Insulin-Loaded Silk Fibroin Microneedles as Sustained Release System.

Silk fibroin has widely been used in biomedical applications for its excellent biocompatibility, degradability, and mechanical properties. Microneedles are a suitable method for transdermal drug delivery. In this work, we have prepared microneedles using silk fibroin as the main material and have added proline to change its crystal structure. The fabricated microneedles are nontoxic and degradable and show relatively slow drug release. Our results indicate that the fibroin/proline microneedles can act as carriers of insulin. Fourier transform infrared (FTIR) observations show that the structure of proline-treated fibroin is transformed from random coils to ß-sheets. A more regular arrangement is formed between the molecular segments. X-ray diffraction patterns show that proline has good compatibility with fibroin and induces the secondary conformation of the microneedles to a Silk I type structure. The needles have enough strength to pierce the stratum corneum of the skin. In vitro release experiments with insulin indicate that the release time from the microneedles is maintained up to 60 h. This system of delivery may provide a painless and effective route of insulin intake for the treatment of diabetic patients.

Highly elastomeric photocurable silk hydrogels.

A photocurable silk fibroin hydrogel is prepared, for the first time, using natural silk protein fibroin and biophotosensitizer riboflavin. Riboflavin is excited by ultraviolet light to generate a triplet state which is transferred to produce active oxygen radicals with singlet oxygen as the main component. Active oxygen radicals can induce chemical cross-linking of amino-, phenol- and other groups in the silk fibroin macromolecules to form a photocurable hydrogel. The different biophysical characterizations of the gelation of this modified fibroin protein solution were studied by using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, microplate reader and texture analyzer. The aggregate structures, surface morphologies, mechanical properties, light transmission and degradation properties of the gel were studied. The investigations showed that the silk fibroin/riboflavin hydrogels predominantly have random coils or alpha helix structures. These gels show resilience up to 90% after 80% compression and a light transmission of up to 97%. The cell culture experiment exhibits that the hydrogel has a satisfactory cytocompatibility.

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.

Silk Fibroin/Polyvinyl Pyrrolidone Interpenetrating Polymer Network Hydrogels.

Silk fibroin hydrogel is an ideal model as biomaterial matrix due to its excellent biocompatibility and used in the field of medical polymer materials. Nevertheless, native fibroin hydrogels show poor transparency and resilience. To settle these drawbacks, an interpenetrating network (IPN) of hydrogels are synthesized with changing ratios of silk fibroin/N-Vinyl-2-pyrrolidonemixtures that crosslink by H2O2 and horseradish peroxidase. Interpenetrating polymer network structure can shorten the gel time and the pure fibroin solution gel time for more than a week. This is mainly due to conformation from the random coil to the ß-sheet structure changes of fibroin. Moreover, the light transmittance of IPN hydrogel can be as high as more than 97% and maintain a level of 90% within a week. The hydrogel, which mainly consists of random coil, the apertures inside can be up to 200 µm. Elastic modulus increases during the process of gelation. The gel has nearly 95% resilience under the compression of 70% eventually, which is much higher than native fibroin gel. The results suggest that the present IPN hydrogels have excellent mechanical properties and excellent transparency.