Swellable silk fibroin microneedles for transdermal drug delivery

In this paper, a swelling-modified silk fibroin (SF) microneedle for transdermal drug delivery is presented. The microneedles undergo a phase transition from a dried and rigid state to a semi-solid, acerose hydrogel state with a controlled 3-dimensional (3D) porous network structure. Different micromolecular reagents have been studied for mixing with aqueous silk fibroin to endow a swellable and insoluble capacity to the SF. The aqueous SF composite is poured on a polydimethylsiloxane (PDMS) mold with arranged micropores on its surface to fabricate SF microneedles with high fidelity and mechanical robustness. The results demonstrate that 2-ethoxyethanol (ECS) modified SF microneedles can easily pierce porcine skin with a depth of ∼200μm in vitro, and transform into semi-solid hydrogels with 50-700nm porous network inside. These swelling-modified microneedles can accomplish a significantly enhanced transdermal drug release capacity in proportion to their swelling characteristics. The better swelling capacity of the microneedles produces larger pores, resulting in higher transdermal drug release kinetics. There is also a relationship between swollen pore dimensions and the molecular weights of encapsulated therapeutics. The controllable properties of these SF microneedles coupled with their high biocompatibility, render swell-to-release ECS/SF composites as viable transdermal delivery devices.