Highly stretchable and tough double network hydrogels via molecular stent

Plant-based Biomass/Polyvinyl Alcohol Gels for Flexible Sensors

Flexible sensors show great application potential in wearable electronics, human-computer interaction, medical health, bionic electronic skin and other fields. Compared with rigid sensors, hydrogel-based devices are more flexible and biocompatible and can easily fit the skin or be implanted into the body, making them more advantageous in the field of flexible electronics. In all designs, polyvinyl alcohol (PVA) series hydrogels exhibit high mechanical strength, excellent sensitivity and fatigue resistance, which make them promising candidates for flexible electronic sensing devices. This paper has reviewed the latest progress of PVA/plant-based biomass hydrogels in the construction of flexible sensor applications. We first briefly introduced representative plant biomass materials, including sodium alginate, phytic acid, starch, cellulose and lignin, and summarized their unique physical and chemical properties. After that, the design principles and performance indicators of hydrogel sensors are highlighted, and representative examples of PVA/plant-based biomass hydrogel applications in wearable electronics are illustrated. Finally, the future research is briefly prospected. We hope it can promote the research of novel green flexible sensors based on PVA/biomass hydrogel.

Fabrication and characterization of novel macroporous hydrogels based on the polymerizable surfactant AAc-Span80 and their enhanced drug-delivery capacity

In this study, macroporous pH-sensitive poly[N-isopropylacrylamide-co-acrylic acid-sorbitan monooleate] hydrogels, termed as PNIPAM-co-AAc-Span80 hydrogels, with an enhanced hydrophobic property and a rich pore structure were prepared by free-radical polymerization in an ethanol/water mixture. The polymerizable surfactant AAc-Span80 was obtained by the esterification of acrylic acid (AAc) and sorbitan monooleate (Span80), which was used to copolymerize with N-isopropylacrylamide (NIPAM). The chemical structure, thermal stability, morphology, and amphipathy of the PNIPAM-co-AAc-Span80 hydrogels were characterized. The results showed that the polymerizable surfactant AAc-Span80 macromolecule introduced into the hydrogels could not only increase the hydrophobic property but also ameliorate the porous network morphology, which was conducive to high adsorption capacity for adriamycin hydrochloride (DOX). The adsorption results showed that the equilibrium adsorption capacity of DOX reached 467.5 mg g⁻¹ within 48 h at pH 7.4, and the hydrophobic interactions and intermolecular hydrogen bonds were the main force in the adsorption process of DOX. The release results demonstrated that the macroporous pH-sensitive hydrogels loaded with DOX could release 98.7% of DOX at pH 5.0, which would be highly beneficial for the release of anti-cancer drugs in the environment of cancer cells. All the results demonstrate that the PNIPAM-co-AAc-Span80 hydrogels have great potential for the delivery of anti-cancer drugs.

PNIPAM-co-AAc-Span80 shows an enhanced hydrophobic property, rich pore structure, and good adsorption performance for DOX. The desorption results demonstrate that 98.7% of DOX can be released efficiently in an acidic environment.

Three-Dimensional Printing of Double-Network Hydrogels: Recent Progress, Challenges, and Future Outlook

Hydrogels are widely used materials due to their biocompatibility, their ability to mimic the hydrated and porous extracellular microenvironment, as well as their ability to tune both mechanical and biochemical properties. However, most hydrogels lack mechanical toughness, and shaping them into complicated three-dimensional (3D) structures remains challenging. In the past decade, tough and stretchable double-network hydrogels (DN gels) were developed for tissue engineering, soft robotics, and applications that require a combination of high-energy dissipation and large deformations. Although DN gels were processed into simple shapes by using conventional casting and molding methods, new 3D printing methods have enabled the shaping of DN gels into structurally complex 3D geometries. This review will describe the state-of-art technologies for shaping tough and stretchable DN gels into custom geometries by using conventional molding and casting, extrusion, and optics-based 3D printing, as well as the key challenges and future outlook in this field.

