Micro-structure,Mechanical Property And In-vitro Degradation Behavior Of Magnesium Alloy Fine Wire For Medical Use

Stapling apparatus has been widely applied in the clinical gastrointestinal reconstruction after gastrectomy.While the titanium staples used in the surgery would be remained in human body forever,which not only would lead to the metal artifact that effect pathology observation later,but also would result in the problems of stenosis of gastroenteric stoma,chronic inflammation and gastrointestinal bleeding that have a negative effect on patients’ physiology and psychology.The biodegradation magnesium alloy staples have significant advantages and application prospect,because it reserves the advantage of the technology of stapleing apparatus,and avoids the disadvantages of the titanium staple.Compared to the present implanted magnesium device in SBF,the true environment that staple stays in is more complicated and severe,the pH value,digestive enzyme,ion types and concentraton in different location of gastrointestinal tract,the residual stress in staple formed in the stapling process,all those facts make the the degradation behavior hard to be evaluated and controlled.So the in vitro degradation in simulated gastrotestinal environment to study the degradation behavior,mechanism and machnical properties in different gastrotestinal position is very important,which could provide theoretical support for the construction of corrosion models,degradation kinetics and evaluation criterion,and have great scientific and practical significance in the structure design,process optimization,life prediction and indication selection of staple.From the results of microscopic structure,corrosion resistance property and mechanical property of the magnesium alloy fine wires(φ=0.3mm)under several heat treatments,the most suitable temperature was selected to get the as-annealed wires,on which then make micro-arc oxidation treatment and PLA coatings,and make the composite wire into staples.This paper evaluated the in vitro biodegradation through the electrochemical tests,immersion tests and tensile tests,observed and analyzed the corossion morphology by stereo microscope and SEM,this research focused on the degradation behavior of staples in simulated intestinal,gastric and body fluids to establish the physical degradation models.The main conclusions are as followed:The annealing process(250 ℃ 30min)leads to the complete recrystallization of the magnesium alloy wire,and the fine and uniform grain size contributes to the good corrosion resistance property and mechanical property including strength and plasticity.After immersion in different simulated fluids for a long time,the degradation amounts of staples show significant difference.The weight loss of staples in simulated gastric fluid(SGF)is only 10%,which is slightly higher in simulated body fluid(SBF),about 20%.The more serious degradation happens in the simulated intestinal fluid(SIF)and simulated gastric and intestinal fluid(pH=4),the weight of staples is only 20-30%of original level.While in simulated gastric and intestinal fluid(pH=6),staples are almost completely degraded.The mechanical properties of composite wires in SGF show the minimum decrease,the tensile strength decreased from 302MPa to 260MPa after immersion for a week,while the mechanical properties of wires in SBF are slightly worse.In the other three simulated fluids,the wires even cannot meet the use requirement.The pH of the simulated fluids and the pancreatic enzymes in the fluids have a great influence in the PLA degradation,and the corrosion of inner magnesium alloy are mainly affected from the pH and ion composition in the corrosion environment.And from the corrosion morphology,it is known that the more serious corrosion occurred in the stress concentration positions.