Thermo-Activated Shape Memory Films Based on Chitosan Reinforced With Silk Fibroin, Obtained by an Environmentally Friendly Process Using a Deep Eutectic Solvent

Abstract

The high environmental impact of petroleum-based polymer has led to the study and application of biopolymers. Silk fibroin and chitosan are biopolymers with high potential for this, but current processes for obtaining films cast with silk fibroin pose significant environmental impacts including the need for use of toxic solvents and additional costs incurred through the required dialysis process. In this work it was proposed to obtain films based on chitosan and reinforced with silk fibroin, using a deep eutectic solvent formed by mixing choline chloride and citric acid. Glycerol was also added to some samples to study its effects as a plasticizer. Shape memory programming was established with tension tests to determine its fixation ratio and application of hot air at 75 °C. Two different activation temperatures were used to observe the recovery ratio, 75 and 50 °C. Silk fibroin helped improve the thermal and mechanical behavior of the films. Shape memory in these films is mainly explained by hydrogen bonding between chitosan and eutectic solvents. Films presented a recovery ratio between 86 and 54%. While shape memory was not significantly influenced by the presence of silk fibroin on its own, the shape memory activation temperature, the plasticization of chitosan by glycerol, and the mechanical reinforcement of silk fibroin enables control of the shape memory parameters of chitosan films. This behavior will allow for its potential application in areas such as biomedicine in actuators for prostheses or as smart packaging in the food industry.