Precise and selective macroscopic assembly of a dual lock-and-key structured hydrogel.

Macroscopic assembly offers immense potential for constructing complex systems due to the high design flexibility of the building blocks. In such assembly systems, hydrogels are promising candidates for building blocks due to their versatile chemical compositions and ease of property tuning. However, two major challenges must be addressed to facilitate application in a broader context: the precision of assembly and the quantity of orthogonally matching pairs must both be increased. Although previous studies have attempted to address these challenges, none have successfully dealt with both simultaneously. Here, we propose topology-based design criteria for the selective assembly of hydrogel building blocks. By introducing the dual lock-and-key structures, we demonstrate highly precise assembly exclusively between the matching pairs. We establish principles for selecting multiple orthogonally matching pairs and achieve selective assembly involving simple one-to-one matching and complex assemblies with multiple orthogonal matching points. Moreover, by harnessing hydrogel tunability and the abundance of matching pairs, we synthesize complementary single-stranded structures for programmable assembly and successfully assemble them in the correct order. Finally, we demonstrate a hydrogel-based self-assembled logic gate system, including a YES gate, an OR gate, and an AND gate. The output is generated only when the corresponding inputs are provided according to each logic.

Expandable ELAST for super-resolution imaging of thick tissue slices using a hydrogel containing charged monomers.

Hydrogels have been utilized extensively as a material for retaining position information in tissue imaging procedures, such as tissue clearing and super-resolution imaging. Immunostaining thick biological tissues, however, poses a bottleneck that restricts sample size. The recently developed technique known as entangled link-augmented stretchable tissue-hydrogel (ELAST) accelerates the immunostaining process by embedding specimens in long-chain polymers and stretching them. A more advanced version of ELAST, magnifiable entangled link-augmented stretchable tissue-hydrogel (mELAST), achieves rapid immunostaining and tissue expansion by embedding specimens in long-chain neutral polymers and subsequently hydrolyzing them. Building on these techniques, we introduce a variant of mELAST called ExELAST. This approach uses charged monomers to stretch and expand tissue slices. Using ExELAST, we first tested two hydrogel compositions that could permit uniform expansion of biological specimens. Then, we apply the tailored hydrogel to the 500-µm-thick mouse brain slices and demonstrated that they can be stained within two days and imaged with a resolution below the diffraction limit of light.

Human hand-inspired all-hydrogel gripper with a high load capacity formed by the split-brushing adhesion of diverse hydrogels.

Human hands are highly versatile. Even though they are primarily made of materials with high water content, they exhibit a high load capacity. However, existing hydrogel grippers do not possess a high load capacity due to their innate softness and mechanical strength. This work demonstrates a human hand-inspired all-hydrogel gripper that can bear more than 47.6 times its own weight. This gripper is made of two hydrogels: poly(methacrylamide-co-methacrylic acid) (P(MAAm-co-MAAc)) and poly(N-isopropylacrylamide) (PNIPAM). P(MAAm-co-MAAc) is extremely stiff but becomes soft above its transition temperature. By taking advantage of the difference in the kinetics of the stiff-soft transition of P(MAAm-co-MAAc) hydrogels and the swelling-shrinking transition of PNIPAM hydrogels, this gripper can be switched between its stiff-bent and stiff-stretched states by simply changing the temperature. The assembly of these two hydrogels into a gripper necessitated the development of a new hydrogel adhesion method, as existing topological adhesion methods are not applicable to such stiff hydrogels. A new hydrogel adhesion method, termed split-brushing adhesion, has been demonstrated to satisfy this need. When applied to P(MAAm-co-MAAc) hydrogels, this method achieves an adhesion energy of 1221.6 J m-2, which is 67.5 times higher than that achieved with other topological adhesion methods.

Strong, Chemically Stable, and Enzymatically On-Demand Detachable Hydrogel Adhesion Using Protein Crosslink.

Achieving strong adhesion between hydrogels and diverse materials is greatly significant for emerging technologies yet remains challenging. Existing methods using non-covalent bonds have limited pH and ion stability, while those using covalent bonds typically lack on-demand detachment capability, limiting their applications. In this study, a general strategy of covalent bond-based and detachable adhesion by incorporating amine-rich proteins in various hydrogels and inducing the interfacial crosslinking of the hydrogels using a protein-crosslinking agent is demonstrated. The protein crosslink offers topological adhesion and can reach a strong adhesion energy of ≈750 J m-2 . The chemistry of the adhesion is characterized and that the inclusion of proteins inside the hydrogels does not alter the hydrogels' properties is shown. The adhesion remains intact after treating the adhered hydrogels with various pH solutions and ions, even at an elevated temperature. The detachment is triggered by treating proteinase solution at the bonding front, causing the digestion of proteins, thus breaking up the interfacial crosslink network. In addition, that this approach can be used to adhere hydrogels to diverse dry surfaces, including glass, elastomers and plastics, is shown. The stable chemistry of protein crosslinks opens the door for various applications in a wide range of chemical environments.

Fabrication of heterogeneous chemical patterns on stretchable hydrogels using single-photon lithography.

Curved hydrogel surfaces bearing chemical patterns are highly desirable in various applications, including artificial blood vessels, wearable electronics, and soft robotics. However, previous studies on the fabrication of chemical patterns on hydrogels employed two-photon lithography, which is still not widely accessible to most laboratories. This work demonstrates a new patterning technique for fabricating curved hydrogels with chemical patterns on their surfaces without two-photon microscopy. In this work, we show that exposing hydrogels in fluorophore solutions to single photons via confocal microscopy enables the patterning of fluorophores on hydrogels. By applying this technique to highly stretchable hydrogels, we demonstrate three applications: (1) improving pattern resolution by fabricating patterns on stretched hydrogels and then returning the hydrogels to their initial, unstretched length; (2) modifying the local stretchability of hydrogels at a microscale resolution; and (3) fabricating perfusable microchannels with chemical patterns by winding chemically patterned hydrogels around a template, embedding the hydrogels in a second hydrogel, and then removing the template. The patterning method demonstrated in this work may facilitate a better mimicking of the physicochemical properties of organs in tissue engineering and may be used to make hydrogel robots with specific chemical functionalities.

Improving Room Temperature Ionic Conductivity of Na3-xKxZr2Si2PO12 Solid-Electrolytes: Effects of Potassium Substitution.

The battery safety and cost remain major challenges for developing next-generation rechargeable batteries. All-solid-state sodium (Na)-ion batteries are a promising option for low-cost as well as safe rechargeable batteries by using abundant resources and solid electrolytes. However, the operation of solid-state batteries is limited due to the low ionic conductivity of solid electrolytes. Therefore, it is essential to develop new compounds that feature a high ionic conductivity and chemical stability at room temperature. Herein, we report a potassium-substituted sodium superionic conductor solid electrolyte, Na3-xKxZr2Si2PO12 (0 ≤ x ≤ 0.2), that exhibits an ionic conductivity of 7.734 × 10-4 S/cm-1 at room temperature, which is more than 2 times higher than that of the undoped sample. The synchrotron powder diffraction patterns with Rietveld refinements revealed that the substitution of large K-ions resulted in an increased unit cell volume, widened the Na diffusion channel, and shortened the Na-Na distance. Our work demonstrates that substituting a larger cation on the Na site effectively widens the ion diffusion channel and consequently increases the bulk ionic conductivity. Our findings will contribute to improving the ionic conductivity of the solid electrolytes and further developing safe next-generation rechargeable batteries.