Dimethyl sulfoxide (DMSO) diffusion in skin tissue Marina D. Kozintseva, Alexey N. Bashkatov, Elina A. Genina, Valery V. Tuchin Department of Optics and Biophotonics Saratov State University, Saratov, Russia Saratov Fall Meeting 2012

Motivation: The possibility of selective translucence of the superficial skin layers is very useful in developing functional imaging and therapeutic techniques. A potential benefit of the optical clearing is the improvement of laser therapeutic techniques that enable sufficient light penetration to a target embedded in tissue. Combination of optical clearing with laser radiation can reduce the laser fluences required for a therapeutic effect. However, in spite of numerous investigations deal with transport of DMSO within biological tissue the problem of estimating the diffusion coefficient of the agent in skin has not been studied in details Goal of the study is to measure the diffusion coefficient of DMSO in skin Saratov Fall Meeting 2012 Saratov State University Department of Optics and Biophotonics

Materials and Methods For this study ten rat skin samples have been used. The samples have been obtained from autopsy and kept in saline during 24 hour until spectroscopic measurements at temperature 4-5°C Measurement of collimated transmittance have been performed using a commercially available spectrometer USB4000-Vis-NIR (Ocean Optics, USA) in the spectral range nm. All measurements were performed at room temperature (about 20°C) As a clearing agent DMSO solution was used. Refractive index of the solution is It has been measured using Abbe refractometer at wavelength 589 nm Saratov Fall Meeting 2012 Saratov State University Department of Optics and Biophotonics

Experimental setup 1.Halogen lamp (HL 2000) 2.Delivering optical fiber 3.Tissue sample 4.Glass cuvette with object plate 5.Receiving optical fiber 6.Multichannel spectrometer (USB4000-Vis-NIR) 7. PC 8. Collimators The scheme of experimental setup for the measurements of collimated transmittance: Saratov Fall Meeting 2012 Saratov State University Department of Optics and Biophotonics

Method for determination of DMSO diffusion coefficient T is the collimated transmittance; µ s is the scattering coefficient; l is the tissue thickness; N is the numerical concentration of the tissue scatterers; a is the scatterers radius; n s = is the refractive index of the scatterers; n I is the refractive index of interstitial fluid of the tissue; and  is the volume fraction of the scatterers; n I0 = is the refractive index of interstitial fluid of skin before DMSO diffusion; n c is the refractive index of the DMSO solution; and C is the concentration of DMSO within skin Determination of DMSO concentration within skin has been performed using the assumption: Saratov Fall Meeting 2012 Saratov State University Department of Optics and Biophotonics

Method for determination of DMSO diffusion coefficient C (t) is the volume-averaged concentration of the DMSO within tissue sample, g/ml; D is the diffusion coefficient, cm 2 /sec Saratov Fall Meeting 2012 Saratov State University Department of Optics and Biophotonics

Method for determination of DMSO diffusion coefficient  is the diffusion time constant, sec; p is the porosity coefficient of skin;  is the volume fraction of scatterers; and D 0 is the DMSO diffusion coefficient in interstitial fluid, cm 2 /sec Saratov Fall Meeting 2012 Saratov State University Department of Optics and Biophotonics

Results: DMSO diffusion The time-dependent transmittance of the rat skin measured at different wavelength concurrently with administration of DMSO solution The transmittance spectra of the rat skin measured concurrently with administration of DMSO solution at different time intervals Saratov Fall Meeting 2012 Saratov State University Department of Optics and Biophotonics

Results: DMSO diffusion coefficient Sample Thickness, mm Diffusion coefficient, cm 2 /sec Sample Thickness, mm Diffusion coefficient, cm 2 /sec 10,63 (3,99  0.21)  ,88 (1,28  2.87)  ,87 (9,98  0.68)  ,33 (7,13  0.72)  ,51 (7,13  2.24)  ,41 (2,59  1.50)  ,32 (1,89  1.78)  ,87 (1,84  0.28)  ,56 (7,94  0.63)  ,47 (4,06  0.04)  =(4,783,045)x10 -6 cm 2 /sec =(4,783,045)x10 -6 cm 2 /sec Saratov Fall Meeting 2012 Saratov State University Department of Optics and Biophotonics

Acknowledgements Saratov Fall Meeting 2012 Saratov State University Department of Optics and Biophotonics Grants # and КО of Russian Foundation of Basis Research Russian Federation governmental contacts , , , and 14.B Grant # Network of Excellence for Biophotonics (PHOTONICS4LIFE) of the Seventh Framework Programme of Commission of the European Communities