Microfluidic chips are tiny chemistry labs. Using electrophoretic, pumping, or capillary action, they pull a fluid into a series of channels. These channels can be used to mix or separate the species within a sample. The sample can be tested off-chip, or the channels can connect to sensors and indicators to detect various things on-chip, from pH levels to blood sugars.
“Imagine you’re a crime scene investigator and you have trace evidence you want to run for DNA tests. Microfluidic chips enable you to test the sample against more suspects than if you had to perform these tests on the macro scale,” says Scott Stephens, CEO and founder of Hummingbird Nano, an ANSYS Startup Program member.
Traditional microfluidic chip fabrication techniques have been linked to reliability issues with the final product. Chips can have clogs, defects or contaminations that affect the flow of the fluid in the chip. And since the channels are micrometer-scaled, it doesn’t take much to have a microfluidic chip fail.
“Customers have told us that they used to throw away half of their chips due to clogging issues,” says Stephens. “Hummingbird Nano’s chips, however, have a smoother flow profile due to their circular cross-section and smoother channel surface resulting in a significant reduction in clog rate. This is a direct result of our microfluidic chip fabrication process — which we model using ANSYS simulations.”
Reliable Microfluidic Chip Fabrication at Injection Molding Speeds
During development, microfluidic chips are often made by etching channels into a base material, using chemicals or lasers. The base materials are then bonded together. However, when production is scaled up using injection molding, these chips may not perform as expected.
The goal is to have laminar flow through the chip, which is difficult when you’re bonding pieces together, or using a manufacturing method that differs from development. Irregularities, clogs and contaminants will affect the performance of these chips.
“Hummingbird Nano solves these problems by producing microfluidic chips that are one solid piece. This way we avoid any overlap issues of bonding parts together. We are also making the channel circular and smoother, which is improving the fluid flow,” explains Stephens.
Hummingbird Nano uses a magnetically actuated ferrofluid to mold the channels within their microfluidic chips. The magnetic fields can be tweaked to shape the channels to a specific purpose. Then, plastic is molded around the ferrofluid until it cures. Once the plastic cures, the magnetic field is turned off and the ferrofluid drains out of the chip.
“The manufacturing process has the flexibility of 3D printing, but it also has the speed of injection molding. That’s a powerful combination because the process scales. We can use it to prototype the chip and scale it up to full production. Since this is the same technology throughout development, we don’t have production switching issues,” says Stephens.
Designing the Microfluidic Chip Fabrication Process Using Simulation
Hummingbird Nano uses ANSYS Pervasive Engineering Simulation to determine how to control the magnetic fields for shaping the ferrofluids into a specific fabrication orientation.
“We used simulation throughout the design of the channels. It helps us determine the shape and scale of the channel. Simulation also helped us solve the design problem of getting channels to intersect, considering the intersection of magnetic fields creates a singularity,” notes Stephens.
Hummingbird Nano also used simulation to see how the ferrofluid reacts once it’s bathed in liquid polymer.
“We started using computational fluid dynamics (CFD) to look at this problem and then added the electromagnetic model to have a multiphysics look at the problem,” says Stephens. “These simulations have been the focus in developing our core microfluidic chip fabrication process.”
One of the benefits of this production process is that a fluid is used to mold another fluid’s channel. Stephens feels that this is the secret to the success of Hummingbird Nano’s chips.
He says, “We mold a fluid against a fluid, so the channels take on that fluid’s surface. Think of how smooth a soap bubble is, we are molding to something with similar surface roughness. We’ve measured and proven that Hummingbird Nano’s microfluidic chips have channels that are 3- to 5-times smoother than the competition’s. This smooth surface will increase the chance that the sample will experience laminar flow when it enters the chip.”