A Highly Elastic and Reversibly Stretchable All‐Polymer Supercapacitor

Multiple stretchability has never been demonstrated as supercapacitors because the hydrogel used cannot fully recover after being heavily deformed. Now, a highly reversibly stretchable all‐polymer supercapacitor was fabricated using a developed double network hydrogel (DN hydrogel) as electrolyte and pure polypyrrole (PPy) as electrode. The DN hydrogel provides excellent mechanical properties, which can be stretched up to 500 % many times and then restore almost 100 % of the original length. To fabricate the fully recoverable stretchable supercapacitor, we annealed a free‐standing pure conducting polymer film as electrode so that the electrodes induced retardance is minimized. The as‐fabricated DN hydrogel/pure conducting polymer supercapacitors can be perfectly recovered from 100 % strain with almost no residual deformation left and the electrochemical performance can be maintained even after 1000 stretches (but not bending).     

Thermoresponsive Double Network Hydrogels with Exceptional Compressive Mechanical Properties

The utility of thermoresponsive hydrogels, such as those based on poly(N‐isopropylacrylamide) (PNIPAAm), is severely limited by their deficient mechanical properties. In particular, the simultaneous achievement of high strength and stiffness remains unreported. In this work, a thermoresponsive hydrogel is prepared having the unique combination of ultrahigh compressive strength (≈23 MPa) and excellent compressive modulus (≈1.5 MPa). This is accomplished by employing a double network (DN) design comprised of a tightly crosslinked, highly negatively charged 1st network based on poly(2‐acrylamido‐2‐methylpropane sulfonic acid (PAMPS) and a loosely crosslinked, zwitterionic 2nd network based on a copolymer of thermoresponsive NIPAAm and zwitterionic 2‐(methacryloyloxy)ethyl]dimethyl‐(3‐sulfopropyl)ammonium hydroxide (MEDSAH). Comparison to other DN designs reveals that this PAMPS/P(NIPAAm‐co‐MEDSAH) DN hydrogel's remarkable properties stem from the intra‐ and internetwork ionic interactions of the two networks. Finally, this mechanically robust hydrogel retains the desirable thermosensitivity of PNIPAAm hydrogels, exhibiting a volume phase transition temperature of ≈35 °C.     

结冷胶与聚乙二醇丙烯酸酯双网络凝胶的制备及生物相容性评价

针对结冷胶脆性较大的问题,将聚乙二醇丙烯酸酯(PEGDA)引入结冷胶,通过紫外交联制备了结冷胶/PEGDA双网络凝胶,并对单组分凝胶和双网络凝胶的溶胀性能、微观形貌、拉伸力学性能、动态压缩性能和流变性能等进行比较.结果表明,双网络凝胶在类生理环境中具有较小的溶胀率和较好的尺寸稳定性,PEGDA的引入能够大幅度提高结冷胶的韧性,双网络凝胶的拉断伸长率可达340%,断裂能达1.01×103J/m2,与天然关节软骨相当.将成纤维细胞种植在凝胶内部进行体外三维立体培养,结果显示,细胞在凝胶内部生存状态良好,双网络凝胶的细胞负载率高于单网络结冷胶,说明该体系在生物医用领域具有良好的应用前景.     

The Construction and Transition of Supramolecular Hydrogels Induced by Cyclodextrin Inclusion

Soft hydrogel nano‐ and micro‐structures have great potential applications in the field of tissue engineering and chemical sensors. In this paper, a supramolecular hydrogel was constructed by combining a triblock copolymer poly(ethylene oxide)₁₀₀‐(propyleneoxide)₇₀‐(ethyleneoxide)₁₀₀ (PEO₁₀₀‐PPO₇₀‐PEO₁₀₀ ) (Pluronic F127), mono‐6‐thio‐β‐cyclodextrins (SH‐β‐CDs), and silver nanoparticles. Here, SH‐β‐CDs couple to the silver nanoparticles via thio groups and include PPO blocks of F127 using the hydrophobic cavity to form pseudo‐polyrotaxanes. Moreover, the hydrogel can be transformed to a homogenous solution by the addition of hydrochloride powder. These results are important for research related to the construction of soft hydrogel materials and control their mechanical properties.     

