The wear powder produced by friction of an artificial joint affects a surrounding tissue, and causes a re-operation accompanied by pain. Thus, the wear properties of the material used in an artificial joint markedly influences the performance and life of an artificial joint. In the ISO standard, the 25% vol% serum solution is using as the lubricant simulated living body environment. The ware property with various materials was compared in 25% vol% serum solution. It was found that the wear properties for materials using clinically is more excellent.

Tungsten short fiber reinforced Ti-6Al-4V alloy has been investigated in terms of its tensile properties, corrosion resistance and cytocompatibility. This composite material was fabricated by a hot isostatic pressing process. The room temperature tensile strength and the 0.2% proof stress were very high, approximately 1300 MPa and 1200 MPa, respectively. These strengths are excellent compared to those of the existing biomaterial of titanium-base. The cytocompatibility of this composite material was evaluated using the anodic polarization test and the cytocompatibility test to clarify the possibility of its application as a structural biomaterial. Anodic polarization tests in Eagle's minimum essential medium and in I mass% lactic acid were carried out to investigate the corrosion resistance of the composite material in vivo. The current density at the entrance to the passive region of the composite material tended to increase more than that of Ti-6Al-4V alloy. However, the passive region was retained at a potential of about 2 V, which is sufficiently high compared to the potential in vivo. In addition, the cytocompatibility was evaluated by investigating the relative growth ratio of fibroblast L929 cells after four days incubation on the test material. The relative growth ratio is obtained as follows: number of cells on the test material/number of cells on the reference material (control). The relative growth ratio of the composite material in making Ti-6Al-4V alloy into a control was 0.9032. According to the result of ICP-MS analysis, the concentration of tungsten in the medium after four days of incubation on the composite material was high compared to that of titanium, aluminum and vanadium.

A new Ti-15Zr-4Nb4Ta alloy without V was implanted in rat tibiae for 6-48 weeks. The new bone formation surrounding the Ti implant in bone marrow, surface analysis of the Ti alloy after implantation, and metal concentrations in dried bone tissue containing new bone were investigated. New bone was well formed around the Ti-15Zr-4Nb-4Ta alloy implanted in bone marrow. The mean thickness of the new bone increased up to 24 weeks after implantation, and changes in the mean thickness thereafter, up to 48 weeks. were very small. The number of corrosion pits observed in the Ti-6Al-4V extra low interstitial (ELI) alloy surface tended to be slightly more than that of the Ti-5Zr-4Nb-4Ta alloy implant. The concentrations of metal elements in the bone tissue containing the new bone tended to increase slightly more than in bones without the implant.

The corrosion resistance of dental alloys was investigated by taking anodic polarization measurements in 1 mass%-lactic acid, artificial saliva, and cell-culture medium solutions. The role of alloying elements in the passive film that formed on the dental alloys by the anodic polarization was examined using X-ray photoelectron spectroscopy. The quantity of metals released from the dental alloy into the 1% lactic acid solution at each anodic potential was compared. In the anodic polarization curves fur the Au and Au-Ag-Pd alloys, the current density tended to decrease with higher Au content. In the Ag alloy, the current density sharply increased in the 1 mass%-lactic acid solution. On the other hand, the passivity zone was slightly seen in the artificial saliva and Eagle's medium solutions. Amalgam had a Low open-circuit potential, and a passivation peak was seen. The peaks of the Au4f and Ag3d orbital were high in the surface of the passive film formed oil the Au and Au-Ag-Pd alloys by anodic polarization in the artificial saliva solution. SnO2 and In2O3 peaks were observed in the passive film formed on the Ag alloy. SnO2 and CuO peaks were seen in the passive film on amalgam surface. In the Au and Au-Ag-Pd alloys, Cu was released most in the low potential region less than 1.0 or 0.5 V us. SCE, respectively. For the Ag alloys, Zn release was most, and Ag, Sn and In were also released. In amalgam, Sn release increased with higher anodic potentials. Cu release also increased at potentials over 0 V. Ag and Hg release increased from potentials over 0.5 V. Considering that the electrode potential measured in the pseudo-oral environment is a maximum of 0.2 V, it is important to examine the effect of Cu and Ag releases far the Au and die Au-Ag-Pd alloys, Zn release for the Ag alloy, and Sn and Cu releases for amalgam.

The new metal matrix composite which is reinforced Ti-6Al-4V alloy with tungsten short fiber was developed. This composite material was made by powder metallurgy. The composite material has the high tensile strength characteristics and the high biocompatibility matrix. Especially the tensile strength of this composite material is very high with about 1300MPa. This is more excellent than the existing biomaterial of the titanium base. Then, the fundamental biocompatibility of this composite material was evaluated to obtain information of whether it can be applicable as a biomaterial. The corrosion resistance of this composite material was evaluated by anodic polarization test in Eagle's minimum essential medium and 1 mass% lactic acid. The current density of entering the passive region of the composite material was higher than that of the Ti-6Al-4V alloy for matrix. But the passive region of the composite material was retained to the potential region of about 2 V, and this retained potential is enough high as compared to die potential in vivo.

Ti alloy disks were separately worn with pins of the same alloy or apatite ceramics in Eagle's medium. Wear powders sterilized in either a heating oven or ethanol were separately added to culture media. The effect of the Ti wear powder sterilized in a heating oven on cell viability was smaller than that of powder sterilized in ethanol. The effect of wear powder generated with the apatite ceramic pin on cell viability was also larger than that generated by the alloy pin. The relative growth ratios of L929 and MC3T3-E1cells for Ti-6Al-4V alloy wear powder sterilized in ethanol decreased from a smaller amount than those of the Ti-15Zr-4Nb-4Ta and Ti-15Sn-4Nb-2Ta alloy wear powders. The concentration of V released from the wear powder into the medium increased moderately with increasing wear powder. This effect was approximately in agreement with the results estimated from medium extraction with high-purity V particles. For the Ti-15Zr-4Nb-4Ta and Ti-15Sn-4Nb-2Ta alloy wear powders sterilized in ethanol, the maximum Ti concentration released from the wear powder was approximately in agreement with the results obtained with high-purity Ti particles. On the contrary, for Zr, Nb, Ta and Sn, the maximum metal concentrations released from the wear powders were lower than those obtained with high-purity metal particles.

The trace amounts of Ti, Al and V in physiological saline solution was simultaneously determined by Inductively Coupled Plasma-Mass Spectrometry. The Al concentration was high in pyrex standard flasks as compared with those of perfluoro alkoxy alkane (PFA) and poly -4-methylpentene-1 (PMP) standard flasks. Also, Ti and V concentrations increased with small amounts of sulfuric acid and hydrochloric acid solutions, while small amounts of nitric acid solution exhibited a negligible effect on the determination of Ti, Al and V concentrations. The Ti determination measured with the isotopes of Ti-46, Ti-47, and Ti-48 in, the Eagle's medium was high as compared with those with the isotopes of Ti-49 and Ti-50. The change in intensity with 0.5 mass ppb indium as the internal standard was small in Eagle's medium and alpha-medium solutions. The intensity of 0.5 mass ppb cobalt internal standard increased With increasing alpha-medium solution but remained the same for the Eagle's medium solution. The simultaneous determination of Ti, Al and V concentrations at approximately more than 1 mass ppb was possible by directly diluting Eagle's medium and alpha-medium solutions 5 to 50 times.