In vitro degradation of polymeric networks of poly(propylene fumarate) and the crosslinking macromer poly(propylene fumarate)-diacrylate

Polymeric networks of poly(propylene fumarate) (PPF) crosslinked with poly(propylene fumarate)-diacrylate (PPF-DA) are currently being investigated as an injectable, biodegradable bone cement. This study examined the effect of crosslinking density, medium pH, and the incorporation of a beta-tricalcium phosphate (beta-TCP) filler on the in vitro degradation of PPF/PPF-DA. Cylindrical specimens were submerged in buffered saline at 37 degrees C and the change in weight, geometry, and compressive mechanical properties were monitored over a 52-week period. All formulations showed an initial increase in modulus and yield strength over the first 12 weeks, achieving maxima of 1307+/-101 and 51+/-3MPa, respectively, for the beta-TCP composite. PPF/PPF-DA networks with the lower crosslinking density demonstrated the greatest degradation with a 17% mass loss. Samples in the lower buffer pH 5.0 compared to physiological pH 7.4 did not show any differences in mass loss, but exhibited a faster decrease in the compressive strength over time. The beta-TCP composites maintained their mechanical properties at the level following their initial increase. These results show that the degradation of PPF/PPF-DA networks can be controlled by the crosslinking density, accelerated at a lower pH, and prolonged with the incorporation of the beta-TCP filler.     

Injectable biodegradable polymer composites based on poly(propylene fumarate) crosslinked with poly(ethylene glycol)-dimethacrylate

New injectable, in situ crosslinkable biodegradable polymer composites were investigated consisting of poly(propylene fumarate) (PPF), poly(ethylene glycol)-dimethacrylate (PEG-DMA), and beta-tricalcium phosphate (beta-TCP). We examined the effects of the PEG-DMA/PPF double-bond ratio and beta-TCP content on the crosslinking characteristics of the composites including the maximum crosslinking temperature and the gel point, as well as the properties of the crosslinked composites such as the compressive strength and modulus, and the water-holding capacity. The maximum crosslinking temperature was constant averaging 39.7 degrees C for the composite formulations tested. The gel points varied from 8.0 +/- 1.0 to 12.6 +/- 2.5 min and were not affected by the relative amounts of PEG-DMA. The compressive strength at yield of PEG-DMA/PPF composites without beta-TCP increased from 5.9 +/- 1.0 to 11.2 +/- 2.2 MPa as the double-bond ratio of PEG-DMA/PPF increased from 0.38 to 1.88. An increase in compressive modulus was also observed from 30.2 +/- 3.5 to 58.4 +/- 6.2 MPa for the same range of the PEG-DMA/PPF double-bond ratio. Also, the addition of beta-TCP (33 wt%) enhanced the mechanical properties of all composites. The equilibrium water content of networks without beta-TCP increased from 21.7 +/- 0.2 to 30.6 +/- 0.2% for a double-bond ratio of PEG-DMA/PPF ranging from 0.38 to 1.88. However, the mechanical properties of the swollen composites under compression were smaller than the dry ones. These data demonstrate the feasibility of fabricating injectable biodegradable polymer composites with engineered mechanical properties for orthopedic tissue engineering.     

Poly(propylene fumarate)/(calcium sulphate/beta-tricalcium phosphate) composites: preparation, characterization and in vitro degradation

This study aimed to prepare a poly(propylene fumarate)/(calcium sulphate/beta-tricalcium phosphate) (PPF/(CaSO(4)/beta-TCP)) composite. We first examined the effects of varying the molecular weight of PPF and the N-vinyl pyrrolidinone (NVP) to PPF ratio on the maximum cross-linking temperature and the composite compressive strength and modulus. Then the in vitro biodegradation behaviour of PPF/(CaSO(4)/beta-TCP) composites was investigated. The effects of varying the molecular weight of PPF, the NVP/PPF ratio and the CaSO(4)/beta-TCP molar ratio on the weight loss and the composite compressive strength and modulus were examined. The cross-linking temperature, which increased with increasing molecular weight of PPF and NVP/PPF ratio, ranged from 41 to 43 degrees C for all formulations. The mechanical properties were increased by a decrease in the NVP/PPF ratio. For all formulations, the compressive strength values fell between 12 and 62 MPa, while the compressive modulus values fell between 290 and 1149 MPa. The weight loss decreased either with increasing molecular weight of PPF or with decreasing NVP/PPF ratio and CaSO(4)/beta-TCP molar ratio during degradation. The compressive strength and modulus increased with decreasing NVP/PPF ratio or decreasing CaSO(4)/beta-TCP ratio. The greatest weight loss over 6 weeks was 14.72%. For all formulations, the compressive modulus values fell between 57 and 712 MPa and the compressive strength fell between 0.5 and 21 MPa throughout 6 weeks degradation. Scanning electron microscopy and X-ray diffraction analysis of the PPF/(CaSO(4)/beta-TCP) composites demonstrated that hydroxyapatite was deposited on the surface of CaSO(4)/beta-TCP granules during degradation.     

