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PubMed2002

Formation of metabolites during biodegradation of linear alkylbenzene sulfonate in an upflow anaerobic sludge bed reactor under thermophilic conditions.

Biodegradation of linear alkylbenzene sulfonate (LAS) was shown in an upflow anaerobic sludge blanket reactor under thermophilic conditions. The reactor was inoculated with granular biomass and fed with a synthetic medium and 3 micromol/L of a mixture of LAS with alkylchain length of 10 to 13 carbon atoms. The reactor was operated with a hydraulic retention time of 12 h with effluent recirculation in an effluent to influent ratio of 5 to 1. A sterile reactor operated in parallel revealed that sorption to sludge particles initially accounted for a major LAS removal. After 8 days of reactor operation, the removal of LAS in the reactor inoculated with active granular biomass exceeded the removal in the sterile reactor inoculated with sterile granular biomass. The effect of sorption ceased after 185 to 555 h depending on the LAS homologs. 40% of the LAS was biodegraded, and the removal rate was 0.5 x 10(-6) mol/h/mL granular biomass. Acidified effluent from the reactor was subjected to dichloromethane extraction followed by gas chromatography/mass spectrometry. Benzenesulfonic acid and benzaldehyde were detected in the reactor effluent from the reactor with active granular biomass but not in the sterile and unamended reactor effluent. Benzenesulfonic acid and benzaldehyde are the first identified degradation products in the anaerobic degradation of LAS.

Alkanesulfonic Acids↗

PubMed2004

Photosynthetically oxygenated salicylate biodegradation in a continuous stirred tank photobioreactor.

A consortium consisting of a Chlorella sorokiniana strain and a Ralstonia basilensis strain was able to carry out sodium salicylate biodegradation in a continuous stirred tank reactor (CSTR) using exclusively photosynthetic oxygenation. Salicylate biodegradation depended on algal activity, which itself was a function of microalgal concentration, light intensity, and temperature. Biomass recirculation improved the photobioreactor performance by up to 44% but the results showed the existence of an optimal biomass concentration above which dark respiration started to occur and the process efficiency started to decline. The salicylate removal efficiency increased by a factor of 3 when illumination was increased from 50-300 microE/m2.s. In addition, the removal rate of sodium salicylate was shown to be temperature-dependent, increasing from 14 to 27 mg/l.h when the temperature was raised from 26.5 to 31.5 degrees C. Under optimized conditions (300 microE/m2.s, 30 degrees C, 1 g sodium salicylate/l in the feed and biomass recirculation) sodium salicylate was removed at a maximum constant rate of 87 mg/l.h, corresponding to an estimated oxygenation capacity of 77 mg O2/l.h (based on a BOD value of 0.88 g O2/g sodium salicylate for the tested bacterium), which is in the range of the oxygen transfer capacity of large-scale mechanical surface aerators. Thus, although higher degradation rates were attained in the control reactor, the photobioreactor is a cost-efficient process which reduces the cost of aeration and prevents volatilization problems associated with the degradation of toxic volatile organic compounds under aerobic conditions.

Aerobiosis↗

PubMed2005

Effects of process stability on anaerobic biodegradation of LAS in UASB reactors.

Anaerobic biodegradation of linear alkylbenzene sulfonates (LAS) was studied in upflow anaerobic sludge blanket (UASB) reactors operated under mesophilic (37 degrees C) and thermophilic (55 degrees C) conditions. LAS C12 concentration in the influents was 10 mg.L(-1), and the hydraulic retention time in the reactors was 2 days. Adsorption of LAS C12 was assessed in an autoclaved control reactor and ceased after 115 days. The reactors were operated for a minimum of 267 days; 40-80% removal of LAS C12 was observed. A temperature reduction from 55 degrees C to 32 degrees C for 30 h resulted in process imbalance as indicated by increase of volatile fatty acids (VFA). The imbalance was much more intense in the LAS amended reactor compared with an unamended reactor. At the same time, the process imbalance resulted in discontinued LAS removal. This finding indicates that process stability is a key factor in anaerobic biological removal of LAS. After a recovery period, the removal of LAS resumed, providing evidence of biological anaerobic LAS degradation. The removal remained constant until termination of experiments in the reactor. Biodegradation of LAS in the mesophilic reactor was at the same level as in the thermophilic reactor under stable conditions.

Alkanesulfonic Acids↗

PubMed2005

Riboflavin- and cobalamin-mediated biodegradation of chloroform in a methanogenic consortium.

