Chairs
Jim Brauker
W. L. Gore and Associates, Inc
PO Box 300
Flagstaff, AZ 86002
800-437-8181
David Clapper
SurModics Inc
Eden Prairie, MN 55344-3523
612-829-2749
Stuart Williams
Biomedical Engineering Program
Univ of Arizona
PO Box 248054
Tucson, AZ 85724
520-626-4707
Joan Zeltinger
Technology Development
Advanced Tissue Sciences Inc
La Jolla, CA 92037-1005
619-713-7959
* Invited paper
SESSION FF1: BIODEGRADABLE POLYMERS
Chairs: David L. Clapper and Joan Zeltinger
Wednesday Morning, April 7, 1999
Salon 15 (M)
8:30 AM *FF1.1
CORRELATIONS BETWEEN POLYMER STRUCTURE, IN-VITRO CELLULAR
RESPONSE, AND IN-VIVO TISSUE BIOCOMPATIBILITY IN A LIBRARY OF DEGRADABLE
POLYMERS. Joachim Kohn , S. Brocchini, K. James, V. Tangpasuthadol, Dept
of Chemistry, E. Tziampazis, P. Moghe, Dept of Chemical and Biochemical
Engineering, Rutgers University, Piscataway, NJ.
Our research effort is focused on the development of degradable
polymers based on the adaptation of combinatorial approaches to polymer
design. Our earlier work has resulted in the identification of non-toxic,
tyrosine-derived diphenols that provide ideal building blocks for the synthesis
of polyiminocarbonates, polycarbonates, polyarylates, polyurethanes, and
polyethers. Tyrosine-derived polycarbonates and polyarylates are particularly
useful in the fabrication of tissue-engineering scaffolds and show a wide
range of physicomechanical properties and interactions with cells. Using
a newly developed library of tyrosine-derived polyarylates, clear correlations
could be identified between the chemical structure of individual polymers,
the adsorption of fibronectin on the polymer surface, and the attachment
(and growth) of various cell lines in vitro. For example, in a series of
polyarylates, the adsorption of fibronectin on the polymer surface could
be manipulated by minor changes in polymer structure. For these polymers,
the amount of fibronectin adsorbed to the polymer surface was predictive
of the ability of rat lung fibroblasts (RLF) and L929 mouse fibroblasts
to attach and grow on these surfaces. In another set of experiments, the
length of an alkyl ester pendent chain could be directly correlated with
the degree of bone bonding in-vivo in a clinically relevant, long-term
fracture fixation model. In summary, within a combinatorially designed
library of polymers, new correlations between polymer structure, ECM protein
adsorption, and the biological response in-vitro and in-vivo can assist
in the identification of optimum material properties for specific tissue
engineering/implant applications.
9:00 AM FF1.2
MICROPOROUS MEMBRANES FROM POLYLACTIDES. S. Gogolewski
, P. Michel, Polymer Research, AO/ASIF Research Institute, Davos, SWITZERLAND.
Bioresorbable polymers are finding an increasing applications
for internal fixation of bone fractures, drug delivery devices or scaffolds
for seeding of cells in tissue engineering. More recently, porous resorbable
membranes and 3-D scaffolds from various polylactides have been used experimentally
for the treatment of segmental long bone defects and defects in the cranio-
and maxilofacial skeleton. Depending on the intended application the membranes
should be of various pore sizes and pore structures. Techniques used for
the preparation of porous polymeric membranes with closed-cell or open-cell
structures primarily involve the salt leaching, the so-called eutectic
solidification, freeze-drying or the phase-inversion process. This study
aimed at the preparation of membranes from polylactides with varying molecular
weight and chemical composition with well-defined porous structures using
the liquid system consisting of polymer solution in good or poor solvents
and various nonsolvents. The membranes produced had the pore size and pore
structure which were dependent on the polymer molecular weight, the molecular
weight distribution, the chemical structure, concentration of polymer in
solution, miscibility of solvent with nonsolvent, differences in the liquids
solubility parameters, temperature, pressure and humidity of the environment,
and the surface free energy of the substrate onto which the membrane was
cast. Increasing the polymer concentration in solution and the rate of
the liquids evaporation decreased the pore size and led to membranes with
the closed-cell structure. Increasing the amount of nonsolvent in the polymer
solution increased the membrane pore size but reduced the membranes mechanical
properties. The use of nonsolvents miscible with the solvents led to porous
membranes with round-shaped, interconnected pores. The use of nonsolvents
which do not mix with the solvents resulted in canal like pores running
perpendicularly to the membrane cross-section.
9:15 AM FF1.3
PHOTOCROSSLINKED POLYANHYDRIDES AS AN IN VIVO POLYMERIZABLE
BIOMATERIAL. Amy K. Burkoth , Kristi S. Anseth, University of Colorado,
Department of Chemical Engineering, Boulder, CO.
A new class of photoreactive biopolymers has been developed
from multifunctional anhydride monomers which can be polymerized in situ.
