Magnesium alloy has been implanted in rats to investigate the in vivo degradation behavior of magnesium for bone implant application. After 9 weeks postoperation, 100% implants were fixed and no inflammation was observed. Histological analysis showed new bone was formed around magnesium implant and no difference was found in the histological microstructure of the new bone and the cortical bone. A degradation or reaction layer, which was mainly composed of Ca, P, O, and Mg, was formed on the surface of magnesium alloy implants. High Ca content in the degradation layer displayed that magnesium could promote the deposition of Ca. Residual area calculation has showed that 10-17% magnesium alloy implant has been degraded in vivo. Compared with that of the controlled rats, no increase in serum magnesium and no disorder of kidney were observed after 15 weeks postoperation. After 18 weeks postoperation, 100% magnesium implants were fixed and no inflammation was observed. About 54% magnesium implant has degraded in vivo. Element analysis showed that Zn and Mn in Mg-Mn-Zn alloy distributed homogeneously in the residual magnesium implant, the degradation layer, and the surrounding bone tissue after 18 weeks implantation, indicating that Zn and Mn elements were easily absorbed by bioenvironment.

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In vivo degradation of magnesium alloy implant, the bone response to the magnesium, and the effect of the degradation of magnesium on the blood composition and organs were investigated by using light microscopy and scanning electronic microscopy with energy dispersive spectrum. Magnesium alloy showed different degradation rates in the marrow channel and the cortical bone. More degradation of magnesium implant was observed in the marrow channel than in the cortical bone. New bone tissue formed around the magnesium implants after 6 weeks implantation but no fibrous capsule was found. There existed two distinct layers separating the new bone tissue from the magnesium implant. On the magnesium implant side, crystalline magnesium calcium phosphate formed on the surface of the implant due to the reaction between the implant and blood or body fluid. On the new bone tissue side was a 10-30-microm membrane comprising two distinct layers with many fibroblasts in the layer close to the new bone tissue. The new bone was in tight contact with the implant through the membrane and phosphate layer due to the good osteoconductivity of the phosphate layer. After 10 and 26 weeks postimplantation, more new bone tissues as well as the membrane were found around the implant. However, no apparent increase in the thickness of the membrane was observed with the increasing of the implantation duration. Blood examination has shown that the degradation of the magnesium implant caused little change to blood composition but no disorder to liver or kidneys.

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Biocorrosion properties and blood- and cell compatibility of pure iron were studied in comparison with 316L stainless steel and Mg-Mn-Zn magnesium alloy to reveal the possibility of pure iron as a biodegradable biomaterial. Both electrochemical and weight loss tests showed that pure iron showed a relatively high corrosion rate at the first several days and then decreased to a low level during the following immersion due to the formation of phosphates on the surface. However, the corrosion of pure iron did not cause significant increase in pH value to the solution. In comparison with 316L and Mg-Mn-Zn alloy, the pure iron exhibited biodegradable property in a moderate corrosion rate. Pure iron possessed similar dynamic blood clotting time, prothrombin time and plasma recalcification time to 316L and Mg-Mn-Zn alloy, but a lower hemolysis ratio and a significant lower number density of adhered platelets. MTT results revealed that the extract except the one with 25% 24 h extract actually displayed toxicity to cells and the toxicity increased with the increasing of the iron ion concentration and the incubation time. It was thought there should be an iron ion concentration threshold in the effect of iron ion on the cell toxicity.

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