Manufacture and study of porous poly(l-lactic acid) (PLLA)/beta-tricalcium phosphate (beta-TCP) composite]

A promising alternative to supply bone substitutes is to develop living tissue substitutes based on biodegradable materials, which is called bone tissue engineering. One of the research high-lights of bone tissue engineering is to design and manufacture scaffolds for cell attaching, migrating, and proliferating. A process which consists of a solvent casting stage, a compression molding stage and a leaching stage has been used to fabricate macroporous composites of poly(l-lactic acid) (PLLA) and beta-tricalcium phosphate (beta-TCP). The effects of the weight fraction of porogen--NaCl, of the weight ratio of PLLA to beta-TCP and of the diameters of beta-TCP on the porosities, the average pore diameters and the compressive yield strength and compressive modulus have been studied. The results showed that the porosities and the average pore diameters increased and the compressive yield strength and modulus decreased when the weight fraction went from 50% to 90%. The compressive yield strength and compressive modulus could be improved by changing the weight ratio of PLLA to beta-TCP and the diameters of beta-TCP in low-porosity composites (lower than 70%). But high-porosity composites (90%) were not reinforced by changing the weight ratio.     

Self-curing acrylic formulations containing PMMA/PCL composites: properties and antibiotic release behavior

Partially biodegradable acrylic composites containing poly(methyl methacrylate)-poly(epsilon-caprolactone) (PMMA/PCL) systems were prepared by mixing the corresponding PMMA/PCL beads (89:11, 86:14, 83:17, and 77:23 weight ratio) used as solid phase with methyl methacrylate (MMA) (liquid phase) in a solid/liquid ratio of 1.5:1. The physical and chemical microheterogeneity of these beads influenced significantly the curing parameters, because several aspects involved in the polymerization reaction are closely related to both morphology and size distribution of the particles. In vitro behavior was studied by immersion in simulated body fluid at pH = 7.4 and 37 degrees C for more than 8 weeks and the composition was followed by 1H-nuclear magnetic resonance spectroscopy. Approximately 2% wt/wt weight loss was observed after a period of 8 weeks for the composites richest in PCL. Mechanical properties of the dry and wet specimens were evaluated by compressive and tensile tests. In all cases, the presence of PCL in the composites provided a significant decrease in both compressive strength and elastic modulus compared with plain PMMA. Tensile and compressive strength also decreased significantly after 2 weeks of immersion in simulated body fluid compared with dry specimens. The self-curing composites based on PMMA/PCL beads and loaded with 3% wt/wt vancomycin were evaluated as carriers for local release of antibiotics. The composite prepared with beads of PMMA/PCL ratio 86:14 was the most effective. It eluted 64% of the initial drug within the first 5 h, allowing progressive release of nearly the total amount of the initial drug (90%) in approximately 2 months. The results obtained suggest that the described composites can be suitable for antibiotic release in non-load bearing graft applications.     

Polylactic acid-phosphate glass composite foams as scaffolds for bone tissue engineering

Phosphate glass (PG) of the composition 0.46(CaO)-0.04(Na(2)O)-0.5(P(2)O(5)) was used as filler in poly-L-lactic acid (PLA) foams developed as degradable scaffolds for bone tissue engineering. The effect of PG on PLA was assessed both in bulk and porous composite foams. Composites with various PG content (0, 5, 10, and 20 wt %) were melt-extruded, and either compression-molded or foamed through supercritical CO(2). Dynamic mechanical analysis on the bulk composites showed that incorporating 20 wt % PG resulted in a significant increase in storage modulus. Aging studies in deionized water in terms of weight loss, pH change, and ion release inferred that the degradation was due to PG dissolution, and dependent on the amount of glass in the composites. Foaming was only possible for composites containing 5 and 10 wt % PG, as an increase in PG increased the foam densities; however, the level of porosity was maintained above 75%. PLA-T(g) in the foams was higher than those obtained for the bulk. Compressive moduli showed no significant reinforcement with glass incorporation in either expansion direction, indicating no anisotropy. Biocompatibility showed that proliferation of human fetal bone cells was more rapid for PLA compared to PLA-PG foams. However, the proliferation rate of PLA-PG foams were similar to those obtained for foams of PLA with either hydroxyapatite or beta-tricalcium phosphate.     