Chloroform (CF) is an important priority pollutant contaminating groundwater. Reductive dechlorination by anaerobic microorganisms is a promising strategy towards the remediation of CF. The objective of this study was to evaluate the use of redox active vitamins as electron shuttles to enhance the anaerobic biodegradation of CF in an unadapted methanogenic consortium not previously exposed to chlorinated compounds. Only negligible degradation of CF was observed in control cultures lacking redox active vitamins. The addition of riboflavin (RF), cyanocobalamin (CNB12), and hydroxycobalamin (HOB12) enabled biodegradation of CF. The reactions were predominantly catalyzed biologically as evidenced by the lack of any CF conversion in heat-killed controls amended with the cobalamins or minor conversion with RF. In live cultures, significant increases in the rate of CF conversion was observed at substoichiometric molar ratios as low as 0.1 to 0.01 vitamin:CF for RF and CNB12, respectively. At the highest molar vitamin:CF ratios tested of 0.2, the first-order rate constant of CF degradation was 5.3- and 91-fold higher in RF and CNB12 amended cultures, respectively, compared to the unamended control culture. The distribution of biotransformation products was highly impacted by the type of redox active vitamin utilized. Cultures supplemented with RF provided high yields of dichloromethane (DCM). On the other hand, cobalamins promoted the near complete mineralization of organochlorine in CF to inorganic chloride and lowered the yield of DCM. In cultures where no or little CF bioconversion occurred, prolonged exposure to CF resulted in cell lysis, as evidenced by the release of intracellular chloride. The results taken as a whole suggest that the anaerobic bioremediation of CF-contaminated sites can greatly be improved with strategies aimed at increasing the concentration of redox active vitamins.

Biodegradation, Environmental↗

PubMed2007

Kinetics of biodegradation of binary and ternary mixtures of PAHs.

The kinetics of biodegradation of mixtures of polycyclic aromatic hydrocarbons (PAHs) by Sphingomonas paucimobilis strain EPA505 were investigated. The investigation focused on three- and four-ring PAHs, specifically 2-methylphenanthrene, fluoranthene, and pyrene. Uptake rates in aerobic batch suspended cultivations were measured for the individual PAHs and their binary and ternary mixtures. It was observed that kinetics were influenced by the mixture composition and the kinetic properties of the components. A material balance equation containing the Monod model was numerically fitted to uptake data to determine extant kinetic parameters for the individual PAHs. Similarly, equations containing kinetic interaction models derived from enzyme kinetics were fitted to the uptake data obtained from experiments with binary and ternary mixtures. The investigation considered the following interaction types: no-interaction (Monod), pure competitive interaction, noncompetitive or mixed-type interaction, uncompetitive inhibition, and nonspecific interaction based on pure competition (SKIP). Model fit was evaluated based on probabilistic and statistical criteria and inferences were reached about underlying interaction mechanisms based on model fit. Mixture kinetics were most adequately simulated by the pure competitive interaction model with mutual substrate exclusivity. This model is fully predictive, relying only on parameters determined in the sole-PAH experiments. It was shown that for low percent inhibition values and with limited data, pure competitive interaction kinetics may not be evident, resembling no-interaction kinetics. This study is a reasonable starting point for understanding and modeling biodegradation of complex PAH mixtures in engineered and natural systems.

Biodegradation, Environmental↗

PubMed1991

Biodegradable screw fixation of rabbit tibia proximal osteotomies.

The purpose of this study was to evaluate a biodegradable poly(L-lactide) (P-L-LA) screw for osteosynthesis under a load-bearing condition. A proximal tibial osteotomy on 25 rabbits was fixed with a biodegradable screw made of P-L-LA. A follow-up study was done at 1, 2, 4, 8, and 16 weeks. In another 25 rabbits, the tibial osteotomy was fixed with stainless steel (SUS) screws of the same size as the P-L-LA screws with a similar follow-up period. Radiographic, histological, microradiographic, and oxytetracycline-labeling studies showed healing of the osteotomy within 4 to 8 weeks. The displacement of fragments and the mass of newly formed bone around the screws were measured by histomorphometric analysis. There was no significant difference in the displacement of the fragments in these two groups and new bone was more abundantly detected in the P-L-LA group than in the SUS group. Histologically, no inflammatory lesion was detected in either group. All osteotomies united without delay and the displacement was minimal, although no external support was applied and the rabbits were allowed to move freely after the operation. The results of this study suggest a possible use for a P-L-LA screw in the clinical treatment of human bone fractures.

