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Microenvironment elasticity influences critical cell functions such as differentiation, cytoskeletal organization, and process extension. Unfortunately, few materials allow elasticity modulation in real-time to probe its direct effect on these dynamic cellular processes. Here, a new approach is presented for the photochemical modulation of elasticity within the cell's microenvironment at any point in time. A photodegradable hydrogel was irradiated and degraded under cytocompatible conditions to generate a wide range of elastic moduli similar to soft tissues and characterized using rheometry and atomic force microscopy (AFM). The effect of the elastic modulus on valvular interstitial cell (VIC) activation into myofibroblasts was explored. In these studies, gradient samples were used to identify moduli that either promote or suppress VIC myofibroblastic activation. With this knowledge, VICs were cultured on a high modulus, activating hydrogel substrate, and uniquely, results show that decreasing the substrate modulus with irradiation reverses this activation, demonstrating that myofibroblasts can be de-activated solely by changing the modulus of the underlying substrate. This finding is important for the rational design of biomaterials for tissue regeneration and offers insight into fibrotic disease progression. These photodegradable hydrogels demonstrate the capability to both probe and direct cell function through dynamic changes in substrate elasticity.

In our previous study, a three-dimensional zein porous scaffold with a compressive Young's modulus of up to 86.6+/-19.9 MPa and a compressive strength of up to 11.8+/-1.7 MPa was prepared, and was suitable for culture of mesenchymal stem cells (MSCs) in vitro. In this study, we examined its tissue compatibility in a rabbit subcutaneous implantation model; histological analysis revealed a good tissue response and degradability. To improve its mechanical property (especially the brittleness), the scaffolds were prepared using the club-shaped mannitol as the porogen, and stearic acid or oleic acid was added. The scaffolds obtained had an interconnected tubular pore structure, 100-380 microm in pore size, and about 80% porosity. The maximum values of the compressive strength and modulus, the tensile strength and modulus, and the flexural strength and modulus were obtained at the lowest porosity, reaching 51.81+/-8.70 and 563.8+/-23.4 MPa; 3.91+/-0.86 and 751.63+/-58.85 MPa; and 17.71+/-3.02 and 514.39+/-19.02 MPa, respectively. Addition of 15% stearic acid or 20% oleic acid did not affect the proliferation and osteogenic differentiation of MSCs, and a successful improvement of mechanical properties, especially the brittleness of the zein scaffold could be achieved.

Hydrolytic degradation studies have been undertaken on Maxon B, a bioresorbable block copolymer of polyglycolic acid (PGA) and polytrimethylene carbonate (TMC). Isotropic and oriented samples were studied by dynamic mechanical measurements over a wide range of temperatures. In addition to mechanical tests, water content and mass loss were also determined on the degraded samples. At early stages of degradation water content was the dominant factor and plasticisation lead to reductions in the glass transition temperatures of the PGA and TMC components. Orientation was shown to give significant improvements in the mechanical properties, including overall increases in modulus and an increase in the glass transition temperature of the PGA component, which is important for the behaviour at body temperature (37 °C). Oriented samples also showed significantly less reduction in mechanical properties on degradation. Simple one-dimensional Takayanagi models were used to provide useful insight into the understanding of the mechanical behaviour.

One of the main issues in tissue engineering is the fabrication of scaffolds that closely mimic the biomechanical properties of the tissues to be regenerated. Conventional fabrication techniques are not sufficiently suitable to control scaffold structure to modulate mechanical properties. Within novel scaffold fabrication processes 3D fiber deposition (3DF) showed great potential for tissue engineering applications because of the precision in making reproducible 3D scaffolds, characterized by 100% interconnected pores with different shapes and sizes. Evidently, these features also affect mechanical properties. Therefore, in this study we considered the influence of different structures on dynamic mechanical properties of 3DF scaffolds. Pores were varied in size and shape, by changing fibre diameter, spacing and orientation, and layer thickness. With increasing porosity, dynamic mechanical analysis (DMA) revealed a decrease in elastic properties such as dynamic stiffness and equilibrium modulus, and an increase of the viscous parameters like damping factor and creep unrecovered strain. Furthermore, the Poisson's ratio was measured, and the shear modulus computed from it. Scaffolds showed an adaptable degree of compressibility between sponges and incompressible materials. As comparison, bovine cartilage was tested and its properties fell in the fabricated scaffolds range. This investigation showed that viscoelastic properties of 3DF scaffolds could be modulated to accomplish mechanical requirements for tailored tissue engineered applications.

