Biomimetic nanocomposite hydrogel promotes tendon healing and tissue regeneration

The new system, termed KGN@PB@CM, combines several advanced elements. Prussian blue (PB) nanozymes act as potent reactive oxygen species (ROS) scavengers, while kartogenin (KGN)-a small molecule that promotes stem cell migration and tenogenic differentiation-is loaded onto the PB core. To enable targeted delivery to inflamed sites, the nanoparticles are coated with macrophage cell membranes, providing homologous targeting capability. Finally, the nanoparticles are embedded in a thermosensitive Pluronic F127/hyaluronic acid (HA‑F127) hydrogel that remains a sol at room temperature but gels rapidly at body temperature, ensuring sustained local release.

We aimed to resolve two major barriers in tendon healing: the persistent inflammatory microenvironment and the lack of efficient tenocyte regeneration. By engineering a macrophage‑membrane‑coated nanoplatform that can both scavenge ROS and deliver KGN, we created a synergistic system that reprograms immune responses while directly promoting tendon‑specific differentiation."

Dr. Huan Li, Department of Articular Orthopaedics, The First People’s Hospital of Changzhou, The Third Affiliated Hospital of Soochow University, Changzhou, China

In vitro experiments confirmed the system's capabilities. The KGN@PB@CM nanoparticles showed excellent ROS scavenging activity in DPPH assays, and they protected tendon‑derived stem cells (TDSCs) from hydrogen peroxide‑induced oxidative damage, as shown by DCFH‑DA staining. Live/dead staining and CCK‑8 assays demonstrated good cytocompatibility, while EdU incorporation revealed significantly enhanced TDSC proliferation in the KGN@PB@CM group.

More importantly, the nanoparticles effectively modulated macrophage polarization. When RAW 264.7 macrophages were stimulated with lipopolysaccharide (LPS) to create a pro‑inflammatory environment, treatment with KGN@PB@CM markedly reduced the expression of M1 markers (iNOS, CD86) and increased M2 markers (CD206, Arg‑1, IL‑10) at both mRNA and protein levels. ELISA assays confirmed decreased secretion of pro‑inflammatory cytokines IL‑1β, IL‑6, and TNF‑α, alongside elevated anti‑inflammatory IL‑10 and TGF‑β1. "This shift from M1 to M2 polarization is critical for transitioning from inflammation to tissue repair," notes Dr. Yan.

The team also evaluated the direct impact on TDSCs. Immunofluorescence staining and qRT‑PCR revealed that KGN@PB@CM significantly up‑regulated key tenogenic markers-including collagen type I (COL1), tenomodulin (TNMD), scleraxis (SCX), and mohawk (MKX)-compared to PB or KGN@PB alone. "KGN released from the nanoparticles recruits endogenous stem cells and drives their differentiation into tenocytes, while the PB core ensures that oxidative stress does not impede this process," adds Dr. Li.

The therapeutic efficacy was tested in a rat Achilles tendon injury model. Four groups were compared: sham, untreated model, negative control hydrogel (NC‑gel), and KGN@PB@CM‑loaded hydrogel (NPs@gel). At 2 and 4 weeks post‑surgery, histological analysis (H&E and Masson's trichrome) showed that the NPs@gel group had well‑aligned collagen fibers, dense extracellular matrix, and significantly lower Bonar histological scores compared to model and NC‑gel groups. Immunofluorescence of tendon tissues confirmed reduced CD86+ M1 macrophages and increased CD206+ M2 macrophages in the NPs@gel group, along with elevated COL1 and TNMD expression and decreased α‑SMA (a fibrosis marker).

Functional recovery was assessed using CatWalk gait analysis. Rats treated with KGN@PB@CM displayed improved paw print area, stride length, and paw pressure, with reduced swing duration-parameters that approached those of sham‑operated animals by week 4. Biomechanical testing further demonstrated that NPs@gel‑treated tendons had significantly higher failure load, tensile strength, stiffness, and Young's modulus compared to control groups, indicating restoration of mechanical integrity.

Histological examination of major organs (heart, lung, spleen, liver, kidney) at 8 weeks showed no signs of inflammation, necrosis, or fibrosis, confirming excellent long‑term biocompatibility. "Our dual‑modulation strategy-anti‑inflammatory and pro‑tenogenic-offers a comprehensive platform for tendon repair," concludes Dr. Yan. "While further studies in larger animal models and longer follow‑up are needed, this biomimetic nanocomposite hydrogel holds great promise for clinical translation, not only for tendon injuries but also for other conditions where immune modulation and tissue regeneration are required.".