| Ultrahigh molecular weight polyethylene (UHMWPE) has been used in orthopedics as a bearing material in artificial joints because of notable properties such as chemical inertness, lubricity, impact resistance, and abrasion resistance. However, wear damages of the UHMWPE have been one of the factors limiting implant longevity. That is, the resultant wear of polyethylene bearing purportedly produces billions of wear particles with submicrometer size that cause adverse pathological reaction in the surrounding tissues leading to osteolysis and joint loosening. Therefore, to improve the wear resistance of the UHMWPE material used for artificial joint is essential.UHMWPE solution was prepared by decalin and paraffin. Gelation mechanism was investigated by gelation time, small angle laser light scattering (SALS) and Wide-angle X-ray diffraction (WAXD). When paraffin as the solvent, paraffin maybe becomes the role of crosslinking point for the UHMWPE moleculars. So the gelation temperature (106～108℃) and spinodal temperature (109℃) of UHMWPE solution prepared by paraffin are much higher than prepared by decalian (83℃and88℃). HV SALS and Polarized microscope (POM) were used to observe the structure of the UHMWPE solution. When the UHMWPE solution prepared by decalin quenched at65～75℃, X-type pattern and continuous structure can be seen, but, for paraffin as the solvent, even at room temperature only circle-type pattern and very small continuous structure can be seen. The Small Angle X-ray Scattering (SAXS) from the both films, however, showed the similar profiles indicating assemblies of crystal lamellae assuring ultradrawing.UHMWPE/HA composite solution was prepared by decalin and paraffin. Viscosity and gelation time were tested, the results shows that the viscosity and gelation time increase with the content of HA when decalin as the solvent, but in paraffin is inverse. When the content of HA reached31.5vol%at83℃, gelation time of UHMWPE/HA solution prepared by decalin shorten from3250s to2700s. However when paraffin as the solvent, the galation time prolonged from1200s to1980s. Scanning electron microscope (SEM) was used to observe the morphology of UHMWPE/HA composite, which indicates HA can be dispersed more uniform when paraffin as the solvent compared with decalin.UHMWPE/Hydroxyapatite (HA) composites which were prepared by the solution method and molded in the narrow temperature range145-153℃. WAXD intensity from UHMWPE film revealed high preferential orientation of the (110) plane with the highest atom density of the PE crystal unit. Attenuated total reflection (ATR) spectra from pristine UHMWPE films and UHMWPE/HA composites revealed that the existing probability of HA agglomerates on the surface layer (at ca.1.4μm depth) of the specimen molded at150℃was much lower than that molded at180℃, and the crystallinity of the thin layer was slightly higher. Furthermore, SEM observation and Energy Dispersive Spectrometer (EDS) spectra revealed that most of the HA agglomerates were covered by UHMWPE in the composites molded at150℃, UHMWPE chains under gelation were crystallized on the surface of HA agglomerates, but the partially flowed off UHMWPE chains from the surface of UHMWPE/HA agglomerates by molding at180℃were not recrystallized on the surface of HA agglomerates. The complex tensile moduli E*, complex shear moduli G*, and complex Poison’s ratio v*were hardly affected by the molding temperatures,150or180℃. Poisson’s ratio for the individual UHMWPE/HA composite and the gradient composite provided that the value became smaller with increasing HA content and tended to be negative beyond23.5vol%HA content, indicating an increase in voids in the spongy-like texture of the composites. Because of the descent degree of a number of voids in sponge-like tissues, surface fraction was smaller with increasing HA contents under high normal load. Of course, the frictional coefficient, wear rate, and bending properties prepared by solution were much superior to those prepared by a kneading method. A series of results suggested that by controlling molding temperature it turned out that the gradient composite prepared by the solution method provides great merits as an acceptable cup of bearing material in an artificial joint.Poly (vinyl alcohol)(PVA) Hydrogels have chemical stability, good biocompatibility, and easy to mold, also with similar structure and tribological properties of biological to natural articular cartilage. However, PVA material has low strength when as the acetabular materials, and difficult to be fixed. Based on this, to prepare a kind of gradient material combining UHMWPE with PVA has low friction coefficient and easy to be fixed.Laponite as a template was used to improve the dispersibility of HA in water. NaCl as the porogen was adopoted to prepare porous UHMWPE/HA composite by the solution method. Its porosity larger than50%and has uniform pore distribution. HA was introduced to reinforce the interfacial bonding effect between the LBL film and the PVA filling porous UHMWPE/HA composite, which has very low friction coefficient (0.017) under1200N near to the friction coefficient of natural articular cartilage. So the results indicated this kind of gradient material has the prospects to be used in for acetabular prosthesis in the future. |
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