The use of tissue-engineering method holds great promise for treating degenerative disc disease [Gan JC, Ducheyne P, Vresilovic E, Shapiro IM. J Biomed Mater Res 2000; 51(4): 596-604]. This concept typically implies that nucleus pulposus (NP) cells are seeded on a scaffold, while the NP tissue is regenerated. Such hybrid implant is inserted into the host intervertebral disc. Because the success of a tissue engineering approach depends on maintenance or restoration of the mechanical function of the intervertebral disc, it is useful to study the initial mechanical performance of the disc after implantation of the hybrid. A three-dimensional finite element model (FEM) of the L2-L3 disc-vertebrae unit has been analyzed. The model took into account the material nonlinearities and it imposed different and complex loading conditions. In this study, we validated the model by comparison of its predictions with several sets of experimental data; we determined the optimal Young's modulus as well as the failure strength for the tissue-engineered scaffold under different loading conditions; and we analyzed the effects of implanted scaffold on the mechanical behavior of the intervertebral disc. The results of this study suggest that a well-designed tissue-engineered scaffold preferably has a modulus in the range of 5-10 MPa and a compressive strength exceeding 1.67 MPa. Implanted scaffolds with such properties can then achieve the goal of restoring the disc height and distributing stress under different loading conditions.

Loosening of the femoral component in a total hip arthroplasty with concomitant bone loss can pose a problem for revision surgery due to inadequate structure in the remaining femur. While impaction allografting has shown promise, it has also shown serious complications, especially with moderate to severe bone loss. It may be possible to stabilize the graft layer with a bioresorbable cement to improve clinical results. This study examines the mechanical properties of a potential morsellized bone-bioresorbable composite. Morsellized bone was mixed with a commercially available bioresorbable cement (α-BSM, Etex Corp.) in compositions of 0%, 25%, 50% and 75% bone. Unconfined compression and diametral tensile and confined compression tests were performed to determine the composite mechanical properties. The composition containing 50% bone tended to exhibit the highest uniaxial strengths, as well as the highest confined compression modulus. The uniaxial compressive strength and stiffness of this composition was in the range of cancellous bone. Uniaxial compressive modulus decreased with increasing bone fraction whereas elongation exhibited the opposite trend. Bone fraction had a significant effect on compressive strength (p

The hypothesis tested in this study was that the self-etching system (Clearfil SE Bond, CSE) is less sensitive to surface moisture variability than the system that uses a separate acid-etching step (Single Bond, SB). Eighteen dentin specimens were bonded to composite using CSE or SB. Three different surface moisture conditions per bonding type (overwet, w; dry, d; and visibly moist, n [normal]) were applied prior to bonding dentin to composite. One cross section of each sample was analyzed with lines of nanoindentations crossing perpendicular to the bonding interface. An additional set of bonded samples was fixed and cross sectioned before the hybrid layer thickness was measured in scanning electron microscopy. The nanoindentations revealed significant differences in indentation modulus (E(i)) and hardness (H) for the hybrid layer comparing SBn, E(i) = 2.7(+/-1.6); H = 0.24(+/-0.1) GPa with SBd, E(i) = 0.9(+/-0.7); H = 0.9(+/-0.05) GPa, respectively, while CSE showed no differences among the groups. A significantly greater demineralized zone below the hybrid layer was found for SBd. The hybrid layer was wider for both CSEd and SBd. In conclusion the hypothesis was verified; CSE exhibited no significant changes of hybrid layer properties (E(i), H) at different hydration conditions, while SB had significant differences, especially after air-drying.

