Reversible Sol-gel Transition Research Articles

Two-dimensional polydopamine nanosheet-based thermosensitive supramolecular hydrogels for photothermal-chemo synergistic treatment of melanoma

The development of injectable thermosensitive hydrogels with photothermal elimination of tumors and precisely controllable drug release properties is critical for tumor eradication. Herein, a novel injectable thermosensitive supramolecular hydrogel PDAns@CPT-peg/α-CD was developed, which was formed by using two-dimensional polydopamine nanosheets (PDAns) as the photothermal backbone, loaded with the PEGylated camptothecin prodrug (CPT-peg) through π-π stacking and hydrophobic binding, and then crosslinked by the introduction of α-cyclodextrin (α-CD) host–guest self-assembly. PDAns as hydrogel skeleton endowed the hydrogel with excellent photothermal conversion effect, and the large specific surface area of PDAns enables efficient loading of hydrophobic anticancer drugs and avoids undesired leakage. Moreover, the dynamic host–guest cross-linking endows the hydrogel with reversible gel-sol transition and injectability, the gel-sol transition temperature can be easily tunable by the CD concentration, under 808 nm laser irradiation, the PDAns@CPT-peg/α-CD hydrogel can be rapidly heated to the temperature required for photothermal therapy, simultaneously triggering the thermosensitive gel-sol transition followed by the on-demand release of CPT-peg. In vivo evaluation demonstrated that the synergistic photothermal-chemotherapeutic effect mediated by PDAns@CPT-peg/α-CD hydrogel almost eradicated melanoma under low-dose NIR laser (0.15 W cm−2) irradiation. This work provides an effective and convenient strategy for constructing a multifunctional hydrogel platform for the photothermal-chemo synergistic treatment of tumors.

Embedded Bioprinting of Tissue-like Structures Using κ-Carrageenan Sub-Microgel Medium.

Embedded three-dimensional (3D) bioprinting utilizing a granular hydrogel supporting bath has emerged as a critical technique for creating biomimetic scaffolds. However, engineering a suitable gel suspension medium that balances precise bioink deposition with cell viability and function presents multiple challenges, particularly in achieving the desired viscoelastic properties. Here, a novel κ-carrageenan gel supporting bath is fabricated through an easy-to-operate mechanical grinding process, producing homogeneous sub-microscale particles. These sub-microgels exhibit typical Bingham flow behavior with small yield stress and rapid shear-thinning properties, which facilitate the smooth deposition of bioinks. Moreover, the reversible gel-sol transition and self-healing capabilities of the κ-carrageenan microgel network ensure the structural integrity of printed constructs, enabling the creation of complex, multi-layered tissue structures with defined architectural features. Post-printing, the κ-carrageenan sub-microgels can be easily removed by a simple phosphate-buffered saline wash. Further bioprinting with cell-laden bioinks demonstrates that cells within the biomimetic constructs have a high viability of 92% and quickly extend pseudopodia, as well as maintain robust proliferation, indicating the potential of this bioprinting strategy for tissue and organ fabrication. In summary, this novel κ-carrageenan sub-microgel medium emerges as a promising avenue for embedded bioprinting of exceptional quality, bearing profound implications for the in vitro development of engineered tissues and organs.

An injectable, chitosan-based hydrogel prepared by Schiff base reaction for anti-bacterial and sustained release applications

Injectable hydrogels, providing sustained release as implanted materials, have received tremendous attention. In this study, chitosan-based hydrogels were prepared via Schiff base reaction of the aldehyde groups on Poly(NIPAM-co-FBEMA) and the amine groups on chitosan. Owing to the dynamic covalent linkage, the SC/PNF hydrogels exhibit pH-responsive, reversible sol-gel transition, injectable, and self-healing capacity. The mechanical strength of SC/PNF hydrogels can be operated simply by switching the composition or solid content of Poly(NIPAM-co-FBEMA) copolymers. Rheological analyses, including frequency sweeps, strain sweep scanning, and dynamic time sweeps, were employed to demonstrate the relationship between storage modulus (G′), loss modulus (G″), and composition of the SC/PNF hydrogels. In vitro release behaviors reveal that vancomycin-loaded SC/PNF hydrogel could contribute to both the initial burst release (over 1000 ppm within 4 h) and the sustained release (3000 ppm for at least 30 days). Pristine SC/PNF hydrogel holds good biocompatibility toward L929 cells and S. aureus that it degrades as incubated with S. aureus. However, vancomycin-wrapped SC/PNF hydrogel possesses a rapid bacterial-killing effect with a clear inhibition zone. In short, the SC/PNF hydrogels deliver not only sustainable release ability but also tunable physical properties, which are expected to be an outstanding candidate for non-invasive, anti-infection applications.