Preparation and compressive strength of alpha-tricalcium phosphate/gelatin gel composite cement.

A novel alpha-tricalcium phosphate (TCP) and gelatin gel composite cement was prepared, and the effects of gelatin content, liquid/powder ratio, setting time, and additives (rod-like hydroxyapatite and CaTiO3 particles) on the microstructure and compressive strength of the setting product were investigated. Addition of gelatin gel to alpha-TCP cement resulted in the formation of a porous solid possessing pores of 20-100 microm in diameter whose pore diameter increased with increasing gelatin gel content. The compressive strength of alpha-TCP cement after 1 week increased from 9.0 to 14.1 MPa with increasing gelatin gel content up to 5 wt % and thereafter decreased. The compressive strength of the cement containing 5 wt % gelatin gel increased with time up to 35 MPa after 1 month whereas without gelatin gel it was approximately 20 MPa. Dispersion of 5 wt % of rod-like hydroxyapatite and CaTiO3 powders with alpha-TCP cement containing 5 wt % gelatin gel increased the compressive strength after 1 week from 14.1 to 31.3 and 34.8 MPa, respectively.     

Whisker-reinforced dental core buildup composites: effect of filler level on mechanical properties

The strength and toughness of dental core buildup composites in large stress-bearing restorations need to be improved to reduce the incidence of fracture due to stresses from chewing and clenching. The aims of the present study were to develop novel core buildup composites reinforced with ceramic whiskers, to examine the effect of filler level, and to investigate the reinforcement mechanisms. Silica particles were fused onto the whiskers to facilitate silanization and to roughen the whisker surface for improved retention in the matrix. Filler level was varied from 0 to 70%. Flexural strength, compressive strength, and fracture toughness of the composites were measured. A nano-indentation system was used to measure elastic modulus and hardness. Scanning electron microscopy (SEM) was used to examine the fracture surfaces of specimens. Whisker filler level had significant effects on composite properties. The flexural strength in MPa (mean +/- SD; n = 6) increased from (95+/-15) for the unfilled resin to (193+/- 8) for the composite with 50% filler level, then slightly decreased to (176+/-12) at 70% filler level. The compressive strength increased from (149+/-33) for the unfilled resin to (282+/-48) at 10% filler level, and remained equivalent from 10 to 70% filler level. Both the modulus and hardness increased monotonically with filler level. In conclusion, silica particle-fused ceramic single-crystalline whiskers significantly reinforced dental core buildup composites. The reinforcement mechanisms appeared to be crack deflection and bridging by the whiskers. Whisker filler level had significant effects on the flexural strength, compressive strength, elastic modulus, and hardness of composites.     

The effects of fibre reinforcement and gold plating on the flexural and tensile strength of PGA/PLA copolymer materials in vitro

Changes in the flexural and/or tensile strength of plates and rods made of PGA/PLA copolymer submerged in water for a period of 4 wk were investigated. During this time, the effects of PGA/PLA fibre self-reinforcement, carbon fibre reinforcement and gold plating on tensile and/or flexural strength were examined. The results were used for evaluation of the surgical applications of PGA/PLA copolymer and its composites.The initial tensile strength of non-reinforced material was 45 Mpa and its flexural strength was 150 MPa: the flexural strength of self-reinforced material was 265 MPa. The tensile strength of carbon fibre reinforced material was 90 MPa and its flexural strength 190 MPa. The initial strengths of plated end unplated samples were the same but plating delayed the loss of the mechanical strength of carbon fibre reinforced samples.After 4 wk the flexural strength of self-reinforced and carbon fibre reinforced samples was decreased to the level of cancellous bone (10–20 MPa) while the flexural strength of non-reinforced samples was below that level (≲ 5 MPa).The results suggested that self-reinforced PGA/PLA composites may be used for the treatment of fractures in cancellous bone. Positive animal experiments led to clinical studies in vivo. These studies showed that there was no difference in outcome between 2 groups of patients with displaced fractures of the ankle treated with metallic implants or PGA/PLA fibre self-reinforced implants, respectively. Self-reinforced biodegradable implants are now used routinely in Helsinki University Central Hospital.     

