Starch as a reinforcement agent for poly(ionic liquid) hydrogels from deep eutectic solvent via frontal polymerization

Robust, transparent, self-healable, recyclable all-starch-based gel with thermoelectric capability for wearable sensor

Conventional all-starch-based (ASB) gels are weak and lack ductility. The preparation of a robust ASB gel with multi-functionalities e.g., self-healing, anti-freezing, conductivity, and so forth, is highly desirable but challenging. Herein, a new kind of ASB gel was prepared by gelatinizing starch in urea and choline chloride solution (UC) with the aid of water. Its tensile strength was up to 1.08 MPa with a tensile strain of 313 %, and this value hardly changed after 10 days ageing. A high healing efficiency of 98 % can be achieved after 1 h of healing at room temperature, and the healed tensile strength reaches up to ca. 1.06 MPa, which is almost the highest value for ASB gel. The resultant ASB gel can surfer from bending and twisting at -80 °C. Moreover, ASB gel also exhibits excellent biocompatibility and biodegradability. In addition, UC endowed the ASB gel with ion conductivity, allowing it to be used as a flexible strain sensor to monitor human movement. The ion-conductive ASB gel also exhibited thermoelectric ability with a Seebeck coefficient of 2.5 mV K-1, which can be further improved to 5 mV K-1 with a maximum output voltage of 252 mV by introducing a gradient of ionic concentration.

Green, tough, and heat-resistant: A GDL-induced strategy for starch-alginate hydrogels

Hydrogels fabricated by non-covalent interaction garnered significant attention for their eco-friendly and robust mechanical attributes, and are often used in food, medicine and other fields. Although starch-alginate hydrogels exhibit high adhesion and are environmentally sustainable, their applications are limited due to their low elasticity and hardness. Addressing this challenge, we introduce a solvent-induced strategy using glucolactone (GDL) to fabricate hydrogels with enhanced strength and thermal resilience. Utilizing corn starch with varying amylose contents, sodium alginate and calcium carbonate to prepare a double network structure. This GDL-induced hydrogel outperforms most previous starch-based hydrogels in mechanical robustness and thermal stability. Typical starch-alginate hydrogel had a homogeneous network structure and exhibited a high tensile stress of 407.57 KPa, and a high enthalpy value of 1857.67 J/g. This investigation furnishes a facile yet effective method for the synthesis of hydrogels with superior mechanical and thermal properties, thereby broadening the design landscape for starch-based hydrogels.

Composite hydrogels based on deep eutectic solvents and lysine for pressure sensors and adsorption of Fe3

This study explored the preparation of a novel composite hydrogel based on deep eutectic solvent (DES) with lysine (Lys) and its application in pressure sensing and Fe3+ adsorption. DES was synthesized from acrylamide (AM) and urea (U) as hydrogen bond donors (HBD) with choline chloride (ChCl) as hydrogen bond acceptor (HBA), and Lys was used as a functional filler, and Lys/P(AM-U-ChCl) composite hydrogels were successfully prepared by frontal polymerization (FP) method. The structure of the hydrogels was characterized in depth using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The effects of Lys content on the mechanical properties, pH-responsive behavior, pressure-sensitive properties, and Fe3+ adsorption capacity of the hydrogels were further analyzed. It was found that the introduction of Lys significantly improved the compressive and pressure-sensitive properties of the hydrogels. The composite hydrogels exhibited excellent swelling equilibrium rates at different pH values. The capacitance change of the hydrogel with 0.5 wt% Lys at 200 g pressure was 2.12-fold higher than that of the hydrogel without Lys addition, and the adsorption efficiency of the hydrogel for Fe3+ was greatly enhanced. This study provides a new idea for the functionalized design of composite hydrogels and demonstrates their great application prospects in high-performance pressure sensors and heavy metal ion adsorption.

Enhanced Stability and Catalytic Activity of a Nanocatalyst with Reusable Ionic Liquid Hydrogels for the Reduction of Organic Pollutants

