Ablation of human nail by pulsed lasers

A focused review on laser- and energy-assisted drug delivery for nail disorders

The purpose of this review is to consolidate and summarize laser-assisted drug delivery (LADD) for nail diseases, particularly onychomycosis and psoriasis. A PubMed search was conducted in June 2023 using search terms (1) "laser assisted drug delivery" AND "nail," (2) "laser" AND "nail," and (3) "nail disorder" AND "laser treatment." References of papers were also reviewed, yielding 15 papers for this review. Fractional ablative CO2 laser (FACL) and Er:YAG laser can be used for LADD of topical medications such as amorolfine, terbinafine, and tioconazole to treat onychomycosis. A fungal culture should be performed to determine the type of dermatophyte, which will help determine which topical will be most effective. Laser settings varied between studies, but overall LADD tended to be more effective than topical treatments alone. Laser-assisted photodynamic therapy (PDT) was also found to be effective in treating onychomycosis. For psoriatic nails, LADD was used to deliver calcipotriol-betamethasone dipropionate foam, tazarotene, triamcinolone, or methotrexate into the nail. Again, LADD was found to be significantly more effective than topical treatment alone. FACL was the only laser noted for use for LADD in both diseases. Laser-assisted drug delivery for nail disease is a newer approach for onychomycosis and nail psoriasis with several benefits and drawbacks. Dermatologists should discuss the option of LADD with their patients who have recalcitrant onychomycosis or nail psoriasis.

Fractional CO2 laser ablation leads to enhanced permeation of a fluorescent dye in healthy and mycotic nails-An imaging investigation of laser-tissue effects and their impact on ungual drug delivery

Purpose

Conventional oral antifungal therapies for onychomycosis (OM) often do not achieve complete cure and may be associated with adverse effects, medical interactions, and compliance issues restricting their use in a large group of patients. Topical treatment can bypass the systemic side effects but is limited by the physical barrier of the nail plate. Ablative fractional laser (AFL) treatment can be used to improve the penetration of topical drugs into the nail. This study visualized the effects of laser ablation of nail tissue and assessed their impact on the biodistribution of a fluorescent dye in healthy and fungal nail tissue.

Methods

For the qualitative assessment of CO₂ AFL effects on healthy nail tissue, scanning electron microscopy (SEM), coherent anti‐Stokes Raman scattering microscopy (CARS‐M), and widefield fluorescence microscopy (WFM) were used. To quantitate the effect of laser‐pretreatment on the delivery of a fluorescent dye, ATTO‐647N, into healthy and fungal nail tissue, ablation depth, nail plate thickness, and ATTO‐647N fluorescence intensity in three nail plate layers were measured using WFM. A total of 30 nail clippings (healthy n = 18, fungal n = 12) were collected. An aqueous ATTO‐647N solution was directly applied to the dorsal surface of 24 nail samples (healthy n = 12, fungal n = 12) and incubated for 4 hours, of which half (healthy n = 6, fungal n = 6) had been pretreated with AFL (30 mJ/mb, 15% density, 300 Hz, pulse duration <1 ms).

Results

Imaging revealed a three‐layered nail structure, an AFL‐induced porous ablation crater, and changes in autofluorescence. While intact fungal samples showed a 106% higher ATTO‐647N signal intensity than healthy controls, microporation led to a significantly increased fluorophore permeation in all samples (p < 0.0001). AFL processing of nail tissue enhanced topical delivery of ATTO‐647N in all layers, (average increase: healthy +108%, fungal +33%), most pronounced in the top nail layer (healthy +122%, fungal +68%). While proportionally deeper ablation craters correlated moderately with higher fluorescence intensities in healthy nail tissue, fungal samples showed no significant relationship.

Conclusion

Fractional CO₂ laser microporation is a simple way of enhancing the passive delivery of topically applied ATTO‐647N. Although the impaired nail plate barrier in OM leads to greater diffusion of the aqueous solution, AFL can increase the permeability of both structurally deficient and intact nails.

