Tough and Self‐Recoverable Thin Hydrogel Membranes for Biological Applications

Tough and self‐recoverable hydrogel membranes with micrometer‐scale thickness are promising for biomedical applications, which, however, rarely be realized due to the intrinsic brittleness of hydrogels. In this work, for the first time, by combing noncovalent DN strategy and spin‐coating method, we successfully fabricated thin (thickness: 5–100 µm), yet tough (work of extension at fracture: 10⁵–10⁷ J m^?3) and 100% self‐recoverable hydrogel membranes with high water content (62–97 wt%) in large size (≈100 cm²). Amphiphilic triblock copolymers, which form physical gels by self‐assembly, were used for the first network. Linear polymers that physically associate with the hydrophilic midblocks of the first network, were chosen for the second network. The inter‐network associations serve as reversible sacrificial bonds that impart toughness and self‐recovery properties on the hydrogel membranes. The excellent mechanical properties of these obtained tough and thin gel membranes are comparable, or even superior to many biological membranes. The in vitro and in vivo tests show that these hydrogel membranes are biocompatible, and postoperative nonadhesive to neighboring organs. The excellent mechanical and biocompatible properties make these thin hydrogel membranes potentially suitable for use as biological or postoperative antiadhesive membranes.     

Dual Physical Crosslinking Strategy to Construct Moldable Hydrogels with Ultrahigh Strength and Toughness

A dual physical crosslinking (DPC) strategy is used to construct moldable hydrogels with ultrahigh strength and toughness. First, polyelectrolyte complex (PEC) hydrogels are prepared through the in situ polymerization of acrylic acid monomers in the concentrated chitosan (Ch) solutions. Subsequently, Ag⁺ ions are introduced into the PEC hydrogels to form coordination bonds between ? NH₂ and ? COOH groups. High‐density electrostatic interaction and coordination bonds endow the DPC hydrogels with high strength and toughness. The mechanical properties of the DPC hydrogels strongly depend on the weight ratio of Ch to poly(acrylic acid) and the loading concentration of Ag⁺ ions. When the loading concentration of Ag⁺ ions is in the range of 1.0–1.5 mol L^?1, DPC 0.10–0.25 hydrogels display the maximum tensile strength (24.0 MPa) and toughness (84.7 MJ m^?3) with a strain of more than 600%. Specially, the DPC hydrogels display an excellent moldable behavior due to the reversible properties of the electrostatic interaction and coordination bonds. The DPC strategy can also be applied in various other systems and opens a new avenue to fabricate hydrogels with outstanding mechanical properties and antibacterial activities.     

Tough Elastomers with Superior Self‐Recoverability Induced by Bioinspired Multiphase Design

Incorporating reversible sacrificial bonds in network polymers not only toughens these materials but also endows them with self‐recoverability. However, self‐recoverability is only realized for dispersed energy less than 10 MJ m^?3. It remains a challenge to achieve simultaneous high stretchability, toughness, and recoverability. Here, inspired by the structure of mussel byssus cuticles, a new design strategy is proposed and demonstrated to improve both the toughness and self‐recoverability of elastomers by introducing a microphase‐separated structure with different physical crosslink densities. This structure can be achieved using a carefully designed comonomer sequence distribution of hydrogen bonding units in an ABA‐type triblock copolymer. The A blocks form hard domains with dense crosslinking that prevents macroscopic deformation, while the B blocks form a softer matrix with sparse and dynamic crosslinks that serve as sacrificial bonds. This elastomer exhibits high toughness (≈62 MJ m^?3), self‐healing, and most notably, excellent self‐recovery (recovery against 650% elongation and 17 MPa tensile stress with a dissipated energy >27 MJ m^?3 at room temperature). This combination of toughness, self‐healing, and self‐recovery expands the range of applications of these advanced dynamic materials.     

