0.037 ± 0.002 under dry and squalane lubricated conditions, respectively. A synergistic combination of a unique joint morphology and internal nanostructure of grasshopper joints were found to be responsible for their exceptional frictional and mechanical properties. Overall, given the exact mechanism by which insect joints reduce friction and wear is still unknown, this original study reveals the main characteristics of the insect joints responsible for their efficient operation and improved tribological properties.
9:00 AM - L5.02
Bioinspired Sensing Devices Based on Molecularly Imprinted Polymers
Kyung Choi 1
1University of California-Irvine Irvine United StatesShow Abstract
Recently, bio-inspired devices are widely investigated to develop advanced biotechnology. There are many challenges for chemists to develop new bio-materials and bio-devices based on functional polymers since the area is a part of the chemical domain, which builds up novel bio-materials at the molecular scales. In this study, we introduce a bio-inspired material, “Molecularly Imprinted Polymer (MIP),” which is a highly cross-linked thermoset with specific molecular recognition function. MIP system can be produced by “Molecular Imprinting Technique,” which is a general protocol for the creation of synthetic receptor sites with specific molecular recognition functions in cross-linked network polymers. Molecular recognition will take place by receptor or binding sites. Synthesis of high affinity receptor sites in MIPs&’ system is a key contribute to achieve high performance bio-sensors/devices. Since microfluidic technique can be also employed to fabricate nano-devices, the microfluidic synthesis was employed to produce high sensitivity MIP&’s particles. Such novel synthetic technique brings novel MIP&’s materials with specific advantages that can&’t be achieved by conventional methods.
9:00 AM - L5.03
Bubble-Propelled Micromotors Powered with Ultralow Catalyst Loading
Aida Martin Galan 1 2 Beatriz Jurado Sanchez 1 Alberto Escarpa Miguel 2 Joseph Wang 1
1University of California-San Diego San Diego United States2University of Alcala Alcala de Henares SpainShow Abstract
The remarkable performance of natural proteins motors have inspired scientist to create nanomotors capable of converting energy into movement and forces. Such nanoscale devices consist of a self-propelled structure equipped with sensing and/or actuating attachments, capable of transporting cargoes in a rapid and controlled manner. Considerable recent efforts have been devoted to reduce the amount of catalyst used to propel such tiny microengines, without diminishing its performance. Herein, we will introduce a new concept of catalytic micromotor powered by ultralow loadings of catalyst. To this end, we will explore the use of high surface area nanomaterials in combination with common catalyst such as platinum. In particular, graphene is a two-dimensional material with extraordinary properties, such as large surface area, excellent thermal and electrical conductivities, optical transparence, and high mechanical strength. Graphene is proposed here as a new material in microengine synthesis for catalyzing the decomposition of hydrogen peroxide to generate oxygen as well as the possibility of taking advantage of its rich chemistry to bond biological structures providing new applications in clinical or biochemical fields.
The newly synthetized microengines will consist in a tubular polymer-graphene/Pt bilayer. The decomposition of hydrogen peroxide using both platinum and graphene as catalytic surfaces generates the oxygen bubbles essential for motion. The conical shape of these microengines and the differential pressure permit to assist the unidirectional expansion of the catalytically generated oxygen bubbles, as well as, their release from one of the tubular openings thrusting the microengine. The synergic effect provoked by Pt and graphene implied excellent speeds of the synthesized microengines and the propulsion with slow quantity of hydrogen peroxide as fuel in the media of analysis.
9:00 AM - L5.04
Reactive Motors for Environmental "Clean-Up"
Beatriz Jurado Sanchez 1 Joseph Wang 1
1UCSD La Jolla United StatesShow Abstract
Self-propelled catalytic nanomotors, capable of converting energy into movement and forces, have shown considerable promise for diverse environmental applications. The continuous movement of microscale machines can be used for transporting water purification nanomaterials throughout contaminated samples, for releasing and dispersing remediation agents over long distances, and for imparting significant mixing during decontamination processes (without external forced convection, e.g., stirring). In this communication we will discuss the development and characterization of catalytic activated Janus particles micromotors and will demonstrate their highly efficient self-propulsion and remarkable water decontamination efficiency. The adsorption properties of diverse active microparticles are combined with an attractive propulsion performance and enhanced fluid dynamics and mixing to offer ‘on-the-fly&’ accelerated water purification processes. Unlike these early nanomotor-based decontamination efforts involving the movement or release of reactive remediation agents, these newly developed micromotors can universally remove and isolate broad range of chemicals (without decomposing them). In particular, we will describe the preparation and behavior of Janus micromotors based on activated carbon microparticles. The improved propulsion performance has been attributed to the microporous Pt surface (on the rough carbon substrate) that offers a greatly enhanced catalytic activity and efficient bubble evolution compared with common Janus micromotors. Accordingly, the new activated carbon based micromotors can operate efficiently in raw viscous real-life environmental media and maintain high speeds in such samples. The continuous movement of multiple activated carbon/Pt micromotors across, along with the high-density tail of microbubbles, results in a greatly enhanced fluid dynamics that leads to a significantly higher water purification efficiency and short clean-up times compared to static activated carbon particles. These newly developed Janus micromotors can reach large areas of a contaminated sample accelerating the decontamination process without external mixing force. The remarkable decontamination power of the new activated carbon micromotor has been demonstrated in connection to a variety of model organic and inorganic pollutants. These new developments are expected to advance rapidly into practical environmental applications. While peroxide-driven motors are used here for proof-of-concept of the self-propelled activated carbon ‘moving-filters&’, recently introduced water-based micromotors would allow to move the activated carbon ‘filters&’ using the water sample itself as an in-situ fuel. Alternately, this concept can be also applied using ultrasound or magnetic based, fuel-free micromotors.
9:00 AM - L5.05
Encapsulation of Bioengineered Enzymes within Porous Polymer Vesicles
Gordon Lee Nish 1 Carlo Montemagno 2
1University of Alberta Edmonton Canada2Univ of Alberta Edmonton CanadaShow Abstract
The major disadvantages of employing isolated enzymes in industrial reaction processes are poor stability and activity half-life of the biological catalyst. The primary goal of the project is to develop a universal and robust method to circumvent these pitfalls. The protective cellular membrane and intracellular environment of a living cell can be effectively mimicked by encapsulating the enzymes within a polymer vesicle. The polymer membrane acts as a barrier from bulk reaction medium and allows for localized high concentration of enzyme.
Polymer vesicles were chosen for their robust mechanical and chemical stability over lipid bilayers. Introducing the enzymes during vesicle formation leads to their entrapment within the polymer membrane. In order for the enzyme-containing vesicles to be effective nanoreactors, the substrate must be capable of diffusing across the polymer bilayer. Passage of substrate and products across the membrane is enabled through hydrophilic pores in the membrane. These pores are introduced through a photochemical reaction enabling necessary enzyme-substrate interactions.
