A team at the Bioengineering Institute of Technology, Universitat Internacional de Catalunya, has developed a DIY coaxial 3D bioprinter by modifying a Creality Ender 3 Pro desktop 3D printer. The open-source system costs under €600 and enables simultaneous extrusion of two hydrogel bioinks through a coaxial nozzle. The device was validated by printing mesenchymal stem cell (MSC)-laden hydrogels with high shape fidelity and cell viability. Details of the project were published in Nature Communications.
Creality, a Chinese manufacturer of low-cost FDM printers, produces the Ender 3 Pro, which was adapted by replacing its hotend with two stepper motor-driven syringe pump extruders. The 3D printer’s motherboard was upgraded to a 32-bit SKR 2.0 Rev B, enabling independent control of both extruders. Firmware was configured using the open-source Marlin platform. A custom coaxial nozzle was fabricated using Liqcreate Clear Impact resin and printed on a Phrozen Sonic Mighty 8K DLP printer. The nozzle featured a 27-gauge inner needle for core material and a 14-gauge shell inlet, assembled concentrically to support coaxial flow.
Two nozzle configurations were tested, both with 200 µm inner diameters and outer diameters of 640 µm and 840 µm, respectively. Flow simulations in COMSOL Multiphysics confirmed that the wider nozzle induced greater velocity differences between shell and core, while the narrower configuration yielded more uniform flow. Rheological testing showed that a thermoresponsive methylcellulose-based shell could crosslink a gelatin-alginate core in situ. Scaffold structures remained stable when extruding core bioink concentrations as low as 0.5% alginate, with elastic modulus halved compared to the 1.5% formulation.
Printing performance was evaluated at a speed of 3 mm/s with flow rates of 0.917 µl/s (narrow nozzle) and 1.529 µl/s (wide nozzle). Scaffold fidelity was quantified by comparing relative height across various core-shell ratios. Structures began to collapse when core flow exceeded 40% without calcium crosslinking, but remained intact when CaCl₂ was included in the shell hydrogel. Large woodpile and vase structures were printed using a gradient extrusion function (M166 command in Marlin), allowing automated variation in core-shell composition over the Z-axis. The printed scaffolds displayed consistent geometry, open porosity, and localized material transitions.
MSCs were harvested from five-week-old male Sprague-Dawley rats following approved protocols at the Autonomous University of Barcelona. Cells were encapsulated in the alginate-gelatin hydrogel core and printed into square scaffold structures using the narrow nozzle configuration at a 30–70 core-shell ratio. Live-dead staining at 1, 7, and 14 days showed high cell viability, with printed conditions exceeding 90% by day 7 and maintaining viability through day 14. Results confirmed that the methylcellulose-based shell allowed sufficient nutrient diffusion and protected embedded cells during extrusion.
Commercial coaxial bioprinters often rely on fixed stainless-steel nozzle designs and lateral feed geometries that limit compatibility with viscous or particulate-rich bioinks. By contrast, the design presented in this study accommodates high-viscosity materials and reduces clogging risk when bioinks are co-optimized with nozzle geometry. The shell layer also prevents dehydration of the core during long print sessions. CAD files, firmware modifications, and a full materials list were published alongside the study to support replication and further development.
This system expands the available toolset for labs exploring complex scaffold architectures without access to high-end bioprinters. While coaxial nozzles inherently reduce resolution due to their dual-channel format, they offer the ability to spatially compartmentalize different materials or cell types. The researchers note that resolution trade-offs are justified in cases requiring mechanical gradient tuning or controlled biological compartmentalization. With its low cost and flexible architecture, the system could support development of multiaxial or microfluidic printheads, enabling broader applications in tissue engineering research.
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Featured image shows schematic of 3D extrusion bioprinter and coaxial nozzle assembly. Image via Nature Communications.
