Physically cross-linked starch/hydrophobically-associated poly(acrylamide) self-healing mechanically strong hydrogel

Multifunctional hydrogels based on photothermal therapy: A prospective platform for the postoperative management of melanoma

Preventing the recurrence of melanoma after surgery and accelerating wound healing are among the most challenging aspects of melanoma management. Photothermal therapy has been widely used to treat tumors and bacterial infections and promote wound healing. Owing to its efficacy and specificity, it may be used for postoperative management of tumors. However, its use is limited by the uncontrollable distribution of photosensitizers and the likelihood of damage to the surrounding normal tissue. Hydrogels provide a moist environment with strong biocompatibility and adhesion for wound healing owing to their highly hydrophilic three-dimensional network structure. In addition, these materials serve as excellent drug carriers for tumor treatment and wound healing. It is possible to combine the advantages of both of these agents through different loading modalities to provide a powerful platform for the prevention of tumor recurrence and wound healing. This review summarizes the design strategies, research progress and mechanism of action of hydrogels used in photothermal therapy and discusses their role in preventing tumor recurrence and accelerating wound healing. These findings provide valuable insights into the postoperative management of melanoma and may guide the development of promising multifunctional hydrogels for photothermal therapy.

One-step of ionic liquid-assisted stabilization and dispersion: Exfoliated graphene and its applications in stimuli-responsive conductive hydrogels based on chitosan

Conductive hydrogels, as novel flexible biosensors, have demonstrated significant potential in areas such as soft robotics, electronic devices, and wearable technology. Graphene is a promising conductive material, but its dispersibility in aqueous solutions exists difficulties. Here, we discover that untreated graphene, after exfoliation by different ionic liquids, can disperse well in aqueous solutions. We investigate the impact of four ionic liquids with varying alkyl chain lengths ([Bmim]Cl, [Omim]Cl, [Dmim]Cl, [Hmim]Cl) on the dispersibility of grapheme, and a dual physically cross-linked network hydrogel structure is designed using acrylamide (AM), acrylic acid (AA), methyl methacrylate octadecyl ester (SMA), ionic liquid@graphene (ILs@GN), and chitosan (CS). Notably, SMA, CS, AA and AM act as dynamic cross-linking points through hydrophobic interactions and hydrogen bonding, playing a crucial role in energy dissipation. The resulting hydrogel exhibits outstanding stretchability (2250 %), remarkable toughness (1.53 MJ/m3) in tensile deformation performance, high compressive strength (1.13 MPa), rapid electrical responsiveness (response time ∼ 50 ms), high electrical conductivity (12.11 mS/cm), and excellent strain sensing capability (GF = 12.31, strain = 1000 %). These advantages make our composite hydrogel demonstrate high stability in extensive deformations, offering repeatability in pressure and strain and making it a promising candidate for multifunctional sensors and flexible electrodes.

Experimental investigation of influence of amide polymer on loess for subgrade

The effects of moisture and drying shrinkage can lead to uneven settlement, cracking, and other diseases in loess subgrade. The objective of this study was to investigate the effects of amide polymer (AP) on the permeability, mechanical properties and crack resistance of loess by orthogonal experiments. The basic properties of AP and the permeability, mechanical properties, and dry-wet variation properties of polymer-modified loess were tested, and a scale model verification and simulation analysis were conducted. In this paper, water migration in subgrade is regulated by improving the water sensitivity of loess. By reducing the variation range of subgrade water content, the stress accumulation in subgrade caused by water is weakened. The results show that the curing time and mechanical properties of AP are directly affected by the oxidant and reducing agent, and the mechanical properties of AP are compatible with the characteristics of loess. AP filled the grain gap and reduced the permeability of loess by 34.05-280.83%. The ductility of polymer-modified loess is significantly increased, and the strain of peak strength is increased by 17.21-126.36%. AP can regulate moisture change, reduce the surface tension between particles, and reduce stress concentration. The strength loss rate was reduced by 19.98-51.21% by enhancing the cracking resistance and weakening the strength loss caused by dry and wet cycling. The increase of upper layer moisture content in the scale model of polymer-modified loess subgrade is reduced by 31.38-36.11%.