Nitroaromatic compounds have a wide range of applications. However, they pose a significant threat to both the environment and human health. Ionic liquid hydrogels (ILs-gels) have emerged as a cost-effective and environmentally friendly option for various applications. However, conventional ILs-gels are known to possess mechanical flaws or defects. The procedure utilized a facile synthesis route that involved the polymerization of acrylamide (AM) and ionic liquids (ILs) to create a novel candidate for nanoparticle absorption. This study resolved this issue by creating toughened hydrophobic combined hydrogels synthesized through the addition of SiO2@poly(butyl acrylate) core-shell inorganic-organic hybrid latex particles (SiO2@PBA) to the AM-ILs mixture. The SiO2@PBA particles were chosen to provide the hydrogels with exceptional stretchability (up to 4050% strain) and high mechanical properties (tensile strength of 126 kPa) by acting as both a nanotoughener and a cross-linking point for hydrophobic linkage. Additionally, the P(AM/ILs)-SiO2@PBA hydrogel served as a template for the in situ and stable formation of palladium (Pd) nanoparticles. By incorporation of these Pd nanoparticles as catalysts into P(AM/ILs)-SiO2@PBA hydrogel carriers, the resulting P(AM/ILs)-SiO2@PBA/Pd hydrogels exhibited the ability to catalyze the degradation of p-nitrophenol. Remarkably, even after 15 applications, the efficiency of the degradation process remained consistently above 90%. Thus, the innovative SiO2@PBA toughened ILs-hydrogel design strategy can be utilized to develop robust and stretchable hydrogel materials for catalytic use in the sewage disposal industry.

Lignosulfonate sodium and ionic liquid synergistically promote tough hydrogels for intelligent wearable human-machine interaction

Flexible wearable devices are garnering significant interest, with conductive hydrogels emerging as a particularly notable category. While many of these hydrogels offer impressive conductivity, they often lack the innate ability to adhere autonomously to human skin. The ideal hydrogel should possess both superior adhesion properties and a wide responsive range. This study introduces a novel double-network conductive hydrogel, synthesized from lignosulfonate sodium and ionic liquid using a one-pot method. The gel's mechanical robustness (fracture elongation of ∼3500 % and tensile strength of ∼130 kPa) and exceptional conductivity sensing performance arise from the synergistic effects of electrostatic interactions, dynamic hydrogen bonding, and a three-dimensional network structure. Additionally, the phenolic hydroxyl and sulfonic groups from lignosulfonate sodium imbue the hydrogel with adhesive qualities, allowing it to easily bond with varied material surfaces. This hydrogel excels in human physiological signal detection and wireless monitoring, demonstrating a rapid response time (149 ms) and high sensitivity (a maximum gauge factor of 10.9 for strains between 400 and 600 %). Given these properties, the flexible, self-adhesive, and conductive hydrogel showcases immense promise for future applications in wearable devices and wireless transmission sensing.

Ultrafast fabrication of deep eutectic solvent flexible ionic gel with high-transmittance, freeze-resistant and conductivity by frontal polymerization

As a common flexible sensing device, gels are widely used in electronic skin, personalized health monitoring, and smart manufacturing. However, gel suffers from temperature sensitivity, long polymerization times or thickness limitations. Deep eutectic solvents (DESs) have abundant hydrogen bond networks and low saturated vapor pressure, which can accelerate the frontal polymerization of ionic gels, and overcome the temperature sensitivity problem. Here, we showed how choline chloride (ChCl)-glycerol (Gly) DES can be used to create ionic gels with different properties and functions by combining them with different monomers (acrylamide (AM), acrylic acid (AA) and itaconic acid (IA)). Subsequently, we revealed the rapid gelation mechanism of PAM-ChCl-Gly ionic gel from multiple perspectives by density functional theory and molecular dynamics simulation, which was then applied to flexible sensing. The experimental results showed that the PAM-ChCl-Gly ionic gel had excellent tensile properties, high transparency, self-adhesion and stability. In addition, its gelation time was only 90 s without heating. ChCl-Gly DES offered a plentiful and stable hydrogen bonding network. PAM-ChCl-Gly ionic gels can detect tiny pressure and strain changes, making them suitable for flexible sensing. This greatly enriched the theoretical research foundation of DES-based ionic gels and broadened their application areas.

Polymer Hydrogels and Frontal Polymerization: A Winning Coupling

Polymer hydrogels are 3D networks consisting of hydrophilic crosslinked macromolecular chains, allowing them to swell and retain water. Since their invention in the 1960s, they have become an outstanding pillar in the design, development, and application of engineered polymer systems suitable for biomedical and pharmaceutical applications (such as drug or cell delivery, the regeneration of hard and soft tissues, wound healing, and bleeding prevention, among others). Despite several well-established synthetic routes for developing polymer hydrogels based on batch polymerization techniques, about fifteen years ago, researchers started to look for alternative methods involving simpler reaction paths, shorter reaction times, and lower energy consumption. In this context, frontal polymerization (FP) has undoubtedly become an alternative and efficient reaction model that allows for the conversion of monomers into polymers via a localized and propagating reaction-by means of exploiting the formation and propagation of a "hot" polymerization front-able to self-sustain and propagate throughout the monomeric mixture. Therefore, the present work aims to summarize the main research outcomes achieved during the last few years concerning the design, preparation, and application of FP-derived polymeric hydrogels, demonstrating the feasibility of this technique for the obtainment of functional 3D networks and providing the reader with some perspectives for the forthcoming years.

