Poster printing

3D Printing of Microfluidic Devices Breaks New Ground in Biomedical Manufacturing | Research & Technology | April 2022

PASADENA, Calif., April 14, 2022 – Researchers at the University of Southern California (USC) have developed a printing technique that could provide the precision required to successfully 3D print microfluidic channels on chips at a scale never before seen before. The technique is called in situ transfer vessel photopolymerization (IsT-VPP).

The use of microfluidic devices – compact test tools made up of tiny channels etched onto a chip – can reduce the cost of drug development and facilitate medical diagnostics. The traditional approach to manufacturing these devices, soft lithography in a cleanroom environment, requires several labor-intensive processes.

While 3D printing offers many advantages for manufacturing biomedical devices, it is not yet sensitive enough to build layers with the fine detail required for microfluidics.

Using the IsT-VPP technique, researchers were able to produce microfluidic channels 10 μm in height and with high precision (at the 2 μm level), without using liquid resin with reduced transparency or reduced manufacturing speed. Vat photopolymerization (VPP) uses a liquid photopolymer resin to build the article to be printed layer by layer. The item is then irradiated with ultraviolet (UV) light, which hardens and hardens the resin with each coat. A build platform moves the printed element up or down so that additional layers can be built on it.

Although the VPP allows for one-step fabrication, its control of the micrometer channels of the microfluidic device is insufficient. The UV light source tends to penetrate deep into the residual liquid resin, hardening and solidifying the material inside the channel walls.

“When you cast the light, ideally you only want to cure one layer of the channel wall and leave the liquid resin inside the channel untouched, but it’s hard to control the depth of cure, because we’re trying to target something that is only a 10 μm gap,” Professor Yong Chen said.

An example of a microfluidic chip created by the USC research team The researchers’ method of fabricating microfluidic devices is compatible with commonly used 405 nm light sources and commercial photocurable resins. Courtesy of Yang Xu.

If the opaque resin allows less light to penetrate than the transparent resin, it is not suitable for the construction of a microfluidic device whose content will be examined under a microscope.

To create the microscale transparent resin channels needed for microfluidic devices, the team developed an auxiliary platform that moves between the light source and the printed device, preventing light from solidifying the liquid in the device walls. ‘a canal.

When the channel roof (i.e. the upper layer part of the device that encloses the channel) is printed, the auxiliary platform is used to prevent light from penetrating the residual liquid resin inside of the channel. The canal roof is then transferred in situ to the built part. All other layers are printed using the standard VPP process. Any residual resin in the channel remains in a liquid state and can be drained off after the printing process to form the channel space.

According to Chen, current commercial processes only allow the creation of a microfluidic channel height at the 100 µm level and provide poor precision control.

“This is the first time we’ve been able to print something where the channel height is at the 10 µm level,” he said. “We can control it very precisely, with an error of plus or minus 1 µm. This is something that has never been done before, so it is a breakthrough in 3D printing small channels.

The USC VPP-based technique is compatible with commonly used 405 nm light sources and commercial photocurable resins. Researchers verified the technique by fabricating multifunctional devices including 3D serpentine microfluidic channels, microfluidic valves, and particle sorting devices.

Chen said the new 3D printing platform, with its micro-scale channels, could provide significant benefits to cancer detection and research.

“Tumor cells are slightly larger than normal cells, which are around 20 µm. Tumor cells could exceed 100 µm,” he said. “Currently, we use biopsies to check for the presence of cancer cells, by cutting an organ or tissue from a patient to reveal a mixture of healthy cells and tumor cells. Instead, we could use simple microfluidic devices to flow the sample through channels with precisely printed heights to separate cells into different sizes so as not to allow these healthy cells to interfere with our detection. .

The IsT-VPP technique for fabricating microfluidic devices could advance the use of VPP for 3D printing devices for applications requiring small gaps with high precision.

“There are so many applications for microfluidic channels,” Chen said. “You can run a blood sample through the channel, mixing it with other chemicals so you can, for example, detect if you have COVID or high blood sugar.”

The research team files a patent application for the 3D printing method and seeks collaborators to commercialize the technique for manufacturing medical test devices.

The research has been published in Nature Communication (