Hydrogels for localized chemotherapy of liver cancer: a possible strategy for improved and safe liver cancer treatment

The systemic drug has historically been preferred for the treatment of the majority of pathological conditions, particularly liver cancer. Indeed, this mode of treatment is associated with adverse reactions, toxicity, off-target accumulation, and rapid hepatic and renal clearance. Numerous efforts have been made to design systemic therapeutic carriers to improve retention while decreasing side effects and clearance. Following systemic medication, local administration of therapeutic agents allows for higher 'effective' doses with fewer side effects, kidney accumulation, and clearance. Hydrogels are highly biocompatible and can be used for both imaging and therapy. Hydrogel-based drug delivery approach has fewer side effects than traditional chemotherapy and can deliver drugs to tumors for a longer time. The chemical and physical flexibility of hydrogels can be used to achieve disease-induced in situ accumulation as well as subsequent drug release and hydrogel-programmed degradation. Moreover, they can act as a biocompatible depot for localized chemotherapy when stimuli-responsive carriers are administrated. Herein, we summarize the design strategies of various hydrogels used for localized chemotherapy of liver cancer and their delivery routes, as well as recent research on smart hydrogels.

A high-performance GelMA-GelMA homogeneous double-network hydrogel assisted by 3D printing

Gelatin methacryloyl (GelMA) is a popular photocrosslinkable hydrogel that has been widely utilized in tissue engineering and regenerative medicine fields due to its excellent biocompatibility, biodegradability and cell response. However, the lack of mechanical properties limits its application. In the present study, a method for the preparation of a GelMA-GelMA (G-G) homogeneous double-network (DN) hydrogel to improve mechanical strength based on DLP 3D printing is proposed. The G-G DN hydrogel was fabricated and characterized in terms of microstructure, mechanical properties and rheological behavior. By modifying the degree of substitution (DS), the polymer concentration of double network crosslinking and the soak time, the novel G-G DN hydrogel could significantly improve the properties of strength, self-recovery and fatigue resistance. After all, the novel porous composite hydrogel (G-G DN hydrogel) could achieve more than twice that of the pure GelMA hydrogel, better fatigue resistance and printable ability. Therefore, it can be a potential choice of applications attracting great attention for its mechanical properties, great transmittance and biocompatibility.

Fast and Highly Efficient Adsorption Removal of Toxic Pb(II) by a Reusable Porous Semi-IPN Hydrogel Based on Alginate and Poly(Vinyl Alcohol)

A porous semi-interpenetrating network (semi-IPN) hydrogel adsorbent with excellent adsorption properties and removal efficiency towards Pb(II) was prepared by a facile grafting polymerization reaction in aqueous medium using natural biopolymer sodium alginate (SA) as the main chains, sodium acrylate (NaA) as the monomers, and poly(vinyl alcohol) (PVA) as the semi-IPN component. FTIR, TGA and SEM analyses confirm that NaA monomers were grafted onto the macromolecular chains of SA, and PVA chains were interpenetrated and entangled with the crosslinked network. The incorporation of PVA facilitates to form pores on the surface of hydrogel adsorbent. The semi-IPN hydrogel containing 2 wt% of PVA exhibits high adsorption capacity and fast adsorption rate for Pb(II). The best adsorption capacity reaches 784.97 mg/g, and the optimal removal rate reaches 98.39% (adsorbent dosage, 2 g/L). In addition, the incorporation of PVA improved the gel strength of hydrogel, and the storage modulus of hydrogel increased by 19.4% after incorporating 2 wt% of PVA. The increase of gel strength facilitates to improve the reusability of hydrogel. After 5 times of regeneration, the adsorption capacity of SA-g-PNaA decreased by 23.2%, while the adsorption capacity of semi-IPN hydrogel only decreased by 10.8%. The adsorption kinetics of the hydrogel in the initial stage (the moment when the adsorbent contacts solution) and the second stage are fitted by segmentation. It is intriguing that the adsorption kinetics fits well with both pseudo-second-order kinetic model and pseudo-first-order model before 60 s, while only fits well with pseudo-second-order adsorption model in the whole adsorption process. The chemical complexing adsorption mainly contribute to the efficient capturing of Pb(II).