Animals↗

PubMed1993

Preliminary biocompatibility screening of several biodegradable phosphate fiber reinforced polymers.

This article describes preliminary biocompatibility screening of three degradable phosphate fibers containing K +, Ca +2/Na + and Na +/Ca +2/Al +3 ions in the polymer chain, and of several different degradable polymers reinforced with these fibers. Biodegradable phosphate fibers of calcium-sodium-metaphosphate (CSM) and sodium-calcium-aluminum-polyphosphate (NCAP) were acutely nontoxic in cellular, tissue, and whole animal evaluations, as determined by standard acute toxicity tests. Histological studies of bone implants sites fabricated from composites of copolymers of poly(E-caprolactone/L-lactide) and poly(ortho ester) reinforced with either CSM or NCAP fibers showed these composite materials to be nontoxic, with no abnormal inflammatory response. However, histological evaluation of muscle implants sites revealed the appearance of necrotic foci associated with implant sites in 12 of 22 NCAP containing composite specimens (p less than 0.05). Results of this preliminary biocompatibility screening suggest CSM fibers may be useful in reinforcing degradable polymers for production of completely biodegradable composites for implant use.

Animals↗

PubMed2002

Synthesis, characterization, and cytocompatibility of elastomeric, biodegradable poly(ester-urethane)ureas based on poly(caprolactone) and putrescine.

The engineering of tissue for mechanically demanding applications in the cardiovascular system is likely to require mechanical conditioning of cell-scaffold constructs prior to their implantation. Scaffold properties amenable to such an application include high elasticity and strength coupled with controllable biodegradative and cell-adhesive properties. To fulfill such design criteria, we have synthesized a family of poly(ester-urethane)ureas (PEUUs) from polycaprolactone and 1,4-diisocyanatobutane. Lysine ethyl ester (Lys) or putrescine was used as chain extenders. To encourage cell adhesion, PEUUs were surface modified with radio-frequency glow discharge followed by coupling of Arg-Gly-Asp-Ser (RGDS). The synthesized PEUUs were highly flexible, with breaking strains of 660-895% and tensile strengths from 9.2-29 MPa. Incubation in aqueous buffer for 8 weeks resulted in mass loss, from >50% (Lys chain extender) to 10% (putrescine chain extender). Human endothelial cells cultured for 4 days with medium containing the degradation products from PEUUs with either the Lys or putrescine chain extender showed no toxic effects. Cell adhesion was 85% of that measured on tissue-culture polystyrene for unmodified PEUU surfaces (p < 0.01) and >160% (p < 0.001) of polystyrene on RGDS-modified PEUUs. These biodegradable PEUUs demonstrate potential for future application as cell scaffolds in cardiovascular tissue-engineering or other soft-tissue applications.

Absorbable Implants↗

PubMed2002

Biodegradation of polycarbonate-based polyurethanes by the human monocytes-derived macrophage and U937 cell systems.

The prominent cell type found on implanted medical devices during the chronic inflammatory response is the monocyte-derived macrophage (MDM). Using an activated in vitro cell system, it was possible to show that MDMs possess esterolytic activities that may contribute to the degradation of polyurethanes. In the present study, the U937 cell line was paralleled to the MDM cell system in order to validate the use of a cell line that could expedite studies on biomaterial biocompatibility and biostability. Using 12-o-tetradecanoylphorbol 13-acetate (PMA), the optimum differentiation time for the U937 cells was 72 h based on biodegradation, degradative potential, and (35)S-methionine uptake. After activation of the cells by resuspending from tissue culture polystyrene plates and reseeding onto a (14)C-labeled polycarbonate-based polyurethane(PCNU), both U937 cells and the MDMs elicited comparable radiolabel release (measure of polymer breakdown) and esterase activity (measure of degradative potential) at 48 h. There was no difference in the effect on radiolabel release and esterase activity elicited by both cell types with inhibitors of protein synthesis, esterase activity, and phospholipase A(2). This established that both cell types likely used similar hydrolytic activities and signaling pathways to cause degradation of the PCNU. Immunoblotting demonstrated that both cell systems secreted monocyte-specific esterase and cholesterol esterase enzymes previously shown to degrade PCNUs. The U937 cell system is more convenient and reproducible than MDMs for pursuing possible biological pathways elucidating the mechanism of polyurethane biodegradation. Once established with U937s, the pathways can then be validated with the more physiologically relevant human MDM cell system.

