Development and characterization of a low-cost in-situ viscosity measurement system for extrusion-based bioprinting

Precise control of bioink viscosity is critical for extrusion-based bioprinting (EBB), yet rheological characterization is typically performed offline under controlled conditions that do not capture the nozzle-confined flow experienced during printing. Here, we present a fully open-source, low-cost in-situ (on-site) viscosity measurement system (IVMS) that acquires extrusion-force data directly at the printhead, providing process-relevant rheological insight during extrusion. A miniature S-beam load cell is integrated between the syringe plunger and the drive mechanism to record extrusion forces at 100 Hz. A custom LM358-based signal-conditioning board shifts the ±5 V sensor output to the Arduino-compatible 0-5 V range, while an offline MATLAB correction pipeline converts the acquired force to pressure and sequentially removes syringe friction losses, Bagley entrance effects, Mooney wall slip, and Rabinowitsch shear-rate distortion to reconstruct the true viscosity–shear-rate curve using Power-Law and Carreau–Yasuda models. Gelatin methacryloyl (GelMA) is used as the primary benchmarking material, with viscosity quantified across multiple flow rates (10¹–10³ s⁻¹), concentrations (5%, 7%, 10% w/v), and temperatures (25, 30, 37 °C) and validated against parallel-plate rheometry. To demonstrate broader applicability, the IVMS is further validated using a gelatin–alginate composite bioink and Laponite B, representing materials with distinct rheological behaviors. After correction, IVMS-derived viscosities showed strong agreement with parallel-plate rheometry and reproduced the expected trends with concentration and temperature. Friction and Bagley terms accounted for ∼90% of the pressure artefacts, while wall-slip and Rabinowitsch adjustments provided fine-scale refinement. While viscosity reconstruction is currently performed offline, the IVMS complements conventional rheometry by enabling on-board, nozzle-confined viscosity estimation under printing-relevant conditions. The system's modular, printer-agnostic architecture supports integration into diverse extrusion-based bioprinting platforms and establishes a foundation for future real-time implementation.