Zonggang Chen, Huanye Liu, Xi Liu, Zhongwu Guo, Fu-Zhai Cui

Journal of Controlled Release 172 (2013) e148–e149

ABSTRACT

The nHAC composites, which are the mineralized fibrils of nanosized hydroxyapatite and collagen, have the same features as natural bone in themain hierarchical microstructure and composition, so it is a bioactive osteoconductor, which has been successfully used for tens of thousands of cases in clinical applications. However, the materials lack handling characteristics because of its solid-preformed block shape. Herein, calcium sulfate hemihydrate (CSH) was introduced into nHAC to develop injectable bone repair materials, and calcium sulfate dihydrate (CSD) was selected as setting accelerator. The morphology, injectability, setting time, mechanical properties and degradation ratios of materials were examined in in vitro cellular activities and in vivo implantation experiments were performed by seeding cells on the materials and implanting the materials into a 13 mm× 10mm box defect in the mandible of rabbits, respectively.

The nHAC/CSH composites have favorable injectability under appropriate conditions. When mixed with water, the materials were transformed into nHAC/CSD composites after final setting. The rod-like crystal structure of CSHwas transformed into the sheet crystal structure of CSD. CSD as setting accelerator has a significant accelerating effect on the setting properties of nHAC/CSH composites. The self-setting time of nHAC/CSH composites can be regulated from more than 100 min to 30 min and even less than 20 min by adding various amounts of setting accelerator. The average compressive strength andmodulus ofmaterials after final setting range from about 2.0 to nearly 20MPa and about 100 to 750.0 MPa with the difference of L/S ratio, setting accelerator content and nHAC content, respectively, which are similar to the mechanical properties of cancellous bone. The degradation rate of the materials matches that of tissue formation. The excellent interactions between the materials and cells imply that the composites as a scaffold can provide a satisfactory biological environment for cell adhesion, migration, and proliferation (Fig. 1A). Its good efficacy in bone regeneration as bone materials strongly supports that the composites can offer adequate stimulus for new bone growth and bone regeneration in the implants (Fig. 1B and C). As injectable bone materials, the nHAC/CSD composites can not only provide a satisfactory biological environment for facilitating cell adhesion, migration, and proliferation but also offer adequate stimulus for growing new bone and bone regeneration in the implants.