Super-tough and rapidly self-recoverable multi-bond network hydrogels facilitated by 2-ureido-4[1H]-pyrimidone dimers

Multi-bond network(MBN) hydrogels contain hierarchical dynamic bonds with different bond association energy as energy dissipation units,enabling super-tough mechanical properties.In this work,we copolymerize a protonated 2-ureido-4[1 H]-pyrimidone(UPy)-contained monomer with acrylic acid in HCl solution.After removing excess HCl,UPy motifs are deprotonated and from dimers,thus generating an UPy-contained MBN hydrogel.The obtained MBN hydrogels(75 wt% watercontent) exhibit super-tough mechanical properties(0.39 MPa to 2.51 MPa tensile strength),with tremendous amount of energy(1.68 MJ/m³ to 11.1 MJ/m³) dissipated by the dissociation of UPy dimers.The introduction of ionic bonds can further improve the mechanical properties.Moreover,owing to their dynamic nature,both UPy dimers and ionic bonds can re-associate after being dissociated,resulting in excellent self-recovery ability(around 90% recovery efficiency within only 1 h).The excellent self-recovery ability mainly originates from the re-association of UPy dimers based on the high dimerization constant of UPy motifs.     

Multi-bond network hydrogels with robust mechanical and self-healable properties

Multi-bond network(MBN) which contains a single network with hierarchical cross-links is a suggested way to fabricate robust hydrogels. In order to reveal the roles of different cross-links with hierarchical bond energy in the MBN, here we fabricate poly(acrylic acid) physical hydrogels with dual bond network composed of ionic cross-links between carboxylFe3+ interactions and hydrogen bonds, and compare these dually cross-linked hydrogels with singly and ternarily cross-linked hydrogels. Simple models are employed to predict the tensile property, and the results confirm that the multi-bond network with hierarchical distribution in the bond energy of cross-links endows hydrogel with effective energy-dissipating mechanism. Moreover, the dually cross-linked MBN gels exhibit excellent mechanical properties(tensile strength up to 500 k Pa, elongation at break ~ 2400%) and complete self-healing after being kept at 50 °C for 48 h. The factors on promoting self-healing are deeply explored and the dynamic multi-bonds are regarded to trigger the self-healing along with the mutual diffusion of long polymer chains and ferric ions.     

Water-Resistant and Stretchable Conductive Ionic Hydrogel Fibers Reinforced by Carboxymethyl Cellulose

Conductive ionic hydrogels (CIH) have been widely studied for the development of stretchable electronic devices, such as sensors, electrodes, and actuators. Most of these CIH are made into 3D or 2D shape, while 1D CIH (hydrogel fibers) is often difficult to make because of the low mechanical robustness of common CIH. Herein, we use gel spinning method to prepare a robust CIH fiber with high strength, large stretchability, and good conductivity. The robust CIH fiber is drawn from the composite gel of sodium polyacrylate (PAAS) and sodium carboxymethyl cellulose (CMC). In the composite CIH fiber, the soft PAAS presents good conductivity and stretchability, while the rigid CMC significantly enhances the strength and toughness of the PAAS/CMC fiber. To protect the conductive PAAS/CMC fiber from damage by water, a thin layer of hydrophobic polymethyl acrylate (PMA) or polybutyl acrylate (PBA) is coated on the PAAS/CMC fiber as a water-resistant and insulating cover. The obtained PAAS/CMC-PMA and PAAS/CMC-PBA CIH fibers present high tensile strength (up to 28 MPa), high tensile toughness (up to 43 MJ/m³), and good electrical conductivity (up to 0.35 S/m), which are useful for textile-based stretchable electronic devices.     

聚乙烯醇硫酸钾水凝胶电机械化学行为研究

通过将交联聚乙烯醇硫酸酯化的方法制备了一种新型电刺激响应性聚乙烯醇硫酸钾(PVSK)智能水凝胶,并探讨了溶液离子强度和pH对PVSK水凝胶的溶胀吸水率、机械性能以及电机械化学行为的影响.结果表明,制备的PVSK水凝胶的平衡溶胀比随NaCl溶液离子强度的增大而减小,在pH2.39～10.83范围内基本不受溶液pH的影响;经不同离子强度和pH的NaCl溶液充分溶胀的PVSK水凝胶具有良好的机械性能,在非接触的直流电场作用下,该水凝胶向电场负极弯曲,凝胶的弯曲速度和弯曲偏转量随外加电场强度的增加而增大,随NaCl溶液离子强度的增大出现临界最大值,但不随溶液pH(2.08～10.53)的改变而改变;在循环电场作用下,PVSK水凝胶的电机械化学行为具有良好的可逆性.     

