Fabrication of Poly(ionic liquid) Hydrogels Incorporating Liquid Metal Microgels for Enhanced Synergistic Antifouling Applications

Hydrogels are ideal for antifouling materials due to their high hydrophilicity and low adhesion properties. Herein, poly(ionic liquid) hydrogels integrated with zwitterionic copolymer-functionalized gallium-based liquid metal (PMPC-GLM) microgels were successfully prepared by a one-pot reaction. Poly(ionic liquid) hydrogels (IL-Gel) were obtained by chemical cross-linking the copolymer of ionic liquid, acrylic acid, and acrylamide, and the introduction of ionic liquid (IL) significantly increased the cross-linking density; this approach consequently enhanced the mechanical and antiswelling properties of the hydrogels. The swelling ratio of IL-Gel decreased eight times compared to the original hydrogels. PMPC-GLM microgels were prepared through grafting the zwitterionic polymer PMPC onto the GLM nanodroplet surface, which exhibited efficient antifouling performance attributed to the bactericidal effect of Ga3+ and the antibacterial effect of the zwitterionic polymer layer PMPC. Based on the synergistic effect of PMPC-GLM microgels and IL, the composite hydrogels PMPC-GLM@IL-Gel not only exhibited excellent mechanical and antiswelling properties but also showed outstanding antibacterial and antifouling properties. Consequently, PMPC-GLM@IL-Gel hydrogels achieved inhibition rates of over 90% against bacteria and more than 85% against microalgae.

4D Multimaterial Printing of Soft Actuators with Spatial and Temporal Control

Soft actuators (SAs) are devices which can interact with delicate objects in a manner not achievable with traditional robotics. While it is possible to design a SA whose actuation is triggered via an external stimulus, the use of a single stimulus creates challenges in the spatial and temporal control of the actuation. Herein, a 4D printed multimaterial soft actuator design (MMSA) whose actuation is only initiated by a combination of triggers (i.e., pH and temperature) is presented. Using 3D printing, a multilayered soft actuator with a hydrophilic pH-sensitive layer, and a hydrophobic magnetic and temperature-responsive shape-memory polymer layer, is designed. The hydrogel responds to environmental pH conditions by swelling or shrinking, while the shape-memory polymer can resist the shape deformation of the hydrogel until triggered by temperature or light. The combination of these stimuli-responsive layers allows for a high level of spatiotemporal control of the actuation. The utility of the 4D MMSA is demonstrated via a series of cargo capture and release experiments, validating its ability to demonstrate active spatiotemporal control. The MMSA concept provides a promising research direction to develop multifunctional soft devices with potential applications in biomedical engineering and environmental engineering.

Ultra-soft and highly stretchable tissue-adhesive hydrogel based multifunctional implantable sensor for monitoring of overactive bladder

A highly stretchable and tissue-adhesive multifunctional sensor based on structurally engineered islets embedded in ultra-soft hydrogel is reported for monitoring of bladder activity in overactive bladder (OAB) induced rat and anesthetized pig. The use of hydrogel yielded a much lower sensor modulus (1 kPa) compared to that of the bladder (300 kPa), while the strong adhesiveness of the hydrogel (adhesive strength: 260.86 N/m) allowed firm attachment onto the bladder. The change in resistance of printed liquid metal particle thin-film lines under strain were used to detect bladder inflation and deflation; due to the high stretchability and reliability of the lines, surface strains of 200% could be measured repeatedly. Au electrodes coated with Platinum black were used to detect electromyography (EMG). These electrodes were placed on structurally engineered rigid islets so that no interfacial fracture occurs under high strains associated with bladder expansion. On the OAB induced rat, stronger signals (change in resistance and EMG root-mean-square) were detected near intra-bladder pressure maxima, thus showing correlation to bladder activity. Moreover, using robot-assisted laparoscopic surgery, the sensor was placed onto the bladder of an anesthetized pig. Under voiding and filling, bladder strain and EMG were once again monitored. These results confirm that our proposed sensor is a highly feasible, clinically relevant implantable device for continuous monitoring OAB for diagnosis and treatment.

In Situ Nanoarchitectonics of a MOF Hydrogel: A Self-Adhesive and pH-Responsive Smart Platform for Phototherapeutic Delivery