The resulting crosslinked networks are dimensionally stable, with minimal
solvent uptake from the environment, and exhibit strengths intermediate
to cortical and trabecular bone, making them favorable candidates for orthopedic
applications. While the strengths of these polymers are controlled by the
degree of crosslinking, the degradation rate of these networks can be controlled
independently by the chemical composition. Specifically, the degree of
hydrophobicity in the backbone chemistry in combination with the hydrolytically
degradable anhydride crosslinks result in a controllable surface erosion
mechanism, with degradation timescales ranging from 48 hours to 1 year.
Furthermore, photopolymerizations provide additional advantages, including
fast curing at ambient temperatures, and spatial and temporal control of
the photoinitiation process, which has opened up the possibility of in
vivo polymerizations. The proposed anhydride monomers react on clinically
acceptable timeframes (seconds to minutes) with the time and heat of polymerization
controlled by the initiation scheme (e.g., light intensity and inititor
concentration). Furthermore, these polymers have shown good biocompatiblity,
with high vascularization and cell in-growth subcutaneously in rats.
10:00 AM FF1.4
IN VITRO DEGRADATION OF POLY[1,6-BIS(ORTHO- CARBOXYPHENOXY)HEXANE
ANHYDRIDE]. Meng Deng, Christi Bedell, Kathryn Uhrich , Rutgers University,
Department of Chemistry, Piscataway, NJ.
Desirable characteristics for implantable polymeric systems
include biocompatibility, suitable physical properties for device fabrication,
and flexibility before and during degradation so that the device does not
fragment during use. Previously, we described polymers that maintain the
desirable characteristics (biodegradability, biocompatibility, mechanical
properties) and overcome the solubility (or processing) problems associated
with aromatic polyanhydrides. This work describes an in vitro degradation
study performed to determine the degradation characteristics of poly[1,6-bis(ortho-carboxyphenoxy)hexane
anhydride] at body temperatures. Polymer was compression-molded into discs
and place into phosphate buffer solution at pH 7.4. Molecular weight, glass
transition temperatures and decomposition temperatures were determined
for each time point up to 35 days. The polymers are fast-degrading: the
molecular weight is only 55% of the original value after three days. The
degradation curve as a function of molecular weight decreased logrithmically
whereas the glass transition temperatures decreased linearly. There was
no significant decrease in polymer decomposition temperatures throughout
the five week study.
10:15 AM FF1.5
BIOMEDICAL SCAFFOLDS FOR TRANSPLANTABLE TISSUE ENGINEERED
SUBSTITUTES. Joan Zeltinger , Lee Landeen, Noushin Dunkelman, Jill Sherwood1,
Linda Griffith2, Jonathan Mansbridge and Ronnda Bartel, Advanced
Tissue Sciences, Inc., La Jolla, CA; 1Therics, Inc., Princeton,
NJ; 2MIT, Department of Chemical Engineering, Cambridge, MA.
In vitro tissue formation by numerous cell types was tested
on biodegradable or biostable synthetic scaffolds to engineer dermis, cartilage
or smooth muscle for human transplantation. Scaffolds differed by their
chemical formulation, structure (e.g., dimensions, architecture, pore size,
or void fraction [VF]) and fabrication (e.g., woven, knitted, felted, braided,
solvent cast as sponges, or TheriForm processed [i.e., 3-D printed]). Materials
included nylon, poly(glycolic acid), poly(ethylene terephthalate), poly(-caprolactone),
poly-L-lactic acid or poly(D,L-lactide co-glycolide) / poly(L-lactic acid).
Human- or animal-derived cells (dermal and arterial fibroblasts, keratinocytes,
articular chondrocytes, arterial smooth muscle cells and arterial endothelial
cells) were cultured on scaffolds under static or dynamic conditions for
up to eight weeks. Analyses were customized per engineered tissue (quantitative
MTT and DNA tests for metabolic activity and cell number, respectively;
DMMB assay for glycosaminoglycans, Sirius Red assay for collagen, image
analyses for pre- and post-culture dimensions, scaffold and tissue mechanics,
and qualitative immunostaining and histology). The data showed that human
and animal cell types adhered to, proliferated and readily produced tissue
within scaffolds of various chemical formulations; however, the ingrowth,
distribution, orientation, and viability of cells and the gross morphology
of constructs were influenced by both cell type and scaffold features (pore
size, VF, fiber density, degradation). The depth and uniformity of colonization
and amount of extracellular matrix formed by chondrocytes, fibroblasts,
smooth muscle cells and endothelial cells corresponded to the pore size
in TheriForm scaffolds. Fibroblast orientation in felt and braided scaffolds
followed the random or linear polymer fiber arrangement, respectively.
Fibroblasts on nylon meshes formed monolayers or 3-D tissue depending on
the particle sieve size. An overview of cell-polymer interactions will
be presented. By prescribing scaffold features, one can potentially regulate
the cellular destination, orientation and extracellular matrix production
on scaffolds in vitro to consistently form viable, confluent tissues for
transplantation.
10:30 AM *FF1.6
APPLICATIONS OF AUTOLOGOUS AND ALLOGENEIC CELL THERAPY.
Frank T. Gentile , Kermit M. Borland, Helen M. Nugent and Daniel R. Omstead
Reprogenesis, Inc., Cambridge, MA.
