Design and synthesis of hydroxyapatite composites containing an mPEG-dendritic poly(L-lysine) star polycaprolactone

The design and synthesis of star polycaprolactone-hydroxyapatite films for use as a biodegradable matrix for bone tissue engineering will be presented. mPEG-dendritic-poly(L-lysine) terminated with glycolic acid residues serve as the star polymer cores for attachment of polycaprolactone by ring-opening polymerization of c-caprolactone. Initial studies involved testing physical blends of the tert-butoxycarbonyl (Boc) and glycolamide terminated dendrons, generations zero through six, with varying concentrations of hydroxyapatite (HA). The star polymer had not only drastically different solubility but also greatly improved film quality. Further improvements were made in film quality and homogeneity by utilizing the star polymers in the presence of a chemical synthesis of hydroxyapatite. The improved films were then tested for their mechanical strength properties. The star polymer from generation 6.5 and 20 wt % of hydroxyapatite exhibited good mechanical properties with an average Young's modulus of 1.77 MPa, tensile strength of 4.19 MPa, and ultimate elongation of 19%. The details of the chemical synthesis of hydroxyapatite in the presence of the star polymer are discussed.