A self-degradable “nanoarmor” coating of medical implant potentiates bone fracture healing

Bionic functional coating plays a pivotal role in promoting internal fixation treatment of bone fracture. However, post-traumatic microenvironment characterized by hypoxia and acidic milieu, as well as high oxidative stress, may largely weaken the function of established coatings. Herein, we anchor two-dimensional H-silicene nanosheet (H-Si) onto hydroxyapatite (HA)-coated metal implant to develop a H-Si@HA composite coating. Benefiting from the intrinsic pH-responsive characteristics, the H-Si@HA maintains stable structure and functionalities in acidic milieu and simulates the superoxide dismutase and peroxidase-like activities, resulting in reactive oxygen species depletion, high oxidative stress suppression and further reversal of the acidic microenvironment. Meanwhile, H-Si@HA protects cells by inducing cellular autophagy. Sequentially, Si⁴⁺ release accompanying the degradation of the H-Si in neutral milieu promotes fracture healing by improving osteogenic-related gene expression of bone mesenchymal stem cells (BMSCs) and SOD1 expression of osteoprogenitor cells. Particularly, differentiated gene expression of BMSCs by the H-Si@HA coating was identified using absolute quantitative transcriptome sequencing, revealing that the H-Si could effectively modulate the expression of core mRNAs which are highly associated with osteogenesis and bone formation through regulating autophagy. Such a self-degradable nanoarmor coating illustrates the great clinic potential to achieve hierarchical and synergistic effect of fracture healing promotion.