Aristolochic Acids↗

PubMed1975

Biodegradable material for bladder reconstruction.

The objective of this study was to develop a biodegradable material for use in reconstructive surgery of the bladder to serve a temporary function until normal regrowth of the host's tissue is completed. The biodegradable material can serve as a base over which the new bladder can regenerate. At the conclusion of the regrowth of the new tissue, the temporary material could be consumed by the body and therefore not have to be removed. Material evaluation showed that 70% acetic anhydride treated bovine pericardium was digested and dissolved in 4 weeks when implanted subcutaneously in dogs. Based upon this, supplementation of the bladder using this material was performed on 5 dogs. One dog showed urinary leakage and was sacrificed after 1 week. In 3 dogs examined 4, 6, and 48 weeks after implantation, respectively, the implanted material had been dissolved. In one animal autopsied at 10.5 months, a small remnant of the material still remained. Post-operative observation of the animals, excretory pyelocystograms and cystometry confirmed that the material applied was useful for experimental urinary bladder supplementation.

Acetates↗

PubMed1978

Experimental bladder substitution using a biodegradable graft of natural tissue.

A controlled canine experimental study has been performed to test the application of a biodegradeable graft to vesical augmentation. The graft, after providing initial bladder enlargement, is progressively reabsorbed while serving as a foundation for the regeneration and healing of the layers of the bladder remnant. Follow-up studies at 1 year revealed no urinary infection, calculi, extravasation of urine, or rejection of the material. Normal bladder capacities were maintained throughout the study and the reconstructed bladders functioned normally. The biodegradable graft was equally successful when applied either to a histologically normal bladder remnant, or to a pathological bladder of intramural fibrosis. These results suggest that this material may be well suited to clinical bladder substitution in humans.

Animals↗

PubMed1983

Preliminary report on the osteogenic potential of a biodegradable copolymer of polyactide (PLA) and polyglycolide (PGA).

A biodegradable copolymer of 50 polylactide: 50 polyglycolide was prepared for implantation into experimentally created osseous defects in the tibias of 25 rats. Similarly prepared defects were made in the humeri of the same rats and these defects did not receive copolymer implants. Upon sacrifice, both the implant treated and untreated sites of the experimentally produced osseous defects were evaluated by gross appearance and by histomorphometric examination using a Zeiss Videoplan Image Analysis System with Osteoplan (version 4.1). The animals were evaluated in groups of five at 7, 14, 21, 28, and 42 days. When compared with bony defects that were not treated with the biocompatible, biodegradable copolymer implant, the implant sites displayed an accelerated rate of healing at 7, 14, 21, and 28 days (p less than 0.001). A similar healing response rate, however, was observed at 42 days (p less than 0.25-0.1). No adverse host tissue responses were observed histologically.

Animals↗

PubMed1983

In vivo biocompatibility studies. I. The cage implant system and a biodegradable hydrogel.

A cage implant system has been utilized to examine the in vivo biocompatibility of a biodegradable hydrogel, poly(2-hydroxy-ethyl-L-glutamine) (PHEG). This system permits the quantitative determination of the components of the inflammatory exudate which surrounds the implanted polymer within the cage system. This system permits the serial examination of exudate components without sacrificing the animal. In addition, this system allows the subsequent removal of the polymer for surface and mechanical studies. Following implantation of the biodegradable hydrogel, quantitative and differential white cell counts of the exudates were determined over a 21-day period. In addition, concomitant extracellular enzyme analyses for alkaline phosphatase, acid phosphatase, prostatic acid phosphatase, leucine amino-peptidase, and Cathepsin B1 were determined. Corresponding control samples from exudates of the cage implant without the polymer were also determined. The two-tailed Student's t-test for unpaired samples was used to statistically compare the control and implanted polymer values for these respective analyses at the various time periods. A comparison of the cellular response for the control system and the PHEG system did not show statistically significant differences during the first 7 days following implantation. The acute inflammatory response, polymorphonuclear leukocyte predominant, was followed by a mild chronic inflammatory response, macrophage and lymphocyte predominant, and during this time period, 8-14 days, macrophages were present in significantly larger numbers for the PHEG system when compared to the control values. Enzymic analysis of the exudates revealed statistically significant differences between control and PHEG values at time intervals where no differences were noted in cell density or population. These results are discussed in terms of cell-polymer interactions leading to cellular activation and enhanced enzyme exocytosis by the inflammatory cells. Stress-strain measurements on implanted PHEG samples showed that significant in vivo degradation had occurred during the acute inflammatory phase of the response, i.e., the first 7 days.