Anisotropic Hybrid Hydrogels with Superior Mechanical Properties Reminiscent of Tendons or Ligaments

Mimicking the hierarchically anisotropic structure and excellent mechanical properties of natural tissues, such as tendons and ligaments, using biomaterials is challenging. Despite recent achievements with anisotropic hydrogels, limitations remain because of difficulties in achieving both structural and mechanical characteristics simultaneously. A simple approach for fabricating hybrid hydrogels with a hierarchically anisotropic structure and superior mechanical properties that are reminiscent of tendons or ligaments is proposed. Alginate–polyacrylamide double‐network (DN) hydrogels incorporated with high aspect ratio mesoporous silica microparticles are stretched and fixed via subsequent drying and ionic crosslinking to achieve multiscale structures composed of an anisotropically aligned polymer network embedded with aligned microparticles. The mechanical properties of hydrogels can be further controlled by the degree of stretching, quantities, and functional groups of inorganic microparticles, and types of crosslinking cations. The subsequent reswelling results in a high water content (>80%) similar to that of natural tendons while high strength, modulus, and toughness are maintained. The optimized anisotropic hybrid hydrogel exhibits a tensile modulus of 7.2 MPa, strength of 1.3 MPa, and toughness of 1.4 MJ m^?3 even in the swollen state, which is 451‐, 27‐, and 2.2 times higher than that observed in the non‐swollen tough DN hydrogel. This study suggests a new strategy for fabricating anisotropic hydrogels with superior mechanical properties to develop new biomaterials for artificial tendons or ligaments.     

Hydrogel−Solid Hybrid Materials for Biomedical Applications Enabled by Surface‐Embedded Radicals

Combinations of hydrogels and solids provide high level functionality for devices such as tissue engineering scaffolds and soft machines. However, the weak bonding between hydrogels and solids hampers functionality. Here, a versatile strategy to develop mechanically robust solid?hydrogel hybrid materials using surface embedded radicals generated through plasma immersion ion implantation (PIII) of polymeric surfaces is reported. Evidence is provided that the reactive radicals play a dual role: inducing surface‐initiated, spontaneous polymerization of hydrogels; and binding the hydrogels to the surfaces. Acrylamide and silk hydrogels are formed and covalently attached through spontaneous reactions with the radicals on PIII activated polymer surfaces without cross‐linking agents or initiators. The hydrogel amount increases with incubation time, monomer concentration, and temperature. Stability tests indicate that 95% of the hydrogel is retained even after 4 months in PBS solution. T‐peel tests show that failure occurs at the tape?hydrogel interface and the hydrogel‐PIII‐treated PTFE interfacial adhesion strength is over 300 N m^?1. Cell assays show no adhesion to the as‐synthesized hydrogels; however, hydrogels synthesized with fibronectin enable cell adhesion and spreading. These results show that polymers functionalized with surface‐embedded radicals provide excellent solid platforms for the generation of robust solid?hydrogel hybrid structures for biomedical applications.     

Covalent Poly(2‐Isopropenyl‐2‐Oxazoline) Hydrogels with Ultrahigh Mechanical Strength and Toughness through Secondary Terpyridine Metal‐Coordination Crosslinks

The present study reports the synthesis of poly(2‐isopropenyl‐2‐oxazoline) (PiPOx) dual‐crosslinked hydrogels by both covalent and physical (i.e., metal–ligand coordination) interactions. First, chemical crosslinking of a modified PiPOx polymer containing terpyridine (TPy) unit is achieved by reacting with azelaic acid (non‐anedioic acid). Transient crosslinks are subsequently introduced by complexation of the TPy units with different divalent transition metal ions. This strategy provides access to hydrogels with superior mechanical properties compared to the pure covalently crosslinked PiPOx hydrogels. The mechanical properties and water uptake of the hydrogels could be easily controlled by swelling in different aqueous metal ion solutions. PiPOx hydrogels swollen in Zn²⁺ solution are found to possess ultrahigh compression strength (9 MPa), remarkable toughness (99 MJ m^?3) and outstanding self‐recoverability (98% toughness recovery after swelling for 60 min without external stimuli), which are among the highest reported in literature to date. These remarkable properties are assigned to the thermodynamically stable, but kinetically labile Zn²⁺‐TPy complexes that produce a dynamic network with fewer imperfections and better adaptive properties under mechanical stress compared to those with other metal ions.     

