Ultralong hydroxyapatite nanowires/collagen scaffolds with hierarchical porous structure, enhanced mechanical properties and excellent cellular attachment

Hydroxyapatite/collagen (HAP/Col) composite porous scaffolds have been extensively investigated in the field of bone tissue engineering due to their similar chemical composition to that of natural bone and good biocompatibility. However, the relatively poor mechanical properties of the HAP/Col composite porous scaffolds limit their application in bone regeneration. In order to overcome these limitations, the hierarchical porous ultralong hydroxyapatite nanowires (UHANWs)/collagen (Col) composite scaffolds with excellent mechanical properties are synthesized by freeze-drying the suspension containing UHANWs and collagen. Compared with the HAP nanorods (HANRs), the highly flexible UHANWs can interweave with each other to construct a threedimensional fabric -like structure in the collagen matrix of the UHANWs/Col scaffolds and significantly improve the mechanical properties of the scaffolds. The Young's modulus of the 70 wt% UHANWs/Col scaffold is about 4 times that of the pure collagen scaffold and 63 times that of the 70 wt% HANRs/Col scaffold. More importantly, in the absence of the collagen matrix, the pure UHANWs inorganic porous scaffold can be synthesized and exhibits relative good mechanical properties. However, the HANRs/Col scaffolds with HANRs weight fractions more than 70 wt% are easily cracked during the fabrication process. Furthermore, compared with the pure collagen and 70 wt% HANRs/Col scaffolds, the 70 wt% UHANWs/Col scaffold exhibits a superior biocompatibility and excellent ability to promote cell adhesion and spreading on the surface of the scaffold. In consideration of their outstanding mechanical properties and excellent cellular attachment performance, the as -prepared hierarchical porous UHANWs/Col scaffolds are promising for applications in various biomedical fields such as bone defect repair.