Physical Crosslinking Research Articles

Induction of polymer-grafted cellulose nanocrystals in hydrogel nanocomposites to increase anti-swelling, mechanical properties and conductive self-recovery for underwater strain sensing

Anti-swelling conductive hydrogels with simultaneous high tensile strength (>1 MPa) and fast self-recovery are promising candidates for underwater strain sensing, but their preparation remains challenging. Herein, novel anti-swelling conductive nanocomposite hydrogels were fabricated based on poly(acrylamide-co-acrylic acid) (P(AM-co-AA)), polymer-grafted cellulose nanocrystals (CNCs) and Fe3+ ions through a strategy combining nano-reinforcing and multiple physical crosslinking. Due to the presence of interfacial H-bonds, polymer-grafted cellulose nanocrystals played important role in endowing hydrogels with anti-swelling capacity and enhanced mechanical performance. The obtained nanocomposite hydrogels exhibited relatively low swelling ratio (2.9–3.3 g/g), high tensile strength (>1.5 MPa), fast self-recovery (86 % recovery of hysteresis within 5 min) and conductivities of 0.0534–0.0593 S/m. The combination of excellent tensile properties and conductivity endowed the hydrogel-based strain sensors with good sensitivity (GF ≈ 0.8) and reliable cycling repeatability in 0–100 % strain range. Notably, the nanocomposite hydrogels can maintain their mechanical and sensing performance after soaking in water for 14 days, making them applicable for human motion detection both in air and underwater. Hence, this work provided a facile method to construct highly robust and anti-swelling CNC-reinforced conductive hydrogels, which have potential applications in underwater strain sensing and beyond.

On the dual crosslinking for functionality enhancement of poly (acrylamide-co-acrylic acid)/chitosan-aluminum (III) ions and its characterization and sensory hydrogel fibers

In this report, we present a dual crosslinking hydrogel fiber made from polyamine saccharides chitosan (CS), synthesized through UV polymerization. This process utilizes Irgacure 2959 and N,N′-Methylenebisacrylamide (MBAA) as initiators, followed by immersion in an aluminum chloride (AlCl3) solution. The resulting hydrogel incorporates a dual crosslinking mechanism, quantitatively studied via Nuclear Magnetic Resonance (NMR) spectroscopy. This mechanism involves chemical crosslinking through radical graft polymerization of acrylamide and acrylic acid onto CS in the presence of MBAA, and physical crosslinking through hydrogen bonding interactions between P(AAm-co-AA) and a metal coordination bond. The mechanical properties of the hydrogel fiber enable it to withstand stresses up to 656 kPa and strains exceeding 300 %. Additionally, the hydrogel fiber exhibits conductivity at 1.96 Scm−1. Serving as a multifunctional material, it acts as a strain sensor and finds utility in optics. Remarkably, it demonstrates the capability to detect human motions such as finger bending and minor deformations like vibrations of the vocal cords. Furthermore, its ability to guide dynamic light makes it promising for optical applications. Consequently, this multifunctional hydrogel fiber emerges as a highly promising candidate for diverse applications in fields such as bioengineering and electronics.

Processable, reversible, and reusable 100 % bio-based pressure sensitive adhesives using nanostarch

We developed a 100 % bio-based pressure sensitive adhesive (PSA) possessing strong adhesion, as well as reusability, recyclability, and on-demand removability. The adhesive formulation is based on a colloidal mixture of starch (specifically amylopectin) nanoparticles and cellulose nanofibrils, combined with an aqueous solution of sorbitol and glycerol. Optimization of water supply and substitution of water with hygroscopic glycerol were implemented to address the challenges caused by the use of high water contents in hydrogels. By leveraging physical crosslinking through hydrogen bonding, we achieved high adhesion strength, reversibility, and reusability with 100 % bio-based materials. The optimal formulation demonstrates excellent rheological and adhesion properties, which are comparable to petrochemical-based adhesives in terms of tack, peel strength, and shear strength. While there are areas for further optimization, this work provides a foundational step towards a more sustainable adhesive industry.

