A Mitochondrial-Based Transfer and Metabolic Remodeling Hydrogel with Immune Responsiveness to Augmented Bone Regeneration

Intercellular mitochondrial transfer has recently been discovered as a strategy for local microenvironment regulation and repair. However, improving the efficiency of mitochondrial transfer and reducing immune rejection caused by implants is challenging for its application in bone regeneration tissue engineering. We found that bone marrow mesenchymal stem cells (BMSC)s can obtain mitochondria from macrophages through tunnel nanotubes (TNT)s. Mitochondria are crucial for the metabolism and function of BMSC. We further designed a composite hydrogel based on aldehyde sodium hyaluronate and chitosan as the network matrix, containing anti-inflammatory dimethyl itaconate (DMI) and macrophage-targeted zwitterionic nanoparticles (MDVNPs). The acidic bone injury microenvironment triggers a reversible Schiff base reaction in response to pH; further, the released DMI upregulates the M2 phenotype of macrophages by reducing the ROS level. Subsequently, MDVNPs with targeting, high transfection, and low immunogenicity accelerated the efficiency of mitochondrial transfer between macrophages and BMSC by increasing the expression of the mitochondrial transfer regulatory protein Rho GTPase 1 (Miro1). In vitro studies have confirmed that promoting mitochondrial transfer can effectively increase adenosine triphosphate (ATP) and oxidative phosphorylation (OXPHOS) levels in BMSC, promoting osteoblastic differentiation. In the mouse model of critical defect, the composite hydrogel (Gel@MDI) can reduce inflammatory reactions, improve energy metabolism, and enhance bone repair by promoting the balance between the immune system and bone metabolism. This study establishes a potential method for the immune microenvironment to enhance cellular mitochondrial bioenergy and achieve tissue regeneration by regulating mitochondrial transfer between cells.