Development and characterization of an injectable cement of nano calcium-deficient hydroxyapatite/multi(amino acid) copolymer/calcium sulfate hemihydrate for bone repair

Xiaotong Qi,¹ Hong Li,² Bo Qiao,¹ Weichao Li,¹ Xinyan Hao,² Jun Wu,¹ Bao Su,¹ Dianming Jiang<sup>1

1</sup>Department of Orthopedics, The First Affiliated Hospital, Chongqing Medical University, Chongqing, People's Republic of China; ²School of Physical Science and Technology, Sichuan University, Chengdu, People's Republic of China

Abstract: A novel injectable bone cement was developed by integration of nano calcium-deficient hydroxyapatite/multi(amino acid) copolymer (n-CDHA/MAC) and calcium sulfate hemihydrate (CSH; CaSO₄ · 1/2H₂O). The structure, setting time, and compressive strength of the cement were investigated. The results showed that the cement with a liquid to powder ratio of 0.8 mL/g exhibited good injectability and appropriate setting time and mechanical properties. In vitro cell studies indicated that MC3T3-E1 cells cultured on the n-CDHA/MAC/CSH composite spread well and showed a good proliferation state. The alkaline phosphatase activity of the MC3T3-E1 cells cultured on the n-CDHA/MAC/CSH composite was significantly higher than that of the cells on pure CSH at 4 and 7 days of culture. The n-CDHA/MAC/CSH cement was implanted into critical size defects of the femoral condyle in rabbits to evaluate its biocompatibility and osteogenesis in vivo. Radiological and histological results indicated that introduction of the n-CDHA/MAC into CSH enhanced new bone formation, and the n-CDHA/MAC/CSH cement exhibited good biocompatibility and degradability. In conclusion, the injectable n-CDHA/MAC/CSH composite cement has a significant clinical advantage over pure CSH cement, and may be a promising bone graft substitute for the treatment of bone defects.

Keywords: calcium-deficient hydroxyapatite, multi(amino acid) copolymer, calcium sulfate hemihydrate, injectability, biocompatibility, osteogenesis