Development and biocompatibility of the injectable collagen/nano-hydroxyapatite scaffolds as in situ forming hydrogel for the hard tissue engineering application.

Injectable hydrogels attract more attention to hard tissue engineering for the fulfilment of the defects with irregular shapes. Therefore, the researchers investigated the biocompatibility and immune response to the injectable PCL-PEG-PCL-Col/nHA hydrogels in a mouse model. The histological examination was done via H&E. The activation of the immune cells was evaluated by using antibodies against the CD68, CD4, and CD8 markers. The expression of CCL-2, BCL-2, IL-10, and CD31 genes was measured. Moreover, serum levels of the ALT, ALP, AST, and Urea were detected. The results of the chemical analysis showed that the collagen and Nano-hydroxyapatite were successfully integrated into the PCL-PEG-PCL hydrogels. The histological examination revealed a delayed biodegradation rate after the addition of the collagen and Nano-hydroxyapatite. No prominent pro-inflammatory response was found at the site of the injection. There are no significant differences in the levels of the CD68 and CD8/CD4 lymphocyte ratio among groups (p > .05). The expression of the CD31, IL-10 was significantly increased in the PCL-PEG-PCL-Col/nHA hydrogel (p < .05). ALT, ALP, AST, and Urea levels were not altered pre- and post-transplantation of the hydrogels (p > .05). These in vivo results demonstrated that the injectable PCL-PEG-PCL-Col/nHA hydrogels are biocompatible and suitable for further research in hard tissue regeneration.