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Low-molecular-weight peptide hydrogels can be formed by self-assembly through weak interactions, but the application of the hydrogel is influenced by its weak mechanical properties. Therefore, it is important to construct low-molecular-weight peptide hydrogels with excellent mechanical properties. In this work, we designed the pentapeptide molecule Fmoc-FFCKK-OH (abbreviated as FFCKK) with a sulfhydryl group, and another low-molecular-weight cross-linker N , N' -methylenebis(acrylamide) (MBA) was introduced to construct a hydrogel with excellent mechanical properties. The secondary structure change process of FFCKK and the assembly mechanism of hydrogel were analyzed using theoretical calculations and experimental characterizations. The occurrence of thiol-ene click chemistry provides covalent interaction in the hydrogel, and the synergistic effect ofcovalent interaction and hydrogen bonding improves the mechanical properties of the hydrogel by nearly 10-fold. The hydrogel was observed to be able to withstand a stress of 368 Pa and to break in a layer-by-layer manner by compression testing. The micromechanics of the hydrogels were characterized, and the excellent mechanical properties of the hydrogels were confirmed. The synergistic approach provides a new idea for the preparation of low-molecular-weight peptide hydrogels and facilitates the expansion of their potential applications in biomedical fields.

Drosera is a small insectivorous plant whose antennae can fold up, encircle, and prey. The rapid movement of the antennae is achieved by the synergistic effect of a double-layer structure with the antennae contracts on the front and expands on the back. In this work, a drosera-inspired dual-actuating double-layer hydrogel actuator is proposed, in which the temperature-responsive poly(N, N-diethyl acrylamide) (PDEAAm) layer acts as the main actuation layer and a moisture-responsive poly(acrylamide) (PAAm) layer acts as the auxiliary actuation layer. In a water environment with low temperature, both the PAAm and PDEAAm layers absorb water and expand with a swelling property. When the temperature exceeds the lower critical solution temperature of PDEAAm, the PDEAAm layer undergoes a hydrophilic-hydrophobic transition and shrinks rapidly. Therefore, the synergistic effect of the double-layer hydrogel enables the double-layer hydrogel to achieve a large bending angle at high temperature. In addition, when designing and fabricating shape-patterned double-layer hydrogels, complex shape changes can be achieved. Due to the physical and chemical properties, the actuator can be used to grab, transport, and release objects. This drosera-inspired double-layer hydrogel actuator has high practical value, which may provide new insights for the design and manufacture of artificial intelligence materials., (© 2021 Wiley-VCH GmbH.)

Hydrogels, as a kind of soft materials, are good candidates for smart skin-like materials. A double network is usually fabricated to improve the mechanical properties of hydrogels, and involves two different kinds of networks. In this work, a novel strategy for preparing single network double cross-linker (SNDCL) hydrogels was proposed and the prepared hydrogels exhibited excellent mechanical properties, including stretchability, compressibility, self-recovery, adhesion, shape memory and mechanical strength. N,N'-Methylenebisacrylamide forms covalent bonds with the network, while citric acid can form multiple weak interactions due to the polycarboxylic structure. This improves the tensile properties (6564%) and compressive properties of the hydrogel, and the hydrogels also exhibit long-lasting self-adhesion ability on various substrates. In addition, the hydrogels with multiple properties can be used as flexible strain sensors, allowing the monitoring of body movements. The hydrogels can hopefully be used in wearable electronic sensor devices and for healthcare monitoring.

A green strategy by integrating surface-initiated metal-free photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) with mussel-inspired polydopamine (PDA) chemistry, was used to fabricate multi-walled carbon nanotubes (MWCNTs)/poly(4-vinylpyridine) (P4VP) nanocomposites. Self-healing nanocomposite hydrogels were facilely designed with these nanocomposites through dynamic supramolecular interactions. Using mussel-inspired PDA chemistry from MWCNTs, nanocomposites (MWCNTs@PDA-P4VP) were successfully prepared by metal-free PET-ATRP with MWCNTs@PDA-Br as an initiator, rhodamine B as photocatalyst, 4-vinylpyridine (4VP) as monomer, respectively. Importantly, the obtained nanocomposite hydrogels had high mechanical strength (2.9 MPa), prior fracture strain (633.8%) and excellent self-healing property (90.6%). These methodologies will provide opportunities for the design of eco-functional materials or flexible biosensors., Competing Interests: Declaration of competing interest There are no conflicts to declare., (Copyright © 2019 Elsevier B.V. All rights reserved.)

In this manuscript, dual network self-healing alginate/guar gum hydrogels with polydopamine-type microcapsules from mesoporous silica nanoparticles were facilely prepared through one-pot method. Glutaraldehyde (GA) was used as a crosslinking agent to crosslink guar gum and sodium alginate, respectively. Metal-ligand interactions as reversible non-covalent bonds make the dual network hydrogels have a high degree of self-healing ability, which FeCl 3 ·6H 2 O was coordinated with sodium alginate and polydopamine on the surface of microcapsules, respectively. The dual network structure significantly enhances the strength of the hydrogels (up to 7.3 MPa). It has also proved that these hydrogels exhibit excellent self-healing performance at ambient temperatures, which self-healing efficiency can reach to 95.5%. The obtained self-healing hydrogels have a promising application prospect for the design and synthesis of functional self-healing materials., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Hydrogels with the properties of self-healing, toughness, stiffness and strength have great potential for use in smart materials. Herein, self-healing and tough hydrogels were successfully prepared after adding modified graphene oxide (GO) composites, which grafted the functional polymers onto the surface of GO. GO@polyacrylonitrile (GO@PAN) was synthesized via surface-initiated atom transfer radical polymerization (SI-ATRP) using GO@BiBB as the ATRP initiator. The nitrile group on GO@PAN was converted to pyridine, for which 2,4,6-triphenylpyrylium tetrafluoroborate (TPPT) was used as the photocatalyst. The prepared GO composite was added into polyacrylic acid (PAA) hydrogels formed by in situ radical polymerization. These tough hydrogels not only have high mechanical strength, but also show excellent self-healing performance. This strategy can provide a novel and universal route for the fabrication of smart hydrogels in biomedical and engineering fields. [ABSTRACT FROM AUTHOR]

Chemical modification of sodium alginate (SA) polymer chains can increase its functional group species. Sodium periodate (SP) was usually used to oxidize the hydroxyl groups on the chain of SA to aldehyde groups, the preparation of oxidized sodium alginate (OSA) using SP is not only complicated, also limits the variety of functional groups on the chain of OSA. By contrast, we have developed an innovative strategy for OSA, in which ammonium persulfate (APS) was used to oxidize SA, providing a clear elucidation of the oxidizing process and mechanism. OSA/PAM hydrogels were synthesized using OSA, the hydrogels possess excellent adhesion properties to various non-metallic and metallic substrates. Tensile and compression tests show that the cross-linked OSA/PAM hydrogels have superior mechanical properties. We exploit OSA/PAM hydrogels as soil adhesive and water-retaining agents for wheat growth. OSA/PAM hydrogels significantly improve the survival time of wheat grown in brown loam soil under a water-shortage environment, and slow down the wilting of wheat in a water-shortage environment and prolong the survival time of wheat in sandy soils. Our trials should make hydrogels important for wheat cultivation in brown loam soils and the development of desert areas. [Display omitted] [ABSTRACT FROM AUTHOR]