Flexible,stretchable and conductive PVA/PEDOT:PSS composite hydrogels prepared by SIPN strategy

Stretchable conductive hydrogels have received significant attention due to their possibility of being utilized in wearable electronics and healthcare devices. In this work, a semi-interpenetrating polymer network (SIPN) strategy was employed to fabricate a set of flexible, stretchable and conductive composite hydrogels composed of polyvinyl alcohol (PVA) in the presence of glutaraldehyde as the crosslinker, HCl as the catalyst and poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) as the conductive medium. The results from FTIR, Raman, SEM and TGA indicate that a chemical crosslinking network and interactions of PVA and PEDOT:PSS exist in the SIPN hydrogels. The swelling ratio of hydrogels decreased with increasing content of PEDOT:PSS. Due to the chemical crosslinking network and interactions of PVA and PEDOT:PSS, PVA networks semi-interpenetrated with PEDOT:PSS exhibited excellent tensile and compression properties. The tensile strength and elongation at breakage of the composite hydrogels with 0.14 wt% PEDOT:PSS were 70 KPa and 239%, respectively. The compression stress of the composite hydrogels with 0.14 wt% PEDOT:PSS at a strain of 50% was about 216 KPa. The electrical conductivity of the hydrogels increased with increasing PEDOT:PSS content. The flexible, stretchable and conductive properties endow the composite hydrogel sensor with a superior gauge factor of up to 4.4 (strain: 100%). Coupling the strain sensing capability to the flexibility, good mechanical properties and high electrical conductivity, we consider that the designed PVA/PEDOT:PSS composite hydrogels have promising applications in wearable devices, such as flexible electronic skin and sensitive strain sensors.     

Effect of Amino Acid Types on the Mechanical and Antimicrobial Properties of Amino Acid-Based Polyionic Liquid Hydrogels

Polyionic liquid hydrogels attract increasing attention due to their unique properties and potential applications. However, research on amino acid-based polyionic liquid hydrogels is still in its infancy stage. Moreover, the effect of amino acid types on the properties of hydrogels is rarely studied to date. In this work, amino acid-based polyionic liquid hydrogels (D/L-PCAA hydrogels) are synthesized by copolymerizing vinyl choline–amino acid ionic liquids and acrylic acids using Al³⁺ as a crosslinking agent and bacterial cellulose (BC) as a reinforcing agent. The effects of amino acid types on mechanical and antimicrobial properties are systematically investigated. D-arginine-based hydrogel (D-PCArg) shows the highest tensile strength (220.7 KPa), D-phenylalanine-based hydrogel (D-PCPhe) exhibits the highest elongation at break (1346%), and L-aspartic acid-based hydrogel (L-PCAsp) has the highest elastic modulus (206.9 KPa) and toughness (1.74 MJ m⁻³). D/L-PCAsp hydrogels demonstrate stronger antibacterial capacity against Escherichia coli and Staphylococcus aureus, and D/L-PCPhe hydrogels possess higher antifungal activity against Cryptococcus neoformans. Moreover, the resultant hydrogels exhibit prominent hemocompatibility and low toxicity, as well as excellent self-healing capabilities (86%) and conductivity (2.8 S m⁻¹). These results indicate that D/L-PCAA hydrogel provides a promise for applications in wound dressings.     

Hofmeister效应辅助的蛋白质基水凝胶应变传感器

以酪蛋白酸钠和明胶为原料, 通过简单的在硫酸铵溶液中浸泡的方法, 借助Hofmeister效应制备了一种强韧导电的酪蛋白酸钠/明胶水凝胶, 克服了蛋白质基水凝胶柔软、 易碎的问题. 测试结果表明, 该水凝胶具有优异的机械性能, 最大拉伸应力为3.55 MPa, 最大拉伸应变为1375%; 水凝胶的最大电导率为0.0954 S/cm, 导电灵敏因子为0.53. 用该水凝胶制备的传感器对不同大小及不同速率的应变均具有分辨能力, 能够监测人体不同部位的运动, 且传感器的信号传输具有稳定性和准确性, 表明该水凝胶是监测人体健康和运动的理想材料. 该水凝胶还具有良好的形状记忆性能. 这一策略为制备全天然蛋白质基水凝胶开辟了新的思路, 扩展了水凝胶在生物医学和电子传感等相关领域的应用前景.     

