Study On Surface Modification And Properties Of Pure Magnesium Used In Tissue Engineering Vascular Stents

Magnesium and its alloy,as the"21st century green engineering materials",has a good biocompatibility,mechanical properties and characteristics of biodegradable absorption.Magnesium has a broad application prospect as biodegradable medical implant material.It is potential blood vessel scaffold material of tissue engineering.However,the corrosion speed of magnesium and its alloys is the main challenge of its application.Magnesium hydroxide is formed when magnesium is corroded,which increases the pH value of the environment to more than 8.In the co-culture process of tissue engineering scaffolds and seed cells,an alkaline environment is not conducive to cell growth.Moreover,in the process of tissue engineering vascularization,the surface of magnesium is not easily recognized by cells due to the lack of biological signals.Therefore,the degradation rate and cell compatibility of magnesium matrix were changed by surface modification.The main research work is divided into the following aspects:?1?Based on the strong adhesion properties and good cell compatibility of polydopamine,and the strong binding force with the matrix of Mg?OH?₂ obtained by water heat treatment,the single PDA film and Mg?OH?₂-PDA composite film are deposited on the surface of pure magnesium.The preparation process of the two films was optimized by single factor analysis.The results show that the optimal concentration and time of PDA film and its composite film are 1g/l,12h and 1.5g/l,20h.The surface of PDA films obtained on pure magnesium is cracked and increased with the increase of dopamine concentration and film forming time.The process of Mg?OH?₂-PDA composite film obtained on pure magnesium is two-tiered approach of the composite of PDA and Mg?OH?₂ and the adverse effect of solution on the Mg?OH?₂ coating,resulted in the defects of microcracks and micropores on the surface of Mg?OH?₂-PDA composite film.After hydrothermal pretreatment of pure magnesium,the microstructure of the Mg?OH?₂ coating provides a better attachment point for the polydopamine particles,resulting in a more uniform polyamine film.?2?On the basis of parameter optimization,the physical and chemical properties,corrosion resistance and cell compatibility of the two films are studied through a series of characterization methods and test methods.The results show that the film thickness of the PDA film obtained on pure magnesium surface was 1?m,and the film thickness of the Mg?OH?₂-PDA composite film obtained was 7.19?m.The hydrophilic group in the PDA film causes the hydrophilicity of the film layer to improve,while the PDA particles cause the surface roughness to increase.After the modification of two PDA films,the corrosion resistance of pure magnesium was significantly improved,especially the corrosion current density of the Mg?OH?₂-PDA composite film decreased by two orders.Moreover,Mg?OH?₂-PDA composite films show better degradation performance in the long-term immersion test,and the integrity of the film layer remained after 28 days of immersion.The modification of PDA and its composite membrane can effectively promote the adhesion,spread and proliferation of vascular endothelial cells,but the promotion effect of Mg?OH?₂-PDA composite films is the best.?3?Based on the surface of pure magnesium is not easily recognized by cells because of the lack of biological signals,and the vascular endothelial growth factor?VEGF?plays an important role in the proliferation,differentiation and migration of vascular endothelial cells,polydopamine is used as the intermediate layer to load growth factor on the surface of pure magnesium.Subsequently,the physicochemical properties,corrosion resistance and cell compatibility of two kinds of PDA film loading growth factors are studied.The results show that vascular endothelial growth factor?VEGF?is successfully fixed on the surface of PDA and its composite film,resulting in increased roughness and hydrophilic enhancement.After load growth factor,the corrosion resistance of the PDA film layer is not significantly affected,but the corrosion resistance of Mg?OH?₂-PDA composite film is reduced.The adhesion,spread and proliferation of the two kinds of PDA film are significantly promoted after the growth factor was fixed on the surface of the PDA and its composite film,but the effect of Mg?OH?₂-PDA composite film is more significant.The research content of this paper is expected to be applied to tissue engineering vascular stents,and to provide certain reference value for reducing the corrosion rate and improving cell compatibility of magnesium material.