Ultrasound-activated piezoelectric hydrogel for local infection control and bone repair in osteomyelitis

Biofilm-associated infection and persistent inflammation make osteomyelitis difficult to eradicate while preserving the capacity for bone repair. Here, we developed an injectable gelatin hydrogel crosslinked by microbial transglutaminase and containing polarized barium titanate (BTO) nanoparticles (mTG-Gel/BTO). The material exhibited pressure-responsive electrical output. Pulsed ultrasound (US) exposure at device settings of 1.5 W cm⁻², 1 MHz, and 50% duty cycle produced time-dependent oxidative activity. The combined treatment reduced viable counts and biofilm-associated readouts for methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli while maintaining RAW 264.7 macrophage viability under the tested conditions. In lipopolysaccharide-stimulated macrophages, mTG-Gel/BTO + US reduced intracellular oxidation-associated fluorescence, increased antioxidant-related transcripts, decreased CD86 expression and TNF-α secretion, and increased CD206 expression and IL-10 secretion. Separate endothelial and osteogenic assays showed enhanced cell migration, network formation, osteogenic differentiation, and matrix mineralization. In a rat tibial MRSA model, mTG-Gel/BTO + US reduced bacterial burden and infection-associated bone destruction and improved radiographic and histological indicators of repair. These findings support an ultrasound-responsive hydrogel strategy that combines local infection control with a cellular environment favorable for bone repair. The formulation integrates physically incorporated BTO with an enzymatically crosslinked gelatin matrix, offering a simple material design for conformal delivery into irregular defects. The injectable mTG-Gel/BTO hydrogel integrates an mTG-crosslinked gelatin network with physically incorporated BTO nanoparticles for local treatment of infected bone defects. Pulsed US activates BTO-associated piezoelectric responses, linking ROS generation to antibacterial and antibiofilm effects and VGCC-mediated Ca²⁺ signaling to macrophage immunomodulation. The resulting pro-regenerative microenvironment promotes angiogenic and osteogenic responses, ultimately supporting vascularized bone regeneration. US, ultrasound; mTG, microbial transglutaminase; BTO, barium titanate; ROS, reactive oxygen species; VGCCs, voltage-gated calcium channels