Investigation of the Dual-Stage Method of Active Er:YLF Laser Drug Delivery Through the Nail and Laser-Induced Transformations of the Drug Extinction Spectrum

BACKGROUND AND OBJECTIVE

A novel dual-stage method for active laser drug delivery (DSLADD) in the treatment of nail diseases is being presented. This method includes sequentially performed microporation of the nail with submillisecond pulses of Er:YLF laser radiation through a layer of an aqueous solution of drug deposited on the nail surface (Stage 1) and exposure this layer to the same laser radiation to deliver drug under the nail plate (Stage 2). The delivery of methylene blue (MB) as one of the possible drugs in the treatment of nail diseases is investigated. The influence of the thickness of the MB layer, as well as the energy and number of applied laser pulses, on the rate of active laser delivery is discussed. To illustrate the possible effect of delivery on the drug delivered, special attention is paid to the deformation of the extinction spectrum of MB solution after laser irradiation.

STUDY DESIGN/MATERIALS AND METHODS

Diode-pumped Er:YLF laser was used for DSLADD. The process of DSLADD under the nail plate was investigated using digital video microscopy. For different values of the thickness of MB solution layer applied to the nail plate and the energy of laser pulses, the number of laser pulses required to create a single through a microchannel in the nail plate and the number of laser pulses required to deliver the solution to the ventral side of the nail plate after its microporation were registered. The mass and the dose of MB solution penetrated under the nail plate, and the rate of MB solution delivery through a single microchannel was determined. Investigation of the influence of Er:YLF laser radiation parameters on the extinction spectrum of the drug was performed using a fiber spectrometer. The extinction spectra of the 0.001% aqueous solution of MB were recorded before and after exposure to a different number of Er:YLF laser pulses with the energy of 1-4 mJ.

RESULTS

It was found that the minimum number of laser pulses required for active Er:YLF laser drug delivery under the nail corresponds to the MB layer thickness of 100 μm and the laser pulse energy of 4 mJ. It is shown that in this case, the rate of active laser delivery of MB solution reaches 0.26 ± 0.03 mg/pulse. The radiation of the Er:YLF laser affects the shape of the extinction spectrum of the aqueous solution of MВ, which is associated with the transition of the dye from the monomeric to dimeric state. Depending on the laser pulse energy, the fraction of a certain conformational state in the aqueous MB solution can decrease or increase, stimulating a possible change in its photodynamic and antiseptic activity.

CONCLUSION

For the first time, a novel DSLADD through the nail has been described and investigated in vitro. It was demonstrated that at Er:YLF laser pulse repetition rate of f = 30 Hz, microporation of the nail plate and drug delivery through a single microchannel will be about 1.5 s. Lasers Surg. Med. © 2021 Wiley Periodicals LLC.

Mechanism of human nail poration by high-repetition-rate, femtosecond laser ablation

Optical poration, or drilling, of the human nail has the potential to drastically improve transungual drug delivery. However, this approach is accompanied by thermal damage to the nail tissue surrounding the laser radiation-created pore. In this paper, fluorescence microscopy has been employed to quantitatively evaluate thermal damage to the nail induced by laser ablation with 80 MHz, nanojoule, femtosecond pulses delivered via a hollow-core fibre. An empirical relation has been established between the intensity of the resulting fluorescence signal and temperature to which the nail was exposed. Using this relationship, detailed temperature maps have been created of the areas surrounding the pores, enabling the mechanism of poration to be better understood. It was deduced that plasma-mediated ablation is primarily responsible for nail tissue ablation at the centre of the pore, while cumulative photothermal processes dominate at the pore edges. It is concluded, furthermore, that temperature mapping represents a useful new tool with which to optimise the process of nail poration. The method is potentially generic and may be applicable to other biological materials.

