Dual Dynamic Network Research Articles

Controlling the Relaxation Dynamics of Polymer Networks by Combining Associative and Dissociative Dynamic Covalent Bonds.

Dynamic polymer networks offer a promising solution to key challenges in polymers such as recyclability, processability, and damage repair. However, the trade-off between combining facile processability, fast self-healing, and high creep resistance remains a major obstacle to implementation. To overcome this, two very distinct dynamic covalent chemistries, Diels-Alder and transesterification, is combined in a single network. The resulting dual dynamic networks offer an unprecedented set of properties and control over the relaxation times. The system decouples the relaxation dynamics of the network from the spatial motifs, and the tuning of the ratio between chemistries enables to control of the relaxation dynamics over six orders of magnitude. Taking advantage of this control, the composition and rheological behavior is optimized to drastically improve the resolution for extrusion-based additive manufacturing of dynamic covalent networks. Additionally, two well-defined and separated stress relaxation peaks are observed at compositions close to 50% of each dynamic chemistry, accentuating the double character of the system's relaxation dynamics. This atypical situation, enables to preparation of self-healing materials with negligible creep, and with shape-memory properties solely leveraging the two distinct relaxation dynamics, instead of the glass transition temperature or the melting point.

ROS responsive conductive microspheres loaded with salvianolic acid B as adipose derived stem cell carriers for acute myocardial infarction treatment

Stem cell therapy is currently the most promising strategy for the treatment of myocardial infarction. However, the development of injectable cell carriers that can scavenge reactive oxygen species (ROS) in the infarct zone to improve transplanted cell survival remains a challenge. Here, we developed a ROS responsive conductive microsphere based on chitosan (CS) and dextran (DEX) with 4-formylphenylboronic acid (4-FPBA) as a cross-linking agent and the addition of graphite oxide (GO) and the anti-inflammatory agent salvianolic acid B (SalB), as a cell delivery carrier for myocardial infarction. These microspheres were crosslinked by dual dynamic networks of Schiff base and phenylborate bonds. The relationship between CS concentration and microsphere particle size, as well as the biocompatibility, ROS responsiveness, anti-inflammatory properties, and effects on myogenic differentiation of H9C2 cells were fully investigated. The microspheres exhibit good biocompatibility, proliferation promoting, differentiation promoting, antioxidant, and anti-inflammatory properties. When applied to mice myocardial infarction models, the ROS responsive conductive microspheres loaded with SalB and adipose derived stem cells (ADSC) exhibited excellent in vivo repair ability. In addition, they reduced myocardial fibrosis and promoted ventricular wall regeneration by promoting the expression of Connexin 43 (Cx43) and CD31, ultimately reshaping the infarcted myocardium, suggesting their great potential as cell delivery carriers for myocardial infarction treatment.

High-performance poly(thioctic acid)-based thermosets featuring upcycling ability for in situ foaming enabled by dual-dynamic networks

High-performance poly(thioctic acid)-based thermosets featuring upcycling ability for in situ foaming enabled by dual-dynamic networks

Self-healing cellulose nanocrystals/fluorinated polyacrylate with double dynamic interactions of coumarin groups and multiple hydrogen bonds

