Starch/ionic liquid/hydrophobic association hydrogel with high stretchability, fatigue resistance, self-recovery and conductivity for sensitive wireless wearable sensors

Conductive hydrogels have been widely used in wearable electronics due to their flexible, conductive and adjustable properties. With ever-growing demand for sustainable and biocompatible sensing materials, biopolymer-based hydrogels have drawn significant attention. Among them, starch-based hydrogels have a great potential for wearable electronics. However, it remains challenging to develop multifunctional starch-based hydrogels with high stretchability, good conductivity, excellent durability and high sensitivity. Herein, amylopectin and ionic liquid were introduced into a hydrophobic association hydrogel to endow it with versatility. Benefiting from the synergistic effect of amylopectin and ionic liquid, the hydrogel exhibited excellent mechanical properties (the elongation of 2540 % with a Young's modulus of 12.0 kPa and a toughness of 1.3 MJ·m-3), self-recovery, good electrical properties (a conductivity of 1.8 S·m-1 and electrical self-healing), high sensitivity (gauge factor up to 26.85) and excellent durability (5850 cycles). The above properties of the hydrogel were closely correlated to its internal structure from hydrophobic association, H-bonding and electrostatic interaction, and can be regulated by changing the component contents. A wireless wearable sensor based on the hydrogel realized accurate and stable monitoring of joint motions and expression changes. This work demonstrates a kind of promising biopolymer-based materials as candidates for high-performance flexible wearable sensors.

Halloysites modified polyethylene glycol diacrylate/thiolated chitosan double network hydrogel combined with BMP-2 for rat skull regeneration

Hydrogel serve as bone tissue engineering have lately received great attention for their good biocompatibility and structures similar to natural extracellular matrices. However, a single component polymer hydrogel is generally detrimental to cell adhesion due to the weaker mechanical properties, which limits their application considerably. In an effort to overcome this disadvantage, we adopt an unconventional dual network hydrogels consisting of the polyethylene glycol diacrylate (PEGDA) covalent network, a thiolated chitosan (TCS) ion crosslinking network and thiolated halloysites (T-HNTs) as reinforcing filler. In addition, bone morphogenetic protein-2 (BMP-2) was loaded into the prepared dual network (DN) hydrogel to improve the bone regeneration function of the DN hydrogel. The resulting PEGDA/TCS/T-HNTs hydrogels showed favourable mechanical property, higher crosslinking density, the lower swelling degree, excellent biocompatibility and cell adhesion ability. The histomorphometric and immunohistochemical analyses revealed the excellent bone regeneration ability for composite hydrogel after implant into rat skull defect. Thus, our results indicated that composite scaffold can be applied as a new bone regeneration biomaterial to be applied as a local drug delivery system with good bone induction performance.

Facile synthesis of self-healing and layered sodium alginate/polyacrylamide hydrogel promoted by dynamic hydrogen bond

Hydrogels are widely used in many fields but generally suffer from low mechanical strength and poor self-healing performance. Here, a novel and facile method was developed to prepare a semi-interpenetrating polymer network (semi-IPN) hydrogel with layered structure and improved properties based on sodium alginate (SA) and polyacrylamide (PAM). Systematic characterizations revealed a formation mechanism of layered structure via hydrogen bonds (HBs) promoted self-assembly of SA in the porous PAM matrix. Also, HBs can also display a key role in enhancing self-healing of the hydrogel, by which the hydrogel possesses a self-healing capacity of 99 % with sprayed by a few of water. Moreover, the layered semi-IPN structure makes the tensile strength of PAMSA hydrogel reach 266 kPa. The fabricated PAMSA hydrogel with layered microstructure containing SA provides a protocol to broaden the functionality and variety of the hydrogels.

Robust and anti-fatigue hydrophobic association hydrogels assisted by titanium dioxide for photocatalytic activity

Currently, robust and functional hydrogels have attracted extensive attention due to their potential applications in wastewater treatment, farmland water conservation and other fields. Herein, a series of hydrophobic association hydrogels assisted by titanium dioxide (TiO2) was fabricated via one-pot in situ photo-induced polymerization. TiO2 nanoparticles could act as both photo-initiators and physical crosslinking points. The TiO2-assisted hydrophobic association hydrogels exhibited a high tensile strength of 306 kPa, superior compression strength of 2.17 MPa and excellent fatigue resistance. Simultaneously, the incorporation of TiO2 endowed the hydrogel with photocatalytic capacity for dye wastewater treatment based on the inherent nature of TiO2. The results indicated that the hydrogels contributed to the degradation of various ionic dyes including methylene blue, rhodamine B and bromophenol blue, and the removal of methylene blue achieved a rate of 96.63%. Significantly, the hydrogel could be repeatedly utilized and the removal rate showed no evident decrease after five cycles, indicating that the hydrogels could be powerful candidates as photocatalysts for dye wastewater treatment.