Rhodamine Mechanophore Functionalized Mechanochromic Double Network Hydrogels with High Sensitivity to Stress

Mechanochromic hydrogels, a new class of stimuli-responsive soft materials, have potential applications in a number of fields such as damage reporting and stress/strain sensing. We prepared a novel mechanochromic hydrogel using a strategy that has been developed to prepare dual-network(DN) hydrogels. A hydrophobic rhodamine derivative(Rh mechanophore) was covalently incorporated into a first network as a cross-linker. This first network embedded with Rh mechanophore within the DN hydrogel was pre-stretched. This guaranteed that the stress could be transferred extensively to the Rh-crosslinked first network once the hydrogel was under an applied force. Interestingly, we found that the threshold stress required to activate the mechanochromism of the hydrogel was less than 200 kPa, and much less than those in previous reports. Moreover, because of the excellent sensitivity of the hydrogel to stress, the DN hydrogel exhibited reversible freezing-induced mechanochromism. Benefiting from the sensitivity of Rh mechanophore to both p H and force, the DN hydrogel showed p H-regulated mechanochromic behavior. Our experimental results indicate that the preparation strategy we used introduces sensitive mechanochromism into the hydrogel and preserves the advantageous mechanical properties of the DN hydrogel. These results will be beneficial to the design and preparation of mechanochromic hydrogels with high stress sensitivity, and foster their practical applications in a number of fields such as damage reporting and stress/strain sensing.     

Drug‐Loaded Elastin‐Like Polypeptide–Collagen Hydrogels with High Modulus for Bone Tissue Engineering

Emphasizing the role of hydrogel stiffness and cellular differentiation, this study develops collagen and elastin‐like polypeptide (ELP)–based bone regenerative hydrogels loaded with recombinant human bone morphogenetic protein‐2 (rhBMP‐2) and doxycycline with mechanical properties suitable for osteogenesis. The drug‐incorporated collagen–ELP hydrogels has significantly higher modulus of 35 ± 5 kPa compared to collagen‐only hydrogels. Doxycycline shows a bi‐phasic release with an initial burst release followed by a gradual release, while rhBMP‐2 exhibits a nearly linear release profile for all hydrogels. The released doxycycline shows anti‐microbial activity against Pseudomonas aeruginosa, Streptococcus sanguinis, and Escherichia coli. Microscopic observation of the hydrogels reveals their interconnected, macroporous, 3D open architecture with pore diameters between 160 and 400 µm. This architecture supports human adipose–derived stem cell attachment and proliferation from initial days of cell seeding, forming a thick cellular sheath by day 21. Interestingly, in collagen and collagen–ELP hydrogels, cell morphology is elongated with stretched slender lamellipodial formation, while cells assemble as spheroidal aggregates in crosslinked as well as drug‐loaded hydrogels. Osteogenic markers, alkaline phosphatase and osteocalcin, are expressed maximally for drug‐loaded hydrogels compared to those without drugs. The drug‐loaded collagen–ELP hydrogels are thus promising for combating bacterial infection and promoting guided bone regeneration.     

Electro‐conductive double‐network hydrogels

Novel electro‐conductive and mechanically‐tough double network polymer hydrogels (E‐DN gels) were synthesized by polymerization of 3, 4‐ethylenedioxythiophene in the presence of a double network hydrogel (DN gel) matrix. The E‐DN gels showed not only excellent mechanical performance, having a fracture stress of 1.4–2.1 MPa, but also electrical conductivity as high as 10^?3 S cm^?1, both under dry and water‐swollen states. The fracture stress and fracture energy of the E‐DN gel was increased by 1.7 and 3.4 times, respectively, as compared with the DN gel. From scanning electron microscope and AFM observations, it was found that electro‐conductive poly(3,4‐ethylenedioxythiophene) (PEDOT) was incorporated into DN gel matrix, apparently due to the formation of a poly‐ion complex with sulfonic acid group of the DN gel network. Thus, PEDOT incorporated into the DN gel matrix greatly improves not only electronic conductivity, but also mechanical properties, reinforcing the double network gel matrix. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Characterization of regenerated starch from 1‐ethyl‐3‐methylimidazolium acetate ionic liquid with different anti‐solvents

A comparison study of the structures and properties of starches regenerated from 1‐ethyl‐3‐methylimidazolium acetate ([Emim][OAc]) using different anti‐solvents (water, ethanol, or both water and ethanol) was conducted. The starch regenerated with water presented a V‐type crystalline structure whereas the one regenerated in ethanol displayed amorphous structure. Moreover, when an ethanol–water–ethanol method was used for regeneration, the product showed a weak V‐type crystalline structure. SAXS and FTIR were also used to investigate the molecular order of native and regenerated starches. With water used for regeneration, the aggregation and rearrangement of starch molecules occurred more easily. The increased enzyme resistance and thermal stability of regenerated starch with water could be ascribed to the rearrangement of molecular chains forming an aggregated structure with some degree of order. The reconstitution of starch molecules during regeneration with different anti‐solvents changed the multiscale structures and properties of the starch. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1231–1238     

