Abstract

The laser-skin interaction was studied using the laboratory albino rat skin as an experimental sample and 10.6 μm wavelength CO₂ laser as a source of irradiation. This study aimed to determine the effect of different laser doses on the skin structure as a trial to understand how laser exerts its medical effects in treating skin problems. It also aimed to determine the relationship between the laser dose and biological effects and thus determine the lowest dose that had highest medical effects with lowest skin damage. Briefly, the rat skin was exposed to CW CO₂ laser at 12.5, 14.1, 15.6 and 17.2 W/cm² for 15 s. Directly after the exposure, biopsies of normal and exposed skin were preserved and fixed for histological studies. The images obtained from the compound light and electron microscopes exerted changes contributed to the interaction of the skin cells to the heat and energy produced by the continuous wave carbon dioxide (CW CO₂) laser during the exposure time. Basically, the tissue damage caused by the laser was mainly due to photothermal effect and increased gradually as the irradiation dose increased. Epidermal loss along with coagulation, homogenous hyalinization, lost of hair associated with shrinkage and collapse of hair follicle structures of varying depths at the-burn sites were detected in the histologic sections. Damage-power density (DPD) relationship was confirmed by measuring the damage depth using the software provided in the light microscope. On the other hand, Scanning electron microscopy (SEM) showed detailed images of the extensive epidermal epithelial cells damage which also increased by increasing the laser dose. Rough surface, partial destruction of intercellular junctions giving rise to loss of adherence between squamous cells and formation of narrow spaces between these cells were the most evident changes detected. The findings may help specialists to choose the best laser parameters for certain applications.

Key words: Lasers, laser-tissue interaction, continuous wave carbon dioxide (CW CO₂)laser, photothermal effect.