To date, this effort has produced very captivating results for several enzymes. Through parameter optimization, it has been possible to encapsulate up to 77% of enzyme initially introduced, which resulted in a 22% increase in catalytic half-life over a period of 24 hours. In addition to this, in comparing the rate of product formation between the isolated and encapsulated enzyme, we have demonstrated that the rate of diffusion of substrate across the polymer membrane has a negligible impact on the reaction rate.
Further experimentation regarding free and encapsulated enzyme kinetics in a controlled reactor will be pursued, in addition to entrapment of significantly less stable enzymes. These early achievements have so far proven the polymer encapsulation of enzyme to be promising technology.
9:00 AM - L5.06
Virus Color Matrix for Cancer Recognition
Lee So-Young 1 Chuntae Kim 1 Won-Geun Kim 1 Oh Jin-Woo 1 So Young Yoo 1
1Pusan National University Busan Korea (the Republic of)Show Abstract
Color sensor such as pregnancy test kit or litmus paper for pH test which changes colors in response to the target is excellently concise analyzing system. Recently our group developed the novel colorimetric sensor utilizing the colored structure of functionalized M13 phage and could detect TNT(tri-nitro-toluene) down to ppb levels with the color changes. Each species of cells produces a unique composition of volatile gas imperceptibly. Lung cancer cells release abnormal composition of gas compared to normal cells. To discriminate the minute gas in ppb levels precisely and concisely, cell discriminating sensor could be applied. Here, we developed a novel cancer recognition sensor using “virus based color matrix (VCM)”. Our results show that our functionalized VCM could rapidly distinguish the unique component of by-products between cancer cell and normal cell. This study demonstrate our tunable VCM could be utilitzed as a novel cancer diagnosis sensor by recognizing human breathe. [This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Korean Government (2013R1A1A3008484 and 2014S1A2A2027641)]
9:00 AM - L5.08
Manipulation of Lateral Buckling of Bio-Inspired Nanowalls
Hyunsik Yoon 1 Jung Gun BaeSang Moon KimWon Bo LeeKookheon Char
1Seoul National University of Science amp; Technology Seoul Korea (the Republic of)Show Abstract
Janus nanostructures have been known as a promising method for realizing asymmetric structures and received attention for several applications such as bio-inspired adhesives, programmable microfluidics because of their unidirectional properties. In this presentation, we realize a bio-inspired Janus nanowall and demonstrate a lateral buckling during a reactive metal deposition on soft polymeric structures. Polymeric nanowalls were fabricated by a replica molding method and metal films were then coated on one side of the polymeric nanowalls in high vacuum condition. We will discuss the manipulation scheme such as metal film thickness, metal coverage on high aspect ratio nanowalls. Also the mechanism of lateral buckling will be addressed.
9:00 AM - L5.09
Investigation of the Dynamic and Diffusional Properties of Supported Membranes on Bioinspired Materials Using HRMAS NMR Spectroscopy
Kimberly Childress 1 Kristin Meyer 1 Bryan Kaehr 2 C. Jeffrey Brinker 2 Todd M. Alam 1
1Sandia National Laboratories Albuquerque United States2Sandia National Labs Albuquerque United StatesShow Abstract
Lipid bilayers on biomimetic surfaces have received considerable attention due to their potential bio- and medical applications. Solid supported lipid bilayers (SLBs) have characteristics similar to those of cells and are used to investigate membrane dynamics, protein-lipid interactions, and surface-lipid interactions. Lipid liposomes themselves are used as drug carriers in several commercial products, and through the rupture and fusion of liposomes formed from the sonication of lipid multilamellar vesicles (MLVs) they become attached to the silica surfaces to form SLBs. There still remain questions concerning the role of surface chemistry, porosity and local membrane curvature on the physical properties of these supported bilayers. In this poster we explore the impact of different bioinspired materials on the local chain dynamics and diffusional properties of surface adsorbed lipids are explored. Model membrane systems (e.g. DMPC, DOPC, and POPC) were supported on spherical solid silica nanoparticles, and on porous silica nanoparticles fabricated from mammalian Red Blood Cell (RBC) templates. Through the use of 1H High-Resolution Magic-Angle Spinning (HRMAS) NMR transverse spin-spin relaxation rates (R2) experiments coupled with pulse field gradient (PFG) diffusion studies, it was possible to directly measure the fluidic properties of the lipid bilayer and the surrounding water environments. HRMAS NMR allows the removal of local magnetic susceptibility interactions in these heterogeneous SLBs, resulting in high resolution NMR spectra where different chemical moieties of the lipid are resolved. The local lipid chain isomerization dynamics are reflected in the R2 experiments and were studied for MLVs and SLBs as a function of temperature for different lipid systems. The individual self-diffusion constants of the water and lipids were determined from the PFG NMR studies, and showed that the lateral diffusion rates of the lipids in MLVs and SLBs were similar, but an order of magnitude slower than the water diffusion. The differences in diffusion rates between multi-lamellar vesicles (MLV) and SLBs, along with differences resulting from use of different silica supports were obtained. Slow motion fluidity of the lipids decreases when adsorbed on a solid support, suggesting a more ordered and tightly-packed membrane structure. Saturated DMPC was more ordered than DOPC on solid supports due to the double bonds in the tails of DOPC. Changes in temperature did not vary the NMR signal intensities observed from the MLV and SLB. In addition, 29Si MAS NMR was used to directly follow silica condensation through the RBC silicification process.
9:00 AM - L5.10
Monte Carlo Study on the Wetting Property of a Hydrophobic Surface Textured with Domed Pillars
Hyojeong Kim 1 Jihye Jang 1 Joonkyung Jang 1
1Pusan National University Busan Korea (the Republic of)Show Abstract
Using a Monte Carlo simulation based on the lattice gas model, we focused on the phase behavior of water confined in the gap between domed pillars. The dry and wet phases of the inter-pillar gap, respectively, were related to the Cassie-Baxter and Wenzel states of a macroscopic droplet deposited on the pillared surface. We studied the domed pillar size effects by systematically varying its height for a fixed ratio of the height to its width.
The periodic arrays of the domed pillars were simulated to shed light on the origin of the unparalleled hydrophobicity of a lotus leaf . As the inter-pillar spacing or the pressure of liquid increases, the liquid on top of the domed pillars penetrated smoothly down into the inter-pillar gap . This wetting transition contrasts with that observed for the gap between rectangular or cylindrical pillars, where a liquid abruptly fills in the inter-pillar gap at a critical inter-pillar spacing or pressure .
Simple analytic expressions of the critical spacing and pressure at which the wetting transition occurs for the domed pillars were derived using continuum theory . These continuum results agreed reasonably well with the present molecular simulations, even for pillars as small as few nanometers in width [2,3].
