Long-Fiber Embedded Hydrogel 3D Printing for Structural\nReinforcement

Hydrogels\nare candidate building blocks in a wide range of biomaterial\napplications including soft and biohybrid robotics, microfluidics,\nand tissue engineering. Recent advances in embedded 3D printing have\nbroadened the design space accessible with hydrogel additive manufacturing.\nSpecifically, the Freeform Reversible Embedding of Suspended Hydrogels\n(FRESH) technique has enabled the fabrication of complex 3D structures\nusing extremely soft hydrogels, e.g., alginate and collagen, by assembling\nhydrogels within a fugitive support bath. However, the low structural\nrigidity of FRESH printed hydrogels limits their applications, especially\nthose that require operation in nonaqueous environments. In this study,\nwe demonstrated long-fiber embedded hydrogel 3D printing using a multihead\nprinting platform consisting of a custom-built fiber extruder and\nan open-source FRESH bioprinter with high embedding fidelity. Using\nthis process, fibers were embedded in 3D printed hydrogel components\nto achieve significant structural reinforcement (e.g., tensile modulus\nimproved from 56.78 ± 8.76 to 382.55 ± 25.29 kPa and tensile\nstrength improved from 9.44 ± 2.28 to 45.05 ± 5.53 kPa).\nIn addition, we demonstrated the versatility of this technique by\nusing fibers of a wide range of sizes and material types and implementing\ndifferent 2D and 3D embedding patterns, such as embedding a conical\nhelix using electrochemically aligned collagen fiber via nonplanar\nprinting. Moreover, the technique was implemented using low-cost material\nand is compatible with open-source software and hardware, which facilitates\nits adoption and modification for new research applications.