Engineered tubular constructs made from soft biomaterials are employed in a myriad of applications in biomedical science. Potential uses of these constructs range from vascular grafts to conduits for enabling perfusion of engineered tissues and organs. The fabrication of standalone tubes or complex perfusable constructs from biofunctional materials, including hydrogels, via rapid and readily accessible routes is desirable. Here we report a methodology in which customized coaxial nozzles are 3D printed using commercially available stereolithography (SLA) 3D printers. These nozzles can be used for the fabrication of hydrogel tubes via coextrusion of two shear-thinning hydrogels: an unmodified Pluronic® F-127 (F127) hydrogel and an F127bisurethane methacrylate (F127-BUM) hydrogel. We demonstrate that different nozzle geometries can be modeled via computer-aided design and 3D printed in order to generate tubes or coaxial filaments with different cross-sectional geometries. We were able to fabricate tubes with luminal diameters or wall thicknesses as small as ~150 μm. Finally, we show that these tubes can be functionalized with collagen I to enable cell adhesion, and human umbilical vein endothelial cells can be cultured on the luminal surfaces of these tubes to yield tubular endothelial monolayers. Our approach could enable the rapid fabrication of biofunctional hydrogel conduits which can ultimately be utilized for engineering in vitro models of tubular biological structures.

We describe the synthesis, characterization and direct-write 3D printing of triblock copolymer hydrogels that have a tunable response to temperature and shear stress. In aqueous solutions, these polymers utilize the temperature-dependent self-association of poly(alkyl glycidyl ether) 'A' blocks and a central poly(ethylene oxide) segment to create a physically crosslinked three-dimensional network. The temperature response of these hydrogels was dependent upon composition, chain length and concentration of the 'A' block in the copolymer. Rheological experiments confirmed the existence of sol-gel transitions and the shear-thinning behavior of the hydrogels. The temperature-and shear-responsive properties enabled direct-write 3D printing of complex objects with high fidelity. Hydrogel cytocompatibility was also confirmed by incorporating HeLa cells into select hydrogels resulting in high viabilities over 24 h. The tunable temperature response and innate shear-thinning properties of these hydrogels, coupled with encouraging cell viability results, present an attractive opportunity for additive manufacturing and tissue engineering applications.

Triple-stimuli responsive hydrogel can be 3D printed and cross-linked in the presence of a photoradical generator and 365 nm UV light.

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