Characterization of Azido-Incorporated <i>Bombyx mori</i> Silk Fibroin as a Drug Carrier Material

Silk fibroin, a natural polymer derived from the domesticated silkworm, <i>Bombyx mori</i>, exhibits remarkable tensile toughness, broad biocompatibility, and biodegradability. We previously developed azido-incorporated silk fibroin (<i>AzidoSilk</i>) using genetic code expansion. <i>AzidoSilk</i> 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, <i>AzidoSilk</i> 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 <i>AzidoSilk</i> via click chemistry modifications. Fluorescent drug models were immobilized on <i>AzidoSilk</i> 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 <i>AzidoSilk</i> materials in a time-dependent manner. In another model, kanamycin was immobilized on <i>AzidoSilk</i> fabric via the same UV-sensitive linker, and its antibacterial activity against <i>Staphylococcus aureus</i> was tested. PBS extracts from kanamycin-immobilized <i>AzidoSilk</i> fabrics after UV irradiation showed significant antibacterial activity against <i>S. aureus</i>. These results demonstrate that <i>AzidoSilk</i> 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. <i>AzidoSilk</i> has broadened the scope of chemical modification of silk fibroin to achieve simpler and more reliable drug delivery.