Mikhail M. Stolnitz

Optical properties of melanin in the skin and skinlike phantoms

Experimental study and computer modeling were used to investigate the optical properties of melanin in the skin and skin-like phantoms. To investigate light scattering by melanosomes in skin we made skin-like phantoms on the base of gelatin with different content of melanin particles. Spectra of total transmittance and diffuse reflectance of the phantoms were obtained in the wavelength range from 400 to 800 nm. Absorption and reduced scattering coefficients of melanin were calculated. Mie theory was used to estimate the optical properties of melanin particles. Wavelength dependence of refractive indices of eumelanin particles (isolated and purified from the ink of the cuttlefish Sepia officinalis) and synthetic melanin particles was estimated.

Monte Carlo study of skin optical clearing to enhance light penetration in the tissue

Result of Monte Carlo simulations of skin optical clearing is presented. The model calculations were carried out with the aim of studying of spectral response of skin under immersion liquids action and calculation of enhancement of light penetration depth. In summary, we have shown that: 1) application of glucose, propylene glycol and glycerol produced significant decreasing of light scattering in different skin layers; 2) maximal clearing effect will be obtained in case of optical clearing of skin dermis, however, absorbed light fraction in skin dermis changed insignificantly, independently from clearing agent and place it administration; 4) in contrast to it, the light absorbed fraction in skin adipose layer increased significantly in case of optical clearing of skin dermis. It is very important because it can be used for development of optical methods of obesity treatment.

Optical clearing of skin tissue produced by application of glucose solution: in vivo study

We present experimental results on optical properties of the human skin controlled by administration ofthe 40%-glucose solution. In vivo reflectance spectra of the human skin were measured. Results of the experimental study of influence of the 40%-glucose solution on reflectance spectra of the human skin are presented. A significant decrease of reflectance of the human skin under action of the osmotic agent is demonstrated. The experiments show that administration of the glucose solution allows for effective control of tissue optical characteristics, that makes skin more transparent, thereby increasing the ability of light penetration through the tissue. Laser Doppler flowmetry has been used for study of skin blood microcirculation under the action of the glucose solution. Results of the experiments demonstrated that at the action of the glucose solution blood perfusion and blood concentration increase, however the mean blood velocity does not change. The presented results can be used in developing functional imaging techniques, including OCT and reflectance spectroscopy. A potential benefit of the optical clearing technique is the improvement of laser therapeutic techniques that rely on sufficient light penetration to a target embedded in tissue.

Mathematical modeling of changes in the optical properties of epidermis due to UV-induced melanogenesis.

In the work the mathematical model of melanogenesis is presented that allows to predict a qualitative change of epidermis absorption and scattering under UV-irradiation. Epidermal sublayers and inhomogeneous melanin distribution are taken into account.

Mathematical modeling of cell proliferation dynamics in psoriatic epidermis sensitized by the furocoumarins under UVA radiation

In the work the mathematical model is presented which describes the processes in the epidermis sensitized by the furocoumarins under UVA-radiation. The model describes the processes at three levels: molecular (the photochemical transformations of the psoralen molecules and their reactions with the DNA-molecules), cellular (proliferation, differentiation and repairing of injuries), and tissue (humoral regulation, space-time cell dynamics in the epidermis). The results of the numerical simulations of both the latent period and psoriasis manifestation are given. The therapeutical effect of the UV-radiation is considered in the framework of the model.

Mathematical model of erythropoiesis dynamics under low-intensity laser and x-radiation

The mathematical model is presented of low-intensity laser radiation influence on the dynamics of the X-irradiated bone marrow tissue erythropoiesis. The process of recovering in postradiation stage of the cells of erythroid series has been investigated for various parameters of laser emission.

Exact solution in one model of cooperative molecular motors

The Julicher and Prost (1995) model of cooperative motion of molecular motors is discussed. Some inaccuracies in original reasoning are corrected. Explicit analytical solution of models equations is derived. Previously unexplored type of cooperative motion (reverse motion in asymmetric potential in absence of external force) is described.

Mathematical modeling of clearing liquid drop diffusion after intradermal injection

The mathematical model of clearing agent diffusion after intradermal injection has been developed. Skin was presented as multilayer medium, but one layer with proper boundary conditions is considered. Analytical solution of the boundary problem for small and large time intervals is obtained.

Dependence of molecular motors dynamics on type of single motor-organelle coupling

Mathematical models construction of motor proteins dynamics at a transport of intracellular organelles is considered with taking into account the rheological properties of organelle membrane and cytoplasm. The possibility of extension of the existing idealized models of hard motors and a transported particle on the this general case is discussed.

Nonlinear cellular dynamics of keratinocytes in normal and psoriatic epidermis under action of UV radiation

The semi-phenomenological model of epidermal cell dynamics is submitted. The model takes into account three types of basal layer keratinocytes (stem, transient amplifying, terminally differentiated), distribution of first two types cells on mitotic cycle stages and resting states, keratinocytes-lymphocytes interactions that provide a positive feedback loop, influence of more differentiated cells on their progenitors that provide a negative feedback loop. Simplified model are developed and its stationary solutions are received. The opportunity of interpretation of some received modes as corresponding to various stages of psoriasis is discussed. Influence of UV-radiation on transitions between various modes of epidermis functioning is qualitatively analyzed.