Polydopamine/polystyrene nanocomposite double-layer strain sensor hydrogel with mechanical, self-healing, adhesive and conductive properties.

Inspired by the adhesion mechanism of natural mussels, polydopamine (PDA) has been widely studied and applied in hydrogels due to its good adhesion to various materials. In this work, a double-layer hydrogel constituted of an adhesive layer and a tough layer was successfully prepared via in-situ polymerization. Adding polystyrene particles into the tough layer could improve the mechanical properties, and the adhesion of various substrates could be achieved with PDA nanoparticles in the adhesive layer. Furthermore, lithium chloride was introduced into the tough layer to endow the bilayer hydrogels with electrical conductivity. Due to the hydrophobic association in the tough layer and hydrogen bond in the adhesive layer, the double-layer hydrogel exhibits self-healing properties. In addition, the NIR light response property of PDA was beneficial to self-healing properties. As a result, it has proved that the prepared bilayer hydrogel has excellent conductivity, toughness (0.18 MPa), adhesion and self-healing properties, which is an ideal flexible wearable strain sensor with high sensitivity and good repeatability, suitable for human motion signal detection.

Healing, flexible, high thermal sensitive dual-network ionic conductive hydrogels for 3D linear temperature sensor.

A temperature sensor based on muti-wall carbon nanotubes (MWCNTs) composite polyacrylamide/Fe3+-polyacrylic acid (PAM/Fe3+-PAA) double network (DN) hydrogels that combines flexibility, thermal sensitivity and self-healing ability is fabricated through in situ polymerization and maceration. Due to the excellent thermal conductivity of carbon nanotubes, the temperature sensitivity of the DN hydrogels are improved and therefore can be exploited as a novel channel material for a temperature sensor. This temperature sensor can be stretched from 0 to 750% strain with the sensitivity as high as 9.4%/°Cat extreme 200% strain. Importantly, the DN hydrogels have excellent self-healing properties that it can still be stretched after cutting and healing. Similarly, the electrical and thermal sensing properties of the DN hydrogels can be self-healed analogous to the self-healing capability of human skin. In addition, DN hydrogels have high stability for bending and torsion, which can avoid errors caused by deformation in the temperature measurement. In order to attaching on nonplanar curvilinear surfaces for practical temperature detection, we designed a linear-shaped hydrogels temperature sensor, which can improve the accuracy by wrapping the surface of the measured object completely in a way that eliminates the influence of air in the holes, enabling it to be potentially integrated in soft robots to grasp real-world information for guiding their actions.

Tough hydrophobic association hydrogels with self-healing and reforming capabilities achieved by polymeric core-shell nanoparticles.

The application range of hydrogels can be greatly widened by improving their mechanical properties. It is still a great challenge to develop hydrogels with good mechanical properties, reliable self-healing properties and remolding ability at the same time. Inspired by biological soft tissue with excellent mechanical properties and self-healing properties, here, a facile method to fabricate poly (styrene-acrylic acid) (P(S-AA)) core-shell nanoparticles with plenty of carboxyl groups on their surface, and their enhancement to hydrophobic association hydrogels was reported. Under stress, the dynamic physical bonds including hydrogen bonding between polymer chains and P(S-AA) core-shell nanoparticles (NPs), and entanglement of hydrophobic chains were destroyed to effectively dissipate energy, and uniform hydrogel network leads to smooth stress-transfer, which makes the core-shell nanoparticles composite hydrophobic association hydrogels (MHA gels) excellent mechanical properties, such as excellent mechanical properties, toughness and ductility, and good self-healing properties as well. These features make the MHA gels have great potential in biomedical applications such as tissue engineering, articular cartilage and artificial skin.

Self-assembling GO/modified HEC hybrid stabilized pickering emulsions and template polymerization for biomedical hydrogels.

Graphene oxide(GO), as an amphiphilic and biocompatible material, is often used to prepare Pickering emulsion. However, the preparation of stable Pickering emulsion by a low concentration of GO is very challenging. In this research, we prepared the hydrophobic modified hydroxyethyl cellulose (mHEC) which contained quaternary ammonium group and GO which the water contact angle was 84°-86°. A stable, low cost, and biocompatible Pickering emulsion was fabricated by a low concentration of GO and different contents of mHEC. The effects of mHEC concentration, electrolyte concentration, pH, and oil/water ratio on the stability of Pickering emulsion were investigated. What's more, we prepared the biomedical macroporous polyacrylamide hydrogel by the GO/mHEC composite stabilized emulsion template for drug controlled-release. The composite hydrogel by Pickering emulsion template is a potential drug controlled-release delivery platforms. Furthermore, our strategy is extremely versatile, as Pickering particles, polymer and the monomer of hydrogel can all be varied.