Active Er-laser drug delivery using drug-impregnated gel for treatment of nail diseases

Active Er-laser drug delivery under the nail plate using a drug-impregnated gel containing liquid methylene blue clusters is demonstrated for the first time. The effect of the agar-agar concentration in the gel and the gel plate thickness on the number of Er:YLF-laser pulses required for formation of a through microhole in the gel and in the nail plate with subsequent active drug delivery is discussed. The influence of the laser pulse energy, the gel plate thickness, and the external pressure applied to the gel on the rate of delivery of methylene blue under the nail plate through a single microhole in it is investigated. It is shown that with a laser pulse energy of 4.0 ± 0.1 mJ, the delivery rate can reach 0.024 ± 0.004 mg/pulse.

Recent Patents on Permeation Enhancers for Drug Delivery Through Nails

The human nail is a unique barrier with a keratinized constitution that favors protection and fine touch. However, many disorders can affect the nail, among them, are the onychomycosis and psoriasis. Systemic oral therapy has been applied to treat these diseases, even presenting disadvantages, including side effects, drug interactions, contraindications, toxicity, high cost and low patient compliance. A great option to succeed in dealing with the problems associated with oral therapy is the topical administration of drugs. However, nail composition, low diffusion through ungual route and reduced tissue bioavailability for topical treatments are limiting factors. These drawbacks can be overcome by promoting penetration through the nails by employing penetration enhancers. The review focuses on patents that highlight permeation enhancers applied to nail drug delivery for the treatment of onychomycosis and psoriasis. Literature and patent searches were conduced regarding the topic of interest. The substantial literature and patent search revealed that permeation enhancers, especially chemicals, are great strategies for promoting the ungual delivery of drugs. Nail topical therapy containing permeation enhancers is an attractive option for delivering localized treatments.

Light treatments of nail fungal infections

Nail fungal infections are notoriously persistent and difficult to treat which can lead to severe health impacts, particularly in the immunocompromized. Current antifungal treatments, including systemic and topical drugs, are prolonged and do not effectively provide a complete cure. Severe side effects are also associated with systemic antifungals, such as hepatotoxicity. Light treatments of onychomycosis are an emerging therapy that has localized photodynamic, photothermal or photoablative action. These treatments have shown to be an effective alternative to traditional antifungal remedies with comparable or better cure rates achieved in shorter times and without systemic side effects. This report reviews significant clinical and experimental studies in the field, highlighting mechanisms of action and major effects related to light therapy; in particular, the impact of light on fungal genetics.

Effect of ablative laser on in vitro transungual delivery

Topical therapy of nail psoriasis using methotrexate has not been realized due to the high molecular weight and low permeability of the compound. In this study, we used a 2940nm fractional ablative laser to disrupt the nail barrier to enhance the in vitro transungual delivery of methotrexate. Bovine hoof membrane-an in vitro model of the human nail-was treated by the laser at different energy levels and pore densities. A successful microporation was characterized by mechanical properties, scanning electron microscopy, Fourier transform infrared spectrophotometer, dye binding, histology, pore uniformity, confocal laser microscopy, nail integrity measurement, and permeation studies. No significant difference in the pore dimension was found in different treatment groups (p>0.05). Increases in pore depth corresponded with increases in the laser energy. Laser ablation was found to affect the mechanical properties of the hoof membrane. In in vitro permeation studies, laser ablation resulted in a significant increase in the drug cumulative delivery, flux, and permeability coefficient as compared to the untreated group (n=3, p<0.05). A change in the laser energy and pore density was found to alter the drug permeability. Thus, transungual methotrexate delivery was enhanced by the fractional laser ablation.

Kagome fiber based ultrafast laser microsurgery probe delivering micro-Joule pulse energies

