Novel approach to obtain composite poly-L-lactide based films blended with starch and calcium phosphates and their bioactive properties

A novel approach for preparation of composite materials based on the poly-L-lactide (PL), starch and calcium phosphates is provided, applying the polymer crazing process in liquid absorption active medium. For composite films preparation, PL and blends of PL and starch have been chosen as polymeric matrixes. Pores formation in the polymer films occurred during the process of uniaxial stretching in the presence of ethanol or water-ethanol mixtures via the solvent-crazing mechanism. The diameter of pores and fibrils in crazed PL was 20-30 nm. Porous polymer matrixes have been loaded with starch, using crazing mechanism, and filled with calcium phosphates (CP) by the countercurrent diffusion method, the content of starch and CP being up to 11.0 and 14.5 wt%, respectively. The obtained composites were investigated by XRD, SEM-EDS and TEM methods. It was found out that the starch filled the porous crazed structure of polymer, while the CP synthesis in the PL pores resulted in the formation of amorphous particles with the diameter of about 20 nm. These CP nanoparticles aggregated into the submicron particles of 100-300 nm in diameter. The bioactivity of the initial and porous poly-L-lactide films, and composites, based on PL with starch and calcium phosphates, was investigated. It was shown that the bioactivity depends on the chemical composition and surface morphology of the prepared materials. After 10 days of cultivation of the pre-osteoblastic MC3T3E1 cells, an intense, 6 times, growth of osteoblast population was achieved for the composite containing calcium phosphates. This result is perceptibly higher than those obtained for other samples (4 times growth) and for the control sample (5 times growth). Based on the results of in vitro tests, it can be concluded that the prepared materials are promising for biomedical applications.