Silicone‐containing polyurea elastomer possessing main‐chain boron–oxygen bonds with delayed stress relaxation and improved adhesive properties

AbstractPolyurea (PU) elastomers have attracted considerable attention in the field of protective polymeric coatings. In this work, a dithiol‐terminated boronic ester was synthesized and used to incorporate dynamic boron–oxygen (B–O) bonds in the PU main chain based on thiol isocyanate while amino‐terminated polydimethylsiloxane (PDMS) was introduced to retain good chain flexibility. The modified PU elastomer was found to have a microphase‐separated structure in which the hard blocks served as physical crosslinks. The glass transition temperature (Tg) slightly increases when dynamic B–O bonds exist while further introduction of PDMS soft segment can lower Tg to −55.63 °C. The introduction of dynamic B–O bonds and diminished hydrogen bonding led to a decrease in mechanical strength and elongation at break. Interestingly, the simultaneous incorporation of PDMS and dynamic B–O bonds is favorable for strain rate dependence and suppressing stress relaxation. The potential for bond‐exchange interactions between the dynamic B–O bonds and hydroxyl groups on metal surfaces substantially improved the adhesion of the PU elastomer to metal substrates. Therefore, our work can offer valuable insights for the structural design of functional PU coatings tailored for anti‐impact applications. © 2024 Society of Chemical Industry.

Eco-Friendly Production of Polyvinyl Alcohol/Carboxymethyl Cellulose Wound Healing Dressing Containing Sericin.

Wound dressing production represents an important segment in the biomedical healthcare field, but finding a simple and eco-friendly method that combines a natural compound and a biocompatible dressing production for biomedical application is still a challenge. Therefore, the aim of this study is to develop wound healing dressings that are environmentally friendly, low cost, and easily produced, using natural agents and a physical crosslinking technique. Hydrogel wound healing dressings were prepared from polyvinyl alcohol/carboxymethyl cellulose and sericin using the freeze-thawing method as a crosslinking method. The morphological characterization was carried out by scanning electron microscopy (SEM), whereas the mechanical analysis was carried out by dynamic mechanical analysis (DMA) to test the tensile strength and compression properties. Then, the healing property of the wound dressing material was tested by in vitro and ex vivo tests. The results show a three-dimensional microporous structure with no cytotoxicity, excellent stretchability with compressive properties similar to those of human skin, and excellent healing properties. The proposed hydrogel dressing was tested in vitro with HaCaT keratinocytes and ex vivo with epidermal tissues, demonstrating an effective advantage on wound healing acceleration. Accordingly, this study was successful in developing wound healing dressings using natural agents and a simple and green crosslinking method.

Natural multi-actives composited hydrogel patches for diabetic wound healing

Biomedical patches have garnered recognition for their efficacy in diabetic wound management. Current research efforts are focused on developing natural and efficient hydrogel patches in order to reduce inherent side effects and enhance therapeutic outcomes. In this study, we present natural multi-actives composited hydrogel patches for diabetic wound management. The novel medical patch was fabricated using freeze-dried grape peel, oligomeric proanthocyanidins (OPC) and puerarin based on spontaneous physical crosslinking. With the incorporation of OPC, the natural patch exhibited favorable photothermal antibacterial properties, effectively inhibiting S. aureus and E. coli under 808 nm near-infrared irradiation. In addition, the grape peel could induce M2 macrophage polarization and scavenge reactive oxygen species, showcasing immunomodulatory effects. Moreover, the puerarin component in the patches was discovered to promote endothelial cell proliferation and migration, thereby facilitating angiogenesis in vitro. Based on these features, we have demonstrated the antibacterial, antioxidant, anti-inflammatory, and angiogenic effects of the patches in vivo. Thus, we believe that the natural multi-actives composite patch holds significant promise for diabetic wound treatment and broader biomedical applications.

