Zwitterionic Hydrogels Research Articles

Synthesis and characterizations of zwitterionic copolymer hydrogels with excellent lubrication behavior

Abstract Various studies on hydrogel applications as cartilage substitutes and artificial joints have been previously conducted. In this study, a copolymer hydrogel comprising zwitterionic sulfobetaine methacrylate (SBMA) and 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers is synthesized in an aqueous system via free-radical polymerization. A P(MPC-co-SBMA) copolymer hydrogel network is formed via the additional polymerization of the alkane carbon–carbon double bond from the combination of MPC and SBMA polymer chains using ethylene glycol dimethacrylate (EGDMA) as the crosslinker. Introduction of MPC in the PSBMA hydrogel under water lubrication improved the compressive stress by almost double and considerably lowered the coefficient of friction (COF) to approximately 0.011. This phenomenon was attributed to the fact that MPC could intertwine with SBMA to increase the crosslink density of the hydrogel and preferentially adhere to the water to reduce the adhesion of the contact between hydrogels, leading to an intertwined copolymer network structure with excellent load-bearing capacity and superior hydration lubrication capability. This study might provide potentially useful information relating to cartilage replacement applications requiring high mechanical strength and excellent friction behavior.

Highly Stretchable, Adhesive, and Mechanical Zwitterionic Nanocomposite Hydrogel Biomimetic Skin.

The artificial skin-like stretchable ionic sensor device usually requires a synergistic effect of reliable adhesion between human machine interface, reasonable mechanical strength, and visually displayable transparency. A plant-inspired zwitterionic hydrogel was prepared through rapid UV initiation in the existence of cellulose nanocrystals as physically crosslinker and reinforcing agent. The resulting transparent zwitterionic nanocomposite hydrogel successfully brings the synergistic advantages of robust adhesive strength between diversified substrates such as skins, plastics, glass, and steels with remarkable mechanical properties of a superior stretchability over 1000% strain, a mechanical tensile strength up to 0.61 MPa, and compressive strength up to 7.5 MPa, manifesting in superior ionic transport performance, simultaneously. Furthermore, the zwitterionic nanocomposite hydrogel was fabricated as a wearable compliant stretchable pressure-strain sensor in the modality of the skin-adhesive patch to be sensitive to human motion such as finger touch and speech recognition for personal healthcare of patient sensory rebuilding and physiological data acquisition. It maintains compressive cycling sensibility at diverse pressure during 0.5, 1.0, and 1.5 Hz, respectively. The multifunctional zwitterionic nanocomposite hydrogel could also be assembled into flexible electrical devices such as luminescent display and information transfer between human and robot communication for mechanosensory electronics and artificial intelligence.

Expansion of primitive human hematopoietic stem cells by culture in a zwitterionic hydrogel

The ability to expand hematopoietic stem and progenitor cells (HSPCs) ex vivo is critical to fully realize the potential of HSPC-based therapies. In particular, the application of clinically effective therapies, such as cord blood transplantation, has been impeded because of limited HSPC availability. Here, using 3D culture of human HSPCs in a degradable zwitterionic hydrogel, we achieved substantial expansion of phenotypically primitive CD34+ cord blood and bone-marrow-derived HSPCs. This culture system led to a 73-fold increase in long-term hematopoietic stem cell (LT-HSC) frequency, as demonstrated by limiting dilution assays, and the expanded HSPCs were capable of hematopoietic reconstitution for at least 24 weeks in immunocompromised mice. Both the zwitterionic characteristics of the hydrogel and the 3D format were important for HSPC self-renewal. Mechanistically, the impact of 3D zwitterionic hydrogel culture on mitigating HSPC differentiation and promoting self-renewal might result from an inhibition of excessive reactive oxygen species (ROS) production via suppression of O2-related metabolism. HSPC expansion using zwitterionic hydrogels has the potential to facilitate the clinical application of hematopoietic-stem-cell therapies.

