Dr. Indrasen Bhattacharya Profile

Dr. Indrasen Bhattacharya

Research Scientist

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Proceedings Article | 4 March 2019 Presentation

Support-free direct 3D-printing of millifluidic and microfluidic chips with tunable stiffness through computed axial lithography (Conference Presentation)

Hossein Heidari, Brett Kelly, Indrasen Bhattacharya, Hayden Taylor

Proceedings Volume 10875, 1087509 (2019) https://doi.org/10.1117/12.2508252

KEYWORDS: Lithography, Microfluidics, Printing, Solids, Prototyping, Lead, Optical alignment, Additive manufacturing, Modeling, Fused deposition modeling

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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.

Proceedings Article | 14 May 2018 Presentation

Computed axial lithography: volumetric 3D printing of arbitrary geometries (Conference Presentation)

Indrasen Bhattacharya, Brett Kelly, Maxim Shusteff, Christopher Spadaccini, Hayden Taylor

Proceedings Volume 10656, 106560P (2018) https://doi.org/10.1117/12.2307780

KEYWORDS: 3D printing, Lithography, Photopolymerization, Reconstruction algorithms, Additive manufacturing, Liquids, Anisotropy, Computational imaging, Computed tomography, Tomography

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Lower-dimensional photopolymerization based additive manufacturing techniques have several drawbacks that currently limit the applicability and scope of 3D printing, including: topological constraints, the requirement for numerous complex support structures that later need to be removed, long print times for complex geometries, relative motion between the liquid resin and printed part, as well as debilitating mechanical weakness and anisotropy resulting from the inherently layered structure of the parts. We propose and demonstrate a novel volumetric 3D printing technique based on one of the most ubiquitous computational imaging methods in the field: computed axial tomography. Computed axial lithography (CAL) is a vat photopolymerization technique that exposes the entire resin volume by projecting images from a multiplicity of angles. The technique is a physical implementation of the filtered back projection algorithm for tomographic reconstruction. We use constrained non-convex optimization in order to generate images that are projected into the resin in order to sculpt a 3-dimensional energy dose that cures the desired arbitrary geometry. This eliminates the requirement for supports and enables complex and nested structures that were previously challenging or impossible to print. Further, the process is layer-less and does not involve any relative motion between the resin and the printed part, which has positive implications for mechanically isotropic part strength. We demonstrate support-less printing of complex geometries containing 10^8-10^9 voxels in 2-4 minutes, orders of magnitude faster than comparable techniques.

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