In vitro and in vivo evaluations on osteogenesis and biodegradability of a β-tricalcium phosphate coated magnesium alloy.

Abstract

Magnesium (Mg) alloys have been demonstrated to be potential orthopedic implants due to their biodegradability in vivo. To enhance its corrosion resistance and improve its osteogenesis, β-tricalcium phosphate (β-TCP) was coated on a Mg alloy (Mg-3AI-1Zn) by phosphating process. In vitro, the human osteosarcoma cell line (SaOS-2) showed significantly good adherence and proliferation on the surface of the β-TCP coated Mg alloy after 24-h incubation. The growth factor bone morphogenetic protein 2 (BMP-2) was highly expressed in SaOS-2 cultured with the β-TCP coated Mg alloy by Western blot analysis (p < 0.05). In vivo, the newborn bone at the implant/bone interface was formed at week 1 and matured at week 4 postimplantation. Villous tissue was found at the implant/bone interface at week 12 postimplantation. The contents of phosphorus and calcium on the surface of the β-TCP coated Mg alloy were decreased at week 4 and week 12 postimplantation, respectively. Immunohistochemical analysis of the experiment results demonstrated that the β-TCP coated Mg alloy implants provided a high BMP-2 expression during the first 4 weeks postimplantation. Compared with the naked Mg alloy which was degraded for 33% in vivo, only 17% of the β-TCP coated Mg alloy was degraded at week 12 postimplantation (p < 0.05). The in vitro cell tests showed that the β-TCP coating provided the Mg alloy with a significantly better surface cytocompatibility, and in vivo results also confirmed that the β-TCP coating exhibited greatly improved osteoconductivity and osteogenesis in the early 12 weeks postoperation period. Moreover, in vivo experiment demonstrated that the β-TCP coating layer could slow down the degradation of the naked Mg alloy at the early stage of implantation.