Poly(L-lactide) nanocomposites containing poly(D-lactide) grafted nanohydroxyapatite with improved interfacial adhesion via stereocomplexation

Biodegradable organic-inorganic composites composed of polylactide (PLA) and hydroxyapatite (HA) are important bone repairing materials, while the dispersibility of nanoscaled HA in PLA and the interfacial adhesion between HA and PLA remained unsatisfactory. In this study, poly(D-lactide) (PDLA) oligomers with different molecular weights were grafted onto HA nanorods (HA-PDLA), and the HA-PDLA hybrids were mixed with poly(L-lactide) (PLLA). Dispersibility of HA-PDLA hybrids in PLLA matrix was investigated, and the formation of PDLA/PLLA stereocomplex at the interface of HA-PDLA and PLLA was studied by characterizations including crystallization, mechanical and thermal properties, taking PLLA grafted HA (HA-PLLA) and unmodified HA as comparisons. Surface grafting of PLLA or PDLA oligomers both significantly improved the dispersibility of HA nanorods in PLLA matrix. Benefiting from PDLA/PLLA stereocomplexation, HA-PDLA could increase the tensile strength and the elongation of resulting PLLA/HA nanocomposites more significantly than HA-PLLA. The interfacial interaction between HA-PDLA and PLLA matrix could be further strengthened by increasing the molecular weights of those grafted PDLA chains on HA, which was verified by changes in crystallization and glass transition behaviors. To sum up, the concept of using PDLA/PLLA stereocomplexation was feasible and effective in preparing PLA-based organic-inorganic nanocomposites targeting bone repairing.