We present the development of a 5 mm, piezo-actuated, ultrafast laser scalpel for fast tissue microsurgery. Delivery of micro-Joules level energies to the tissue was made possible by a large, 31 μm, air-cored inhibited-coupling Kagome fiber. We overcome the fiber's low NA by using lenses made of high refractive index ZnS, which produced an optimal focusing condition with 0.23 NA objective. The optical design achieved a focused laser spot size of 4.5 μm diameter covering a 75 × 75 μm2 scan area in a miniaturized setting. The probe could deliver the maximum available laser power, achieving an average fluence of 7.8 J/cm2 on the tissue surface at 62% transmission efficiency. Such fluences could produce uninterrupted, 40 μm deep cuts at translational speeds of up to 5 mm/s along the tissue. We predicted that the best combination of speed and coverage exists at 8 mm/s for our conditions. The onset of nonlinear absorption in ZnS, however, limited the probe's energy delivery capabilities to 1.4 μJ for linear operation at 1.5 picosecond pulse-widths of our fiber laser. Alternatives like broadband CaF2 crystals should mitigate such nonlinear limiting behavior. Improved opto-mechanical design and appropriate material selection should allow substantially higher fluence delivery and propel such Kagome fiber-based scalpels towards clinical translation.

Femtosecond pulsed laser ablation to enhance drug delivery across the skin

Laser poration of the skin locally removes its outermost, barrier layer, and thereby provides a route for the diffusion of topically applied drugs. Ideally, no thermal damage would surround the pores created in the skin, as tissue coagulation would be expected to limit drug diffusion. Here, a femtosecond pulsed fiber laser is used to porate mammalian skin ex vivo. This first application of a hollow core negative curvature fiber (HC-NCF) to convey a femtosecond pulsed, visible laser beam results in reproducible skin poration. The effect of applying ink to the skin surface, prior to ultra-short pulsed ablation, has been examined and Raman spectroscopy reveals that the least, collateral thermal damage occurs in inked skin. Pre-application of ink reduces the laser power threshold for poration, an effect attributed to the initiation of plasma formation by thermionic electron emission from the dye in the ink. Poration under these conditions significantly increases the percutaneous permeation of caffeine in vitro. Dye-enhanced, plasma-mediated ablation of the skin is therefore a potentially advantageous approach to enhance topical/transdermal drug absorption. The combination of a fiber laser and a HC-NCF, capable of emitting and delivering femtosecond pulsed, visible light, may permit a compact poration device to be developed.

Insights into drug delivery across the nail plate barrier

Topical therapy is at the forefront in treating nail ailments (especially onychomycosis and nail psoriasis) due to its local effects, which circumvents systemic adverse events, improves patient compliance and reduces treatment cost. However, the success of topical therapy has been hindered due to poor penetration of topical therapeutics across densely keratinized nail plate barrier. For effective topical therapy across nail plate, ungual drug permeation must be enhanced. Present review is designed to provide an insight into prime aspects of transungual drug delivery viz. nail structure and physiology, various onychopathies, techniques of nail permeation enhancement and in vitro models for trans-nail drug permeation studies. Updated list of drug molecules studied across the nail plate and key commercial products have been furnished with sufficient depth. Patents pertinent to, and current clinical status of transungual drug delivery have also been comprehensively reviewed. This is the first systematic critique encompassing the detailed aspects of transungual drug delivery. In our opinion, transungual drug delivery is a promising avenue for researchers to develop novel formulations, augmenting pharmaceutical industries to commercialize the products for nail disorders.

The use of the Er:YAG 2940nm laser associated with amorolfine lacquer in the treatment of onychomycosis

Onychomycosis is a common disease, accounting for up to 50% of all ungual pathologies. We have been developing a clinical trial (ClinicalTrials.gov: NCT01528813) using a 2940nm Er:YAG laser to fractionally ablate human nails in vivo, aiming to increase topical amorolfine lacquer delivery to the nail unit, increasing the efficacy of topical treatment of distal and lateral subungual onychomycosis. Partial results have shown an increase in areas of nail plate free of disease. We believe that ablative lasers can increase the efficacy of topical onychomycosis treatment.

Prospect for feedback guided surgery with ultra-short pulsed laser light

The controlled cutting of tissue with laser light is a natural technology to combine with automated stereotaxic surgery. A central challenge is to cut hard tissue, such as bone, without inducing damage to juxtaposed soft tissue, such as nerve and dura. We review past work that demonstrates the feasibility of such control through the use of ultrafast laser light to both cut and generate optical feedback signals via second harmonic generation and laser induced plasma spectra.