Probing Surface Hydration and Molecular Structure of Zwitterionic and Polyacrylamide Hydrogels.

A hydrogel is a hydrophilic cross-linked polymer network which can contain a large amount of water. Hydrogels with distinguished interfacial physical toughness were analyzed for their potential application as antifouling coating materials, utilizing sum frequency generation (SFG) spectroscopy as the interfacial analytical technique. The surface structures of one sulfobetaine (SBMA) zwitterionic hydrogel (ZWHG) and two polysaccharide hydrogels (PHGs) were probed in air; their interfacial structures with silica were examined using SFG in water and protein solutions, respectively. Both ZWHG and PHGs interfaces in water were dominated by strongly hydrogen-bonded water molecules, but the bonding strength associated with ZWHG was much stronger. Although all hydrogels experienced interfacial change in the presence of protein solutions, after cleaning, the zwitterionic hydrogel interface recovered almost completely while the other two hydrogels were subject to irreversible protein adsorption. Additionally, orientational analysis of ZWHG methyl groups in water was conducted and related to the superior hydrogen-bonding strength of water molecules at the ZWHG interface. The interfacial structures of hydrogel materials probed by SFG can be correlated to their antifouling properties. This research highlighted the critical role that hydrogen-bonding strength of interfacial water molecules play for antifouling applications.

A Modular and Practical Synthesis of Zwitterionic Hydrogels through Sequential Amine-Epoxy "Click" Chemistry and N-Alkylation Reaction.

In this work, the amine-epoxy “click” reaction is shown to be a valuable general tool in the synthesis of reactive hydrogels. The practicality of this reaction arises due to its catalyst-free nature, its operation in water, and commercial availability of a large variety of amine and epoxide molecules that can serve as hydrophilic network precursors. Therefore, hydrogels can be prepared in a modular fashion through a simple mixing of the precursors in water and used as produced (without requiring any post-synthesis purification step). The gelation behavior and final hydrogel properties depend upon the molecular weight of the precursors and can be changed as per the requirement. A post-synthesis modification through alkylation at the nitrogen atom of the newly formed β-hydroxyl amine linkages allows for functionalizing the hydrogels. For example, ring-opening reaction of cyclic sulfonic ester gives rise to surfaces with a zwitterionic character. Finally, the established gelation chemistry can be combined with soft lithography techniques such as micromolding in capillaries (MIMIC) to obtain hydrogel microstructures.

Development of Nanoporous Polyurethane Hydrogel Membranes for Cell Encapsulation

Cell encapsulation for treatment of diseases like type 1 diabetes (T1D) has great potential when used in combination with development of insulin responsive beta cells. However, for translation of this therapy into clinical practice, there is a need for suitable encapsulation devices. Here, we report development of polyurethane-zwitterionic acrylate double network-based membranes for macro device-based cell encapsulation. Polyurethane hydrogels with 60 to 90% water content (WC) were evaluated for permeability and hydrogels with 80 and 90% WC were found to have highest permeability. Structural characterization of these hydrogels’ samples prepared cryogenically by scanning electron microscopy (cryo-SEM) revealed that 90% WC hydrogels were nanoporous with large interconnected pores. Tuning of porosity and structure was achieved by blending of hydrogels with varying WC resulting in pores of ~ 200 nm size. These membranes supported viability of encapsulated cells after removal of cytotoxic leachables by ethanol treatment. Double network formation was performed by UV polymerization and incorporation of zwitterionic groups was confirmed by ATR and WC of hydrogels. Varying of zwitterion type is allowed for tuning of WC of hydrogels. Gene expression of RAW 264.7 macrophages on exposure to the hydrogels found the zwitterionic double network hydrogels to be less stimulating than the bare hydrogel. To determine translational potential of the hydrogel, sterilization of the hydrogels using supercritical carbon dioxide was evaluated. Survivor enumeration testing revealed that the kill rate for the process ~ 1 log10 per 8 min and 2-h treatment is sufficient for sterility assurance level (SAL) of 10−6. Thus, we have developed hydrogel polyurethane membranes suitable for cell encapsulation in macro devices. We want to develop a device for cell encapsulation which is needed for treating diseases like T1D. In these devices, cells will be loaded and implanted in the body. These encapsulated cell secretions would provide the function of various endocrine organs. We have developed a hydrogel-based nanoporous membrane which would hold the cells and allow for exchange of nutrients and cell secretions. After the development of membrane, future studies will focus on evaluating the immune response to the hydrogel as well as long term delivery of immune modulatory drugs to prevent fibrosis. Various drug encapsulation and delivery designs will be evaluated for controlled localized delivery of the drugs. The optimum combination would then be combined with the hydrogels device and test their efficacy in regulating cell viability and immune response in animal models.