 Extrand, C. W. Langmuir 2011, 27, 6920
 Kim, H.; Lee, S. I.; Matin, M.; Zhang, Z.; Jang, J.; Ha, M.Y.; Jang, J. J. Phys. Chem. C in Press
 Kim, H.; Saha, J. K.; Jang, J. J. Phys. Chem. C2012, 116, 19233
 Huang, X.; Margulis, C. J.; Berne, B. J. P. Natl. Acad. Sci. USA 2003, 100, 11953
9:00 AM - L5.11
Modeling and Experiment Reveal Mutable Inverse Temperature Transition in Elastin-Like and Silk-Elastin-Like Protein Polymers
Anna Tarakanova 1 Wenwen Huang 2 David L Kaplan 2 Markus Buehler 1
1MIT Cambridge United States2Tufts University Medford United StatesShow Abstract
Elastin is a key mammalian extracellular matrix protein found in the human body, conferring resilience, compliance and elasticity to the lungs, blood vessels and skin. Soluble elastin-like peptides can be engineered into a range of physical forms, from hydrogels and scaffolds to fibers and artificial arteries, finding numerous applications in medicine and engineering as “smart polymers”. Importantly, elastin is a great candidate as a platform material for novel biomaterial design as it exhibits a highly tunable response spectrum, with reversible phase transition capabilities at a temperature of 40-60oC. Here, we designed a library of elastin-like protein material models, using classical Molecular Dynamics and Replica Exchange Molecular Dynamics methods, to study the effect of sequence and environmental triggers on elastin&’s structural transition, exposing molecular mechanisms controlling these transitions that have been poorly understood until now. This library is a valuable standalone resource for recombinant protein design and synthesis and may elucidate the design of composite elastin-based materials. As an example of such a system, we study silk-elastin-like protein polymers (SELPs). Silk is uniquely strong, exhibiting strength values that surpass those of engineering materials such as Kevlar and steel. Thus, SELPs, which have repeating silk and elastin blocks, combine the distinctive properties of the composing parts to achieve strong and extensible, mutable biomaterials. We use simulations and experiment to study the effect of silk to elastin ratio in SELPs, finding a close correlation. These results suggest a facility for creating highly specific materials that can react controllably to triggers, opening up avenues for applications in drug delivery and smart material design.
9:00 AM - L5.12
Direct-Write, Cell-Like Materials
Bryan Kaehr 1 Lauren Zarzar 2
1Sandia National Laboratories Albuquerque United States2MIT Cambridge United StatesShow Abstract
The success of biological systems rests upon the ability to direct biochemical reactions using asymmetric recognition and catalysis under strict compartmentalization. Efforts to engineer directional propulsion of bioinspired nanomachines such as catalytic nanomotors similarly require asymmetric placement of a catalytic entity (e.g., platinum). Alternatively, placement of catalysts within asymmetric compartments can facilitate directional ‘cell-like&’ reactions and prove useful for systems ranging from micropumps to microfluidic chemical reactors and energy converters. Here we describe a multiphoton lithography (MPL) method to create arbitrary 3D biomolecular and multicomponent composites. We demonstrate that MPL is a straightforward route to fabricate microscale patterns of nanocrystalline platinum and palladium that display excellent catalytic, electrical, and electrochemical properties. These materials can be integrated within 3D MPL-defined microenvironments to generate directed autonomous particle and fluid transport. This preliminary work demonstrates patterning and compartmentalization of catalytic activity at the scale of biological cells, showing that the flow of reactants and products can be strictly directed. Moreover, compartmentalization is achieved using biological materials that can remain active (e.g. using enzymes or ligand binding proteins such as avidin) and potentially direct anisotropic self-assembly of additional functionalities such as lipids. These direct-write, cell-like systems provide an exciting platform for the construction of living materials.
9:00 AM - L5.13
Microspinners: Controlling Rotational Frequency in Self-Phoretic Janus Devices
Richard Archer 1 Andrew Campbell 1 Stephen Ebbens 1
1University of Sheffield Sheffield United KingdomShow Abstract
Autonomous micron scale swimming devices are a class of active materials which show directed propulsion at low Reynolds numbers, giving translational displacements far exceeding that of Brownian motion without the need for external actuation. Such devices use catalytic decomposition of dissolved fuels by spatially separated inert and active sections to generate motion by phoretic or bubble release phenomena.
Here we consider spherical Janus particles with one hemisphere coated in Platinum which produce motion by decomposing hydrogen peroxide. In usual conditions these devices have been shown to produce a thrust vector orientated away from their active cap. However a small increase in rotational diffusion rate as fuel concentration increases above that expected for pure Brownian diffusion has also been reported, thought to be caused by physical imperfections in the hemispherical cap generating angular velocity1. Extending this idea, here we control the active cap shape using a glancing angle metal deposition method described by Pawar et al2. Specifically we look at the effect of breaking the active hemisphere symmetry to unbalance the propulsive force and generate an angular velocity. Recently, rapidly spinning particles have been shown in a range of applications such as causing cell apoptosis3 and directing nerve growth through generation of shear forces in the microfluidic environment4. However, deploying these phenomena is currently limited by a reliance on external fields to generate well controlled spin, motivating this study to develop an autonomous alternative.
Our results demonstrate that tilting colloidal crystals on a planar surface between 0 and 80o, with respect to the directional platinum vapour results in propulsive Janus particles with average rotational frequencies tuneable from 0.25 up to 2.62 Hz. Simple geometrical analysis shows that the cap symmetry is broken due to shadowing effects of neighbouring particles in the crystal lattice. This is confirmed by repeating the experiment at sparse colloidal coverage, where particles show low angular velocity at all tilt angles.
While autonomous micron scale spinning devices have been previously reported by random self-assembly of two or more Janus particles, the resulting angular velocity was not well contolled5. Consequently this work extends the potential to investigate and deploy many interesting rotational driven phenomena.
1 J. Howse, et al, Phys. Rev. Lett. 99, 048102 (2007).
2 A.B. Pawar and I. Kretzschmar, Langmuir 24, 355 (2008).
3 M. Domenech, et al, ACS Nano 7, 5091 (2013).
4 T. Wu, et al, Nat. Photonics 6, 62 (2011).
5 S. Ebbens,et al, Phys. Rev. E 82, 015304 (2010).
9:00 AM - L5.14
Catalytic/Bio-Catalytic Driven Janus Mesoporous Silica Nano-Motors
Xing Ma 1 Samuel Sanchez 1
1Max-Planck Institute for Intelligent Systems Stuttgart GermanyShow Abstract
Nano-motors capable of delivering small molecule cargos are fabricated based on Janus mesoporous silica nanoparticles (MSNP). The particle size is tunable from 40 nm to 90 nm. A monolayer of nano-sized MSNP is first prepared and one side of the MSNP is capped with either catalytic layer of Pt or non-catalytic layer of SiO2 by electron beam evaporation, to produce Janus nanoparticles. The Pt coating side can directly provide driving force for the active motion of the Janus mesoporous silica nano-motors (JMSNM) by catalytically decomposition of H2O2. Alternatively, for the case of SiO2 coating, natural enzyme catalase can be functionalized onto the non-coated side of JMSNP via chemical linkage, triggering H2O2 decomposition via bio-catalytic reaction. Enhanced diffusion of the JMSNM upon addition of H2O2 fuel was characterized by dynamic light scattering (DLS). The trajectory of individual JMSNM(90nm) was recorded by optical microscopy and enhancement of the diffusion coefficient was confirmed by theoretical calculation. The nano-sized channels with internal pore diameter about 2-3 nm can be utilized for cargo loading and delivery. The high porosity of the mesoporous silica can ensure high cargo loading capacity comparing to rigid ones. Sustained release of cargo molecules from these JMSNM indicates the great potential of using the JMSNM for drug delivery in future biomedical applications.
