First Assessment of a Carbon Monoxide Laser and a Thulium Fiber Laser for Fractional Ablation of Skin.

BACKGROUND AND OBJECTIVES: A recent generation of 5,500 nm wavelength carbon monoxide (CO) lasers could serve as a novel tool for applications in medicine and surgery. At this wavelength, the optical penetration depth is about three times higher than that of the 10,600 nm wavelength carbon dioxide (CO2 ) laser. As the amount of ablation and coagulation is strongly influenced by the wavelength, we anticipated that CO lasers would provide extended coagulation zones, which could be beneficial for several medical applications, such as tissue tightening effects after laser skin resurfacing. Until now, the 1,940 nm wavelength thulium fiber (Tm:fiber) laser is primarily known as a non-ablative laser with an optical penetration depth that is eight times higher than that of the CO2 laser. The advantage of lasers with shorter wavelengths is the ability to create smaller spot sizes, which has a determining influence on the ablation outcome. In this study, the ablation and coagulation characteristics of a novel CO laser and a high power Tm:fiber laser were investigated to evaluate their potential application for fractional ablation of the skin. STUDY DESIGN/MATERIALS AND METHODS: Laser-tissue exposures were performed using a novel CO laser, a modified, pulse-width-modulated CO2 laser, and a Tm:fiber laser. We used discarded ex vivo human skin obtained from abdominoplasty as tissue samples. Similar exposure parameters, such as spot size (108-120 µm), pulse duration (2 milliseconds), and pulse energy (~10-200 mJ) were adjusted for the different laser systems with comparable temporal pulse structures. Laser effects were quantified by histology. RESULTS: At radiant exposures 10-fold higher than the ablation threshold, the CO laser ablation depth was almost two times deeper than that of the CO2 laser. At 40-fold of the ablation threshold, the CO laser ablation was 47% deeper. The ablation craters produced by the CO laser exhibited about two times larger coagulation zones when compared with the CO2 laser. In contrast, the Tm:fiber laser exhibited superficial ablation craters with massive thermal damage. CONCLUSIONS: The tissue ablation using the Tm:fiber laser was very superficial in contrast to the CO laser and the CO2 laser. However, higher etch depths should be obtainable when the radiant exposure is increased by using higher pulse energies and/or smaller spot sizes. At radiant exposures normalized to the ablation threshold, the CO laser was capable of generating deeper ablation craters with extended coagulation zones compared with the CO2 laser, which is possibly desirable depending on the clinical goal. The effect of deep ablation combined with additional thermal damage on dermal remodeling needs to be further confirmed with in vivo studies. Lasers Surg. Med. © 2020 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.

Assessment of skin lesions produced by focused, tunable, mid-infrared chalcogenide laser radiation.

BACKGROUND: Traditionally, fractional laser treatments are performed with focused laser sources operating at a fixed wavelength. Using a tunable laser in the mid-infrared wavelength range, wavelength-dependent absorption properties on the ablation process and thermal damage formation were assessed with the goal to obtain customizable tissue ablations to provide guidance in finding optimized laser exposure parameters for clinical applications. METHODS: Laser tissue experiments were carried out on full thickness ex vivo human abdominal skin using a mid-infrared tunable chromium-doped zinc selenide/sulfide chalcogenide laser. The laser has two independent channels: a continuous wave (CW) output channel which covers a spectrum ranging from 2.4 µm to 3.0 µm with up to 9.2 W output power, and a pulsed output channel which ranges from 2.35 µm to 2.95 µm. The maximum pulse energy of the pulsed channel goes up to 2.8 mJ at 100 Hz to 1,000 Hz repetition rate with wavelength-dependent pulse durations of 4-7 ns. RESULTS: Total ablation depth, ablation efficiency, and coagulation zone thickness were highly correlated to wavelength, pulse width, and pulse energy. Using the same total radiant exposure at 2.85 µm wavelength resulted in 10-times smaller coagulation zones and 5-times deeper ablation craters for one hundred 6 ns pulses compared to one 100 ms pulse. For a fixed pulse duration of 6 ns and a total radiant exposure of 2.25 kJ/cm2 the ablation depth increased with longer wavelengths. CONCLUSION: The tunable laser system provides a useful research tool to investigate specific laser parameters such as wavelength on lesion shape, ablation depth and thermal tissue damage. It also allows for customization of the characteristics of laser lesions and therefore facilitates the selection of suitable laser parameters for optimized fractional laser treatments. Lasers Surg. Med. 50:961-972, 2018.© 2018 Wiley Periodicals, Inc.

Effects of deviation from focal plane on lesion geometry for ablative fractional photothermolysis.

