Dye-assisted laser skin closure with pulsed radiation: An in vitro study of weld strength and thermal damage

Previous laser skin welding studies have used continuous wave delivery of radiation. However, heat diffusion during irradiation prevents strong welds from being achieved without creating large zones of thermal damage. Previously published results indicate that a thermal damage zone in skin greater than 200 μm may prevent normal wound healing. We propose that both strong welds and minimal thermal damage can be achieved by introducing a dye and delivering the radiation in a series of sufficiently short pulses. Two-cm-long incisions were made in guinea pig skin, in vitro. India ink and egg white (albumin) were applied to the wound edges to enhance radiation absorption and to close the wound, respectively. Continuous wave (cw), 1.06 μm, Nd:yttrium-aluminum-garnet laser radiation was scanned over the weld producing ∼100 ms pulses. The cooling time between scans and the number of scans was varied. The thermal damage zone at the weld edges was measured using a transmission polarizing light microscope. The tensile strength of the welds was measured using a tensiometer. For pulsed welding and long cooling times between pulses (8 s), weld strengths of 2.4±0.9 kg/cm² were measured, and lateral thermal damage at the epidermis was limited to 500±150 μm. With cw welding, comparable weld strengths produced 2700±300 μm of lateral thermal damage. The cw weld strengths were only 0.6±0.3 kg/cm² for thermal damage zones comparable to pulsed welding.