Poly-L-lactide (PLLA) is one of the most significant members of a group of polymers regarded as bioabsorbable. Degradation of PLLA proceeds through hydrolysis of the ester bonds in the polymer chains and is influenced significantly by the polymer's molecular weight and crystallinity. To evaluate the effects of processing and sterilisation on these properties, PLLA pellets were either compression moulded or extruded, subjected to annealing at 120 degrees C for 4h and sterilised by ethylene oxide (EtO) gas. Procedures were used to evaluate the mechanical properties, molecular weight and crystallinity. Upon processing, the crystallinity of the material fell from 61% for the PLLA pellets to 12% and 20% for the compressed and extruded components, respectively. After annealing, crystallinity increased to 43% for the compression-moulded material and 40% for the extruded material. Crystallinity further increased upon EtO sterilisation. A slight decrease in molecular weight was observed for the extruded material through processing, annealing and sterilisation. Young's modulus generally increased with increasing crystallinity, and extension at break and tensile strength decreased. The results from this investigation suggest that PLLA is sensitive to processing and sterilisation, altering properties critical to its degradation rate.

The mechanical properties of a tissue can be evaluated by determining the response of the structure to mechanical loading. This can be accomplished only when the tissue has been prepared with minimum to no artifacts, thus preserving its structure. In this study it was hypothesized that the structure of cementum is inhomogeneous, contributing to a significant variation in mechanical properties of cementum. Therefore, the goals of the study were to identify potential artifacts generated by conventional sample preparation techniques such as polishing and ultrasectioning and subsequently characterize the prepared specimens using an atomic force microscope (AFM) and an AFM-nanoindenter. Comparisons between cryofractured, ultrasectioned and polished specimens concluded that ultrasectioned surfaces have significantly lower average surface roughness 'R(a)' (p

The objective of this study was to compare the hardness and modulus of the continuum of direct tooth-colored restorative materials using a depth-sensing microindentation approach. The effects of thermal fatigue on mechanical properties were also evaluated. Six restorative materials representing the continuum were selected. They included an ormocer (Admira [AM], Voco), a giomer (Beautifil [BF], Shofu), a compomer (Dyract Extra [DE], Dentsply), a minifill composite (Esthet-X [EX], Dentsply), resin-modified (Fuji II LC [FL], GC) and highly viscous (Fuji IX [FN], GC) glass ionomer cements (GICs). Fourteen specimens (3 mm wide x 3 mm long x 2 mm deep) were made for each material. The specimens were randomly divided into two groups and treated as follows: Group A--stored in distilled water at 37 degrees C for 30 days; Group B--thermal cycled for 5000 cycles (35 degrees C [28s], 15 degrees C [2s], 35 degrees C [28s], 45 degrees C [2s]) and stored for 26.5 days. Hardness and modulus of the materials were determined using depth-sensing microindentation testing with the Instron MicroTester. Hardness was computed by dividing the peak load over the maximum projected contact area while modulus was calculated by analysis of the loading/unloading load-displacement (P-h) curves and the analytical model according to Oliver and Pharr (J. Mater. Res. 7 (1992) 1564). Results were analyzed using ANOVA/Scheffe's post hoc test and independent samples T-test (p0.05). Hardness ranged 46.44-72.65 and 49.11-78.97 HV, while modulus ranged 7.86-12.78 and 8.12-13.13 GPa for Groups A and B, respectively. Although the ranking of mechanical properties were generally similar for both groups, disparities in statistical differences between materials were observed between Groups A and B for both hardness and modulus. For both groups, BF was significantly harder than DE, AM, FL and EX was significantly harder than FL. The modulus of FN was significantly greater than EX, DE, AM and FL was significantly stiffer than AM. With the exception of BF, no significant change in hardness and modulus was observed for all materials with thermocycling. The hardness and modulus of some glass ionomer-based/containing materials may be comparable or even superior to minifill and ormocer composites. Thermal fatigue should be considered when comparing mechanical properties between materials.

Effect of poly(e-caprolactone) (PCL) content on the bioactivity and mechanical properties of PCL/silica hybrid was investigated. The PCL/silica hybrids with different PCL contents were prepared through co-condensation reaction with triethoxysilane end capped PCL and tetraethyl orthosilicate. The higher the PCL content in the hybrid, the lower the apatite-forming rate and showed polymer-like ductile–tough fracture behavior. On the contrary, the lower the PCL content in the hybrid, the higher the apatite-forming rate and showed ceramic-like hard–brittle fracture behavior. At the intermediate PCL content, the apatite-forming rate and its mechanical properties showed also intermediate behaviors. The highest tensile strength and Young’s modulus could be obtained at intermediate PCL content and they were around 20 and 600 MPa, respectively, while the strain at failure was around 50%. This new kind of hybrid material is likely to have the potential to be used as a bone repairing material because of its apatite-forming ability and the mechanical properties comparable to human cancellous bone.