Metal-organic frameworks (MOFs) have dramatically changed the fundamentals of drug delivery, catalysis, and gas storage as a result of their porous geometry, controlled architecture, and ease of postsynthetic modification. However, the biomedical applications of MOFs still remain a less explored area due to the constraints associated with handling, utilizing, and site-specific delivery. The major drawbacks associated with the synthesis of nano-MOFs are related to the lack of control over particle size and inhomogeneous dispersion during doping. Therefore, a smart strategy for the in situ growth of a nano-metal-organic framework (nMOF) has been devised to incorporate it into a biocompatible polyacrylamide/starch hydrogel (PSH) composite for therapeutic applications. In this study, the post-treatment of zinc metal ion cross-linked PSH with the ligand solution generated the nZIF-8@PAM/starch composites (nZIF-8, nano-zeolitic imidazolate framework-8). The ZIF-8 nanocrystals thus formed have been found to be evenly dispersed throughout the composites. This newly designed nanoarchitectonics of an MOF hydrogel was found to be self-adhesive, which also exhibited improved mechanical strength, a viscoelastic nature, and a pH-responsive behavior. Taking advantage of these properties, it has been utilized as a sustained-release drug delivery platform for a potential photosensitizer drug (Rose Bengal). The drug was initially diffused into the in situ hydrogel, and then the entire scaffold was analyzed for its potential in photodynamic therapy against bacterial strains such as E. coli and B. megaterium. The Rose Bengal loaded nano-MOF hydrogel composite exhibited remarkable IC₅₀ values within the range of 7.37 ± 0.04 and 0.51 ± 0.05 μg/mL for E. coli and B. megaterium. Further, reactive oxygen species (ROS) directed antimicrobial potential was validated using a fluorescence-based assay. This smart in situ nanoarchitectonics hydrogel platform can also serve as a potential biomaterial for topical treatment including wound healing, lesions, and melanoma.

A bio-inspired, ultra-tough, high-sensitivity, and anti-swelling conductive hydrogel strain sensor for motion detection and information transmission

Conductive hydrogels are excellent candidates for the next-generation wearable materials and are being extensively investigated for their potential use in health monitoring devices, human-machine interfaces, and other fields. However, their relatively low mechanical strength and performance degradation due to swelling have presented challenges in their practical application. Inspired by the multiscale heterogeneous architecture of biological tissue, a dynamic cross-linked, ultra-tough, and high-sensitivity hydrogel with a swelling resistance characteristic was fabricated by the principle of multiple non-covalent interaction matching and a step-by-step construction strategy. A heterogeneous structure was constructed by the combination of a 'soft' hydrophobic-conjugated micro-region structural domain with inter/intra-molecular hydrogen bonding and π-π stacking along with 'rigid' cross-linking via strong ionic coordination interactions. Reversible cross-linking synergies and variations in the content of rigid and flexible components guaranteed the hydrogel to undergo flexible and efficient modulation of the structures and gain excellent mechanics, including elongation at break (>2000%), toughness (∼60 MJ m^-3), and recovery (>88%). Notably, hydrogels displayed good anti-swelling properties even in solutions with different pH (pH 2-11) and solvents. Moreover, the hydrogel further exhibited fast response (47.4 ms) and high sensitivity due to the presence of dynamic ions (Fe³⁺, Na⁺, and Cl^-); therefore, it was assembled into a sensor to detect various human motions and used as a signal transmitter for the encryption and decryption of information according to Morse code. This study provides basis for the development of a variety of robust and flexible conductive hydrogels with multifunctional sensing applications in next-generation wearable devices.

From Supramolecular Hydrogels to Multifunctional Carriers for Biologically Active Substances

Supramolecular hydrogels are 3D, elastic, water-swelled materials that are held together by reversible, non-covalent interactions, such as hydrogen bonds, hydrophobic, ionic, host-guest interactions, and metal-ligand coordination. These interactions determine the hydrogels' unique properties: mechanical strength; stretchability; injectability; ability to self-heal; shear-thinning; and sensitivity to stimuli, e.g., pH, temperature, the presence of ions, and other chemical substances. For this reason, supramolecular hydrogels have attracted considerable attention as carriers for active substance delivery systems. In this paper, we focused on the various types of non-covalent interactions. The hydrogen bonds, hydrophobic, ionic, coordination, and host-guest interactions between hydrogel components have been described. We also provided an overview of the recent studies on supramolecular hydrogel applications, such as cancer therapy, anti-inflammatory gels, antimicrobial activity, controlled gene drug delivery, and tissue engineering.

Constructing Co-N-C Catalyst via a Double Crosslinking Hydrogel Strategy for Enhanced Oxygen Reduction Catalysis in Fuel Cells