In this work, self-healing cellulose nanocrystals/fluorinated polyacrylate with dual dynamic networks of photoreversible crosslinking network and high-density hydrogen bonds was prepared by Pickering emulsion polymerization. The main work was to study the effects of 7-(2-methacryloyloxy)-4-methylcoumarin (CMA) and 2-ureido-4[1H]-pyrimidinone methyl methacrylate (UPyMA) monomer dosage on emulsion polymerization and latex film properties. The monomer conversion increased first and then decreased as the CMA and UPyMA monomer dosage increased, while a reverse trend was noted for the particle size and particle size distribution. Incorporating UPyMA allowed the rapid formation of hydrogen bonds at the crosslinking sites, which increased the interaction force between the healing surfaces. Besides, reversible photocrosslinking reaction of coumarin groups provided another support for self-healing performance. Moreover, the influence of self-healing temperature, self-healing time and UV irradiation on the self-healing ability was also systematically investigated The tensile strength of the prepared cellulose nanocrystals/fluorinated polyacrylate latex film exhibited a self-healing efficiency of 91.4 % under 365 nm UV irradiation and 80 °C for 12 h. The latex film had excellent thermal stability as was shown by TG and DTG analyses. The outstanding self-healing capability of latex film was attributed to the reversible photodimerization of coumarin groups and multiple hydrogen bonds. In addition, the water-oil repellent and mechanical properties of the latex films were improved as the CMA and UPyMA monomer dosage increased.

Fabrication of dual dynamic crosslinking polyurethane networks towards self-healing, resist fatigue, and highly stretchable ionic skins

The limited anti-fatigue performance of self-healing polyurethane elastomers under high-strain conditions restricts their application in high-performance ionic skins. Herein, a polyurethane network (PU-DDN) synergistically reversibly crosslinked by dynamic thiourethane bonds and hydrogen bonds was synthesized successfully. This dual reversibly crosslinking strategy not only endowed the polyurethane network with an excellent fatigue resistance (showing a residual strain of only 63 % after 10 uninterrupted cyclic tensile tests at 400 % strains), but also imparted it with a high strength (6.12 MPa) and stretchability (611.42 %). Owing to the thermo-reversibility of dual dynamic networks, the damaged PU-DDN heated at 100 °C for 3h could fully restore its initial mechanical properties. Subsequently, transparent stretchable ionic skins were fabricated by mixing the PU-DDN with ionic liquids. A resulting highly-sensitive ionic skin (GF1 = 1.25, GF2 = 2.01) named PU-DDN/IL20 demonstrated exceptional durability, which could produce repeatable electrical signals even after 2000 cycles of stretching to an extensive deformation of 400 %. Meanwhile, it can also monitor human motions, showcasing its promising potential in the realm of intelligent wearable applications.

Fast Self-Healing Hyaluronic Acid Hydrogel with a Double-Dynamic Network for Skin Wound Repair.

Developing extracellular matrix-derived hydrogel with a fast self-healing capacity to provide a sustainable moist environment able to accelerate wound healing is highly desired for full-thickness skin wound repair. In this study, a fast self-healing hyaluronic acid hydrogel with a dual dynamic network was constructed through a primary reversible acylhydrazone bond formed between aldehyde-modified hyaluronic acid, 3,3'-dithiobis (propionyl hydrazide) (DTP), and secondary dynamic ionic interactions between κ-carrageenan (KC) and K+. Because of the presence of various dynamic covalent bonds such as the acylhydrazone bond, disulfide bond, and noncovalent bonds including hydrogen bonding and ionic interactions, as well as the notable thermoreversible nature of KC, the resultant hydrogel could be self-healed rapidly within 30 min under physiological temperature with a self-healing efficiency of 100%, which was significantly better than other hyaluronic acid hydrogels, as reported previously. Besides, the hydrogel displayed excellent cytocompatibility. According to this study, the hydrogel was administered into the wounds and achieved a superior performance of promoting full-thickness skin wound healing by increasing granulation tissue formation, deposition of collagen as well as the acceleration of re-epithelialization and neovascularization, compared to commercial products, e.g., gauze and 3 M hydrocolloid. We also anticipate that this strategy of double-dynamic network cross-linking can be adopted to fabricate self-healing materials for multiple applications.

