Polymer-encapsulated Sm-doped nano-hydroxylapatite and its antibacterial property☆

Hydroxylapatite (HAp), owing to its excellent biocompatibility, is a promising carrier for lanthanide ions to encourage antibacterial activity. However, hydroxylapatite powder would still require modification to ensure the optimal integration of antibacterial characteristics. In this study, Sm-doped nano-hydroxylapatite (SmHAp) was synthesized by spontaneous mineralization of amorphous SmHAp precursors, which ensures a homogeneous distribution of Sm3+ within bulk SmHAp. Powder X-ray diffraction and its Pawley fitting results for SmHAp indicate the lattice substitution of Ca2+ with Sm3+, resulting in the lattice distortion in SmHAp compared to pure HAp. Meanwhile, polymer-encapsulated Sm-doped nano-hydroxylapatite composite (p_SmHAp) was synthesized by a dual-step polymerization involving UV curing of an outer crust and heat treatment for bulk reaction completion. Irgacure 2959 and a toluene solution of AIBN were used as catalysts for the radical polymerization process. The antibacterial property of p_SmHAp was evaluated by observing the growth of Sporosarcina pasteurii (ATCC 11859) both in the solid and the liquid medium, correlating with the Sm fraction and SmHAp’s crystallinity in p_SmHAp. These bacteriostatic rings' diameters exceed 20 mm, demonstrating that p_SmHAp with a SmHAP/p_SmHAp mass ratio of 0.1 and Sm/(Ca+Sm) molar ratio of 0.05−0.1 effectively releases Sm3+, serving as a strong antibacterial agent.