The clinical problem the material targets is stubbornly common. Autologous bone grafting remains the gold standard, but it carries donor site morbidity, limited graft supply, and surgical risk. Injectable hydrogels can conform to irregular defects through minimally invasive delivery, yet they are typically too soft for load-bearing applications and often require external triggers such as photo-crosslinking to stiffen. The new material, built from regenerated silk fibroin, tyramine-modified carboxymethyl cellulose, and a hybrid of MXene nanosheets with cellulose nanofibers, sidesteps that limitation by maturing autonomously once inside the body.

The self-reinforcement mechanism is a story of molecular choreography. After the precursor solution is injected, an enzymatic horseradish peroxidase and hydrogen peroxide system triggers phenolic crosslinking of the tyramine-modified cellulose, gelling the material in roughly 100 to 300 seconds depending on formulation. Over the following days, the confined environment created by the cellulose network restricts the mobility of silk fibroin chains, nudging them from random coils into aligned beta-sheet crystalline domains. Meanwhile, the MXene-cellulose nanosheets act as templates, offering abundant hydrogen-bonding sites that guide the orientation of those beta-sheets along their surfaces. The result is a progressively ordered, densely packed network whose compressive modulus climbs nearly tenfold, from about 0.08 megapascals at day zero to roughly 0.85 megapascals by day five.

That mechanical trajectory matters because it is rare. In an Ashby plot comparison against other self-reinforcing injectable hydrogels reported in the literature, the optimized formulation occupied a distinctly superior region of the mechanical-injectability landscape. The gel also demonstrated practical shape-filling, uniformly occupying an irregular defect carved into a porcine femur, and it retained more than 90 percent of its dry weight after 28 days of degradation testing, with moderate swelling between 160 and 180 percent. Implanted samples harvested at 14 and 28 days kept their compressive strength, suggesting the material holds the line during the critical early window of repair.

The electrical side of the design is equally deliberate. Bone’s native piezoelectricity arises from collagen and mineral converting mechanical stress into charge, and the team sought to recreate that transduction within a soft matrix. Rather than relying on rigid piezoelectric ceramics like barium titanate or zinc oxide, which aggregate and resist biodegradation, the researchers used Ti3C2Tx MXene modified with cellulose nanofibers. Spectroscopic analysis showed hydrogen-bond-mediated coupling between the cellulose hydroxyl groups and MXene surface terminations, which improved interfacial polarization and produced a higher dielectric constant with lower dielectric loss in model composites.

Under cyclic compression at 0.1 megapascals, the hydrogel’s output scaled dramatically with both MXene-cellulose concentration and maturation time. The unmodified silk-cellulose gel produced only about 10 millivolts, but the optimized 0.4 percent MXene-cellulose formulation generated up to 60 millivolts by day seven, a signal that rose in lockstep with beta-sheet formation and dipole alignment. The composite achieved a piezoelectric voltage coefficient of 22.6 millivolts per meter per newton and a markedly increased figure of merit, while outputs remained stable over 100 seconds of continuous cycling and scaled nearly linearly with applied pressure. Piezoresponse force microscopy confirmed strong nanoscale amplitude and near-180-degree phase contrast, hallmarks of well-aligned piezoelectric domains. The authors note that because MXene is not a classical piezoelectric crystal, the response is best attributed to interface-mediated electromechanical coupling across the composite network rather than intrinsic crystal piezoelectricity.

Crucially, the generated signals fall within the biologically relevant range known to activate calcium signaling in bone-forming cells. In vitro, bone marrow mesenchymal stem cells and endothelial cells cultured alongside the mechanically activated hydrogel proliferated faster than those exposed to unstimulated gels, with stimulation at four compression cycles per minute proving optimal. Alkaline phosphatase staining and alizarin red mineralization assays showed the strongest early and late osteogenic differentiation in the stimulated group, and Western blotting plus quantitative PCR confirmed upregulation of RUNX2, osteopontin, and osteocalcin. Scratch wounds, Transwell migration, and tube-formation assays added that endothelial cells formed more extensive capillary-like networks under piezoelectric stimulation, with angiogenic genes including CD31, von Willebrand factor, and VEGF elevated, painting a pro-regenerative microenvironment on both the bone and vascular fronts.