Dual dynamic network structures of recyclable epoxy resins with high strength and toughness via sacrificial hydrogen-bonding clusters and imine bonds: surpassing the strength-toughness trade-off

Thermosetting epoxy resins with high strength, high toughness, and recyclability are strongly sought after, but due to crosslinked structure, balancing strength and toughness and achieving degradation and reprocessing of resins is a challenge. Enhancing strength without compromising toughness during designing recyclable epoxy resin is a challenging task. Herein, a solution is demonstrated where isofluorodioxanone diisocyanate (IPDI), Poly (propylene glycol) bis(2-aminopropyl ether) (D230), and naturally occurring vanillin synthesized a novel imine-functionalized epoxy monomer (IDV-EP), and cured with diamino-diphenylmethane (DDM), 2-(4-aminophenyl)-1H-benzimidazol-5-amine (APBIA) and 4, 4-diamino benzoyl triphenylamine (DABA), respectively, for the purpose of building different contents of the sacrificial hydrogen-bonding clusters (SHBC) in topological network structures. As the hydrogen-bonding (H-bonding) binding energy of the crosslinked network increases, the strength and toughness of the resin were increased concurrently, SHBC was demonstrated to be a feasible method to achieve the strength-toughness trade-off of thermosets, in which IDV-EP-DABA illustrated a tensile strength of 90 MPa, an elongation at break of 16.5%, as well as toughness of 9.73 MJ/m3, which was higher than that of the ordinary bisphenol A-type epoxy thermosetting resin (DGEBA/DDM) by 1.8, 3.7 as well as 6.7 times, respectively. Furthermore, the covalent adaptive networks (CANs) formed by imine bonds provide the resins with effective capabilities for swift degradation (rapid degradation in acid/solvent, room temperature and static conditions) and reprocessing (only a slight decrease in the mechanical properties after hot pressed at 180°C/10 MPa for 15 minutes) , showcasing promising prospects for sustainable utilization.

Rapidly recyclable, monomer recovery and flame-retardant bio-based polyimine networks

With the development of a circular economy and sustainable environment, efficient and sustainable recycling of useful chemicals from thermosets is of great significance. However, most commercial thermosetting materials are difficult to reprocess, degrade, and recycle due to their permanent cross-linked network, and the preparation process consumes much fossil energy and causes serious environmental pollution problems. Furthermore, the high flammability makes them unsafe during service life and limits their applications. Herein, we used renewable lignin derivative vanillin as bio-based materials to synthesize a trialdehyde monomer (TMP) with phosphorus element and developed the bio-based polyimine dynamic networks with excellent comprehensive properties including outstanding reprocess ability, degradation recyclability, and fire resistance performance based on polyetherimide and 4-aminophenyl disulfide. The prepared bio-based polyimine materials with the dual dynamic networks (BPDNs) exhibited outstanding mechanical property with tensile strength of 61.6 MPa, super-rapid degradation rate and high monomer recovery rates of 70.5 %. The prepared BPDNs samples showed great flame retardancy with V0 rating and V1 rating in UL-94 vertical burning test and high LOI value of 29 %. Moreover, BPDNs could be reprocessed within 10 min at elevated temperatures (150 °C). This work provides a very effective method to prepare bio-based advanced thermosetting materials with multiple functions.

Thermoreversible XNBR-based conductive composites with dual dynamic networks for strain sensors

Endowing conductive composites with thermoreversible properties is important for improving the stability and extending the service life of the material, and is in line with today's concept of green chemistry....

Self-healing polyacrylates based on dynamic disulfide and quadruple hydrogen bonds.

Herein, a self-healing polyacrylate system was successfully prepared by introducing crosslinking agents containing disulfide bonds and monomers capable of forming quadruple hydrogen bonds through free radical copolymerization. This polymer material exhibited good toughness and self-healing properties through chemical and physical dual dynamic networks while maintaining excellent mechanical properties, which expanded the development path of self-healing acrylate materials. Compared to uncrosslinked and single dynamically crosslinked polymers, its elongation at break was as high as 437%, and its tensile strength was 5.48 MPa. Due to the presence of dual reversible dynamic bonds in the copolymer system, good self-healing was also achieved at 60 °C. In addition, differential scanning calorimetry and thermogravimetric analysis measurements confirmed that the thermal stability and glass transition temperature of the material were improved owing to the presence of physical and chemical cross-linking networks.

