Fabrication and characterization of Eri silk fibers-based sponges for biomedical application

Cocoon-derived semi-domesticated Ed silk fibers still lack exploitation for tissue engineering applications due to their poor solubility using conventional methods. The present work explores the ability to process cocoon fibers of non-mulberry Ed silk (Samia/Philosamia ricini) into sponges through a green approach using ionic liquid (IL) - 1-buthyl-imidazolium acetate as a solvent. The formation of beta-sheet structures during Eri silk/IL gelation was acquired by exposing the Ed silk/IL gels to a saturated atmosphere composed of two different solvents: (i) isopropanol/ethanol (physical stabilization) and (ii) genipin, a natural crosslinker, dissolved in ethanol (chemical crosslinking). The sponges were then obtained by freeze-drying. This approach promotes the formation of both stable and ordered non-crosslinked Eri silk fibroin matrices. Moreover, genipin-crosslinked silk fibroin sponges presenting high height recovery capacity after compression, high swelling degree and suitable mechanical properties for tissue engineering applications were produced. The incorporation of a model drug - ibuprofen - and the corresponding release study from the loaded sponges demonstrated the potential of using these matrices as effective drug delivery systems. The assessment of the biological performance of ATDC5 chondrocyte-like cells in contact with the developed sponges showed the promotion of cell adhesion and proliferation, as well as extracellular matrix production within 2 weeks of culture. Sponges' intrinsic properties and biological findings open up their potential use for biomedical applications. Statement of Significance This work addresses the preparation and characterization of non-mulberry cocoon-derived Ed silk sponges. The insolubility of cocoons-derived non-mulberry silkworms impairs their processability and applications in the healthcare field. We used a green approach with ionic liquids to overcome the lack solubility of such silk fibers. The formation of beta-sheet structures into Ed-based sponges was physically and chemically induced. The sponges were obtained by freeze-drying. The developed structures exhibited flexibility to adapt and recover their shapes upon application and subsequent removal of load, high swelling degree, ability to load an anti-inflammatory drug and to promote its sustained release. They promoted in vitro cellular adhesion, proliferation and extracellular matrix production of a chondrocyte-like cell line, opening up their potential application for biomedical applications. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.