The deepest finding, and the one that gives the study its subtitle, lies in the epigenetics. RNA sequencing revealed that piezoelectric stimulation shifted stem cells toward calcium signaling and histone acetylation programs. Fluo-4 calcium imaging showed a surge of intracellular calcium within 30 minutes of stimulation, and Western blots confirmed phosphorylation of CaMKII and CREB, the canonical calcium-dependent cascade. Downstream, the acetyltransferase P300 rose, and histone H3 lysine 9 acetylation, a reversible mark tied to transcriptional activation, climbed in a dynamic, time-dependent pattern that peaked around 24 hours before partially declining. Chelating calcium with BAPTA or inhibiting P300 with C646 abolished both the acetylation signal and the osteogenic boost, establishing causality rather than mere correlation.

To find which genes the acetylation actually switched on, the team performed CUT&Tag profiling of H3K9ac and integrated it with the transcriptomic data. The overlap pointed squarely at PTH1R, the parathyroid hormone 1 receptor, a central regulator of bone remodeling whose promoter showed enriched H3K9ac and whose mRNA and protein levels rose under stimulation but fell when P300 was blocked. Pharmacologically antagonizing PTH1R suppressed RUNX2, osteopontin, and osteocalcin expression and reduced mineralization even under active piezoelectric stimulation, completing a coherent mechanistic chain: mechanical load becomes electricity, electricity opens calcium channels, calcium activates P300, P300 acetylates histones, and acetylated chromatin unlocks PTH1R-driven osteogenic transcription.

The in vivo evidence sealed the story. In a rat femoral condyle defect model, micro-computed tomography at 6 and 12 weeks showed substantially greater bone mineral density, bone volume fraction, trabecular thickness, and trabecular number in the piezoelectric hydrogel group compared with controls, plain silk gels, or the non-piezoelectric composite. Fluorochrome double labeling revealed a higher mineral apposition rate, and histology showed dense trabecular architecture with robust collagen deposition. Immunohistochemistry confirmed elevated H3K9ac and PTH1R in the new bone, mirroring the in vitro cascade. Blood chemistry and organ histology showed no hepatic or renal abnormalities, and an ex vivo porcine bone model confirmed the implanted gel still produced repeatable voltage under bone-like loading. Together, the results sketch a material that does not merely plug a hole in the skeleton but actively speaks the skeleton’s native electrical language, converting each step a patient takes into an epigenetic instruction to rebuild.

Subject of Research: Injectable self-reinforcing piezoelectric hydrogel for bone defect regeneration via epigenetic regulation

Article Title: An Injectable and Self‐Reinforced Piezoelectric Hydrogel for Irregular Bone Defects Regeneration: Dynamic Epigenetic Regulation Approach

Article References: Huang, Y.-K., Li, J., Yang, M.-M., Jia, C., Gong, Q.-X., Yuan, G.-C., Zhou, D., Shen, W.-H., Chen, Z.-G., Dong, Z.-R., Huang, J.-W., Peng, J., Su, D.-H., Zhao, M.-D., Dong, J., & Jiang, L.-B. (2026). An Injectable and Self‐Reinforced Piezoelectric Hydrogel for Irregular Bone Defects Regeneration: Dynamic Epigenetic Regulation Approach. Advanced Science, Article e77911. https://doi.org/10.1002/advs.77911

Image Credits: AI Generated

DOI: 10.1002/advs.77911

Keywords: piezoelectric hydrogel, bone regeneration, MXene, silk fibroin, epigenetics, H3K9 acetylation, PTH1R, calcium signaling, stem cells, injectable biomaterials, tissue engineering, Injectable