Zwitterionic Hydrogel Incorporated Graphene Oxide Nanosheets with Improved Strength and Lubricity.

Graphene oxide (GO) has been evaluated as a multifunctional cross-linker or reinforcement agent in composite hydrogels. In this study, a nanocomposite hydrogel consisting of GO nanosheets and zwitterionic poly(sulfobetaine methacrylate) (PSBMA) was synthesized in an aqueous system via chemical and physical cross-linking effects. GO nanosheets were well dispersed in the hydrogels and effectively cross-linked into the sulfobetaine methacrylate (SBMA) polymer chains through the electrostatic interactions. The PSBMA hydrogel exhibited a significant enhancement in the compressive stress (close to a 5-fold increase) and a remarkablereduction in the coefficient of friction (COF) (corresponding to a decline of 52-76%) after the embedding of GO nanosheets. These improvements indicate the existence of synergetic interaction and good compatibility between GO nanosheets and the PSBMA hydrogel matrix, which results in an intertwined network structure with higher load-bearing capacity and better lubrication properties. This study provides potential in the development of new graphene-polymer composites, which is beneficial for cartilage replacement with high mechanical properties and excellent lubrication characteristics.

Facile synthesis of macroporous zwitterionic hydrogels templated from graphene oxide-stabilized aqueous foams

HypothesisConventional strategies based on emulsion templates to produce porous materials are complicated and not environmental-friendly, thus inspiring a facile and novel approach via polymerization of aqueous foams. Graphene oxide (GO) has been proved as a very efficient Pickering stabilizer for oil-in-water or water-in-oil emulsions, however, it has rarely (if any) been used to stabilize aqueous foams. It is of high interest to prepare GO-stabilized aqueous foams and subsequent porous hydrogels after polymerization of the aqueous phase. ExperimentsGO was slightly hydrophobized with cetyltrimethylammonium bromide (CTAB) and then used to stabilize aqueous foams containing a water-soluble monomer, N-(3-Sulfopropyl)-N-methacroyloxyethyl-N,N-dimethylammonium betaine (SBMA). After polymerizing the aqueous phase, macroporous zwitterionic hydrogels (PSBMA) were prepared. The pore morphology of macroporous PSBMA were observed by a field-emission scanning electron microscope. FindingsThe wettability of modified GO by both water and air, indeed has a significant influence on the air bubble size and size distribution as well as the pore size of resulting macroporous PSBMA hydrogels. The pore size and pore interconnectivity of the hydrogels can be tailored by simply varying the surface property and concentration of GO in water. PSBMA hydrogels exhibit a pronounced uptake of aqueous NaCl solutions and efficient separation of oil-in-water emulsions.

