A game changer for medical testing devices

Microfluidic devices are compact testing tools made of tiny channels carved onto a chip for testing liquid, particle, and cell properties at a microscale. However, production of the devices is labor intensive, and while 3D printing has offered many advantages for biomedical device manufacturing, its techniques were previously not sensitive enough to build layers with the minute detail required for microfluidic devices. Until now.

Researchers at the University of Southern California (USC) Viterbi School of Engineering have developed a highly specialized 3D printing technique that allows microfluidic channels to be fabricated on chips at a precise microscale. The research was led by Daniel J. Epstein Department of Industrial and Systems Engineering Ph.D. graduate Yang Xu and Professor of Aerospace and Mechanical Engineering and Industrial and Systems Engineering Yong Chen, in collaboration with Professor of Chemical Engineering and Materials Science Noah Malmstadt and Professor Huachao Mao at Purdue University.

The team used vat photopolymerization 3D printing technology which harnesses light to control the conversion of liquid resin material into its solid end state.

“This is the first time we’ve been able to print something where the channel height is at the 10-µm level; and we can control it to an error of ±1µm. This is something that’s never been done before, so this is a breakthrough in the 3D printing of small channels,” Chen says.

Vat photopolymerization makes use of a vat filled with liquid photopolymer resin, from which a printed item is constructed layer by layer.

Ultraviolet (UV) light is then flashed onto the object, curing and hardening the resin at each layer. As this happens, a build platform moves the printed item up or down so additional layers can be built onto it.

But when it comes to microfluidic devices, vat photopolymerization has some disadvantages in the creation of the tiny wells and channels required. The UV light source often penetrates deeply in the residual liquid resin, curing and solidifying material within the walls of the device’s channels, which would clog the finished device.

Chen says current commercial processes only allow for the creation of a channel height at the 100µm level with poor accuracy control, because the light penetrates a cured layer too deeply, unless you are using an opaque resin that doesn’t allow as much light penetration.

“But with a microfluidic channel, typically you want to observe something under a microscope, and if it’s opaque, you can’t see the material inside, so we need to use a transparent resin,” Chen notes.

To accurately create channels in clear resin at a microscale level suitable for microfluidic devices, the team developed an auxiliary platform that moves between the light source and printed device, blocking the light from solidifying the liquid within the walls of a channel so the channel roof can be added separately to the top of the device. The residual resin remaining in the channel would still be in a liquid state and can then be flushed out after the printing process to form the channel space.

“There are so many applications for microfluidic channels,” Chen says.

A particle sorter, a type of microfluidic chip, uses different sized chambers to separate different sized particles, offering significant benefits to cancer detection and research.

“Right now, we use biopsies to check for cancer cells; cutting organ or tissue from a patient to reveal a mix of healthy cells and tumor cells. Instead, we could use simple microfluidic devices to flow (the sample) through channels with accurately printed heights to separate cells into different sizes, so we don’t allow those healthy cells to interfere with our detection.”

University of Southern California (USC) Viterbi School of Engineering
https://viterbischool.usc.edu