Preparation and characterization of tannin/fibroin protein photothermal composite hydrogel

To develop an eco-friendly and safe wound dressing with antibacterial properties and multiple functionalities,tannin/fibroin protein (TA/SF) complex hydrogel was prepared by heating and the addition of tannin (TA) inducing the conformation change of silk fibroin (SF), and then tannin/fibroin protein-iron (TA/SF-Fe) complex hydrogel was fabricated by the further introduction of iron ions to TA/SF. The interaction between TA and fibroin protein was studied by UV spectrum, fluorescence spectrum and circular dichroism for explaining the gelation mechanism of TA/SF-Fe hydrogel. The hydrogels were characterized by FTIR, XRD, XPS, SEM and rheometer, and the photothermal conversion properties, antioxidant properties and antibacterial activities of the hydrogels were studied. The results indicate that the secondary structure of fibroin protein is changed from random coil to β-folded conformation by TA, promoting the formation of hydrogel. The microstructure of the hydrogel is gradually to be orderly and the strength is improved due to the hydrogen bonding between TA and fibroin protein. The cross-linking degree of fibroin protein is increased after introduction of iron ions, leading to the enhancement of strength and self-healing property of TA/SF-Fe hydrogel exhibits the antioxidant and antibacterial activity, and the free radical scavenging rate and antibacterial rate of 2.5TA/SF can reach 91.2% and 73.2% respectively with the increase of TA content. TA/SF-Fe hydrogel shows excellent photothermal conversion ability and stability, and its bacterial inhibition rate through photothermal effect can reach 97.9%. These findings suggest that TA/SF and TA/SF-Fe hydrogels are good bacteriostatic materials and can be a novel effective wound dressings.