Patterning proteins on a budget: using an inexpensive inkjet printer
Several different models of inexpensive commercial inkjet printers can be modified to print biochemical reagents, including proteins, onto flat surfaces. This is a preferred low-cost method for fabricating modest numbers of diagnostic devices. Over the last decade several research laboratories have described how they have modified commercial inkjet printers to print things other than the inks for which they were designed. Printer types have ranged from expensive commercial models to low-cost home office printers.
There have always been trade-offs in their use, particularly if protein solutions are to be printed—there is not yet a “perfect” printer for this purpose. The high shear rates involved in ejection of protein solutions have been reported to denature some proteins, but there are conflicting reports. Thermal inkjet printers (or bubble-jet printers) rely on very rapid heating of the “ink” to high temperatures to create a transient bubble that pushes the ink out of the printer head. While this heating appears to have little effect on most of the protein ejected in the droplet, there is a tendency of the ink to “cook” on the heater surface, so that while there may be little damage to most of the molecules in the ejected droplet, over time the heater itself becomes fouled with denatured protein. As the thickness of the (thermally-insulating) denatured protein layer increases with the number of droplets ejected, jetting performance degrades and eventually fails altogether. Piezoelectric printers would seem to be “safer” for molecules that can thermally denature. However, there are also failure modes for piezoelectric heads, and as these are often “permanent” in a printer, failure of the print head often necessitates replacement of the entire printer. Furthermore, different manufacturers have different methods of converting graphic elements to patterns of ink dots, making it difficult to deliver single droplets on demand, as is common with high-end printers.
We have had some success in our laboratory. Here, we describe how to adapt an Epson R280, to print protein solutions. We chose this printer model due to the following features:
- Piezoelectric printing (vs. thermal, "better" for proteins)
- Availability of refillable ink cartridges (clean and modifiable)
- CD printing (stationary flat substrate, no need to feed thruogh or bend brittle substrates)
- Acceptable resolution (1.5 pL drop size, 5760 x 1440 dpi resolution)
- Low cost (~$100 US dollars)
- Simple to adapt with minimal hardware modifications or knowledge of proprietary software
A procedure for printing proteins onto CDs with the Epson R280 was described previously by Cohen, et al. (reference below). The procedure given here includes additional detail and provides some simplifications. The key issue is tricking the printer into thinking that it is printing ink onto a CD when it is not. The method requires minimal modifications of the printer and uses common lab supplies. One very valuable feature of this particular printer modification is that one can replace the large ink cartridge with a small plastic pipette tip; this allows use of microliter volumes of precious reagents, rather than needing to fill the entire ink cartridge.
Figure 1: Images of printer modifications. A) The Epson R280 printer. B) Foil covering for the CD tray to trick the printer into thinking that a CD is present. Devices to be printed are placed on the foil. C) Modification of the “ink” reservoir using a trimmed pipette tip (P200). Ink cartridges must be present for the printer to function. To trick the printer, the ink cartridge is trimmed to fit around the pipette tip; the cartridge has no fluid in it.
Typical protein solutions used in bioassays likely have fluid properties different from normal printer ink. Fluid properties for effective printing are given by the inverse of Ohnesorge’s number,
Z = (sqrt(rho*gamma*alpha))/nu
where rho is the fluid density, gamma is the surface tension, alpha is the printer aperture (90 microns for the Epson R280), and nu is the fluid viscosity. Z should be between 1 and 10 for optimal inkjet printing with this printer (J. Mater. Chem., 2008, 18, 5717-5721). For our printing, we used protein solutions in phosphate buffered saline, and we added a surfactant (Triton X-100) to modify surface tension and fluid viscosity (we found that at Z=46, solutions still printed well).
Step-by-step instructions for printer modification and printing procedures are given here. We will soon publish a paper that describes printing on devices for diagnostic assays. We hope that these instructions are useful to the community. We are also eager to get feedback, corrections, and improvements to these instructions from the community, as well as to disseminate instructions developed by other groups for adapting printers.
A few (of many) journal articles are as follows (more are given in the instructions):
- D.J. Cohen, R. C. Morfino and M. M. Maharbiz, “A Modified Consumer Inkjet for Spatiotemporal Control of Gene Expression,” PLoS One, 4 (2009).
- Derby, Brian, “Bioprinting: inkjet printing proteins and hybrid cell-containing materials and structures,” Journal of Materials Chemistry, 18, 5717-5721 (2008).