Real-time monitoring flexible hydrogels based on dual physically cross-linked network for promoting wound healing

To achieve smart and personalized medicine, the development of hydrogel dressings with sensing properties and biotherapeutic properties that can act as a sensor to monitor of human health in real-time while speeding up wound healing face great challenge. In the present study, a biocompatible dual-network composite hydrogel (DNCGel) sensor was obtained via a simple process. The dual network hydrogel is constructed by the interpenetration of a flexible network formed of poly(vinyl alcohol) (PVA) physical cross-linked by repeated freeze-thawing and a rigid network of iron-chelated xanthan gum (XG) impregnated with Fe³⁺ interpenetration. The pure PVA/XG hydrogels were chelated with ferric ions by immersion to improve the gel strength (compressive modulus and tensile modulus can reach up to 0.62 MPa and 0.079 MPa, respectively), conductivity (conductivity values ranging from 9 × 10⁻⁴ S/cm to 1 × 10⁻³ S/cm) and bacterial inhibition properties (up to 98.56%). Subsequently, the effects of the ratio of PVA and XG and the immersion time of Fe³⁺ on the hydrogels were investigated, and DNGel3 was given the most priority on a comprehensive consideration. It was demonstrated that the DNCGel exhibit good biocompatibility in vitro, effectively facilitate wound healing in vivo (up to 97.8% healing rate) under electrical stimulation, and monitors human movement in real time. This work provides a novel avenue to explore multifunctional intelligent hydrogels that hold great promise in biomedical fields such as smart wound dressings and flexible wearable sensors.     

Hydrogels of chemically cross-linked and organ-metallic complexed interpenetrating PEG networks

The aim of the present work was to prepare a well-defined hydrogel of chemically cross-linked and organ-metallic complexed interpenetrating PEG networks. The hydrogel was synthesized via the reaction of copper(I)- catalyzed 1,3-dipolar azide-alkyne cycloaddition(CuA AC) with poly(ethylene glycol)-dopamine(PEG-DA)("Click Chemistry") followed by complexation with Fe~(3+) ions to crosslink the polymeric network. The chemical composition and morphology of the resulting hydrogels were characterized by Fourier transform infrared spectroscopy(FTIR), ~1H-NMR and scanning electron microscopy(SEM). Swelling ratio, mechanical strength, conductivity, and degradation behaviors of the hydrogels were also studied. The effect of the polymer chain length on properties of hydrogels was explored. The compressive strength of hydrogels could reach as high as 13.1 MPa with a conductivity of 2.2 × 10~(-5) S·cm~(-1). The hydrogels also exhibited excellent thermal stability even at a temperature of 300 °C, whereas degradation of the hydrogel after 7 weeks was observed under a physiological condition. In addition, the hydrogel exhibited a good biocompatibility based on its in vivo performance through an in vivo subcutaneous implantation model. No inflammation and no obvious abnormality of the surrounding tissue were observed when the hydrogel was subcutaneously implanted for 2 weeks. This work is a step towards creating a new pathway to synthesize hydrogels of interpenetrating networks which could be of important applications in the future research.     

Highly stretchable,self-adhesive,and self-healable double network hydrogel based on alginate/polyacrylamide with tunable mechanical properties

A number of synthetic hydrogels suffer from low mechanical strength. Despite of the recent advances in the fabrication of tough hydrogels, it is still a great challenge to simultaneously construct high stretchability, and self-adhesive and self-healing capability in a hydrogel. Herein, a new type of double network hydrogel was prepared based on irreversible cross-linking of polyacrylamide chains and Schiff-base reversible cross-linking between glycidyl methacrylate-grafted ethylenediamine and oxidized sodium alginate (OSA). The combination of both cross-linkings and their synergistic effect provided a novel hydrogel with high strength, stretchable, rapid self-healing, and self-adhesiveness to different material. Besides, the hydrogels with diverse OSA content could maintain their original shapes after loading–unloading tensile test. The resulting hydrogel has a great potential in various fields for supporting and load-bearing substance.     

层状纳米纤维素膜/PVA复合水凝胶的制备与力学性能研究

采用叠层复合与物理相分离的方法制备了层状纳米细菌纤维素(BC)膜/聚乙烯醇( PVA)复合水凝胶.研究了聚乙烯醇的质量百分数、BC膜的复合层数以及制备条件对复合水凝胶力学性能的影响;通过扫描电镜( SEM)观察比较了复合水凝胶中BC膜层与PVA界面结合情况.结果表明,复合水凝胶的力学性能与PVA的质量百分数和BC膜含水...     

