The cell membrane is like a rampart protecting a castle — a defensive barrier to keep out invaders while selectively allowing necessary resources inside. To surmount that defense and get molecules into cells, scientists typically use chemicals or electricity to open pores in the cell membrane. Another technique is to simply jab the cell with a glass micropipette. Unfortunately, both of these processes can result in cellular abnormalities and reduced cell viability.
Printing cells using an inkjet printer is not a new idea. In 2004, Thomas Boland, then at Clemson and now director of biomedical engineering at the University of Texas at El Paso, printed sheets of solid animal tissue by filling inkjet cartridges with animal cells, or "bio-ink” (2). Following up on that work, Boland, Delphine Dean, and colleagues investigated how the printing process affects cell viability. “We hypothesized that because the cells were forced through the [printing] nozzle, they were probably experiencing some membrane disruption,” says Dean.
The team indeed found that the printing process causes transient pores to appear in the cell membrane, but that result did not have any effect on cell viability (3). In fact, up to 95% of the printed cells remained healthy and functioning, a statistic no different than if one were to simply pipette cells onto a slide, says Dean.
In a video and paper published this month in JoVE, the Journal of Visualized Experiments, the Clemson team describes how to easily print cells using an inkjet printer. The process can be done in a day and involves three steps: modifying the printer to bypass the automatic paper feed and print onto glass slides instead; emptying and cleaning a stock printer cartridge; and preparing the “bio-ink” solution.
After the cells are printed onto a slide, the pores remain open for up to two hours. Thousands of cells can be printed, and made permeable, in a matter of minutes — dramatically faster than micropipetting molecules into cells one at a time. The pores reach about 10 nm in diameter, and therefore would not be effective for injecting larger proteins or particles.
In an attempt to visualize how the outside forces affect a cell’s cytoplasm, Dean used the technique to introduce fluorescently labeled g-actin monomers — bits of a cytoskeleton that bind filaments inside the cell — into printed cells. Cells that were printed rapidly took up the monomers and glowed green. “It was a nice way to visualize the cell’s internal structures in a living cell,” says Dean. Non-printed cells incubated with the monomers for three hours did not glow.
Bioprinting is efficient and cost-effective, the authors write, and now adds a new trick to the molecular biologist’s repertoire — incorporating molecules into the cell cytoplasm. “Converting and using the inkjet printer with cells is relatively easy to do,” says Dean. “People shouldn't be scared to try it.”
1. Owczarczak, A. B. et al. 2012. Creating transient cell membrane pores using a standard inkjet printer. J. Vis. Exp. 61:e3681.
2. Xu, T. et al. 2004. Construction of high-density bacterial colony arrays and patterns by the ink-jet method. Biotechnol Bioeng. 85:29-33.
3. Cui, X. et al. 2010. Cell damage evaluation of thermal inkjet printed Chinese hamster ovary cells. Biotechnol Bioeng. 106:963-9.