3D Printing for Microfluidics

Picture credit: Convery N, Gadegaard N, 30 years of microfluidics (2019), Micro and Nano Eng. 2 

“My personal opinion is that in the next few years, nobody is going to be doing microfluidics in the clean room, there’s no reason to do so. 3D printing is a technology that can do it so much better — with better choice of materials, with the possibility to really make the structure that you would like to make. When you go to the clean room, many times you sacrifice the geometry you want to make. And the second problem is that it is incredibly expensive.” -- L. F. Velásquez-García, Principal Research Scientist, MIT Microsystem Technology Laboratories, USA, MIT News

Microfluidics devices has been conventionally produced by molding poly(dimethylsiloxane) (PDMS) in a cleanroom environment using soft lithography technology. This involves a primarily manual process that include PDMS curing, assembly, bonding and inlet punching. The cleanroom requirement also makes the fabrication very expensive. This costly process is necessary in order to achieve the desirable properties such as biocompatibility, elastomeric, optical transparency, gas permeability, high precision, high resolution and so on. 

In the recent decades, there has been an exciting rise in microfluidics chip commercialization and deployment of complex geometry for microfluidics system. Following this progress, the microfluidics community from academia and start-ups starts to look into an alternative to conventional PDMS fabrication. 3D printing or stereolithography, particularly the one with professional-grade digital light processing (DLP) technology, has shown consistent track record of successful adoption in many microfluidics laboratories. We present the most relevant requirements for the microfluidics system in the following table. You can see an overview of the strengths and limitations of different 3D printing technologies in the context of microfluidics fabrication, and then compare it with the PDMS fabrication method. Here, we have omitted 3D printing using two-photon-polymerization (2PP) despite of its resolution and precision capability due to its extremely high cost and turn-over time. 

 

  PDMS soft lithography

3D Printing 

Digital Light Processing 

(DLP)

3D Printing 

Multi Jet Modelling

(MJM)

3D Printing 

Fused Deposition Modelling

(FDM)

3D geometry capability Manual stacking an bonding of different layers with high challenge in layers alignment. This only works for orthogonal channel connections. Nozzles and coils are not possible  Unrestricted 3D capability Unrestricted 3D capability  Only works for circular channel cross-sections and orthogonal junctions
Microchannels resolution  

Very high (optical diffraction from photolithography)


5 µm wide channels can be achieved, but 85% of the microfluidic devices on the market have a channel size of 100 - 200 µm

 

Depends on the quality of 3D printer engineering and machinery

 

100 µm channels were reported in a peer-reviewed work, 400 µm channels are standard
 

Depends on the manual postprocessing skill.

 

750 µm is standard
 

Depends on the quality of 3D printer engineering and machinery

 

350 µm channels were reported in a peer-reviewed work
Chemical composition of material PDMS DLP photopolymer or photoresin MJM photopolymer or photoresin Thermoplastics
Solvent compatibility Water-impermeable, but not resistant to organic solvents Water-impermeable and organic solvent resistant photoresins are available Unknown Thermoplastics are water resistant, with varying chemical resistance
Gas permeability Very good gas permeability to remove air bubbles

Poor gas permeability

 

But air bubble removal can be done via bubble trap architecture
Unknown

Poor gas permeability

 

But air bubble removal can be done via bubble trap architecture
Mechanical property Elastomeric and isotropic Photoresins with similar property with PDMS are available Orientation can affect the elasticity Highly anisotropic in between the layers
Optical clarity Clear and transparent Clear and transparent photoresins are available Clear and transparent photoresins are available Clear and transparent thermoplastics are available
Biocompatibility Biocompatible Biocompatible photoresins are available Biocompatible photoresins are available Biocompatible thermoplastics are available
Production automation Not possible

Semi-automated

Postprocessing is needed to drain channels and remove support structures

Semi-automated

Postprocessing is needed to remove materials from channels

Fully automated

 

From this summary, it can be seen that the DLP 3D printing is capable of delivering the desirable properties achieved by PDMS soft lithography. With the benefit of the digital nature of the technique, its much lower cost (no cleanroom is needed) and its much higher throughput; the microfluidics are already in the era of 3D-printed microfluidics advances.

It is quite straightforward to see the case for adopting DLP 3D printing in your microfluidics laboratory. The next crucial step is choosing the right machines and equipments among the brands within this booming industry. The right machinery, engineering and customer support will ensure that the technology help you in realizing the full potential and impact of your microfluidics R&D.  

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