We have developed an autologous cell therapy to treat
two urological disorders: vesicoureteral reflux in pediatric patients and
urinary stress incontinence in adults. This product contains autologous
cells (chondrocytes) suspended in a crosslinked alginate hydrogel which
is injected submucosally at critical sites surrounding the ureteral orifice
(in reflux) or the urethra and bladder neck (in incontinence). In reflux,
the cell-alginate matrix serves as a bulking agent to prevent retrograde
flow of urine from the bladder to the ureter and kidney. In incontinence,
the bulking agent allows proper closure of the urethral sphincter. The
key manufacturing components of this product are: 1) isolation of chondrocytes
from an auricular cartilage biopsy, 2) expansion, and possible cryopreservation,
of those cells in vitro, and 3) formulation of the cells into a crosslinked
alginate hydrogel matrix. Similar approaches (i.e. autologous cells injected
in a hydrogel matrix) are under active investigation in a number of other
therapeutic areas. We are also actively developing an allogeneic cell therapy
using endothelial cells to re-establish vascular homeostasis following
vascular injury.
SESSION FF2: IN VITRO AND IN VIVO EVALUATIONS OF
BIOMATERIALS
Chairs: Jim Brauker and Stuart K. Williams
Wednesday Afternoon, April 7, 1999
Salon 15 (M)
1:30 PM *FF2.1
CLINICAL AND HISTOLOGICAL OBSERVATIONS OF SEAREMATRIX
- POROUS SURFACED SILICONE RUBBER IN TWO TO EIGHT WEEK SHEEP RECIPIENTS
OF DIRECT CARDIAC COMPRESSION DEVICES DCC. William J. Seare, Jr.
, Seare Biomatrix Systems, Inc., Salt Lake City, UT; Yifei Huang, Takeshi
Yuasa, Stephen N. Hunyor, Cooperative Research Centre for Cardiac Technology,
Sydney, NSW, AUSTRALIA.
Introduction - Body implant and device placements
continue to be disappointing for both short and long term use. The body
responds by forming scar tissue and collagen capsules. The stimulation
of healthy, non-scarred, vascularized tissue at the tissue-implant interface
has been elusive. A new materials fabricating technology (SeareMatrix
SM) has been shown to prevent
fibrous capsule formation and promote vascularity. SM
creates advantages for implants and devices both during the initial biointegration
and during long periods of implantation, in term of mechanical or bacterial
challenge. We have extended the application of this new technology in achieving
tissue adhesion and promoting vascularity by studying its biointegration
on the surface of a device implanted onto the heart.
Aim - The purpose of this study was to investigate
the time-related extent and quality of the biointegration of SeareMatrix
onto the surface of a beating heart in adult sheep.
Methods - Four Merino cross adult sheep were implanted
for 8 weeks {n=2}, 3 weeks {n=1}, and 2 weeks {n=1} with DCC devices integrally
fabricated from SM silicone rubber.
Cardiac parameters were examined with and without direct cardiac compression,
including pressure-volume loops and cardiac output, x-ray fluoroscopy with
image intensification (with and without contrast injection), echocardiography
for cardiac wall movement. In one eight week sheep, effective cardiac assist
over four hours was undertaken.
Results - At explant, all animals showed complete
attachment of vascularized non-scarred biointegrated tissues on both epicardially
opposed and pericardially opposed device surfaces. There were no areas
of seroma, hematoma or detachment present. In an eight week animal, an
area of smooth (non-treated) silicone surface 2 cm x 8 cm opposed against
the epicardial surface (used to allow sizing for the device) showed significant
thickening and scarring. No such scarring was seen where SM
biointegration occurred in adjacent areas. Dissection of the pericardial
and epicardial surfaces of the device was readily accomplished with finger
dissection, with the release similar to Velcro
strips being separated. The SeareMatrix
released without clinical or histologic damage to the coronary vessels.
Histology confirmed features in previous studies. There were arterioles,
venules, and capillaries in a loose collagen background with a mild histiocytic
response. In the area where a smooth part of the device contacted the epicardial
surface, a fibrous capsule ten times the thickness of the thin overlying
loose collagen membrane adjacent to the SeareMatrix
was found. Untreated Dacron
mesh at the periphery of the implanted device showed typical incomplete
tissue penetration with microcyst formation and dense interfiber fibrosis,
accompanied by signs of acute and chronic inflammation.
Discussions - DCC devices have found limited clinical
acceptance for reasons of infection, materials failure and catastrophic
ejection of the device from the heart if suction is removed. The use of
SeareMatrix as tissue interface
on DCC device shows promise in overcoming many of the drawbacks of previous
DCC devices.
2:00 PM *FF2.2
MICE THAT LACK THE ANGIOGENESIS INHIBITOR, THROMBOSPONDIN
2, MOUNT AN ALTERED FOREIGN BODY REACTION CHARACTERIZED BY INCREASED VASCULARITY.
Themis R. Kyriakides, Dept of Biochemistry; Kathleen J. Leach, Allan S.
Hoffman, Buddy D. Ratner, Dept of Bioengineering; Paul Bornstein , Dept
of Biochemistry, University of Washington, Seattle, WA.
