Dual-network Hydrogel Research Articles

Thermally trainable dual network hydrogels

Inspired by biological systems, trainable responsive materials have received burgeoning research interests for future adaptive and intelligent material systems. However, the trainable materials to date typically cannot perform active work, and the training allows only one direction of functionality change. Here, we demonstrate thermally trainable hydrogel systems consisting of two thermoresponsive polymers, where the volumetric response of the system upon phase transitions enhances or decreases through a training process above certain threshold temperature. Positive or negative training of the thermally induced deformations can be achieved, depending on the network design. Importantly, softening, stiffening, or toughening of the hydrogel can be achieved by the training process. We demonstrate trainable hydrogel actuators capable of performing increased active work or implementing an initially impossible task. The reported dual network hydrogels provide a new training strategy that can be leveraged for bio-inspired soft systems such as adaptive artificial muscles or soft robotics.

Understanding Gel-Powers: Exploring Rheological Marvels of Acrylamide/Sodium Alginate Double-Network Hydrogels.

This study investigates the rheological properties of dual-network hydrogels based on acrylamide and sodium alginate under large deformations. The concentration of calcium ions affects the nonlinear behavior, and all gel samples exhibit strain hardening, shear thickening, and shear densification. The paper focuses on systematic variation of the alginate concentration-which serves as second network building blocks-and the Ca2+-concentration-which shows how strongly they are connected. The precursor solutions show a typical viscoelastic solution behavior depending on alginate content and pH. The gels are highly elastic solids with only relatively small viscoelastic components, i.e., their creep and creep recovery behavior are indicative of the solid state after only a very short time while the linear viscoelastic phase angles are very small. The onset of the nonlinear regime decreases significantly when closing the second network (alginate) upon adding Ca2+, while at the same time the nonlinearity parameters (Q0, I3/I1, S, T, e3/e1, and v3/v1) increase significantly. Further, the tensile properties are significantly improved by closing the alginate network by Ca2+ at intermediate concentrations.

Novel exposition on reinforcement mechanism of nanoparticles doped gels for early diagnosis of Parkinson's disease

The early diagnosis of parkinson's disease (EDPD) is of vital importance in preventing dysfunctions of patients and improving their healthcare level. However, the smart devices currently used for EDPD are seriously restricted by the inflexibility, unwieldiness and insensitivity. Herein, polyaniline nanoparticles@ (chitosan-polyacrylic acid) (PANI NPs@(CS-PAA)) hydrogel is prepared with in-situ generated PANI NPs to regulate the performances of CS-PAA dual network (DN) hydrogel. Both the mechanical performances (the elongation at break at 1144% and the toughness at ∼318.36 kJ m−3) and the conductivity (at 9.30 S m−1) are significantly improved. However, both properties do not increase linearly with ANI concentration, but show an inverted-V trend with an inflection point. To investigate the inherent mechanism between PANI NPs and the hydrogels, the measurement with dynamic light scattering, X-ray photoelectron spectroscopy and X-ray diffraction are employed. A superimposed effect of hydrogen bonding between the amide groups of CS-PAA and the imine groups of PANI and hydrophobic association of benzene rings is revealed to play an important role in the propeties of PANI NPs@(CS-PAA) hydrogel. The resultant hydrogel provides high reliable data when serving as flexible electrode in electrocardiogram detection, and regular mornitoring results with fast response time of 0.4 s for EDPD.

Multifunctional high-simulation 3D-printed hydrogel model manufacturing engineering for surgical training.

Advanced bionic organ models with vivid biological structures and wetness and softness are essential for medical-surgical training. Still, there are many challenges in the preparation process, such as matching mechanical properties, good feedback on surgical instruments, reproducibility of specific surgical scenarios, and distinguishability between structural levels. In this paper, we achieved tissuemimicking dual-network (DN) hydrogels with customizable stiffness by adjusting the composition of the hydrogel matrix and the immersion time of the ionic solution to match different biological soft tissues precisely. Combined with advanced threedimensional (3D) printing fabrication techniques, various performance-tunable bionic hydrogel organ models with structural complexity and fidelity, including kidney, liver, pancreas, and vascular tissues, were perfectly fabricated. The simulation and applicability of the model were also simulated for the forced change of the suture needle in the puncture and suture of a single tissue and between different tissues, the cutting of substantive organs by ultrasonic scalpel, the coagulation and hemostasis of blood vessels, the visualization of the internal structure under ultrasound, and the microwave ablation of liver tumors. By constructing advanced biomimetic organ models based on hydrogel with specific and tunable properties, the development of surgical training, medical device testing, and medical education reform will be significantly promoted.

