Electrostatic interaction is strong but usually diminishes in high ionic-strength environments. Biosystems can use this interaction through adjacent cationic-aromatic amino acids sequence of proteins ...even in a saline medium. Application of such specific sequence to the development of cationic polymer materials adhesive to negatively charged surfaces in saline environments is challenging due to the difficulty in controlling the copolymer sequences. Here, we discover that copolymers with adjacent cation-aromatic sequences can be synthesized through cation-π complex-aided free-radical polymerization. Sequence controlled hydrogels from diverse cation/aromatic monomers exhibit fast, strong but reversible adhesion to negatively charged surfaces in seawater. Aromatics on copolymers are found to enhance the electrostatic interactions of their adjacent cationic residues to the counter surfaces, even in a high ionic-strength medium that screens the electrostatic interaction for common polyelectrolytes. This work opens a pathway to develop adhesives using saline water.
We report the extraordinary toughness, hysteresis, self-recovery, and persistent fatigue resistance of an anisotropic hydrogel with single-domain lamellar structure, consisting of periodical stacking ...of several thousands of rigid, hydrophobic bilayers in the ductile, hydrophilic polymer matrix. The stratified lamellar bilayers not only diffract light to exhibit magnificent structural color but also serve as reversible sacrificial bonds that dissociate upon deformation, exhibiting large hysteresis as an energy dissipation mechanism. Both the molecular dissociation and lipid-like mobile nature of bilayers dramatically enhance the resistance to crack propagation by suppressing the stress concentration at the crack tip with the formation of extraordinary crack blunting. This unique toughening phenomenon could allow deep insight into the toughening mechanism of the hydrogel-like soft materials such as biological soft tissues.
Abstract Soft supporting tissues in the human body, such as cartilages and ligaments, are tough materials firmly fixed to bones. These soft tissues, once injured, cannot regenerate spontaneously in ...vivo . Developing tough and biocompatible hydrogels as artificial soft supporting tissues would substantially improve outcomes after soft tissue injury. Collagen is the main rigid component in soft connective tissues which is organized in various hierarchical arrays. We have successfully developed a novel class of collagen fibril-based tough hydrogels based on the double network concept using swim bladder collagen (SBC) extracted from Bester sturgeon fish. The DN hydrogels, SBC/PDMAAm, are composed of physically/chemically crosslinked anisotropic SBC fibril as the first network and neutral biocompatible poly(N,N′-dimethylacrylamide) (PDMAAm) as the second network. The anisotropic structure of SBC fibril, which is well retained in the DN hydrogels, is formed by free injection method, taking advantage of the excellent fibrillogenesis capacity of SBC. The denaturation temperature of collagen is improved in the DN hydrogels. These DN gels possess anisotropic swelling behavior, exhibiting excellent mechanical properties comparable to natural cartilage. The 4 weeks implantation of the gels in the osteochondral defect of rabbit knee also shows excellent biomechanical performance in vivo . Furthermore, the hydroxyapatite (HAp) coated DN gels, HAp/SBC/PDMAAm gels, strongly bond to bone after 4 weeks. This new class of collagen-based hybrid DN gels, as soft and elastic ceramics, having good biomechanical performance and strong bonding ability with bone would expand the choice for designing next-generation orthopedic implants such as artificial cartilage, bone defect repair material in the load-bearing region in the body.
We detected the spin polarization due to charge flow in the spin nondegenerate surface state of a three-dimensional topological insulator by means of an all-electrical method. The charge current in ...the bulk-insulating topological insulator Bi1.5Sb0.5Te1.7Se1.3 (BSTS) was injected/extracted through a ferromagnetic electrode made of Ni80Fe20, and an unusual current-direction-dependent magnetoresistance gave evidence for the appearance of spin polarization, which leads to a spin-dependent resistance at the BSTS/Ni80Fe20 interface. In contrast, our control experiment on Bi2Se3 gave null result. These observations demonstrate the importance of the Fermi-level control for the electrical detection of the spin polarization in topological insulators.
Understanding the energy dissipation mechanism during deformation is essential for the design and application of tough soft materials. We show that, in a class of tough and self-healing polyampholyte ...hydrogels, a bicontinuous network structure, consisting of a hard network and a soft network, is formed, independently of the chemical details of the hydrogels. Multiscale internal rupture processes, in which the double-network effect plays an important role, are found to be responsible for the large energy dissipation of these hydrogels.
Double‐network hydrogels (DN gels), despite their high water content, are the strongest and toughest soft and wet materials available. However, in conventional DN gels, which show extraordinarily ...high mechanical performance comparable to that of industrial rubbers, the first network must be a strong polyelectrolyte and this requirement greatly hinders the widespread application of these gels. A general method involving the use of a “molecular stent” for the synthesis of tough DN gels using any hydrophilic polymer as the first network is reported. This is the first reported method for the synthesis of tough DN gels using various neutral or weak polyelectrolyte hydrogels as the first network. This method helps extend the DN gel concept to various functional polymers and may increase the number of applications of hydrogels in various fields.
