Digital light processing in a hybrid atomic force microscope: In Situ, nanoscale characterization of the printing process

Synergistic Fire Resistance of Nanobrick Wall Coated 3D Printed Photopolymer Lattices

Photopolymer additive manufacturing has become the subject of widespread interest in recent years due to its capacity to enable fabrication of difficult geometries that are impossible to build with traditional manufacturing methods. The flammability of photopolymer resin materials and the lattice structures enabled by 3D printing is a barrier to widespread adoption that has not yet been adequately addressed. Here, a water-based nanobrick wall coating is deposited on 3D printed parts with simple (i.e., dense solid) or complex (i.e., lattice) geometries. When subject to flammability testing, the printed parts exhibit no melt dripping and a propensity toward failure at the print layer interfaces. Moving from a simple solid geometry to a latticed geometry leads to reduced time to failure during flammability testing. For nonlatticed parts, the coating provides negligible improvement in fire resistance, but coating of the latticed structures significantly increases time to failure by up to ≈340% compared to the uncoated lattice. The synergistic effect of coating and latticing is attributed to the lattice structures' increased surface area to volume ratio, allowing for an increased coating:photopolymer ratio and the ability of the lattice to better accommodate thermal expansion strains. Overall, nanobrick wall coated lattices can serve as metamaterials to increase applications of polymer additive manufacturing in extreme environments.

3D printing of sacrificial thioester elastomers using digital light processing for templating 3D organoid structures in soft biomatrices

Biofabrication allows for the templating of structural features in materials on cellularly-relevant size scales, enabling the generation of tissue-like structures with controlled form and function. This is particularly relevant for growing organoids, where the application of biochemical and biomechanical stimuli can be used to guide the assembly and differentiation of stem cells and form architectures similar to the parent tissue or organ. Recently, ablative laser-scanning techniques was used to create 3D overhang features in collagen hydrogels at size scales of 10-100µm and supported the crypt-villus architecture in intestinal organoids. As a complementary method, providing advantages for high-throughput patterning, we printed thioester functionalized poly(ethylene glycol) (PEG) elastomers using digital light processing (DLP) and created sacrificial, 3D shapes that could be molded into soft (G' < 1000 Pa) hydrogel substrates. Specifically, three-arm 1.3 kDa PEG thiol and three-arm 1.6 kDa PEG norbornene, containing internal thioester groups, were photopolymerized to yield degradable elastomers. When incubated in a solution of 300 mM 2-mercaptoethanol (pH 9.0), 1 mm thick 10 mm diameter elastomer discs degraded in <2 h. Using DLP, arrays of features with critical dimensions of 37 ± 4µm, resolutions of 22 ± 5µm, and overhang structures as small as 50µm, were printed on the order of minutes. These sacrificial thioester molds with physiologically relevant features were cast-molded into Matrigel and subsequently degraded to create patterned void spaces with high fidelity. Intestinal stem cells (ISCs) cultured on the patterned Matrigel matrices formed confluent monolayers that conformed to the underlying pattern. DLP printed sacrificial thioester elastomer constructs provide a robust and rapid method to fabricate arrays of 3D organoid-sized features in soft tissue culture substrates and should enable investigations into the effect of epithelial geometry and spacing on the growth and differentiation of ISCs.