Conductive “Smart” Hybrid Hydrogels with PNIPAM and Nanostructured Conductive Polymers

Stimuli‐responsive hydrogels with decent electrical properties are a promising class of polymeric materials for a range of technological applications, such as electrical, electrochemical, and biomedical devices. In this paper, thermally responsive and conductive hybrid hydrogels are synthesized by in situ formation of continuous network of conductive polymer hydrogels crosslinked by phytic acid in poly(N‐isopropylacrylamide) matrix. The interpenetrating binary network structure provides the hybrid hydrogels with continuous transporting path for electrons, highly porous microstructure, strong interactions between two hydrogel networks, thus endowing the hybrid hydrogels with a unique combination of high electrical conductivity (up to 0.8 S m^?1), high thermoresponsive sensitivity (significant volume change within several seconds), and greatly enhanced mechanical properties. This work demonstrates that the architecture of the filling phase in the hydrogel matrix and design of hybrid hydrogel structure play an important role in determining the performance of the resulting hybrid material. The attractive performance of these hybrid hydrogels is further demonstrated by the developed switcher device which suggests potential applications in stimuli‐responsive electronic devices.     

Cellulose Nanofibrils Enhanced,Strong, Stretchable,Freezing‐Tolerant Ionic Conductive Organohydrogel for Multi‐Functional Sensors

To date, ionic conducting hydrogel attracts tremendous attention as an alternative to the conventional rigid metallic conductors in fabricating flexible devices, owing to their intrinsic characteristics. However, simultaneous realization of high stiffness, toughness, ionic conductivity, and freezing tolerance through a simple approach is still a challenge. Here, a novel highly stretchable (up to 660%), strong (up to 2.1 MPa), tough (5.25 MJ m^?3), and transparent (up to 90%) ionic conductive (3.2 S m^?1) organohydrogel is facilely fabricated, through sol–gel transition of polyvinyl alcohol and cellulose nanofibrils (CNFs) in dimethyl sulfoxide‐water solvent system. The ionic conductive organohydrogel presents superior freezing tolerance, remaining flexible and conductive (1.1 S m^?1) even at ?70 °C, as compared to the other reported anti‐freezing ionic conductive (organo)hydrogel. Notably, this material design demonstrates synergistic effect of CNFs in boosting both mechanical properties and ionic conductivity, tackling a long‐standing dilemma among strength, toughness, and ionic conductivity for the ionic conducting hydrogel. In addition, the organohydrogel displays high sensitivity toward both tensile and compressive deformation and based on which multi‐functional sensors are assembled to detect human body movement with high sensitivity, stability, and durability. This novel organohydrogel is envisioned to function as a versatile platform for multi‐functional sensors in the future.     

Inorganic Ionic Oligomers Induced Organic-Inorganic Synergistic Toughening Enabling Mechanical Robust and Recyclable Nanocomposite Hydrogels

Mechanical robust hydrogels are ideal for applications in energy, environment, biomedicine, and structural engineering materials fields. However, high strength and high toughness are usually in conflict with each other, and simultaneously achieving both of them within a hydrogel has been challenging. Herein an organic-inorganic synergistic toughening strategy is reported via in-situ inorganic ionic polymerization of calcium phosphate oligomers within polymer composite networks composed of polyvinyl alcohol chains and aramid nanofibers. The composite hydrogels are provided with a prestress-induced hierarchically fibrous structure through the assembly, which resulted in the mechanical strength and toughness up to 24.15 ± 1.12 MPa and 15.68 ± 1.78 MJ m⁻³, respectively, surpassing most toughened hydrogels. Through lamination and crosslinking, bulk hydrogels with controllable mechanical anisotropy and significant energy absorption/dissipation ability are produced. Moreover, the recycling and regeneration of the hydrogels are easily realized owing to the physically crosslinked network and acid-induced dissolution of the inorganic units of the hydrogels, which lays a foundation for the sustainable large-scale production and application of the hydrogels. This study provides an alternative approach for the development of mechanical robust and recyclable nanocomposite hydrogels for various applications including soft body armor, flexible electronics, soft robotics, etc.     