Peptide dendrimer-crosslinked inorganic-organic hybrid supramolecular hydrogel for efficient anti-biofouling

A novel kind of inorganic-organic hybrid supramolecular hydrogel with excellent anti-biofouling capability was developed. The hydrogel was formed via ionic interaction between the negative-charged sodium polyacrylate (SPA) entwined clay nanosheets (CNS) and positive-charged polyhedral oligomeric silsesquioxane (POSS) core-based generation one (L-Arginine) dendrimer (POSS-R).     

Directed neural stem cell differentiation on polyaniline-coated high strength hydrogels

Stem-cell-based neural regeneration has received significant attention, as it has potential to restore functionality to diseased or damaged neural tissues that have a limited ability to self-repair or regenerate. Culturing neural stem cells (NSCs) on hydrogel substrates has been shown to facilitate differentiation to neural progenitors, but this has only been achieved on very soft hydrogels, greatly increasing the difficulty of manufacture and limiting their wide applications. Here, we realized the differentiation of NSCs to neural and glial progenitors on high-strength hydrogels. Hydrogen-bonding-strengthened conductive hydrogels (PVV-PANI) were synthesized through one-pot copolymerization of 2-vinyl-4,6-diamino-1,3,5-triazine, 1-vinylimidazole and polyethylene glycol diacrylate, followed by post-coating with polyaniline (PANI). Diaminotriazine-diaminotriazine hydrogen bonding dramatically increases their mechanical strength, while copolymerization with VI pronouncedly promotes the adsorption of PANI particles, endowing the hydrogels with electrical conductivity. These hydrogels exhibit tensile strengths up to 1.16 MPa, a 559% breaking strain, a 9.9 MPa compressive strength and up to 16.7 mS/cm conductivity. Importantly, PVV-PANI hydrogels support the attachment, proliferation, and differentiation of NSCs, and allow the efficient induction of neural and glial differentiation via electrical stimulation. This work demonstrates high-strength conductive hydrogels can serve as an electroactive soft-wet platform for modulating the specific differentiation of NSCs, a significant step towards cell-based therapies for neurological diseases.     

Mechanically tough dry-free ionic hydrogel microfibers swollen in aqueous electrolyte prepared by microfluidic devices

Soft conducting materials in the shape of microfibers with various functional geometries are crucial for soft electronics. To develop highly stretchable conducting microfibers, a microfluidic method is used to prepare hydrogels in a double-network structure. Based on the coagulation of chitosan in cold water and simultaneous photopolymerization and photocrosslinking of N-isopropylacrylamide and N-diethylacrylamide, long microfibers with controlled uniform diameters can be obtained at the junction of a coaxially aligned microchannel device. After further reinforcement of the chitosan chain and exchange of the medium of the hydrogel microfiber with an aqueous electrolyte of lithium bis(trifluoromethanesulfonyl)imide, the prepared ionic hydrogel exhibits high conductivity and stretchability and dry-free properties. Owing to its mechanical robustness and ionic conductivity, we envision a highly stretchable soft electrode with the prepared ionic hydrogel microfiber that can be stretched up to 900%. This fiber has potential for applications in soft electronics and wearable devices.     

Electroresponsive Behavior of Sulfonated Benzal Poly(vinyl alcohol) Hydrogel Under Direct-Current Electric Field

A novel sulfonated benzal poly(vinyl alcohol) (S-B-PVA) hydrogel was prepared by sulfonating benzal poly(vinyl alcohol) hydrogel with concentrated sulfuric acid, and its swelling properties, mechanical properties, and electroresponsive behavior in Na₂SO₄ solutions were studied. The results indicated that the water take-up ability of the hydrogel decreased with the increasing ionic strength of Na₂SO₄ solution. The Young's modulus, elongation at break and tensile strength of the hydrogel swollen in deionized water is 8.38 MPa, 22.2% and 3.14 MPa, respectively. The hydrogel swollen in Na₂SO₄ solution bent toward the cathode under non-contact dc electric fields, and its bending speed and equilibrium strain increased with the increasing of applied voltage. The electroresponsive behavior of the hydrogel was also affected by the electrolyte concentration of external Na₂SO₄ solution, and there is a critical ionic strength of 0.1 at which the maximum equilibrium strain of the hydrogel occurs. Under a cyclically varying electric field, the hydrogel exhibited a good reversible bending behavior.     

