A Study on the Rheological Parameters of Silk Fibroin Solutions for Electrohydrodynamic Fabrication

Abstract

Silk fibroin (SF) was fabricated using the electrohydrodynamic (EHD) process in order to prepare nanoscale fibers. Despite the high potential of SF nanofibers in biomedical applications, the EHD fabrication of SF has yet to be thoroughly studied. Most SF studies have focused on stable fiber formation, even though particles can be formed using the same process. Thus, the aim of this study is to provide a comprehensive understanding of EHD in the fabrication of SF from particles to fibers in the context of certain rheological properties of SF solution. In addition, a rheological parameter is proposed in order to predict the mode of EHD fabrications as well as product size, regardless of the concentration and molecular weight of SF. Samples of SF with different molecular weight were prepared by controlling the dissolution time of SF in CaCl2/EtOH/H2O solution. The average molecular weight of SF particles was reduced with increased dissolution time. Four different SF samples were prepared with dissolution times of 5, 30, 60 and 180 min, which were designated as SFC005, SFC030, SFC060 and SFC180, respectively. Initially, SF microparticles were prepared using a 1 M LiCl/DMSO solvent. Microparticles of about 200 μm were prepared

their shape was determined by the shear viscosity of the SF solution, regardless of the concentration and molecular weight of SF. Since formic acid (FA) and hexafluoroisopropanol (HFIP) are the most common solvents used in the EHD fabrication of SF, both the shear and dynamic viscosity of SF in these solvents was investigated. With both FA and HFIP solvents, the mode of the EHD fabrication was determined by the solution plateau modulus, regardless of the concentration and molecular weight of SF. The size of EHD products can be predicted using a rheological parameter. The size of particles can be predicted using the zero shear viscosity, whereas the size of fibers can be predicted using the solution plateau modulus. In conclusion, the proposed rheological parameters for SF solutions may be used in the future for the precise control of EHD fabrications.