Wound healing: biological effects of Nd:YAG laser on collagen metabolism in pig skin in comparison to thermal burn.

Pig skin was treated with the Nd:YAG laser at 1,060 nm or electrocautery, at energy densities of 649 +/- 20 J/cm2 and 612 J/cm2, respectively. Biopsies of treated areas and of normal skin were performed at 7, 14, and 60 days after treatment and processed for histology, electron microscopy and biochemical assays. Wound healing, as shown histologically, was similar in both treated groups. Depth of injury appeared to reach reticular dermis at day 7 in each treated group. However, thermal burn was more destructive of regular collagen, whereas the laser appeared to damage deep dermal blood vessels without destroying surrounding connective tissue. Biochemical assays revealed increased collagen production and increased collagenolytic activity 7 days after laser injury. However, by day 60, there was a reduction in total collagen content in laser treated skin below that of normal skin, which correlated with decreased collagen synthesis and unchanged collagenolytic activity. In burn specimens there was an initial decrease in total collagen content which reverted to normal by day 60. Active collagen degradation occurred at all 3 time points, but a marked increase in synthetic activity occurred as the burn scar was laid down. Laser treatment resulted in reduction of the amount of collagen below that in burn scarred or normal skin, suggesting that classical scar formation may be inhibited. These results indicate that the Nd:YAG laser may be useful for the treatment of keloids and hypertrophic scars.