Tough robust dual responsive nanocomposite hydrogel as controlled drug delivery carrier of asprin

Smart mechanical strong hydrogels have gained increasing attention in the last decade. A novel tough robust biocompatible and dual pH- and temperature- responsive poly (N-isopropylacrylamide)/clay (Laponite XLS)/gold nanoparticles (Au-S-S NPs)/caboxymethyl chitosan (CMCTs) nanocomposite hydrogel was synthesized by a facile one-pot in situ free radical polymerization, using clay and Au-S-S NPs as the cross-linkers instead of toxic organic molecules. By tuning the crucial factors, concentration of Au-S-S NPs, CMCTs and clay, the obtained hydrogels exhibited the highest tensile stress of 535.5 kPa at the breaking deformation of 1579.5%. Furthermore, these synthesized hydrogels were tough enough and simultaneously owned a fast recoverability after unloaded in 15 min at room temperature. Moreover, effects of the above factors on swelling and swelling-shrinking behaviors of the prepared hydrogels were investigated in detail. In addition, these designed hydrogels also possessed a controlled drug release property of asprin by adjusting their inner crosslink density. Owing to this property, they could be used as the potential drug delivery carriers in future.

Ethylcellulose Oleogels: Structure, Functionality, and Food Applications

The structuring edible oils by nontraditional means has become a popular strategy for improving the lipid profile of food products while retaining the functionality of a crystalline triglyceride network. Although numerous oleogelator systems have now been identified, the polymer gelator ethylcellulose (EC) may present the greatest potential for applications in a diverse range of food systems which require unique physical attributes and structuring properties in the fat phase. The first portion of this chapter will provide a brief overview of oleogelation strategies, outline the basic physical characteristics of the polymer EC, and describe the mechanism of gelation and some basic physical characteristics of EC oleogels. The subsequent sections will highlight different strategies which have been identified to manipulate the rheological and mechanical properties of these gels, including the addition of food-grade surfactants and other amphiphilic molecules, modulating bulk solvent polarity, and through the formation of EC/hybrid gelator systems. The final section will highlight various applications in food systems reported in the literature, outline recent work investigating the effect of structuring edible oils with EC on digestibility, and the potential applicability of these oleogels as a delivery vehicle for lipid-soluble molecules. The potential applications for EC oleogels in complex food systems are quite promising, and the strategies for manipulating their physical properties may also extend their applicability into the pharmaceutical, cosmetic, and manufacturing industries.

Robust and Mechanically and Electrically Self-Healing Hydrogel for Efficient Electromagnetic Interference Shielding

Autonomously self-healing hydrogels have received considerable attentions due to their capacity for repairing themselves spontaneously after suffering damage, which can provide a better stability and a longer life span. In this work, a robust and mechanically and electrically self-healing hydrogel with an efficient electromagnetic interference (EMI) shielding performance was successfully fabricated via the incorporation of multiwalled carbon nanotubes (MWCNTs) into the hydrophobically associated polyacrylamide (PAM) hydrogels by using cellulose nanofiber (CNF) as the dispersant. It was been found that CNF could not only assist the homogeneous dispersion of MWCNTs but also effectively enhance the mechanical property of the resultant hydrogels. As a result, the optimal tensile strength (≈0.24 MPa), electrical conductivity (≈0.85 S m^-1), and EMI shielding effectiveness (≈28.5 dB) were achieved for the PAM/CNF/MWCNT composite hydrogels with 1 wt % MWCNTs and 0.3 wt % CNF, which showed 458, 844, and 90% increase over (≈0.043 MPa, ≈0.09 S m^-1, and ≈15 dB, respectively) the PAM hydrogel. More encouragingly, these composite hydrogels could rapidly restore their electrical conductivity and EMI shielding effectiveness after mechanical damage at room temperature without any external stimulus. With outstanding mechanical and self-healing properties, the prepared composite hydrogels were similar to human skin, but beyond human skin owing to their additional satisfactory electrical and EMI shielding performances. They may offer promising and broad prospects in the field of simulate skin and protection of precision electronics.

A POSS based hydrogel with mechanical robustness, cohesiveness and a rapid self-healing ability by electrostatic interaction

A molecularly dispersed nano-material called POSS-NH₂-AA was synthesized to construct a hybrid hydrogel with a rapid self-healing ability (stress 8 kPa) and excellent mechanical performance (a strain of 4683% and a stress of 37.8 kPa). The hydrogel also exhibits good cohesiveness to materials, such as plastics, glass and iron. The backbone of the POSS makes the hydrogel much stronger than the hydrogel without POSS, which accounts for the improvement in its properties. This process is facile and useful to construct mechanically strong and self-healable materials.

Self-healable, tough and highly stretchable hydrophobic association/ionic dual physically cross-linked hydrogels

In this work, we describe a novel method for the production of tough and highly stretchable hydrogels with self-healing behavior, tensile strength of 150–300 kPa and stretch at break of 2400–2800%.

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.

Preparation and properties of polyacrylamide/polyvinyl alcohol physical double network hydrogel

A novel physical double network hydrogel (PDN gel) composed of physically cross-linked PVA and hydrophobically associated polyacrylamide (HAPAM) has been successfully prepared by one-pot in situ polymerization and subsequent freeze–thaw cycling.