Disruption of the thrombospondin 2 gene in mice results
in a complex phenotype characterized chiefly by abnormalities in fibroblasts,
connective tissues, and blood vessels. Consideration of this phenotype
suggested to us that the foreign body reaction (FBR) might be altered in
thrombospondin 2 (TSP2)-null mice. To investigate the participation of
TSP2 in the FBR, silicone rubber (polydimethylsiloxane, PDMS) and oxidized
PDMS (ox-PDMS) disks were implanted in TSP2-null and control mice. Adherence
of TSP2-null and control skin fibroblasts in vitro was also evaluated on
both types of disks. Normal fibroblasts grew as a monolayer on both surfaces,
but attachment of the cells to the ox-PDMS was weak and sensitive to movement.
TSP2-null fibroblasts grew as aggregates on both surfaces, and their adherence
was also compromised on ox-PDMS. After a four week implantation period,
both types of PDMS elicited a FBR with a collagenous capsule in both the
TSP2-null and control mice. However, strikingly, the collagenous capsule
that formed in TSP2-null mice was highly vascularized and thicker than
that formed in normal mice. In addition, abnormally shaped collagen fibers
were observed in capsules from mutant mice. These observations indicate
that the presence or absence of an extracellular matrix component, TSP2,
can influence the nature of the FBR, in particular its vascularity. The
expression of TSP2 could therefore provide a molecular target for local
inhibitory measures when vascularization of the tissue surrounding an implanted
device is desired.
2:30 PM FF2.3
FTIR-FEW SPECTROSCOPY: NEW DIAGNOSTIC TOOL FOR MATERIALS
RESEARCH. Natalia Afanasyeva , Angelique Brooks, Reinhard Bruch, Department
of Physics, University of Nevada Reno, Reno, NV.
The investigations of complicated, soft condensed material
such as human and animal skin and polymer surfaces on a molecular level
have been developed using Fourier Transform Infrared Fiberoptic Evanescent
Wave (FTIR-FEW) spectroscopic method. These types of surfaces are very
difficult to investigate by traditional FTIR methods even with the use
of accessories. The FTIR-FEW technique is sensitive enough to detect changes
in the vibrational spectra of polymer and skin surfaces without heating
or damaging it. In addition, this method is fast (15 seconds), remote (fiber
length up to 3 meters), nondestructive in real time and on-line with computer
for rapid (10 seconds) treatment of large database of spectral statistical
results. For the first time we have recorded surface of the human skin
tissue non-invasively in vivo. Surface and bulk (within the epidermis),
spectra of normal, acupoints, pre-cancerous and cancerous skin tissue have
been analyzed in detail. The depth of penetration of the evanescent wave
into the tissue is about 10-15 m
utilizing this technique. In addition to skin, we have measured the surfaces
of polyethylene crumpled bags and rumpled films, as well as polytetrafluoroethylene.
Weak but distinct spectra were also obtained for carbon fibers (black thin
fibers with a diameter of about 10 m).
This method could be developed and applied to: polysaccharides, proteins,
gels, and granular materials of small sizes, etc. In this paper, we present
this new fiberoptical FTIR method for many applications including biomedicine,
industry, and geology.
3:15 PM *FF2.4
TISSUE REPLACEMENT AND REPAIR USING ELASTIN BIOMATERIALS.
Kenton W. Gregory , Michio Kajitani, Yasmin Wadia, Monica Hinds, Rui-Quing
Qian, Kristy Hanna, Shalaby Shalaby1, Andrew Barofsky, Oregon
Medical Laser Center, Providence St. Vincent Medical Center, Portland,
OR; 1 Poly-Med, Inc., Anderson, SC.
Elastin is an extracellular matrix protein that has excellent
properties for tissue replacement and repair-excellent durability, thermal
and chemical stability with active cell signaling, and little reported
cross species antigenicity. Elastin was investigated as a biomaterial for
arterial and gastrointestinal tissue replacement using biodegradable cyanoacrylates
or dye targeted tissue fusion for deployment. Elastin biomaterials (EB)
of porcine origin were isolated, prepared in sheets or tubes, autoclaved
and stored in 80% ethanol. Conventional sutures,methoxy-propyl cyanoacrylates
(PolyMed) or laser fusion using indocyanine green dye applied at tissue
interfaces to selectively absorb 800 nm pulsed diode laser energy (5 ms
5 J) pulses joined the EB to native arterial or duodenal tissues in vitro
and in vivo studies using anesthetized 40 kg domestic swine. EB, application
integrity and host response were assessed acutely and up to 2 months. Excellent
tissue bonding could be achieved by all means and minimal thrombogenicity
and chronic inflammatory response was observed. No infections of the biomaterial
was observed. We conclude that elastin may be an excellent native protein
biomaterial for vascular and gastrointestinal tissue replacement and repair.
3:45 PM FF2.5
OSTEOGENIC CELLS IN NANO-HA/COLLAGEN MATRIX. C. Du, F.Z.
Cui , Q.L. Feng, Tsinghua Univ, Dept of Materials Science and Engineering,
Beijing, P.R. CHINA; X.D. Zhu, Beijing Medical Univ., China-Japan Friendship
Hospital, Beijing, P.R.CHINA; K. deGroot, Leiden Univ., Biomaterials Research
Group, NETHERLANDS.
