Characterization of Azido-Incorporated Bombyx mori Silk Fibroin as a Drug Carrier Material

Silk fibroin, a natural polymer derived from the domesticated silkworm, Bombyx mori, exhibits remarkable tensile toughness, broad biocompatibility, and biodegradability. We previously developed azido-incorporated silk fibroin (AzidoSilk) using genetic code expansion. AzidoSilk contains synthetic azido groups that can be selectively attached to any functional molecule in a bioorthogonal manner through click chemistry. Click chemistry provides high yields and minimal byproducts. In this study, AzidoSilk was characterized as a drug carrier material for on-demand drug delivery systems (DDS) because effective drug loading and controllable release by external stimuli can be achieved with AzidoSilk via click chemistry modifications. Fluorescent drug models were immobilized on AzidoSilk film and woven fabric via a UV-sensitive bifunctional linker using click chemistry. Azido-selective immobilization of the drug models was confirmed, and upon irradiation with 365 nm UV light, the drug models were gradually released from the AzidoSilk materials in a time-dependent manner. In another model, kanamycin was immobilized on AzidoSilk fabric via the same UV-sensitive linker, and its antibacterial activity against Staphylococcus aureus was tested. PBS extracts from kanamycin-immobilized AzidoSilk fabrics after UV irradiation showed significant antibacterial activity against S. aureus. These results demonstrate that AzidoSilk can be used as a drug carrier material for on-demand DDS. In this system, changes in linker design can expand the range of external stimuli usable for drug release, depending on the application. AzidoSilk has broadened the scope of chemical modification of silk fibroin to achieve simpler and more reliable drug delivery.