Ungual and transungual drug delivery

Topical therapy is desirable in treatment of nail diseases like onychomycosis (fungal infection of nail) and psoriasis. The topical treatment avoids the adverse effects associated with systemic therapy, thereby enhancing the patient compliance and reducing the treatment cost. However the effectiveness of the topical therapies has been limited due to the poor permeability of the nail plate to topically applied therapeutic agents. Research over the past one decade has been focused on improving the transungual permeability by means of chemical treatment, penetration enhancers, mechanical and physical methods. The present review is an attempt to discuss the different physical and chemical methods employed to increase the permeability of the nail plate. Minimally invasive electrically mediated techniques such as iontophoresis have gained success in facilitating the transungual delivery of actives. In addition drug transport across the nail plate has been improved by filing the dorsal surface of the nail plate prior to application of topical formulation. But attempts to improve the trans-nail permeation using transdermal chemical enhancers have failed so far. Attempts are on to search suitable physical enhancement techniques and chemical transungual enhancers in view to maximize the drug delivery across the nail plate.

Surgical applications of femtosecond lasers

Femtosecond laser ablation permits non-invasive surgeries in the bulk of a sample with submicrometer resolution. We briefly review the history of optical surgery techniques and the experimental background of femtosecond laser ablation. Next, we present several clinical applications, including dental surgery and eye surgery. We then summarize research applications, encompassing cell and tissue studies, research on C. elegans, and studies in zebrafish. We conclude by discussing future trends of femtosecond laser systems and some possible application directions.

Femtosecond laser ablation of the stapes

A femtosecond laser, normally used for LASIK eye surgery, is used to perforate cadaveric human stapes. The thermal side effects of bone ablation are measured with a thermocouple in an inner ear model and are found to be within acceptable limits for inner ear surgery. Stress and acoustic events, recorded with piezoelectric film and a microphone, respectively, are found to be negligible. Optical microscopy, scanning electron microscopy, and optical coherence tomography are used to confirm the precision of the ablation craters and lack of damage to the surrounding tissue. Ablation is compared to that from an Er:YAG laser, the current laser of choice for stapedotomy, and is found to be superior. Ultra-short-pulsed lasers offer a precise and efficient ablation of the stapes, with minimal thermal and negligible mechanical and acoustic damage. They are, therefore, ideal for stapedotomy operations.

Effects of femtosecond laser irradiation on osseous tissues

BACKGROUND AND OBJECTIVE

Few studies have investigated femtosecond (fs) lasers for cutting bone tissue.

STUDY DESIGN/MATERIALS AND METHODS

A 775 nm, 1 kHz, 200 femtosecond, up to 400 microJ laser system was used to irradiate in vitro calcified cortical bone samples and bone tissue culture samples.

RESULTS

The ablation threshold in cortical bone was 0.69+/-0.08 J/cm(2) at 775 nm and 0.19+/-0.05 J/cm(2) at 387 nm. Plasma shielding experiments determined that the ablation plume and the plasma significantly affect material removal at high repetition rates and appear to generate thermal transients in calcified tissue. Confocal analysis revealed intact enzymatic activity on the surface of cells immediately adjacent to cells removed by fs laser irradiation.

CONCLUSIONS

These experiments demonstrate that fs lasers used for bone tissue cutting do not appear to generate significant temperature transients to inactivate proteins and that cellular membrane integrity is disrupted for only a few cell layers.