Cationic Azobenzenes as Light-Responsive Crosslinkers for Alginate-Based Supramolecular Hydrogels.

Azobenzene photoswitches are fundamental components in contemporary approaches aimed at light-driven control of intelligent materials. Significant endeavors are directed towards enhancing the light-triggered reactivity of azobenzenes for such applications and obtaining water-soluble molecules able to act as crosslinkers in a hydrogel. Here, we report the rational design and the synthesis of azobenzene/alginate photoresponsive hydrogels endowed with fast reversible sol-gel transition. We started with the synthesis of three cationic azobenzenes (AZOs A, B, and C) and then incorporated them in sodium alginate (SA) to obtain photoresponsive supramolecular hydrogels (SMHGs). The photoresponsive properties of the azobenzenes were investigated by UV-Vis and 1H NMR spectroscopy. Upon irradiation with 365 nm UV light, the azobenzenes demonstrated efficient trans-to-cis isomerization, with complete isomerization occurring within seconds. The return to the trans form took several hours, with AZO C exhibiting the fastest return, possibly due to higher trans isomer stability. In the photoresponsive SMHGs, the minimum gelation concentration (MGC) of azobenzenes was determined for different compositions, indicating that small amounts of azobenzenes could induce gel formation, particularly in 5 wt% SA. Upon exposure to 365 nm UV light, the SMHGs exhibited reversible gel-sol transitions, underscoring their photoresponsive nature. This research offers valuable insights into the synthesis and photoresponsive properties of cationic, water-soluble azobenzenes, as well as their potential application in the development of photoresponsive hydrogels.

Thermally Reversible Gel-Sol Transition of Hydrogels via Dissociation and Association of an Artificial Protein Nanocage.

Oligomeric protein nanocages often disassemble into their subunits and reassemble by external stimuli. Thus, using these nanocages as cross-linkers for hydrogel network structures is a promising approach to allow hydrogels to undergo stimuli-responsive gel-sol transitions or self-healing. Here, we report hydrogels that show a reversible gel-sol transition resulting from the heat-induced dissociation and reassociation of protein nanocages. The hydrogel contained the 60-mer artificial protein nanocage, TIP60, as a supramolecular cross-linker for polyethylene glycol network structures. The hydrogel showed a gel-to-sol transition upon heating at a temperature above the melting point of TIP60 and immediately returned to a gel state upon cooling to room temperature. During the heating and cooling treatment of the hydrogel, small-angle X-ray scattering analysis suggested the dissociation and reassociation of TIP60. Furthermore, we demonstrated redox-responsive cargo release from TIP60 in the hydrogel. These results showed the potential of TIP60 as a component of multi-stimuli-responsive hydrogels.

Preparation and properties of hydrogel photonic crystals assembled by biodegradable nanogels

