Zinc oxide nanoparticle chelated phosphocreatine-grafted chitosan composite hydrogels for enhancing osteogenesis and angiogenesis in bone regeneration

Leidong Lian¹Dingli Xu²Chaonan He¹Zhe Luo²Han Yu²Botao Liu²Ke Zhou¹Liangjie Lu¹Kaifeng Gan^1*

• ¹Ningbo Medical Centre Lihuili Hospital, Ningbo, China
• ²Ningbo University Health Science Center, Ningbo, China

The natural polysaccharide-based injectable hydrogels have showed significant interest to use as 3D scaffolds for critical-sized bone defect repair. Here, we incorporated ZnO nanoparticles (NPs) into a newly synthesized water-soluble phosphocreatine-functionalized chitosan (CSMP) water solution to form an injectable hydrogel (CSMP-ZnO) via supramolecular combination between phosphate groups in CSMP and Zinc in ZnO NPs. The phosphocreatine in this hydrogel not only provides sites to combine with ZnO NPs form supramolecular binding but also serves as the reservoir to control Zn2+ release. The results show that the lyophilized CSMP-ZnO hydrogels presented a porous structure with some small holes in the pore wall, as shown by scanning electron microscopy. Rheological characterizations revealed that the mechanical properties of the hydrogels were almost maintained upon the addition of ZnO NPs. In vitro experiments showed that the CSMP-ZnO hydrogel exhibits excellent angiogenic and osteogenic properties compared with the CSMP hydrogel. The as-released Zn2+ ions promote the high expression of osteoblast collagen 1 proteins and accelerate bone mineralization by activating the BMP2/SMAD signaling pathway. In vivo, the as-released Zn2+ ions promot osteoblastic proliferation and the mineralization of osteoblasts inside the CSMP-ZnO scaffolds. Immunofluorescence for RUNX2, COL-1, and CD31, showed that stable vasculature could be formed inside the CSMP-ZnO scaffolds. Both the in vitro and in vivo results demonstrate that CSMP-ZnO hydrogel shows promise for bone regeneration, suggesting a new strategy for tissue engineering and regeneration in the future.