Diabetes is a metabolic disorder characterized by insulin resistance or impaired insulin secretion. Chronic hyperglycemia associated with diabetes can lead to severe damage in multiple organs, including the heart, vasculature, eyes, kidneys, and nervous system. Approximately 20 % of individuals with diabetes develop diabetic ulcers because of hyperglycemia-induced infections, poor circulation, reduced levels of growth factors, and neuropathy stemming from neurovascular complications [1].

Diabetic ulcers are classified as chronic wounds, as the healing process remains arrested in the inflammatory phase. In healthy tissues, wound healing follows a tightly regulated sequence of hemostasis, inflammation, proliferation, and remodeling [2]. During the inflammatory phase, immune cells migrate to the injury site, where they clear cellular debris and pathogens via phagocytosis. Simultaneously, fibroblasts and keratinocytes begin migrating to cover the wound area. This phase is also marked by an increase in reactive oxygen species (ROS) levels. In the subsequent proliferative phase, keratinocyte migration supports re-epithelialization and neovascularization, during which ROS levels normally decline. However, in diabetic conditions, persistent hyperglycemia leads to continuous ROS generation due to impaired glucose metabolism. In this environment, epidermal cells exhibit abnormal proliferation, while ineffective clearance of debris and pathogens—attributable to T-cell dysfunction—exacerbates inflammation. This results in increased production of pro-inflammatory cytokines and a concurrent reduction in growth factor synthesis [2].

Oxidative stress associated with elevated ROS levels under hyperglycemic conditions disrupts essential cellular functions such as proliferation, migration, and protein synthesis in fibroblasts, keratinocytes, and endothelial cells. This, in turn, impairs angiogenesis and contributes to axonal degeneration and neuropathy by reducing ATP synthesis. Furthermore, the accumulation of advanced glycation end-products (AGEs) negatively impacts extracellular matrix (ECM) integrity and remodeling. As a result, diabetic ulcers are characterized by a prolonged inflammatory phase and compromised tissue regeneration due to insufficient remodeling processes [2,3].

Photobiomodulation (PBM) is a therapeutic technique that utilizes low-level laser therapy (LLLT) to modulate cellular activity and promote tissue regeneration. LLLT is a low-intensity, non-thermal, non-invasive, and non-ablative method that employs lasers, light-emitting diodes (LEDs), and non-ionizing light sources—particularly in the visible red and near-infrared spectra. Light-based therapies have demonstrated effectiveness in enhancing tissue regeneration, reducing inflammation, and alleviating pain [[4], [5], [6]].

PBM modulates the expression of genes involved in tissue repair by influencing cellular redox states and reducing oxidative stress within the wound microenvironment [7,8]. During photostimulation, photons are absorbed by intracellular chromophores—primarily mitochondrial enzymes—which lead to enhanced ATP production. This increase in cellular energy activates multiple signaling pathways mediated by cytokines and growth factors. Notably, PBM has been shown to stimulate critical signaling cascades such as ERK1/2 MAPK (extracellular signal-regulated kinase/mitogen-activated protein kinase), Wnt (Wingless-related integration site), PI3K/AKT (phosphatidylinositol 3-kinase/protein kinase B), and Notch pathways. These pathways play essential roles in regulating the proliferation, migration, and differentiation of fibroblasts, keratinocytes, and endothelial cells [8].

Clinically, PBM is employed in the treatment of various types of wounds, including diabetic ulcers, venous ulcers, pressure sores, and burns, due to its ability to promote deep tissue regeneration. The effectiveness of PBM depends on specific parameters, such as wavelength (typically 660–904 nm), pulse frequency (0–80 Hz), pulse structure, total energy, and fluence (2–25 J/cm2). These parameters are closely linked to cellular responses and therapeutic outcomes [5,7,9].

Several studies have explored the use of different wavelengths and intensities in wound healing. For instance, Hopkins et al. utilized an 820 nm wavelength at varying intensities in clinical trials to assess wound healing outcomes [10]. Yasukawa et al. applied LLLT in rat models to evaluate its effects on wound healing [11]. Prabhu et al. conducted spectroscopic and histological analyses of wounds treated with 632.8 nm irradiation, demonstrating enhanced tissue repair [12]. Solmaz et al. investigated the proliferative effects of 635 nm and 809 nm wavelengths both in vitro and in vivo, finding that 635 nm significantly improved healing, while 809 nm had no observable effect [13]. He et al. used 600 nm light to stimulate fibroblast activation during wound healing [5]. Additionally, Neto et al. demonstrated that blue light photostimulation in an in vivo burn model enhanced re-epithelialization and growth factor secretion while reducing inflammation [6]. Numerous others in vivo studies have employed wavelengths such as 660, 808, and 810 nm for the treatment of diabetic wounds, further supporting the efficacy of PBM in regenerative medicine [4,[14], [15], [16], [17]].

This study aimed to investigate the effects of PBM on wound healing under diabetic conditions. For the first time, this study explored the synergistic effects of wavelengths within the “therapeutic window” on diabetic wound from multiple perspectives—including ECM formation, re-epithelialization, and angiogenesis—human dermal fibroblasts (HDFs), keratinocytes (HS2), and endothelial cells (HUVECs) cultured under hyperglycemic conditions were utilized in in vitro experiments. In contrast to the monochromatic light sources commonly employed in literature, a polychromatic light source was used in this study. This approach offers several distinct advantages: i) it provides a broad wavelength spectrum in the range of 600–1200 nm, ii) it delivers polarized light, which not only conserves energy but also ensures significantly greater tissue penetration compared to conventional sources, and iii) it features a treatment area approximately 10 times larger (0.3 m2) than that of typical monochromatic devices.