Super Tough Hydrogels Research Articles

Strong and tough polyacrylamide/Laponite nanocomposite hydrogels modified with 1-butyl-3-methylimidazolium chloride salt

In this paper, the physicochemical double cross-linking nanocomposite hydrogels were prepared. Due to the addition of ionic liquid (1-butyl-3-methylimidazolium chloride salt), Laponite cannot spontaneously form a high thixotropic gel in water. The homogeneously dispersed Laponite nanosheets act as dynamic physical crosslinking sites, which cooperate with the chemical crosslinking center of MBA in the polymer chain segments and build a super-strong and super-tough hydrogel network structure. The PAM/Laponite/IL nanocomposite hydrogel achieves excellent tensile strength up to 1191 Kpa, a high tensile strain of 6842%, and a very high toughness of 26.62 MJ/m3. In this paper, an effective mechanism to enhance the mechanical properties of the hydrogel is proposed based on the structural evolution of Laponite. This highly flexible nanocomposite hydrogel shows excellent potential as a load-bearing material.

3D printed microstructured ultra-sensitive pressure sensors based on microgel-reinforced double network hydrogels for biomechanical applications.

Hydrogel-based wearable flexible pressure sensors have great promise in human health and motion monitoring. However, it remains a great challenge to significantly improve the toughness, sensitivity and stability of hydrogel sensors. Here, we demonstrate the fabrication of hierarchically structured hydrogel sensors by 3D printing microgel-reinforced double network (MRDN) hydrogels to achieve both very high sensitivity and mechanical toughness. Polyelectrolyte microgels are used as building blocks, which are interpenetrated with a second network, to construct super tough hydrogels. The obtained hydrogels show a tensile strength of 1.61 MPa, and a fracture toughness of 5.08 MJ m-3 with high water content. The MRDN hydrogel precursors exhibit reversible gel-sol transitions, and serve as ideal inks for 3D printing microstructured sensor arrays with high fidelity and precision. The microstructured hydrogel sensors show an ultra-high sensitivity of 0.925 kPa-1, more than 50 times that of plain hydrogel sensors. The hydrogel sensors are assembled as an array onto a shoe-pad to monitor foot biomechanics during gaiting. Moreover, a sensor array with a well-arranged spatial distribution of sensor pixels with different microstructures and sensitivities is fabricated to track the trajectory of a crawling tortoise. Such hydrogel sensors have promising application in flexible wearable electronic devices.

An ultrasound-induced MXene doped PAM–SA super-tough hydrogel

Here we reported a novel ultrasound-induced polymerization to achieve a polyacrylamide–sodium alginate (SA) dual network hydrogel via a redox reaction with MXene (Ti3C2) as a reductant and potassium persulfate (KPS) as an oxidant.

Correction: An ultrasound-induced MXene doped PAM–SA super-tough hydrogel

Correction for ‘An ultrasound-induced MXene doped PAM–SA super-tough hydrogel’ by Keyi Li et al., J. Mater. Chem. C, 2023, 11, 1908–1918, https://doi.org/10.1039/D2TC04665B.

Super Tough Hydrogels with Self-adaptive Network Facilitated by Liquid Metal

Super Tough Hydrogels with Self-adaptive Network Facilitated by Liquid Metal

Self-Healable and Super-Tough Double-Network Hydrogel Fibers from Dynamic Acylhydrazone Bonding and Supramolecular Interactions.

Macroscopic hydrogel fibers are highly desirable for smart textiles, but the fabrication of self-healable and super-tough covalent/physical double-network hydrogels is rarely reported. Herein, copolymers containing ketone groups were synthesized and prepared into a dynamic covalent hydrogel via acylhydrazone chemistry. Double-network hydrogels were constructed via the dynamic covalent crosslinking of copolymers and the supramolecular interactions of iota-carrageenan. Tensile tests on double-network and parental hydrogels revealed the successful construction of strong and tough hydrogels. The double-network hydrogel precursor was wet spun to obtain macroscopic fibers with controlled drawing ratios. The resultant fibers reached a high strength of 1.35 MPa or a large toughness of 1.22 MJ/m3. Highly efficient self-healing performances were observed in hydrogel fibers and their bulk specimens. Through the simultaneous healing of covalent and supramolecular networks under acidic and heated conditions, fibers achieved rapid and near-complete healing with 96% efficiency. Such self-healable and super-tough hydrogel fibers were applied as shape memory fibers for repetitive actuating in response to water, indicating their potential in intelligent fabrics.

Bacterial cellulose reinforced double-network hydrogels for shape memory strand

Tough hydrogels with shape memory property are highly desirable for actuators and smart engineering materials. Herein, super-tough polyacrylamide/iota-carrageenan double-network hydrogels were synthesized via a one-pot radical polymerization and strengthened by incorporating bacterial cellulose microclusters, through the intermolecular hydrogen bonds and topological interlock between microclusters and polymer network. Such hydrogels were able to withstand over 200 kPa of tensile stress, or be stretched over 27 times of initial length, and reached a high toughness of ∼2000 kJ/m3. By tension-drying and post-annealing treatments on the strongest hydrogel, dry strands were fabricated to withstand over 100 MPa of tensile stress. Moreover, these strands presented water-stimulated shape memory by a recovery ratio of 84.3 % in 4 min. Based on these characteristics, this super-tough hydrogel may serve as smart textile or actuator for a variety of applications.

