| With excellent biocompatibility,biological safety and similar mechanical property to human bone,magnesium alloys have found wide application in the medical implant.After implantation,AZ31 magnesium alloy which can gradually dissolve and be absorbed,shows excellent prospects in the field of degradable hard tissue repair materials.Till now,AZ31 alloy has achieved a good therapeutic effect in clinical application.However,previous studies on AZ31 alloy were usually carried out under the normal conditions of simulated body fluids,and few work has been done on special patients,such as hyperglycemia,hyperuricemia and hyperlactatemia.Study on the corrosion of AZ31 magnesium alloy under special humoral conditions is of guiding significance for determining the appropriate design for alloy implant.In order to evaluate the effect of blood glucose,lactic acid and uric acid concentration on the reliability of AZ31 magnesium alloy medical implant,the corrosion of AZ31 alloy was studied in some simulated physiological solutions.The corrosion products,surface morphology changes before and after immersion were characterized using XRD,EDX,XPS,SEM with the corrosion process followed by electrochemical methods and immersion tests.The results indicate that:(1)The effect of glucose concentration on corrosion behaviour of AZ31 magnesium alloy was studied in physiological saline with glucose concentration of 1 g dm-3 in health people,and 2 g dm-3 and 4 g dm-3 for patients with hyperglycemia,and neat physiological saline without glucose as a blank control.At the initial stage of immersion,AZ31 magnesium alloy in physiological saline has a high corrosion rate of 20.99 mm y-1.The corrosion of magnesium alloy is time-dependent.As the glucose concentration increases,the anode process of the magnesium alloy is suppressed,and the corrosion rate of the AZ31 magnesium alloy decreases significantly.When the glucose concentration is 4 g dm-3,the corrosion rate of the alloy decline to 8.99 mm y-1.Although it is significantly lower than that in the solution without glucose,the corrosion rate is still quite high.It means that the adsorption of glucose on the alloy surface can inhibit the initiation of corrosion to a certain extent.During long-term immersion,the dissolution of CO2 from the air results incomposition changes of corrosion products.Basic carbonates such as Mg2(OH)2CO3·3H2O and Mg2(OH)2CO3·4H2O are formed,but the content is low.The layer of corrosion products on the surface of the magnesium alloy accumulate during immersion and decreases the corrosion rate significantly to 2.02 mm y-1 in physiological saline without glucose.The addition of glucose affects the nucleation and growth of corrosion products,which promotes the formation of basic carbonates,increases the dissolution of CO2 and lower the pH of the solution.The corrosion rate of AZ31 magnesium alloy first decreases and then accelerates with increaseing of the glucose concentration.The corrosion rate of AZ31 alloy reduces to 1.44 mm y-1 in solution with 1 g dm-3 glucose.As the glucose concentration increases,the surface corrosion layer becomes looser,and the protection ability towards the material becomes weak,and the corrosion rate of AZ31 alloy increases to 1.74 mm y-1 in solution with 4 g dm-3 glucose.However,the effect of glucose concentration on the corrosion of magnesium alloys in physiological salineis relatively weak.(2)The effect of blood glucose concentration on corrosion behaviour of AZ31 magnesium alloy was studied in Hank's balanced salt solution(HBSS)with glucose concentration of 0 g dm-3,1 g dm-3,2 g dm-3 and 4 g dm-3.The research shows that the corrosion rate of magnesium alloy in HBSS without glucose is the highest of 0.44 mm y-1.As the glucose concentration increases,the corrosion rate decreases.When the glucose concentration is 4 g dm-3,the corrosion rate of the alloy is the lowest of 0.29 mm y-1.Ca8H2(PO4)6 5H2O)and(Ca10(PO4)6(OH)2 was formed in the corrosion products such on the surface of AZ31 magnesium alloys,which can significantly inhibit corrosion.Glucose can effectively inhibit the corrosion of magnesium alloys in HBSS,which can be attributed to the the formation of Ca-P compounds on the surface of magnesium alloys due to the addtion of glucose.(3)The effect of lactic acid concentration on corrosion behaviour of AZ31 magnesium alloy was studied in HBSS with lactic acid concentration of o mmol dm-3,2 mmol dm-3,4 mmol dm-3,8 mmol dm-3 and 16 mmol dm-3.The research shows that the corrosion rate of the AZ31 magnesium alloy first decreases and then increases with the increasing concentration of lactic acid.The corrosion rate of magnesium alloys in 2 mmol dm-3 lactic acid is the lowest of 1.703 mm y-1.As the lactic acid concentration increases,the corrosion rate increases.When the lactic acid concentration is 16 mmol dm-3,the corrosion rate is the highest of 37.581 mm y-1.With the extension of the immersion time,lactic acid is gradually consumed,while the solution pH increases slowly,the corrosion of the magnesium alloy is inhibited.The pH of the solution decreases with increasing the concentration of lactic acid is the main reason for the accelerating the corrosion of the magnesium alloy.Lactic acid can significantly affect the electrochemical behaviour of AZ31 magnesium alloy.(4)The effect of uric acid concentration on corrosion behaviour of AZ31 magnesium alloy was studied in Hank's balanced salt solution without glucose(HBSSWG).The lactic acid concentration is 0 mmol dm-3,0.2 mmol dm-3,0.4 mmol dm-3,0.6 mmol dm-3 and 0.8 mmol dm-3.The corrosion rate of magnesium alloys first decreased and then increased with the increases of uric acid concentration.When the uric acid concentration is less than 0.6 mmol dm-3,the corrosion of AZ31 magnesium alloy is significantly inhibited,and the corrosion rate decreases to 1.5 7 mm y-1.For uric acid concentration of 0.8 mmol dm-3,the corrosion of the alloy accelerated significaltly,and the corrosion rate increased to 3.88 mm y-1.The analysis shows that 2,6,8-trihydroxypurine ion is beneficial to the formation of the surface layer and inhibits the anode process of AZ31 magnesium alloy.Uric acid can significantly affect the electrochemical behaviour of AZ31 magnesium alloy. |
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