Polychromatic photobiomodulation accelerates diabetic wound repair via pro-angiogenic and anti-inflammatory mechanisms

Abstract

This study aimed to evaluate the histological and molecular effects of polychromatic photobiomodulation (PBM, 600–1200 nm), delivered at varying treatment frequencies, on wound healing in a streptozotocin (STZ)-induced diabetic rat model. To minimize inter-subject variability, three full-thickness excisional wounds were created on the dorsum of each diabetic rat and assigned to one of three groups: untreated Negative Control (NC), once-daily PBM (PBM1), or twice-daily PBM (PBM2). Treatments were administered using a polychromatic light source (600–1200 nm) placed 30 cm away from the wounds at an irradiance of 0.038 W/cm² with escalating fluences over a six-day period. Skin samples were harvested on Days 7 and 14 post-wounding and analyzed using Masson’s Trichrome staining and immunohistochemistry for VEGF, VEGFR2, TGF-β, TGF-βR2, CD163, and TNF-α. The PBM2 regimen significantly enhanced re-epithelialization, collagen deposition, and angiogenesis compared to both PBM1 and untreated controls. Immunohistochemical analysis demonstrated early and pronounced expression of VEGF and CD163, along with sustained activation of TGF-βR2 in the PBM2 group. TNF-α expression was significantly reduced, particularly in the PBM2-treated wounds, suggesting accelerated resolution of inflammation and enhanced M2 macrophage polarization. Masson’s Trichrome staining further confirmed the presence of denser and more organized collagen fibers in PBM2-treated wounds. Collectively, these findings indicate that twice-daily polychromatic PBM facilitates diabetic wound healing through synergistic proangiogenic, anti-inflammatory, and fibroproliferative pathways. This study supports the further optimization of PBM protocols for the effective management of chronic wounds.