Highly Water‐Rich Robust Coating for Separating Immiscible Liquids Mixtures of Wide Range of Surface Tension Differences

AbstractDeveloping mechanically robust and chemically tolerant coatings that maintain a high water content remains an extremely challenging task to pursue to date. Here, an optimum reinforcement of a hollow nano‐clay i.e., halloysite in a dual crosslinked and interpenetrating polymeric network is introduced to yield a high (≈95 wt%) water content coating with an ability to improve toughness (9.9 ± 0.6 MJm−3 Vs. 0.5 ± 0.03 MJ m−3) of a deformable fibrous substrate. The association of covalent and physical crosslinking chemistries provides essential tolerance against exposures to diverse severe chemically complex conditions, including extremes of pH, seawater, river water, and organic solvents. High water content in the prepared hydrogel network endows a robust bio‐inspired underwater nonadhesive superoleophobicity with oil contact angle of 160.7 ± 0.2° and force of oil‐droplet adhesion of 8.7 ± 0.3 µN. This approach provides a liquid selective filtrating membrane with ultrahigh crude oil/water separation efficiency (99.7%), superior intrusion pressure (3.5 ± 0.4 kPa), relatively high separation flux (11,162 Lm−2 h−1), and the ability to perform even when the surface tension of aqueous phase is brought down to similar of oily phase. Moreover, a mixture of immiscible, non‐aqueous liquids having differences in surface tension below 2.5 mN m−1 is successfully separated.

A bioadhesive pacing lead for atraumatic cardiac monitoring and stimulation in rodent and porcine models.

Current clinically used electronic implants, including cardiac pacing leads for epicardial monitoring and stimulation of the heart, rely on surgical suturing or direct insertion of electrodes to the heart tissue. These approaches can cause tissue trauma during the implantation and retrieval of the pacing leads, with the potential for bleeding, tissue damage, and device failure. Here, we report a bioadhesive pacing lead that can directly interface with cardiac tissue through physical and covalent interactions to support minimally invasive adhesive implantation and gentle on-demand removal of the device with a detachment solution. We developed 3D-printable bioadhesive materials for customized fabrication of the device by graft-polymerizing polyacrylic acid on hydrophilic polyurethane and mixing with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to obtain electrical conductivity. The bioadhesive construct exhibited mechanical properties similar to cardiac tissue and strong tissue adhesion, supporting stable electrical interfacing. Infusion of a detachment solution to cleave physical and covalent cross-links between the adhesive interface and the tissue allowed retrieval of the bioadhesive pacing leads in rat and porcine models without apparent tissue damage. Continuous and reliable cardiac monitoring and pacing of rodent and porcine hearts were demonstrated for 2 weeks with consistent capture threshold and sensing amplitude, in contrast to a commercially available alternative. Pacing and continuous telemetric monitoring were achieved in a porcine model. These findings may offer a promising platform for adhesive bioelectronic devices for cardiac monitoring and treatment.

Highly Sensitive Flexible Capacitive Pressure Sensor Based on a Multicross-Linked Dual-Network Ionic Hydrogel for Blood Pressure Monitoring Applications.

