Abstracts Category : Other

Magnesium-Based Bioresorbable Medical Implants: Improvement to Standardization

by Qiaomu Tian

Medical implants are devices that are often placed inside the human body to provide support to organs and tissues. Magnesium (Mg) shows great potentials as bioresorbable medical implants. Specifically, Mg is cytocompatible with many human cells in vitro and in vivo. Mg naturally degrades in the human body, which eliminates the secondary removal procedure of the implant. The primary degradation product, Mg ions, is an essential element which participates in over 300 enzymatic metabolisms. As a light metal, Mg possesses an adequate mechanical strength, even for the load-bearing condition in orthopedic device applications.We conducted concentration-dependent tests of Mg degradation products, i.e., Mg ions, OH- ions, MgO and Mg(OH)2, with representative cell models. For human urothelial cells, pH of 8.6 showed cytotoxicity, and Mg ions of 10 mM showed a decrease in cell proliferation rate. We investigated three major strategies to improve Mg, that is, surface coating, alloying and composite. A bioactive, protective surface coating will control degradation rate, and possibly induce a positive tissue response to Mg. Alloying of Mg with other metal elements can potentially result in alloys with improved corrosion resistance and mechanical strength. Sintering Mg powders with calcium phosphates could result in Mg composite with lower degradation rate.In an attempt to establish the consensus standard of the testing Mg-based implant, we design three different in vitro culture methodologies to mimic different in vivo cell-biomaterial interactions. Direct culture is suitable in vitro method when it is important to evaluate direct cell attachment on the biomaterial surfaces. Direct exposure culture isdesirable in vitro method for investigating the response of well-established cells in the body with newly implanted biomaterials. Exposure culture method is appropriate for evaluating cell-biomaterial interactions in the same environment, where they are not in direct contact. Due to the continuous degradation of Mg, cells that were direct contact or indirect contact with Mg substrates, both responded differently to different culture methodologies. A loading apparatus that we designed indicated that Mg under load had a significantly faster degradation rate. Thus, future evaluation of Mg should also take specific loads of different applications into account.