Degradation Behavior Of PLA-based Composite Reinforced With Magnesium Alloy Under Dynamic Loading

Poly-lactic acid(PLA)has high brittleness and its acid degradation products could trigger inflammation easily,while biomedical magnesium alloys has poor corrosion resistance and would generate hydrogen gas during the degradation process,which greatly restrict their clinical applications.In order to make up for their weakness and improve the comprehensive performances,PLA based-composite reinforced unidirectionally with high-strength magnesium alloy wires was prepared by hot-pressing.The mechanical properties including tensile strength,bending strength of the composite were studied.On this basis,a systematic study on the degradation behaviors of pure PLA and the composite in simulated dynamic physiological stress environment with different stresses,frequencies and temperatures was carried out.Finally the degradation kinetics of the composite was discussed preliminarily.Mechanical properties of PLA are significantly improved by the strengthening effect of micro-arc oxidized magnesium alloy wires.Tensile strength and bending strength of the composites with 10 vol%magnesium alloys reach about 78 MPa and 137 MPa,which are respectively 1.4 and 1.23 times of those of pure PLA.After 21 days degradation in 37 ? Kirkland physiological solution under different dynamic stress at 1 Hz,the weight loss of the composite is obvious,which may be ralated to the corrosion of magnesium alloy wires.Meanwhile,with the increase of the stress,the molecular weight of PLA is continuously reduced.However,the synergistic degradation of magnesium alloy could delay the decrease rate of PLA molecular weight.After 21 days degradation in 37 ? physiological solution under different frequency at 0.9 MPa,with the increase of frequency,the bending strength and molecular weight of PLA are both decreased.When the dynamic frequency is increased from 0.5 Hz to 2.5 Hz,the molecular weight and the bending strength of pure PLA are decreased by 25%and 31%,respectively,and the molecular weight of PLA and the bending strength of the composite are decreased by 23%and 21%.In addition,the synergistic effect of dynamic frequency and stress is more significant than that of single factor on the degradation of pure PLA and the composite.In the simulated dynamic physiological stress environment at 1Hz and 0.1 MPa,the increase of temperature significantly accelerated the degradation of PLA.When the temperature was increased from 37 ? to 50 ?,the PLA molecular weight of the composite is decreased by 51%and bending strength of the composite is decreased by about 19.8%after 15 days degradation.During the degradation process of the composite,poly-lactic acid and magnesium alloy inhibit each other and promote each other.The corrosion rate of magnesium alloy wire is slow at the initial stage due to the protection of oxide ceramic layer.Its resistance value fluctuates firstly and then stabilizes.Finally,combined with the relationship among the molecular weight of PLA,the degradation time and the temperature,the degradation kinetics of the composite was constructed.It is found that in certain degradation conditions,there is a good linear relationship between the viscosity average molecular weight and the bending strength of pure PLA and the composite.