Crosslinking of Silk Fibroin Bearing Azido Groups in Its Non-Repetitive Regions

Abstract

　　Incorporation of an unnatural amino acid bearing an azido group, 4-azido-L-phenylalanine, into the non-repetitive regions of silk fibroin has enabled its facile modification using azido groups as chemical handles. We have previously investigated crosslinking of fibroin using a bifunctional chemical crosslinker and found that the crosslinking reactions hardly proceeded between fibroin molecules. The difficulty of crosslinking was probably due to the steric constraint between fibroin molecules as well as the low abundance of azido groups. In this study, we investigated crosslinking of fibroin having an approximately 2.5-fold increase in azido groups. The results showed that the fibroin with an increase in azido groups was more prone to crosslinking. We infer that the azido groups exhibit different reactivities according to their incorporated positions in the non-repetitive regions, and that the increased incorporation of azido groups improved the likelihood of azido groups being in the positions most advantageous for crosslinking.