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Soft lithography provides a convenient technique for prototyping miniaturized fluidic systems. However, 3D-printing techniques offer shorter lead times and greater three-dimensional design freedom, as well as circumventing the manual alignment and inter-layer bonding challenges of soft lithography. As a result, attention has moved towards additive fabrication solutions.
Fused deposition modelling (FDM), inkjet, and stereolithographic projection-based 3D-printing solutions have demonstrated the possibility of printing master molds as well as encapsulated fluidic networks directly. However, all of these techniques typically require the use of solid support structures when printing overhanging features as are required for encapsulated fluidic channels. This support material is time-consuming or, in some cases, entirely impractical to remove from small-scale, encapsulated channels. Additionally, most existing printing techniques are limited to materials that are orders of magnitude higher in elastic modulus than biological tissue. Finally, process-induced surface roughness makes microscopy challenging.
In contrast, we have introduced a new additive technique, computed axial lithography (CAL), which enables volumetric 3D-printing by illuminating a rotating volume of photosensitive material with a 3D light intensity map constructed from the angular superposition of many 2D projections. The projections are computed via the exponential Radon transform followed by iterative optimization. Oxygen inhibition-induced thresholding of the materials’ dose response enhances patterning contrast. Here, we report the application of CAL to fabricate transparent 3D fluidic networks in highly compliant and resilient methacrylated gelatin hydrogels, as well as in stiffer acrylates. Uncured resin provides mechanical support during printing, so the need for solid support structures is eliminated.
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