Hemp fiber reinforced dual dynamic network vitrimer biocomposites with direct incorporation of amino silane

Natural fiber composites are inexpensive and renewable alternatives to traditional fiber reinforced polymers (FRPs). However, existing natural fiber composites primarily rely on petrochemical based thermosetting matrices, which are difficult to recycle due to their stable crosslinked network structures. To address this challenge, it is desirable to develop natural fiber composites with inherently recyclable biobased matrices. In this study, we developed a dual dynamic network vitrimer matrix from hempseed oil and limonene derivatives and demonstrated its application in hemp fiber reinforced composites. To improve the weak interface between hemp fiber and the polymer matrix, a common challenge in the realm of natural fiber composites, we directly incorporated amino silane into the vitrimer matrix. The amino silane participated in the polymer network, increasing the crosslink density and toughening the matrix, as evidenced by the significant improvement of impact strength from 3.5 kJ/m2 to 10.3 kJ/m2. Moreover, the incorporation of amino silane resulted in a lower water absorption by 11 % in a 7-day soaking for the composites, demonstrating improved fiber/matrix interfacial interaction. Furthermore, our biobased vitrimer matrix exhibits both imine and hydroxy-ester dynamic bonds, which enable the recycling of the biocomposite through a mild and cost-effective aminolysis process (100 °C, 3 h, ambient pressure). The decomposed polymer matrix was successfully reused as a polyol for polyurethane adhesives, and the surface morphology of recovered hemp fibers was analyzed and compared with that of the original fibers. These findings will help broaden the use of vitrimers for practical natural fiber composite applications, raise awareness of the problem of recycling natural fiber composite waste, and shed light on the interfacial challenge of natural fiber reinforced vitrimer composites.

A dual dynamic network self-healing bio-based vitrimer and its application in multiply recyclable carbon fiber reinforced polymers

The preparation of carbon fiber reinforced polymers (CFRP) using vitrimer with hydroxyl ester bonds as matrix requires harsh degradation conditions. To solve this problem, tung oil-based triglycidyl ester (TOTGE) and 4-aminophenyl disulfide (APD) are cured to fabricate a TOTGE−APD vitrimer with a dual dynamic network of hydroxyl ester and disulfide bonds. The TOTGE−APD vitrimer exhibits a low dynamic bond exchange activation energy (66.51 kJ/mol) due to the introduction of disulfide bonds and can achieve stress relaxation at 100 °C, thus exhibiting excellent self-healing and recycling properties. After crushing/remodeling, tensile strength of the remodeling sample can achieve 97.5% the original sample. Due to the disulfide and ester group in the vitrimer, CFRP prepared with TOTGE−APD vitrimer can be degraded in mercaptoehtanol, ethanolamine, and ethylene glycol, achieving multiple recycling.

Closed-Loop Recycling of Carbon Fiber-Reinforced Composites Enabled by a Dual-Dynamic Cross-linked Epoxy Network

The development of covalent adaptable networks has addressed the issue that conventional epoxy thermosets are difficult to degrade and reprocess, but the greater challenge lies in how to overcome the trade-off between excellent degradability and mechanical properties such as stiffness and extensibility. Herein, a new concept of a dual-dynamic cross-linked network composed of dynamic covalent and non-covalent bonds (imine bonds and hydrogen bonds) was proposed for closed-loop recovery of epoxy thermosets/composites. Among them, the additional non-covalent crosslinks were constructed through the designed imine-containing hardener as the medium. The cooperative effects of hydrogen-bond interactions and molecular interlocking of rigid–flexible molecular chains enhanced greatly the stiffness and ductility, and the recoverable energy dissipation enabled the prepared epoxy thermoset to have excellent fracture toughness. Its tensile strength and impact strength reached ∼80.3 MPa and ∼24.2 kJ/m2, respectively. Importantly, driven by the pH-sensitive feature of the dual-dynamic network, the resultant thermoset was completely degraded within 3 h. Along the closed-loop sustainable route, the recoverable oligomer from the thermoset/matrix resin showed good potential in toughening brittle materials with a 55–94% increase in impact strength. Further, the recovered CF cloths that kept their usage value were re-prepared into new high-performance composites, realizing the conversion of waste to high-value applications.