Tough hydrogels can be synthesized from any hydrophilic polymer by the double‐network (DN) concept using a molecular stent. The synthesized St‐DN gels have excellent strength and toughness comparable to those of conventional tough DN gels and industrial rubbers. This is a promising method for strengthening various functional hydrogels and increasing the scope of their application in various fields.
The double network concept, based on the fracture of sacrificial bonds, has been revolutionary toward the creation of robust soft materials. Based on the essence of double network hydrogels, ...macroscale, three-dimensional printed rigid sacrificial networks are embedded within silicone rubber stretchable matrices. Preferential fracture of the sacrificial network results in a ∼60 time increase in stiffness and a ∼50% increase in the work of extension compared with the neat matrix. Maximizing yield strength while maintaining multistep internal fracture occurs when the strength of the sacrificial network approaches the strength of the matrix. Upon determining the optimal sacrificial network strength, the sacrificial bond section density can be increased to maximize energy dissipation and toughening efficiencies up to ∼70% of the maximum theoretical toughness are achieved. High toughness and dissipation are achieved because topological interlocking enables significant force transmission to the sacrificial network at smaller length scales than interfacial adhesion, allowing much higher sacrificial bond density. This method is general and can be used with a variety of materials systems, without requiring strong interfacial adhesion, contrasting traditional composite systems. Demonstrating that the double network concept can be used at length scales far beyond the molecular scale will have important implications toward the development of future structural materials.
Coating solid surfaces with tough hydrogels is necessary for the practical application of hydrogels in various fields. Here a simple yet versatile method for coating tough double network (DN) ...hydrogels onto a wide range of solid surfaces, including various materials and geometries is reported. Particle‐based double network (P‐DN) gels that combine ease‐of‐use and significantly strong mechanical properties are utilized. The P‐DN gel coating process involves two steps. First, the solid surface (plastic, rubber, ceramic, and/or metal) is treated to form a thin, physically bound primer layer containing radical initiators. The pre‐gel solution is then applied to the treated surface, followed by photo‐induced polymerization. The P‐DN gel coatings show high toughness, with one notable formulation reaching over 1000 J m‐2 in a 90º peeling test. The coatings also show high stability against long‐term water‐storage, elevated temperatures, and solvent exposure. Moreover, it is demonstrated that the P‐DN gel‐coated surfaces exhibit low friction properties with high wear resistance, by pin‐on‐flat tests. The simple coating process can be used even on surfaces with complex geometries, including 3D shapes. This work will enable the use of DN gels in applications such as biocompatible lubricants, scratch resistance coatings, and anti‐fouling paints.
A simple yet versatile method for coating tough particle‐based double network (DN) hydrogels onto a wide range of solid surfaces, including various materials and geometries are reported. The establishment of a method to coat hydrogels on diverse surfaces of arbitrary shape will enable the use of DN gels in applications such as biocompatible lubricants, scratch resistance coatings, and antifouling paints.
High modulus, toughness, and fatigue resistance are usually difficult to be obtained simultaneously in rubbery materials. Here, we report that by superimposing the nanophase separation structure in ...double network (DN) elastomers using immiscible polymers, the modulus, fracture energy, and energy release rate of fatigue threshold are enhanced all together by 13, 5, and 5 times, respectively. We reveal that the interplay between the DN structure and the nanophase separation structure brings two effects synergistically: (1) formation of nanoclusters overstresses and homogenizes the sacrificial network, thereby remarkably increasing the modulus and yielding stress and (2) the nanoclusters act as viscoelastic nanofillers dissipating energy and pinning the crack propagation, thereby significantly enhancing toughness and fatigue resistance. This work provides a facile approach to superimpose high-order structures in DN materials for excellent mechanical performance. The clarified synergetic effects should be universal for DN materials made of immiscible polymers. We believe that this work will facilitate more studies on elastomers and gels along this line.
Bone tissues possess excellent mechanical properties such as compatibility between strength and flexibility and load bearing owing to the hybridization of organic/inorganic matters with anisotropic ...structure. To synthetically mimic such an anisotropic structure of natural organic/inorganic hybrid materials, we carried out hydroxyapatite (HAp) mineralization in stretched tough double network (DN) hydrogels. Anisotropic mineralization of HAp took place in stretched hydrogels, as revealed by high brightness synchrotron X-ray scattering and transmission electron microscopic observation. The c-axis of mineralized HAp aligned along the stretching direction, and the orientation degree S calculated from scattering profiles increased with increasing in the elongation ratio λ of the DN gel, and S at λ = 4 became comparable to that of rabbit tibial bones. The morphology of HAp polycrystal gradually changed from spherical to unidirectional rod-like shape with increased elongation ratio. A possible mechanism for the anisotropic mineralization is proposed, which would be one of the keys to develop mechanically anisotropic organic/inorganic hybrid materials.
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