Highly recyclable and super-tough hydrogel mediated by dual-functional TiO2 nanoparticles toward efficient photodegradation of organic water pollutants

A novel photocatalytic hydrogel was prepared by loading TiO2 nanoparticles (TiO2 NPs) onto the surface of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized chitin nanofibers (TOCNs), which were further incorporated into the polyacrylamide (PAM) matrix. The resultant hydrogel exhibited a macro-porous structure with a low density (~1.45 g/cm3) and high water content (~80%). The well-dispersed TiO2 NPs not only acted as a crosslinking agent for bridging the three-dimensional porous network structure, but also endowed the hydrogel with good catalytic activity. After the introduction of TiO2 accounting for 10 wt% of the hydrogel mass, the hydrogels showed compressive strength of 1.46 MPa at 70% strain, tensile stress of 316 kPa, tensile strain of 310%, toughness of 47.25 kJ/m3 and fatigue resistance. Compared with neat TOCN-PAM hydrogel, the uniaxial compressive and tensile strengths of the TiO2-TOCN-PAM10 hydrogel increased 6.35-fold and 3.70-fold, respectively. Furthermore, the removal of methyl orange (MO) was attributed to the synergistic effect of the adsorption and photocatalytic degradation of the hydrogels. The hydrogels adsorbed up to 8.5% of MO after 150 min of adsorption and a photocatalytic degradation rate of 97.3% achieved after 90 min of UV irradiation at pH = 2. Especially, the TiO2-TOCN-PAM10 hydrogel exhibited excellent recycling performance: its MO removal efficiency was around 96% even after 10 reuse cycles. The as-prepared hydrogels, with characteristics of excellent stretchability, photocatalytic activity and recyclability, are expected to be used in alleviating organic pollutants in practical wastewater treatments.

Facile preparation and characterization of super tough chitosan/poly(vinyl alcohol) hydrogel with low temperature resistance and anti-swelling property

Facile preparation of super tough hydrogels with low temperature tolerance and anti-swelling property is still a challenging task for researchers. Meanwhile, the vast majority of tough hydrogels were obtained though chemical crosslinking and complicated synthesis or processing method accompanying a large number of harmful chemical reagents. Herein, the super tough chitosan/poly(vinyl alcohol) (CS/PVA) hydrogels (the maximum compressive strength of 18.97 MPa at a strain of 80% and the maximum tensile strength of 4.02 MPa at a strain of 406.4%) were successfully prepared via a simple post-treatment method. CS/PVA hydrogels were firstly prepared by freezing-thawing process and then soaking in saturated sodium chloride aqueous solution. The resultant hydrogels possess excellent swelling resistance and low temperature tolerance. This work shows that the post-treatment of immersing in saline solution is a feasible way to prepare super tough hydrogels with low temperature tolerance and anti-swelling property. This also would enlarge the application areas of CS.

Super-tough hydrogels from shape-memory polyurethane with wide-adjustable mechanical properties

Recoverable hydrogels with high strength and toughness have been fabricated from hydrophilic and thermoplastic polyurethane (HTPU), which chains consist of hydrophilic polyethylene glycol (PEG) segment of high crystallinity and hydrophobic segment with strong hydrogen-bonding groups. This HTPU absorbed high amount of water, during which the PEG crystals swollen and dissolved, while the hydrophobic segments still held the adjacent chains together, forming a stable hydrogel. Even at equilibrium swelling state (89 wt% water), the HTPU hydrogel exhibited high modulus (0.4 MPa), high strength (2.6 MPa), and large strain at break (~500%). The effect of water content on the tensile properties of HTPU hydrogels was carefully studied at different levels of swelling. Interestingly, the hydrogels demonstrated a transition from a typical tough plastic to a tough elastomer when the water content reached 35 wt% of the hydrogel, with breaking strength of 10.0 MPa and fracture energy of 59.7 MJ/m3 at maximum strain over 1600%. The results from differential scanning calorimetry, Fourier transform infrared spectroscopy, and microscope measurements showed that the wide adjustability of this HTPU mechanical property was a result of the changes in its crystallinity, hydrogen-bonding, and hydrophobic association. Furthermore, the shape-memory performance of the HTPU was studied with heat and water stimuli and found faster at heating to 70 °C than that by immersion in water: 10 s versus 10 min. This study may widen the application of HTPU biodegradable polymers and provide new frontiers for the design of tough hydrogels by network structure control.

Multiple Shape Memory, Self-Healable, and Supertough PAA-GO-Fe3+Hydrogel

A multiple shape memory and self-healing poly(acrylic acid)-graphene oxide-Fe3+ (PAA-GO-Fe3+) hydrogel with supertough strength is synthesized containing dual physically cross-linked PAA network by GO and Fe3+. The first GO cross-linked hydrogel can be reversibly reinforced by immersing in FeCl3/HCl and pure water and softened by immersing in HCl. The tensile strength is 2.5 MPa with the break strain of 700%. Multiple shape memory capability is found depending on this unique feature, the hydrogel can be fixed in four temporary shapes by adjusting the immersing time in FeCl3/HCl and pure water, and recovered in sequence by immersing in HCl. This hydrogel also exhibits perfect self-healing behavior, the cut as-prepared hydrogel is almost completely healed by immersing in FeCl3/HCl. Besides, the hydrogel shows enhanced electrical conductivity with the presence of GO and Fe3+. This supertough hydrogel provides a new way to design soft actuators.

3D printing of an extremely tough hydrogel

A super tough hydrogel with tunable mechanical properties was 3D printed.