The Effect of 810 Nanometer Diode Laser Irradiation on Healing of Full-Thickness Skin Wounds in Rats

T hroughout history, there have been many advances made in wound management. Research on new modalities to enhance wound healing is ongoing at most medical centers. One such modality is laser irradiation. Laser irradiation as a phototherapeutic means for the stimulation and/or acceleration of wound healing began in the 1970s by Mester and colleagues.^1,2 Since then, approximately 2,000 studies have been published, producing a wide range of results. Despite extensive research, controversy as to the effects of the laser on wound healing remains.^3,4 This controversy is in part due to: 1. Difficulty in comparing the results of previous research because of the large number of laser systems and experimental conditions employed 2. Prior research that lacked accurate documentation of exact irradiation protocols 3. Prior research that lacked incorporation of suitable controls.¹ The authors concluded that further investigation of laser irradiation for wound healing was indicated and, therefore, investigated the effect of laser irradiation on wound healing in rats at different points in time. The extent of wound healing was based on wound tensile strength and histological characteristics. The wavelength and dose selected for the experiment fall within a range of wavelengths and doses previously shown to accelerate wound healing.^1,5–8 The authors’ hypothesis is that 810nm diode laser irradiation will accelerate healing of full-thickness skin wounds in rats. Materials and Methods Animals. Healthy, adult, male Sprague-Dawley rats (Harlan Sprague-Dawley Inc., Indianapolis, Indiana) weighing approximately 200–224g each were used for experimental groups. Animals were fed a standard diet and given water as needed. The animals were housed individually within standard micro-isolator cages located in a controlled environment (temperature 68–72?F, humidity approximately 60%, 12-hour light cycle) for the duration of the experiment. Wounding procedure. Animals were divided into two groups with 10 animals per group. Animals were anesthetized with a ketamine-xylazene mixture. The dorsum of each animal was then shaved and cleansed with betadine. Full-thickness 2cm longitudinal incisions were made on the animals’ dorsal surfaces using a number 15 scalpel blade. The wound edges were approximated using three 4.0 nylon sutures. The wounds received no dressings. Laser irradiation. An 810 nanometer (nm) diode laser (Laser Bandage 800, CAO Group, Inc., Sandy, Utah) was used for wound irradiation. The laser had a power output of 500mW with an elliptical spot size of 10mm x 2mm at a distance of 1cm. The intensity of the laser was 3184.713mW/cm². The animal wounds were irradiated daily for two seconds, which gave a dose of 6.368J/cm²/wound for each treatment. Both experimental and control groups received daily treatment, with the exception that the control groups received sham irradiation. The first daily doses of irradiation were initiated approximately 30 minutes after the wounds were inflicted. Animals were treated for a total of four days, eight days, and 12 days. On Days 5, 9, and 13, 10 animals from both groups were sacrificed using CO₂ asphyxiation. Their wounds were carefully harvested and cut using a die for standardization of wounds for later tensile strength measurements. The skin specimens were then sent for tensile strength measurements and histological examination (Figure 1). Tensile strength measurements. Wound-breaking strength was measured using a mechanical tester (INSTRON, Model 4202, Canton, Massachusetts). The initial lengths of the specimens were approximately 2cm. Specimens were stretched at a constant rate of 12.5mm/min until the specimen broke. The measurements were recorded using a personal computer with LabVIEW software (National Instruments Corporation, Austin, Texas) and then plotted on a graph. The load versus displacement curve for each specimen was recorded. The maximal breaking strength was computed from the maximal point in this curve. After tensile strength measurements were completed, the specimens were placed into individual containers containing formalin and sent to pathology for histological examination. Histological examination. Histological examination and evaluation were performed by an independent observer. Each slide was given a score that correlated with a stage of healing. Scores with lower values were equivalent to earlier stages of healing, and scores with higher values were equivalent to later stages of healing. The criteria used to score the wounds observed the degree of inflammation, re-epithelialization, cellular invasion, cellular organization, granulation tissue formation, collagen deposition, and vascularity. The criteria used to score the specimens were based on criteria obtained and utilized by previous investigators.^9–12Statistical evaluation. The mean and standard deviation were calculated for each experimental group. A two-tailed Student’s t-test was calculated to look for significant differences at the p