Nano-HA/collagen (nHAC) composite that mimics the natural
bone in both composition and microstructure to some extent was expected
to be a good matrix for tissue engineering of bone. Using organ culture
techniques and a convolving method, we developed a three dimensional osteogenic
cells/nHAC construct in vitro . The interaction between cells and
materials was investigated by histology, scanning electron microscopy and
transmission electron microscopy. Spindle-shaped cells migrating out of
bone fragments continuously proliferated and migrated throughout the network
of the coil. The porous nHAC scaffold provided a microenvironment resembling
that seen in vitro and cells within the composite eventually acquired
a tridimensional polygonal shape. Collagenous matrix was synthesized at
the interface of cells and nHAC. The collagen fibers were observed obliquely
oriented to the surface of the material, suggesting the bioactivity and
bone-bonding property of the composite. The mineralization of this matrix
was observed to involve matrix-vesicle mediated process.
4:00 PM FF2.6
PARTICLE SIZE EFFECTS ON OSTEOBLAST ATTACHMENT TO AND
MINERALIZATION OF POLYMETHYLMETHACRYLATE- HYDROXYAPATITE COMPOSITES. S.
Ruan1, A. Winnard2, J. Lannutti 1, A.
Moursi2, R. Seghi2, 1Department of Materials
Science & Engineering, 2College of Dentistry, The Ohio State
University, Columbus, OH.
The mechanical properties of ceramic-polymer composites
are controlled in part by the surface area of the reinforcing phase. Hydroxyapatite
(HA) was explored as a reinforcement for polymethylmethacrylate (PMMA),
long a component of bone cement. HA particle size was varied to determine
the influence of this parameter on the attachment, proliferation, viability,
morphology and mineralization of primary rat calvarial osteoblasts obtained
from fetal (day 21) rat calvariae by collagenase digestion. Attachment
was assessed after a 4 hr incubation followed by washing. Proliferation
was examined by culturing osteoblasts followed by fluorimetry of dye-containing
media on days 2, 4, 6 and 8. In contrast to the attachment results, osteoblast
proliferation on day 8 was found to be significantly higher on PMMA/HA
than on Ti/HA. Primary rat osteoblasts formed a multilayered cell culture
and produced an extensive, well-organized extracellular matrix (ECM) within
3 days of plating. Mineralization of the ECM began within 14 days. Morphology,
ECM production and mineralization were examined by electron microscopy
and immunohistochemistry at both early and late time points. Cell viability
was examined on day 14 by acradine-orange staining. No clear correlations
between cell proliferation and HA particle size were obvious although ECM
production showed dependence on loading.
4:15 PM FF2.7
BIOMIMETIC INTERPENETRATING POLYMER NETWORK (IPN) AS
ORTHOPEDIC BIOMATERIAL. Guy P. Beauregard, Susan P. James , Rocky Mountain
Materials Research, Department of Mechanical Engineering, Colorado State
University, Fort Collins, CO.
A novel, biomimetic, interpenetrating polymer network
(IPN) between poly-L-lysine (PLL) and ultra high molecular weight polyethylene
(UHMWPE) has been synthesized in an attempt to decrease wear in joint prostheses.
A gradient IPN of cationic PLL and UHMWPE has been synthesized (in the
surface of bulk UHMWPE) to recruit the poly-anion, hyaluronic acid, from
the synovial fluid. It is hypothesized that the hyaluronic acid molecules
and their associated hydration layer will improve lubrication between the
articulating surfaces, thus lowering both friction and wear. The synthesis
involves four steps. Siylation of the PLL-HBr to PLL-SiMe3 utilizing
bis(trimethylsiyl)acetamide (BSA). Swelling of the UHMWPE in a solution
of PLL-SiMe3/xylenes at 60C with ultrasonics. Crosslinking of
the PLL-SiMe3 within the UHMWPE with 1,8-diisocyanatooctane
(a.k.a. OMDI). Finally, de-swelling and drying of the IPN under vacuum
at 50C. Visual observations show an adhered film on the IPN surface. Reflective
FTIR spectra contain the characteristic peaks associated with UHMWPE. Two
additional peaks, at 3410 and 1690 cm-1, are associated PLL.
SEM shows a morphology dominated by PLL spheres with diameters ranging
from <1 micron up to 3 micron. This shows that the PLL-SiMe3
has been crosslinked by the OMDI and was not rinsed away by either xylenes
or sonicated water rinses. High contact angle of the PLL in contact with
the UHMWPE demonstrate that the PLL has been de-silylated and returned
to its hydrophilic nature. The spheres attached to the surface of the UHMWPE
indicate that PLL has infiltrated the UHMWPE physical network and is entangled
there.
4:30 PM FF2.8
IN VITRO FIBROBLAST GROWTH ON TRIETHYLENE GLYCOL DIMETHACRYLATE
POLYMER REINFORCED WITH NANOPOROUS SILICA: EFFECT OF CERAMIC LOADING. Janice
Taylor1, John J. Lannutti 2 and Robert R. Seghi3,
1Center for Biomedical Engineering, 2Department of
Materials Science & Engineering, 3College of Dentistry,
The Ohio State University, Columbus, OH.
