Laser photobiostimulation of wound healing: Reciprocity of irradiance and exposure time on energy density for splinted wounds in diabetic mice

Abstract

We have used a 660 nm laser diode in genetic diabetic mice to stimulate the healing of wounds covered with a Tegaderm HP dressing that causes a retardation of contraction (splinted wounds). The influence of irradiance (power density) on wound healing has been examined with the same energy dose delivered to the wounds. This energy dose caused maximal stimulation of healing in a previous study. A circular excisional wound was made on the left flank of diabetic mice using a 5-mm skin punch, and covered with a Tegaderm HP dressing. Four different treatments were tested: Treatment 1, not irradiated (control); treatment 2, 100 mW, 20 seconds; treatment 3, 50 mW, 40 seconds; treatment 4, 25 mW, 80 seconds. Treatments were given daily for 7 days. The irradiances for treatments 2, 3, and 4 were estimated to be 233-313, 116-156, and 58-78 mW/cm(2), respectively. In total, 53 mice were used. Wounds were harvested on day 14 and healing assessed from hematoxylin-eosin stained sections examined by light microscopy. The wounds were splinted in 42 of the mice, and splinting caused a retardation of healing. The findings showed that wound healing was stimulated to a similar extent by treatments 2, 3, and 4 and occurred mainly by reepithelization and granulation tissue formation. The laser parameters used represent an energy dose of 2.0 J per irradiation and, for an estimated area of irradiation of 32-43 mm(2), corresponds to an energy density of 4.7-6.3 J/cm(2). Irradiation 660 nm with irradiances estimated to be 233-313, 116-156, and 58-78 mW/cm(2) and an estimated energy density of 4.7-6.3 J/cm(2) each day for 7 days stimulated healing to a similar extent in splinted wounds of diabetic mice.