Journal of biomedical materials research最新文献

Bioglass, in bulk form, has been used to bond to the body's hard and soft tissues in many surgical and dental applications over the past 18 years. There is also a large potential use of Bioglass, in powder or paste from, to fill irregular-shaped bony defects caused by local or systemic disease, congenital malformations, or trauma in the fields of otolaryngology and dental sciences. A quality assurance test procedure to analyze powdered Bioglass to guarantee that the bioactivity of the glass has been maintained during manufacturing was developed. Herein states the quality assurance test procedure, test variables, and test criteria to assure the bioactivity of Bioglass powders made from known bioactive bulk Bioglass samples. Also described herein is the path taken to develop the test procedure and test criteria and experiments performed to study the test variables.

Tensile properties and pressure-diameter-axial force relations of a newly developed small-diameter arterial graft were determined and compared to those of commercially available grafts and natural arteries. The material was synthesized from 4,4'-diphenylmethane diisocyanate, polytetramethylene glycol, and polyethylene oxide, chain-extended with ethylene glycol. Porous conduits (3-mm internal diameter) were fabricated of this material by means of a phase separation technique, and their outer surfaces were covered with woolly polyester net in order to prevent excessive dilation. Mechanical tests indicated that the polyurethane graft has distensibility and strength similar to that of natural arteries, and has been proved to be useful for the arterial reconstruction, particularly for the replacement of small-diameter blood vessels.

Two sets of electrode arrays made of either 25- or 50-microns-diameter Teflon-insulated platinum-iridium wire and Teflon have been developed for chronic intracortical electrical stimulation. Cortical histological studies were performed following acute and chronic implantation in cats. While some neural damage resulted from the implantations of either array configuration, a unique set of problems was associated with each diameter wire. Arrays with 50-microns electrodes and lead wires tended to maintain interelectrode spacing upon implantation, but the percutaneous leads retained residual stress which made array implantation difficult. Arrays with 25-microns electrodes and lead wires suffered from changes in interelectrode spacing upon implantation, but were much easier to manipulate during surgery. Both array configurations demonstrated some movement after implantation. It is concluded that a chronic intracortical stimulating electrode array of this geometry should have the following properties: 1) the penetrating electrodes and supporting substrate must be stiff (to maintain interelectrode spacings upon implantation), and 2) the percutaneous leads must be extremely flexible (to avoid array movement after implantation).

To develop better blood compatible polymer for long-term biomedical applications, poly(ethylene oxide) (PEO) grafted and/or heparin immobilized polyurethanes (PUs) were made by novel surface modification. Their blood compatibilities were investigated using in vitro platelet adhesion test, APTT, PT, immobilized heparin bioactivity measurement, and ex vivo rabbit A-A shunt test. In platelet adhesion tests, PEO grafted PU surfaces, compared to PU control, displayed very little platelet adhesion and activation, and this effect was more significant as the molecular weight of PEO increased from 200 to 2000. Also, the degree of platelet adhesion was lower in the heparinized PU surfaces than that of PU control. The immobilized heparin showed a greater effect on intrinsic blood coagulation factors than on extrinsic ones, whereas the PU-PEO surface was independent of blood coagulation factors. Lowering both in vitro platelet adhesion and activation led to a prolongation in the ex vivo occlusion time. In particular, the heparinized PU-PEO surfaces displayed enhanced blood compatibility due to the synergistic effects of PEO and heparin.

Alumina ceramic has good biocompatibility, high mechanical strength, and excellent lubrication properties. However, it is bioinert and does not bond with bone tissue. Therefore, to promote mechanical bonding, we have developed an alumina ceramic material coated with alumina ceramic beads using identical alumina ceramic binder. In this study, we evaluated the bone bonding capability of this material under load-bearing conditions along with its mechanical properties. The test pieces with or without bead-coating were implanted into the load-bearing portions of the medial and lateral femoral condyles of adult mongrel dogs. The dogs were euthanized 4, 8, and 24 weeks after implantation, and the pull-out test and histological examination were performed. The uncoated implants showed signs of loosening similar to those observed clinically. In contrast, the bonding strength of the bead-coated implants was significantly greater than that of the uncoated implants and increased with implantation time. This increase in strength differs from the results obtained in the non-load-bearing experiments, in which a plateau was seen relatively early after implantation. Results of histological examination suggested that this increase was caused by thickening of ingrown trabeculae, which could be observed as early as 4 weeks after implantation, at the bone-implant interface. In addition, the mechanical properties of the bead-coated alumina ceramic were comparable to those of grooved alumina ceramic which has been used clinically. These results indicate the possibility for clinical application of the bead-coated alumina ceramic.

Bone attachment to two classes of hydroxyapatite (HA) coated polymers was evaluated mechanically and histologically. Particulate HA was molded into the surface of thermoplastic implants and cast into the surface of thermoset implants. Coated and uncoated implants of both types were implanted in the distal femurs of rabbits for four and twelve weeks. After sacrifice, the bone/implant interface was evaluated mechanically via a push-out test with a servohydraulic test system. Paired statistical analysis revealed significantly greater shear strengths for coated vs. uncoated implants for both polymer systems at both time periods. Mixed mode of failure occurred with particle removal from the polymer surface and from the bone. One animal at each time period was saved for histology. Histology at both time periods indicated direct bone apposition to the HA coating as compared to a fibrous encapsulation about the uncoated implants. This was confirmed with backscatter scanning electron microscopy and scanning acoustic microscopy. Hydroxyapatite coatings significantly improve the bond strength between polymers and bone by allowing direct bone apposition and some mechanical interlocking with the bone.

Recent evidence suggests that bone phosphate exists almost entirely as hydroxyapatite (HA). The relative deficiency of calcium and presence of substantial HPO2-4 in bone phosphate indicates modification of the ideal HA structure, however. An inability to resolve closely spaced lines in fine grained materials, coupled with the limited periodicity of the thin mineral crystals of bone have prevented definitive characterization of the structure of bone mineral using standard X-ray diffraction (XRD) techniques. We have applied computer deconvolution XRD techniques to aid in the resolution of component overlapped profiles from bone, synthetic hydroxyapatite (HA) and mixtures of bone and synthetic HA resulting from implantation studies. In the course of this resolution process separate profiles were resolved from the (002) profile of bone derived HA. The ratio of integrated intensities of these profiles to the intensity of the profile of synthetic HA appears to provide an approximate measure of the ratio of bone to synthetic HA in a given sample. The finding of shoulders on the (002) peak of bone provides the basis for resolution into separate profiles. The asymmetry of these shoulders in mature bone cannot be attributed to crystallinity, particle size, or computer artifact. The same finding has been previously reported in hydrolyzed, deproteinated bone. Further work will be needed to resolve the question of whether the structural heterogeneity implied by profile geometry is the result of multiple HA phases, surface layer structure involving hydrolysis and calcium absences, or some other factor.