Sustainable strategies for waterborne electrospinning of biocompatible nanofibers based on soy protein isolate

Electrospun nanofibers have gained great interest in many fields of research from water and air filtration or food packaging to medical use as scaffolds for tissue engineering, drug delivery systems and wound bandages. Proteins such as soy protein isolate (SPI) are biodegradable and safe polymers that can be purified from renewable and sustainable sources, and are thus interesting as building blocks for sustainable and biocompatible nanofiber-based materials. Sufficient solvent evaporation and intermolecular entanglement are required for efficient nanofiber formation. Electrospinning of proteins is therefore often achieved using organic solvents, strong bases or surfactants, which limits the safety, sustainability and usability of protein-based nanofibers. In this work, green and biocompatible electrospun nanofibers with a high content of SPI (up to 75% (w/w)) were fabricated with polyethylene oxide (PEO) as a co-spinning polymer and with water being the only solvent, thus avoiding use of any organic solvent, strong base or surfactant. A thorough biophysical assessment based on microscopy and spectroscopies, and a rheological profiling of SPI suggested that disassembly of larger structures into smaller in the SPI suspension and increase of SPI solubility improved the electrospinnability of SPI. The content of SPI in the nanofibers affected the morphology as visualized by scanning electron microscopy, brittleness assessed by dy-namic mechanical analysis, and aqueous stability of the nanofibers, which are key parameters for the future use of SPI-based nanofibers. The biocompatibility of the electrospun SPI/PEO nanofibers was demonstrated by exposure of human epithelial cell monolayers (TR146) to the nanofibers without loss of cell viability. We propose that the presented strategies can serve as a universal workflow for waterborne electrospinning of other proteins or protein isolates.