The characteristic time of glucose diffusion measured for muscle tissue at optical clearing

Abstract

The study of agent diffusion in biological tissues is very important to understand and characterize the optical clearing effects and mechanisms involved: tissue dehydration and refractive index matching. From measurements made to study the optical clearing, it is obvious that light scattering is reduced and that the optical properties of the tissue are controlled in the process. On the other hand, optical measurements do not allow direct determination of the diffusion properties of the agent in the tissue and some calculations are necessary to estimate those properties. This fact is imposed by the occurrence of two fluxes at optical clearing: water typically directed out of and agent directed into the tissue. When the water content in the immersion solution is approximately the same as the free water content of the tissue, a balance is established for water and the agent flux dominates. To prove this concept experimentally, we have measured the collimated transmittance of skeletal muscle samples under treatment with aqueous solutions containing different concentrations of glucose. After estimating the mean diffusion time values for each of the treatments we have represented those values as a function of glucose concentration in solution. Such a representation presents a maximum diffusion time for a water content in solution equal to the tissue free water content. Such a maximum represents the real diffusion time of glucose in the muscle and with this value we could calculate the corresponding diffusion coefficient.

Software development for estimation of optical clearing agent’s diffusion coefficients in biological tissues

“…The efficiency of the treatment can be evaluated and quantified if the diffusion properties of the chemical used are known for the desired tissue. Some results have been reported for the diffusion time and diffusion coefficients of some chemical agents in specific biological tissues but the techniques used to evaluate these parameters are diverse [4][5][6][7][8][9].…”

“…Such treatment is completely reversible by natural rehydration in vivo and by assisted rehydration on ex vivo tissue samples [10]. The potential of the optical immersion clearing technique is very significant to be used with clinical procedures that apply light for diagnostic and treatment purposes [2,7,14].…”

“…This way, the individualization of the two mechanisms needs a refined method that produces accurate results. Such a method is described in literature [8,13] and we have recently proven its concept experimentally as described in our recent publications [7,10,18]. In those papers we describe how we have used thickness and collimated transmittance (Tc) measurements made from thin muscle samples under treatment with glucose and ethylene glycol (EG) solutions to estimate the diffusion time, diffusion coefficient and viscosity of these agents in muscle.…”

“…Our research has produced additional results. Those additional results were the estimated diffusion properties of water inside the muscle [10,18] and the amount of free water content in the natural muscle [7,10].…”

“…The time when the saturation regime begins depends on the sample, its geometry and also on the OCA concentration used to perform the treatment. As an example, for treatments of muscle samples with glucose solutions, we have observed that the beginning of the saturation regime occurs at a later period of time if we increase the glucose concentration in the solution from 20% to 40% [7]. This variation is imposed by the free water content in the tissue and the OCA concentration we use.…”