Optical clearing agent perfusion enhancement via combination of microneedle poration, heating and pneumatic pressure

Abstract

Background and Objective: Optical clearing agents (OCAs) have shown promise for increasing the penetration depth of biomedical lasers by temporarily decreasing optical scattering within the skin. However, their translation to the clinic has been constrained by lack of practical means for effectively perfusing OCA within target tissues in vivo. The objective of this study was to address this limitation through combination of a variety of techniques to enhance OCA perfusion, including heating of OCA, microneedling and/or application of pneumatic pressure over the skin surface being treated (vacuum and/or positive pressure). While some of these techniques have been explored by others independently, the current study represents the first to explore their use together. Study Design/Materials and Methods: Propylene glycol (PG) OCA, either at room-temperature or heated to 458C, was topically applied to hydrated, body temperature ex vivo porcine skin, in conjunction with various combinations of microneedling pre-treatment (0.2 mm length microneedles, performed prior to OCA application), vacuum pre-treatment (17-50 kPa, performed prior to OCA application), and positive pressure post-treatment (35-172 kPa, performed after OCA application). The effectiveness of OCA perfusion was characterized via measurements of transmittance, reduced scattering coefficient, and penetration depth at a number of medicallyrelevant laser wavelengths across the visible spectrum. Results: Topical application of room-temperature (RT) PG led to an increase in transmittance across the visible spectrum of up to 21% relative to untreated skin. However, only modest increases were observed with addition of various combinations of microneedling pre-treatment, vacuum pre-treatment, and positive pressure post-treatment. Conversely, when heated PG was used in conjunction with these techniques, we observed significant increases in transmittance. Using an optimal PG perfusion enhancement protocol consisting of 458C heated PG þ microneedle pre-treatment þ 35 kPa vacuum pre-treatment þ 103 kPa positive pressure post-treatment, we observed up to 68% increase in transmittance relative to untreated skin, and up to 46% increase relative to topical RT PG application alone. Using the optimal PG perfusion enhancement protocol, we also observed up to 30% decrease in reduced scattering coefficient relative to untreated skin, and up to 20% decrease relative to topical RT PG alone. Finally, using the optimal protocol, we observed up to 25% increase in penetration depth relative to untreated skin, and up to 23% increase relative to topical RT PG alone. Conclusions: The combination of heated PG, microneedling pre-treatment, vacuum pre-treatment, and positive pressure-post treatment were observed to significantly enhance the perfusion of topically applied PG. Although further studies are required to evaluate the efficacy of combined perfusion enhancement techniques in vivo, the current results suggest promise for facilitating the translation of OCAs to the clinic.

Biomedical Applications of Tissue Clearing and Three-Dimensional Imaging in Health and Disease

“…These agents are commonly known as SOCAs (skin optical clearing agents) and generally adjust skin refractive indexes and induce packaging of scatterers such as collagen fibers ( Tuchina et al., 2019 ) by dehydration-driven reduction of skin thickness ( Wen et al., 2010 ). Several penetration enhancers are widely used to facilitate their diffusion and improve their clearing power; they can be classified into chemical penetration enhancers such as propylene glycol, DMSO ( Zaytsev et al., 2020 ), ethanol ( Zaytsev et al., 2020 ), azone ( Zhao et al., 2016 ), dimethyl sulfoxide ( Genina et al, 2020 ), oleic acid ( Zaytsev et al., 2020 ), and thiazone ( Zaytsev et al., 2020 ) (the last four ones achieve penetration enhancement by dissolving Stratum Corneum lipids) ( Zaytsev et al., 2020 ), and physical penetration enhancers, such as ultrasounds (sonophoresis) ( Genina et al, 2020 ), microneedles ( Yoon et al., 2010 ), lasers (FLMA, fractional laser microablation) ( Genina et al., 2020a ), pneumatic pressure ( Damestani et al., 2014 ), heat ( Damestani et al., 2014 ), or abrasive instruments (microdermabrasion) ( Genina et al, 2020 ). Different combinations of penetration enhancers have been applied to improve the efficacy of several clearing agents.…”

“…Besides, it has been shown that combined application of microneedles and sonophoresis can enhance diffusion rate of 70% glycerol up to 2.3-fold compared with microneedling alone ( Yoon et al., 2010 ) and that FLMA in combination with sonophoresis highly increases clearing speed of PEG-300 ( Genina et al., 2020a ). Additionally, combination of skin cleaning, microdermabrasion, sonophoresis, and glycerol application allowed improved signal detection in photoacoustic flow cytometry ( Menyaev et al., 2013 ), and merging of propylene glycol, heated to 45°C, microneedling, vacuum pre-treatment, and application of positive pressure increased porcine skin transparency up to 25% ( Damestani et al., 2014 ).…”

In vivo skin optical clearing for improving imaging and light-induced therapy: a review

“…However, in realistic in vivo applications, the optical clearing effect of agents is sometimes unsatisfactory due to the dense stratum corneum seriously hindering agent penetration into the skin. To overcome this barrier, researchers have proposed various physical methods to promote the penetration of OCAs, including laser irradiation, 13 fractional laser microablation, 34 adhesive tape stripping, 35 sandpaper rubbing, 36 sonophoresis, 37 microneedle, 38 flashlight irradiation, 39 and more. These methods enhance the OCA penetration by directly removing the stratum corneum and part of the living epidermis, creating microchannels in the skin or generating heat effects to locally disrupt the stratum corneum.…”

Evaluation of laser bacterial anti‐fouling of transparent nanocrystalline yttria‐stabilized‐zirconia cranial implant

“…Using optical coherence tomography (OCT), we demonstrated the initial feasibility of nc‐YSZ cranial implants within the context of cortical imaging of an acute murine model . For optical clearing of the scalp temporarily, our study on delivery techniques of optical clearing agents (OCA) such as propylene glycol (PG) showed that the combination of heated PG, microneedling and vacuum pretreatments, and positive pressure post‐treatment significantly enhanced the perfusion of this topically applied OCA .…”