Heat-Induced Actuator Fibers: Starch-Containing Biopolyamide Composites for Functional Textiles

This study introduces the development of a thermally responsive shape-morphing fabric using low-melting-point polyamide shape memory actuators. To facilitate the blending of biomaterials, we report the synthesis and characterization of a biopolyamide with a relatively low melting point. Additionally, we present a straightforward and solvent-free method for the compatibilization of starch particles with the synthesized biopolyamide, aiming to enhance the sustainability of polyamide and customize the actuation temperature. Subsequently, homogeneous dispersion of up to 70 wt % compatibilized starch particles into the matrix is achieved. The resulting composites exhibit excellent mechanical properties comparable to those reported for soft and tough materials, making them well suited for textile integration. Furthermore, cyclic thermomechanical tests were conducted to evaluate the shape memory and shape recovery of both plain polyamide and composites. The results confirmed their remarkable shape recovery properties. To demonstrate the potential application of biocomposites in textiles, a heat-responsive fabric was created using thermoresponsive shape memory polymer actuators composed of a biocomposite containing 50 wt % compatibilized starch. This fabric demonstrates the ability to repeatedly undergo significant heat-induced deformations by opening and closing pores, thereby exposing hidden functionalities through heat stimulation. This innovative approach provides a convenient pathway for designing heat-responsive textiles, adding value to state-of-the-art smart textiles.

Highly Conductive, Anti-Freezing Hemicellulose-Based Hydrogels Prepared via Deep Eutectic Solvents and Their Applications

Hydrogels containing renewable resources, such as hemicellulose, have received a lot of attention owing to their softness and electrical conductivity which could be applied in soft devices and wearable equipment. However, traditional hemicellulose-based hydrogels generally exhibit poor electrical conductivity and suffer from freezing at lower temperatures owing to the presence of a lot of water. In this study, we dissolved hemicellulose by employing deep eutectic solvents (DESs), which were prepared by mixing choline chloride and imidazole. In addition, hemicellulose-based DES hydrogels were fabricated via photo-initiated reactions of acrylamide and hemicellulose with N, N'-Methylenebisacrylamide as a crosslinking agent. The produced hydrogels demonstrated high electrical conductivity and anti-freezing properties. The conductivity of the hydrogels was 2.13 S/m at room temperature and 1.97 S/m at -29 °C. The hydrogel's freezing point was measured by differential scanning calorimetry (DSC) to be -47.78 °C. Furthermore, the hemicellulose-based DES hydrogels can function as a dependable and sensitive strain sensor for monitoring a variety of human activities.

Preparation of SA/P(U-AM-ChCl) composite hydrogels by frontal polymerization and its performance study

Deep eutectic solvent (DES) was synthesized from urea (U), acrylamide (AM) and choline chloride (ChCl), sodium alginate (SA) was selected as filler, and SA/P(U-AM-ChCl) composite hydrogel was prepared by thermal initiation frontal polymerization (FP). The hydrogels were characterised by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The effects of SA on the swelling properties, mechanical properties and self-healing properties of the composite hydrogels were investigated. The results show that the swelling properties of the composite hydrogel with the addition of SA are greatly enhanced due to the large number of hydroxyl groups contained in the SA chain. The tensile strength of the hydrogel gradually increased with increasing SA content, with the maximum tensile strength increasing by a factor of 2.89. The self-healing efficiency of the composite hydrogel gradually increased with the increase of SA, and the healing rate of FP5 reached 94.4% after 48 h of healing. This study provides a simple and rapid method for the preparation of composite hydrogels with good mechanical properties and self-healing properties.

Deep Eutectic Systems as Novel Vehicles for Assisting Drug Transdermal Delivery

In recent years, deep eutectic systems (DES) emerged as novel vehicles for facilitating the transdermal delivery of various drugs, including polysaccharides, proteins, insulin, vaccine, nanoparticles, and herb extracts. The objective of this study is to conduct a comprehensive review of the application of DES to transdermal drug delivery, based on previous work and the reported references. Following a brief overview, the roles of DES in TDDS, the modes of action, as well as the structure-activity relationship of DES are discussed. Particularly, the skin permeation of active macromolecules and rigid nanoparticles, which are the defining characteristics of DES, are extensively discussed. The objective is to provide a comprehensive understanding of the current investigation and development of DES-based transdermal delivery systems, as well as a framework for the construction of novel DES-TDDS in the future.