Ceramic-reinforced polymers have obvious similarities
to normal hard tissues. In direct dental restorations, such composites
are commonly used in contact with gingival tissue. Their ability to bond
with such tissue plays a critical role in the long-term success of such
implants. We conducted a series of experiments aimed at resolving the effect
of ceramic loading on cell proliferation when said ceramic is of limited
biological compatibility. We used silica, SiO2, suspended in
a standard dental matrix, triethylene glycol dimethacrylate (TEGDMA). Gingival
fibroblasts derived from healthy human adults were used for in vitro cell
viability studies. Passage lines 2-5 were incubated at 37C
in a humidified environment containing 5% CO2. At days 1, 3
, 5, and 7 the disks were incubated in Alamar Blue and fluorescence readings
taken at excitation wavelengths of 560 nm. Population results indicated
that silica had negative consequences for cell growth, thereby improving
little on the cytotoxicity of pure TEGDMA. Not surprisingly, rougher surfaces
resulted in increased cell proliferation. Microscopy was used to examine
the correlation between composite substructure and cell proliferation.
4:45 PM FF2.9
HOLLOW POWDER BIOMATERIALS. David J. Sypeck and Haydn
N.G. Wadley, University of Virginia, School of Engineering and Applied
Science, Department of Materials Science and Engineering, Charlottesville,
VA.
Porous structures based upon hollow metal spheres with
thin walls and strong interparticle bonds are a new class of cellular materials
that posess excellent weight specific mechanical properties and an array
of multi-function capabilities. A by-product of inert gas atomization,
hollow spherical powders are available from a variety of metal and alloy
systems including those of biomedical interest such as stainless steel
and titanium. One significant advantage of structures fabricated from hollow
powders is the ability to engineer the structure with a desired set of
properties through control of the sphere type, size and mix, wall thickness
and bond strength. Functionally graded biomaterials with controlled amounts
open and closed porosity can be made stiff, strong and very light in weight.
Such structures allow fluids to flow through them, facilitate fixation
owing to their surface porosity and can be designed to have properties
which mimic that of the structure they set out to replace. In this work,
hollow metal powders are separated by size, shape and density. They are
then consolidated to a porous structure and their compressive mechanical
properties are assessed. Future applications as biomaterials are discussed.
SESSION FF3: POSTER SESSION:
BIOMEDICAL MATERIALS
Chairs: David L. Clapper and Joan Zeltinger
Wednesday Evening, April 7, 1999
8:00 P.M.
Salon 7 (M)
FF3.1
ON THE PIEZOELECTRIC OF ANIONIC COLLAGEN FILMS. Julio
C. Goes , Sonia D. Figueiro, Jose Airton C. de Paiva and A.S.B. Sombra,
Departamento de Fisica, LONLCM, Universidade Federal do Ceara (UFC), Fortaleza-Ceara,
BRAZIL.
Polymeric composite materials, both of natural and synthetic
origin, constitute by far the broadest and most diverse class of biomaterials.
Collagen have great potencial, in the field of bioactive biomaterials.
Collagen, the most abundant protein of the animal kingdom, has a long history
as biomaterial. We can find it in prostheses of heart valves, in artificial
skins, in contact lenses and in injectable gels for soft tissue augmentation.
In this work we did a study of the physicochemical, dielectric and piezoelectric
properties of anionic collagen films, considering the development of new
biomaterials which have potential applications in coating of cardiovascular
prostheses, support for cellular growth and in systems for controlled drug
delivery. Results obtained from shrinkage temperature of collagen membranes,
casted in pH 7.4, showed that the native collagen membranes had highest
thermal stability than anionic collagen films. The piezoelectric strain
tensor element d14, the elastic constant s55, and the dielectric permittivity
e11 were measured for the native collagen and anionic collagen films. Resonance
measurement of the piezoelectric strain constant d14 of native collagen
film gives 0.066 pC/N, while samples of anionic collagen obtained with
alkacaline treatment give 0.072 pC/N. We believe that alcaline tratment
lead to an increase of the organization of the microscopic structure of
the sample, which could result in an increase of the piezoelectricity.
FF3.2
EFFECT OF POLARITY OF PIEZOELECTRIC CERAMIC PZT ON CRYSTALLIZATION
OF CALCIUM PHOSPHATE. Chunlai Ma , Xiaodan Sun and Hengde Li, Tsinghua
University, Department of Material Science and Engineering, Beijing, P.R.CHINA.
This work is studied on effects of polarity of polarized
ferroelectric ceramic of lead zirconato titanate (PZT) on crystallization
of calcium phosphate from saturated solution. The PZT was choose as a substrate
for his high polarizability. Started PH level of the saturated solution
is about 7.0, polarized samples are with d33 equal to 300x10-12
and 450x1012 C/N, respectively. Precipitates on PZT substrate
were analyzed and specified by Scanning Electric Microscopy(SEM), Energy
Dispersive X-ray Linear Scanning(EDXLS) and X-ray diffraction(XRD). PH
level of the solutions was measured in certain interval time. The results
showed that Ca-P layers are deposited on the positive and negative pole
surface of either non-polarized or post-polarized PZT immersed in same
condition; Although the size and regularity of deposits were very different
on different substrate faces, yet the mineral films morphologically were
all made up two similar layers: microcrystalline cluster-shape layer adjacent
to the substrate and long sheet-like crystal layer which is closely grown
on the former layer; Depending on the different substrate faces, the growing
rate of the sheet-like layer is different and the order of that from large
to small scope is: on N-pole surface > on non-polarized surface > on P-pole
surface meanwhile the cluster layers on different faces were nearly the
same in thickness of about 4-6 m.
