Rapid optical tissue clearing using poly(acrylamide-co-styrenesulfonate) hydrogels for three-dimensional imaging.

Optical tissue clearing methods are attractive for three-dimensional imaging of intact tissues and organs. A CLARITY (clear lipid-exchanged acrylamide-hybridized rigid imaging/immunostaining/in situ-hybridization-compatible tissue-hydrogel) method using polyacrylamide gels was recently developed. In the current study, we used poly(acrylamide-co-styrenesulfonate) gels as a polyelectrolyte gel for a passive CLARITY method. First, radical copolymerization of acrylamide (AAm) and sodium p-styrenesulfonate (SS) at different ratios was performed. The composition of the copolymer could be controlled by changing the monomer ratio. With increased SS content, the molecular weight decreased and the refractive index slightly increased. The poly(AAm-co-SS) hydrogels with a higher SS content were more swollen and looser. The clearing time could be reduced using the poly(AAm-co-SS) hydrogel with a higher SS content. Three-dimensional fluorescence imaging of the poly(AAm-co-SS) hydrogel-cleared tissues was successfully performed after treatment using a blue fluorescent DNA stain. Therefore, the use of the poly(AAm-co-SS) hydrogel improved the clearing process in the passive CLARITY method, and the technique is useful for fluorescence imaging of DNA.