Development of chitosan/tannic acid/corn starch multifunctional bilayer smart films as pH-responsive actuators and for fruit preservation.

The design of intelligent films for pH-responsive actuators fully constructed from natural biopolymers remains challenging. This study used natural biopolymers to develop a new type of smart and multifunctional chitosan/tannic acid/corn starch (CHT/TA/CS) bilayer films, which can be used for pH-responsive actuators and fruit preservation. We studied the microstructural morphology, physicochemical, antioxidant, antimicrobial properties of the films. Compared with the CHT film, the water vapor permeability (WVP) values of the CHT/TA/CS bilayer films were reduced by 3.1 times, and the tensile strength was increased by 4.6 times. The CHT/TA/CS bilayer films also exhibited high 1,1-diphenyl-2-picrylhydrazyl (DPPH) (94.6%) and hydroxyl (OH) (97.5%) radical scavenging activity. The bilayer films had good antimicrobial activity. The CHT/TA/CS bilayer films exhibited different directional deformation behaviors in acid-base solutions and could be used as pH-responsive actuators. By changing the solution's pH, the bilayer films could grab and release heavy objects 21 times heavier than themselves. Furthermore, the CHT/TA/CS bilayer coating prolonged the bananas' storage time from three to six days, and its weight loss was reduced by 14%. The developed CHT/TA/CS bilayer films have potential application in degradable materials, soft robotics fields, and food packaging materials.