Optical clearing allows tissue visualization under preservation of organ integrity. Optical clearing of organs with a physiological change in three-dimensional geometry (e.g. lung) would additionally allow visualization of macroscopic and microscopic tissue geometry. A prerequisite, is the preservation of the tissue mechanics of the optically cleared lung tissue. We investigated the impact of optical and dielectric properties of clearing solutions on biomechanics and clearing potency in porcine tissue strips of healthy lungs. After fixation, bleaching and rehydration four methods of optical clearing were investigated using eight protocols. The mechanical and optical properties of the cleared lung tissue strips were investigated before, during and after the biochemical optical clearing process. Fresh strips were used as controls. Best balance between clearing and preserved mechanics was found for clearing with a 1:1 mixture of dimethylsulfoxide and aniline. Our findings show that, (i) the degree of tissue transparency and translucency correlated with the refractive index of the clearing solution index (r=0.976, p=0.0004; and r=0.91, p=0.0046), (ii) tissue mechanics were affected by dehydration and the type of clearing solution, and (iii) tissue biomechanics and geometry correlated with the clearing solution's dielectric constant (r=-0.98, p<0.00001; and r=0.69, p=0.013). We show that the lower the dielectric constant of the clearing solutions, the larger the effect on tissue stiffness. This suggests that the dielectric constant is an important measure in determining the effect of a clearing solution on lung tissue biomechanics. Optimal tissue transparency requires complete tissue dehydration and a refractive index of 1.55 of the clearing solution.
- optical clearing
- refractive index
- dielectric constant
- Copyright © 2016, Journal of Applied Physiology