Preparation of Chitin Hydrogel Under Mild Conditions

Both the amount of water and the number of calcium ions are main factors affecting the dissolution of chitin in calcium chloride dihydrate-saturated methanol (calcium solvent). The higher degree of N-acetylation of the chitin was also indicated by its higher solubility in calcium solvent. The chitin hydrogel was prepared by adding a large excess of water to the chitin solution with vigorous stirring, followed by extensive dialysis against water or by filtration to remove the methanol and calcium ions. The water content of the chitin hydrogel was approximately 94–96% (w/v) and could be controlled by centrifugation. The chitin gel was also prepared by the addition of a large excess of alcohol, such as ethanol and iso-propanol, and these protocols were found to be effective under anhydrous conditions because the alcohols were exchangeable with other organic solvents in solution. The chitin hydrogel was more susceptible to lysozyme than to chitinase, and showed and a poor susceptibility to chitosanase. A α-chitin-type crystalline structure was regenerated from chitin sheets prepared from both α-chitin and β-chitin solutions in calcium solvent, but the β-chitin-type sheet was formed from the β-chitin hydrogel prepared by mechanical agitation in water. The α-chitin hydrogel solidified when thawed after freezing, but the β-chitin hydrogel prepared by mechanical agitation maintained its gel form even after prolonged freezing. Animal studies revealed a low toxicity for the chitin sheet and an acceleration of epidermal cell regeneration.     

A Tissue‐Penetrating Double Network Restores the Mechanical Properties of Degenerated Articular Cartilage

Incorporation of an interpenetrating polymer network into an existing single polymer network enables augmentation of the original substrate's mechanical properties, and translation of this concept from purely synthetic materials to natural–synthetic hybrid systems provides the opportunity to reinforce mechanical properties of bulk biological substrates. In many disease states, the mechanical properties of bodily tissues deteriorate rendering them prone to further material failure. Herein, a tissue‐supplementing technique is described in which an interpenetrating biomimetic hydrogel is polymerized in situ throughout cartilage tissue. The treatment restores the inferior compressive properties of osteoarthritic cartilage to that of healthy cartilage, preferentially localizing to weaker regions of tissue. Furthermore, the treatment technique preserves cartilage under harsh articulation conditions, showing promise as a materials‐based treatment for early‐stage osteoarthritis.     

A fast on-demand preparation of injectable self-healing nanocomposite hydrogels for efficient osteoinduction

Injectable hydrogels have been considered as promising materials for bone regeneration,but their osteoinduction and mechanical performance are yet to be improved.In this study,a novel biocompatible injectable and self-healing nano hybrid hydrogel was on-demand prepared via a fast(within 30 s) and easy gelation approach by reversible Schiff base formed between-CH=O of oxidized sodium alginate(OSA) and-NH_2 of glycol chitosan(GCS) mixed with calcium phosphate nanoparticles(CaP NPs).Its raw materials can be ready in large quantities by a simple synthesis process.The mechanical strength,degradation and swelling behavior of the hydrogel can be readily controlled by simply controlling the molar ratio of-CH=O and-NH_2.This hydrogel exhibits pH responsiveness,good degradability and biocompatibility.The hydrogel used as the matrix for mesenchymal stem cells can significantly induce the proliferation,differentiation and osteoinduction in vitro.These results showed this novel hydrogel is an ideal candidate for applications in bone tissue regeneration and drug delivery.     

Colloidal stability of oleic- and ricinoleic-acid-coated magnetic nanoparticles in organic solvents

Polyacrylic acid (PAA) and polyacrylamide (PAAm) double network (DN) hydrogels with high mechanical strength (about 1.5 MPa) are obtained when two kinds of monomer solutions of 4M AA with 5 mol% crosslinker and 4M AAm with 0.1 mol% crosslinker are used for the optimal preparation. Their high mechanical strength can be maintained even at high water content (above 50%) and at external stimuli (solvent and pH). This optimized DN hydrogel is used to develop the PAA/PAAm inverse opal hydrogel with DN structure by twice infiltration-polymerization and colloidal templating. Its photonic stop band can be tuned by controlling the solvent and pH. It first shows a small red-shift (about 20 nm), and then a large blue-shift (about 180 nm) with the increased ethanol content. For pH response, the DN inverse opal hydrogel has a large stop-band shift of about 140 nm when the pH increases from 1.2 to 5.6. Moreover, the DN inverse opal hydrogel also shows rapid recovery ability without hysteresis phenomenon in strong acidic environment, good reproducibility and durability. The interaction between the independently crosslinked PAA network and PAAm network plays a significant role in determining the response performance.     

