Study On Fabrication And Degradation Of Silk Fibroin Coated Magnesium Alloy Composite Structure

Biodegradable implants,acting as “smart” implants,have attracted increasing interest.The main driving force to develop biodegradable implants is their degradation properties in the physiological environment.Mg and its alloys possesse good biodegradability,biocompatibility and suitable mechanical properties,which can avoid the second surgery and reduce the “stress shielding”.But the rapid corrosion of Mg based alloys in physiological conditions has hindered their development.In order to solve this problem,a suitable ceramic coating on Mg alloy is usually employed,but ceramic coating has low toughness and flex ural strength.As an natural organic biological material,silk fibroin is biodegradable and biocompatible,and its degradation rate is slower than that of magnesium.It also can be used as a drug carrying and widely used in the growth of cells.This paper mainly explores the preparation process of the silk fibroin coated Mg-Zn-Ca alloy composite structure.Forming the organic molecules and inorganic metal composite structures.Under the protection of silk protein,magnesium alloys used as artificial bone materials obtain good degradation rate and sufficient mechanical strength.Systematically investigating the surface topography,connection strength and interface of the composite structure and the preparation process of the silk fibroin coated Mg-Zn-Ca alloy composite structure is obtained.Then making a degradation in vivo and in vitro test and biological compatibility test for Silk fibroin coated magnesium alloy samples.By comparison,summarizing that the magnesium alloy composite structure has the effect of delay degradation.The mechanism of low temperature connection and the degradation model is proposed.The results show that Mg-Zn-Ca alloy after surface modified by APTES surface,formed a solid surface modification layer,for which APTES molecular hydroxyl can produce dehydration reaction with the hydroxyl groups on the surface of the magnesium alloy.Amino groups exposed on the modified surface easily react with carboxyl and hydroxyl groups of the fibroin protein molecules,forming chemical bond connection.The interface is transformed from a purely physical connection to a physical connection and a chemical connection,thereby enhancing the bonding strength interface.After the test of the nanometer indentation instrument,the surface scratches were uniform,the silk protein membrane was free of shedding and tearing,and the interface was not defective and the connection was close.Silk fibroin coated Mg-Zn-Ca alloy composite structure in vitro degradation rate about One-eighth of the magnesium alloy itself.In vivo degradation rate about one-third of the magnesium alloy itself,compared with the in vitro degradation,degradation rate is slower than in vitro degradation.The implant does not cause inflammation in the surrounding tissue and maintains the m echanical stability of the magnesium alloy.The results of cytotoxicity test showed that the composite structure of magnesium alloy coated with silk fibroin was well biocompatible and had no toxic effect on the cells.Compared with uncovered magnesium allo y,the silk fibroin covered one improved the surface density of the surface-coated cells and the biocompatibility of the magnesium alloy surface,states the cell adhesion growth.The analysis of silk fibroin thin films before and after degradation showed t hat silk fibroin itself did not degrade obviously.It was the ions in the body fluid that can penetrate into the interior through the nano-sized film of the silk fibroin thin film and react with the magnesium which results into the degradation.