Microfluidics is the manipulation and study of sub-microscopic liter liquids. Technologies that use microfluidics are found in many multidisciplinary fields, from engineering to biology. Experiments can be performed on a device approximately the size of a dollar coin, reducing used reagents, wastes produced, and overall costs. Experiments can be conducted precisely at the microscale level, reducing reaction time and improving control over reaction conditions.
The current gold standard for the fabrication of microfluidic devices is soft lithography, where elastomeric material is cast on a mold made in a clanroom. Although there are multiple desirable characteristics for creating microfluidic channels, soft lithography is a process that is difficult to automate. Typically, soft lithography has a design-to-prototype cycle for a few days.
3D printing emerges as an attractive alternative to soft lithography. Only in a matter of hours 3D printers can turn design into real working prototypes, the introduction of recent low cost 3D printers can make 3D printing generally more accessible to researchers. Existing 3D printing techniques for the fabrication of microfluidic devices have some limitations, that is;
- Content available for 3D printing (eg optical transparency, flexibility, biocompatibility),
- Acquired dimensions of microhannel tubes, by professional 3D printers
- Integration of 3D printed microfluidics with functional materials or substrates.
To meet these challenges, researchers at the University of Singapore's Technology and Technology (SUTD) soft fluidics lab have developed an alternative method of applying 3D printing for micro-channel creation. Researchers applied direct ink writing (DIW) 3D printing of fast-healing silicone sealants to rapidly fabricate microfluidic devices on various substrates (e.g., glass, plastic and membranes). The composition of liquid channels is determined by the patterned silicon sealant, while the top and bottom transparent substrates give the channels to seal. The use of transparent substrates allows researchers to create a channel image using a microscope. This method also allows the formation of microfluidic channels that are dynamically analogous to the parameters, which serve as small channels as well as tunable flow resistors.
"By controlling the distance between the top and bottom substrates, we were able to reduce the channel width to about 30 microns. This would be difficult to obtain on this side dimension of the channels if commercially available 3D printers were employed," said the lead author. Terry Ching, a graduate student from SUTD's Engineering Product Development column.
"Our approach to applying DIW 3D printing essentially allows the straightening of the micro-channel on any flat substrate," said Michino Hashimoto, Assistant Professor of the project's principal investigator.
The team also demonstrated the ease of patterning of silicon barriers directly on an f-the-shelf printed circuit board (PCB), immediately integrating the electrodes into the micro-channel that would act as a real-time flow sensor. The keratinocyte cells showed rapid integration of the semi-impermeable membrane into the microchannels for culture.
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