Preparation Of PTFE Composite Acid-resistant Coating On Pure Magnesium Surface And Its Degradation Performance

As a new generation of esophageal scaffold implantation materials,it is required to have good mechanical properties,biocompatibility and degradability,as well as good corrosion resistance.Magnesium alloy compared with other traditional medical metal materials,its biggest characteristic is biodegradable in the human body,so as to avoid the traditional medical implant material out secondary bring mental and physical double injury to patients,so the magnesium and magnesium alloys in the more recent received extensive attention in the field of medical materials,the biodegradable without removing magnesium alloy stent has huge potential.Esophageal stents typically require14 days of service in the body.However,unmodified bare magnesium or magnesium alloy stents may corrode too quickly in acidic environments to meet service requirements,leading to implantation failure.Therefore,this paper will regulate the degradation rate of magnesium matrix and improve its biocompatibility through surface modification,so as to avoid secondary stenosis caused by rapid corrosion in the esophagus.The main research work is divided into the following parts:（1）Mg（OH）2/PDA-PEI/PTFE composite coating was prepared and its preparation process was optimized.The Mg（OH）2 pretreated layer was prepared on the surface of magnesium substrate by hydrothermal method to improve the corrosion property of the substrate and the adhesion to the dopamine transition layer.Then,PDA-PEI intermediate transition layer was prepared on Mg（OH）2 layer by chemical impregnation method,so that PTFE coating could adhere to it well.Finally,the PTFE layer was prepared on the upper PDA/PEI.Single factor analysis was used to optimize the preparation process of three kinds of coatings.The results showed that the optimal process of Mg（OH）2 membrane was in the Na OH solution with p H=12 and the hydrothermal treatment time was 4 hours.The optimum process of PDA/PEI membrane was as follows:DA/PEI concentration 1.5g/L,film forming time 10 h;The optimal process of PTFE film is PI concentration of 1g/L,curing temperature of 320℃.After hydrothermal treatment,Mg（OH）2 improved the effective site for the deposition of DA/PEI,and PEI prevented the aggregation of PDA.Therefore,uniform PDA/PEI film was prepared on Mg（OH）2 film,and PDA/PEI film provided strong adhesion property for the subsequent preparation of PTFE film.（2）A series of analysis and characterization of the composite film were carried out.The results show that the Mg（OH）2 film is in the shape of microammeter needle sheet,with a thickness of about 23μm,a contact Angle of 17.7° and a roughness of 0.696μm.The PDA/PEI film was floccule with a thickness of about 2.67μm,the contact Angle increased to 24.5°,and the roughness decreased to 0.18μm.This was due to the dual effects of the cross-linking reaction between the hydrophilic groups of dopamine,phenolic hydroxyl group and amino group,PDA and PEI,which produced more aromatic rings of hydrophobic groups,and the uniform deposition of DA/PEI on the Mg（OH）₂ film.The thickness of the film is about 5.76μm,the contact Angle is increased to 145.6°,and the roughness is increased to 0.307μm.It was found that the binding force of Mg（OH）2 and PDA/PEI film was the best,and the binding force of PTFE film was the second.（3）The corrosion degradation of modified magnesium alloys was investigated by electrochemical and immersion experiments.The electrochemical results show that the corrosion current densities of the three coatings are reduced by 3,4 and 5 orders of magnitude,respectively,and the corrosion resistance of the modified magnesium substrate is greatly improved.The results show that the Mg（OH）2 and PDA/PEI coatings can only resist the corrosion of acidic environment in a very short time.With the corrosion progress,a new magnesium phosphate coating will be formed on the substrate to prevent the corrosion progress.However,the new magnesium phosphate coating will continue to be corroded after the replacement of corrosion solution.After soaking in PBS solution with p H=5 for 3 days,the PTFE composite coating still showed good hydrophobicity.After soaking for 14 days,the coating still existed on the surface of the sample,but warping,peeling and pits appeared in some areas,which indicated that the PTFE composite coating had good corrosion resistance.The cytocompatibility study showed that the PDA/PEI coating sample could inhibit the proliferation of fibroblasts and epithelial cells,but the cytocompatibility of the coating was improved after the modification of PTFE,and the proliferation rate of fibroblasts and epithelial cells was significantly increased.The cytotoxicity met the requirements of biomaterials.The results of this study indicate that PTFE composite coating modified pure magnesium is expected to be used in the treatment of esophageal stenosis device,and provide certain reference value for the development of medical esophageal stent implantation.