Composite Materials Based on Carbonatapatite and Polylactides: Synthesis and Study of Physical and Mechanical Properties

Composite materials based on bioresorbable polyesters and various calcium phosphates are extremely promising for bone tissue engineering. However, used fillers such as hydroxyapatite (HAp) or β-tricalcium phosphate do not fulfil the requirements for use in bone defect repair, as they are not able to impart high mechanical performance and desired biological properties to the composite at the same time. The aim of this study is to develop new types of bone substitute materials and composites based on them, which will provide optimal bone resorption and growth, as well as mechanical parameters corresponding to cortical bone (Young's modulus from 3 GPa and strength from 40 MPa). This study was the first to synthesise micro- and nanoscale carbonatapatite (CAp) with different morphologies (plates and hexagonal prisms). The use of lamellar carbonatapatite (pCAp) and amphiphilic block copolymers of poly(ethylene phosphoric acid) (PEPA) allowed to increase significantly the mechanical properties of polylactide-based composites - Young's modulus from 2.1 GPa to 3.29 GPa at break and from 3.3 GPa to 10.1 GPa at bending without noticeable loss of strength, which is achieved due to reinforcing filler and effective compatibiliser. Composites with 50 wt.% of lamellar pCAp content and with 60 wt.% using the compatibiliser achieved mechanical performance of cortical bone. A comparative study of (co)polymers based on lactic and glycolic acids showed the advantage of using L-methylglycolide (L-MeGL) for synthesis. The Young's modulus Ef for L-MeGL-based composites was found to be higher than that of PLLA and poly(L-lactide-co-glycolide) based composites with a lactide to glycolide fragment ratio of 85:15 (PLGA 85/15). In the hydrolytic degradation experiment, composites containing (co)polymers based on L-MeGL turned out to be more stable than composites with PLGA, since such a polymer does not contain such long glycolide blocks characteristic of PLGA.