BACKGROUND AND OBJECTIVE: Fractional Photothermolysis (FP) is a method of skin treatment that generates a thermal damage pattern consisting of multiple columns of thermal damage, also known as microscopic treatment zones (MTZs). They are very small in diameter and are generated by application of highly focused laser beams. In order to obtain the smallest spot size, the treatment should be performed in the focal plane. Any deviation from the focal plane (DFP) results in an increase of spot size. FP devices typically utilize distance holders in order to facilitate exposures at this specific location. In spite of the use of distance holders, DFP can occur. In particular, variations of contact pressure to the skin surface and anatomical treatment areas of high surface curvature may be prone to DFP during FP treatments. The impact of such distance variation on lesion geometry, such as depth and diameter of the thermal injury, has not previously been evaluated. The objective of this study was to investigate the relation between DFP and the resulting lesion geometry for a selected ablative fractional device. MATERIAL AND METHODS: A handpiece of an ablative fractional laser (DeepFX, UltraPulse Encore, Lumenis, Yokneam, Israel) was mounted to a rigid stand. Full thickness human skin obtained from abdominoplasty was mounted to a separate stand perpendicular to the handpiece. The tissue stand allowed the distance between the handpiece and the tissue to be adjusted to produce a variation up to ±3 mm from the focal plane. A 1 × 1 cm(2) scanning area of 169 MTZs, 50 mJ energy per MTZ, 120 µm nominal spot size, was applied at -3, -2, -1, 0, +1, +2, and +3 mm deviated from the focal plane. Minus (-) and plus (+) signs indicate decreasing and increasing distance between the handpiece and the tissue, respectively. Depth and diameter of the laser induced tissue lesions were assessed and quantified. RESULTS: DFPs produced a significant alteration of the lesion geometry. DFPs of -3, -2, -1, 0, +1, +2, +3 mm resulted in average lesion depths of 1,020 (-40%), 1,180 (-31%), 1,400 (-18%), 1,700 (0%), 1,620 (-5%), 780 (-55%), 680 (-60%) µm, and average lesion diameters of 314 (+26%), 311 (+25%), 273 (+10%), 248 (0%), 256 (+3%), 316 (+27%), 359 (+44%) µm, respectively. The underlined values represent the focal plane. The percentage changes relative to values at focal plane are in parentheses. CONCLUSIONS: A relatively minor DFP has a marked impact on the thermal injury profile, including lesion depth and diameter, of the laser-exposed tissue. Such marked changes of the thermal injury profile might affect the wound healing, safety, and efficacy of ablative fractional resurfacing procedures. Clinicians should carefully maintain the focal plane during ablative fractional treatment for reproducible results. The presented data are device specific and the clinical impact of such alteration of thermal injury profile warrants further investigation. Lasers Surg. Med. 48:555-561, 2016. © 2016 Wiley Periodicals, Inc.

Rapid fibrin plug formation within cutaneous ablative fractional CO2 laser lesions.

BACKGROUND: Ablative fractional laser procedures have been shown to facilitate topical drug delivery into the skin. Past studies have mainly used ex vivo models to demonstrate enhanced drug delivery and in vivo studies have investigated laser created channels over a time course of days and weeks rather than within the first few minutes and hours after exposures. We have noticed rapid in vivo fibrin plug formation within ablative fractional laser lesions impairing passage through the laser created channels. MATERIAL AND METHODS: In vivo laser exposures were performed in a porcine model. A fractional CO2 laser (AcuPulse™ system, AcuScan 120™ handpiece, Lumenis, Inc., Yokneam, Israel) was programmed in quasi-continuous wave (QCW) mode, at 40W, 50 mJ per pulse, 5% coverage, nominal 120 µm spot size, 8 × 8 mm square pattern, 169 MTZs per scan. Six millimeters punch biopsies were procured at 0, 2, 5, 10, 15, 30, 60, 90 minutes after completion of each scan, then fixed in 10% formalin. 12 repeats were performed of each time point. Skin samples were processed for serial vertically cut paraffin sections (5 µm collected every 25 µm) then H&E and special immunohistochemistry staining for fibrin and platelet. Dimensions of Microscopic Treatment Zones (MTZs) and extent of fibrin plug were assessed and quantified histologically. Ex vivo laser exposures of the identical laser parameter were performed on porcine and human skin at different storage conditions. RESULTS: Histology procured at various predetermined time intervals after in vivo fractional CO2 laser exposures revealed a rapidly forming fibrin plug initiating at the bottom of the MTZ lesions. At longer time intervals, the fibrin plug was extending towards the superficial sections. Within the first 5 minutes, more than 25% length of the entire laser-ablated channel was filled with a fibrin plug. With increased time intervals, the cavity was progressively filled with a fibrin plug. At 90 minutes, more than 90% length of the entire laser-ablated channel was occluded. Ex vivo exposures failed to produce any significant fibrin plug formation. CONCLUSIONS: The current study has demonstrated rapid fibrin plug formation after ablative fractional laser procedures. It was shown that the passage through laser created pathways is critically time dependent for in vivo exposures. In contrast, ex vivo exposures do not exhibit such time dependent passage capacity. In particular, drug, substance, and cell delivery studies for ablative fractional laser treatments should take early fibrin plug formation into consideration and further investigate the impact on transdermal delivery.