Antimicrobial and Mechanical Properties of Ag@Ti3C2Tx-Modified PVA Composite Hydrogels Enhanced with Quaternary Ammonium Chitosan.

Polyvinyl alcohol (PVA) is a polymeric material with good biocompatibility, excellent hydrophilicity, and a large number of hydroxyl groups. However, due to its insufficient mechanical properties and poor inhibition of bacteria, it has a lack of applications in wound dressings, stent materials, and other fields. In this study, a simple method was used to prepare composite gel materials: Ag@MXene-HACC-PVA hydrogels with a double-network structure were prepared using an acetal reaction. Due to the double cross-linked interaction, the hydrogel has good mechanical properties and is resistant to swelling. The adhesion and bacterial inhibition were enhanced due to the addition of HACC. In addition, the strain sensing properties of this conductive hydrogel were stable, and the GF (specification factor) was 1.7617 at 40-90% strain. Therefore, the dual-network hydrogel with excellent sensing properties, adhesion properties, antibacterial properties, and cytocompatibility has potential applications in biomedical materials, especially as a tissue engineering repair material.

Luminescent dual-network hydrogels based on terpyridine-Eu(III) supramolecular coordination: Fluorene as antenna

The synthesis of a series of side-chain π-conjugated fluorene and terpyridine-functionalized hydrophilic poly(acrylamide) hydrogels via radical random copolymerization was reported. Based on the coordination of terpyridines and europium (III) ions, the dual-network hydrogels containing chemical covalent cross-linking bonds and metallo-supramolecular cross-linking bonds were prepared. Their structures and properties were studied systematically via NMR, IR, SEM, UV–vis absorption spectra, photoluminescence spectra and rheological. The photophysical properties showed that there was Förster energy transfer from conjugated chromophores (emission wavelength at 359–435 nm) to the europium emitter. The water content and the ratio of the energy donor and acceptor in the hydrogels make important influences on the energy transfer and then the emission color of the resulting dual-network hydrogel can be regulated from blue to red via controlling the degree of the energy transfer. Meanwhile, the dual-network hydrogels exhibited small and uniform pore structure and good mechanical properties with large storage and loss moduli.

Hyaluronic acid-based dual network hydrogel with sustained release of platelet-rich plasma as a diabetic wound dressing

In recent years, the incidence of diabetic skin ulcers has increased. Because of its extremely high disability and fatality rate, it brings a huge burden to patients and society. Platelet-rich plasma (PRP) contains a large number of biologically active substances and is of great clinical value in the treatment of various wounds. However, its weak mechanical properties and the consequent abrupt release of active substances greatly limit its clinical application and therapeutic efficacy. Here, we chose hyaluronic acid (HA) and ε-polylysine (ε-PLL) to prepare a hydrogel with the ability to prevent wound infection and promote tissue regeneration. At the same time, using the macropore barrier effect of the lyophilized hydrogel scaffold, platelets in PRP are activated with calcium gluconate in the macropores of the scaffold carrier, and fibrinogen from PRP is converted in a fibrin-packed network forming a gel that interpenetrates the hydrogel scaffold carrier, thus creating a double network hydrogel with slow-release of growth factors from degranulated platelets. The hydrogel not only showed better performance in functional assays in vitro, but also showed more superior therapeutic effects in reducing inflammatory response, promoting collagen deposition, facilitating re-epithelialization and angiogenesis in the treatment of full skin defects in diabetic rats.

Topological Optimisation Structure Design for Personalisation of Hydrogel Controlled Drug Delivery System.

Personalised controlled drug delivery systems (CDDSs) can adjust drug concentration levels according to patient needs, which has enormous research prospects in precision medicine. In this study, the topological optimisation method was utilised in the structural design of a hydrogel CDDS to achieve a parameter-based adjustment of the drug average concentration in the hydrogel. A polyacrylamide/sodium alginate dual-network hydrogel was selected as a drug carrier, and tetracycline hydrochloride was used as a model drug. The topological optimisation model of the hydrogel CDDS was developed. The effects of the mesh size, target concentration, and volume factor on the optimised results were investigated. Hydrogel flow channel structures were obtained, which satisfied the different target concentrations. To verify the rationality of the optimisation model, in vitro drug release experiments were carried out. The results show that the hydrogel CDDS can control drug release within 7 days, and the drug release tends to follow zero-order release behaviour. The adjustable average concentration of tetracycline hydrochloride in hydrogel CDDS is recommended in the range of 20.79 to 31.04 mol/m3. This novel method provides a reference for personalised structure design of CDDS in the context of precision medicine.