Effect of reinforcement particle size on in vitro behavior of beta-tricalcium phosphate-reinforced high-density polyethylene: a novel orthopedic composite

Beta-tricalcium phosphate-reinforced high-density polyethylene (beta-TCP/HDPE) is a new biomaterial, which was made to simulate bone composition and study its capacity to act like bony tissues. This material was produced by replacing mineral component and collagen soft tissue of bone with beta-TCP and HDPE, respectively. The biocompatibility of composite samples with different volume fractions of TCP (20, 30, and 40 vol %) and two different particle sizes (80-100 and 120-140 mesh size) was examined in vitro using the osteoblast cell line G-292 by proliferation, alkaline phosphatase (ALP) production, and cell adhesion assays. Cell-material interaction on the surface of the composites was observed by scanning electron microscopy (SEM). The effect of beta-TCP particle size on behavior of the osteoblast cell line was compared between two groups of the composite samples containing smaller and larger reinforcement particle sizes as well as with those of a negative control. In general, results showed that the composite samples containing larger particles supported a higher rate of proliferation and ALP production by osteoblast cells after 3, 7, and 14 days of incubation compared to the composite samples with smaller particle size and control. Furthermore, more cells were attached to the surface of composite samples containing larger particle size when compared to the smaller particle size composites (p<0.05). This number was nearly equal with numbers adhered on negative control [tissue culture polystyrene (TPS)] and significantly higher in comparison with composite control [polyethylene (PE)] (p<0.05). Adhered cells presented a normal morphology by SEM and many of the cells were seen to be undergoing cell division. These findings indicate that beta-TCP/HDPE composites are biocompatible, nontoxic, and in some cases, act to stimulate proliferation of the cells, ALP production, and cell adhesion when compared to the control counterparts. Furthermore, beta-TCP/HDPE samples with larger reinforcement particle size were shown to possess better biological properties.     

Acrylic bone cements modified with beta-TCP particles encapsulated with poly(ethylene glycol)

Beta-tricalcium phosphate (beta-TCP) has been encapsulated with poly(ethylene glycol) (PEG) to improve the filler/cement interface, and it was later incorporated to a poly(methyl methacrylate) bone cement in order to obtain cements with improved stability in the long term. Size and size distribution of the agglomerates forming the initial powder was drastically changed after its dispersion in a PEG aqueous solution. Whereas the initial beta-TCP particles had a 584 microm average diameter, the treated particles (TCP-PEG) presented more than 60% of the particles in a range of 2-6 microm. The effect of adding the treated particles to an acrylic cement was evaluated in terms of curing parameters, in vitro behaviour and mechanical performance. The presence of the TCP-PEG particles did not affect either peak temperature or setting time, indicating a good homogeneity of polymerising mass in contrast to the effect observed with the plain beta-TCP particles, which gave rise to higher setting times. In vitro behaviour studies revealed hydration degree values of the modified cements comparable to that of PMMA cements. Early stages of water uptake was Fickian in nature for all the experimental formulations indicating that the water absorption followed a diffusion controlled mechanism. After 3 months of storage in SBF the experimental formulations presented values of compressive strength in the range 76-78 MPa, higher than the minimum required by ISO 5833 (70 MPa) and those of tensile strength in the range 42-48 MPa, higher than the minimum reported for commercial formulations (30 MPa), but no significant differences in the strengths and elastic modulus were observed with the treatment of the filler particles. This observation was confirmed by ESEM analysis of the tensile fracture surfaces, which revealed a rather good cohesion between the bioceramic particles with some gaps around them, independently of the type of particles. The themogravimetric analysis of dry and wet specimens showed a higher dissolution rate of the plain beta-TCP particles in comparison to the encapsulated ones, indicating that the PEG adsorbed on the surface of the TCP particles could be a way to control the resorbability of the bioceramic component.     

