Cellulose nanocrystal reinforced polyvinyl alcohol hydrogels with multi-stimulus responsive behavior and self-healing properties

Objective Hydrogels have a wide range of applications in areas such as biosensors, wound dressings, tissue engineering, controlled drug release and supercapacitors. Traditional polyvinyl alcohol (PVA) hydrogels have relatively single functions and lack self-healing ability, which limits their applications to a certain extent. Therefore, it is essential to endow PVA hydrogels with multi-stimulus responsiveness and self-healing ability to broaden their potential applications.

Method In this study, self-healing PVA/CNC/sodium tetraborate hydrogels (PCBs) with excellent mechanical properties and multi-stimulus responsive behaviors were prepared by introducing cellulose nanocrystal (CNC) and borate bonds into PVA and combining them with freeze-thaw treatment.

Result (1) The addition of CNC and sodium tetraborate significantly enhanced the mechanical properties of PCBs. When the mass ratio of PVA/CNC/ sodium tetraborate was 10∶1.5∶1 (PCB_0.1), the tensile strength of PCB_0.1 was 4.4 times higher than PVA hydrogel. Moreover, the hydrogel PCB_0.1 exhibited excellent self-healing properties, which showed a self-healing efficiency higher than 90%. (2) The PCB_0.1 exhibited multi-stimulus response behavior. PCB_0.1 showed excellent reversible gel-sol transition behaviors under external environmental stimuli such as temperature and pH. (3) When the tensile strain of PCB_0.1 increased from 60% to 220%, significant changes in its optical properties were observed. Under polarized light, the interference color of hydrogel gradually shifted from blue to green, yellow, red, and purple. (4) PCB_0.1 exhibited ionic responsiveness and showed sensitivity to \textSO_4^2 - and Ca²⁺.

Conclusion The PVA/CNC/sodium tetraborate composite hydrogels with multi-stimulus responsive behavior and self-healing ability can be prepared successfully by simply mixing PVA, CNC, and sodium tetraborate and then subjecting them to freeze-thaw treatment. These hydrogels are easy to prepare and have the advantages of low cost, high strength, and good responsiveness, which show certain application potential in the fields of multi-functional sensors and anti-counterfeiting.