The deposit minerals are consist of OCP and DCPD. There are significantly
influence of polarity on orientation of sheet-like crystalline(OCP) and
which growing on the N-pole face of PZT were developed with (002) preferred
orientation. The possible mechanism of effect of polarity on Ca-P crystallization
from solution is discussed.
FF3.3
PROPERTIES OF POLY (-
HYDROXYALKANOATES) COMPOSITE AS IMPLANT BIOMATERIAL. Rubén Sánchez
, Norma Galego, Chavati Rozsa, Polymer Section, Advanced Material Laboratory,
North Fluminense State University, Campos, R.J., BRAZIL.
Various synthetic materials have been routinely utilized
as reinforcement for bone. These selected primarily on the bases of their
compatibility, adequate fracture toughness and fatigue strength. In considering
the replacement of bone by mechanical equivalent composite it is pertinent
to start from the microestructure of bone itself. Hydroxyapatites (HA)
composite were used as reforcing phase with similar chemical and structural
characteristic of the human bond. By the other hand the bacterial PHB and
copolymers P(HB-co-xHV), used as second
composite components, beside being biocompatible, exhibit a appropiate
mechanical properties (Young's Modulus 3.5 to 1.2 GPa). The rate of chemical
hydrolysis of PHAs is very slow in vitro, may be in off
to biomedical implants where the bioactivity of HA and the biodegradability
of PHA can be combined to avoid particle migration from the implant region
before growth of a new tissue and a favorable answer to induce a bone formation
taking advantage of the slow polymer degradation. The PHB and copolymers
P(HB-co-xHV) (5, 8, 14 and 22HV)
previously characterizated were used to formulation hydroxyapatite composites.
The polymer composites were studied between 20 to 40
of PHA composition. The mechanical testing were develped using hydroxyapatite
(HA) of synthetic and natural origin with particle diameter of 0.1 mm and
PHA polyesters. The mixture were prepared and homogenization at different
composition and pressing by hot press at temperature 5C
above melting point of respective polyesters. The composite properties
like variation of mechanical properties under wet condition (by function
of polymer structures and loaded of inorganic phase) were studied. The
fracture region was explored by Scanning Electron Microscopic (SEM). The
composite P(HB-co-8HV) (30)
showed a mechanical strength to compression between dense bond (137.8 MPa)
and spongy bond (41.4 MPa). The mechanical properties of HA/PHA composite
constitute a promise results to use for orthopedic purposes.
FF3.4
ION BEAM BOMBARDMENT FOR TREATMENT OF GPC BIOMATERIAL'S
SURFACE. Marcello G. Rodrigues , Robert L. Zimmerman, FFCLRP-USP, Dept
of Physics and Mathematics, Ribeirão Preto/SP, BRAZIL; Eric K. Williams,
Daryush Ila, Alabama A&M University, Center For Irradiation of Materials,
Normal, AL.
Glassy Polymeric Carbon (GPC) is an amorphous organic
polymeric carbon material widely used as bio-material mainly in the manufacturing
of prosthetic heart due to high inertness and chemical bio-compatibility.
But, in spite of these characteristics, GPC mechanical valves still may
present thromboembolic problems related with the interface between its
surface and the biological tissue mainly due to the natural cicatrization
process over the replaced artifact. In fact, thromboembolism is today the
most important problem to be solved in cardiac prosthesis research and
it can yield dysfunction of the cardiac valve. Thromboresistence can be
improved by treatment of the surface of the GPC devices. We have used energetic
ion bombardment (10 MeV ion gold, 6 MeV ion carbon, 5 MeV ion silicon and
8 MeV ion oxygen), in many fluences (1013 to 1016
atoms/cm2), for increasing the roughness of GPC artifacts. The
samples were prepared at 700C (where
the material presents high density of pores available) and 1500C
(final stages of carbonization, where the GPC is a very hard and smooth
material and non-permeable). The improved roughness can make the GPC artifacts
more biocompatible. Our results with this method showed that: a) Independent
on HTT, the roughness of GPC artifacts can be increased and controlled
with ion bombardment and such improvement can be of the order of 10 times.
b) It was verified that the roughness increase is less for samples prepared
at higher temperatures. c) In general, the roughness increasing seems to
be function of the fluence with peaks around 1014 atoms/cm2.
d) By comparisons with early results, the absorption of lithium by the
GPC pieces is related to its roughness. Although the roughness obtained
is less than the minimum allowed for effective increasing in the biocompatibility,
the methodology is pointed in the right direction.