Photocurable 3D Printing of High Toughness and Self-Healing Hydrogels for Customized Wearable Flexible Sensors

Currently, most customized hydrogels can only be processed via extrusion-based 3D printing techniques, which is limited by printing efficiency and resolution. Here, a simple strategy for the rapid fabrication of customized hydrogels using a photocurable 3D printing technique is presented. This technique has been rarely used because the presence of water increases the molecular distance between the polymer chains and reduces the monomer polymerization rate, resulting in the failure of rapid solid-liquid separation during printing. Although adding cross-linkers to printing inks can effectively accelerate 3D cross-linked network formation, chemical cross-linking may result in reduced toughness and self-healing ability of the hydrogel. Therefore, an interpenetrated-network hydrogel based on non-covalent interactions is designed to form physical cross-links, affording fast solid-liquid separation. Poly(acrylic acid (AA)-N-vinyl-2-pyrrolidone (NVP)) and carboxymethyl cellulose (CMC) are cross-linked via Zn²⁺-ligand coordination and hydrogen bonding; the resulting mixed AA-NVP/CMC solution is used as the printing ink. The printed poly(AA-NVP/CMC) hydrogel exhibited high tensile toughness (3.38 MJ m⁻³) and superior self-healing ability (healed stress: 81%; healed strain: 91%). Some objects like manipulator are successfully customized by photocurable 3D printing using hydrogels with high toughness and complex structures. This high-performance hydrogel has great potential for application in flexible wearable sensors.     

A Novel Design Strategy for Fully Physically Linked Double Network Hydrogels with Tough,Fatigue Resistant,and Self‐Healing Properties

Double network (DN) hydrogels with two strong asymmetric networks being chemically linked have demonstrated their excellent mechanical properties as the toughest hydrogels, but chemically linked DN gels often exhibit negligible fatigue resistance and poor self‐healing property due to the irreversible chain breaks in covalent‐linked networks. Here, a new design strategy is proposed and demonstrated to improve both fatigue resistance and self‐healing property of DN gels by introducing a ductile, nonsoft gel with strong hydrophobic interactions as the second network. Based on this design strategy, a new type of fully physically cross‐linked Agar/hydrophobically associated polyacrylamide (HPAAm) DN gels are synthesized by a simple one‐pot method. Agar/HPAAm DN gels exhibit excellent mechanical strength and high toughness, comparable to the reported DN gels. More importantly, because the ductile and tough second network of HPAAm can bear stress and reconstruct network structure, Agar/HPAAm DN gels also demonstrate rapid self‐recovery, remarkable fatigue resistance, and notable self‐healing property without any external stimuli at room temperature. In contrast to the former DN gels in both network structures and underlying association forces, this new design strategy to prepare highly mechanical DN gels provides a new avenue to better understand the fundamental structure‐property relationship of DN hydrogels, thus broadening current hydrogel research and applications.     

Bioinspired Structural Composite Hydrogels with a Combination of High Strength,Stiffness, and Toughness

In the development of artificial hydrogels, emulating the mechanical properties of biological tissues with a desirable combination of stiffness and toughness is crucial. To achieve such properties, a design principle inspired by a natural structural composite to wet hydrogels is applied. The bioinspired structural composite hydrogel consisting of layered microplatelets and polymer matrix with strong polymer–platelet interactions is fabricated by a facile method, that is, drying-induced unidirectional shrinkage and rehydration process coupled with secondary ionic crosslinking. The resulting hydrogels exhibit a combination of high tensile strength and elastic modulus (on the order of several MPa) and high fracture energy (up to ≈ 2 kJ·m⁻²). The results suggest the potential of the bioinspired approach that is limitedly applied in dry composites for developing mechanically robust composite hydrogels.     