Composites which comprise a bioactive filler and ductile polymer matrix are desirable as implant materials since both their biological and mechanical properties can be tailored for a given application. In the present study three-point bending was used to characterise biomedical materials composed of glass-ceramic apatite–wollastonite (A–W) particulate reinforced polyethylene (PE) (denoted as AWPEX). The effects of filler volume fraction, varied from 10 to 50 vol%, and average particle size, 4.4 and 6.7 μm, on the bending strength, yield strength, mode of fracture, Young's modulus and strain to failure were investigated. HAPEX™, a commercially used composite of hydroxyapatite and polyethylene, with a 40 vol% filler content, was used for comparison. Increasing the filler content caused an increase in Young's modulus, yield strength and bending strength, and a decreased strain to failure. When filler particle size was increased, the Young's modulus, yield and bending strengths were found to be slightly reduced. A transition in fracture behaviour from ductile to brittle behaviour was observed in samples containing between 30 and 40 vol% filler.

A transparent and slight yellow chitosan (CS)/hydroxyapatite (HA) nanocomposite with high performed, potential application as internal fixation of bone fracture was prepared by a novel and simple in situ hybridization. The method solves the problem of the nano-sized particle aggregation in polymer matrix. XRD, TEM and SEM were used to determine component and morphology of the composite. Results indicated that nano-HA particles were dispersed well in CS matrix, which can also be proved by the transparent appearance of composite rod, and that the structure of composite is assembled by CS molecule in the order of layer-by-layer. The mechanical properties of the composite were evaluated by using bending strength and modulus, and compared with some other bone replacement materials such as PMMA and bone cement. The initial mechanical properties of bending strength and modulus of composite are 86 MPa and 3.4 GPa, respectively, which is double or triple times stronger than that of PMMA and bone cement. It was found that the bending strength and modulus of CS/HA with ratio of 100/5 (wt/wt) is slightly higher than that of pure CS rod. The addition of HA can also reduce the ratio of water absorption of composite, which postponed the retention of mechanical properties of CS/HA composite under moisture condition. The phenomenon can be predicted with the fit exponential function according the data measured.

A β type titanium alloy, Ti–29Nb–13Ta–4.6Zr, was newly designed and developed for biomedical applications. The new alloy contains non-toxic elements such as Nb, Ta, and Zr. In the present study, phases that appeared in the new alloy through various aging treatments were characterized by hardness tests and microstructural observations in order to identify the phase transformation. Fatigue properties of the new alloy were investigated. Young’s modulus and cyto-toxicity of the new alloy were also evaluated. Precipitated phases distribute homogeneously over the whole specimen, and they are α phase, a small amount of ω phase, and β phase when the new alloys are subjected to aging treatment at 673 K for 259.2 ks after solution treatment at 1063 K for 3.6 ks. The fatigue strength of the new alloy subjected to aging at 673 K for 259.2 ks after solution treatment at 1063 K for 3.6 ks is much better than when subjected to other aging treatments. In this case, the fatigue limit is around 700 MPa. Young’s modulus of the new alloy is much smaller than that of Ti–6Al–4V ELI. The cyto-toxicity of the new alloy is equivalent to that of pure Ti. Therefore, it is proposed that the new alloy, Ti–29Nb–13Ta–4.6Zr, will be of considerable use in biomedical applications.

A non-resonant forced vibration, dynamic mechanical analyser was employed to measure the viscoelastic characteristics of soft lining materials at 1 Hz, after storage in distilled water at mouth temperature for periods up to and including one year. The six commercial products included methacrylate, silicone, and phosphazine based polymers and the one experimental material was a methacrylate. Water sorption of the soft liners, recorded by change in sample mass, ranged from -4.39 to +48.57% and their solubilities from 0.13 to 13.58%, after one year. The heat-cured silicone was the most stable polymer in water in contrast to its autopolymerised counterpart. The excessive water uptake of this latter material resulted in a massive reduction in modulus. At the other extreme one methacrylate with a high plasticiser content hardened substantially after ageing (modulus changed from 5.87 to 72.3 MPa). Changes in loss tangent data were relatively small for all the polymers tested, even for materials with high water uptake. Reduced leaching and/or plasticiser content have led to a more stable generation of soft lining materials.