Exploiting platinum-group-metal (PGM)-free electrocatalysts with remarkable activity and stability toward oxygen reduction reaction (ORR) is of significant importance to the large-scale commercialization of proton exchange membrane fuel cells (PEMFCs). Here, a high-performance and anti-Fenton reaction cobalt-nitrogen-carbon (Co-N-C) catalyst is reported via employing double crosslinking (DC) hydrogel strategy, which consists of the chemical crosslinking between acrylic acid (AA) and acrylamide (AM) copolymerization and metal coordinated crosslinking between Co²⁺ and P(AA-AM) copolymer. The resultant DC hydrogel can benefit the Co²⁺ dispersion via chelated Co-N/O bonds and relieve metal agglomeration during the subsequent pyrolysis, resulting in the atomically dispersed Co-Nx/C active sites. By optimizing the ratio of AA/AM, the optimal P(AA-AM)(5-1)-Co-N catalyst exhibits a high content of nitrogen doping (12.36 at%) and specific surface area (1397 m² g^-1 ), significantly larger than that of the PAA-Co-N catalyst (10.59 at%/746 m² g^-1 ) derived from single crosslinking (SC) hydrogel. The electrochemical measurements reveal that P(AA-AM)(5-1)-Co-N possesses enhanced ORR activity (half-wave potential (E_1/2 ) ≈0.820 V versus the reversible hydrogen electrode (RHE)) and stability (≈4 mV shift in E_1/2 after 5000 potential cycles in 0.5 m H₂ SO₄ at 60 ºC) relative to PAA-Co-N, which is higher than most Co-N-C catalysts reported so far.

Waxy rice amylopectin towards stretchable elastic conductive hydrogel for human motion detection

Dynamic hydrogen-bonding interaction brings waxy rice amylopectin element into polyacrylamide network to elicit a stretchable elastic composite hydrogel for sensing application.

Stereocomplexation of Poly(Lactic acid) and Chemical Crosslinking of Ethylene Glycol Dimethacrylate (EGDMA) Double-Crosslinked Temperature/pH Dual Responsive Hydrogels

Physical crosslinking and chemical crosslinking were used to further improve the mechanical properties and stability of the gel. A temperature/pH dual sensitive and double-crosslinked gel was prepared by the stereo-complex of HEMA-PLLA20 and HEMA-PDLA20 as a physical crosslinking agent, ethylene glycol dimethacrylate (EGDMA) as a chemical crosslinking agent, and azodiisobutyronitrile (AIBN) as an initiator for free radical polymerization. This paper focused on the performance comparison of chemical crosslinked gel, a physical crosslinked gel, and a dual crosslinked gel. The water absorption, temperature, and pH sensitivity of the three hydrogels were studied by a scanning electron microscope (SEM) and swelling performance research. We used a thermal analysis system (TGA) and dynamic viscoelastic spectrometer to study thermal properties and mechanical properties of these gels. Lastly, the in vitro drug release behavior of double-crosslinked hydrogel loaded with doxorubicin under different conditions was studied. The results show that the double-crosslinked and temperature/pH dual responsive hydrogels has great mechanical properties and good stability.

Effects of surfactant and ionic concentration on properties of dual physical crosslinking self-healing hydrogels by hydrophobic association and ionic interactions

Two kinds of dual crosslinking hydrogels have adjustable mechanical properties, self-healing and self-recovery performances.

Influence of Sodium Salts on the Swelling and Rheology of Hydrophobically Cross-linked Hydrogels Determined by QCM-D

Hydrophobically modified copolymers provide a versatile platform of hydrogel materials for diverse applications, but the influence of salts on the swelling and material properties of this class of hydrogels has not been extensively studied. Here, we investigate model hydrogels with three different sodium salts with anions chosen from the classic Hofmeister series to determine how these counterions influence the swelling and mechanical properties of neutral hydrogels. The gel chosen was based on a statistical copolymer of dimethylacrylamide and 2-(N-ethylperfluorooctane sulfonamido) ethyl acrylate (FOSA). Our measurements utilize a quartz crystal microbalance with dissipation (QCM-D) to quantify both swelling and rheological properties of these gels. We find that a 1 mol/L solution of Na₂SO₄, corresponding to a kosmotropic anion, leads to nearly a 2.6-fold gel deswelling and correspondingly, the complex modulus increases by an order of magnitude under these solution conditions. In contrast, an initial increase in swelling and then a swelling maximum is observed for a 0.02 mol/L concentration in the case of a chaotropic anion, NaClO₄, but the changes in the degree of gel swelling in this system are not directly correlated with changes in the gel shear modulus. The addition of NaBr, an anion salt closer to the middle of the chaotropic to kosmotropic range, leads to hydrogel deswelling where the degree of deswelling and the shear modulus are both nearly independent of salt concentration. Overall, the observed trends are broadly consistent with more kosmotropic ions causing diminished solubility ("salting out") and strongly chaotropic ions causing improved solubility ("salting in"), a trend characteristic of the Hoffmeister series governing the solubility of many proteins and synthetic water-soluble polymers, but trends in the shear stiffness with gel swelling are clearly different from those normally observed in chemically cross-linked gels and are correspondingly difficult to interpret. The salt specificity of swelling and mechanical properties of nonionic hydrogels is important for any potential application in which a wide range of salt concentrations and types are encountered.

Self-healing and tough GO-supported hydrogels preparedviasurface-initiated ATRP and photocatalytic modification

Hydrogels with the properties of self-healing, toughness, stiffness and strength have great potential for use in smart materials.