Stimuli‐Responsive Donor–Acceptor and DNA‐Crosslinked Hydrogels: Application as Shape‐Memory and Self‐Healing Materials

Carboxymethyl cellulose (CMC) chains are functionalized with self‐complementary nucleic acid tethers and electron donor or electron acceptor functionalities. The polymer chains crosslinked by the self‐complementary duplex nucleic acids and the donor–acceptor complexes as bridging units, yield a stiff stimuli‐responsive hydrogel. Upon the oxidation of the electron donor units, the donor–acceptor bridging units are separated, leading to a hydrogel of lower stiffness. By the cyclic oxidation and reduction of the donor units, the hydrogel is reversibly transformed across low and high stiffness states. The controlled stiffness properties of the hydrogel are used to develop shape‐memory hydrogels. In addition, CMC hydrogels crosslinked by donor–acceptor complexes and K⁺‐stabilized G‐quadruplexes reveal stimuli‐responsive properties that exhibit dually triggered stiffness functions. While the hydrogel bridged by the two crosslinking motifs reveals high stiffness, the redox‐stimulated separation of the donor–acceptor complexes or the crown‐ether‐stimulated separation of the G‐quadruplex bridges yields two alternative hydrogels exhibiting low stiffness states. The control over the stiffness properties of the dually triggered hydrogel is used to develop shape‐memory hydrogels, where the donor–acceptor units or G‐quadruplex bridges act as “memories”, and to develop triggered self‐healing process of the hydrogel.     

Dipole–Dipole and H‐Bonding Interactions Significantly Enhance the Multifaceted Mechanical Properties of Thermoresponsive Shape Memory Hydrogels

High strength hydrogels were previously constructed based on dipole–dipole and hydrogen bonding reinforcement. In spite of the high tensile and compressive strengths achieved, the fracture energy of the hydrogels strengthened with sole noncovalent bondings was rather low due to the lack in energy dissipating mechanism. In this study, combined dipole–dipole and hydrogen bonding interactions reinforced (DHIR) hydrogels are synthesized by one‐step copolymerization of three feature monomers, namely acrylonitrile (AN, dipole monomer), acrylamide (AAm, H‐bonding monomer), and 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS, anionic monomer) in the presence of PEGDA575, a hydrophilic crosslinker. The electrostatic repulsion from PAMPS allows the gel network to absorb water readily, and meanwhile the synergistic effect of dipole–dipole and H‐bonding interactions enable the DHIR hydrogel to withstand up to 8.3 MPa tensile stress, 4.8 MPa compressive stress and 140–716% elongation at break with the fracture energy reaching as high as 5500 J/m². In addition, this DHIR hydrogel exhibits reversible mechanical properties after undergoing cyclic loading and unloading. Interestingly, the DHIR hydrogels with appropriate compositions demonstrate temperature‐tunable mechanical properties as well as accompanied shape memory effect. The dual noncovalent bonding strengthening mechanism reported here offers a universal strategy for significantly enhancing the comprehensive mechanical properties of hydrogels.     

Strong and Ultra-Tough Supramolecular Hydrogel Enabled by Strain-Induced Microphase Separation

