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An injectable and self-setting bone repair materials (nano-hydroxyapatite/collagen/calcium sulfate hemihydrate, nHAC/CSH) was developed in this study. The nano-hydroxyapatite/collagen (nHAC) composite, which is the mineralized fibril by self-assembly of nano-hydrocyapatite and collagen, has the same features as natural bone in both main hierarchical microstructure and composition. It is a bioactive osteoconductor due to its high level of biocompatibility and appropriate degradation rate. However, this material lacks handling characteristics because of its particle or solid-preformed block shape. Herein, calcium sulfate hemihydrate (CSH) was introduced into nHAC to prepare an injectable and self-setting in situ bone repair materials. The morphology of materials was observed using SEM. Most important and interesting of all, calcium sulfate dihydrate (CSD), which is not only the reactant of preparing CSH but also the final solidified product of CSH, was introduced into nHAC as setting accelerator to regulate self-setting properties of injectable nHAC/CSH composite, and thus the self-setting time of nHAC/CSH composite can be regulated from more than 100 min to about 30 min and even less than 20 min by adding various amount of setting accelerator. The compressive properties of bone graft substitute after final setting are similar to those of cancellous bone. CSD as an excellent setting accelerator has no significant effect on the mechanical property and degradability of bone repair materials. In vitro biocompatibility and in vivo histology studies demonstrated that the nHAC/CSH composite could provide more adequate stimulus for cell adhesion and proliferation, embodying favorable cell biocompatibility and a strong ability to accelerate bone formation. It can offer a satisfactory biological environment for growing new bone in the implants and for stimulating bone formation.

This study investigated how human adipose stem cells (hASCs) could be influenced by surface chemistry. Self-assembled monolayers of alkanethiolates on gold were introduced as a surface chemistry model to provide a range of functional groups such as OH, COOH, NH₂, Phenyl, SH, Br, and CH₃ on surfaces. Initially, morphological changes of hASCs in response to different surface chemistries were observed with focal adhesion. Cell growth behaviour evaluated by Cell Counting Kit-8 (CCK8) assay (Dojindo Molecular Technologies Inc., Shanghai, China) and cytoskeletal F-actin Biochem Kit™ (Denver, CO, USA) staining revealed a descending order of growth rate on the following surfaces: NH₂ > SH > COOH > Phenyl > Br > OH > CH₃. The mRNA expressions of lineage specific markers including alkaline phosphatase (ALP), osteocalcin (OCN), type II collagen, aggrecan, peroxisome proliferator-activated receptor gamma (PPARγ), and fatty acid binding protein-2 (aP2), were determined using real-time reversed transcriptase-polymerase chain reaction (RT-PCR). Results revealed that NH₂ favoured hASC differentiation toward osteogenic, while phenyl and SH promoted chondrogenic differentiation of hASCs with a high level up-regulation of type II collagen and aggrecan. hASCs on Br increased in PPARγ and aP2 expression, indicating adipogenic differentiation. These results highlight the vital role of surface chemistry on the modulation of hASC differentiation and suggests chemical methods for designing biomaterials for stem cell-based tissue regeneration.

A novel injectable bone cement based on mineralized collagen was reported in this paper. The cement was fabricated by introducing calcium sulfate hemihydrate (CaSO(4).1/2H(2)O, CSH) into nano-hydroxyapatite/collagen (nHAC). The workability, in vitro degradation, in vitro and in vivo biocompatibility of the cement (nHAC/CSH) were studied. The comparative tests via in vitro and in vivo showed that the nHAC/CSH composite cement processed better biocompatibiltiy than that of pure CSH cement. The results implied that this new injectable cement should be very promising for bone repair.

Comparative investigations of bone regeneration performance for calcium sulfate hemihydrate (CaSO(4).(1/2)H(2)O; CSH) only and CSH with mineralized collagen are reported in this article. The mineralized collagen is the nanohydroxyapatite/collagen (nHAC). The investigations included biocompatibility in vitro and performance of bone repair in vivo. Quantitative and qualitative biocompatibility assays with bone stromal stem cells were performed. A critical box-shaped defect model in the mandible of the rabbit was used to evaluate the bone-remodeling ability of CSH and nHAC/CSH. Results in vitro indicated that the nHAC/CSH significantly improved bioactivity compared with that of CSH, especially in promoting cell adhesion. Further, a higher bone remodeling activity was observed around nHAC/CSH composite than the CSH, especially at the early stage of remodeling. This result means that nHAC/CSH could cause an earlier accelerator and better osseointegration for bone repair than CSH only.

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