Preparation Of Magnesium Phosphate Based Piezoelectric Bone Cement And Its Corrosion Resistance On AZ31B Alloy

Magnesium phosphate bone cement(MPC)is a kind of solidified cement made by acidalkali reaction from re-burned magnesia and phosphate.It has the characteristics of short setting time,high early strength,small volume shrinkage,good bonding performance and biodegradability.However,it always takes a long time for bone remodel due to the limited ability to induce bone regeneration of MPC.Therefore,prepare magnesium phosphate-based piezoelectric bone cement BT/MPC through adding different content(20%-70%)of barium titanate.The piezoelectric coefficient,compressive strength and morphology of hydration products were investigated.Furthermore,graphene was added to construct piezoelectric pathway for further improve the piezoelectric coefficient of the composite cement.These samples could decrease the degradation rate of bone cement and guide calcium deposition to accelerate bone integration and then shorten the bone repair time.Then,the degradation and osteoinductivity of composite bone cement were used on the surface of AZ31B alloy to reduce the corrosion rate,further match the degradation rate with the growth rate of new bone.The corrosion evolution process and mechanism of magnesium alloy with piezoelectric cement coating in SBF were also discussed.The main conclusions are as follows:(1)BT/MPC bone cement has piezoelectric properties.As the BT content increased,the piezoelectric coefficient d33 increases from 0.16pC/N to 3.49pC/N.The compressive strength of all groups meet the requirements of bone implant materials.The compressive strength of BT40(the content of BT is 40%)is the highest,reaching 84.82 MPa.The piezoelectric coefficients of composite piezoelectric cement can be further significantly improved throgh adding different graphene content to successfully construct piezoelectric pathways.The piezoelectric coefficient of BT50 group increased from 1.21pC/N to 6.31pC/N at graphene content was 0.5wt.%,increased by 421%.(2)The results of SBF mineralization in vitro showed that the negative charge on the surface of BT50G0.5 was beneficial to the migration of calcium and phosphorus ions in SBF.It guided calcium and phosphorus salts to form flocculent clusters or flower-like slab-like sediments on the surface of the sample,which could effectively slow down the degradation rate of magnesium phosphate-based bone cement and have good osteoinductivity,to promote bone integration and shorten the period of bone repair.(3)MAO 20 was prepared by micro-arc oxidation on the surface of AZ31B,and BT50G0.5 coating of piezoelectric bone cement was prepared by tape casting.The tensile bond strength between cement coating and matrix was 6.83 MPa.The corrosion potential was-0.3165V,which was 1.315V higher than that of AZ31B matrix.And the corrosion current density was reduced to 1.378-6A/cm2,which was two orders of magnitude lower than that of AZ31B matrix.After 7 days of SBF corrosion,the weight loss rate and corrosion rate were 1.03%and 3.33 mm/y respectively.The results show that the polarized negative surface charge of the piezoelectric cement coating can lead to calcium salt deposition,reduce the corrosion rate,and achieve the matching of degradation and deposition rate.