Flexible capacitive pressure sensors based on ionic hydrogels (IHs) have garnered significant attention in the field of wearable technology. However, the vulnerability of traditional single-network hydrogels to mechanical damage and the complexity associated with preparing double-network hydrogels present challenges in developing a highly sensitive, easily prepared, and durable IH-based flexible capacitive pressure sensor. This study introduces a novel multicross-linked dual-network IH achieved through the physical and chemical cross-linking of polymers polyvinyl alcohol (PVA) and chitosan (CS), ionic solution H3PO4, and cross-linking agent gum arabic. Flexible capacitive pressure sensors, characterized by high sensitivity and a broad pressure range, are fabricated by employing mesh as templates to design cut-corner cube microstructures with high uniformity and controllability on the IHs. The sensor exhibits high sensitivity across a wide pressure range (0-290 kPa) and with excellent features such as high resolution (∼1.3 Pa), fast response-recovery time (∼11 ms), and repeatable compression stability at 25 kPa (>2000 cycles). The IHs as a dielectric layer demonstrate long-term water retention properties, enabling exposure to air for up to 100 days. Additionally, the developed sensor shows the ability to accurately measure the pulse wave within the small pressure range. By combining the pulse wave acquired by the sensor with a trained neural network model, we achieve successful blood pressure (BP) prediction, meeting the standards set by the Association for the Advancement of Medical Instrumentation and the British Hypertension Society. Ultimately, the sensor proposed in this study holds promising prospects for broad applications in high-precision wearable medical electronic devices.

Self-assembly of curdlan molecules for the formation of thermally induced gels

The differences in the self-assembly process between cold-set (CCS) and heat-set (CHS) curdlan gels were investigated using micro-differential scanning calorimetry, atomic force microscopy, and small-angle X-ray diffraction. The results indicate that the triple-helix structure of curdlan dissociated into single helices in its suspension state (C-SUS) at 65 °C. Upon cooling to around 38 °C, these single helices assembled into long, thick fibers with a height of up to 11.50 nm, contributing to the gel structure of CCS. Heating C-SUS from 65 °C to 90 °C caused the single helices to transform into triple helices due to hydrophobic interactions. Subsequent cooling to 25 °C, led to the formation of short, thick bundles with a height of up to 8.78 nm, forming the network structure of CHS gel. As a consequence, CHS gels exhibited higher hardness and elasticity but lower fatigue resistance. This is attributed to an increased degree of physical cross-linking, as evidenced by a reduction in the size (Ξ) and spacing (ξ) of high-density domains within the gel structure, and a simpler mechanism of energy dissipation through alignment of the molecular chain segment. These findings are valuable for the design and development of curdlan-based gels with tailored mechanical properties.

SYNTHESIS AND STUDY OF THE INFLUENCE OF ALKALI CONCENTRATION AND TEMPERATURE ON THE PHYSICOCHEMICAL PROPERTIES OF CRYOGELS BASED ON GELATIN AND CHITOSAN

Much of the polymer research is focused on improving existing polymers or developing new biomaterials with tunable properties. Natural polymers that have certain segments that contribute to an additional therapeutic effect are more often used as a biocompatible polymer. Polymers can be produced using a variety of methods, including covalent cross-linking, dynamic covalent cross-linking, physical cross-linking, cryopolymerization, 3D printing, electrospinning, etc. Cryopolymerization is a unique method and has several advantages over other methods. By cryofreezing it is possible to obtain a porous structure in which the size and volume of the pores can be controlled by changing the concentration of the initial monomers and temperature. The purpose of this study is to determine the effect of alkali concentration and cryopolymerization temperature on the properties of cryogels. The objects of study in this work are cryogels based on gelatin and chitosan. Methodology. The functional groups of the cryogels were determined by IR spectroscopy. The results of a study of the sorption and desorption of polymers are presented. The results of polymer degradation in phosphate-saline solution over 8 weeks are also shown. These studies were based on changes in mass, that is, they were carried out using the gravimetric method. Conclusion. The results of a study of the influence of alkali concentration and temperature on the physicochemical properties of cryogels based on gelatin and chitosan are presented. Cryogels based on gelatin and chitosan are synthesized without the use of harmful chemical cross-linking agents, which makes them attractive for tissue engineering.

