Wounds can have devastating consequences for health, causing chronic pain, loss of body parts, and can even lead to death. Despite a multitude of methods employed by modern medicine to facilitate wound healing, some wounds, particularly diabetic, post chemotherapy, and radiation ulcers, remain recalcitrant to all treatments. Therefore, novel approaches are required to induce reliable wound healing.
Can laser treatment improve the outcome? The jury is still out. Despite numerous reports on the benefits of laser light illumination for wound repair, there are also studies that claim otherwise.
In the following article, we will try to summarize the claimed benefits, discuss proposed mechanisms of action, and address technical issues that may contribute to the controversy surrounding laser wound treatment.
• Pressure ulcers. Irradiation enhances the healing and closure of nonhealing chronic venous insufficiency ulcers. After irradiation with 635nm or 810nm light at constant fluence (4 J/cm2) and fluence rate (10 mW/cm2) a 13-times reduction in the ulcer area was observed compared to the control placebo therapy, with full granulation and closure of the ulcers in 86% of the patients. Similar results were reported also for treatment with other wavelengths: 637nm, 660–670nm, and 956nm. However, irradiation with 730nm and 980nm did not show any beneficial effect. Moreover, 980nm treatment revealed edema, denuded epithelium, and persisting inflammatory infiltrate in the wound bed.
• Diabetic wounds. There are reports that irradiation with laser light at 633nm results in inducing a 1.6-fold increase in the healing of recalcitrant diabetic foot ulcers. Also, applying 660nm and 890 nm at a power density of 10 mW/cm2 and irradiance of 4 J/cm2 resulted in a significant wound area reduction, with 75% of the ulcers achieving 90–100% healing in 90 days. However, treatment with 730nm and 980 nm wavelengths does not stimulate healing.
• Antibacterial actions. Bacteria are primarily responsible for poor wound healing. The disinfection properties of UV light are well-documented. However, exposure to ultraviolet radiation is a major risk factor for most skin cancers. Several studies indicate that laser light with safe longer wavelengths may accelerate bacteria-infested wound healing by killing the bacteria, although different bacterial strains are killed by different wavelengths. In-vitro experiments with light in the wavelength range between 400–800nm at 120 J/cm2 result in a 62%, 83%, and 56% reduction in the colony count of E. coli, streptococcus aureus, and streptococcus marcescens, respectively, but no reduction in the viability of pseudomonas aeruginosa. Irradiation with 530nm is useful for deactivating bacteria such as streptococcus mutans, a significant contributor to dental caries.
• Angiogenesis. Several experiments performed with different wavelengths (460nm, 530nm, 550nm and 790nm) at 1.91 J/cm2 power density indicated that laser light regulates genes for enhancing wound healing by inducing a major increase in dermal angiogenesis cell proliferation, improved blood flow, neovascularization, and skin regeneration. Moreover, very recently, blue light has been demonstrated to be mostly responsible for NO formation by endothelial cells. Since NO formation leads to vasodilatation and subsequent increase in microcirculatory blood flow, the use of blue light may be of great importance for formation of new blood vessels.
• Axon regeneration. The use of laser treatment of peripheral nerve damage has been shown to be effective in several recent studies. Treating injured rats with 780nm laser light with 10-190mW power and total energy of 0.15-90 J resulted in a significant increase in the total number of axons, especially of the large size, and in a better regeneration compared to control animals. In another animal study, the beneficial effect of 660nm laser with the energy density of 4 J/cm2 power density of 0.354 W/cm2 was reported. The effect of different wavelengths was studied in a mouse model with traumatic brain injury. Mice treated with 36 J/cm2 at 665nm and 810nm (but not with 730nm or 980nm) had a significant improvement in Neurological Severity Score.
There appears to be a consensus among animal model studies that laser light enhances healing by disinfecting wounds, promoting cell proliferation, accelerating collagen synthesis, and promoting the formation of granulation tissue. In sharp contrast, human clinical studies concerning the effects of lasers on would healing remain contradictory, with some studies reporting beneficial effects on tissue repair and others showing no effect.
One has to understand that in vitro studies use monolayer cell cultures, where the penetration depth of light is not relevant, but for in vivo ulcer treatment the penetration depth is essential. Also, considerable variation in the research design, methodology, and irradiation parameters employed, can make it difficult to draw a direct comparison between animal and clinical studies.
Mechanisms of laser wound healing
Absorption of light in mitochondria by cytochrome c oxidase is considered to be the principal mechanism of light action on biological tissue. It increases the mitochondrial respiratory chain activity, resulting in elevated levels of ATP in superficial tissues and the brain, the release of nitric oxide (NO) and reactive oxygen species (ROS), all of which lead to wound healing and prevent tissue necrosis.
It is also reported that exposure to light increases gene expression and the release of various growth factors and cytokines involved in wound healing.
Undoubtedly, disinfection of wounds by laser light plays a beneficial role in wound healing.
Simple heating of the wounded tissue by laser light may also be a factor in stimulating and/or accelerating healing.
Although the precise underlying mechanisms of laser wound healing are not well understood, a significant body of laboratory and clinical data indicate that it could be a valuable addition to the clinical toolset, and further studies are required to determine the optimal set of parameters that induces the best wound healing.
Laser diodes for wound healing
In order to determine the optimal set of laser parameters for the most efficacious treatment, it is important to standardize the clinical dosing and delivery protocols. Akela Laser had developed laser diode systems and delivery tools that provide uniform illumination of the treated wound with tight control of the power density and dose. These systems are available at any wavelength, as well as with multiple wavelengths that provide deeper penetration of light into a tissue.
These laser diode systems are perfectly suited for further clinical studies that are required to determine the combination of wavelengths and power that are most effective in inducing rapid and complete wound healing.