The purpose of this study was to characterize the deformation properties of a range of long-term denture soft lining materials using dynamic mechanical thermal analysis. Specimens were subjected to sinusoidal shear deformation at a frequency of 1 Hz and a strain of 64 microns peak to peak over a temperature range of 30–70 °C. The technique simulated the type and rate of deformation soft lining materials would experience clinically, thus producing more relevant results than previously used methods. Shear modulus G ′, dissipative modulus G ′' and mechanical loss tangent G′' G′ were obtained for each material. With increasing temperature the moduli of the acrylic materials decreased, indicating an increased compliance and greater deformation. The silicone (Molloplast B) and alternative formulation (Novus) properties were generally insensitive to temperature over the range chosen. The mechanical loss tangent values of the acrylics fell continuously with temperature, suggesting that the plasticization process lowered the T g values below 30 †C, the lowest temperature of testing.

A predictive model for hydroxyapatite-reinforced polyethylene composite has been developed using the finite element analysis method. The simulation is based on the analysis of a representative cell. Results for the complete material can be derived using a spatial statistical material model. Predicted values of Young's modulus are found to be in reasonable agreement with experimentally measured values over a wide range of hydroxyapatite volume fraction. The predictive model can be used to investigate the micromechanical behaviour of the material. This investigation leads to significant elucidation of the failure processes for this material.

In vivo and in vitro studies were designed to characterize the material degradation associated with implantation of carbon fibre-reinforced polysulphone (C/PS). Composite plates were compression moulded for both studies, and a fibre orientation of 0 degrees with the long axis and a fibre volume fraction of approximately 55% were used. The in vitro experiment involved soaking three groups of four plates each at 4, 12 and 26 wk in 0.9% saline solution at 37 degrees C. The plates were measured for weight gain after each time period and mechanically tested non-destructively in four-point bending to determine modulus. The in vivo experiment involved implanting three groups of eight composite plates (24 total) subcutaneously in the abdomens of 12 rabbits (two implants/animal). Implants were harvested at 4, 12 and 26 wk after implantation and evaluated for changes in weight or modulus of elasticity. In vitro results showed a statistically significant (P less than 0.05 paired t-test) increase in weight for all time periods: 0.41, 1.25 and 0.93% weight gain for the 4, 12 and 26 wk periods respectively. In vivo results were similar to those in vitro: 0.66, 1.06 and 1.15% weight gain for the 4, 12 and 26 wk periods respectively (P less than 0.05 paired t-test). There was no statistically significant difference between the pre- and post-implantation modulus of elasticity for any time period in vivo or in vitro. However, in both studies, on average, the modulus tended to increase with environmental exposure.

As acidic monomers of self-etching adhesives are incorporated into dental adhesives at high concentrations, the adhesive becomes more hydrophilic. Water sorption by polymers causes plasticization and lowers mechanical properties. The purpose of this study was to compare the water sorption and modulus of elasticity (E) of five experimental neat resins (EX) of increasing hydrophilicity, as ranked by their Hoy's solubility parameters and five commercial resins. Methods After measuring the initial modulus of all resin disks by biaxial flexure, half the specimens were stored in hexadecane and the rest were stored in water. Repeated measurements of stiffness were made for 3 days. Water sorption and solubility measurements were made in a parallel experiment. Results None of the specimens stored in oil showed any significant decrease in modulus. All resins stored in water exhibited a time-dependent decrease in modulus that was proportional to their degree of water sorption. Water sorption of EX was proportional to Hoy's solubility parameter for polar forces ( δ p ) with increasing polarity resulting in higher sorption. The least hydrophilic resin absorbed 0.55 wt% water and showed a 15% decrease in modulus after 3 days. The most hydrophilic experimental resin absorbed 12.8 wt% water and showed a 73% modulus decrease during the same period. The commercial resins absorbed between 5% and 12% water that was associated with a 19–42% reduction in modulus over 3 days.

