Chemical bonding of polycaprolactone on the surface of hydroxyapatite via silanization and ring opening polymerization

In this study, surface modification of hydroxyapatite (HAp) by grafting polycaprolactone (PCL) is described. This method is carried out into two steps: (1) A treatment of HAp powder with a mixture of tetraorthosilicate (TEOS) and 3-aminopropyl-etriethoxysilane (APTES) to introduce amine groups and enhance nucleophilicity of surface functionalities; (2) Initiation of the Ring Opening Polymerization (ROP) of the ε-caprolactone (CL) in the presence of the silanized HAp. Moreover, the impact of the reaction time (24, 48 and 72 h) on the grafting amount of PCL is performed. The results of FTIR analysis confirmed the presence of carbonyl groups on the silanized HAp, providing evidence of grafting of PCL on the HAp surface. WAXS pattern showed no formation of a secondary phase after surface modification and the crystallinity is preserved. SEM/TEM analysis revealed a homogenous surface powder composed of irregular nanoscale crystals. TGA analysis indicated the dependence of PCL graft amount on the reaction time. Finally, the effect of surface modification on HAp/PCL nanocomposites morphology was investigated.