FF3.5
EFFECT OF STERILIZATION PROCESSES ON THE IONÍS
RELEASE OF NiTi ALLOYS. B. Thierry1, M. Tabrizian 1,
O. Savadogo2, C. Trepanier3, L'H. Yahia1,
1Biomedical Engineering Institute, Ecole Polytechnique of Montreal,
2Metallurgical Department, Ecole Polytechnique of Montreal,
3Nitinol Devices & Components (NDC).
As a potential biomaterial for many medical applications,
NiTi alloys derive their good corrosion resistance from a homogeneous oxide
layer, mainly composed of TiO2. This passive surface layer,
similar to the one observed on titanium-based alloys, provides them their
good stability in most corrosive environment. However, due to the aggressiveness
of the human environment, the release of metallic ions (nickel and titanium)
in the surrounding tissue can occur which may affect the biocompatibility
of such alloys. Indeed, it has been demonstrated that Ni ions (from pure
nickel) induce DNA strand breaks, DNA-protein cross-link and chromosomal
aberrations. Since sterilization processes are able to modify the biomaterial
surface, they may modify the amount of metallic ions released during implantation,
and thus modify the implant toxicity. The aim of this work is to study
the effect of sterilization techniques on the corrosion resistance and
the ionís release of NiTi alloys.
To achieve these goals, surface characterizations and
cyclic polarization assays were undertaken on electropolished NiTi discs
processed by commonly used sterilization techniques such as Steam Autoclave,
EtO, Dry Heat, Plasma Sterrad-100S and Peracetic Acid. The passive diffusion
of Ni and Ti from processed NiTi was measured by atomic absorption spectrophotometry
in Hankís physiological solution.
From our results, calculation of corrosion rates (ASTM
G102) based on Faraday's law indicated a mean Mass loss Rates of 4.3 10-7
mg/cm2s for NiTi. Some slight differences in processed NiTi
may be related to the surface modifications observed by AFM and AES. We
are now evaluating in vitro toxicity of released ions in physiological
solution.
FF3.6
SEM ANALYSIS OF Nd-YAG LASER INDUCED MODIFICATION ON
MATERIALS FOR APICAL MICROSURGERY. Marco Melis, Norberto Berna , Alessandro
Benvenuti, Dpt of Experimetal Medicine, Univ. La Sapienza, Rome, ITALY;
Gabriele Pecora, Dpt of Endodontics, Univ. of Pennsylvania, Philadelphia,
PA; Fabrizio Pierdominici, Sebastiano Tosto, Dpt of Innovation, ENEA Casaccia,
Rome, ITALY.
The recent introduction of processing and diagnostic techniques
like laser and surgical microscope, has significantly modified procedures
and materials of apical dental microsurgery. The Nd-YAG laser is particularly
suitable for the microsurgery because the beam can be veiculated by an
optical fiber and focused to realize an istantaneus local sterilizzation.
However the thermal shock due to the laser pulses can induced dimensional
instability and microleaks of the filling materials on the apex whit possibility
of persistent apical inflammation. This result is in contrast with the
main purpose of apicectomy i.e. to eradicate irritant substances coming
from the root canal system and to eliminate the potential cause of inflammation
in the apical zone. The present paper aim to investigate the dimentional
and morphological changes of three different material used for retrograde
filling of new apex after Nd-YAG laser irradiation.The Endo-Tecnic Nd-YAG
pulsed laser ha a pulse length of 800 nanoseconds with a repetition rate
of 50Hz. The emission wawelength is 1064 microns and the diameter of the
optical fibre is 300 microns. The ouput power was no greater than 10W.
In this study, we have irradiated 12 sample for each material embebbed
in plexiglas supports having a depth of 3mm and different shapes in order
to simulate the real condition expected in vivo apical microsurgery. After
hardening, the sample were irradiated with different power levels of the
laser beam and then cutted perpendicularly to the vertical axis by a microtome.
These cross section were investigated by SEM.
FF3.7
ADDITION OF SYNTHETIC POLYMERS ALTERS STRUCTURE AND MECHANICAL
PROPERTIES OF MUCUS GELS. Rebecca Kuntz Willits , W. Mark Saltzman, Cornell
University, School of Chemical Engineering, Ithaca, NY.
Mucosal surfaces of the body are exposed continuously
to pathogens that are able to penetrate the semi-permeable mucus layer.
The prevalence of serious, often life threatening, infectious sexually
transmitted diseases is increasing; therefore the need for better methods
of disease prevention is escalating. We propose that altering the physical
structure of the mucus gel might inhibit the migration of infectious agents.
Mucus gels are composed of large glycoproteins which entangle to form a
complex network of fibers. We examined several non-toxic synthetic polymers,
such as polyethylene glycol (PEG), polyacrylic acid and polyvinyl pyridine,
to determine their effect on the structure of the mucus gel. Using scanning
electron microscopy, we visualized the three-dimensional fiber network
and found that the addition of either low (3400) or high (1
106) molecular weight PEG caused the fiber network to collapse
into a film. Because mucus is composed of greater than 90
water, the gels were also examined using rheological methods that determine
the dynamic properties of the gel in a more natural state. As a model for
one mode of disease transmission, which may be particularly relevant for
HIV exchange between partners, these results were correlated to changes
in white blood cell migration rates within the gel constructs.