Poly(epsilon-caprolactone) (PCL)/continuous bioglass fibre composite was prepared using the monomer transfer moulding technique coupled with a surface initiated polymerisation. The bioglass fibres were surface treated with an amine ended silane in order to initiate polymerisation of epsilon-caprolactone from the fibre surface. Surface initiated polymerisation significantly improved the Young's modulus and flexural strength and water resistance of the composite. Initial in vitro biocompatibility assessment suggests that amine ended silane treatment of bioglass fibres before their inclusion in the composite does not have a negative effect on the biological responses in terms of macrophage activation as measured by IL-1beta release and craniofacial osteoblast attachment.

Microstructure characterization and property evaluation of high velocity oxy-fuel (HVOF) sprayed hydroxyapatite (HA) splats and coatings were conducted in the present study as a function of the proportion of melting that occurred in HA particles during HVOF spray. In vitro behavior of single and folded HA splats in simulated body fluid was also investigated. Results showed that phase composition of as-sprayed HA coatings was influenced significantly by the melt fraction in HVOF sprayed particles. Melt fraction of the HA powders were experimentally determined from particle morphology analysis. It was found that the spray parameters and starting powder size influenced the melt fraction of the particles. In vitro investigation of individual HA splats made from different HA particles revealed decisive role of local phase composition in influencing their dissolution/precipitation behavior during the test. Furthermore, Raman spectroscopy qualitative inspection on the sprayed HA particles (partial melted) revealed that thermal decomposition occurred within the melted part rather than the unmelted zone. Young's modulus and micro-hardness of the as-sprayed particles and coatings were determined using nano-indentation technique. The resolidified zone of the sprayed HA particles exhibited an average Young's modulus value of 41.25 GPa. The measured values ranged from 23.1 to 65.3 GPa. The unmelted part of the HA powders showed a markedly narrower range. Young's modulus value of 83.9 GPa (±9.4 GPa) was recorded for this region. This succinctly highlight the difference between the unmelted region and melted regions of a HA particle. Young's moduli values measured on HVOF coatings were found to mirror the trend found in the spheroidised particles and splats with apt fidelity. Accepted version

A group of Ti(60)Cu(14)Ni(12)Sn(4)M(10) (M=Nb, Ta, Mo) alloys was prepared using arc melting and copper mold casting. The as-prepared alloys have a composite microstructure containing a micrometer-sized dendritic beta-Ti(M) phase dispersed in a nanocrystalline matrix. These new alloys exhibit a low Young's modulus in the range of 59-103 GPa, and a high yield strength of 1037-1755 MPa, together with large plastic strains. The combination of high strength and low elastic modulus offers potential advantages in biomedical applications.

Vascular constructs were formed by embedding rat aortic smooth muscle cells in three-dimensional matrices of Type I collagen, fibrin, or a mixture of collagen and fibrin in a 1:1 ratio, at total matrix protein concentrations of 2 and 4 mg/ml. Morphological and mechanical properties were evaluated after 6 days in culture, and the effect of cyclic mechanical strain on collagen–fibrin mixture constructs was also studied. Constructs made with the lower protein concentration compacted to the greatest degree, and fibrin was found to enhance gel compaction. Each matrix type exhibited a characteristic stress–strain profile. Pure collagen had the highest linear modulus and pure fibrin had the lowest. The ultimate tensile stress was strongly dependent on the degree of gel compaction, and collagen–fibrin mixtures at 2 mg/ml total protein content exhibited the highest values. Application of cyclic mechanical strain to collagen–fibrin mixture constructs caused a significant increase in gel compaction and a decrease in cell proliferation. The linear modulus, ultimate tensile stress and toughness of the constructs were all augmented by mechanical strain. These results demonstrate that the properties of engineered vascular tissues can be modulated by the combination of selected extracellular matrix components, and the application of mechanical stimulation.

A rabbit model was developed to evaluate the compressive mechanical properties of cancellous bone defects treated with particles of selected bone graft substitute materials. A novel feature of the model was the precise retrieval of the site of implantation. A notable finding was a 9-fold increase in the modulus of elasticity of the defect implanted with a synthetic hydroxyapatite material after 26 weeks when compared to the modulus of the trabecular bone normally at the site. The compressive modulus of lesions treated with particles of a natural bovine bone mineral (anorganic bovine bone) was closer to the normal modulus of the cancellous bone at the site. While the compressive strength of the anorganic bone particles was less than that of normal bone, the site implanted with the bone mineral particles achieved compressive strength greater than normal after 6 weeks. Moreover, the anorganic bone particles accelerated the increase in strength of the lesion, at 6 weeks exceeding the strength achieved by the untreated defect after 26 weeks. The potential problem associated with the disparity in the compressive modulus between sites implanted with the synthetic HA particles and surrounding bone is discussed.