 L. Baraban, D. Makarov, R. Streubel, I. Mönch, D. Grimm, S. Sanchez*, O. G. Schmidt. ACS Nano2012, 6, 3383.
 S. Sánchez*, A. A. Solovev, Y. F. Mei, O. G. Schmidt. J. Am. Chem. Soc.2010, 132, 13144.
 L. Baraban, M. Tasinkevych, M. N. Popescu, S. Sanchez*. Soft Matter, 2012,8, 48.
9:00 AM - L5.15
Collisions Involving Chemically Active Spherical Janus Colloids
Mihail Nicolae Popescu 1 William Eric Uspal 1 Mykola Tasinkevych 1 Siegfried Dietrich 1
1Max Planck Institute for Intelligent Systems Stuttgart GermanyShow Abstract
The challenge of enabling micrometer-scale objects to self-propel in a liquid environment has received significant interest in the last decade. One route to achieve this is to employ colloids capable of promoting catalytically activated chemical reactions in order to extract chemical free energy from the surrounding environment and to transform it into mechanical energy [1,2]. For example, by covering part of the surface of a spherical colloid with a catalyst promoting a chemical reaction in the surrounding solution, concentration gradients can be created along the surface of the particle and self-phoretic propulsion emerges .
The self-phoretic motion of these active colloids is such that hydrodynamic and chemical fields decay with the distance from the particle in a similar manner . When their motion occurs near walls or near other particles, one can expect a rich behavior to emerge from the interplay of the two fields. The results recently reported in  for an active Janus sphere near a hard wall indeed reveal several complex steady-states, including sliding and hovering, which goes beyond hydrodynamic interactions effects [5,6]. Furthermore, the outcomes of pair collision for such active particles, e.g., an alignment of their symmetry axes, significantly influences the emergent collective behavior. Yet, in most studies this is either heuristically postulated  or approximated by a far field result .
In this work we present a study of head-on collisions between (i) an active particle and an interface, i.e., a hard or soft wall, respectively, and (ii) two active particles. Taking advantage of the co-linear alignment of the symmetry axis with the normal to the wall or the axis of the other particle, we have obtained analytical solutions for the general case of an arbitrary percentage of catalyst coverage of the Janus particle and various physically plausible boundary conditions at the particle and at the wall. The results are critically discussed in the context of previously proposed "collision-rules" and effective models for active particles [7-9].
1. R.F. Ismagilov et al, Angew. Chem., Int. Ed., 41, 652 (2002).
2. W.F. Paxton et al, JAchS 126, 13424 (2004); J.R. Howse et al, Phys. Rev. Lett. 99, 048102 (2007).
3. R. Golestanian et al, New J. Phys. 9, 126 (2007).
4. William Uspal et al, arXiv:1407.3216 (2014).
5. S.E. Spagnolie and E. Lauga, J. Fluid Mech. 700, 105 (2012).
6. K. Ishimoto and E.A. Gaffney, Phys. Rev. E 88, 062702 (2013).
7. M.C. Marchetti et al, Rev. Mod. Phys. 85, 1143 (2013); J. Barre et al, J. Stat. Phys., in press (2014).
8. R. Soto and R. Golestanian, Phys. Rev. Lett. 112, 068301 (2014); O. Pohl and H. Stark, Phys. Rev. Lett. 112, 238303 (2014).
9. B. ten Hagen et al, J. Phys.: Condensed Matter 23, 194119 (2011).
9:00 AM - L5.16
Rotaxane-Based Molecular Muscles
Carson J. Bruns 2 1 Marco Frasconi 2 3 Zhixue Zhu 2 Damien Sluysmans 4 Anne-Sophie Duwez 4 Samuel I Stupp 2 J Fraser Stoddart 2
1University of California, Berkeley Berkeley United States2Northwestern University Evanston United States3Instituto Italiano di Tecnologia Genova Italy4University of Liegrave;ge Liegrave;ge BelgiumShow Abstract
A natural source of inspiration for designing artificial molecular machines is muscle tissue, a material that relies on the hierarchical organization of motor proteins (myosin) and filaments (actin) to produce the force and motion that underpin locomotion, circulation, digestion, and many other essential life processes. Muscle is characterized at both macroscopic and microscopic length scales by its ability to generate forces that vary the distance between two points at the expense of chemical energy. Materials that mimic this function are desired for many applications involving the transduction of mechanical energy. Rotaxanes are a class of mechanically interlocked molecules that satisfy these criteria by virtue of having movable filamentous components, the relative positions of which can be controlled by external stimuli [1,2]. We describe two classes of rotaxanes - namely, daisy chains and oligorotaxane foldamers - which are able to generate nanoscale forces and motions similar to those generated by natural muscle.
‘Daisy chains&’ are rotaxanes comprising self-complementary ring-rod monomers cross-threaded into cyclic or acyclic oligo/polymers, which can be designed to undergo dramatic length changes in response to stimuli. We have applied a click chemistry protocol for rotaxane synthesis to the development of two new classes of electrochemically and thermally switchable daisy chains - one of them is neutral and organic soluble , while the other is charged and water-soluble . Their molecular contractions and expansions have been characterized and quantified by MD simulations, NMR and UV/Vis spectroscopies, and cyclic voltammetry.
We have also prepared a family of oligorotaxanes which adopt well defined, highly folded secondary structures in solution, stabilized by pi-donor/pi-acceptor charge transfer and hydrogen bonding interactions [5,6]. In principle, these oligorotaxane foldamers can be induced to fold and unfold (i.e., expand and contract) by modulating the strength of their intramolecular noncovalent bonds with chemical, thermal, electrochemical, or mechanical stimuli. We highlight the recent results of single-molecule pulling experiments on these foldamers using an AFM cantilever. Atomic force spectroscopy reveals the successive rupture of folded domains in the oligorotaxanes as they are stretched, as well as a capacity to generate force while re-folding against a load.
