Poly(L-lactic acid)/vaterite composite coatings on metallic magnesium

Poly(L-lactic acid)/vaterite composite materials were coated onto metallic magnesium substrates to control rapid degradation and to improve biocompatibility. Two types of composites were prepared by adding 30 and 60 wt% of vaterite to poly(L-lactic acid) (PLLA). The composite coating layer that contained 30 wt% vaterite in the PLLA matrix had almost no pores on the surface and suppressed the initial rapid degradation of the Mg substrate. After immersion in a culture medium for 7 days, pores of 0.5-1.0 μm in diameter formed on the surface. The composite coating layer that contained 60 wt% vaterite with pores of 1.0-2.0 μm in diameter on the surface did not suppress the degradation of the Mg substrate. During immersion, the pH of the media near the composite coating surfaces was maintained at 7.4-7.5 because of the degradation of PLLA and because the vaterite particles dissolved in the solution. Proliferation of murine osteoblast-like cells (MC3T3-E1) on the substrates was improved using composite coatings. Cells on the coating that contained 60 wt% vaterite had significantly higher proliferation than those on a bare Mg substrate. Our coating provides the optimum combination to suppress the initial Mg degradation and to promote cell growth on the coating surface by adjusting the vaterite content in the composite.