Architected hydrogels are widely used in biomedicine, soft robots, and flexible electronics while still possess big challenges in strong toughness, and shape modeling. Here, inspired with the universal hydrogen bonding interactions in biological systems, a strain-induced microphase separation path toward achieving the printable, tough supramolecular polymer hydrogels by hydrogen bond engineering is developed. Specifically, it subtly designs and fabricates the poly (N-acryloylsemicarbazide-co-acrylic acid) hydrogels with high hydrogen bond energy by phase conversion induced hydrogen bond reconstruction. The resultant hydrogels exhibited the unique strain-induced microphase separation behavior, resulting in the excellent strong toughness with, for example, an ultimate stress of 9.1 ± 0.3 MPa, strain levels of 1020 ± 126%, toughness of 33.7 ± 6.6 MJ m⁻³, and fracture energy of 171.1 ± 34.3 kJ m⁻². More importantly, the hydrogen bond engineered supramolecular hydrogels possess dynamic shape memory character, i.e shape fixing at low temperature while recovery after heating. As the proof of concept, the tailored hydrogel stents are readily manufactured by 3D printing, which showed good biocompatibility, load-bearing and drug elution, being beneficial for the biomedical applications. It is believed that the present 3D printing of the architected dynamic hydrogels with ultrahigh toughness can broaden their applications.     

A Universal Strategy for Tough Adhesion of Wet Soft Material

Achieving adhesion between hydrogels and diverse materials in a facile and universal way is challenging. Existing methods rely on special chemical or physical properties of the hydrogel and adherends, which lead to limited applicability and complicated pretreatments. A stitch‐bonding strategy is proposed here by introducing a polymer chain with versatile functional group and triggerable crosslinking property inspired by catechol chemistry. The polymer chain can stitch the hydrogel by forming a network in topological entanglement with the preexisting hydrogel network, and directly bond to the adherend surface by versatile chemical interactions. Through this, the polymer chain solution works as a universal glue for facile adhesion of hydrogels to diverse substrates like metals, glasses, elastomers, plastics, and living tissues, without requiring any chemical design or pretreatment for the hydrogel and adherends. The adhesion energy between polyacrylamide hydrogel and diverse substrates can reach 200–400 J m^?2, and it can reach ≈900 J m^?2 with a toughened polyacrylic acid polyacrylamide hydrogel. The mechanism of stitch‐bonding strategy is illustrated by studying various influence factors.     

In Situ Synthesis of Mechanically Robust,Transparent Nanofiber-Reinforced Hydrogels for Highly Sensitive Multiple Sensing

Hydrogels that are both highly conductive and mechanically robust have demonstrated great potential in various applications ranging from healthcare to soft robotics; however, the creation of such materials remains an enormous challenge. This study presents an in situ synthesis strategy for developing bioinspired chemically integrated silica-nanofiber-reinforced hydrogels (SFRHs) with robust mechanical and electronic performance. The strategy is to synthesize soft hydrogel matrices from acrylamide monomers in the presence of well-dispersed silica nanofibers and vinyl silane, which generates homogenous SFRHs with innovative interfacial chemical bonds. The resultant SFRHs exhibit excellent mechanical properties including high mechanical strength of 0.3 MPa at a fracture strain of 1400%, high Young's modulus of 0.11 MPa (comparable to human skin), and superelasticity over 1000 tensile cycles without plastic deformation, while maintaining high transmittance (≥83%). In parallel, the SFRHs show enhanced ionic conductivity (3.93 S m⁻¹) and can monitor multiple stimuli (stretching, compressing, and bending) with high sensitivity (gauge factor of 2.67) and ultra-durability (10 000 cycles). This work may shed light on the design and development of tough and stretchable hydrogels for various applications.     

Self‐Assembled Injectable Nanocomposite Hydrogels Stabilized by Bisphosphonate‐Magnesium (Mg2+) Coordination Regulates the Differentiation of Encapsulated Stem Cells via Dual Crosslinking

