A Quantitative Description for Designing the Extrudability of Shear-Thinning Physical Hydrogels.

Physically associated hydrogels (PHs) capable of reversible transitions between solid and liquid-like states have enabled novel strategies for 3D printing, therapeutic drug and cell delivery, and regenerative medicine. Among the many design criteria (e.g., viscoelasticity, cargo diffusivity, biocompatibility) for these applications, engineering PHs for extrudability is a necessary and critical design criterion for the successful application of these materials. As the development of many distinct PH material systems continues, a strategy to determine the extrudability of PHs a priori will be exceedingly useful for reducing costly and time-consuming trial-and-error experimentation. Here, a strategy to determine the property-function relationships for PHs in injectable drug delivery applications at clinically relevant flow rates is presented. This strategy-validated with two chemically and physically distinct PHs-reveals material design spaces in the form of Ashby-style plots that highlight acceptable, application-specific material properties. It is shown that the flow behavior of PHs does not obey a single shear-thinning power law and the implications for injectable drug delivery are discussed. This approach for generating design criteria has potential for streamlining the screening of PHs and their utility in applications with varying geometrical (i.e., needle diameter) and process (i.e., flow rate) constraints.