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Abstract Low-cost 3D printing has become increasingly important in biomedical research, enabling rapid fabrication of custom cell culture devices, fixtures, and biohybrid robotic components. However, little is known about how common sterilization procedures and prolonged cell culture exposure impact the mechanical properties of commercially available resins. In this study, we analyzed five candidate 3D-printable resins-three rigid (Asiga DentaGUIDE, Liqcreate Bio-Med Clear, Phrozen AquaGray 8K) and two elastomeric (Asiga DentaGUM, Formlabs Silicone 40A)-to evaluate the effects of ethanol/UV and autoclave sterilization on material properties in phosphate-buffered saline (PBS) at physiological conditions. Using stress-strain data from tensile and compressive mechanical tests, elastic moduli, ultimate tensile strength, and strain at break were compared across sterilization techniques. Results showed that sterilization significantly altered the mechanical properties of rigid resins, with Phrozen AquaGray 8K and Liqcreate Bio-Med Clear exhibiting large reductions in tensile stiffness and strength, while Asiga DentaGUIDE retained greater stability. In contrast, elastomeric resins were more robust: Asiga DentaGUM and Formlabs Silicone 40A demonstrated minimal or non-significant changes across sterilization methods, though post-treatment protocols influenced variability. Notably, several rigid resins also exhibited substantially lower moduli in PBS compared to manufacturer-reported values. These findings emphasize the need for experimental validation of 3D printed resin properties under intended use conditions and suggest that Asiga DentaGUIDE and Formlabs Silicone 40A are promising candidates for biohybrid applications. Overall, this work provides critical guidance for selecting sterilization-compatible materials for biomedical devices and biohybrid robotics. 

Stimuli-responsive hydrogels are candidate building blocks for soft robotic applications due to many of their unique properties, including tunable mechanical properties and biocompatibility. Over the past decade, there has been significant progress in developing soft and biohybrid actuators using naturally occurring and synthetic hydrogels to address the increasing demands for machines capable of interacting with fragile biological systems. Recent advancements in three-dimensional (3D) printing technology, either as a standalone manufacturing process or integrated with traditional fabrication techniques, have enabled the development of hydrogel-based actuators with on-demand geometry and actuation modalities. This mini-review surveys existing research efforts to inspire the development of novel fabrication techniques using hydrogel building blocks and identify potential future directions. In this article, existing 3D fabrication techniques for hydrogel actuators are first examined. Next, existing actuation mechanisms, including pneumatic, hydraulic, ionic, dehydration-rehydration, and cell-powered actuation, are reviewed with their benefits and limitations discussed. Subsequently, the applications of hydrogel-based actuators, including compliant handling of fragile items, micro-swimmers, wearable devices, and origami structures, are described. Finally, challenges in fabricating functional actuators using existing techniques are discussed. 

The emergence of soft robots has presented new challenges associated with controlling the underlying fluidics of such systems. Here, we introduce a strategy for additively manufacturing unified soft robots comprising fully integrated fluidic circuitry in a single print run via PolyJet three-dimensional (3D) printing. We explore the efficacy of this approach for soft robots designed to leverage novel 3D fluidic circuit elements—e.g., fluidic diodes, “normally closed” transistors, and “normally open” transistors with geometrically tunable pressure-gain functionalities—to operate in response to fluidic analogs of conventional electronic signals, including constant-flow [“direct current (DC)”], “alternating current (AC)”–inspired, and preprogrammed aperiodic (“variable current”) input conditions. By enabling fully integrated soft robotic entities (composed of soft actuators, fluidic circuitry, and body features) to be rapidly disseminated, modified on demand, and 3D-printed in a single run, the presented design and additive manufacturing strategy offers unique promise to catalyze new classes of soft robots.