Antibacterial conductive polyacrylamide/quaternary ammonium chitosan hydrogel for electromagnetic interference shielding and strain sensing

The utilization of biomass-based conductive polymer hydrogels in wearable electronics holds great promise for advancing performance and sustainability. An interpenetrating network of polyacrylamide/2-hydroxypropyltrimethyl ammonium chloride chitosan (PAM/HACC) was firstly obtained through thermal-initiation polymerization of AM monomers in the presence of HACC. The positively charged groups on HACC provide strong electrostatic interactions and hydrogen bonding with the PAM polymer chains, leading to improved mechanical strength and stability of the hydrogel network. Subsequently, the PAM/HACC networks served as the skeletons for the in-situ polymerization of polypyrrole (PPy), and then the resulting conductive hydrogel demonstrated stable electromagnetic shielding performance (40 dB), high sensitivity for strain sensing (gauge factor = 2.56). Moreover, the incorporation of quaternary ammonium chitosan into PAM hydrogels enhances their antimicrobial activity, making them more suitable for applications in bacterial contamination or low-temperature environments. This conductive hydrogel, with its versatility and excellent mechanical properties, shows great potential in applications such as electronic skin and flexible/wearable electronics.

Insights into starch-based gels: Selection, fabrication, and application

Starch a natural polymer, has made significant advancements in recent decades, offering superior performance and versatility compared to synthetic materials. This review discusses up-to-date diverse applications of starch gels, their fabrication techniques, and their advantages over synthetic materials. Starch gels renewability, biocompatibility, biodegradability, scalability, and affordability make them attractive. Also, advanced theoretical foundations and emerging industrial technologies could further expand their scope and functions inspiring new applications.

Thermoresponsive injectable self-healing hydrogel containing polydopamine-coated Fe/Mo-doped TiO2 nanoparticles for efficient synergistic sonodynamic-chemodynamic-photothermal-chemo therapy

A smart hydrogel loading multifunctional nanoparticles and anticancer drugs was designed to achieve synergistic therapy against tumors with high efficiency and specificity. The thermoresponsive injectable self-healing hydrogel was prepared through the Schiff base between aldehyde-functionalized poly(2-(2-methoxyethoxy) ethyl methacrylate)-co-oligo(ethylene glycol) methacrylate-co-2-hydroxyethyl methacrylate) (P(MEO2MA-co-OEGMA-co-HEMA), APMOH) and hydroxypropyl chitosan (HPCS). The polydopamine-coated Fe/Mo-doped titanium dioxide nanoparticles (PDA@dTiO2 NPs) were prepared and dispersed into the hydrogel with anticancer drug doxorubicin (DOX). PDA@dTiO2 NPs as sonosensitizers can convert oxygen into singlet oxygen (1O2) under ultrasound (US) irradiation, achieving sonodynamic therapy (SDT). They were also considered nanoenzymes, generating oxygen to supply an oxygen source for SDT, producing hydroxyl radical (·OH) to achieve chemodynamic therapy (CDT), and eliminating glutathione (GSH) to enhance the level of oxidative stress. After near-infrared (NIR) irradiation, the temperature of the hydrogel increased due to the photothermal ability of the polydopamine (PDA) layer. When the temperature reached the hydrogel's lower critical solution temperature (LCST), the hydrophilic-hydrophobic transformation occurred, and the hydrogel volume contracted. Consequently, the release rate of PDA@dTiO2 NPs and DOX increased, improving the therapeutic effects. The nanocomposite hydrogel system can achieve synergistic sonodynamic-chemodynamic-photothermal-chemo therapy (SDT-CDT-PTT-CT) for tumors, providing a novel platform for synergistic tumor treatment.

Application of Solvent-Assisted Dual-Network Hydrogel in Water-Based Drilling Fluid for Lost Circulation Treatment in Fractured Formation

During oil and gas well construction, lost circulation caused substantial nonoperation time and extra costs, and hydrogel, resilient and environmentally friendly, was one of the major types of material for lost circulation treatment. To migrate the weak bonding and hydrothermal degradation of conventional single network hydrogels, dual network (DN) hydrogel was prepared and immersed in solvents of polyethylene glycol (PEG), ethylene glycol, and glycerol. The swelling of DN gels at different temperatures was studied with water content and swelling rate tests, and the gel structural and morphology was characterized with attenuated total reflectance infrared spectroscopy (ATR-IR) and scanning electron microscopy test. Then, the compression test and fracture plugging performance test were conducted to study the strength of the gel. The results show that compared to those in ethylene glycol and glycerin, DN gel after immersion in PEG (DN-PEG) exhibits greater compression strength and better plugging performance even at high temperatures. The compression strength of DN-PEG was twice that of DN hydrogel before immersion, and its fracture plug breaking pressure can reach over 10.0 MPa. After undergoing hydrothermal treatment at 90 °C, the compression strength of the DN-PEG was nearly 20 times that of the DN hydrogel, and the fracture plug breaking pressure was still 2.81 MPa. According to ATR-IR spectroscopy, as the molecular weight of the solvent increases, more hydroxyl groups in the PEG have better ability to bind with hydrogen bonds, which greatly inhibits the swelling and polymer chain breakage, thereby reducing hydrothermal degradation in the strength of the dual-network hydrogel. Our work proposed an effective method to reduce the degradation of hydrogel in water at high temperature, and the prepared DN-PEG hydrogel was a promising material for lost circulation treatments in fractured formation.

