Does the Size of Microgels Influence the Toughness of Microgel‐Reinforced Hydrogels?

Abstract

Rapid advances in the biomedical field increasingly often demand soft materials that can be processed into complex 3D shapes while being able to reliably bear significant loads. Granular hydrogels have the potential to serve as artificial tissues because they can be 3D printed into complex shapes and their composition can be tuned over short length scales. Unfortunately, granular hydrogels are typically soft such that they cannot be used for load‐bearing applications. To address this shortcoming, individual microgels can be connected through a percolating network, such that they introduce the double network toughening mechanism into granular hydrogels. However, the influence of the microgel size and concentration on the processing and toughness of microgel‐reinforced hydrogels (MRHs) remains to be elucidated. Here, it is demonstrated that processing and toughness depend on the inter‐microgel connectivity, while the stress at break is solely dependent on the microgel size. These findings offer an in‐depth understanding of how liquid‐ and paste‐like precursors containing soft, deformable microgels can be processed into bulk microstructured soft materials and how the size and concentration of these microgels influence the mechanical properties of microgel‐reinforced hydrogels.

Influence of Microgel and Interstitial Matrix Compositions on Granular Hydrogel Composite Properties

“…Lastly, it is important to note that as an alternative approach, dried microgels could be added to an interstitial precursor solution to form a granular hydrogel composite upon rehydration, which may overcome the impact of interstitial matrix dilution. [ 18 , 19 , 21 , 22 ] In this approach, drying and rehydration of microgels would have to be fully characterized to understand the impact on mechanical properties.…”

“…For example, Amstad and colleagues fabricated polyacrylamide‐based granular hydrogel composites for 3D printing applications. [ 5 , 20 , 21 ] In another example, Poletti and colleagues developed poly(ethylene glycol)‐based (PEG) granular hydrogel composites consisting of PEG microgels and an interstitial matrix of either cellulose [ 22 ] or silk fibers [ 19 ] for further reinforcement. It has also been shown that granular hydrogel composites can greatly improve print fidelity when compared to bulk hydrogels without microgels.…”

Rheological responses of microgel suspensions with temperature-responsive capillary networks

“…In general, rheological properties of microgel suspensions depend on their shape, 32 size, 33 polydispersity, 28 stiffness, 34 and external conditions ( e.g. , temperature and pressure 23,35 ).…”

“…In general, rheological properties of microgel suspensions depend on their shape, 32 size, 33 polydispersity, 28 stiffness, 34 and external conditions (e.g., temperature and pressure 23,35 ). In this work, a close packing of relatively larger microgels provides a large interparticle contact area because of a higher microgel size dispersity, which generates increased friction between microgels in microgel suspensions.…”

Multi-material 3D Printing of Mechanochromic Double Network Hydrogels for On-Demand Patterning

“…In this work, we employ a multi-material microgel DIW printing method to fabricate the mechanochromic hydrogels in arbitrary shapes. The printing ink is composed of the microgels containing polymerizable monomers, which is prepared following similar procedures in the microgel printing methods. − We first prepare a polyelectrolyte network embedded with mechanophores inside. The polyelectrolyte hydrogel is freeze-dried and ground.…”