Morphological effects of nanosecond- and femtosecond-pulsed laser ablation on human middle ear ossicles

We evaluate the feasibility of nanosecond-pulsed and femtosecond-pulsed lasers for otologic surgery. The outcome parameters are cutting precision (in micrometers), ablation rate (in micrometers per second), scanning speed (in millimeters per second), and morphological effects on human middle ear ossicles. We examine single-spot ablations by a nanosecond-pulsed, frequency-tripled Nd:YAG laser (355 nm, beam diameter 10 microm, pulse rate 2 kHz, power 250 mW) on isolated human mallei. A similar system (355 nm, beam diameter 20 microm, pulse rate 10 kHz, power 160-1500 mW) and a femtosecond-pulsed CrLi:SAF-Laser (850 nm, pulse duration 100 fs, pulse energy 40 microJ, beam diameter 36 microm, pulse rate 1 kHz) are coupled to a scanner to perform bone surface ablation over a defined area. In our setups 1 and 2, marginal carbonization is visible in all single-spot ablations of 1-s exposures and longer: With an exposure time of 0.5 s, precise cutting margins without carbonization are observed. Cooling with saline solution result is in no carbonization at 1500 mW and a scan speed of 500 mms. Our third setup shows no carbonization but greater cutting precision, although the ablation volume is lower. Nanosecond- and femtosecond-pulsed laser systems bear the potential to increase cutting precision in otologic surgery.

Modified Emmet's operation for ingrown nails using the Er:YAG laser

BACKGROUND

Ingrowing nails are a common problem. Standard procedure is surgery according to Emmet (a gynecologist) or Emmert (a surgeon) where postoperative pain, swelling and bleeding are major side effects and traumatic damage of the nail organ is not completely avoidable. Laser surgery may provide an alternative with less tissue damage.

METHODS

We compared 138 patients with 212 affected great toe nails (98 males, 40 females) were bloodless Emmet's operation was performed with digital nerve block with 11 patients (12 affected nails) using an Er:YAG laser for atraumatic nail plate removal. Pain was registered by a semiquantitative pain scale (ranging from "zero--no pain" to "10--maximum pain"). Swelling was scored from "0--absent" to "3--severe". Side effects like bleeding, infection or relapse were registered.

RESULTS

Emmet's nail operation: Pain was scored 7.8+/-3.2 on the operation day (evening), 5.3+/-3.1 (day 1) and 3.8+/-4.0 (day 3). Swelling was scored 2.7+/-1.8 (operation day, evening), 2.1+/-1.9 (day 1) and 1.3+/-2.1 (day 3). Wound healing lasted 16.8+/-3.3 days. The infection rate was 2.4%, i.e. 5 of 212 nails. The relapse rate after 6 months was 12 of 212 nails (5.7%). Spicules were observed in 9 of 212 nails (4.2%). Laser procedure: Pain was scored 8.0+/-1.9 (operation day, evening), 4.1+/-1.5 (day 1) and 0.7+/-2.3 (day 3). The swelling was scored 2.4+/-1.8 (operation day, evening), 1.5+/-0.9 (day 1) and 0.9+/-1.3 (day 3). Wound healing was complete after 12.9+/-3.5 days. Infections and relapse were not observed. In one case spicules occurred after 5 months. No other side effects were noted.

CONCLUSIONS

The modified Emmet's operation for ingrown nails using the Er:YAG laser provides a safe method with increased efficacy that causes less pain and swelling, a faster healing and less complications.

Ultrashort pulse laser ossicular ablation and stapedotomy in cadaveric bone

BACKGROUND AND OBJECTIVE

The purpose of this study was to evaluate the ablation of ossicular tissue using a 1,053 nm Ti:Sapphire chirped pulse amplifier laser system configured to deliver ultrashort pulses of 350 femtoseconds (fs) (3.5x10(-13) seconds) in cadaver temporal bone.

STUDY DESIGN/MATERIALS AND METHODS

Ablation of the formalin-fixed incus and stapes was performed using an ultrashort pulse laser (USPL) (0.4 mm beam diameter, pulse fluence of 2.0 J/cm2, and pulse repetition rate of 10 Hz). The ablation rate was measured using optical micrometry, and crater surface morphology examined using scanning electron microscopy.

RESULTS

The laser produced precise bone ablation at a rate of 1.26 microm/pulse, with almost no evidence of thermal damage, and very little evidence of photomechanical injury.

CONCLUSIONS

Ultrashort pulse lasers may provide a useful clinical tool for otologic and skull base surgery, where precise hard tissue ablation is required adjacent to critical structures.