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

AbstractHigh‐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.

Mechanical switching of a comblike dual dynamic polymer network

Hydrogels are polymer networks swollen in water and, therefore, suitable for biomedical applications. For this purpose, hydrogels have to mimic the functionality and mechanics of natural tissues. In drug delivery, for example, the diffusion is crucial and can be controlled through targeted variation of the network mesh-size. In tissue engineering, on the other side, the mechanics plays a fundamental role and can be strengthened through the use of two interpenetrated polymer networks, realizing a double network, or with two dynamic motifs anchored in one common network, realizing a dual dynamic network (DDN). However, current knowledge encompasses mainly nonlinear rheological characterization of these networks. We intend to fill this gap and provide a systematic linear rheological study. To realize this strategy, we combine two supramolecular motifs in a common network, thereby realizing a comblike DDN with the ability to change the building blocks on demand. In our DDN, a tetra-poly(ethylene) glycol (pEG) (the first building block) is functionalized on each arm with two dynamic motifs: terpyridine capable of undergoing metal-complexation with different divalent metal ions, and a thermo-responsive unit consisting of poly(N-isopropylacrylamide) (pNIPAAm) (the second building block) that is capable of undergoing temperature-dependent nano-phase-separation. In particular, we change the molar mass of the tetra-pEG-terpyridine and the pNIPAAm grafted chains. In addition, we investigate two different metal ions that form complexes with the terpyridine. With this platform, we tune the elastic properties on demand, and we systematically study the structure–property relationships with oscillatory shear rheology in the linear regime.

Dual dynamic network system constructed by waterborne polyurethane for improved and recoverable performances

The implementation of the dynamic crosslinking network toward the commodity polymers such as polyurethane has been much highlighted for resource conservation and environmental protection. This work demonstrates a feasible dual dynamic network (DDN) construction of waterborne polyurethane (WPU) by using a biobased trifunctional ketose, 1,3-dihydroxyacetone (DHA) serving as the chain extender. The WPU dispersion was compatible well with the post-added adipic acid hydrazide (ADH) as the water soluble crosslinking agent. When the one-pot system of WPU-ADH was cast into films, covalent adaptive network (CAN) was formed through the condensation of ketohydrazine and carbonyl groups driven by the evaporation of water. The produced acylhydrazone groups would also contribute to the strengthen on the H-bonding crosslinking network. The synergism of the two sets of the networks provided not only the improved mechanical performances, but their > 95% recovery efficiencies on the 28 MPa of strength and 750% fracture elongation in the self-healing, reprocessing and welding tests under moderate heating. In addition, the WPU exhibited as an effective adhesive to metal with the adhesive strength sustained after four times of deconstruction-rebonding circles. The all commercially available components, feasible preparation together with the excellent and recoverable performances suggest an industrializable resolution for the sustainability of environmental friendly WPU materials.