Bioactive composite for keratoprosthesis skirt

In this study, the fabrication and properties of a synthetic keratoprosthesis skirt for use in osteo-odonto-keratoprosthesis (OOKP) surgery are discussed. In the search for a new material concept, bioactive glass and polymethyl methacrylate (PMMA)-based composites were prepared. Three different bioactive glasses (i.e. 45S5, S53P4 and 1-98) and one slowly resorbing glass, FL107, with two different forms (i.e. particles and porous glass structures) were employed in the fabrication of specimens. In in vitro studies, the dissolution behaviour in simulated aqueous humour, compressive properties, and pore formation of the composites were investigated. According to the results, FL107 dissolved very slowly (2.4% of the initial glass content in three weeks); thus, the pore formation of the FL107 composite was also observed to be restricted. The dissolution rates of the bioactive glass-PMMA composites were greater (12%-17%). These faster dissolving bioactive glass particles caused some porosity on the outermost surfaces of the composite. The slight surface porosity was also confirmed by a decrease in compressive properties. During six weeks' in vitro dissolution, the compressive strength of the test specimens containing particles decreased by 22% compared to values in dry conditions (90-107?MPa). These results indicate that the bioactive composites could be stable synthetic candidates for a keratoprosthesis skirt in the treatment of severely damaged or diseased cornea.     

Crosslinking characteristics of an injectable poly(propylene fumarate)/beta-tricalcium phosphate paste and mechanical properties of the crosslinked composite for use as a biodegradable bone cement.

We investigated the crosslinking characteristics of an injectable composite paste of poly(propylene fumarate) (PPF), N-vinyl pyrrolidinone (N-VP), benzoyl peroxide (BP), sodium chloride (NaCl), and beta-tricalcium phosphate (beta-TCP). We examined the effects of PPF molecular weight, N-VP/PPF ratio, BP/PPF ratio, and NaCl weight percent on the crosslinking temperature, heat release upon crosslinking, gel point, and the composite compressive strength and modulus. The maximum crosslinking temperature did not vary widely among formulations, with the absolute values falling between 38 degrees and 48 degrees C, which was much lower than that of 94 degrees C for poly(methyl methacrylate) bone cement controls tested under the same conditions. The total heat released upon crosslinking was decreased by an increase in PPF molecular weight and a decrease in N-VP/PPF ratio. The gel point was affected strongly by the PPF molecular weight, with a decrease in PPF molecular weight more rapidly leading to a gel point. An increase in initiator concentration had the same effect to a lesser degree. The time frame for curing was varied from 1-121 min, allowing the composite to be tailored to specific applications. The compressive strength and compressive modulus values increased with decreasing N-VP/PPF, increasing NaCl content, and increasing BP/PPF ratio. For all formulations, the compressive strength values fell between 1 and 12 MPa, and the compressive modulus values fell between 23 and 265 MPa. These data suggest that injectable PPF/beta-TCP pastes can be prepared with handling characteristics appropriate for clinical orthopedic applications and that the mechanical properties of the cured composites are suitable for trabecular bone replacement.     

Investigation of crystallinity, molecular weight change, and mechanical properties of PLA/PBG bioresorbable composites as bone fracture fixation plates

In this study, bioresorbable phosphate-based glass (PBG) fibers were used to reinforce poly(lactic acid) (PLA). PLA/PBG random mat (RM) and unidirectional (UD) composites were prepared via laminate stacking and compression molding with fiber volume fractions between 14% and 18%, respectively. The percentage of water uptake and mass change for UD composites were higher than the RM composites and unreinforced PLA. The crystallinity of the unreinforced PLA and composites increased during the first few weeks and then a plateau was seen. XRD analysis detected a crystalline peak at 16.6° in the unreinforced PLA sample after 42 days of immersion in phosphate buffer solution (PBS) at 37°C. The initial flexural strength of RM and UD composites was ～106 and ～115?MPa, whilst the modulus was ～6.7 and ～9?GPa, respectively. After 95 days immersion in PBS at 37°C, the strength decreased to 48 and 52?MPa, respectively as a result of fiber-matrix interface degradation. There was no significant change in flexural modulus for the UD composites, whilst the RM composites saw a decrease of ～45%. The molecular weight of PLA alone, RM, and UD composites decreased linearly with time during degradation due to chain scission of the matrix. Short fiber pull-out was seen from SEM micrographs for both RM and UD composites.     

