Hofmeister Effect‐Assisted Strong Natural Biopolymer‐Based Hydrogels with Multi‐Functions

Strong, tough, and elastic poly(vinyl alcohol)/polyacrylamide DN hydrogels based on the Hofmeister effect for articular cartilage replacement

Traditional hydrogels are usually weak and brittle, which limit their application in articular cartilage replacement because cartilage is generally strong, tough, and elastic in nature. Therefore, it is highly desirable to construct hydrogels to mimic the mechanical properties of the native articular cartilage. Herein, in this work, poly(vinyl alcohol)/polyacrylamide (PVA/PAM) DN hydrogels were prepared by in situ polymerization, which were then treated with Hofmeister series ions (Cit3-, SO42-, and Cl-) to achieve H-PVA/PAM DN hydrogels. Among the three Hofmeister ions, the DN hydrogel treated with Cit3- (named PVA/PAM-Cit) showed the densest microstructure and the highest crystallinity degree. In this context, PVA/PAM-Cit exhibited a tensile strength of 18.9 ± 1.6 MPa, a compressive strength of 102.3 ± 7.9 MPa, a tensile modulus of 10.6 ± 2.1 MPa, a compressive modulus of 8.9 ± 0.8 MPa, and a roughness of 66.2 ± 4.2 MJ m-3, respectively, which were the highest strength and modulus, and the second highest toughness when compared with those of the reported PVA and PVA based DN hydrogels so far. It also showed an extreme high elasticity, which could maintain a stress of 99.2% after 500 cycles of fatigue testing. Additionally, PVA/PAM-Cit can promote the adhesion, spreading and proliferation of chondrocytes. These results verify that such a strong, tough, and elastic hydrogel could be a novel candidate material for articular cartilage replacement.

Transparent, Stretchable, and Adhesive Conductive Ionic Hydrogel-Based Self-Powered Sensors for Smart Elderly Care Systems

Nowadays, with the intensification of the aging society, the demand for elderly care and medical services is increasing and the elderly care and health systems are facing serious challenges. Therefore, it is imperative to develop a smart elderly care system to achieve real-time interaction between the elderly, the community, and medical personnel and to improve the efficiency of caring for the elderly. Here, we prepared ionic hydrogels with stable properties of high mechanical strength, high electrical conductivity, and high transparency by the one-step immersion method and used them in self-powered sensors for smart elderly care systems. The complexation of Cu²⁺ ions with polyacrylamide (PAAm) endows ionic hydrogels with excellent mechanical properties and electrical conductivity. Meanwhile, potassium sodium tartrate prevents the generated complex ions from precipitating into precipitates, thus ensuring the transparency of the ionic conductive hydrogel. After optimization, the transparency, tensile strength, elongation at break, and conductivity of the ionic hydrogel reached 94.1% at 445 nm, 192 kPa, 1130%, and 6.25 S/m, respectively. By processing and coding the collected triboelectric signals, a self-powered human-machine interaction system attached to the finger of the elderly was developed. The elderly can complete the transmission of distress and basic needs by simply bending their fingers, greatly reducing the pressure of inadequate medical care in an aging society. This work demonstrates the value of self-powered sensors in the field of smart elderly care systems, showing a wide implication in human-computer interface.