Structure and biocompatibility improvement mechanism of highly oriented poly(lactic acid) produced by solid die drawing

Highly oriented long-chain-branched poly(lactic acid) (LCB-PLA) was fabricated through solid die drawing technology for the purpose of further improving the mechanical properties and biocompatibility of PLA as bone fixation materials. Compared with neat PLA, higher draw ratio can be obtained for LCB-PLA during the drawing process, which led to the sharp increase of the mechanical properties of PLA samples. For LCB-PLA sample with 13.2 of draw ratio, the tensile strength and modulus reached up to 235.4 MPa and 8.2 GPa, respectively, which satisfied the requirement of the weight-bearing implant fixation. The MTT and ALP results suggested that the proliferation, differentiation and ALP activity of osteoblasts on the surface of PLA samples increased with draw ratio. In addition, cells with flat and extension morphology adhered and grew better, and the spreading area of cells on LCB-PLA samples was larger than that on PLA samples, which suggested that long chain branching and uniaxial orientation exhibited optimal role in promoting cell growth and maintaining their morphology. After orientation, due to the increase of crystallinity and CH3 content on the sample surface, the hydrophobicity increased, promoting the protein adsorption and thus the cell adhesion on it; moreover, cell adhered more stably on the C O enriched and grooved surfaces of the oriented samples, further improving the cell reproduction and aggregation.