Improved injectability and in vitro degradation of a calcium phosphate cement containing poly(lactide-co-glycolide) microspheres

An injectable calcium phosphate cement (CPC) containing 30 wt.% poly(lactide-co-glycolide) (PLGA) microspheres was developed in the present study. Sodium citrate solution was used as the cement liquid phase. The effects of sodium citrate concentration on the injectability, rheological properties, mechanical strength and self-setting properties of CPC containing PLGA microspheres were systematically investigated. The in vitro degradation behavior of the composite during immersion in phosphate buffer solution was also studied. With an increase in sodium citrate concentration, the viscosity and yield stress of the paste were reduced, thereby improving the injectability. At a sodium citrate concentration of 15%, the injectability of the paste reached 95%. The compressive strength of the specimen was also enhanced by the addition of sodium citrate. The specimens had a compressive strength of 32.24+/-2.72 MPa at 15% sodium citrate concentration, compared to 22.15+/-3.60 MPa for the specimen without sodium citrate. The in vitro degradation results demonstrate that incorporated PLGA microspheres can provide the required high strength to CPC in the early stage, which would gradually degrade to create macropores for bone ingrowth. In conclusion, an in situ macropore-generable CPC exhibited excellent injectability and high early strength, and should be a promising material for bone repair and bone reconstruction.     

Strong and bioactive composites containing nano-silica-fused whiskers for bone repair

Self-hardening calcium phosphate cement (CPC) sets to form hydroxyapatite with high osteoconductivity, but its brittleness and low strength limit its use to only non-stress bearing locations. Previous studies developed bioactive composites containing hydroxyapatite fillers in Bis-GMA-based composites for bone repair applications, and they possessed higher strength values. However, these strengths were still lower than the strength of cortical bone. The aim of this study was to develop strong and bioactive composites by combining CPC fillers with nano-silica-fused whiskers in a resin matrix, and to characterize the mechanical properties and cell response. Silica particles were fused to silicon carbide whiskers to roughen the whisker surfaces for enhanced retention in the matrix. Mass ratios of whisker:CPC of 1:2, 1:1 and 2:1 were incorporated into a Bis-GMA-based resin and hardened by two-part chemical curing. Composite with only CPC fillers without whiskers served as a control. The specimens were tested using three-point flexure and nano-indentation. Composites with whisker:CPC ratios of 2:1 and 1:1 had flexural strengths (mean+/-SD; n=9) of (164+/-14) MPa and (139+/-22) MPa, respectively, nearly 3 times higher than (54+/-5) MPa of the control containing only CPC fillers (p<0.05). The strength of the new whisker-CPC composites was 3 times higher than the strength achieved in previous studies for conventional bioactive composites containing hydroxyapatite particles in Bis-GMA-based resins. The mechanical properties of the CPC-whisker composites nearly matched those of cortical bone and trabecular bone. Osteoblast-like cell adhesion, proliferation and viability were equivalent on the non-whisker control containing only CPC fillers, on the whisker composite at whisker:CPC of 1:1, and on the tissue culture polystyrene control, suggesting that the new CPC-whisker composite was non-cytotoxic.     

Novel injectable and in situ curable glycolide/lactide based biodegradable polymer resins and composites

Novel in situ polymerizable liquid three-arm biodegradable oligomeric polyesters based upon glycolic acid (GA), L-lactic acid (LLA), and their copolymers are synthesized and characterized. Injectable and in situ curable polymer neat resins and their composites formulated with bioabsorbable beta-tricalcium phosphate are prepared at room temperature using photo- and redox-initiation systems, respectively. The cured neat resins show the initial compressive yield strength (YCS, MPa), modulus (M, MPa), ultimate compressive strength (UCS, MPa), and toughness (T, kN mm), ranging from 4.0 to 20.1, 201.5 to 730.2, 82.7 to 310.5, and 1.02 to 3.93. The cured composites show the initial YCS, M, UCS and T, ranging from 27.7 to 56.4, 1440 to 4870, 81.6 to 158.9, and 0.94 to 1.97. Increasing GA/LLA ratio increases all the initial compressive strengths of both neat resins and composites. Increasing filler content increases YCS and M but decreases UCS and T. A diametral tensile strength test shows the same trend as a compressive strength test. There seems to be an optimal flexural strength for the composite at the filler content around 43%. An increasing molar ratio increases curing time but decreases the degree of conversion (DC). An increasing filler content increases curing time but decreases exotherm and DC. During the course of degradation, all the materials show a burst degradation behavior within 24 h, followed by an increase in CS. The poly(glycolic acid) neat resin completely loses its strength at around Day 45. The composites completely lose their strengths at different time intervals, depending on their molar ratio and filler content. The degradation rate is found to be molar ratio and filler-content dependent.     

