DIFFUSION OF PEG-200 IN SKIN TISSUE

BASHKATOV,
ELINA A. GENINA, VALERY V. TUCHIN

SARATOV STATE UNIVERSITY

for improvement of optical methods for diagnostics and therapy of

various diseases constantly increases because they are safe and relatively inexpensive. The main criteria of the choice of OCA for the tissue clearing are:
The refractive index of OCA should be close to that of the main tissue scatterers (collagen and elastin fibers or cell membranes);
OCA should be hyperosmotic liquid;
Biocompatibility. Among the most popular OCAs, there are glycerol, polyethylene glycols, propylene glycol, and glucose. They are biocompatible and do not damage tissues seriously at the short-time action.

The Motivation of the Study

optical and structural parameters of rat skin under the action

of polyethylene glycol-200 ex vivo

To measure the diffusion coefficient of polyethylene glycol-200 in skin tissue

Tissues Under the Action of an Optical Clearing Agent
Osmotic dehydration

of a tissue
Partial replacement of an interstitial fluid by the clearing agent
Structural modification of dissociation of tissue collagen (after prolonged action of the clearing agent)

40 samples (10 samples for research of kinetic of every

parameter: the collimated transmittance, the weight, the thickness and the area) of skin of laboratory albino outbred rats were used. The samples size was about 10×15 mm2. The hair was carefully removed from the surface of the post mortem rat bodies using depilatory cream "Veet" (Reckitt Benckiser, France). Subcutaneous adipose layer was carefully removed from the skin samples.

viscous liquid
Biocompatible
Polymer of ethylene glycol (C2H6O2) (class of diols)
Molecular weight

200 Dalton
Refractive index 1.46
Chemical formula:
C2nH4n+2On+1

lamp HL-2000
2, 4 – collimators 74-ACR
3 – cuvette with

a
skin sample fixed
on the frame
5 – spectrometer
USB-4000-Vis-NIR
6 – PC

kinetics of weight W(t), thickness l(t) and area S(t) changing

owing to dehydration the following empirical equation was used:

where A(t = 0) is the initial value of weight, thickness or area; τ is the characteristic time constant, which describes the dehydration rate; B is the coefficient, which describes the dehydration degree; and B0 is the residual value of weight, thickness, or area after the dehydration

simple approach suggested by Oliveira et al. (Oliveira L.M., et

al, Laser Physics, Vol. 23(7), 075606, 2013)

The diffusion is characterized by Fick’s law:

The diffusion time constant of PEG-200 () is related to the diffusion coefficient (D) and sample thickness (l) as:


In a first-order approximation, solution of the diffusion equation has the form:


The collimated transmittance can be described by the equation:



The diffusion coefficient of PEG-200 in skin can be calculated as:

The Diffusion Coefficient Estimation

collimated transmittance in different moments




Typical time dependence of the collimated

transmittance on different wavelengths

Time dependence of the weight




Time dependence of the area




Time dependence

of the thickness

of PEG-200

the Experiment
Before optical clearing
After 120 min of clearing

Rat Skin Tissue Ex Vivo
(1.203±0.122)×10-7 cm2/s

polyethylene glycol (PEG) with molecular weight 200 Dalton was studied

ex vivo. The collimated transmittance was measured at the wavelength range 500-900 nm. It was found that collimated transmittance of skin samples increased, whereas weight, thickness and area of the samples decreased during PEG penetration in skin tissue. A mechanism of the optical clearing under the action of PEG is discussed. Taking into account the kinetics of volume and thickness of the skin samples, diffusion coefficient of PEG-200 in skin tissue has been estimated as (1.203±0.122)×10‑7 cm2/s. The presented results can be useful for enhancement of many methods of laser therapy and optical diagnostics of skin diseases and localization of subcutaneous neoplasms.