Thermally induced physical hydrogels formed through the sol–gel transition of nanogels usually lose structural color above phase transition temperature (Tp). Herein, temperature/pH/redox-responsive nanogels that undergo sol–gel transition still keep structural colors above the Tp have been synthesized and studied. N-isopropylacrylamide (NIPAm) was copolymerized with N-tert-butylacrylamide (TBA) and N-acrylamido-l-phenylalanine (Aphe) to form P(NIPAm/TBA/Aphe) nanogel crosslinked with N,N’-bis(acryloyl)cystine (BISS) (referred to as PNTA-BISS). PNTA-BISS nanogel with a broad range of biodegradable crosslinker BISS content can achieve a reversible sol–gel transition above the Tp, surprisingly, while PNTA nanogels with a comparable content of biodegradable N,N’-Bis(acryloyl)cystam (BAC) crosslinker (referred to as PNTA-BAC) didn’t form sol–gel transition. Although BISS and BAC possess same disulfide bonds with redox properties, BISS, unlike BAC, is water-soluble and features two carboxyl groups. The mechanism by which PNTA-BISS nanogels form hydrogel photonic crystals has been deeply explored with temperature-variable NMR. The results showed the introduction of Aphe with both steric hindrance and carboxyl groups greatly slowed down the shrinkage of PNTA-BISS nanogels. Therefore, PNTA-BISS nanogels can form sol–gel transition and further structural color of hydrogel photonic crystals due to carboxyl groups above the Tp. Furthermore, the properties of biodegradable hydrogel photonic crystals above the Tp were investigated for the first time, attributed to the presence of the strong reducing agent 1,4-dithiothreitol (DTT). When loaded with doxorubicin (DOX), PNTA-BISS exhibited favorable degradation properties under the influence of DTT. In summary, the PNTA-BISS nanogel, in addition to its in-situ gelation capabilities, demonstrated degradability, potentially providing a novel nanoplatform for applications in drug delivery, biotechnology, and related fields.

Water-stable boroxine structure with dynamic covalent bonds

Boroxines are significant structures in the production of covalent organic frameworks, anion receptors, self-healing materials, and others. However, their utilization in aqueous media is a formidable task due to hydrolytic instability. Here we report a water-stable boroxine structure discovered from 2-hydroxyphenylboronic acid. We find that, under ambient environments, 2-hydroxyphenylboronic acid undergoes spontaneous dehydration to form a dimer with dynamic covalent bonds and aggregation-induced enhanced emission activity. Intriguingly, upon exposure to water, the dimer rapidly transforms into a boroxine structure with excellent pH stability and water-compatible dynamic covalent bonds. Building upon these discoveries, we report the strong binding capacity of boroxines toward fluoride ions in aqueous media, and develop a boroxine-based hydrogel with high acid–base stability and reversible gel–sol transition. This discovery of the water-stable boroxine structure breaks the constraint of boroxines not being applicable in aqueous environments, opening a new era of researches in boroxine chemistry.

Out-of-Equilibrium Mechanical Disruption of β-Amyloid-Like Fibers using Light-Driven Molecular Motors.

Artificial molecular motors have the potential to generate mechanical work on their environment by producing autonomous unidirectional motions when supplied with a source of energy. However, the harnessing of this mechanical work to subsequently activate various endoenergetic processes that can be useful in materials science remains elusive. Here, it is shown that by integrating a light-driven rotary motor through hydrogen bonds in a β-amyloid-like structure forming supramolecular hydrogels, the mechanical work generated during the constant rotation of the molecular machine under UV irradiation is sufficient to disrupt the β-amyloid fibers and to trigger a gel-to-sol transition at macroscopic scale. This melting of the gel under UV irradiation occurs 25 °C below the temperature needed to melt it by solely using thermal activation. In the dark, a reversible sol-gel transition is observed as the system fully recovers its original microstructure, thus illustrating the possible access to new kinds of motorized materials that can be controlled by advanced out-of-equilibrium thermodynamics.

Thermally Healable Electrolyte-Electrode Interface for Sustainable Quasi-Solid Zinc-ion Batteries.

Quasi-solid zinc-ion batteries using hydrogel electrolytes show great potential in energy storage devices owing to their intrinsic safety, fewer side reactions and wide electrochemical windows. However, the dendrite issues on the zinc anodes cannot be fundamentally eliminated and the intrinsic anode-electrolyte interfacial interspace is rarely investigated. Here, we design a dynamically healable gelatin-based hydrogel electrolyte with a highly reversible sol-gel transition, which can construct a conformal electrode-electrolyte interface and further evolve into a stable solid-solid interface by in situ solidification. The unique helical gelatin chain structure provides a uniform channel for zinc ion transport by the bridging effect of sulfate groups. As a consequence, the dynamically healable interface enables dendrite-free zinc anodes and repeatedly repairs the anode-electrolyte interfacial interspaces by the reversible sol-gel transition of gelatin electrolyte to retain long-lasting protection for sustainable zinc-ion batteries.

Eu3+-Directed Supramolecular Metallogels with Reversible Quadruple-Stimuli Response Behaviors.