Non-covalently crosslinked networks MXene-doped poly(eutectic) conductive elastomers with antimicrobial, self-healing, tunable mechanical properties, and wide temperature durability

Poly(eutectic) elastomers, as an emerging category of flexible electronic materials, have garnered growing interest for their cost-effectiveness, non-volatility, and biocompatibility. Nonetheless, they encounter challenges including limited functionalities, sensitivity, durability, and mechanical properties. This study involved synthesizing various MXene-doped poly(eutectic) elastomers using robust acrylamide and soft acrylic acid as organic monomers, minor MXene nanosheets as inorganic fillers and physical crosslinkers, and a rapid in-situ photopolymerization method within 2 min. Owing to the synergistic effect of thermodynamic self-assembly, high-density hydrogen bonding, and cation-dipole interactions in the matrix networks, the resulting non-covalently crosslinked elastomers exhibited remarkable mechanical strength (up to ∼ 16.2 MPa) and impressive tensile properties (nearly 700 %), along with rapid electrical self-healing (within 0.046 s) and the ability to withstand loads up to 2500 times their weight following self-healing without fracturing. Notably, these elastomers also demonstrated excellent microstrain (1 %–10 %) sensitivity with a gauge factor of 2.02, wide temperature tolerance (−20 °C ∼ 60 °C), outstanding harsh temperature durability (−20 °C) exceeding 22,000 cycles, and antibacterial properties. Furthermore, these elastomers-assembled strain sensors displayed real-time and rapid response in human motion detection and wireless signal transmission, presenting a promising approach for designing functionally integrated elastomeric materials.

Extremely sensitive mechanochromic photonic hydrogels with ultrahigh mechanical properties for multicolor displays by naked eyes

Photonic soft materials, especially responsive photonic hydrogels (RPHs) with periodic permittivity on the submicroscale, have been garnering interest as colorimetric indicators and mechanochromic sensors. However, the fabrication of RPHs with both bright discoloration, satisfactory mechanical properties, and excellent mechanochromic sensitivity to meet the practical applications is still a great challenge. Herein, we develop a novel photonic crystal material using a Fe3O4 array embedded poly(N-isopropylacrylamide-co-acrylamide)/ laponite-XLS (PNA-XLS) hydrogel, which is dual-cross-linked by chemical and physical cross-linkers. Due to the interaction of sparse chemical links and apposite physical links between the polymeric networks, the PNA-XLS exhibits a significant energy dissipation and high deformation capacity, with an enhanced tensile strength above 819 kPa and elongation above 1015 %. It almost has a full-color tunable range and shows bright discoloration that can be reversibly actuated by bending, stretching, and small pressures (Pa level), with extremely high sensitivities of pressure (161 nm kPa−1) and tension (1.52 nm %−1). Moreover, its self-adhesion (133 kPa) would make it be an appealing candidate to develop portable sensors or wearable devices without auxiliary adhesive tools. Besides, elastic hydrogels with programmable and multicolor patterns can be designed by the mask-assisted UV photopolymerization of regional pregel solution. Therefore, such hydrogel has a great application potential in colorimetric indicators, mechanochromic sensors, anti-counterfeiting and wearable devices.

Acryloyl chitosan as a macro-crosslinker for freezing-resistant, self-healing and self-adhesive ionogels-based multicompetent flexible sensors

Here, a polysaccharide derivative acryloyl chitosan (AcCS) is exploited as macro-crosslinker to synthesize a novel ionogel poly (acrylic acid-co-1-Vinyl-3-butyl imidazolium chloride) (AA-IL/AcCS) via a one-pot method. AcCS provides abundant physical and chemical crosslinking sites contributing to the high mechanical stretchability (elongation at break 600 %) and strength (tensile strength 137 kPa) of AA-IL/AcCS. The high-density of dynamic bonds (hydrogen bonds and electrostatic interactions) in the network of ionogels enables self-healing and self-adhesive features of AA-IL/AcCS. Meanwhile, AA-IL/AcCS exhibits high ionic conductivity (0.1 mS/cm) at room temperature and excellent antifreeze ability (−58 °C). The AA-IL/AcCS-based sensor shows diverse sensory capabilities towards temperature and humidity, moreover, it could precisely detect human motions and handwritings signals. Furthermore, AA-IL/AcCS exhibits excellent bactericidal properties against both gram-positive and gram-negative bacteria. This work opens the possibility of polysaccharides as a macro-crosslinkers for preparing ionogel-based sensors for wearable electronics.

