The microfluidics market is expected to reach $7.5 billion by 2020, up from $3.1 billion in 2015, at a compound annual growth rate of 19.3%, according to Market & Markets. The microfluidics market has grown over the last decade due to the growing pharmaceutical and biotechnology research funding, rising incidences of lifestyle diseases and rising geriatric population. However, high prices of microfluidic proteomic and genomic analysis platforms, low market visibility for current microfluidic products and reluctance among researchers to use microfluidic technology are inhibiting growth, according to the report.
To a large extent, creating easier methods for manufacturing could help counteract these barriers. Tony Holtz, a technical specialist at Proto Labs, says the traditional manufacturing methods won’t work well for microfluidic parts. CNC or injection molding, he says don’t work because the parts require very flat surfaces, with clear, thin and shallow features.
“These are difficult to produce in a mold that is milled and hand-polished,” Holtz explains, noting that the small sizes of the features are not distinguishable. The pressures in injection molding can roll the edges; ejector pins play an important role in removing parts from a mold, but they also introduce cosmetic flaws that are challenging to manage in microfluidic parts. “The process is not impossible and we still create microfluid parts with injection molding, but there are better ways,” Holtz says.
Instead of injection molding, Holtz says Proto Labs prefers to use a process called stereolithography (SL). “We use an ultraviolet laser drawing on the surface of a thermoset resin material.” High-resolution SL can produce features in layer as thin as 0.002 in.,, fine enough detail to satisfy microfluidics requirements.
Holtz notes that Proto Labs recommends channel sizes of 0.025 in. square cross sections with a minimum wall thickness of 0.004 in. for X and Y dimensions and 0.016 in. for the Z dimension. Of course, he says, some clients need even smaller features and may need staff engineers to come up with designs to meet those needs.
Special builds for clarity
One of the chief concerns for microfluidics designers is the clarity of the final part. Holtz says achieving that level of clarity required Proto Labs to create a special system for the parts. The company uses a substrate build on a clear sheet of acrylic, which yields a surface that needs minimal polishing.
“In particular, the down faces need to be smooth and clear with minimal post-build processing,” he explains. Proto Labs developed its SL so that there are no support structures on the down faces so the surfaces retain the highest clarity. Up facing surfaces need the next best clarity and are followed by any vertical surfaces. All surfaces are sanded or polished to remove visible layers on the flat surfaces.