Dual Network Hydrogel with High Mechanical Properties, Electrical Conductivity, Water Retention and Frost Resistance, Suitable for Wearable Strain Sensors.

With the progress of science and technology, intelligent wearable devices have become more and more popular in our daily life. Hydrogels are widely used in flexible sensors due to their good tensile and electrical conductivity. However, traditional water-based hydrogels are limited by shortcomings of water retention and frost resistance if they are used as the application materials of flexible sensors. In this study, the composite hydrogels formed by polyacrylamide (PAM) and TEMPO-Oxidized Cellulose Nanofibers (TOCNs) are immersed in LiCl/CaCl2/GI solvent to form double network (DN) hydrogel with better mechanical properties. The method of solvent replacement give the hydrogel good water retention and frost resistance, and the weight retention rate of the hydrogel was 80.5% after 15 days. The organic hydrogels still have good electrical and mechanical properties after 10 months, and can work normally at -20 °C, and has excellent transparency. The organic hydrogel show satisfactory sensitivity to tensile deformation, which has great potential in the field of strain sensors.

High-Sensitivity Composite Dual-Network Hydrogel Strain Sensor and Its Application in Intelligent Recognition and Motion Monitoring

Flexible electronic sensors are attracting more and more attention because of their outstanding flexibility and foldability. Based on this background, a composite hydrogel with excellent flexibility, good stability, and high sensitivity is prepared in this work. This high-performance hydrogel is composed of polyacrylamide, sodium alginate, MXene, and PEDOT:PSS through dynamic supramolecular cross-linking. The electrical conductivity is significantly enhanced by the addition of the conductive polymer PEDOT:PSS and MXene. Hydrogel conductivity increased by 150% with the addition of conductive materials at the same tensile strain. It exhibits high sensitivity (GF = 1.99) and excellent linearity over a wide operating range of 1000% of strain, which ensures the detection performance of the hydrogel sensor under large strain conditions. In addition, it has excellent repeatability (600 cycles) and fast response/recovery times (0.624 s/0.912 s). Due to this excellent performance, it was made into a smart sensor to explore its application in smart electronic skin. The hydrogel sensor and data acquisition module were integrated for real-time monitoring of pressure. We combine it with deep learning algorithms to provide a new solution for human motion recognition, such as joint flexion, facial expression change, health monitoring, and handwriting recognition.

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

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

Carbon Quantum Dot/Chitosan-Derived Hydrogels with Photo-stress-pH Multiresponsiveness for Wearable Sensors.

In recent years, hydrogels have attracted extensive attention in smart sensing owing to their biocompatibility and high elasticity. However, it is still a challenge to develop hydrogels with excellent multiple responsiveness for smart wearable sensors. In this paper, a facile synthesis of carbon quantum dots (CQDs)-doped cross-linked chitosan quaternary/carboxymethylcellulose hydrogels (CCCDs) is presented. Designing of dual network hydrogels decorated with CQDs provides abundant crosslinking and improves the mechanical properties of the hydrogels. The hydrogel-based strain sensor exhibits excellent sensitivity (gauge factor: 9.88), linearity (R2 : 0.97), stretchable ability (stress: 0.67MPa; strain: 404%), good cyclicity, and durability. The luminescent properties are endowed by the CQDs further broaden the application of hydrogels for realizing flexible electronics. More interestingly, the strain sensor based on CCCDs hydrogel demonstrates photoresponsiveness (ΔR/R0 ≈20%) and pH responsiveness (pH range ≈4-7) performance. CCCDs hydrogels can be used for gesture recognition and light sensing switch. As a proof-of-concept, a smart wearable sensor is designed for monitoring human activities and detecting pH variation in human sweat during exercise. This study reveals new possibilities for further applications in wearable health monitoring.

