Team:Penn/WaxPrinting
What is Wax Printing?
Wax printing is used to fabricate microfluidic paper analytical devices (µPADs). In the past decade, µPADs have emerged as a valuable platform for designing point of care diagnostic devices for use in low resource settings. Paper-based microfluidics have many benefits compared to existing assays. Paper microfluidics require a low sample volume, are easy to use, portable, highly sensitive, and do not necessitate expensive laboratory equipment or highly trained manpower. Wax printing provides a low cost fabrication of paper microfluidics with high throughput advantages.
Why Paper?
Paper has become a popular substrate for constructing microfluidic analytical devices because it is low cost, portable, and disposable. Through patterning paper with hydrophobic barriers, hydrophilic channels are created that allow capillary-based fluid flow without the need of any pumps. Only small sample volumes are needed to power the device which is important with limited sample sizes. The simplicity of paper microfluidics as analytical devices allows them to be used by anyone at anytime for diagnosis and analysis, no well trained medical professionals or high tech equipment is needed to run the test. Paper microfluidics thus show potential as point of care (POC) diagnostic devices in resource limited settings where individuals do not have access to fast and sensitive diagnosis for serious health problems.
How are Paper Microfluidics Currently Made?
Current methods of paper microfluidics fabrication is not limited to wax. Other materials such as PDMS, alkenyl ketene dimers, and other hydrophobic polymers are also used to create hydrophobic barriers in paper microfluidic devices. In addition to wax printing, PDMS printing, inkjet etching, plasma treatment, and laser cutting are also used to fabricate devices. The low cost of wax makes wax printing a particularly attractive method of fabrication. Currently, wax printing is achieved through wax screen printing, wax dipping, or wax ink printing. Wax screen printing and wax dipping have low reproducibility and low flexibility in design changes. Wax ink printing requires a commercial printer such as the Xerox color cube. After printing, the device must be heated to allow full permeation of wax through the paper capillary channels. The xerox color printer is expensive (~$1500) as well as its wax ink cartridges (~$60) and is also no longer manufactured.
Table 1 : Comparison of fabrication methods of paper microfluidics. Wax printing is an ideal prototyping method because of its quick production speed, low cost, and low complexity.