Nanocomposite hydrogels consist of a polymer matrix embedded with nanoparticles (NPs), which provide the hydrogels with unique bioactivities and mechanical properties. Incorporation of NPs via in situ precipitation in the polymer matrix further enhances these desirable hydrogel properties. However, the noncytocompatible pH, osmolality, and lengthy duration typically required for such in situ precipitation strategies preclude cell encapsulation in the resultant hydrogels. Bisphosphonate (BP) exhibits a variety of specific bioactivities and excellent binding affinity to multivalent cations such as magnesium ions (Mg²⁺). Here, the preparation of nanocomposite hydrogels via self‐assembly driven by bisphosphonate‐Mg²⁺ coordination is described. Upon mixing solutions of polymer bearing BPs, BP monomer (Ac‐BP), and Mg²⁺, this effective and dynamic coordination leads to the rapid self‐assembly of Ac‐BP‐Mg NPs which function as multivalent crosslinkers stabilize the resultant hydrogel structure at physiological pH. The obtained nanocomposite hydrogels are self‐healing and exhibit improved mechanical properties compared to hydrogels prepared by blending prefabricated NPs. Importantly, the hydrogels in this study allow the encapsulation of cells and subsequent injection without compromising the viability of seeded cells. Furthermore, the acrylate groups on the surface of Ac‐BP‐Mg NPs enable facile temporal control over the stiffness and crosslinking density of hydrogels via UV‐induced secondary crosslinking, and it is found that the delayed introduction of this secondary crosslinking enhances cell spreading and osteogenesis.     

Multiple Structure Reconstruction by Dual Dynamic Crosslinking Strategy Inducing Self-Reinforcing and Toughening the Polyurethane/Nanocellulose Elastomers

High-performance elastomers are expected to possess excellent healing and recycling ability, damage resistance in conjunction with high strength and toughness. Herein, a dual dynamic crosslinking strategy is implemented by multiple hydrogen and disulfide bonds to obtain a novel amorphous and transparent polyurethane/nanocellulose elastomer with excellent self-healing, self-reinforcing and toughening performance. First, hydrogen bonds are introduced in TEMPO-oxidized cellulose nanofibers (TCNF) by modification with 2-ureido-4[1H]-pyrimidone (UTCNF), while disulfide bonds (SS) are introduced in the polyurethane (PU) main chain, leading to the formation of dual dynamic cross-linking networks. The PU-SS-UTCNF elastomer can fully self-heal within 4.0 h at 50 °C. Surprisingly, for the first time, the PU-SS-UTCNF elastomer also self-strengthens and self-toughens after multiple hot-pressing, with tensile strength and toughness that increase by up to 401% and 257% compared to original elastomer samples, up to 50.0 MPa and 132.5 MJ m^-3. The self-strength and self-toughening effects are attributed to 1) reconstruction of dual dynamic networks that increase the cross-linking degree during the multiple hot-pressing processes; 2) multiple hydrogen bonds in the system are beneficial to the orientation of highly crystallized UTCNF, as a replacement of stress-induced process in deformation under external tensile force.     

A Mineralized High Strength and Tough Hydrogel for Skull Bone Regeneration

Over the past decade, high strength hydrogels have been intensively investigated. However, developing high strength biofunctional hydrogels for eliciting bone regeneration has been rarely reported. In this work, a mineralized high strength and tough hydrogel is synthesized by one‐step copolymerization of acrylonitrile, 1‐vinylimidazole, and polyethylene glycol diacrylate, followed by in situ precipitation mineralization. It is demonstrated that the CN? CN dipole–dipole pairings combined with the interaction of CaP nanocrystals with polymer chains contribute to tremendous increase of tensile/compressive strength, modulus, and fracture energy up to 6.1 MPa, 11.5 MPa, 6.47 MPa, and 7935 J m^?2, respectively. The biomineralization is shown to facilitate the attachment and proliferation of C2C12 cells in vitro. This biomineralized hydrogel scaffold is implanted into an 8 mm diameter critical‐size of calvarial defect of rats to evaluate the bone regeneration. 12 week postsurgery results reveal that the mineralized hydrogel exhibits the highest bone volume and density within the defect as measured by computed tomography and histology. This mineralized high strength and tough hydrogel offers a broad range of possibilities to be developed as biofunctional scaffold to promote the reconstruction and regeneration of not only bone, but also load‐bearing connective tissue.