Dear Readers,

This week I did a cursory search for hydrogel products and commercialized hydrogels. What I discovered were numerous results in pharmaceutical, cosmetic, and contact lens products. This result surprised me because I expected more hits in soft robotics or tissue engineering.

Given all the talk about how hydrogels have similar microstructure to human tissue, I would have expected human mimics to be developed and commercialized.

Perhaps the challenges in these applications are more difficult to address that the aforementioned industries?

In my unsolicited quest to balance the odds like Thanos, I decided to make this week a special edition solely on hydrogels for soft robotics.

Research Updates

Programmable Nanocomposites Of Cellulose Nanocrystals And Zwitterionic Hydrogels For Soft Robotics (Link)

• The authors synthesized programmable nanocomposites of cellulose nanocrystals and zwitterionic hydrogels for soft robotics applications.

• These nanocomposites are prepared by copolymerizing zwitterionic monomers and a small amount of methacrylic acid in the presence of cellulose nanocrystals, which form a liquid crystalline phase and can be aligned by shear forces.

• Methacrylic acid increases the mechanical strength of the resulting hydrogel by enhancing the hydrophobic association using methyl groups.

• Alignment of cellulose nanocrystals induces anisotropic swelling and mechanical properties in the nanocomposites, which can be programmed to achieve complex shape transformations such as bending, twisting, and folding.

• The nanocomposites show high cytocompatibility and minimal protein adsorption, which are desirable for biointerface applications like biomedical soft robots.

3D Shape Morphing Of Stimuli-responsive Composite Hydrogels (Link)

• This is a review on the 3D shape morphing behavior of stimuli-responsive composite hydrogels, which are hydrogels that combine a hydrogel matrix with other materials to enhance their functionality and performance.

• The article discusses the chemistry of different types of hydrogel, fabrication techniques, mechanisms of shape morphing, and the various stimuli that can induce shape changes.

• 3D shape morphing of composite hydrogels can be achieved by designing inhomogeneous swelling, anisotropic deformation, or programmable actuation.

• There are potential applications of shape morphable composite hydrogels in fields such as soft robotics, information encryption, biomedical research, flexible electronics, and engineered living materials.

Thermoresponsive Double-network Hydrogel/Elastomer Hybrid Bilayer Laminates With High Interfacial Toughness And Controllable Shape Deformations (Link)

• The authors designed thermoresponsive hydrogel/elastomer hybrid bilayer laminates that can change shape and bend in response to temperature and cationic stimuli.

• The hybrid bilayer laminates are composed of a PNaAMPS/P(NIPAM-co-AAm) double network (TDN) hydrogel layer and a polydimethylsiloxane (PDMS) elastomer layer.

• TDN hydrogel has tunable lower critical solution temperature (LCST) and can swell or shrink depending on the temperature. Meanwhile, PDMS elastomer provides mechanical strength to the laminates.

• The interface between the hydrogel and elastomer layers is strengthened by grafting the TDN hydrogel network onto the benzophenone-activated PDMS surface. Three debonding behaviors were observed: adhesive failure, adhesive-cohesive co-failure, and cohesive failure.

• The hybrid bilayer laminates exhibit reversible and controllable shape deformations. Its degree of bending can be tuned by changing the hydrogel/elastomer thickness ratio, the cation type and concentration, and the near-infrared light irradiation.

• These hybrid bilayer laminates have potential applications in tissue engineering, biosensors, soft robots, and wearable electronics.

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