3D gel printing of magnetic hydrogel scaffolds assisted by in-situ gelation in a water level-controlled crosslinker bath

Polyvinylalcohol/chitosan (PVA/CS) is an excellent dual-network hydrogel material, but some significant challenges remain in fabricating composites with specific structures. In this study, 3D gel printing (3DGP) combined with a water-level controlled crosslinker bath was proposed for the rapid in-situ prototyping of PVA/CS/Fe3O4 magnetic hydrogel scaffolds. Specifically, the PVA/CS/Fe3O4 hydrogels were extruded into the crosslinker water to achieve rapid in-situ gelation, improving the printability of hydrogel scaffolds. The effect of the PVA/CS ratio on the rheological and mechanical properties of dual-network magnetic hydrogels was evaluated. The printing parameters were systematically optimized to facilitate the coordination between the crosslinking water bath and printer. The different crosslinking water baths were investigated to improve the printability of PVA/CS/Fe3O4 hydrogels. The results showed that the printability of the sodium hydroxide (NaOH) crosslinker was significantly better than that of sodium tripolyphosphate (TPP). The magnetic hydrogels (PVA: CS= 1: 1) crosslinked by NaOH had better compressive strength, swelling rate, and saturation magnetization of 1.17 MPa, 92.43%, and 22.19 emu/g, respectively. The MC3T3-E1 cell culture results showed that the PVA/CS/Fe3O4 scaffolds promoted cell adhesion and proliferation, and the scaffolds crosslinked by NaOH had superior cytocompatibility. 3DGP combined with a water-level controlled crosslinker bath offers a promising approach to preparing magnetic hydrogel materials.

Phosphoserine enhanced Cu-doped bioactive glass dynamic dual-network hydrogel for craniofacial bone defect repair.

Flexible hydrogels containing various osteogenic inorganic constituents, which can accommodate complicated shape variations, are considered as ideal grafts for craniofacial bone defect reconstruction. However, in most hybrid hydrogels, poor interaction between the polymer network and particles has detrimental effects on hydrogel rheological and structural properties, clinical manipulation and repair efficacy. In this article, we designed and prepared a series of hyaluronic acid composite hydrogel containing Cu-doped bioactive glass (CuBG) and phosphoserine (PS), in which hyaluronic acid was modified by methacrylate groups and phenylboronic acid groups to form a double crosslinked network. PS acted as an interaction bridge of CuBG particles and HAMA-PBA network to improve the mechanical properties of the composite hydrogels. The CuBG/PS hydrogels exhibited suitable rheological properties (injectable, self-healing, shape-adaptable), bone tissue integrating ability and anti-bacterial property. Meanwhile, we found that CuBG and PS have synergistic effect on improving osteogenic efficiency both in vitro and in vivo, particularly when the ratio of CuBG to PS is lower than 3 (9CB/3PS). This work provided a versatile and scalable approach to enhanced the interaction within inorganic particles and polymer network in hydrogels without extra modification on components.

Highly stable flexible supercapacitors enabled by dual-network polyampholyte hydrogel without additional electrolyte additives

High-performance dual-network polyampholyte hydrogel is designed for flexible supercapacitors with remarkable mechanical stability and thermal and cycling stability. The dual-network hydrogel is produced through physical and chemical cross-linking between the random copolymer of the monomers containing Na+ and Cl- ions and high-viscosity xanthan gum. It shows high ionic conductivity (38.84 mS cm−1), low activation energy (0.089 eV), satisfactory mechanical properties, fire-resistant, and sturdy contact with electrodes. In addition, the self-containing mobile ions inside the hydrogel electrolyte without extra electrolyte additives help to significantly reduce the concentration polarization. Accordingly, the quasi-solid supercapacitor based on active carbon delivers super mechanical and thermal stability with no significant capacitance reduction after various deformations, compressing, and different temperatures. Besides, it delivers high specific capacitance of 110F g−1 at 0.5 A/g with 87.6 % retention after 10,000 cycles, showing maximum energy density and power density of 33.1 Wh kg−1 and 200.1 W kg−1. Notably, high capacitance retention (84.2 %) can be maintained after 7500 cycles even at 50 ℃. Therefore, this work provides a promising strategy to produce a kind of multifunctional hydrogel electrolyte for highly stable and durable next-generation flexible energy storage devices.

