In vitro testing is the controlled process of testing biological materials outside of the living organism in a synthetic environment set-up within laboratory equipment. Experimenting with tissues in culture can facilitate drug discovery with researchers able to systematically manipulate the tissue and test different drugs or drug combinations using a safer artificial ecology.
Conversely, when studying a whole system where many cells interact with each other, it has proven difficult to keep the tissue alive for more than a few days. Microfluidics is the science of controlling minute amounts of liquids in networks of channels with dimensions from tens to hundreds of micrometers. It is in this way reagents and sample size can be greatly miniaturized to simulate whole system biology, however, these also have a short shelf-life.
Keeping sample tissue alive
Now, a study from researchers at RIKEN develops a new system for keeping functional tissue viable for long-term study once transferred from an animal to a culture medium. The team states their proof-of-concept experiment shows tissue explanted to their microfluid device from a mouse brain remained viable after almost one month in culture. The opensource study is published in the journal Analytical Sciences.
Previous studies show microfluidic devices are important platforms to culture and observe biological tissues. Microfluidic devices, in particular, have been shown to be inferior to conventional tissue culturing in terms of tissue viability, a sustainable culturing period, and ease of tissue handling and observation.
On top of this, explanted tissues can maintain their functions for only hours to days in microfluidic devices, although their observations are desired for weeks. This, in turn, can lead to incomplete and inaccurate data. The current study develops a polydimethylsiloxane (PDMS) device incorporated with a porous hydrophilic PTFE membrane which cultured functional brain tissue successfully for 25 days far longer than conventional cultures.
The current study engineers a microfluidic device with a semi-permeable channel surrounded by an artificial membrane and solid PDMS walls. The membrane is partially coated with PDMS to form hydrophilic and hydrophobic portions; the uncoated hydrophilic membrane area formed a semi-permeable channel with the PDMS microstructure, while the PDMS-coated membrane area formed an impermeable channel.
Results show the tissue benefited from having the culture medium circulate within the microchannel and pass through the permeable membrane, which allowed proper gas exchange, something conventional immersed tissue cultures have trouble accomplishing efficiently.
The device was tested using tissue from the mouse suprachiasmatic nucleus, which governs circadian rhythms in the brain. Circadian rhythm activity in the brain was linked to the production of a highly fluorescent protein for analytical purposes.
Tissue-in-culture lived for 25 days
By measuring the level of bioluminescence coming from the brain tissue, it was possible to see the tissue kept alive by their system stayed active and functional for over 25 days with circadian activity. In contrast, neural activity in tissue kept in a conventional culture decreased by 6% after only 10 hours.
The team surmises they successfully cultured living tissue for 25 days by using a simple microfluidic device with a semi-permeable channel that produced higher quality results than conventional culture. For the future, the researchers state they now plan to run long term experiments using their system to observe the formation of blood vessels and the movements of cells during organoid formation.
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