Biocompatibility and osteogenesis of refractory metal implants, titanium, hafnium, niobium, tantalum and rhenium

To evaluate the biocompatibility of refractory metals, titanium, hafnium, niobium, tantalum and rhenium were implanted in rats, and histological observation and elemental mapping were performed by X-ray scanning analytical microscope (XSAM) and electron probe microanalyzer (EPMA). The titanium, hafnium, niobium, tantalum and rhenium wires were implanted in the subcutaneous tissue of the abdominal region and in femoral bone marrow of rats for either 2 or 4 weeks. No inflammatory response was observed around the implants, and all the implants were encapsulated with thin fibrous connective tissue. No dissolution of these metals was detected by XSAM in the soft tissue. Histological examination of the hard tissue showed that the amount of new bone formation decreased slightly from the second to the fourth week after implantation, and that the percentage of bone in contact with the implant increased markedly over the same period. No dissolution of these metals was detected by EPMA in the hard tissue. The Ca and P intensities in the mapping images of newly formed bone were higher after 4 weeks than those after 2 weeks, which suggests that the newly formed bone continued to mature from 2 to 4 weeks after implantation. These results indicate that titanium, hafnium, niobium, tantalum and rhenium have good biocompatibility and osteoconductivity.