The Study On Preparation And Properties Of PLA/BC/HAp Composites

Polymer such as polylacticacid(PLA) has many particular properties,such as good biocompatibility,degradable in vivo.Therefore it is widely used in clinic especially in bone regeneration field.PLA is only suitable for the non-load-bearing applications because of its low mechanical strength.Therefore it is necessary to enhance its strength by composite method.Bacterial cellulose(BC),which produced by acetobacter xylinum in culture medium,is a unique biopolymer in terms of 3-dimentional network,biocompatibility and high mechanical strength. Hydroxyapatite(HAp),which is the major component of human bone,has excellent bioactivity and it is able to guide bone regeneration.This paper is focused on preparation PLA/Hap/BC composite with excellent properties applied in bone regeneration.In the composite,the excellent mechanical strength of BC,the bioactivity of Hap,and the degradability and plasticity of PLA were combined.The work mainly concentrated on the following four parts:1.The mechanical strength of pure BC and PLA were investigated.The experiment result showed that the fracture mode of PLA was ductile and the tensile strength of PLA was 35 MPa only.Compared with neat PLA,BC was brittle fracture and show superior tensile strength with the value of 102 MPa.Then we prepared PLA/BC composites by pre-impregnation and solution casting method.The tensile strength of PLA/BC was much higher than that of pure PLA.Besides,the microcrystalline BC(MCBC) was prepared and the mechanical properties were investigated with different content MCBC in the PLA/MCBC composites.The results showed that MCBC had excellent dispersion in PLA and the modulus distribution of was more centralized than PLA/BC.But their mechanical property was not as good as expection owing to various factors.2.The composites tensile strength model was built to predict the tensile strength of composites with different PLA content.It was found that the test results were lower than the culculated performance.This phenomena could be explained by the poor interfacial adhesion between PLA and BC.In order to solve this problem, polyethylene glycol(PEG) was employed to improve the interfacial adhesion of composites.With the help of PEG,the tensile strength of PLA/BC and PLA/MCBC increased 12%and 30%,respectively.The surface free energy of PLA was calculated by contact angle,and test results indicated that the hydrophobicity was obviously improved.3.The dispersing process of HAp in PLA was investigated.The method by coating with PEG and pre-treatment by freeze drying was adopted to replace ultrasonic.SEM image showed that the dispersion of HAp in PLA was obviously improved.The mechanical test results indicated that the tensile strength was improved with 30%.The mechanical properties were investigated with different HAp content in the composites.The results indicated that the tensile strength and elastic modulus of PLA/HAp increased at first,and then decreased gradually,while the breaking elongation decreased continuously.4.A PLA/BC/HAp composite was prepared.When PLA content was 40%and HAp content was 10%,the tensile strength of the compsite reached 77 MPa,which is double to pure PLA.The prepared composite remedy the poor mechanical property of pure PLA and it can meet the requirement the properties for bone regeneration.