Saratov Fall Meeting 2015 International Symposium Optics and Biophotonics – III Conference on Internet Biophotonics – VIII September 22-25, 2015, Saratov, Russia Saratov State University Fractional laser ablation as physical enhancement of skin optical clearing Elina A. Genina1,2*, Alexey N. Bashkatov1,2, Leonid E. Dolotov1, Ekaterina A. Kolesnikova1, Georgy S. Terentyuk1, and Valery V. Tuchin1,2,3 1Remote Controlled Theranostic System Lab, Saratov State University, Saratov, Russia, 2Tomsk State University, Tomsk, Russia 3Institute of Precise Mechanics and Control of RAS, Saratov, Russia *eagenina@yandex.ru

Outline Motivation Transcutaneous Delivery of Optical Clearing Agent Objectives Methods and Materials Results Conclusion Acknowledgements

Motivation During the last 25 years the interest to the development and application of optical methods in clinical functional imaging of physiological conditions, diagnostics and therapy of cancer, and other diseases is permanently growing• One of simple and efficient methods of solving the problem of increasing the depth and quality of intratissular structure imaging, as well as of increasing the precision of spectroscopic information from the deep tissue layers and the blood, is the temporary reduction of the tissue light scattering• T. Vo-Dinh (Ed.), Biomedical Photonics Handbook, CRC Press, Boca Raton, FL, USA (2003); second edition (2014). D. Zhu, et al, Laser & Photonics Reviews 7(5), 732-757 (2013). Tuchin V.V. Journal of Biomedical Photonics & Engineering, 1(1), 3-21 (2015).

According to Web of Science, PubMed and other sources, the interest to the optical clearing methods is permanently growing, which is caused by the progress of optical and laser technologies for application in biology and medicine• E.A. Genina, et al, Journal of Biomedical Photonics & Engineering, 1(1), 22-58 (2015).

Transcutaneous Delivery of Optical Clearing Agent The main advantages of transcutaneous administration of optical clearing agent (OCA) are: minimal invasiveness or even noninvasiveness improved pharmacokinetics targeted delivery

Skin Barrier Follicular transport Intercellular transport (hydrophilic OCAs) Transcellular transport (lipophilic OCAs) Stratum corneum Dermis Follicle Living epidermis 10 - 20 μm 75 - 150 μm The stratum corneum and underlying living epidermis represent a barrier separating body from the environment and makes penetration of OCA deep into the skin a rather difficult problem

The basic options for improving transdermal delivery: skin barrier elimination stratum corneum/epidermis perforation stratum corneum penetration

Fractional laser microablation (FLMA) can be one of the prospective method for targeted OCA delivery into the skin Microablation mode Microperforation mode ablation zone E=0.8J

Objectives Development of method of transcutaneous delivery of OCAs The study of agent penetration with different modes of the laser fractional ablation of skin

Methods and Materials Four rats in vivo Polyethylene glycol with molecular weight 300 Dalton (PEG-300) and refractive index 1.457 (930 nm) The Palomar Lux2940 erbium laser (Palomar Medical Products Ltd., USA) with two modes: Mode I - ablation of skin upper layer with pulse energy 0.8 J and pulse duration 5 ms Mode II – microperforation with pulse energy 1 J and pulse duration 5 ms OCT monitoring (OCP930SR, Thorlabs, USA), ~930 nm

Design of the experiment FLMA Application of PEG-300 OCT-monitoring during 60-70 min

Model In accordance with the single-scattering model (SSM) the measured signal in OCT system is defined as i(z) is the OCT signal, µt is the total attenuation coefficient µt=µa+µs, z is the probing depth of tissue In the SSM, the reflected power is proportional to exp(–μtz), i.e. A is the coefficient of proportionality equal to P0α(z), P0 is the optical power launched into the tissue, and B is the background signal The attenuation coefficient has been obtained by the minimization of the target function Rexp is OCT signal measured on the depth z and Ni is the number of measured points in the depth of the tissue (on the z-axis)

For this case A = 1230.4, B = 79.7, and μt = 90.3 cm-1 Typical B-scan of skin with marked selection regions (51 A-scans for averaging) and region of interest (a) and plot of the averaged A-scan and the fitted curve using the single-scattering model (b) For this case A = 1230.4, B = 79.7, and μt = 90.3 cm-1

Results Mode I Mode II ablation of skin upper layer Channels area of damage is 66 mm2 depth of damage is ~100 μm area of damage is 88 mm2 64 vertical micro-channels depth of damage in a channel is <150 μm Channels 0.3 mm 0.3 mm

Kinetics of attenuation coefficient normalized on the initial value (intact skin) during optical clearing

Effectiveness of dermis optical clearing:

Conclusion FLMA induced a swelling of damaged skin, which increased light scattering in tissue Laser perforation was more effective for optical clearing process than laser surface ablation because of less area of damage (less swelling)

Acknowledgements The work was carried out under the support by Russian Federation Governmental No. 14.Z50.31.0004 designed to support scientific research projects implemented under the supervision of leading scientists at Russian institutions of higher education and the Tomsk State University Academic D.I. Mendeleev Fund Program

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