Synthesis and properties of poly(acrylamide‐co‐acrylic acid)/polyacrylamide superporous IPN hydrogels

Poly(acrylamide‐co‐acrylic acid)/polyacrylamide [P(AM‐co‐AA)/PAM] hydrogel with superporous and interpenetrating network (IPN) structure was prepared by a prepolymerization reaction and a synchronous polymerization reaction and frothing process. Scanning electron microscope (SEM) images show that the resultant hydrogel possesses abundant interconnected pores. DSC indicates that the porous structure enhances the swelling ratio and reduces the interaction between water and the hydrogel. In contrast, the IPN by PAM decreases water absorbency and enhances water retentivity. It is found that a superporous stucture in the hydrogel increases the equilibrium swelling ratio and decreases the compressive strength of the hydrogel. On the other hand, the increase in AM oligomer (oligo‐AM) amount decreases the equilibrium swelling ratio and improves the compressive strength of the hydrogel. Therefore, the two‐steps synthesis method can be used to construct a hydrogel with superporous and IPN structure. The swelling and mechanical properties of the hydrogel can be improved effectively. Copyright © 2008 John Wiley & Sons, Ltd.     

Self‐Assembly of Amphiphilic Janus Dendrimers into Mechanically Robust Supramolecular Hydrogels for Sustained Drug Release

Compounds that can gelate aqueous solutions offer an intriguing toolbox to create functional hydrogel materials for biomedical applications. Amphiphilic Janus dendrimers with low molecular weights can readily form self‐assembled fibers at very low mass proportion (0.2 wt %) to create supramolecular hydrogels (G′?G′′) with outstanding mechanical properties and storage modulus of G′>1000 Pa. The G′ value and gel melting temperature can be tuned by modulating the position or number of hydrophobic alkyl chains in the dendrimer structure; thus enabling exquisite control over the mesoscale material properties in these molecular assemblies. The gels are formed within seconds by simple injection of ethanol‐solvated dendrimers into an aqueous solution. Cryogenic TEM, small‐angle X‐ray scattering, and SEM were used to confirm the fibrous structure morphology of the gels. Furthermore, the gels can be efficiently loaded with different bioactive cargo, such as active enzymes, peptides, or small‐molecule drugs, to be used for sustained release in drug delivery.     

A soft lithography method to generate arrays of microstructures onto hydrogel surfaces

Materials bearing microscale patterns on the surface have important biomedical applications such as scaffolds in tissue engineering, drug delivery systems, sensors, and actuators. Hydrogels are an attractive class of materials that has excellent biocompatibility, biodegradability, and tunable mechanical properties that meet the requirements of the aforementioned applications. Generating patterns of intricate microstructures onto the hydrogel surfaces, however, is challenging due to properties such as the crosslinking density, low mechanical strength, adhesion, or chemical incompatibility of hydrogels with various molds. Here, we report the use of a soft lithography technique to successfully transfer arrays of micropillars onto a poly(2‐hydroxyethyl methacrylate)‐based hydrogel. The swelling of the hydrogel in solvents, such as phosphate‐buffered saline, deionized water, 60% ethanol, and absolute ethanol, facilitates the reproducible replication of the pattern. Furthermore, the micropillar pattern promotes the attachment of HeLa cells onto this hydrogel which is not inherently adhesive when unpatterned. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1144–1157     

A Double Network Hydrogel with High Mechanical Strength and Shape Memory Properties

Double network (DN) hydrogels as one kind of tough gels have attracted extensive attention for their potential applications in biomedical and load-bearing fields. Herein, we import more functions like shape memory into the conventional tough DN hydrogel system. We synthesize the PEG-PDAC/P(AAm-co-AAc) DN hydrogels, of which the first network is a well-defined PEG (polyethylene glycol) network loaded with PDAC (poly(acryloyloxyethyltrimethyl ammonium chloride)) strands, while the second network is formed by copolymerizing AAm (acrylamide) with AAc (acrylic acid) and cross-linker MBAA (N, N'-methylenebisacrylamide). The PEG-PDAC/P(AAm-co-AAc) DN gels exhibits high mechanical strength. The fracture stress and toughness of the DN gels reach up to 0.9 MPa and 3.8 MJ/m³, respectively. Compared with the conventional double network hydrogels with neutral polymers as the soft and ductile second network, the PEG-PDAC/P(AAm-coAAc) DN hydrogels use P(AAm-co-AAc), a weak polyelectrolyte, as the second network. The AAc units serve as the coordination points with Fe³⁺ ions and physically crosslink the second network, which realizes the shape memory property activated by the reducing ability of ascorbic acid. Our results indicate that the high mechanical strength and shape memory properties, probably the two most important characters related to the potential application of the hydrogels, can be introduced simultaneously into the DN hydrogels if the functional monomer has been integrated into the network of DN hydrogels smartly.     

