The second issue facing researchers are limits imposed by the actual process and the materials:
2D extrusion mold-based designs: Lithography works by etching down or building up designs in only the Z direction. As such only geometric shapes like circles, squares, vertical walls can be implemented. While some items like domes or pyramids are possible, draft angles much harder to create. Structures like beads-on-a-string or complex cantilevered designs are only possible through 3D printing.
Limited Aspect Ratios: Structures made by traditional methods are limited in height to base aspects, generally at 2:1 dependent on the cross-section in XY in PDMS. When transferring to hot-embossing or injection molding this ratio is negatively affected as the feature sizes shrink.
Example: Reasonable success can be had creating pillars of 100um cross section constructed 200um height in PDMS, hot-embossing or injection molding. However, below 50um the aspect ratio of PDMS will be 1:2 and injection molding closer to 1:1/2. In 3D printing this limit is not present and even at 50 um, 3D printing can still attain 500 um height, representing a 1:10 ratio and 5x improvement over traditional fabrication methods.
These same limits for 3D printing do not exist. We have successfully created 20 um pillars at 200um tall, representing a 1:10 aspect. This can be increased by adding buttresses or ties between the pillars at different heights to create extremely strong internal truss systems. Overall, this increases both surface area and possible flow-rates. Resulting in overall processing power improvements for microfluidic devices; as the available surface-area and flow-rate increase allowing higher signal over background.
Prototype is Production: Several papers dive into the changing materials and difficulties moving from PDMS to high-production. Skyphos provides our clients with a significant advantage in that one material can be used from prototype through production. And, while our standard chips are direct mounted to glass slides for use in microscopy, we can print a thin layer of the same polymer on the slide – creating a envelope around channels and chambers.
These improvements eliminate
Challenges arising from material strength or flexibility
Design restrictions based on thermoplastic polymers, and e
Problems transferring lab-based geometries and designs to high throughput fabrication
surface charge issues, including multi-material hydrophobicity differences