1. Molecular Machines Muscle Up. Nature Nanotech.2013, 8, 9
2. Rotaxane-Based Artificial Muscles. Acc. Chem. Res.2014, 47, 2186
3. An Electrochemically and Thermally Switchable [c2]Daisy Chain Rotaxane. Angew. Chem., Int. Ed.2014, 53, 1953
4. Redox-Switchable Daisy Chain Rotaxanes Driven by Radical-Radical Interactions. J. Am. Chem. Soc.2014, 136, 4714
5. Synthesis and Solution-State Dynamics of Donor-Acceptor Oligorotaxane Foldamers. Chem. Sci.2013, 4, 1470
6. Mechanically Interlaced and Interlocked Donor-Acceptor Foldamers. Adv. Polym. Sci.2013, 261, 271
9:00 AM - L5.18
Synchronization in Hybrid Self-Oscillating Gel/Piezoelectric MEMS
Victor V. Yashin 1 Steven P. Levitan 1 Anna C. Balazs 1
1University of Pittsburgh Pittsburgh United StatesShow Abstract
Our goal is to develop materials that compute by using non-linear oscillating chemical reactions to perform spatio-temporal recognition tasks. The material of choice is a polymer gel undergoing the oscillatory Belousov-Zhabotinsky reaction. The novelty of our approach is in employing hybrid gel-piezoelectric micro-electro-mechanical systems (MEMS) to couple local chemo-mechanical oscillations over long distances by electrical connection. Our modeling revealed that (1) interaction between the MEMS units is sufficiently strong for synchronization; (2) the mode of synchronization depends on the number of units, type of circuit connection (serial of parallel), and polarity of the units; (3) each mode has a distinctive pattern in phase of oscillations and generated voltage. The results indicate feasibility of using the hybrid gel-piezoelectric MEMS for oscillator based unconventional computing.
9:00 AM - L5.19
An Artificial Molecular Pump
Chuyang Cheng 1 Paul McGonigal 1 J Fraser Stoddart 2
1Northwestern University Evanston United States2Northwestern University Evanston United StatesShow Abstract
One of the distinguishing features of living organisms is their proclivity to employ molecular machinery on a grand scale to power their metabolic processes. For example, the active transport of ions and small molecules across cell membranes, using transmembrane protein pumps to create concentration gradients of ions, such as Na+, K+ and Ca2+, in addition to protons, whose stored potential may then be used as a secondary energy resource in metabolic processes, e.g., ATP synthesis. During billions of years of evolution, these proteins have developed finely tuned secondary and tertiary structures capable of harnessing external fuel to exert precise control over the noncovalent forces—the potential energy land-scape of energy barriers and wells—experienced by their cargos in order to drive them energetically uphill, temporarily away from thermodynamic equilibrium.
Recently, an artificial system that can transport molecules unidirectionally and autonomously, using light as the only energy source, has been developed in our laboratory.1 An improved system2 has been designed to pump the CBPQT4+ rings from bulk solution onto a long chain repetitively and progressively. We have named it a molecular pump. The prototypical molecular pump consists of a dumbbell containing a 3,5-dimethylpyridinium (Py+), a 4,4prime;-bipyridinium (BIPY2+), an isopropylphenyl (IPP) and a long chain terminated by a bulky stopper. The CBPQT4+ ring is repelled by the Py+ and BIPY2+ initially, upon reduction with activated zinc dust, and the Coulombic repulsion between Py+ and the CBPQT2(+bull;) ring decreases dramatically, forming a thermodynamically stable trisradical complex3,4BIPY+bull;Igrave; CBPQT2(+bull;) within seconds. When re-oxidized to the fully charged state, the electrostatic Py+ barrier is recovered, forcing the CBPQT4+ ring to jump over the steric barrier (IPP) onto the long chain, trapping it there. When the redox process is repeated, a second CBPQT4+ ring can be pumped onto the long chain. It is anticipated that this molecular motor can pump more than two CBPQT4+ rings if the chain is long enough.
1) Li, H. et al., J. Am. Chem. Soc.2013, 135, 18609-18620
2) Cheng, C. et al., J. Am. Chem. Soc., ASAP, DOI: 10.1021/ja508615f
3) Trabolsi, A. et al., Nature Chem.2010, 2, 42-49.
4) Fahrenbach, A. C. et al., J. Am. Chem. Soc.2012, 134, 3061-3072.
9:00 AM - L5.20
Gravitactic Janus Sphere Swimming Devices
Andrew I Campbell 1 Stephen Ebbens 1
1The University of Sheffield Sheffield United KingdomShow Abstract
Synthetic swimming devices produce enhanced motion in a fluid environment beyond that due to Brownian phenomena and have the potential for use in many applications, including targeted drug delivery and transport of materials in microfluidic devices. Typically, the autonomous propulsion of spherical Janus swimming devices relies on the asymmetrical decomposition of a dissolved fuel (e.g. H2O2) resulting from the presence of a catalyst (e.g. platinum) on one hemisphere of the device. Whilst propelling, the swimming devices are still subject to Brownian and rotational phenomena resulting in a random and frequently changing direction of travel. Directional control is currently achieved through, for example, the use of an external field (e.g. magnetic, electric), somewhat negating the use of an autonomous propulsion system.
We present recent experimental results where we demonstrate that simple fluorescent polystyrene Janus sphere swimmers (2 - 5 µm) coated on one hemisphere with a 10nm thick layer of platinum and suspended in 10 wt% H2O2 solution, can exhibit gravitaxis. This is reminiscent of gravitactic algae and opens up a biomimetic approach to autonomous directional control. Analysis of the 2D and 3D trajectories (from particle image velocimetry) of our swimmers shows that as the sphere size and cap weight increase, there is a switch from swimming in random directions to swimming upward against gravity. We develop a simple mathematical model based on Boltzmann statistics that describes our experimental data, enabling predictions of the cap weight required for gravitaxis for a given sphere size. We also discuss the effect of ‘spin&’ in the swimmer trajectories, arising from inhomogeneities in the catalytic cap, which has the effect of reducing or ‘switching-off&’ gravitaxis as angular velocity (omega;) is increased.
9:00 AM - L5.21
Jinxing Li 1 Joseph Wang 1
1University of California, San Diego La Jolla United StatesShow Abstract
The rapid miniaturization of devices and machines has fueled the information technology revolution and stimulated the recent development and evolution of nanotechnology. To create smaller features, continuous improvements have been achieved by the implementation of high-resolution lithography techniques. However, such state-of-the-art machines and systems themselves have also become complex and expensive, prompting unconventional solutions for actuation and manufacturing. Drawing from the self-propelled nano-machines ubiquitous in nature, synthetic nanoscale robots have recently been used to demonstrate similar advanced performance and fascinating functionality. Here we report a new nano-patterning approach, named ‘nanomotor lithography&’, which translates the autonomous movement trajectories of nanorobots into controlled surface features. As a proof of principle, we use metallic nanowire motors as mobile nanomasks and Janus sphere motors as near-field nanolenses to manipulate light beams for generating a myriad of nanoscale features through modular nanomotor design. The complex spatially defined nanofeatures using these dynamic nanoscale optical elements can be achieved through organized assembly and remote guidance of multiple nanomotors. Such ability to transform predetermined paths of moving nanomachines to defined surface patterns provides a unique nanofabrication platform for creating diverse nanodevices.
