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Optical clearing of muscle with propylene glycol

Skeletal muscle presents an internal fibrous structure. The existence of muscle fibers surrounded by interstitial fluid originates an internal step refractive index profile that causes light scattering. One way to minimize this effect inside a muscle is to perform an optical clearing treatment, using an adequate solution that presents a refractive index higher than the interstitial fluid. We have studied muscle spectral transmittance during sample immersion in propylene glycol. With the collection of transmittance spectra registered during a period of 20 minutes of immersion we could represent spectral transmittance evolution for several wavelengths and verify that the tissue samples have become more translucent. The optical clearing effect created in the tissue samples was characterized by an increase of 45% above the natural transmittance and the variations observed in tissue mass, pH and global refractive index. We also identified the initial mechanisms of agent diffusion into the tissue and consequent tissue dehydration from the spectral transmittance evolution. The histological analysis of variations caused in the internal structure of the tissues permitted to better explain the optical clearing effect created. Considering a mathematical model developed in previous studies, we could estimate the amount of agent that was inserted into the tissue samples.