Highly stretchable, ionic conductive and self‐recoverable zwitterionic polyelectrolyte‐based hydrogels by introducing multiple supramolecular sacrificial bonds in double network

ABSTRACTZwitterionic hydrogels have been explored for applications in electrochemical devices very recently due to their high water retention ability and interesting electrochemical properties. The use of zwitterionic hydrogels in devices requires them tough and recoverable or healable from fatigue damage. Herein, a double network zwitterionic hydrogel contains a reversible noncovalent interaction crosslinked polyvinyl alcohol (PVA) first network, together with a covalent/noncovalent hybrid crosslinked acrylamide and sulfobetaine methacrylate copolymer (P(AM‐co‐SBMA)) second network, was fabricated by a simple two‐steps methods of copolymerization and freezing/thawing. The reversible hydrogen bonds, crystalline domain, and electrostatic interactions in the double networks work as sacrificial bonds to dissipate energy and toughen the materials when hydrogel deforms. The broken bonds can reform upon unloading endowing the recovery of hydrogels' properties with the assistance of the elastic covalent network. The optimal hydrogels are highly stretchable (fracture strain 970%), tough (fracture toughness 693 kJ m−3), rapidly recoverable (65% toughness recovery and 75% stiffness recovery after resting 5 min at room temperature) and with widely tunable mechanical properties by multibond crosslinking. Meanwhile, the zwitterionic counterions of SBMA moieties endow the tough and recoverable hydrogels extremely high intrinsic ionic conductivities (7.49 S m−1) at room temperature. This work not only provides a simple strategy for fabricating tough and recoverable zwitterionic hydrogels but also demonstrates multifunctional properties of the zwitterionic hydrogels, which possess a great potential to fulfill flexible devices applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47783.

Biofouling Control Using Nano Silicon Dioxide Reinforced Mixed-Charged Zwitterionic Hydrogel in Aquaculture Cage Nets.

Biofouling in aquaculture cages negatively affects the farm productivity, and it requires huge sums of money and labor for its management. A superhydrophilic pseudozwitterionic hydrogel, N-isopropylacrylamide (NIPA) + [2-(methacryloyloxy)ethyl]trimethylammonium (TMA) + 3-sulfopropyl methacrylate (SA) copolymer, is considered as a potential antifouling agent. The present study aimed to synthesize a nano silicon oxide reinforced NIPA-TMA-SA mixed-charged zwitterionic hydrogel over polyaniline-coated polyethylene aquaculture cage nets through the in situ microwave reaction and to test its biofouling resistance. The study highlighted the formation of stable coating over polyethylene, four different treatments, and their effective inhibition of fouling compared with the untreated one. Six month's immersions of treated nettings in the estuarine environments demonstrated that the biofouling inhibition by nano silicon oxide reinforced zwitterionic hydrogel-coated polyethylene was unable to satisfy the industrial standards but made the samples free from hard-shelled fouling organisms compared with untreated controls. More research is needed to improve the quality of the coatings. The mixed-charged zwitterionic hydrogel with nano silicon oxide showed medium hydrophilic nature. Fourier transform infrared, scanning electron microscopy, and spectroscopic evaluation showed the successful formation of hydrogel over the aquaculture cage net. Nano silicon oxide reinforced in the matrix through hydrogen and coordination bonding between NH2 and carbonyl of the polymeric chain, respectively.

Anti-biofouling and functionalizable bioinspired chitosan-based hydrogel coating via surface photo-immobilization

Zwitterionic polymer is a new generation of anti-fouling materials with its good resistance to protein and bacterial adhesion. Constructing the anti-fouling surfaces with zwitterionic polymer has been regarded as an effective approach for improving the biocompatibility and biofunctionality of clinic devices. Herein, we reported a facile approach to construct a biodegradable anti-biofouling and functionalizable hydrogel coating via photo-immobilization using commercial polyethylene terephthalate (PET) films as the substrate, based on zwitterionic glycidyl methacrylate-phosphorylcholine-chitosan (PCCs-GMA). The surface structure and physicochemical properties of zwitterionic PCCs-GMA hydrogel coating were investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM) and static water contact angle measurement, and its functionalizable sites were detected by fluorescence labeling. Compared with the pristine PET and cationic chitosan - GMA and hydroxypropyltrimethyl ammonium chloride chitosan (HTCC) - GMA hydrogel coatings, zwitterionic PCCs-GMA hydrogel coating exhibited excellent biocompatibility, and significantly reduced protein adsorption for three model proteins of fibrinogen, immunoglobulin and lysozyme, repelled platelet adhesion, as well as showed a high resistance to bacterial attachment of Escherichia coli and Staphylococcus aureus and superior anti-fouling properties to MRC-5 cells. The results indicated that photo-immobilized zwitterionic PCCs-GMA hydrogel coating has perspective as a dual functional platform with integrated antifouling and further biofunctional properties for various biomedical applications.

