Additive Soft Matter Design by UV-Induced Polymer Hydrogel Inter-Crosslinking.

Talika A Neuendorf,Julian Thiele,Niclas Weigel,Michelle Vigogne

doi:10.3390/gels8020117

Talika A Neuendorf, Julian Thiele + Show 2 more

Open Access

https://doi.org/10.3390/gels8020117

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Abstract

In recent years, stimuli-responsive hydrogels have gained tremendous interest in designing complex smart 4D materials for applications ranging from biomedicine to soft electronics that can change their properties on demand over time. However, at present, a hydrogel’s response is often induced by merely a single stimulus, restricting its broader applicability. The controlled hierarchical assembly of various hydrogel building blocks, each with a tailored set of mechanical and physicochemical properties as well as programmed stimulus response, may potentially enable the design and fabrication of multi-responsive polymer parts that process complex operations, like signal routing dependent on different stimuli. Since inter-connection stability of such building blocks directly accompanies the transmission of information across building blocks and is as important as the building property itself to create complex 4D materials, we provide a study on the utility of an inter-crosslinking mechanism based on UV-induced 2,3-dimethylmaleimide (DMMI) dimerization to inter-connect acrylamide-based and N-isopropylacrylamide-based millimeter-sized cubic building blocks, respectively. The resulting dual-crosslinked assemblies are freestanding and stable against contraction–expansion cycles in solution. In addition, the approach is also applicable for connecting microfluidically fabricated, micrometer-sized hydrogel spheres, with the resulting assemblies being processable and mechanical stable, likewise resisting contraction–expansion in different solvents, for instance.

Highlights

Accepted: 9 February 2022The concept of controlled hierarchical assembly of building blocks is a well-known theme in our lives, e.g., when constructing stone walls, playing with interlocking plastic bricks, or looking at cellular organization in organisms
We investigated the UV-induced DMMI dimerization to inter-connect hydrogel building blocks towards polymer supragels
We studied the applicability of the approach for millimeter-sized, cubic structures with flat surfaces formed from acrylamide

Summary

Introduction

Accepted: 9 February 2022The concept of controlled hierarchical assembly of building blocks is a well-known theme in our lives, e.g., when constructing stone walls, playing with interlocking plastic bricks, or looking at cellular organization in organisms. The idea of utilizing small building blocks with different colors or shapes to build up larger objects enables the constructor to tailor individually local and global properties, shape, size, and appearance of the final part. The transfer of this concept to the field of materials science and additive manufacturing to create assemblies of building blocks exhibiting distinct properties and yielding complex multifunctional materials still remains a challenge. Several groups have already developed various assembly techniques and inter-connection concepts utilizing hydrogel-based building blocks towards multifunctional materials. The authors fabricated polyethylene glycol methacrylate-based hydrogels by a photomask approach to yield cubic structures with approximate dimensions

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