Acid Phosphatase↗

PubMed2003

Synthesis and characterization of a novel polymer-ceramic system for biodegradable composite applications.

The objective of this study was to develop a biodegradable polymer resin that could be used for the fabrication of an interpenetrating phase composite (IPC) made of porous calcium polyphosphate (CPP) and an organic polymer resin. The resin was synthesized from a polycarbonate-based divinyl oligomer and monomers containing ionic groups. The physical and chemical properties of the polymer resin and polycarbonate-based divinyl oligomer were characterized by gel permeation chromatography, Fourier transform infrared spectroscopy, and swelling studies. The in vitro degradation of the polymer resins was assessed using cholesterol esterase in a buffer solution at 37 degrees C for 3 weeks. Scanning electron microscopy of the degraded samples indicated that the hydrolysis of the resin was catalyzed by the enzyme. The relative interfacial shear strength between the polymer resin and the CPP ceramic was studied using a microbond test. The addition of ionic groups into the polymer resin chains appeared to improve the chemical bonding between the polymer and the CPP. Preliminary mechanical properties of the IPC were investigated by determining bending strength using a three point bending test. The data showed a sevenfold increase in strength over that of the monolithic CPP, and the addition of more ionic groups into the resin led to a higher bending strength for the newly formed CPP/polycarbonate resin system. Sample cross sections of the IPC examined using scanning electron microscopy suggested that the resin had infiltrated almost all of the pores of the CPP. The results of this study indicate that the IPC could potentially be used for fabricating novel biodegradable load-bearing implants.

Biocompatible Materials↗

PubMed2003

Preparation, degradation, and calcification of biodegradable polyurethane foams for bone graft substitutes.

Autogenous cancellous bone graft is used to heal critical-size segmental long bone defects and defects in the maxillofacial skeleton. Harvesting of bone graft is traumatic, causes morbidity of the donor site, and often results in complications. Thus, there is a need for new biologically functional bone graft substitutes that, instead of autogenous bone graft, could be used to facilitate bone regeneration in critical-size defects. Porous biodegradable elastomeric polyurethane scaffolds combined with the patient's own bone marrow could potentially be such bone substitutes. The elastomeric bone substitute prevents shear forces at the interface between bone and rigid, e.g., ceramic bone substitutes and establishes an intimate contact with the native bone ends, thus facilitating the proliferation of osteogenic cells and bone regeneration. Crosslinked 3D biodegradable polyurethane scaffolds (foams) with controlled hydrophilicity for bone graft substitutes were synthesized from biocompatible reactants. The scaffolds had hydrophilic-to-hydrophobic content ratios of 70:30, 50:50, and 30:70. The reactants used were hexamethylene diisocyanate, poly(ethylene oxide) diol (MW = 600) (hydrophilic component), and poly(epsilon-caprolactone) diol (M(w) = 2000), amine-based polyol (M(w) = 515) or sucrose-based polyol (M(w) = 445) (hydrophobic component), water as the chain extender and foaming agent, and stannous octoate, dibutyltin dilaurate, ferric acetylacetonate, and zinc octoate as catalysts. Citric acid was used as a calcium complexing agent, calcium carbonate, glycerol phosphate calcium salt, and hydroxyapatite were used as inorganic fillers, and lecithin or solutions of vitamin D(3) were used as surfactants. The scaffolds had an open-pore structure with pores whose size and geometry depended on the material's chemical composition. The compressive strengths of the scaffolds were in the range of 4-340 kPa and the compressive moduli in the range of 9-1960 kPa, the values of which increased with increasing content of polycaprolactone. Of the two materials with the same amount of polycaprolactone the compressive strengths and moduli were higher for the one containing inorganic fillers. The scaffolds absorbed water and underwent controlled degradation in vitro. The amount of absorbed water and susceptibility to degradation increased with the increasing content of the polyethylene oxide segment in the polymer chain and the presence in the material of calcium complexing moiety. All polyurethane scaffolds induced the deposition of calcium phosphate crystals, the structure and calcium:phosphorus atomic ratio of which depended on the chemical composition of the polyurethane and varied from 1.52-2.0.