Examination of functional zwitterionic polymer hydrogels based on polypyridinium salt by a convenient cross-linker

In this work, two novel zwitterionic polymer hydrogels (Gel-P4VP-psl (d), Gel-P4VP-bpa (d)) and cationic polymer hydrogels (Gel-P4VP-eb (f)) were prepared for the first time. The differences of functionality between cationic polymer hydrogels and zwitterionic polymer hydrogels were studied fully. The results showed that when the molar quantity ratio of cross-linker/pyridinium unit in Gel-P4VP-psl (d) and Gel-P4VP-bpa (d) was about 0.25:1, they would have proper mechanical property, excellent antibacterial ability and antifouling ability. Correspondingly, the charge quantity ratios of negative charges/positive charges in Gel-P4VP-psl (d) and Gel-P4VP-bpa (d) could be calculated to be 1:2 theoretically. Although Gel-P4VP-eb (f) with only positive charges had strongly antibacterial ability, being lack of negative charges in cationic polymer hydrogels made its antifouling ability disappear completely. Gel-P4VP-psl (d) and Gel-P4VP-bpa (d) have potential in the application of antibacterial and antifouling materials.

Self-healing zwitterionic sulfobetaine nanocomposite hydrogels with good mechanical properties.

The development of zwitterionic hydrogels possessing both excellent self-healing and mechanical properties is of great significance. Herein, a class of zwitterionic sulfobetaine nanocomposite hydrogels was prepared by UV-initiated copolymerisation of zwitterionic sulfobetaine monomer N,N-dimethyl-N-(3-methacrylamidopropyl)-N-(3-sulfopropyl) ammonium betaine (DMAPMAPS) and 2-hydroxyethyl methacrylate (HEMA) in the presence of exfoliated clay platelets uniformly dispersed in an aqueous medium. The effects of the hydrogel compositions, including the DMAPMAPS/HEMA mass ratio and the amount of clay, on the self-healing behaviors and mechanical properties of the nanocomposite hydrogels were investigated. The results indicate that the fabricated zwitterionic sulfobetaine nanocomposite hydrogels can autonomously repair incisions or cracks at ambient temperature without the need for any stimulus and possess excellent mechanical properties.

Zwitterionic poly(sulfobetaine methacrylate) hydrogels with optimal mechanical properties for improving wound healing in vivo.

Zwitterionic hydrogels, as highly hydrated and soft materials, have been considered as promising materials for wound dressing, due to their unique antifouling and mechanical properties. While the viscoelasticity and softness of zwitterionic hydrogels are hypothetically essential for creating adaptive cellular niches, the underlying mechanically regulated wound healing mechanism still remains elusive. To test this hypothesis, we fabricated zwitterionic poly(sulfobetaine methacrylate) (polySBMA) hydrogels with different elastic moduli prepared at different crosslinker contents, and then applied the hydrogels to full-thickness cutaneous wounds in mice. In vivo wound healing studies compared the mechanical cue-induced effects of soft and stiff polySBMA hydrogels on wound closure rates, granulation tissue formation and collagen deposition. Collective results showed that the softer and more viscoelastic hydrogels facilitated cell proliferation, granulation formation, collagen aggregation, and chondrogenic ECM deposition. Such high wound healing efficiency by the softer hydrogels is likely attributed to stress dissipation by expanding the cell proliferation, the up-regulation of blood vessel formation, and the enhanced polarization of M2/M1 macrophages, both of which would provide more oxygen and nutrients for cell proliferation and migration, leading to enhanced wound repair. This work not only reveals a mechanical property-wound healing relationship of zwitterionic polySBMA hydrogels, but also provides a promising candidate and strategy for the next-generation of wound dressings.