[Ref] Jinxing Li, Wei Gao, Renfeng Dong, Allen Pei, Sirilak Sattayasamitsathit, Joseph Wang, “Nanomotor Lithography”, Nature Communications, 2014, 5, 5026.
9:00 AM - L5.22
Water Cleaning Micro and Nanomotors
Jemish Parmar 1 Samuel Sanchez 1 Xing Ma 1
1Max Planck Institute for Intelligent Systems Stuttgart GermanyShow Abstract
Catalytic micromotors are self-propelled in nature and require no external force for autonomous mobility in aqueous solutions. They rely on degradation of a chemical fuel added to the water or use the water itself for their mobility . Recent research demonstrated dye , and chemical warfare agent degradation , heavy metal removal  and oil removal  capabilities of such micromotors.
Since the first demonstration of catalytic micromotors a decade ago , platinum has been mainly used as a catalyst to decompose hydrogen peroxide fuel [2-5]. Platinum is a noble metal available in nature, but due to its rarity and significant cost, platinum&’s applications as a catalyst for large scale systems is limited. Here, we present an alternative inexpensive iron based catalyst for hydrogen peroxide fuel systems using a Fenton like reaction. Fenton like reactions are highly oxidative because of the production of hydroxyl radicals  and are ideal for powering micromotors with bubble propulsion. The new type of catalytic micromotors fabricated using iron based heterogeneous catalyst will significantly reduce the cost and increase the efficiency of micromotors for environmental remediation. The motile motors act as a highly active, microscale heterogeneous Fenton like system carrying out catalytic wet oxidation of different organic species present in the contaminated aqueous solutions. The catalytic motors have the capability to be captured and reused for further chemical decontamination. The optimization of parameters such as temperature, shape, size and material composition will be presented as well their specificity to different organics and reusability. Here, we demonstrate a simple and inexpensive substitute to traditional platinum based micromotors that will have significant applications in aqueous waste removal and decontamination.
1. Li, J., et al., Water-Driven Micromotors for Rapid Photocatalytic Degradation of Biological and Chemical Warfare Agents. 2014.
2. Soler, L., et al., Self-propelled micromotors for cleaning polluted water. ACS nano, 2013. 7(11): p. 9611-9620.
3. Jurado#8208;Sánchez, B., et al., Self#8208;Propelled Activated Carbon Janus Micromotors for Efficient Water Purification. Small, 2014.
4. Guix, M., et al., Superhydrophobic alkanethiol-coated microsubmarines for effective removal of oil. ACS nano, 2012. 6(5): p. 4445-4451.
5. Paxton, W.F., et al., Catalytic nanomotors: autonomous movement of striped nanorods. Journal of the American Chemical Society, 2004. 126(41): p. 13424-13431.
6. Zepp, R.G., B.C. Faust, and J. Hoigne, Hydroxyl radical formation in aqueous reactions (pH 3-8) of iron (II) with hydrogen peroxide: the photo-Fenton reaction. Environmental Science & Technology, 1992. 26(2): p. 313-319.
9:00 AM - L5.23
Long Range Self-assembly of Microcapsules Regulated via the Repressilator Signaling Network
Henry Shum 1 Victor V. Yashin 1 Anna C. Balazs 1
1University of Pittsburgh Pittsburgh United StatesShow Abstract
Utilizing a biomimetic feedback network, we design microcapsules that self-organize on a planar substrate. Three microcapsules act as localized sources of distinct chemicals that diffuse through the surrounding fluid medium. Production rates are modulated by a regulatory network known as the repressilator: each chemical species represses the production of the next in a cycle. The form of repression is modeled by the Hill function. Analysis of the repressilator system with immobile sources reveals conditions on the maximum production rates and capsule separation distances that result in either steady or oscillatory. We point out characteristics that are dependent on the value of the Hill coefficient, n. We then extend the model to allow movement of the microcapsules over the substrate, induced by gradients in surface energy due to adsorbed chemicals. We numerically simulate this advection-diffusion-reaction system with solid-fluid interactions by combining lattice Boltzmann, immersed boundary and finite difference methods. Under this framework, we construct systems in which the three capsules assemble, forming a close-packed triad. Chemical oscillations are shown to be critical to this assembly. By adjusting parameters, the triad can either remain stationary or translate as a cohesive group. Stationary triads can also be made to “turn off”, producing chemicals at minimal rates, after assembly.
9:00 AM - L5.24
Squeezing or Stretching Molecules between Mica Sheets as a Possible Way to Facilitate Electron Transfer
Helen Greenwood Hansma 1
1UC Santa Barbara San Mateo United StatesShow Abstract
Mechanical energy from moving mica sheets is a possible renewable energy source for the origin of life. [1-3] Energy is needed for prebiotic molecular syntheses, among other things. The Reverse Tricarboxylic Acid Cycle is a reductive reaction cycle proposed for the prebiotic synthesis of amino acids, sugars, and other molecules before the existence of enzymes in living organisms.  Can moving muscovite mica sheets lower the energy barriers for the chemical reduction of molecules such as succinate and citrate by deforming these molecules? A unit cell of mica, KAl2(AlSi3O10)(OH)2, has a delocalized hydrogen available for reducing molecules of the Reverse Tricarboxylic Acid Cycle, such as oxalosuccinate or oxaloacetate. A precedent for this idea comes from research showing that mechanical energy alters the reaction kinetics of disulfide reduction. 
1. Hansma, H G (2009) In Probing Mechanics at Nanoscale Dimensions. N. Tamura, A. Minor, C. Murray and L. Friedman.Warrendale, PA, Materials Research Society. 1185: II03-15.
2. Hansma, H G (2010) Journal of Theoretical Biology 266:175.
3. Hansma, H G (2013) J. Biol. Struct. Dynamics 31:888.
4. Smith, E., H.J. Morowitz, and S.D. Copley, in Protocells: bridging nonliving and living matter, S. Rasmussen, et al., Editors. 2009, The MIT Press: Cambridge, MA. p. 433-460.