Recent advances in biopolymer-based hydrogels and their potential biomedical applications

Hydrogels are three-dimensional networks of polymer chains containing large amounts of water in their structure. Hydrogels have received significant attention in biomedical applications owing to their attractive physicochemical properties, including flexibility, softness, biodegradability, and biocompatibility. Different natural and synthetic polymers have been intensely explored in developing hydrogels for the desired applications. Biopolymers-based hydrogels have advantages over synthetic polymers regarding improved cellular activity and weak immune response. These properties can be further improved by grafting with other polymers or adding nanomaterials, and they structurally mimic the living tissue environments, which opens their broad applicability. The hydrogels can be physically or chemically cross-linked depending on the structure. The use of different biopolymers-based hydrogels in biomedical applications has been reviewed and discussed earlier. However, no report is still available to comprehensively introduce the synthesis, advantages, disadvantages, and biomedical applications of biopolymers-based hydrogels from the material point of view. Herein, we systematically overview different synthesis methods of hydrogels and provide a holistic approach to biopolymers-based hydrogels for biomedical applications, especially in bone regeneration, wound healing, drug delivery, bioimaging, and therapy. The current challenges and prospects of biopolymers-based hydrogels are highlighted rationally, giving an insight into the progress of these hydrogels and their practical applications.

Highly Flexible and Self-Healing Supercapacitor Enabled by Physically Crosslinking Polymer Hydrogel Electrolyte

Preparation of flexible supercapacitors with excellent mechanical properties and self-healing properties is of great significance but still remains a challenge. A self-healable conductive hydrogel based on poly N-hydroxyethyl acrylamide (PHEAA) is fabricated as electrolyte for supercapacitors. The design of the physically cross-linked dual network, and rich hydrogen bonds endow the hydrogel with robust mechanical properties and strong self-healing ability. The hydrogel exhibited an excellent stretchability (723 %) and a high ionic conductivity (21.8 mS/cm). Specially, by in situ growth of electrode film, a non-laminated supercapacitor is obtained with flexibility and self-healing ability. Due to the non-laminated structure, the supercapacitor can work stably under bending and punching. The supercapacitor possessed an areal capacitance of 253.1 mF/cm2 and the capacitance retention was 80 % after five cutting-healing cycles. The pseudo-capacitance contribution of the supercapacitor after self-healing was discussed. It is noteworthy that the supercapacitor maintains the ability to power a clock after self-healing.

Double network hydrogels: Design, fabrication, and application in biomedicines and foods

Research on the design, fabrication, and application of double network (DN) hydrogels, assembled from pairs of polymers, has grown recently due to their unique structural, physicochemical, and functional properties. DN hydrogels can be designed to exhibit a broader range of functional attributes than single network (SN) ones, which extends their applications in various fields. There has been strong interest in the development of biopolymer DN hydrogels because of their environmental, sustainability, and safety benefits. However, there is limited knowledge on the formation and application of these novel materials. This article reviews the principles underlying the design and fabrication of hydrogels using different crosslinking approaches, including covalent and/or non-covalent bonding, and the formation mechanisms, network structures, and functional attributes of different DN hydrogels. The impact of polymer composition, structural organization, and bonding on the mechanical and functional properties of DN hydrogels is reviewed. Potential applications of these hydrogels are highlighted, including in tissue engineering, biomedicines, and foods. The functional attributes of DN hydrogels can be tailored to each of these applications by careful selection of the biopolymers and crosslinking mechanisms used to assemble them. Finally, areas where further research are needed to overcome the current limitations of DN hydrogels are highlighted.

