Poly(acrylamide‐co‐acrylic acid)/chitosan semi‐interpenetrating hydrogel for pressure sensor and controlled drug release

Machine Learning-Enhanced Biomass Pressure Sensor with Embedded Wrinkle Structures Created by Surface Buckling

Flexible piezoresistive sensors are core components of many wearable devices to detect deformation and motion. However, it is still a challenge to conveniently prepare high-precision sensors using natural materials and identify similar short vibration signals. In this study, inspired by microstructures of human skins, biomass flexible piezoresistive sensors were prepared by assembling two wrinkled surfaces of konjac glucomannan and k-carrageenan composite hydrogel. The wrinkle structures were conveniently created by hardness gradient-induced surface buckling and coated with MXene sheets to capture weak pressure signals. The sensor was applied to detect various slight body movements, and a machine learning method was used to enhance the identification of similar and short throat vibration signals. The results showed that the sensor exhibited a high sensitivity of 5.1 kPa-1 under low pressure (50 Pa), a fast response time (104 ms), and high stability over 100 cycles. The XGBoost machine learning model accurately distinguished short voice vibrations similar to those of individual English letters. Moreover, experiments and numerical simulations were carried out to reveal the mechanism of the wrinkle structure preparation and the excellent sensing performance. This biomass sensor preparation and the machine learning method will promote the optimization and application of wearable devices.

Strong, conductive, and freezing-tolerant polyacrylamide/PEDOT:PSS/cellulose nanofibrils hydrogels for wearable strain sensors

Hydrogels with prominent flexibility, versatility, and high sensitivity play an important role in the design and fabrication of wearable sensors. In particular, these flexible conductive hydrogels exhibit elastic modulus that is highly compatible with human skin, demonstrating the great potential for flexible sensing. However, the preparation of high-performance hydrogel-based sensors that can restrain extreme cold conditions is still challenging. Herein, a novel anti-freezing composite hydrogel with superior conductivity based on polyacrylamide (PAM), LiCl, and PEDOT:PSS coated cellulose nanofibrils (PAM/PEDOT:PSS/CNF) is constructed. The addition of CNF increased the hydrogen bonding sites of the molecular chains in the micro, thus improving the mechanical strength and the conductivity of the hydrogel in the macro. The hydrogels achieve a high tensile strength of 0.19 MPa, compressive strength of 0.92 MPa, and dissipation energy of 41.9 kJ/m³. Otherwise, LiCl increases the interactions between the colloidal phase and water molecules, endowing the hydrogels with excellent freezing tolerance. Specifically, the optimized hydrogel of 45 % LiCl exhibited stable mechanical properties at -40 °C. Finally, the composite hydrogel was used to assemble flexible sensors with high sensitivity of 10.3 MPa^-1, which can detect a wide range of human movements and physiological activities.

MOF-implanted poly (acrylamide-co-acrylic acid)/chitosan organic hydrogel for uranium extraction from seawater

In this study, a composite hydrogel with a low swelling ratio, excellent mechanical properties, and good U (VI) adsorption capacity was developed by incorporating a metal-organic framework (MOF) with a poly (acrylamide-co-acrylic acid)/chitosan (P(AM-co-AA)/CS) composite. The CS chain, which contains NH₂, reduces the swelling ratio of the hydrogel to 4.17 after 5 h of immersion in water. The coordinate bond between the MOF and carboxyl group on the surface of P(AM-co-AA)/CS improves the mechanical properties and stability of P(AM-co-AA)/CS. The U(VI) adsorption capacity of P(AM-co-AA)/CS/MOF-808 is 159.56 mg g^-1 at C₀ = 99.47 mg L^-1 and pH = 8.0. The adsorption process is well fitted by the Langmuir isotherm and pseudo-second-order model. The P(AM-co-AA)/CS/MOF-808 also exhibits good repeatability and stability after five adsorption-desorption cycles. The uranium adsorption capacity of the developed adsorbent after one month in natural seawater is 6.2 mg g^-1, and the rate of uranium adsorption on the hydrogel is 0.21 mg g^-1 day^-1.

Tubular chitosan hydrogels with a tuneable lamellar structure programmed by electrical signals

The discovery of facile methods to create complex lamellar structures in hydrogels, which mimic the exquisite structures in nature, remains a great challenge. In this work, an ordered lamellar structured hydrogel from the stimuli-responsive amino-polysaccharide chitosan is fabricated by an electro-assembly process, during which the diffusion of OH^- and the electrophoresis of the chitosan chains play important roles. Importantly, a complex ordered/disordered structure of chitosan hydrogel can be regulated with high fidelity by programming the input electrical signals.

Composite Polyvinylpyrrolidone-Sodium Alginate-Hydroxyapatite Hydrogel Films for Bone Repair and Wound Dressings Applications

Today, the synthesis of biocompatible and bioresorbable composite materials such as “polymer matrix-mineral constituent,” which stimulate the natural growth of living tissues and the restoration of damaged parts of the body, is one of the challenging problems in regenerative medicine. In this study, composite films of bioresorbable polymers of polyvinylpyrrolidone (PVP) and sodium alginate (SA) with hydroxyapatite (HA) were obtained. HA was introduced by two different methods. In one of them, it was synthesized in situ in a solution of polymer mixture, and in another one, it was added ex situ. Phase composition, microstructure, swelling properties and biocompatibility of films were investigated. The crosslinked composite PVP-SA-HA films exhibit hydrogel swelling characteristics, increasing three times in mass after immersion in a saline solution. It was found that composite PVP-SA-HA hydrogel films containing HA synthesized in situ exhibited acute cytotoxicity, associated with the presence of HA synthesis reaction byproducts—ammonia and ammonium nitrate. On the other hand, the films with HA added ex situ promoted the viability of dental pulp stem cells compared to the films containing only a polymer PVP-SA blend. The developed composite hydrogel films are recommended for such applications, such as membranes in osteoplastic surgery and wound dressing.

Bio-based, self-adhesive, and self-healing ionogel with excellent mechanical properties for flexible strain sensor

Bio-based ionogels with versatile properties are highly desired for practical applications. Herein, we designed a novel self-healing, anti-freezing, and self-adhesive ionogel with excellent sensor capability. The ionogel was obtained by cross-linking amino groups (chitosan) and aldehyde groups (dextran oxide) to form Schiff-base bonds in the ionic liquids (EMIMOAc) with TA. Ionogels inherited the superior electrical conductivity of ionic liquids (IG₂, 1.1 mS cm^-1). Due to the dynamic reaction of Schiff-base bonds, the obtained IG₂ possessed self-healing properties (self-healing efficiency = 89%). The presence of TA also provided the ionogel with excellent self-adhesive properties (IG₂/TA, adhesive strength to hogskin = 8.05 kPa). Owing to the low freezing point and low vapor pressure of ionic liquids, ionogels were endowed with anti-freeze properties and resistance to solvent volatility. Moreover, the ionogel can act as a strain sensor, and exhibited excellent sensitivity and sensing performance. Our work provided a green and effective method in preparation of the high performance ionogel sensor, which could accommodate future practical industrial applications.