Physically cross-linked PVA/f-MWCNTs nanocomposite hydrogel with enhanced thermal, mechanical, and dielectric properties

This work offers a new method for the preparation of poly (vinyl alcohol)/f-MWCNTs nanocomposite hydrogel. Employing a physical cross-linking method, fabricated high-strength nanocomposite hydrogel in one step at room temperature without following the traditional repeated freeze-thaw method. Optical microscopy images indicate the uniform dispersion of f-MWCNTs in the PVA matrix with average agglomerate size of 5–6 µm. Morphology investigation showed entangled, more dense network structure after addition of f-MWCNTs. Scissoring of inter chain H-bonding and establishing of intermolecular H-bonding between -OH and -COOH group of PVA and f-MWCNTs examined by ATR-FTIR. Delay in thermal degradation of PVA/f-MWCNTs nanocomposite hydrogel with f-MWCNTs suggested by thermos-gravimetry analysis. Improved melting and crystalline temperature examined by differential scanning calorimetry. PVA/f-MWCNTs nanocomposite hydrogel showed ⁓ 5 and 6 times of modulus and hardness respectively than pristine PVA hydrogel. Oscillatory rheology analysis suggests the robust gel-like network formed upon addition of f-MWCNTs into the PVA matrix. PVA/f-MWCNTs nanocomposite hydrogel showed 13 times dielectric constant than pristine PVA hydrogel along with small dielectric loss investigated by broadband dielectric spectroscopy (BDS). Enhanced thermal, mechanical and dielectric properties make the fabricated PVA/f-MWCNTs nanocomposite hydrogel a potential candidate for the energy storage device and electronics application.

A universal solvent-replacement strategy to convert alginate hydrogels into mechanically strong and transparent alginate eutectogels for sensitive strain sensors

Eutectogels based on natural polymers have attracted significant attention as an alternative to easily dehydrated hydrogels and expensive ionogels in the development of flexible strain sensors. The feasibility of employing eutectogels derived from pure natural polymers could be greatly enhanced if their mechanical properties satisfy the requirements of applications. Herein, alginate eutectogels (AEs) with high mechanical properties (tensile strain 217 % and strength 2.26 MPa at fracture), and excellent transparency (over 90 %) are acquired via CaCl2 inducing ionic crosslinking and subsequent deep eutectic solvents (DESs, composed of glycerol and choline chloride) initiating physical crosslinking with a universal solvent- replacement strategy. Among them, sodium alginate, a natural polysaccharide polymer, is selected as representative supporting scaffolds and forms water-insoluble alginate hydrogels (AHs) in CaCl2 coagulation bath. The exchange of DESs with water of AHs not only restrengthens the polymer network by physical crosslinking, but also endows the obtained AEs with long-term solvent retention and high temperature resistance. In addition, the AEs not only have high reliability but also exhibit better linear sensitivity in a wide strain range (0–200 %). In particular, the AEs display multiple sensitivity to stretching, bending, and human motions, demonstrating feasibility as sensitive strain sensors.

A Cellulose-Based Dual-Crosslinked Framework with Sensitive Shape and Color Changes in Acid/Alkaline Vapors.

Cellulose detectors, as green sensors, are some of the defensive mechanisms of plants which combat environmental stresses. However, extracted cellulose struggles to fulfil these functionalities due to its rigid physical/chemical properties. In this study, a novel cellulose dual-crosslinked framework (CDCF) is proposed. This comprises a denser temporary physical crosslinking bond (hydrogen bonding) and a looser covalent crosslinking bond (N,N-methylenebisacrylamide), which create deformable spaces between the two crosslinking sites. Abundant pH-sensitive carboxyl groups and ultralight, highly porous structures make CDCF response very sensitive in acid/alkaline vapor environments. Hence, a significant shrinkage of CDCF was observed following exposure to vapors. Moreover, a curcumin-incorporated CDCF exhibited dual shape and color changes when exposed to acid/alkaline vapors, demonstrating great potential for the multi-detection of acid/alkaline vapors.

