Depth of tissue ablation and residual thermal damage caused by a pixilated 2,940 nm laser in a swine skin model

Low-fluence treatment with a novel fractionated 2,910-nm fiber laser improves photodamage

BACKGROUND

Facial rejuvenation by lasers that target water has been a mainstay of esthetic laser treatments for decades. Modern lasers more commonly treat a fraction of the skin surface using ablative, semi-ablative, or nonablative pulses.

METHODS

Twenty subjects with visible evidence of chronic photoaging on the face were enrolled in this study. All subjects received two full-face, single-pass treatments spaced 2 months apart with the superficial mode of a 2910 nm fiber laser with an estimated penetration depth of 10 μm, 25% coverage, delivered in a 15 mm × 15 mm square microbeam pattern. A blinded comparison of pretreatment and 3-month post-treatment images was performed. Evaluation of biopsy samples for laser-tissue effects was performed on three separate subjects and biopsies were harvested 1-day post-treatment, 1-week post-treatment, and 2-weeks post-treatment.

RESULTS

Blinded evaluation of digital images revealed an average improvement score of 25.1 ± 14.5 (mean ± SEM) or 25.1%, using an 11-point scale evaluating overall improvement in photoaging (p < 0.001). Post-treatment effects were limited to mild-to-moderate erythema and edema, and the pain was rated a 1.9 out of a maximum of 10. Histology demonstrated superficial changes in the stratum corneum and epidermis with dermal inflammation present at 1-day post-treatment and 1-week post-treatment, with a return to baseline at 2 weeks.

CONCLUSIONS

The 2910 nm fiber laser is safe and effective for improving mild photodamage, with minimal discomfort and downtime. Dermal inflammation results from very superficial epidermal injury and may contribute to clinical improvement.

Risk assessment of excess drug and sunscreen absorption via skin with ablative fractional laser resurfacing : optimization of the applied dose for postoperative care

The ablative fractional laser is a new modality used for surgical resurfacing. It is expected that laser treatment can generally deliver drugs into and across the skin, which is toxicologically relevant. The aim of this study was to establish skin absorption characteristics of antibiotics, sunscreens, and macromolecules via laser-treated skin and during postoperative periods. Nude mice were employed as the animal model. The skin received a single irradiation of a fractional CO2 laser, using fluences of 4-10 mJ with spot densities of 100-400 spots/cm(2). In vitro skin permeation using Franz cells was performed. Levels of skin water loss and erythema were evaluated, and histological examinations with staining by hematoxylin and eosin, cyclooxygenase-2, and claudin-1 were carried out. Significant signs of erythema, edema, and scaling of the skin treated with the fractional laser were evident. Inflammatory infiltration and a reduction in tight junctions were also observed. Laser treatment at 6 mJ increased tetracycline and tretinoin fluxes by 70- and 9-fold, respectively. A higher fluence resulted in a greater tetracycline flux, but lower skin deposition. On the other hand, tretinoin skin deposition increased following an increase in the laser fluence. The fractional laser exhibited a negligible effect on modulating oxybenzone absorption. Dextrans with molecular weights of 4 and 10 kDa showed increased fluxes from 0.05 to 11.05 and 38.54 μg/cm(2)/h, respectively. The optimized drug dose for skin treated with the fractional laser was 1/70-1/60 of the regular dose. The skin histology and drug absorption had recovered to a normal status within 2-3 days. Our findings provide the first report on risk assessment of excessive skin absorption after fractional laser resurfacing.

Evidence of 5-aminolevulinic acid (ALA) penetration increase due to microdrilling in soft tissue using femtosecond laser ablation

Photodynamic therapy (PDT) is a therapeutic technique mainly applied to the treatment of malignant and pre-malignant lesions, which induces cell death by the combined effect of a photosensitizer, irradiation in a proper wavelength, and molecular oxygen. One of the main limitations of PDT using 5-aminolevulinic acid (ALA) is the superficial volume of treatment, mainly due to the limited penetration of topical photosensitization. In this context, the present study investigates if a laser micromachining producing microchannels on the tissue surface could improve ALA penetration and result in an increase in the treatment depth. The laser micromachining under femtosecond regime was performed on the tissue surface of rat livers. Conventional PDT was applied and the induced depth of necrosis with or without laser micromachining was compared. The results showed an increase of more than 20% in the depth of necrosis when the femtosecond laser micromachining was performed before the treatment with the PDT.