Smart luminescent materials that have the ability to reversibly adapt to external environmental stimuli and possess a wide range of responses are continually emerging, which place higher demands on the means of regulation and response sites. Here, europium ions (Eu3+)-directed supramolecular metallogels are constructed by orthogonal self-assembly of Eu3+ based coordination interactions and hydrogen bonding. A new organic ligand (L) is synthesized, consisting of crown ethers and two flexible amide bonds-linked 1,10-phenanthroline moieties to coordinate with Eu3+. Synergistic intermolecular hydrogen bonding in L and Eu3+-L coordination bonding enable Eu3+ and L to self-assemble into shape-persistent 3D coordination metallogels in MeOH solution. The key to success is the utilization of crown ethers, playing dual roles of acting both as building blocks to build L with C2-symmetrical structure, and as the ideal monomer for increasing the energy transfer from L to Eu3+'s excited state, thus maintaining the excellent luminescence of metallogels. Interestingly, such assemblies show K+, pH, F-, and mechano-induced reversible gel-sol transitions and tunable luminescence properties. Above findings are useful in the studies of molecular switches, dynamic assemblies, and smart luminescent materials.

Injectable, shear-thinning, photocrosslinkable, and tissue-adhesive hydrogels composed of diazirine-modified hyaluronan and dendritic polyethyleneimine.

In the present study, we report the first synthesis of diazirine-modified hyaluronic acid (HA-DAZ). In addition, we also produced a precursor polymer solution composed of HA-DAZ and dendritic polyethyleneimine (DPI) that showed strong shear-thinning properties. Furthermore, its viscosity was strongly reduced (i.e., from 5 × 105 mPa s at 10-3 s-1 to 6 × 101 mPa s at 103 s-1), substantially, which enhanced solution injectability using a 21 G needle. After ultraviolet irradiation at 365 nm and 6 mW cm-2, the HA-DAZ/DPI solution achieved rapid gelation, as measured using the stirring method, and its gelation time decreased from 200 s to 9 s as the total concentrations of HA-DAZ and DPI increased. Following UV irradiation, the storage modulus increased from 40 to 200 Pa. In addition, reversible sol-gel transition and self-healing properties were observed even after UV irradiation. This suggests that the HA-DAZ/DPI hydrogel was crosslinked in multiple ways, i.e., via covalent bonding between the diazirine and amine groups and via intermolecular interactions, including hydrogen bonding, electrostatic interactions, and hydrophobic interactions. A lap shear test showed that the HA-DAZ/DPI hydrogel exhibited strong adhesiveness as a fibrin glue following UV irradiation. Finally, the HA-DAZ/DPI hydrogel showed higher tissue reinforcement than fibrin glue in an ex vivo burst pressure test of the porcine esophageal mucosa.

A Sol-Gel Transition and Self-Healing Hydrogel Triggered via Photodimerization of Coumarin.

Reversible chemical covalency provides a path to materials that can degrade and recombine with appropriate stimuli and which can be used for tissue regeneration and repair. However, designing and preparing efficient and quickly self-healing materials has always been a challenge. The preparation strategies of photoresponsive gels attract a lot of attention due to their precise spatial and temporal control and their predetermined response to light stimulation. In this work, the linear copolymer PAC was synthesized via precipitation polymerization of acrylic acid and 7-(2-acrylate-ethoxylated)-4-methylcoumarin. The coumarin groups on the copolymer PAC side chains provide a reversible chemical cross-linking via photostimulation, which achieves reversible regulation of the gel network structure. The concentration of 18 wt% PAC solution produces gelation under irradiation with 365 nm. In contrast, PAC gel is restored to soluble copolymers under irradiation with 254 nm. Meanwhile, the mechanical and self-healing properties of the gel were also explored. It is demonstrated that the cracks of the gel can be repaired simply, quickly, and efficiently. Furthermore, the PAC copolymer shows an excellent adhesion property based on the reversible sol-gel transition. Thus, the PAC gel has considerable potential for applications in engineering and biomedical materials.

Motorized Photomodulator: Making A Non-photoresponsive Supramolecular Gel Switchable by Light.