Rapid preparation of N-CNTs/P(AA-co-AM) composite hydrogel via frontal polymerization and its mechanical and conductive properties

Deep eutectic solvent (DES) was prepared by using acrylic acid (AA) and acrylamide (AM) as hydrogen bonding donors (HBD) and choline chloride (ChCl) as hydrogen bonding receptors (HBA). Nitrogen-doped carbon nanotubes (N-CNTs) were dispersed in DES as fillers, and N-CNTs/P(AA-co-AM) composite hydrogels were prepared by FP. The interaction mode between the hydrogel and N-CNTs was characterized by Fourier infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The mechanical properties, pH response and electrical conductivity of the composite hydrogels were studied. The results showed that the mechanical properties of the hydrogel were significantly enhanced with the increase of N-CNT content. The tensile strength and compressive strength of the FP4 composite hydrogel reached 5.42 MPa and 4.29 MPa, respectively. Due to the dissociation of carboxyl groups in AA in an alkaline environment the composite hydrogel showed excellent pH response performance. The conductivity of the hydrogel was also found to be improved with the content of N-CNTs. When the content of N-CNTs is 1.0 wt%, the conductivity of the hydrogel was 4.2 times higher than that of the hydrogel without N-CNTs, and connecting it to a circuit can make an LED lamp emit bright light. In this study, a simple and green method was proposed to prepare composite hydrogels with excellent mechanical properties and electrical conductivity by FP of DES in less than 5 min.

This study provides a rapid and low-energy method for the preparation of nanocomposite hydrogels with excellent mechanical properties and electrical conductivity.

Deep Eutectic Solvents for Starch Treatment

In this review, the application of deep eutectic solvents (DESs) as starch solvents, plasticizers and for other treatment has been described. Starch, as one of the most abundant biopolymers, is considered for forming new biodegradable materials. This new approach, referring to applying deep eutectic solvents for dissolving starch, its plasticization and other modifications, was presented. A DES could be a good alternative for common starch plasticizers (e.g., glycerol, urea) as well as recently considered ionic liquids. The high variety of DES component combinations makes it possible to obtain materials with the properties specific for given applications.

3D printing and properties of cellulose nanofibrils-reinforced quince seed mucilage bio-inks

Plant-based hydrogels have attracted great attention in biomedical fields since they are biocompatible and based on natural, sustainable, cost-effective, and widely accessible sources. Here, we introduced new viscoelastic bio-inks composed of quince seed mucilage and cellulose nanofibrils (QSM/CNF) easily extruded into 3D lattice structures through direct ink writing in ambient conditions. The QSM/CNF inks enabled precise control on printing fidelity where CNF endowed objects with shape stability after freeze-drying and with suitable porosity, water uptake capacity, and mechanical strength. The compressive and elastic moduli of samples produced at the highest CNF content were both increased by ~100% (from 5.1 ± 0.2 kPa and 32 ± 1 kPa to 10.7 ± 0.5 and 64 ± 2 kPa, respectively). These values ideally matched those reported for soft tissues; accordingly, the cell compatibility of the printed samples was evaluated against HepG2 cells (human liver cancer). The results confirmed the 3D hydrogels as being non-cytotoxic and suitable to support attachment, survival, and proliferation of the cells. All in all, the newly developed inks allowed sustainable 3D bio-hydrogels fitting the requirements as scaffolds for soft tissue engineering.

Rapid preparation of PAM/N-CNT nanocomposite hydrogels by DEM frontal polymerization and its performance study

In this study, a simple and eco-friendly method was proposed to efficiently prepare nanocomposite hydrogels with excellent mechanical properties and satisfactory pH response behaviour by frontal polymerization (FP) of DEM in close to 4 minutes. Acrylamide (AM) and choline chloride (ChCl) were used as raw materials to synthesize deep eutectic monomers (DEMs). Nitrogen-doped carbon nanotubes were dispersed in DEMs as fillers, and poly(acrylamide)/nitrogen-doped carbon nanotube (PAM/N-CNT) nanocomposite hydrogels were prepared by FP. The non-covalent interactions between PAM hydrogels and N-CNTs was verified by Fourier infrared spectroscopy. The mechanical properties of PAM/N-CNT nanocomposite hydrogels were investigated, as well as the swelling and pH response properties. The results showed that the compressive strength of PAM hydrogels was significantly enhanced by the addition of N-CNTs due to the hydrophobic interaction of N-CNTs, which also causes sensitive response properties of the PAM hydrogels in acid solution.

In this study, a simple and eco-friendly method was proposed to efficiently prepare nanocomposite hydrogels with excellent mechanical properties and satisfactory pH response behaviour by frontal polymerization of DEM in close to 4 minutes.