A simple route to interpenetrating network hydrogel with high mechanical strength

A simple two-step method was introduced to improve the hydrogel mechanical strength by forming an interpenetrating network (IPN). For this purpose, we synthesized polyacrylate/polyacrylate (PAC/PAC), polyacrylate/polyacrylamide (PAC/PAM), polyacrylamide/polyacrylamide (PAM/PAM) and polyacrylamide/poly(vinyl alcohol) (PAM/PVA) IPN hydrogels. The PAC/PAC IPN and PAC/PAM IPN hydrogels showed compressive strength of 70 and 160 kPa, respectively. For the PAM/PAM IPN and PAM/PVA IPN hydrogels, they exhibited excellent tensile strength of 1.2 and 2.8 MPa, and elongations at break of 1750% and 3300%, respectively. A strain relaxation was also observed in the case of PAM series IPN hydrogels. From FTIR, TGA and SEM measurements, we confirmed that physical entanglement, hydrogen bonds and chemical crosslinking played major roles in improving hydrogel strength and toughening. The two-step technique contributes to the understanding of ideal networks, provides a universal strategy for designing high mechanical strength hydrogels, and opening up the biomedical application of hydrogels.     

Self‐Healing Gelatin Hydrogels Cross‐Linked by Combining Multiple Hydrogen Bonding and Ionic Coordination

Self‐healing hydrogels have been studied by many researchers via multiple cross‐linking approaches including physical and chemical interactions. It is an interesting project in multifunctional hydrogel exploration that a water soluble polymer matrix is cross‐linked by combining the ionic coordination and the multiple hydrogen bonds to fabricate self‐healing hydrogels with injectable property. This study introduces a general procedure of preparing the hydrogels (termed gelatin‐UPy‐Fe) cross‐linked by both ionic coordination of Fe³⁺ and carboxyl group from the gelatin and the quadruple hydrogen bonding interaction from the ureido‐pyrimidinone (UPy) dimers. The gelatin‐UPy‐Fe hydrogels possess an excellent self‐healing property. The effects of the ionic coordination of Fe³⁺ and quadruple hydrogen bonding of UPy on the formation and mechanical behavior of the prepared hydrogels are investigated. In vitro drug release of the gelatin‐UPy‐Fe hydrogels is also observed, giving an intriguing glimpse into possible biological applications.

     

Preparation and characterization of a novel stimuli-responsive nanocomposite hydrogel with improved mechanical properties

A novel stimuli-responsive organic/inorganic nanocomposite hydrogel (NC hydrogel) with excellent mechanical properties was synthesized by in situ polymerization of 2-(2-methoxyethoxy) ethyl methacrylate (MEO(2)MA), oligo (ethylene glycol) methacrylate (OEGMA) and acrylic acid (AAc), as the polymeric matrix (PMOA), and fibrillar attpulgite (AT), as the reinforcer and cross-linker. The effect of the AT content on the mechanical properties for the swollen and dried NC hydrogels was determined by tensile testing and dynamic mechanical analysis (DMA), respectively. The tensile testing results showed that the incorporation of AT nanoparticles significantly enhanced the mechanical properties of NC hydrogels. As the content of AT increased, the tensile strength, tensile modulus and effective cross-linked chain density increased. The DMA results showed that the storage modulus of AT/PMOA NC hydrogels was increased and the glass transition temperatures shifted to higher temperature compared to the pure PMOA hydrogel, which further indicated that the enhancement of mechanical property depended upon the presence and content of AT. In addition, the faster swelling rates of the NC hydrogels were observed in comparison with the corresponding physically cross-linked PMOA hydrogel, except for 1% AT/PMOA sample. However, the deswelling kinetics of NC hydrogels was obviously retarded.     

A pH‐sensitive,strong double‐network hydrogel: Poly(ethylene glycol) methyl ether methacrylates–poly(acrylic acid)

We here describe new double network (DN) hydrogels with excellent mechanical strength and high sensitivity to pH changes. The first polymer network has a bottle brush structure and is formed from oligo‐monomers of poly(ethylene glycol) methyl ether methacrylate (PEGMA). Poly(acrylic acid) (PAA) is used as the second network. This double network features strong intermolecular interactions between the neutral poly(ethylene glycol) (PEG) side chains of PPEGMA and the non‐ionized carboxylic acid groups of the PAA second network. When immersed in solutions with a pH below ～4 the DN hydrogels have a low swelling ratio and are opaque as a result of solvent‐polymer phase separation driven by the formation of dense hydrogen‐bonded clusters. The compression strength (～8 MPa) is at least 14 times higher than the analogous single networks. When immersed in solutions with a pH >4, the hydrogels are transparent and exhibit a high swelling ratio with a compression strength of ～1 MPa. The PEG side chain length can be readily controlled without greatly altering the overall DN topology by choosing PEGMA monomers having different PEG side chain lengths. Longer PEG side branches give higher compression and tensile strengths at pH <4 when hydrogen bonded clusters form. The robust nature of these DN gels over a wide pH range may be useful for applications such as artificial muscles and controlled release devices. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012