Photosensitizer fluorescence and singlet oxygen luminescence as dosimetric predictors of topical 5-aminolevulinic acid photodynamic therapy induced clinical erythema.

The need for patient-specific photodynamic therapy (PDT) in dermatologic and oncologic applications has triggered several studies that explore the utility of surrogate parameters as predictive reporters of treatment outcome. Although photosensitizer (PS) fluorescence, a widely used parameter, can be viewed as emission from several fluorescent states of the PS (e.g., minimally aggregated and monomeric), we suggest that singlet oxygen luminescence (SOL) indicates only the active PS component responsible for the PDT. Here, the ability of discrete PS fluorescence-based metrics (absolute and percent PS photobleaching and PS re-accumulation post-PDT) to predict the clinical phototoxic response (erythema) resulting from 5-aminolevulinic acid PDT was compared with discrete SOL (DSOL)-based metrics (DSOL counts pre-PDT and change in DSOL counts pre/post-PDT) in healthy human skin. Receiver operating characteristic curve (ROC) analyses demonstrated that absolute fluorescence photobleaching metric (AFPM) exhibited the highest area under the curve (AUC) of all tested parameters, including DSOL based metrics. The combination of dose-metrics did not yield better AUC than AFPM alone. Although sophisticated real-time SOL measurements may improve the clinical utility of SOL-based dosimetry, discrete PS fluorescence-based metrics are easy to implement, and our results suggest that AFPM may sufficiently predict the PDT outcomes and identify treatment nonresponders with high specificity in clinical contexts.

Gene profiling analysis of the early effects of ablative fractional carbon dioxide laser treatment on human skin.

BACKGROUND: The use of carbon dioxide (CO2) laser-mediated ablative fractional resurfacing (AFR) is currently under extensive clinical investigation, but the molecular mechanisms underlying this process are unclear. OBJECTIVES: To determine the early expressed genes that are upregulated in human skin after treatment using a CO2 fractional laser. METHODS: Whole human skin was irradiated using an AFR CO2 laser, and changes in gene expression after 2 and 24 hours were analyzed using microarray analysis. The results were validated using reverse transcriptase polymerase chain reaction (RT-PCR). Laser scanning confocal microscopy (LSCM) was used to investigate the expression of the validated proteins after AFR CO2 laser treatment of skin that had been biopsied from seven Korean patients. RESULTS: Gene expression profiling showed that the most significantly upregulated genes in these skin samples were those encoding Wnt5a, cysteine-rich angiogenic inducer 61 (CYR61), and heat shock protein (HSP) 90. These results were confirmed using real-time RT-PCR and LSCM. CONCLUSIONS: Irradiation using an AFR laser may induce the expression of Wnt5a, CYR61, and HSP90 in human skin during the early remodeling phases, suggesting that the induction of proteins may be the preceding event that is associated with the clinical effects of laser treatment.

Facilitation of transcutaneous drug delivery and vaccine immunization by a safe laser technology.

Full-surface laser ablation has been shown to efficiently disrupt stratum corneum and facilitate transcutaneous drug delivery, but it is frequently associated with skin damage that hampers its clinic use. We show here that a safer ablative fractional laser (AFL) can sufficiently facilitate delivery of not only patch-coated hydrophilic drugs but also protein vaccines. AFL treatment generated an array of self renewable microchannels (MCs) in the skin, providing free paths for drug and vaccine delivery into the dermis while maintaining integrity of the skin by quick healing of the MCs. AFL was superior to tape stripping in transcutaneous drug and vaccine delivery as a much higher amount of sulforhodamine B (SRB), methylene blue (MB) or a model vaccine ovalbumin (OVA) was recovered from AFL-treated skin than tape-stripped skin or control skin after patch application. Following entry into the MCs, the drugs or OVA diffused quickly to the entire dermal tissue via the lateral surface of conical-shaped MCs. In contrast, a majority of the drugs and OVA remained on the skin surface, unable to penetrate into the dermal tissue in untreated control skin or tape stripping-treated skin. Strikingly, OVA delivered through the MCs was efficiently taken up by epidermal Langerhans cells and dermal dendritic cells in the vicinity of the MCs or transported to the draining lymph nodes, leading to a robust immune response, in sharp contrast to a weak, though significant, immune response elicited in tape stripping group or a basal immune response in control groups. These data support strongly that AFL is safe and sufficient for transcutaneous delivery of drugs and vaccines.