Absorbable Implants↗

PubMed2003

Vascularization and tissue infiltration of a biodegradable polyurethane matrix.

Urethanes are frequently used in biomedical applications because of their excellent biocompatibility. However, their use has been limited to bioresistant polyurethanes. The aim of this study was to develop a nontoxic biodegradable polyurethane and to test its potential for tissue compatibility. A matrix was synthesized with pentane diisocyanate (PDI) as a hard segment and sucrose as a hydroxyl group donor to obtain a microtextured spongy urethane matrix. The matrix was biodegradable in an aqueous solution at 37 degrees C in vitro as well as in vivo. The polymer was mechanically stable at body temperatures and exhibited a glass transition temperature (Tg) of 67 degrees C. The porosity of the polymer network was between 10 and 2000 microm, with the majority of pores between 100 and 300 microm in diameter. This porosity was found to be adequate to support the adherence and proliferation of bone-marrow stromal cells (BMSC) and chondrocytes in vitro. The degradation products of the polymer were nontoxic to cells in vitro. Subdermal implants of the PDI-sucrose matrix did not exhibit toxicity in vivo and did not induce an acute inflammatory response in the host. However, some foreign-body giant cells did accumulate around the polymer and in its pores, suggesting its degradation is facilitated by hydrolysis as well as by giant cells. More important, subdermal implants of the polymer allowed marked infiltration of vascular and connective tissue, suggesting the free flow of fluids and nutrients in the implants. Because of the flexibility of the mechanical strength that can be obtained in urethanes and because of the ease with which a porous microtexture can be achieved, this matrix may be useful in many tissue-engineering applications.

Animals↗

PubMed2003

Spatially organized layers of cardiomyocytes on biodegradable polyurethane films for myocardial repair.

Tissue engineering constructs should match the physical and mechanical properties of the native tissue. This implies that pliable scaffolds might be better suited for soft-tissue applications than rigid polymeric materials. In this study, we examined spatially organized cardiomyocyte cultures on biodegradable, elastomeric polyurethane films patterned by microcontact printing of laminin lanes. The resulting cardiomyocyte patterns on polyurethane displayed a similar morphology to those previously achieved for up to 7-10 days on other substrates, such as polystyrene dishes. However, the integrity of the cardiomyocyte patterns on thin, spin-cast or solvent-cast polyurethane films was retained for up to 4 weeks in culture. When additional cardiomyocytes (labeled with Cell Tracker reagents) were seeded onto the patterned cultures, secondary and tertiary cell populations aligned between and on top of the primary patterned cells to form a multilayered, organized tissue construct approximately 2-3 cell layers thick. In addition, dense, highly aligned monolayers of patterned cardiomyocytes were able to contract the thin, solvent-cast polyurethane films. These results indicate that elastomeric, biodegradable polyurethane films can serve as an appropriate scaffold material to support stably the engineering of spatially organized layers of cardiomyocytes in vitro. This approach may serve as a novel method for transplantation of organized cardiac tissue constructs to the heart for myocardial repair.

Animals↗

PubMed2003

Biodegradation of polyurethane under fatigue loading.

A method utilizing expansion of a diaphragm-type film specimen was developed to study in vitro biodegradation of poly(etherurethane urea) (PEUU) under conditions of dynamic loading (fatigue). A finite element model was used to describe the strain state, which ranged from uniaxial at the edges of the film to balanced biaxial tensile strain at the center. During testing, the film was exposed to a H(2)O(2)/CoCl(2) solution, which simulated in vivo oxidative biodegradation of PEUU. The extent of chemical degradation was determined by infrared analysis. Physical damage of the film surface was characterized by optical microscopy and scanning electron microscopy. Dynamic loading did not affect the rate of degradation relative to unstressed and constant stress (creep) controls in regions of the film that experienced primarily uniaxial fatigue; however, degradation was accelerated in regions that experienced balanced biaxial or almost balanced biaxial fatigue. It was concluded that the combination of dynamic loading and biaxial tensile strain accelerated oxidative degradation in this system. Chemical degradation produced a brittle surface layer that was marked by numerous pits and dimples. Physical damage of the surface in the form of cracking occurred only in fatigue experiments. Cracking was not observed in unstressed or creep tests. Cracks initiated at the dimples produced by chemical degradation, and propagated in a direction that was determined by the strain state.

Biocompatible Materials↗