Magnesium produces oxide film in corrosion medium. Mg(OH)₂ is porous, and cannot effectively protect magnesium alloy. The speed of degradation is associated with alloy element proportion, surrounding temperature, pH value and negative ion concentration. Magnesium is an active metal, easily reacts with many solutions, especially chloridion solution. Cl^- can transform Mg(OH)₂ into MgCl₂. Magnesium-zinc alloy delays degraded velocity and improves biocompatibility^[9-10] , and has good mechanical function and corrosion resistance. Thermokalite-treated magnesium-calcium alloy^[11] has no toxic effect on L929 cells cultured for 7 days. Degraded time is consistent with bone regeneration and healing, and increased alloy element can elevate the mechanical function and corrosion resistance of magnesium^[12] . In this study, the degradation of magnesium-zinc alloy was observed by X-ray. On day 14 following implantation, magnesium-zinc alloy unevenly degraded. Changes in metal size were not large. However, magnesium-zinc alloy was greatly degraded on day 28, with the presence of magnesium-zinc alloy fragment shadow. Because of the gas in intestinal tract, the gas produced by degradation of magnesium-zinc alloy cannot be observed. Intestinal tract healing needs 5-7 days. The magnesium-zinc alloy keeps a certain form and mechanical function on day 14 following implantation, exerts its fixation effects, and can satisfy the time requirement of intestinal tract healing. These further confirmed that magnesium-zinc alloy can be used as implant material for anastomosis of the digestive canal.
Magnesium and its alloy as medical material for degradation are mainly employed in cardiovascular stent, bone fixation and porous repair. In this study, pathological sections of liver, kidney and intestine showed hepatocytes were not swollen or necrotic. The bile duct did not demonstrate obvious distension and deposition. No edema or necrosis was detected in renal glomerulus. Intestinal villus regularly arranged, without necrosis or defluxion. No inflammatory cell infiltration was determined in various layers. A previous study^[13] has revealed that a total of 71 magnesium alloy stent was implanted into 63 patients with coronary artery stenosis. The stenosis rate of blood vessel was decreased from 61.5% to 12.6%, without markedly postoperative complications. Numerous studies^[14-16] have exhibited that magnesium alloy stick gradually degraded; there are many active osteoblasts and osteocytes surrounding the magnesium alloy. These suggested that magnesium alloy as degraded bone fixation material has good biocompatibility and mechanical function. F.Witte et al studies^[17-18] have demonstrated that magnesium alloy-made porous stent was implanted into rabbit femur. A large number of magnesium stent was degraded 3 months later. No osteolysis was found surrounding the stent, and the stent did not impact surrounded tissues, but elevated formation of extracellular non-mineralized matrix and mineralized rate of the tissue surrounding the magnesium stent. Therefore, magnesium alloy has good biocompatibility, and can be used as neotype degradable implant material.
In summary, no significant difference in liver and kidney function and serum magnesium concentration was determined in magnesium alloy group, medical titanium group and sham-operated group at the same time point following implantation (P > 0.05). Liver, kidney and intestine pathological staining did not demonstrate liver and kidney cell necrosis and inflammatory cell infiltration, but showed that the incision of the intestinal tract was well healed; without perforation or inflammatory reaction. X-ray exhibited the degradation of magnesium-zinc alloy in the intestine, and the magnesium-zinc alloy exhibited good fixation effects in the early phase of degradation. Thus, it meets the time for wound healing. These illustrated that the changes in liver and kidney function are consistent among magnesium alloy group, medical titanium group and sham-operated group. Magnesium-zinc alloy has no effects on liver and kidney functions, without toxic reaction, which indicated that magnesium-zinc alloy is safe in vivo. Primary zoology toxicity test laid the foundation for toxicity study of human test. The degradable magnesium-zinc alloy is in line for implant material (such as anastomotic nail) of the intestinal tract, instead of pure titanium, and diminishes in vivo complications induced by pure titanium and finally relives patients’ pain.