Traditionally, microfluidic devices are fabricated using silicon-patterned masks with positive surface features which are made using soft photolithography. The process includes spin-coating a silicon wafer with SU-8 photoresist (light-sensitive material) and then using the patterned mask to expose specific areas of the wafer with a high-power UV light. The exposure changes the composition of exposed parts and a solvent is used to dissolve the non-exposed parts, leaving behind embossed features (elevation depends upon the thickness of photoresist and exposure time). The features are replicated onto PDMS ( poly dimethyl siloxane) as depressions and sealed with another flat PDMS slab or glass using Plasma treatment. Another method for making the mould is reactive-ion-etching but it’s time taking and requires clean-room facility.
Hence, there have been attempts to make the moulds with 3D Printing or make an entire 3D Printed device. The resolution of 3D Printers has significantly improved in the past decade with the resolution being about 500 microns for Stratasys® Polyjet 3D Printers to sub-50 microns for the recent Multijet 3D Printers from 3DS® and Ultra HD DLP-SLA 3D Printers.
A multilayer sandwiching approach: assembled device (on-left), flowing fluorecent dye through the device to check for any leakage (right).
I have been making sub-100 micron moulds on Multijet 3D Printer for past one year. A big challenge with this method was that the surface of the polymer used here is not suitable for curing PDMS and hence I started coated the surface with mould-release agents to facilitate the curing and easy release of device post-curing.
I have also recently started trying fabrication of an entirely 3D printed microfluidic device and I have successfully tested the biocompatibility of the device which is essential for cell-culture and MTT assays.
Figure 2: The proliferation of Prostate Cancer Cells proves biocompatibility of the PDMS Microfluidic Device made from a 3D Printed Mould. ©ankitaryan