Get in line! Using electricity to pattern living cells

Written by: Ritu Raman

Original article: Bajaj et al. Advanced Healthcare Materials 2012
The Gist of It:
Imagine being able to replace a diseased or damaged tissue or organ with new tissue that looked and acted just the same. That is just what scientists are trying to do in the new field of “tissue engineering”! By putting living cells and proteins together bit by bit, like LEGO® building blocks, they hope to build replacement tissues that can safely integrate with your body and help you return to normal, healthy life after an illness or injury. There are many challenges that must be addressed before scientists can do this reliably and for large numbers of patients, though. One of these challenges is being able to control the placement and orientation of very small living cells, a process called patterning, and assemble these cells into precise and complex multi-cellular configurations. A single cell ranges from about 1–100 microns. For comparison, a human hair is usually 17–181 microns thick, so you can imagine how hard it would be to pattern something that small into a reliable 3D shape! Bajaj and colleagues propose one solution to this problem using a phenomenon known as dielectrophoresis (DEP). When cells are placed in a non-uniform electric field generated by electrodes (metal conductors), DEP exerts a force on them that makes them align parallel to the electrode. When you turn off the electric field, the cells lose their alignment. In this study, the authors mixed cells with a light-sensitive liquid solution that could become a solid in response to a laser. They placed the cell-liquid mix on top of electrodes, turned on the electric field to align the cells, and then shined a laser on the solution to turn it into a solid before turning off the electric field. The cells were then fixed in their aligned position inside the solid material. Using this approach, the researchers showed that they could reliably and quickly pattern many cells into complex configurations, creating a new tool that other scientists can use for tissue engineering. I’m so excited to see how people use this in the future! Are you?
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An electric field is used to line up cells into complex patterns. This phenomenon is called dielectrophoresis!

The Nitty Gritty:
Bajaj et al. patterned two types of murine cells, embryonic stem cells and skeletal muscle myoblasts, inside poly (ethylene glycol) diacrylate hydrogels. The pre-polymer solution containing cells was pipetted onto glass slides patterned with electrodes and placed within a stereolithographic 3D printer. Cell patterning was achieved by powering the electrodes with a waveform generator outputting a 10 Vpp, 1–10 MHz sinusoid. Live/dead assays confirmed cell viability in response to DEP-based patterning.
Original Research Article: Bajaj, P., et al. “Patterned three‐dimensional encapsulation of embryonic stem cells using dielectrophoresis and stereolithography.” Advanced Healthcare Materials 2 (2013): 450-458.
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