Abstract
In vivo tissue transparency in the visible light spectrum is beneficial for many research applications that use optical methods, whether it involves in vivo optical imaging of cells or their activity, or optical intervention to affect cells or their activity deep inside tissues, such as brain tissue. The classical view is that a tissue is transparent if it neither absorbs nor scatters light, and thus absorption and scattering are the key elements to be controlled to reach the necessary transparency. This review focuses on the latest genetic and chemical approaches for the decoloration of tissue pigments to reduce visible light absorption and the methods to reduce scattering in live tissues. We also discuss the possible molecules involved in transparency.
Highlights
Many animals have transparent tissues or are completely transparent in their everyday life
Some can even become entirely transparent at will, such as certain cephalopod mollusks that change the light adsorption of their skin (Zylinski and Johnsen, 2011) [1], depending on pictorial depth cues and directional illumination (Zylinski et al, 2016) [2]
16-kDa α-crystallin homologue survive at higher temperatures, and transparency-promoting agents, and it is possible that in Mycobacterium the dominant protein produced by stationary-phase culturesthat in vitro, but it is crystallins are the is cause of the transparent-to-opaque transition
Summary
Many animals have transparent tissues or are completely transparent in their everyday life. Given enough directional changes due to multiple instances of refraction and reflection, the tissue, though nonabsorbing, will be opaque and nontransparent (Johnsen, 2001; Zueva et al, 2016) [17,18] Complete transparency, which is advantageous in predator–prey competitions, can only be attained with aquatic animals, because the RI of their natural habitat can be matched to the cytoplasm RI. This complete transparency is difficult to achieve in animals that live in air or on land, and these animals usually have few transparent tissues. Transparency within the visible spectrum can be “partially restored” by newly developed digital microscopy methods, such as transmission matrix inversion (Xu et al, 2017; Cua et al, 2017) [19,20], which may overcome light scattering problems
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