Modification of proteins to improve their electrospinning capability: Evolution of pre-treatment systems from traditional to emerging techniques

A major challenge in electrospinning (ESP) of proteins is their spinnability. So, protein modification systems before fabrication of electrospun fibers are necessary, as reviewed in this paper. Traditional modification systems include thermal processing, pH changes, organic solvents, and application of natural biopolymers. On the other hand, novel systems include crosslinkers, ultrasonication, ozonation, microwave processing, and high hydrostatic pressure (HHP) treatment. Different natural biopolymers e.g., polysaccharides (maltodextrin, pullulan, hydroxypropyl methylcellulose, and guar gum) or proteins (gelatin) have been applied as carriers for ESP of proteins which result in no employment of synthetic carriers such as polyvinyl alcohol. In fact, these biopolymers modify the solvent properties (including electrical conductivity, viscosity, and surface tension), reduce the polyelectrolyte protein character, and improve chain entanglement, all of which are required for the formation of uniform nanofibers from proteins. Crosslinking substantially improves water contact angle, barrier properties, insolubility and thermal stability of the blended nanofibers in case of glucose crosslinker. HHP pretreatment causes higher viscosity (up to 57%) and disordered structure as well as lower surface tension (up to 0.56 mN/m) and ordered structure of soy protein isolate-polyvinyl alcohol ESP solution, all of which are suitable for a successful ESP process. In conclusion, novel modification systems seem to be promising candidates for protein refinement before ESP although more studies regarding their comparison with traditional systems are still required before a comprehensive judgement. • Viscosity and morphology of fibers are more affected by pH rather than temperature. • Ozonation pretreatment leads to better fiber morphology than ultrasonication. • High hydrostatic pressure caused higher viscosity and disordered structure and thinner fibers. • More studies of impact of new modification ways on electrospinning are required.