A Visual, In-Expensive, and Wireless Capillary Rheometer for Characterizing Wholly-Cellular Bioinks

Area of Science:

• Materials Science
• Biomaterials Engineering
• Rheology

Background:

• Commercial rheometers are costly and lack design flexibility.
• In situ visualization is crucial for understanding complex fluid behavior.
• Existing methods require specialized facilities and complex setups.

Purpose of the Study:

• To develop a low-cost, wireless, and versatile rheometer for in situ microstructural analysis.
• To validate the performance of the new rheometer with complex fluids.
• To characterize the rheological properties and microstructural evolution of wholly-cellular bioinks.

Main Methods:

• Development of a low-cost ($300) visual, inexpensive, and wireless rheometer (VIEWR) using 3D-printed and off-the-shelf components.
• Validation of VIEWR measurements using steady-state and transient flow tests on complex fluids.
• Application of particle image velocimetry for microstructural flow profile analysis.
• Characterization of wholly-cellular bioinks using the VIEWR and visualization of aggregate morphology.
• Construction of hyperbolic extensional-flow geometries using digital light processing for extensional viscosity measurements.

Main Results:

• The VIEWR successfully captured complex flow behaviors and validated against commercial systems.
• Microstructural flow profiles and yield-plane evolution were visualized.
• Spatiotemporal evolution of aggregate morphology in bioinks was captured, revealing complex yield-stress and viscoelastic responses.
• Extensional viscosity was measured at varying deformation rates, with aggregate alignment and stretching visualized.
• Jamming and viscoelastic deformation of aggregates were identified as contributors to extensional viscosity.

Conclusions:

• The VIEWR provides a low-cost, flexible, and accessible platform for rheological measurements with in situ visualization.
• The device enables detailed characterization of complex fluids, particularly wholly-cellular bioinks.
• Understanding aggregate behavior under flow is critical for predicting bioink performance.