Rapid gelation of dual physical network hydrogel with ultra‐stretchable, antifreezing, moisturing for stable and sensitive response

AbstractDual physical network hydrogel possesses robust energy dissipation mechanism. However, the demanding conditions of the second monomer radical polymerization aren't benefit for the dispersion of conductive filler. Moreover, the stable and sensitive response under extreme environment puts forward the requirements for mechanical, antifreezing and moisture retention properties. Herein, a dual physical networks hydrogel (polyacrylic acid‐chitosan‐graphene/glycerol, noted as PAA‐CS‐G/Gly) was prepared rapidly (<0.5 h) without chemical cross‐linking agents at room temperature. The rapid gelation, ionic coordination of Ag+ together with certain viscosity chitosan promoted the dispersion of graphene. PAA‐CS‐G/Gly showed ultra‐stretchable properties (~2500%), good toughness (3.11 MJ/m3), breaking strength (0.27 MPa) and fatigue resistance. PAA‐CS‐G/Gly had good adhesion properties, outstanding tolerance for freezing (−80°C) and moisture retention. More importantly, PAA‐CS‐G/Gly strain sensor had excellent sensitivity (GF, up to 9.449) at 300% ~ 900% strain. It could sensitively detect human joint movements and even subtle activities such as talking and swallowing. PAA‐CS‐G/Gly hydrogel is expected to adhere directly to the human body for flexible monitoring of human size movement under extreme environmental conditions.

An ultrasound-induced MXene doped PAM–SA super-tough hydrogel

Here we reported a novel ultrasound-induced polymerization to achieve a polyacrylamide–sodium alginate (SA) dual network hydrogel via a redox reaction with MXene (Ti3C2) as a reductant and potassium persulfate (KPS) as an oxidant.

Herbal molecule-mediated dual network hydrogels with adhesive and antibacterial properties for strain and pressure sensing.

Multifunctional integration is the focus of hydrogel-based flexible sensors, and formation of a dual network (DN) could shed light on the fabrication of hydrogels with multifunctionality and enhanced properties. In this study, a DN hydrogel was fabricated by the self-assembly of herbal molecule glycyrrhizic acid (GA) as the first hydrogel network and subsequent photocrosslinking of methacrylated sodium alginate (SA-MA) to form the second network. Profiting from the good compatibility between the two hydrogel networks, the obtained DN hydrogels with a homogeneous porous microstructure were endowed with remarkably enlarged stretching (114.5%) and compression (74.4%) strains. In addition, they were demonstrated to display excellent bacteriostatic activity (>99.9%) against Escherichia coli and Staphylococcus aureus owing to the synergetic antibacterial effect of GA and SA-MA. The DN hydrogels as strain sensors possessed high sensitivity (GF = 1.39), linear sensing (R 2 > 0.99), rapid response (180 ms), and good stability (1300 times) for human motion detection. Besides, the DN hydrogels could also be used to conduct pressure sensing such as application of heavy weights and even human pulses. All results suggest that the developed DN hydrogels have great potential in serving as epidermal and implantable flexible sensors for human health monitoring.

Anti-swelling hydrogels based on surfactant–polymer interactions for underwater sensing with excellent mechanical properties

We synthesized an anti-swelling, tough, double-crosslinked, dual-network hydrogel, P(AA-SMA)-CMC-Na, for underwater sensing.

A photocrosslinked methacrylated carboxymethyl chitosan/oxidized locust bean gum double network hydrogel for cartilage repair.

Repairing articular cartilage defects is a great challenge due to the poor self-regenerative capability of cartilage. Inspired by active substances found in the natural cartilage extracellular matrix, we used methacrylated carboxymethyl chitosan (MA-CMCS) and oxidized locust bean gum (OLBG) as the hydrogel backbone, and prepared a photocrosslinked dual network hydrogel containing allicin and decellularized cartilage powder (DCP). The rheological, swelling and water retention capacities of MA-CMCS@OLBG-Allicin/DCP (MCOAC) hydrogels were investigated to confirm the successful preparation of hydrogels suitable for cartilage repair. The MCOAC hydrogels showed good antibacterial ability to kill S. aureus and E. coli and anti-inflammatory properties due to the introduction of allicin. Furthermore, MA-CMCS@OLBG-Allicin/DCP hydrogels presented good cytocompatibility due to the addition of DCP, which could promote chondrocyte proliferation and promote the differentiation of BMSCs to chondrocytes. Further studies in vivo demonstrated that the DCP-contained MCOAC hydrogel exhibited superior performance in promoting cartilage tissue growth and wound healing in articular cartilage defects. Thus, the MCOAC hydrogel is a promising cartilage repair hydrogel with potential for clinical use.