Determining electrospun morphology from the properties of protein-polymer solutions

Integrating natural macromolecules, e.g. proteins, is a progressive trend in the fabrication of biocompatible sub-micrometer fibers with tunable diameters using the electrospinning technique. The correlation between solution properties and electrospun morphology is critical; it is quite clear for synthetic linear polymer solutions but remains uncertain for solutions with protein. Here, we report the determination of electrospun morphology in protein-polymer solutions of poly(ethylene oxide) (PEO) and zein, a storage protein from corn. The viscosity of the zein/PEO mixed solutions can be well described using the Lederer-Roegiers equation and decreases with the increase of the fraction of zein. The surface tension sharply decreases above a critical concentration at the saturation of the interfacial monolayer. Correspondingly, the different electrospun morphologies - from bead, coexisting bead and fiber, to fiber and ribbon - were mapped onto a ternary phase diagram and a viscosity contour plot. Such coupling provides a clear way to determine the electrospun morphology from solution properties. The occurrence of electrospun fibers partially follows two empirical rules, while the critical point revealed from surface tension has the best approximation. The diameters of electrospun fibers were found to have a scaling relationship against concentration, zero-shear viscosity and surface tension of solutions. These scaling exponents were compared with those from typical polymer solutions. The analysis suggests that aqueous ethanol gives different solvent qualities to zein and PEO solutions, resulting in the irregular shape in the phase diagram that correlates solution properties and electrospun morphologies.