Thermosensitive double network of zwitterionic polymers for controlled mechanical strength of hydrogels.

Zwitterionic hydrogels have promising potential as a result of their anti-fouling and biocompatible properties, but they have recently also gained further attention due to their controllable stimuli responses. We successfully synthesized two zwitterionic polymers, poly(2-methacryloyloxyethyl phosphorylcholine) (poly-MPC) and poly(2-(methacryloyloxy)ethyl dimethyl-(3-sulfopropyl)ammonium hydroxide) (poly-DMAPS), which have complementary ionic sequences in their respective zwitterionic side groups and likely form an interpenetrating double network to improve their mechanical strength. The synthesized poly-MPC was blended in a poly-DMAPS matrix (MD gel) and showed high viscosity, while poly-DMAPS was blended in a poly-MPC hydrogel (DM gel) and revealed UCST behavior as the temperature increased. In addition, cross-section images of the MD hydrogel exhibited its compact and uniform structure, while the DM gel was found to exhibit a porous micro-structure with clear boundaries. The results explained the low viscosity of the DM gel, which was also confirmed via 3D Raman mapping. To sum up, the preliminary data demonstrated that binary zwitterionic hydrogels have thermosensitive mechanical properties, promoting further bio-applications in the future, such as in wound healing.

Optical stereolithography of antifouling zwitterionic hydrogels.

This paper reports the rapid 3D printing of tough (toughness, UT, up to 141.6 kJ m-3), highly solvated (φwater∼ 60 v/o), and antifouling hybrid hydrogels for potential uses in biomedical, smart materials, and sensor applications, using a zwitterionic photochemistry compatible with stereolithography (SLA). A Design of Experiments (DOE) framework was used for systematically investigating the multivariate photochemistry of SLA generally and, specifically, to determine an aqueous SLA system with an additional zwitterionic acrylate, which significantly increases the gelation rate, and the resilience of the resulting hybrid hydrogels relative to an equivalent non-ionic polyacrylamide hydrogel. Specifically, the resulting zwitterionic hybrid hydrogels (Z-gels) can be tuned over a large range of ultimate strains, ca. 0.5 < γult < 5.0, and elastic moduli, ca. 10 < E < 1000 kPa, while also demonstrating a high resilience under cyclic tensile loading. Importantly, unlike traditional chemistry, increasing the elastic modulus of the Z-gels does not necessarily reduce the ultimate strain. Moreover, the Z-gels can be rapidly printed using a desktop commercial SLA 3D printer, with relatively low photoirradiation dosages of visible light (135 to 675 mJ cm-2 per 50-100 μm layer). Compared with the counterpart polyacrylamide hydrogels, the Z-gels have greater antifouling properties and exhibit 58.2% less absorption of bovine serum albumin.

Zwitterionic superabsorbent polymer hydrogels for efficient and selective removal of organic dyes.