5. Wiita, A.P., et al., 2007, Nature450:124.
L3: Bio- and Molecular Machines I
Wednesday AM, April 08, 2015
Moscone West, Level 2, Room 2006
9:45 AM - *L3.01
Motor-Driven Assembly of Dynamic, Self-Healing Lipid and Polymer Nanotube Networks
Nathan Bouxsein 1 Ian M Henderson 1 Walter Paxton 1 George David Bachand 1
1Sandia National Laboratories Albuquerque United StatesShow Abstract
Interconnected and highly reticulated lipid organelles such as the Golgi apparatus are critical to a wide range of physiological processes including the sorting, packaging, and trafficking of macromolecules. While these structures provide a matrix for organizing membrane constituents and providing localized confinement, the lumen represents a continuous nanofluidic network for the transport of proteins and small molecules throughout the cells. Dynamic assembly and reorganization of these lipid structures is facilitated by the motor proteins that dissipate chemical energy to actively manipulate the building blocks of these non-equilibrium structures. Here, we describe a system in which synthetic interconnected, millimeter-scale nanofluidic networks were formed from the cooperative interaction between motor protein-based transport and lipid and/or polymer vesicles. Specifically, the energy-driven transport of microtubule filaments by kinesin motors in this system is used to provide a “pulling force” that acts on multilamellar vesicles, connected via biotin-streptavidin bonds, and extrudes lipid/polymer nanotubes radially outward from the vesicle. Moreover, random collisions of microtubules with the vesicle and nanotubes results highly bifurcated, millimeter-scale networks that are capable of self-repair (i.e., while the nanotubes are continuously elongating and collapsing, the overall network morphology is largely maintained). Regulation of network morphology and properties was explored by adjusting the lipid and polymer composition of the vesicles. We demonstrate significant differences in the size, number of branches, and fluidity among nanotube networks formed by lipid only, polymer only, and composite lipid/polymer vesicle. As this work moves forward, the focus will be on characterizing the connectivity of multi-vesicle networks and interstitial transport of materials as a model system for studying biomolecular transport and communication.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy&’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
10:15 AM - L3.02
Dynamic Molecular Motors Form Specific Patterns under Mechanical Stimulation
Akira Kakugo 1
1Hokkaido University Sapporo JapanShow Abstract
Groups of self-propelled organisms, such as bacteria, fungi, cells and animals, often generate diverse motion patterns through collective motion, which is the most common display of coordinated behaviour. In response to external perturbations, the motion patterns dynamically change formation on a large scale. This is an ability to adapt to the environment. However, the effect of the external perturbation in the rearrangement of motion patterns remains poorly understood, mainly because of the complexity of performing in vitro investigations. Self-propelled molecular motor systems, such as actin/myosin or microtubule/dynein, have been employed to simulate collective motion in vitro to understand the underlying universal principles behind this phenomenon. For instance, actins and microtubules exhibit collective motion forming a wave-like or a torus pattern when they are driven by myosin or dynein, respectively, grafted on a substrate in the presence of adenosine tri-phosphate (ATP). Utilising this simple model system, we studied response of collective motion of microtubules to external perturbation, e.g., stretching stimuli, which are a ubiquitous physiological perturbation mode. Upon the application of single step stretching stimuli above a threshold stretching strain, the collective motion of microtubules moving in random directions oriented perpendicular to the stretch axis. Once the collective motion oriented, it was preserved for a long time. In contrast, the application of cyclic stretching stimuli, even at the threshold stretching strain, rearranged the collective motion of microtubules to form a unique zigzag pattern that maintained ~60 and ~120° steady alternating angles with the stretching axis. Thus, depending on the extent and mode of stimulation, collective motion reacts differently and attains preferential orientations. This work will provide insights in understanding the stimulus responsiveness of collective motion, which in turn will help the understanding of the evolution of emergent functions from self-propelled organisms.
10:30 AM - L3.03
Uncovering Guiding Mechanisms of Microtransporters Driven by Motor Proteins
Takahiro Nitta 1 Yuki Ishigure 1
1Gifu University Gifu JapanShow Abstract
Kinesin and myosin are biological molecular machines, involved in intracellular transports and muscle contractions, respectively. These biological molecular machines can be utilized to drive microdevices, such as MEMS and lab-on-a-Chip. In pursuing such applications, combined micro/nanofabricated substrates, gliding assays serve as a basis, where cytoskeletal filaments are driven by their associated motors adhered on microfabricated substrates. Guiding of the filaments is one of key issues to realize the applications. However, detailed mechanisms of guiding of filaments by the microfabricated walls are not fully understood. Here, by using a computer simulation, we investigated the detailed mechanisms.
Microtubules and actin filaments were modeled as inextensible elastic rods. Time evolutions of conformations of the filaments were computed with a Brownian dynamics simulation. Kinesin and myosin motors were modeled as linear springs. Once bound, motor heads were assumed to move toward specific ends of the cytoskeletal filaments. Hence, the filaments were propelled toward the opposite direction. In addition, normal forces were applied when the filaments collided against the microfabricated guiding walls and the track surfaces.
The simulation revealed detailed mechanisms of guiding of the filaments with microfabricated tracks. For example, at a chemical edge, microtubules were found to be guided through zipping of kinesin motors located at the edge, which overturned previous assumptions of analytical modelings. Such findings were enabled with high spatial and temporal resolutions that the simulation provided.
In summary, we showed that the computer simulation is useful in investigating the mechanisms of the guiding. Insights obtained from the simulation would be useful in designing microdevices driven by the biological molecular machines.
11:15 AM - *L3.04
Bio-Energy Storage Devices Based on Hybrid Nanostructures
Seunghun Hong 1
1Seoul National University Seoul Korea (the Republic of)Show Abstract
Recently, bioinspired nanomachines based on protein motors have been extensively studied due to its various advantages such as a high fuel efficiency. A key component to build practical bioinspired nanomachine systems can be a bio-energy storage device which can store biological fuel (e.g. ATP) and release it at a desired moment to activate the machines. In this presentation, we will discuss two types of bio-energy storage devices based on hybrid nanostructures (i.e. graphene, nanowires, polymers etc): 1) polymer-graphene hybrid structure-based bio-energy storage devices and 2) nano-storage wires. In case of polymer-graphene based storage devices, the polymer structures store ATP, and the stored ATP can be released for a desired time period by external electrical stimuli through the graphene electrode. The nano-storage wires are comprised of a metal nanoelectrode part and a polymer segment holding ATP, and they can be deposited onto desired regions of solid substrates to build a flexible bio-energy storage device. Using these devices, we can control the ATP supply through external electrical stimuli and turn on and off the protein motor activities in real time. Future prospects and possible applications of these devices also will be discussed.
11:45 AM - L3.05
Space Partitioning by Whole Organism Motile Devices
Dan Veniamin Nicolau 1
1McGiil University Montreal CanadaShow Abstract
Protein molecular motors are natural nano-machines that convert the chemical energy obtained from the hydrolysis of adenosine triphosphate (ATP) into mechanical work which is central to cellular motion, muscle contraction, cell division and a multitude of other critical biological processes. The exceptional efficiency of protein molecular motors, together with their small scale, prompted an increasing number of studies focused on their integration in hybrid micro- and nanodevices. However, and despite tremendous progress in the engineering of molecular motors, much needs to be learnt from Nature, in particular regarding the cooperative behaviour of molecular motors in vivo.
