Bone Replacement Applications Research Articles

Fabrication of Bioactive Glass-Ceramics by Selective Laser Sintering

The feasibility of processing glass-ceramics using the layer manufacturing technique, selective laser sintering (SLS), to produce parts with suitable biological and mechanical properties for use in bone replacement applications, has been investigated. Glass-ceramics derived from glasses based on several different systems have been considered. Initial experiments using an apatite-mullite glass-ceramic (4.5SiO2⋅3Al203⋅1.6P2O5⋅3CaO⋅2CaF2) demonstrated the ability to process glass-ceramic materials using this technique, creating parts with a strength similar to that of cancellous bone, and a porous structure that was shown in vivo to be suitable for the ingrowth of bone. Concerns over the inability of the apatite-mullite material to form an apatite layer on its surface when soaked in a simulated body fluid (SBF) has led to the development of Al2O3-free glasses based on the systems (50-x)CaO⋅45SiO2⋅5P2O5⋅xCaF2 and (48-x)CaO⋅45SiO2⋅5P2O5⋅2CaF2⋅xNa2O. These materials have demonstrated good in vitro bioactivity, and therefore have good potential as candidates for processing by an indirect SLS method for the production of custom-made bone implants.

Indirect selective laser sintering of an apatite-mullite glass-ceramic for potential use in bone replacement applications

The feasibility of using indirect selective laser sintering (SLS) to produce parts from glass-ceramic materials for bone replacement applications has been investigated. A castable glass based on the system SiO2 x Al2O3 x P2O5 x CaO x CaF2 that crystallizes to a glass-ceramic with apatite and mullite phases was produced, blended with an acrylic binder, and processed by SLS. Green parts with good structural integrity were produced using a wide range of processing conditions, allowing both monolayer and multilayer components to be constructed. Following SLS the parts were post-processed to remove the binder and to crystallize fully the material, evolving the apatite and mullite phases. The parts were heated to 1200 degrees C using a number of different time-temperature profiles, following which the processed material was analysed by differential thermal analysis, X-ray diffraction, and scanning electron microscopy, and tested for flexural strength. An increase in strength was achieved by infiltrating the brown parts with a resorbable phosphate glass, although this altered the crystal phases present in the material.

Injection molding of a starch/EVOH blend aimed as an alternative biomaterial for temporary applications

Biodegradable polymers show great potential to be used as materials for temporary implants and bone replacement applications in orthopedics. However, its use in high load-bearing applications will depend on the successful development of biode- gradable implants with a mechanical performance matching that of human bone. This article describes the optimization of the injection molding process of an alternative biodegradable starch-based polymer aimed at biomedical applications. A blend of starch with a copolymer of ethylene-vinyl alcohol (SEVA-C) was studied. Both conventional injection molding and shear controlled orientation (SCORIM) were optimized with the support of design of experiments and analysis of variance techniques. The mechanical characterization was performed by tensile testing. The structure developed within the moldings was assessed by wide-angle X-ray diffraction and differential scanning calo- rimetry. Increases up to 30% in the tangent modulus and 20% in the ultimate tensile strength compared with conventional molding were achieved with the application of SCORIM. The holding pressure and the frequency of the shear applied have the strongest influence on the morphology development and consequently on the mechan- ical performance. The solidification of SEVA-C at high cavity pressures enhances stiffness for long durations of the shearing stage in SCORIM. However, the effect of viscous heating of SEVA-C is important and ought to be considered. A decrease of the material phase miscibility in SEVA-C occurs as result of the shear fields imposed. The microstructure evaluation suggests that the mechanical properties enhancement in SCORIM molded SEVA-C is attributable to preferred orientation developed during processing. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1303-1315, 2000

Treatments to induce the nucleation and growth of apatite-like layers on polymeric surfaces and foams.

In this work, a bioactive glass is used as a percusor of calcium-phosphate (Ca-P) film deposition onto several polymer-based materials. Both bioinert (high molecular weight polyethylene, HMWPE), and biodegradable (corn starch-based blends, SEVA-C) polymers, unreinforced or reinforced with hydroxylapatite (HA), were coated by the very simple proposed route. Also polyurethane (PU) foams, with an open-cell structure, were mineralized by the proposed method. In fact, it was possible to induce the growth of the Ca-P films not only at the surface, but also in the bulk of the PU foam. These cellular materials are intended for cancellous bone replacement applications. The morphology of the formed films was strongly dependent on the used substrate, its polar character, and on the presence of HA in its composition, as observed by SEM. Nevertheless, a well defined needly like structure was observed in all samples at high magnifications. The Ca:P ratios of the films were between 1.5 and 1.7, i.e. in the range of tricalcium phosphate-hydroxylapatite. Raman spectroscopy and thin-film x-ray diffraction (XRD) evidenced the formation of mostly amorphous calcium-phosphate films. After scraping the coating from the polymer surface and heat-treating the resulting powder at 1000 degrees C for 1 h, HA and beta-tricalcium phosphate (TCP) typical peaks were found on XRD patterns.

Abundant postoperative calcification of an elastomer: matrix calcium phosphate-polymer composite for bone reconstruction

In this experiment the behaviour of an 80/20 PEO/PBT copolymer in bone defeets was assessed. Porous cylinders were press-fit inserted into the diaphyseal femur of goats and evaluated by light and electron microscopy and X-ray microanalysis. The most important finding in this study was that almost complete calcification throughout the implant was displayed after 26 weeks. The 80/20 PEO/PBT copolymer did not contain calcium and phosphorus prior to implantation, however, it apparently has the ability to take up considerable amounts of calcium and phosphate postoperatively, resulting in a calcium phosphate-polymer composite. As a consequence of the high calcification rate of 80/20 cylinders, bone-bonding (a continuum between calcification of the material surface and bone) was encountered as early as 3 weeks after implantation. Union of the 5 mm defect was observed at 6 weeks and ingrowth was frequently centripetal. After 26 weeks bone tissue occupied most of the pore area and was often seen in continuity with the calcified polymer. We conclude that an elastomeric matrix that is capable of abundant postoperative calcification behaves favourably with respect to the repair of bone defects. Porous 80/20 PEO/PBT copolymer is, therefore, a promising alternative for bone-replacement applications.