Researchers have created see-through mice and rats using a new technique for so-called tissue clearing.
In a paper published Thursday in the journal Cell, a California Institute of Technology professor and her colleagues said they had turned a dead mouse transparent in a week’s time, while a rat specimen took two weeks to treat.
The technique, which can also be used to create transparent organs for study, builds on previous tissue clearing processes that have revolutionized anatomical research.
While scientists have attempted to create see-through organ and tissue samples since the 1800s, researchers have relied primarily on the sectioning of samples - slicing organs into extremely thin cross sections and examining these pieces in succession.
“That’s been useful but it’s also been slow and tedious,” said senior study author Viviana Gradinaru, an assistant professor of biology and biological engineering at Caltech.
Recent advancements in tissue clearing have enabled researchers to study nerve connections and organ structures without having to slice them up, providing scientists with new insights into previously hidden anatomical structures.
In order to render organs or entire bodies transparent, scientists remove those lipids, or fats, that make tissues opaque. This is accomplished by exposing the specimen to detergents, although removal of the lipids leads to other problems.
“If you remove the lipids and don’t do anything else, the entire tissue collapses, because the lipids are in a way the skeleton of a building,” Gradinaru said.
In order to maintain the sample’s shape, researchers fill it with a hydrogel. The hydrogel forms a network of polymer chains that stick to proteins and other compounds, creating a gelatin-like supporting structure.
Once this is done, the lipids can be flushed from the tissue.
Previous techniques have relied on immersing tissue samples in the lipid-removing solution. However, Gradinaru and her colleagues said they had succeeded in speeding up the clearing process by pumping by the hydrogel and the detergent through blood vessels.
They have dubbed their technique PARS, or perfusion-assisted agent release in situ.
Previous clearing techniques have taken much longer to execute and damaged samples. Gradinaru said the new technique avoided this damage and, if an animal has been genetically altered to produce fluorescent proteins as a study tool, the clearing agents do not remove them.
Could the process be used on a human body?
“As long as you have a preserved circulatory system, the method is scalable,” Gradinaru said. “In theory it could.”
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