Tuning Dual-Dynamic Network Materials through Polymer Architectural Features

Tuning Dual-Dynamic Network Materials through Polymer Architectural Features

Bioinspired dual dynamic network hydrogels promote cartilage regeneration through regulating BMSC chondrogenic differentiation

How to improve the therapeutic efficacy of cell delivery during mechanical injection has been a great challenge for tissue engineering. Here, we present a facile strategy based on dynamic chemistry to prepare injectable hydrogels for efficient stem cell delivery using hyaluronic acid (HA) and poly(γ-glutamic acid) (γ-PGA). The combination of the guest–host (GH) complexation and dynamic hydrazone bonds enable the HA/γ-PGA hydrogels with physical and chemical dual dynamic network and endow hydrogels a stable structure, rapid self-healing ability, and injectability. The mechanical properties, self-healing ability, and adaptability can be programmed by changing the ratio of GH network to hydrazine bond cross-linked network. Benefitting from the dynamic cross-linking networks, mild preparation process, and cytocompatibility of HA/γ-PGA hydrogels, bone marrow mesenchymal stem cells (BMSCs) show high cell viability in this system following mechanical injection. Moreover, HA/γ-PGA hydrogels can promote BMSC proliferation and upregulate the expression of cartilage-critical genes. Notably, in a rabbit auricular cartilage defect model, BMSC-laden HA/γ-PGA hydrogels can effectively promote cartilage regeneration. Together, we propose a general strategy to develop injectable self-healing HA/γ-PGA hydrogels for effective stem cell delivery in cartilage tissue engineering.

Injectable stretchable self-healing dual dynamic network hydrogel as adhesive anti-oxidant wound dressing for photothermal clearance of bacteria and promoting wound healing of MRSA infected motion wounds

Due to the frequent movement and stretching of skin, traditional wound dressings are difficult to adapt to motion wounds on the stretchable parts of the body surface (e.g. elbow, hip and knee). Moreover, chronic motion wounds are often accompanied by infections. To address these issues, a series of injectable adhesive self-healing photothermal dual dynamic Schiff base network hydrogels were developed based on adipic dihydrazide modified hyaluronic acid, benzaldehyde group functionalized poly(ethylene glycol)–co-poly(glycerol sebacate) and cuttlefish melanin nanoparticles, and their excellent tissue adhesion, stretchability and self-healing properties enable them to adapt to the frequent movement of motion wounds. Meanwhile, the hydrogels can prevent and treat motion wound infections through photothermal antibacterial therapy, and exhibit multifunctions (including anti-oxidation, hemostasis, exudate absorption and sustained release property) to promote wound healing. In in vivo normal and infected full-thickness skin defect motion wound models, the hydrogel dressings significantly prevented wound infections and promoted wound healing with milder inflammation, higher granulation tissue thickness and collagen disposition. Overall, the adhesive self-healing photothermal hydrogels can adapt to frequent movement of motion wounds, and can improve infection and promote healing in both normal and infected motion wounds, indicating their great potential in motion wound treatment in clinics.

Novel titin-inspired high-performance polyurethanes with self-healing and recyclable capacities based on dual dynamic network

It is still a huge challenge that integrating excellent mechanical performance and high healing efficiency into self-healing materials at the same time, even if numerous dynamic bonds have been explored in preparing of self-healing materials in the last 20 years. Herein, we reported a novel titin-inspired strategy to prepare the polyurethanes via introducing dual dynamic network which contained the physical cross-linking of quadruple hydrogen bonds formed by 5-(2-hydroxyethyl)-6-methyl-2-aminouracil (UPy) dimers and the covalent cross-linking of Diels-Alder (D-A) bonds. Specially, relying on the synergistic effect of the dual dynamic network, the resulting polyurethane F50U50-PU exhibited admirable mechanical performance, such as a super-high strength of 51.9 MPa, a superb toughness of 166.7 MJ/m3 and a large elongation at break of 930%. Meanwhile, on account of the dynamic feature of quadruple hydrogen bonds and D-A bonds, the resulting polyurethane showed a high heat-induced healing efficiency of 91.2%. More importantly, the polyurethanes could be recycled by hot-pressing process to regain their initial mechanical properties and integrity. And it was also used as substrate to construct self-healing conductive device, which displayed splendid self-healing of electrical conductivity after damage. It can be envisioned that the polyurethanes with both superior mechanical performance and high healing efficiencies have great application prospect in multifarious fields.