**6. Diabetic wound healing in animals and patients (diabetic foot ulcers (DFU))**

DM is the general name for a heterogeneous group of metabolic disorder characterized by high blood glucose levels that result from defects in insulin secretion and/or action [9]. The per‐ centage of the population diagnosed with DM continues to increase. A study projects that as many as one in three US adults may have DM by the year 2050 if current trends continue. The expense of DM in the United States, at more than \$174 billion per year in 2007, is anticipated to become an increasingly large financial burden in the future [10].

DFUs are a common problem among individuals with DM. These ulcers are among the most serious complications of DM that may result in amputation and mortality [11]. The prevalence of DFU in people with DM vary from 4% to 10% with a lifetime incidence as high as 25% [12]. Treatment of diabetic foot is extremely hard because these wounds are delineated by delayed healing; often result in chronic wound [13]. It has been reported that the 5‐year mortality leading to lower extremity amputations may be as high as 68% [14]. Therefore, successful treatment of diabetic ulcers is a field of huge importance [15].

Many elements considered to be sources for the lack of healing in diabetic wounds involve peripheral neuropathy, the presence of an impaired immune system, peripheral microvascular disease, glycation of hemoglobin that leads to inadequate oxygen delivery to tissues, altera‐ tions in the red blood cell membrane [13] due to glycation, interchange in the proportion of type III to type I collagen in the skin [16], impaired biomechanical properties of the diabetic skin [17], impaired proliferation of skin fibroblasts [18], and impaired l‐lactate production [19]. The diabetic wound is a disorder of the wound healing process, especially in the inflammatory and proliferative phases [13], pathologic angiogenesis [20], and a significant diminishing of the tensile strength of wound repair, detected in studies on diabetic animal models [21].

According to a review of the literature, numerous in vitro and in vivo studies, as well as clinical trials have reported positive effects of LLLT on the wound healing process both in animals and human patients.
