Continuous fiber extruder for desktop 3D printers toward long fiber embedded hydrogel 3D printing.

Recent advances in Freeform Reversible Embedding of Suspended Hydrogels (FRESH), a technique that is compatible with most open-source desktop 3D printers, has enabled the fabrication of complex 3D structures using a wide range of natural and synthetic hydrogels, whose mechanical properties can be modified by embedding long fibers into printed hydrogels. However, fiber extruders dedicated for this application are not commercially available or previously reported. To address this, we have designed a continuous fiber extruder (CFE) that is compatible with low-cost, open-source desktop 3D printers, and demonstrated its performance using a Flashforge Creator-pro printer with a Replistruder-2.0 print-head. Key characteristics of the CFE include: (1) it is affordable, accessible and user-friendly to the 3D printing community due to its low fabrication cost and compatibility with open-source hardware and software, (2) it can embed user-defined 2D and 3D features using long fibers into different types of hydrogels, (3) it works with fibers of different mechanical properties and sizes, (4) it can modify mechanical properties of FRESH printed hydrogels via long fiber embedding.

Long-Fiber Embedded Hydrogel 3D Printing for Structural Reinforcement.

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