Porous, resorbable, fiber-reinforced scaffolds tailored for articular cartilage repair.

Porous 75:25 poly(D,L-lactide-co-glycolide) scaffolds reinforced with polyglycolide fibers were prepared with mechanical properties tailored for use in articular cartilage repair. Compression testing was performed to investigate the influence of physiological testing conditions, manufacturing method, anisotropic properties due to predominant fiber orientation, amounts of fiber reinforcement (0 to 20 wt, %), and viscoelasticity via a range of strain rates. Using the same testing modality, the mechanical properties of the scaffolds were compared with pig and goat articular cartilage. Results showed that mechanical properties of the scaffolds under physiological conditions (aqueous, 37 degrees C) were much lower than when tested under ambient conditions. The manufacturing method and anisotropy of the scaffolds significantly influenced the mechanical properties. The compressive modulus and yield strength proportionally increased with increasing fiber reinforcement up to 20%. From 0.01 to 10 mm/mm/min strain rate, the compressive modulus increased in a logarithmic fashion, and the yield strength increased in a semi-log fashion. The compressive modulus of the non-reinforced scaffolds was most similar to the pig and goat articular cartilage when compared using similar testing conditions and modality, but the improvement in yield strength using the stiffer scaffolds with fiber reinforcement could provide needed structural support for in vivo loads.     

Promotion of bone formation using highly pure porous beta-TCP combined with bone marrow-derived osteoprogenitor cells

Beta-tricalcium phosphate (TCP) exhibits rapid degradation and weak mechanical properties, which has limited its application as bone graft substitutes, though it has good biocompatibility and osteoconductivity. We hypothesized that a composite of highly pure porous beta-TCP and bone marrow-derived osteoprogenitor cells (BMO) could improve bone formation, and slow down the degradation of beta-TCP. A highly pure porous beta-TCP with 75% porosity was fabricated. The pores averaged 200-400 microm in diameter, with interconnecting paths 100-200 microm. Blocks of beta-TCP 5 mm3 were combined with BMO, and incubated 2 weeks with (+) or without (-) osteogenic medium. They were then implanted into subcutaneous sites of syngeneic rats for 24 weeks. These composites were harvested at different time points. The alkaline phosphatase activity and bone osteocalcin content of the composites (+) were much higher than corresponding values in the composites (-) of the control group (p<0.01). Light microscopy revealed mature bone and lots of blood vessels only in the TCP/BMO composite (+). The amount of newly formed bone increased until week 24. Slow resorptive activity could be found. The mechanical parameters of the composites were much improved over those of dry beta-TCP blocks. These results showed that tissue engineering treatment on incubating the composites of beta-TCP and BMO cells in osteogenic medium results in a good osteogenic activity.     

Transformations in CDHA/OCP/beta-TCP scaffold during ageing in simulated body fluid at 36.5 degrees C

The transformations that took place in a scaffold composed of CDHA/OCP/beta-TCP by ageing in SBF at 36.5 degrees during 14 days were studied. A carbonated-apatite layer was formed during immersion in SBF on the surface of the scaffold and part of the OCP present in the inner core of the material was also transformed into apatite. The precipitated apatite layer exhibited the typical globular morphology characteristic of bioactive materials. The content of CDHA increased from 14 to 29 wt % at the expense of the content of OCP that decreased from 39 to 29 wt %. beta-TCP content dropped slightly from 47 to 42 wt %. Total porosity (from 56.1% +/- 0.6% to 62.4% +/- 0.5%) and real density (from 2.58 +/- 0.01 to 2.79 +/- 0.01 g/cm(3)) increased, and diametral tensile (from 2.1 +/- 0.3 to 0.9 +/- 0.1 MPa) and compressive strengths (from 8.5 +/- 1.0 to 6.8 +/- 0.6 MPa) decreased during ageing. The in vitro results showed that the scaffold composed of CDHA, OCP, and beta-TCP is bioactive and partially resorbable. It seems to be suitable for in situ bone regeneration procedures.