A novel zwitterionic superabsorbent polymer hydrogel [ZI-SAH] was synthesized by free radical polymerization and used for the removal of crystal violet (CV) and congo red (CR) from an aqueous medium. ZI-SAH was composed of pH-sensitive monomers poly(3-acrylamidopropyl) trimethylammoniumchloride (APTMACl) and 2-acrylamido-2-methylpropanesulphonic acid (AAMPSA). The hydrogel was characterized by SEM and FT-IR spectroscopy, while the visco-elastic behavior was studied using rheological tests. The hydrogel showed a point of zero charge (PZC) at pH 7.2 and high swelling abilities of 3715% at pH 9 and 3112% at pH 5. The cationic crystal violet (CV) and anionic congo red (CR) dyes were employed to investigate the removal ability of ZI-SAH using the batch adsorption method. The materials became more selective towards oppositely charged dyes at pH 5 and 9. The effects of parameters such as contact time, initial concentration of dyes, pH, ZI-SAH dosage and ionic strength on the removal performance were investigated. A kinetic study was carried out via Lagergren pseudo first order and pseudo second order kinetics. The adsorption efficiencies of ZI-SAH were 13.6 mg g−1 for CV and 9.07 mg g−1 for CR with % removal values of 97 and 89, respectively. The thermodynamic parameters, namely, ΔG°, ΔH° and ΔS° were determined, and the negative value of free energy showed that the process of adsorption was spontaneous. ZI-SAH was recycled and reused in five consecutive cycles with removal efficiency > 75%.

Flexible and wearable strain sensors based on tough and self-adhesive ion conducting hydrogels.

Inspired by biosystem, ionic hydrogels have been extensively studied as promising materials for wearable or implantable devices. Herein, we report novel ionic hydrogels that comprise dynamically crosslinked polyzwitterion and physically crosslinked polyvinyl alcohol, which demonstrate excellent mechanical properties, repeatable self-adhesion, and high and linear strain sensitivity. The obtained hydrogels can be directly attached to human skin as sensors to detect or monitor physiological signals.

Tough, Adhesive, Self-Healable, and Transparent Ionically Conductive Zwitterionic Nanocomposite Hydrogels as Skin Strain Sensors.

It is desired to create skin strain sensors composed of multifunctional conductive hydrogels with excellent toughness and adhesion properties to sustain cyclic loadings during use and facilitate the electrical signal transmission. Herein, we prepared transparent, compliant, and adhesive zwitterionic nanocomposite hydrogels with excellent mechanical properties. The incorporated zwitterionic polymers can form interchain dipole-dipole associations to offer additional physical cross-linking of the network. The hydrogels show a high fracture elongation up to 2000%, a fracture strength up to 0.27 MPa, and a fracture toughness up to 2.45 MJ/m3. Moreover, the reversible physical interaction imparts the hydrogels with rapid self-healing ability without any stimuli. The hydrogels are adhesive to many surfaces including polyelectrolyte hydrogels, skin, glasses, silicone rubbers, and nitrile rubbers. The presence of abundant zwitterionic groups facilitates ionic conductivity in the hydrogels. The combination of these properties enables the hydrogels to act as strain sensors with high sensitivity (gauge factor = 1.8). The strategy to design the tough, adhesive, self-healable, and conductive hydrogels as skin strain sensors by the zwitterionic nanocomposite hydrogels is promising for practical applications.

Encapsulation of AgNPs within Zwitterionic Hydrogels for Highly Efficient and Antifouling Catalysis in Biological Environments.

Silver nanoparticles (AgNPs) have been widely used as catalysts in a variety of chemical reactions owing to their unique surface and electronic properties, but their practical applications have been hindered by severe aggregation. The immobilization of AgNPs is crucial to preventing their aggregation or precipitation as well as to improving their reusability. Herein, we developed a facile route for the reductant-free in situ synthesis of AgNPs in zwitterionic hydrogels. Via this method, the embedded AgNPs had a uniform distribution, high activity, and antibiofouling capability. The catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using polycarboxybetaine-AgNPs (PCB-AgNPs) could achieve >95% conversion efficiency within 5 min. Meanwhile, the normalized rate constant knor (10.617 s-1mmol-1) was higher than that of most of the reported immobilized nanocatalysts. More importantly, in a biofouling environment, PCB-AgNPs could still exhibit >97% initial catalytic activity while AgNPs in the PSB or PHEMA hydrogel lost ∼60% activity. This strategy holds great potential for the immobilization of nanoparticle catalysts, especially for applications in biological environments.