Seeing inside someone’s heart. Stretching the mind. These aren’t just turns of phrase but something that researchers can physically do with help from polymer science and microscopy. Massachusetts Institute of Technology chemical engineer Kwanghun Chung has found a way to turn organs into flexible, transparent hydrogels (Nat. Methods 2020, DOI: 10.1038/s41592-020-0823-y).
When he was a postdoc, Chung helped develop a way to render brain tissue transparent and fixed in polyacrylamide, but the resulting samples were brittle. Chung and his team have now adjusted the amounts of acrylamide, cross-linker, and initiator to create an entangled hydrogel rather than a cross-linked one. Because the long polymer chains are entangled, the links can slip around one another, giving the gel structural integrity but also flexibility and stretchability. The team call the technique ELAST (entangled link-augmented stretchable tissue-hydrogel).
When their polymer formulation infuses biological tissues, cells and molecules become entangled in a stretchy gel. That makes fragile tissues easier to handle and can speed up the process of fluorescently labeling cells or biomolecules. Instead of waiting for imaging probes to diffuse through a thick sample, they can stretch out ELASTicized samples and apply a solution of fluorescent probes, maximizing the contact between the labels and the samples and speeding up the labeling process. When the gel snaps back to its original shape, it’s ready for imaging and the next round of labeling. Chung hopes to use the technique to make a comprehensive map of the human brain.