The Study On The Biodegradable Polylactic Acid Composites

Polylactic acid (polylactide, PLA) is a kind of biodegradable polymer, and its biocompatibility has been approvaled by the U.S. Food and Drug Administration (FDA). PLA biodegrade into CO2 and H2O in vivo, and the intermediate product is the normal glucose, therefore, PLA degradation in vivo will not have adverse effects on the organism. Mechanical strength of PLA decreased gradually during degradation, the stress can slowly transferred to the fracture site, avoiding the stress shielding effect, and PLA possesses better thermal molding properties, so it is an ideal kind of implantation material. However, polylactic acid independently serve as bone fixation material has many problems such as: lower mechanical strength; acidic degradation products lead to the body aseptic inflammation; lack of capacity of osseointegration. Therefore, the modification of polylactic acid to improve its performance has become a focus in the world.In this work, nano-hydroxyapatite (n-HA) was used to prepare HA/PLA composites, which can improved the initial strength and the rigid, slowedown the degradation rate in early stage. Using gelatin to modify the surface of nano-hydroxyapatite particles to improve the interface strength with polylactic acid matrix; Prepareing composites under the nano-hydroxyapatite sol system to improve the dispersion uniformity of nano-hydroxyapatite particles in the PLA matrix.Because of the HA particles difficult to dissolve and absorpte, its neutralization effect on the acid environment caused PLA degradation should be improved. Magnesium possess good biocompatibility and presents alkaline after degradation, therefore,in this work, magnesium particles were used to compound with PLA to neutralizate the local acidic environment and reduce stimulation to human tissue. Melt mixing mehod was used to prepare Mg / PLA composite and properties of this composites were studied in this paper.As a results:1,Via surface modification of hydroxyapatite particles by gelatin ,chemical bonding can be achieved between polylactic acid matrix interface and hydroxyapatite particles ,which can improve the interface bonding strength.2,Using nano-hydroxyapatite sol system to prepare composites is beneficial to the hydroxyapatite particles uniform dispersed in the PLA matrix .3, The testing results of mechanical properties of this two composites show that : With the increasing of the content of hydroxyapatite particles, the mechanical strength of HA/PLA firstly increases and then decreases, there is a best range of hydroxyapatite particle content.,in this preparation conditions is 5%. The addition of 3%wt Mg particles decreased the tensile strength, but the flexural strength of composites increased. 4,The results of vitro degradation in SBF show that: n-HA/PLA composites exhibited good biological activity, there is the formation of apatite adsorption layer on the composite surface; n-HA can decrease the degradation acid of pure PLA; and the addition of Mg particles further decrease the degradation acidic environment.5,The research of tribology properties of n-HA/PLA and Mg / PLA composites show that: wear resistance of this two composites decreases with the increasing of load. the addition of n-HA and Mg particles can improve the wear resistance of polylactic acid matrix.