Dual polymer networks: a new strategy in expanding the repertoire of hydrogels for biomedical applications

Inspired by the double network hydrogel systems we report the formulation of dual networks, which expands the repertoire of this class of materials for potential biomedical applications. The tough dual network hydrogels were designed through sequential interpenetrating polymer formation, applying green chemistry and low-cost methods, devoid of any initiator-activator complexes that may pose risks in biomedical applications. The dual networks were synthesized in two steps, firstly the water soluble poly(vinyl alcohol) was subjected to cryogelation that formed the first network, which was then expanded by intrusion of a dilute solution of sodium alginate and complexed with a solution of calcium chloride under ambient conditions and further freeze-thawed. These hydrogels are flexible, ductile and porous with the ability to absorb and retain fluids as well as possess the versatility to easily incorporate biological molecules/drugs/antibiotics to be applied in tissue matrices or drug delivery systems. The dual network hydrogels can be tailored to have varying mechanical properties, shapes, size, thickness and particularly can be made physically porous if required, to suit the users intended application.

Preparation and Characterization of Hydrophobic-Associated Microspheres for Deep Profile Control in Offshore Oilfields

Microspheres have excellent sealing performances such as injectivity, bridging-off, deep migration, and deformation performances, but their plugging effects are limited by the fast swelling rate and poor viscoelasticity. In this study, we synthesized a novel modified microsphere with polymerizable surfactant monomers and cationic monomers. We investigated the influence factors on the swelling performance and rheological properties of the microspheres and explored the ways to improve the plugging performance of hydrophobic-associating microspheres. The association behaviors in aqueous media of poly(acrylamide-co-methacry loyloxyethyl trimethyl ammonium chloride-co-n-dodecyl poly(etheroxy acrylate) P(AM-DMC-DEA) are proven to be mediated by the DEA content. Moreover, the hydrophobic association interaction has a strong effect on the performance of microspheres such as swelling properties, the rheological performance, and plugging properties. The swelling properties of microsphere studies exhibited the slow swelling rate. The rheological performance measurements showed significant improvements; yield stress, and creep compliance increased rapidly from 404 to 2060 Pa and 3.89 × 10−4 to 1.41 × 10−2 1/Pa, respectively, with DEA content in microspheres rising from 0.0% to 0.22%. The plugging properties of microspheres were enhanced by the slow swelling performance and good viscoelasticity.

pH-Tunable mechanical hydrogels prepared via transforming non C–C covalent synergistic interactions

Hydrogels with pH-tunable mechanical properties were prepared via transforming the synergistic interactions of hydrogen bonding, metal coordination and hydrophobic effects.

A physically cross-linked self-healable double-network polymer hydrogel as a framework for nanomaterial

Physically cross-linked double-network hydrogels with different first networks act as a framework for graphene.

High-Strength, Tough, Fatigue Resistant, and Self-Healing Hydrogel Based on Dual Physically Cross-Linked Network

Hydrogels usually suffer from low mechanical strength, which largely limit their application in many fields. In this Research Article, we prepared a dual physically cross-linked hydrogel composed of poly(acrylamide-co-acrylic acid) (PAM-co-PAA) and poly(vinyl alcohol) (PVA) by simple two-steps methods of copolymerization and freezing/thawing. The hydrogen bond-associated entanglement of copolymer chains formed as cross-linking points to construct the first network. After being subjected to the freezing/thawing treatment, PVA crystalline domains were formed to serve as knots of the second network. The hydrogels were demonstrated to integrate strength and toughness (1230 ± 90 kPa and 1250 ± 50 kJ/m(3)) by the introduction of second physically cross-linked network. What̀s more, the hydrogels exhibited rapid recovery, excellent fatigue resistance, and self-healing property. The dynamic property of the dual physically cross-linked network contributes to the excellent energy dissipation and self-healing property. Therefore, this work provides a new route to understand the toughness mechanism of dual physically cross-linked hydrogels, hopefully promoting current hydrogel research and expanding their applications.