Biomimetic fabrication and freeze-casting of collagen-apatite hydrogels for bone tissue engineering

Collagen-apatite (Col-Ap) scaffolds have been widely employed for bone tissue engineering. In the current study, we fabricated Col-Ap hydrogels with a biomimetic structure and freeze-dried Col-Ap hydrogels with a hierarchical lamellar structure. Col-Ap hydrogel was prepared using a biomimetic approach combining self-assembling of collagen molecules with simultaneous mineralization in a modified simulated body fluid (m-SBF). A novel two-temperature process involving gelation at 25 ^oC and then 40 ^oC was applied to increase the diameter of mineralized collagen fibers. Col-Ap hydrogel consisting of collagen bundles reinforced by apatite nano-particles was further subjected to self-compression and controlled freeze-casting. The freeze-dried hydrogel exhibits a hierarchical lamellar structure consisting of co-aligned macro and micro pores. Moreover, this novel lamellar structured scaffold supports the attachment and spreading of MC3T3-E1osteoblasts. Therefore, owing to the biomimetic composition, hierarchical lamellar structure and good biocompatibility of this novel freeze-dried Col-Ap hydrogel, it has great potential to be used in bone tissue engineering applications.