The influence of glutaraldehyde as a crosslinking agent to increase the strength of collagen matrices for cell culture was examined in this study. Collagen solutions of 1% were treated with different concentrations (0-0.2%) of glutaraldehyde for 24 h. The viscoelasticity of the resulting collagen gel solution was measured using dynamic mechanical analysis (DMA), which demonstrated that all collagen gel solutions examined followed the same model pattern. The creep compliance model of Voigt-Kelvin satisfactorily described the change of viscoelasticity expressed by these collagen gel solutions. These crosslinked collagen gel solutions were freeze-dried to form a matrix with a thickness of about 0.2-0.3 mm. The break modulus of these collagen matrices measured by DMA revealed that the higher the degree of crosslinking. the higher the break modulus. The compatibility of fibroblasts isolated from nude mouse skin with these collagen matrices was found to be acceptable at a cell density of 3 x 10(5) cells/cm2 with no contraction, even when using a concentration of glutaraldehyde of up to 0.2%.

The time dependent, viscoelastic characteristics of a number of dental soft liners (occasionally called resilient liners) were investigated using a dynamic mechanical analyser (DMA). The materials consisted of eight commercial products including methacrylate, silicone and phosphazine-based soft polymers as well as two experimental formulations. The DMA used was of the forced vibrational variety. The test conditions, such as frequency and temperature, were chosen to mimic in use (masticatory) conditions. A wide variety of behaviour was observed and accounted for. This included a seven fold range in the storage modulus (2.79–19.7 MPa) and a 50-fold range in the loss tangent (0.029–1.52) at 37°C and 1 Hz. The materials could generally be divided into either rubbery behaviour with low modulus and loss tangent, i.e. the silicones, or leathery behaviour with both higher modulus and loss tangent, i.e. the methacrylates. A search of the literature did not find a universally preferred set of properties, although a possible link with residual ridge resorption is indicated.

An experimental investigation was undertaken to measure the intrinsic elastic properties of several of the microstructural components of human vertebral trabecular bone and tibial cortical bone by the nanoindentation method. Specimens from two thoracic vertebrae (T-12) and two tibiae were obtained from frozen, unembalmed human male cadavers aged 57 and 61 years. After drying and mounting in epoxy resin nanoindentation tests were conducted to measure Young's modulus and the hardness of individual trabeculae in the vertebrae and single osteons, and interstitial lamellae in the tibiae. Measurements on the vertebral trabeculae were made in the transverse direction, and the average Young's modulus was found to be 13.5 +/- 2.0 GPa. The tibial specimens were tested in the longitudinal direction, yielding moduli of 22.5 +/- 1.3 GPa for the osteons and 25.8 +/- 0.7 GPa for the interstitial lamellae. Analysis of variance showed that the differences in the measured moduli are statistically significant. Hardness differences among the various microstructural components were also observed.

Dynamic mechanical analysis (DMA) has been used to characterize the viscoelastic properties of four suture materials, Prolene, Maxon, Vicryl and silk. The technique identified the main transitions for the sutures and frequency multiplexing was used to define the variation of modulus with time. The monofilament Prolene has a beta transition and the monofilament Maxon has an alpha transition close to room temperature, indicating that both materials exhibit a change in stiffness with time. The alpha transitions (Tgs) of silk and Vicryl occur at temperatures significantly above room temperature and frequency multiplexing data indicate that both materials exhibit stable moduli with respect to time at room temperature. Determination of the viscoelastic behaviour through DMS appears to be very useful in predicting the performance of suture materials.

The shear modulus and elastic limit in shear were determined for a number of polymers of clinical interest, using a static torsion method. In particular, ultra-high modulus polyethylene was studied as a function of draw ratio, and compared with corresponding Young's modulus data. Materials of high shear moduli of potential clinical value are described.