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Deciphering granular hydrogel mechanics

Contact deformations of microgel building blocks are at the origin of granular hydrogel macroscale properties

Granular hydrogels are viscoelastic, packed assemblies composed of microgel building blocks jammed together. Unlike colloidal-scale microgels, interstitial voids between the granular-scale microgel particles stay large enough to allow for cell migration and proliferation. Accordingly, these materials have received attention in the fields of wound healing and cardiac repair. That said, current understanding of the relationships between microgel building blocks and hydrogels properties is poor, which in turn hinders rational, property-based engineering of these materials. Recently, Börte Emiroglu, in collaboration with the Macromolecular Engineering Laboratory at ETH Zürich, has investigated these relationships using a combination of experimental and modelled contact mechanics.

The microgel building blocks were first produced using state-of-the-art droplet-based microfluidic templating, yielding highly monodisperse particles of tunable stiffness (based on the polymer fraction in the initial droplet). After jamming to create the macroscale assembly, dynamic oscillatory rheology was used to assess how microgel deformations control the nonlinear rheology of granular hydrogels. Subsequently, the team developed a contact mechanics model to account for the deformable nature of the microgels and the impact of the building blocks stiffness on deformation behavior. Interestingly, they found that the system could be accurately represented as a collection of two-body interactions and were able to calculate important macroscale properties such as the plateau modulus and viscosity of the granular hydrogels, which were in agreement with experimental data. Furthermore, the newly gained structure-properties knowledge was successfully applied to the 3D-printing of jammed granular hydrogels, providing valuable insights into the choice of certain parameters, such as the extrusion pressure.

Through an elegant combination of experimental and modeling workflows, this study wonderfully displays how granular hydrogel macroscale behaviors can be rationalized based on its microgel building block properties.

Written by Thomas Moragues

Read the accepted manuscript here

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