Introducing photo-responsive molecules offers an attractive approach for remote and selective control and dynamic manipulation of material properties. However, it remains highly challenging how to use a minimal amount of photo-responsive units to optically modulate materials that are inherently inert to light irradiation. Here we show the application of a light-driven rotary molecular motor as a "motorized photo-modulator" to endow a typical H-bond-based gel system with the ability to respond to light irradiation and create a reversible sol-gel transition. The key molecular design feature is the introduction of a minimal amount (2 mol %) of molecular motors into the supramolecular network as photo-switchable non-covalent crosslinkers. Advantage is taken of the subtle interplay of the large geometry change during photo-isomerization of the molecular motor guest and the dynamic nature of a supramolecular gel host system. As a result, a tiny amount of molecular motors is enough to switch the mechanical modulus of the entire supramolecular systems. This study proves the concept of designing photo-responsive materials with minimum use of non-covalent light-absorbing units.

Countercation Engineering of Graphene-Oxide Nanosheets for Imparting a Thermoresponsive Ability.

Graphene-oxide (GO) nanosheets, which are oxidized derivatives of graphene, are regarded as promising building blocks for functional soft materials. Especially, thermoresponsive GO nanosheets have been widely employed to develop smart membranes/surfaces, hydrogel actuators, recyclable systems, and biomedical applications. However, current synthetic strategies to generate such thermoresponsive GO nanosheets have exclusively relied on the covalent or non-covalent modification of their surfaces with thermoresponsive polymers, such as poly(N-isopropylacrylamide). To impart a thermoresponsive ability to GO nanosheets themselves, we focused on the countercations of the carboxy and acidic hydroxy groups on the GO nanosheets. In this study, we established a general and reliable method to synthesize GO nanosheets with target countercations and systematically investigated their effects on thermoresponsive behaviors of GO nanosheets. As a result, we discovered that GO nanosheets with Bu4N+ countercations became thermoresponsive in water without the use of any thermoresponsive polymers, inducing a reversible sol-gel transition via their self-assembly and disassembly processes. Owing to the sol-gel transition capability, the resultant dispersion can be used as a direct writing ink for constructing a three-dimensionally designable gel architecture of the GO nanosheets. Our concept of "countercation engineering" can become a new strategy for imparting a stimuli-responsive ability to various charged nanomaterials for the development of next-generation smart materials.

In situ forming mesoporous polydopamine nanocomposite thermogel for combined chemo-photothermal therapy of intraocular cancer

Intraocular cancers such as retinoblastoma and uveal melanoma will induce severe vision loss or even death. Herein, a versatile nanocomposite thermogel based on hexanoyl glycol chitosan (HGC) and mesoporous polydopamine nanoparticles (MPDA NPs) was designed for potential use as an intraocular “drug depot” for the treatment of intraocular tumors. The integrated HGC-MPDA thermogel showed reversible sol-gel transition property as well as injectable and in-situ gelation abilities. The incorporated MPDA NPs endowed the thermogel with outstanding NIR laser-based photothermal conversion ability and enabled NIR light-controlled drug release. Moreover, in vitro study revealed that drug-loaded thermogel (HGC-MPDA@DOX) with the aid of 808 nm laser irradiation possessed superior anticancer effect than any single treatment via synergistic chemo-photothermal therapy. The present study demonstrated that HGC-MPDA could serve as a multifunctional platform for sustained and NIR light-responsive intravitreal drug delivery, avoiding repetitive injection, and the localized chemo-photothermal therapy provides a promising strategy against intraocular tumors.

Polyimide solution with reversible sol-gel transition by construction of dynamic π-π stacking

Constructing fully rigid chain polyimides with reversible sol-gel/gel-sol transition is significant for developing high-performance and functional materials. π-π stacking, a typical weak interaction, has attracted great interest in producing functional gels, but less has been reported in polyimide organogels. This work developed new polyimide organogels using π-π interactions by incorporating bisbenzoxazole moieties with fully coplanar structures in polyimides. The reversible sol-gel transition behavior with temperature and strain response was systematically studied using rheological methods. DFT simulations, temperature-dependent NMR, UV–Vis, and fluorescence spectroscopy results confirmed the existence of the dynamic π-π interactions in polyimides. Based on the success, we further combined sol-gel methods and non-solvent phase separation methods to prepare a new type of nanofiltration (NF) membranes. The resulting NF membranes showed a higher rejection of methylene blue (rejections of 99.6%) and a good permeability of sodium salt (rejections of 5.1–7.7%), showing great promise for selective filtration of industrial dye wastewater.