Hydrogels from Amorphous Calcium Carbonate and Polyacrylic Acid: Bio‐Inspired Materials for “Mineral Plastics”

Given increasing environmental issues due to the large usage of non‐biodegradable plastics based on petroleum, new plastic materials, which are economic, environmentally friendly, and recyclable are in high demand. One feasible strategy is the bio‐inspired synthesis of mineral‐based hybrid materials. Herein we report a facile route for an amorphous CaCO₃ (ACC)‐based hydrogel consisting of very small ACC nanoparticles physically cross‐linked by poly(acrylic acid). The hydrogel is shapeable, stretchable, and self‐healable. Upon drying, the hydrogel forms free‐standing, rigid, and transparent objects with remarkable mechanical performance. By swelling in water, the material can completely recover the initial hydrogel state. As a matrix, thermochromism can also be easily introduced. The present hybrid hydrogel may represent a new class of plastic materials, the “mineral plastics”.     

TGF‐β1‐Modified Hyaluronic Acid/Poly(glycidol) Hydrogels for Chondrogenic Differentiation of Human Mesenchymal Stromal Cells

In cartilage regeneration, the biomimetic functionalization of hydrogels with growth factors is a promising approach to improve the in vivo performance and furthermore the clinical potential of these materials. In order to achieve this without compromising network properties, multifunctional linear poly(glycidol) acrylate (PG‐Acr) is synthesized and utilized as crosslinker for hydrogel formation with thiol‐functionalized hyaluronic acid via Michael‐type addition. As proof‐of‐principle for a bioactivation, transforming growth factor‐beta 1 (TGF‐β1) is covalently bound to PG‐Acr via Traut's reagent which does not compromise the hydrogel gelation and swelling behavior. Human mesenchymal stromal cells (MSCs) embedded within these bioactive hydrogels show a distinct dose‐dependent chondrogenesis. Covalent incorporation of TGF‐β1 significantly enhances the chondrogenic differentiation of MSCs compared to hydrogels with supplemented noncovalently bound TGF‐β1. The observed chondrogenic response is similar to standard cell culture with TGF‐β1 addition with each medium change. In general, multifunctional PG‐Acr offers the opportunity to introduce a range of biomimetic modifications (peptides, growth factors) into hydrogels and, thus, appears as an attractive potential material for various applications in regenerative medicine.     

Biphasic Synergistic Gel Materials with Switchable Mechanics and Self‐Healing Capacity

A fabrication strategy for biphasic gels is reported, which incorporates high‐internal‐phase emulsions. Closely packed micro‐inclusions within the elastic hydrogel matrix greatly improve the mechanical properties of the materials. The materials exhibit excellent switchable mechanics and shape‐memory performance because of the switchable micro‐ inclusions that are incorporated into the hydrogel matrix. The produced materials demonstrated a self‐healing capacity that originates from the noncovalent effect of the biphasic heteronetwork. The aforementioned characteristics suggest that the biphasic gels may serve as ideal composite gel materials with validity in a variety of applications, such as soft actuators, flexible devices, and biological materials.     

Structural Versatility in Slide‐Ring Gels: Influence of Co‐Threaded Cyclodextrin Spacers

We describe a one‐pot strategy for the fabrication of novel slide‐ring (SR) gels based on supramolecular polyrotaxane structures with cyclodextrin‐derived cross‐links and additional free cyclodextrin ring spacers co‐threaded onto the polymer backbones. Photoinitiated thiol‐yne click coupling leads to facile hydrogel fabrication from pseudo‐polyrotaxanes prepared in situ from β‐cyclodextrin derivatives and bifunctional polyethylene glycol (PEG). The obtained SR gels were characterized by NMR spectroscopy using a polyrotaxane model compound with the ratio of cyclodextrin sliding spacers to PEG backbone controlled by adjusting the feed ratio of the starting materials. This structural tuning leads to dramatic changes in the rheological properties, mechanical properties, and swelling behavior of the SR gels. In addition, the coupling of simple synthetic procedures with enhanced properties offers a versatile approach to novel elastomeric materials. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1156–1165