Filamentous fungi are very successful in colonizing micro-confined maze-like networks (e.g., soil, wood, leaf litter, plant and animal tissues), suggesting that they may be efficient solving agents of geometrical problems. The growth behaviour and optimality of space-searching algorithms of several fungal species has been tested in microfluidic mazes and networks. First, it was found that the growth behaviour of all species was strongly modulated by the geometry of micro-confinement. Second, the fungi used a complex growth and space-searching strategy comprising two algorithmic subsets: (i) long-range directional memory of individual hyphae and (ii) inducement of branching by physical obstruction. Third, stochastic simulations using experimentally measured parameters showed that this strategy maximizes both survival and biomass homogeneity in micro-confined networks, producing optimal results only when both algorithms are synergistically used. Further studies suggest that directional memory is ‘stored&’ in microtubule skeleton, whereas collision induced branching is controlled by turgor pressure. These studies open the possibility of designing antifungal treatments based on nano-mechanical rather than chemical mechanisms; and of reverse engineering of natural algorithms for non-trivial mathematical problems.
 Hanson, K.L., Nicolau, D.V., Jr, Filipponi, F., Wang, L., Lee, A.P. Nicolau, D.V. Small, 2006, 2, 1212-1220.
 Held, M, Edwards, C., Nicolau, D.V. Fungal Biology, 2011, 493-505.
12:00 PM - L3.06
How the Hairs of Honey Bees Stick to and Flick off Pollen
Guillermo Javier Amador 1 Megha Mathews 1 D'Andre Waller 1 Mari Nguyen 1 Todd Sulchek 1 David Hu 1 Marguerite Matherne 1
1Georgia Institute of Technology Atlanta United StatesShow Abstract
Honey bees can collect 8 times their body weight in pollen during a single day of foraging. This large amount of particle accumulation can have effects on their sensing, flight stability, and maneuverability. In this study, we investigate the role of honey bee hair arrays in the accumulation and removal of pollen and other micron-scaled particulates. The body of a honey bee is covered by millions of morphologically diverse hairs, each thought to play a specialized role in the transfer of pollen from flowers to the hive. Through the use of high speed videography, anatomic alterations of honey bee limbs, and atomic force microscopy (AFM), we characterize the mechanics of honey bee hairs during grooming. In high speed videography of bees using their legs to clean themselves, we observe deflected hairs hurling pollen particles at accelerations over 100 times earth's gravity. By covering the hairs on the legs with wax, we discover the importance of hair-on-hair interactions during grooming. Using AFM, we determine the flexural stiffness of the hairs and the adhesive forces between hairs and pollen. By identifying the physical mechanisms involved in grooming, we may motivate bio-inspired designs for dust-controlling lenses, sensors, and solar panels.
12:15 PM - L3.07
Towards Inchworm: An Artificial Molecular Motor with Power Stroke
Cassandra Sekol Niman 1 2 Martin J Zuckermann 3 Martina Balaz 1 2 Jonas O Tegenfeldt 1 2 Paul M. G. Curmi 4 5 Nancy R Forde 3 Heiner Linke 1 2
1Lund University Lund Sweden2Nanometer Structure Consortium (nmc@LU) Lund Sweden3Simon Fraser University Vancouver Canada4University of New South Wales Sydney Australia5Centre of Applied Medical Research Sydney AustraliaShow Abstract
Processive molecular motors are thought to utilize a "power stroke" whereby chemical changes are converted into conformational changes, facilitating forward motion. We have developed a concept for a synthetic molecular motor, the Inchworm (IW), which harnesses salt-induced changes in DNA conformation1 to achieve power strokes.2 We report Brownian dynamics simulations of IW that predict step sizes ~ 1 µm and stall forces ~ 0.1 pN, determined by the DNA entropic spring constant.
To implement and control IW we must switch between four different solutions (of varied salt concentration) surrounding DNA confined in a nanochannel while monitoring its response. We have developed nanochannels of radii 100 - 400 nm, with 10-20 nm wide top-slits through which buffers are exchanged via diffusion from adjacent microfluidic channels3. Nanochannels are made in SiO2 to allow for imaging through the substrate and surface functionalization compatibility. To cycle through four buffers specifically designed microchannels are used4. We measure changes in intensity when fluids containing fluorescent molecules are switched, with and without a pressure difference over the nanochannels. Characterization of the device shows the ability to change solutions in-situ, to control IW without fluid flow in the nanochannels, and with a fluid flow suitable for stall force measurements, in accordance with our IW simulations.
 W. Reisner et al., PRL 2007, 99, 058302;  C.S.Niman et al., Nanoscale 2014, DOI:10.1039/C4NR04701J;  M.Graczyk et al., J. Vac. Sci. & Technol. B 2012, 30, 6;  C.S.Niman et al., Lab Chip 2013, 13, 2389
12:30 PM - *L3.08
Magnetic Microrobots with Programmed Magnetic Properties
Salvador Pane 1 George Chatzipirpiridis 1 Christian Peters 2 Naveen Shamsudhin 1 Olgac Ergeneman 1 Xiangzhong Chen 1 Christofer Hierold 2 Bradley Nelson 1
1ETH Zurich Zurich Switzerland2ETH Zurich Zurich SwitzerlandShow Abstract
Magnetic micro- and nanoswimmers have become increasingly important during the last decade as promising platforms for environmental and biomedical applications.1 The use of external magnetic fields is an advantageous approach for manipulation of micro- and nanoagents because most environments such as human tissues or aquatic ecosystems are transparent to magnetic fields.2 Additionally, a wide variety of magnetic fields such as complex non-uniform magnetic field gradients, rotating or oscillating magnetic fields can be employed to maneuver specific small agent designs in a wide variety of fluids.
In this talk, we will show that each specific magnetic actuation principle is strongly related to the approach in which magnetic building blocks have been manufactured, their geometry and their ferromagnetic behavior. For example, hard-magnetic tubular microstructures fabricated by electroforming display rolling locomotion if microtubes are perpendicularly magnetized to their long axis.3 Also, the application of magnetic fields during the production of magnetic microagents can lead to shape-independent anisotropy magnetic microarchitectures. This principle, known, as programmable anisotropy, can significantly improve the maneuverability of microrobots, and it has been successfully applied to fabricate superparamagnetic nanocomposite-based helical and hemispherical microswimmers.4,5
1. S. Schuerle et al., IEEE Trans. Mag.49 (2012), 321.
2. G. Chatzipirpiridis et al., Adv Healthc Mater.4 (2015), 209.
3. G. Chatzipirpiridis et al., IEEE Trans. Mag.50 (2014), 5400403.
4. C. Peters et al., Adv. Funct. Mater. 24 (2014), 5269.
5. O. Ergeneman et al., Nanoscale, 6 (2014) 10495.