Granular Hydrogels as Brittle Yield Stress Fluids

Area of Science:

• Materials Science
• Rheology
• Biomedical Engineering

Background:

• Granular hydrogels are vital in biomedical fields.
• Existing rheological methods often overlook transient yielding and unyielding behaviors.
• A comprehensive understanding of granular hydrogel rheology is needed for advanced applications.

Purpose of the Study:

• To characterize the steady and transient rheology of granular hydrogels.
• To apply the Kamani-Donley-Rogers (KDR) model with Brittility (Bt) to granular hydrogels.
• To identify key microgel properties and granular compositions influencing rheological behavior.

Main Methods:

• Utilized oscillatory shear testing combined with the Kamani-Donley-Rogers (KDR) model and Brittility (Bt).
• Investigated polyethylene glycol and gelatin microgels with varying properties and granular compositions.
• Quantified steady-state and transient rheological parameters.

Main Results:

• Granular hydrogels exhibit behavior as brittle yield stress fluids.
• The KDR model with Bt effectively captures granular hydrogel rheology across diverse parameters.
• Monotonic relationships were observed between composition and elastic modulus, structural viscosity, and brittility.
• Mixtures showed lower yield stress compared to monolithic hydrogels.
• Microgel size distribution and polymer fraction were most influential in monolithic hydrogels.

Conclusions:

• The KDR model with Bt provides a quantitative framework for understanding granular hydrogel rheology.
• This framework is crucial for the rational design of hydrogels for applications such as injection, in situ stabilization, and 3D bioprinting.
• The study highlights the importance of transient rheological properties in hydrogel design.