Multifunctional double-network hydrogel with antibacterial and anti-inflammatory synergistic effects contributes to wound healing of bacterial infection

Wound infection not only hinders the time sequence of tissue repair, but also may lead to serious complications. Multifunctional wound dressings with biocompatibility, excellent mechanical properties and antibacterial properties can promote wound healing during skin infection and reduce the use of antibiotics. In this study, a multifunctional dual-network antibacterial hydrogel was constructed based on the electrostatic interaction of two polyelectrolytes, hydroxypropyl trimethyl ammonium chloride chitosan (HACC) and sodium alginate (SA). Attributing to the suitable physical crosslinking between HACC and SA, the hydrogel not only has good biocompatibility, mechanical property, but also has broad-spectrum antibacterial properties. In vivo results showed that the hydrogel could regulate M2 polarization, promote early vascular regeneration, and create a good microenvironment for wound healing. Therefore, this hydrogel is an effective multifunctional wound dressing. Consequently, we propose a novel hydrogel with combined elements to expedite the intricate repair of wound infection.

Exploring Applications and Preparation Techniques for Cellulose Hydrogels: A Comprehensive Review.

Cellulose hydrogels, formed either through physical or chemical cross-linking into a three-dimensional network from cellulose or its derivatives, are renowned for their exceptional water absorption capacities and biocompatibility. Rising demands for sustainable materials have spurred interest in cellulose hydrogels, attributed to their abundant supply, biodegradability, and non-toxic nature. These properties highlight their extensive potential across various sectors including biomedicine, the food industry, and environmental protection. Cellulose hydrogels are particularly advantageous in applications such as drug delivery, wound dressing, and water treatment. Recent large-scale studies have advanced our understanding of cellulose preparation and its applications. This review delves into the fundamental concepts, preparation techniques, and current applications of cellulose hydrogels in diverse fields. It also discusses the latest advances in nano-lignin-based hydrogels, providing a comprehensive overview of this promising material and offering insights and guidance for future research and development.

Hydrogels composite optimized for low resistance and loading–unloading hysteresis for flexible biosensors

With the advancement of wearable and implantable medical devices, hydrogel flexible bioelectronic devices have attracted significant interest due to exhibiting tissue-like mechanical compliance, biocompatibility, and low electrical resistance. In this study, the development and comprehensive performance evaluation of poly(acrylic acid)/ N,N′-bis(acryloyl) cystamine/ 1-butyl-3-ethenylimidazol-1-ium:bromide (PAA/NB/IL) hydrogels designed for flexible sensor applications are introduced. Engineered through a combination of physical and chemical cross-linking strategies, these hydrogels exhibit strong mechanical properties, high biocompatibility, and effective sensing capabilities. At 95 % strain, the compressive modulus of PAA/NB/IL 100 reach up to 3.66 MPa, with the loading–unloading process showing no significant hysteresis loop, indicating strong mechanical stability and elasticity. An increase in the IL content was observed to enlarge the porosity of the hydrogels, thereby influencing their swelling behavior and sensing functionality. Biocompatibility assessments revealed that the hemolysis rate was below 5 %, ensuring their suitability for biomedical applications. Upon implantation in rats, a minimal acute inflammatory response was observed, comparable to that of the biocompatibility control poly(ethylene glycol) diacrylate (PEGDA). These results suggest that PAA/NB/IL hydrogels hold promise as biomaterials for biosensors, offering a balance of mechanical integrity, physiological compatibility, and sensing sensitivity, thereby facilitating advanced healthcare monitoring solutions.