A novel multi-scale pressure sensing hydrogel for monitoring the physiological signals of long-term bedridden patients

For long-term bedridden patients who need to wear diapers, the timely replacement of diapers is very important to ensure their quality of life. Therefore, it is urgent to develop a pressure sensor that can monitor the physiological conditions of patients in real time. Inspired by the multi-scale network structure of the multi-fiber protein in the muscle, a multi-scale hydrogel as a pressure sensor was prepared by introducing micron-scale hydrogel microspheres as physical crosslinking agents. Compared with the traditional polyacrylamide hydrogel (0.17 MPa of compressive strength), the multi-scale hydrogel showed a higher compressive strength of up to 1.37 MPa. Meanwhile, the hydrogel exhibited better pressure sensitivity (0.59 kPa-1) than the existing hydrogels (0.27-0.40 kPa-1). The sensor prepared by this hydrogel could monitor the patient's physiological condition (urine outflow and urinary filling) in real time through the conductivity response to ion concentration and pressure, and then transmit the signal to the caregivers in time to avoid skin damage. This multi-scale hydrogel provided a great convenience for the physiological monitoring of long-term bedridden patients by acting as a pressure sensor.

A Biphasic Hydrogel with Self-Healing Properties and a Continuous Layer Structure for Potential Application in Osteochondral Defect Repair

The treatment of osteochondral defects remains challenging due to the limited healing capacity of cartilage and the poor results of traditional methods. Inspired by the structure of natural articular cartilage, we have fabricated a biphasic osteochondral hydrogel scaffold using a Schiff base reaction and a free radical polymerization reaction. Carboxymethyl chitosan (CMCS), oxidized sodium alginate (OSA), and polyacrylamide (PAM) formed a hydrogel (COP) as the cartilage layer, while hydroxyapatite (HAp) was incorporated into the COP hydrogel to obtain a hydrogel (COPH) as an subchondral bone layer. At the same time, hydroxyapatite (HAp) was incorporated into the COP hydrogel to obtain a hydrogel (COPH) as an osteochondral sublayer, combining the two to obtain an integrated scaffold for osteochondral tissue engineering. Interlayer interpenetration through the continuity of the hydrogel substrate and good self-healing properties due to the dynamic imine bonding of the hydrogel resulted in enhanced interlayer bond strength. In addition, in vitro experiments have shown that the hydrogel exhibits good biocompatibility. It shows great potential for osteochondral tissue engineering applications.

Sodium alginate reinforced polyacrylamide/xanthan gum double network ionic hydrogels for stress sensing and self-powered wearable device applications

Strong and ductile sodium alginate (SA) reinforced polyacrylamide (PAM)/xanthan gum (XG) double network ionic hydrogels were constructed for stress sensing and self-powered wearable device applications. In the designed network of PXS-Mⁿ⁺/LiCl (short for PAM/XG/SA-Mⁿ⁺/LiCl, where Mⁿ⁺ stands for Fe³⁺, Cu²⁺ or Zn²⁺), PAM acts as a flexible hydrophilic skeleton, and XG functions as a ductile second network. The macromolecule SA interacts with metal ion Mⁿ⁺ to form a unique complex structure, significantly improving the mechanical strength of the hydrogel. The addition of inorganic salt LiCl endows the hydrogel with high electrical conductivity, and meanwhile reduces the freezing point and prevents water loss of the hydrogel. PXS-Mⁿ⁺/LiCl exhibits excellent mechanical properties and ultra-high ductility (a fracture tensile strength up to 0.65 MPa and a fracture strain up to 1800%), and high stress-sensing performance (a high GF up to 4.56 and pressure sensitivity of 0.122). Moreover, a self-powered device with a dual-power-supply mode, i.e., PXS-Mⁿ⁺/LiCl-based primary battery and TENG, and a capacitor as the energy storage component was constructed, which shows promising prospects for self-powered wearable electronics.

Polymer Gels: Classification and Recent Developments in Biomedical Applications

Polymer gels are a valuable class of polymeric materials that have recently attracted significant interest due to the exceptional properties such as versatility, soft-structure, flexibility and stimuli-responsive, biodegradability, and biocompatibility. Based on their properties, polymer gels can be used in a wide range of applications: food industry, agriculture, biomedical, and biosensors. The utilization of polymer gels in different medical and industrial applications requires a better understanding of the formation process, the factors which affect the gel's stability, and the structure-rheological properties relationship. The present review aims to give an overview of the polymer gels, the classification of polymer gels' materials to highlight their important features, and the recent development in biomedical applications. Several perspectives on future advancement of polymer hydrogel are offered.