Advancing Bioink Homogeneity in Extrusion 3D Bioprinting with Active In Situ Magnetic Mixing

Maintaining uniform cell and hydrogel distribution in extrusion 3D bioprinting is a critical challenge, especially for long-duration or high-throughput prints. We present a magnetically-actuated mixer (MagMix), a compact modular in situ platform that integrates into standard extrusion bioprinters to actively homogenize bioinks in real-time. MagMix utilizes an internal propeller driven by a servo-controlled external magnet, enabling continuous, active, tunable speed mixing without altering bioink formulation. Computational simulations and experimental validation enable optimizing propeller geometry and mixing parameters. We demonstrate the utility of MagMix across commonly used cellular bioinks with different viscosities to demonstrate that active in situ mixing prevents cell sedimentation, improves cell viability, and eliminates nozzle clogging over extended print sessions while preserving 3D print quality and cell differentiation capacity. MagMix can be readily integrated into any extrusion bioprinting workflow and offers a scalable, bioink-agnostic solution to improve reproducibility and functionality in bioprinted constructs for applications in tissue engineering.