Organic‒inorganic semi-interpenetrating networks with orthogonal light- and magnetic-responsiveness for smart photonic gels

Living matter has the ability to perceive multiple stimuli and respond accordingly. However, the integration of multiple stimuli-responsiveness in artificial materials usually causes mutual interference, which makes artificial materials work improperly. Herein, we design composite gels with organic‒inorganic semi-interpenetrating network structures, which are orthogonally responsive to light and magnetic fields. The composite gels are prepared by the co-assembly of a photoswitchable organogelator (Azo-Ch) and superparamagnetic inorganic nanoparticles (Fe3O4@SiO2). Azo-Ch assembles into an organogel network, which shows photoinduced reversible sol-gel transitions. In gel or sol state, Fe3O4@SiO2 nanoparticles reversibly form photonic nanochains via magnetic control. Light and magnetic fields can orthogonally control the composite gel because Azo-Ch and Fe3O4@SiO2 form a unique semi-interpenetrating network, which allows them to work independently. The orthogonal photo- and magnetic-responsiveness enables the fabrication of smart windows, anti-counterfeiting labels, and reconfigurable materials using the composite gel. Our work presents a method to design orthogonally stimuli-responsive materials.

Thermoresponsive nanocomposite hydrogels based on Gelatin/poly (N–isopropylacrylamide) (PNIPAM) for controlled drug delivery

This study is focused on developing thermoresponsive nanocomposite hydrogels based on gelatin by the incorporation of a thermoresponsive polymer, poly (N–isopropylacrylamide) (PNIPAM), that can undergo a sol–gel transition by physiological conditions with the aim of minimally invasive drug delivery. Various hybrid nanocomposite hydrogels consisting of gelatin as the matrix and acetaminophen–loaded PNIPAM nanoparticles were prepared using response surface methodology through the design of experiment software. PNIPAM nanoparticles were synthesized using the photopolymerization technique. Nanocomposite hydrogels were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), swelling capacity, hydrolytic degradation, antibacterial and cell viability measurements, and release studies. Narrow size distribution of PNIPAM nanoparticles was observed, indicating successful polymerization and good size control by the reactor size. The system exhibited a reversible sol–gel transition around 37 °C, close to body temperature. The swelling capacity of nanocomposite hydrogel was found to decrease above the phase transition temperature. Drug–loaded gelatin–PNIPAM nanocomposite hydrogels indicated the antibacterial activity against the gram–positive and gram–negative species. Hydrogels with a lower ratio of PNIPAM to gelatin demonstrated a lower amount, more uniform, and delayed release compared to the other hydrogels, indicating good potential for drug delivery targeted purposes.

Divergent approach to nanoscale glycomicelles and photo-responsive supramolecular glycogels. Implications for drug delivery and photoswitching lectin affinity.

The field of stimuli-responsive supramolecular biomaterials has rapidly advanced in recent years, with potential applications in diverse areas such as cancer theranostics, tissue engineering, and catalysis. However, designing molecular materials that exhibit predetermined hierarchical self-assembly to control the size, morphology, surface chemistry, and responsiveness of the final nanostructures remains a significant challenge. In this study, we present a divergent synthetic approach for the fabrication of spherical micelles and functional 1D-glyconanotube-based photoresponsive gels from structurally related diazobenzene/diacetylene glycolipids. The resulting nanostructures were characterized using NMR, TEM, and SEM, confirming the formation of spherical and tubular nanostructures in both the gel and solution states. Upon UV irradiation, a reversible gel-sol transition was observed, resulting from the photoswitching of the azobenzene unit from the stretched trans form to the compact, metastable cis form. Our gels were shown to enable spatio-temporal control of the adhesion and release of the lectin Concanavalin A, demonstrating potential use as regenerable biomaterials to fight against infections with toxins and pathogens. Additionally, our micelles and gels were evaluated as nanocontainers for loading and controlled release of hydrophobic dyes and antitumoural agents, suggesting their possible use as smart theranostic drug delivery systems.

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.