Microfluidics is the manipulation and study of sub-microscopic liters of fluids. Technologies that utilise microfluidics are found in many multidisciplinary fields ranging from engineering to biology. Experiments can be performed on a device roughly of the size of a dollar coin, reducing the amount of reagents used, wastes produced, and the overall costs. Experiments can be conducted precisely at microscale levels, offering reduced reaction times and improved control over the reaction conditions.
Current gold standard for the fabrication of microfluidic devices is soft lithography, where elastomeric materials are casted on a mold fabricated in a cleanroom. Despite multiple desirable characteristics to fabricate microfluidic channels, however, soft lithography is a manual process that is difficult to automate. Typically, soft lithography has a design-to-prototype cycle of a few days.
3D printing emerged as an attractive alternative to soft lithography. Not only can 3D printers turn design into actual working prototypes in the order of hours, recent introduction of low-cost 3D printers make 3D printing more accessible in general to researchers. Current 3D printing technologies for the fabrication of microfluidic devices have a few limitations, namely;
- available materials for 3D printing (e.g. optical transparency, flexibility, biocompatibility),
- achievable dimensions of microchannels by commercial 3D printers,
- integration of 3D printed microfluidics with functional materials or substrates.
To overcome these challenges, researchers from the Singapore University of Technology and Design's (SUTD) Soft Fluidics Lab have developed an alternative method to apply 3D printing for the fabrication of microchannels. The researchers applied direct ink writing (DIW) 3D printing of fast-curing silicone sealant to fabricate microfluidic devices rapidly on various substrates (e.g. glass, plastic, and membranes). The design of fluidic channels is determined by the patterned silicone sealant, while the top and bottom transparent substrates serve to seal the channels. The use of transparent substrates allows the researchers to image the channel using a microscope. This method also permits the fabrication of microfluidic channels that are dynamically tunable in dimensions, which served as small channels as well as tunable flow resistors.
"By controlling the distance between the top and bottom substrates, we were able to precisely reduce the channel width up to around 30 microns. This lateral dimension of the channels would be difficult to obtain if commercially available 3D printers were employed," said lead author Terry Ching, a graduate student from SUTD's Engineering Product Development pillar.
"Our approach to apply DIW 3D printing allows direct patterning of microchannels essentially on any flat substrate" said Assistant Professor Michinao Hashimoto, the principal investigator of the project.
The team also demonstrated the ease of patterning of silicone barriers directly on an off-the-shelf printed circuit board (PCB), immediately integrating electrodes into the microchannels that would function as real-time flow sensors. Rapid integration of semi-permeable membranes to microchannels for culturing Keratinocyte cells was demonstrated.
The paper was published in Sensors and Actuator B: Chemical, an interdisciplinary journal dedicated to publishing original works that demonstrate significant progress beyond the current state of the art along with applicability to solve meaningful analytical problems. This research project was conducted by SUTD's Soft Fluidics Lab (https://www.facebook.com/SoftFluidics/) in collaboration with Professor Yi-Chin Toh's research group at the National University of Singapore.