(98aq) Influence of Solvent Volatility On the Formation of Core-Shell Hollow Microfibers By Triaxial Electrospinning

Abstract

Electrospinning is a polymer processing technique that uses an electric field to produce nano and microfibers. Co-axial and triaxial electrospinning are modified methods for preparing fibers with multi layered walls. In triaxial electrospinning three different polymers solutions are supplied into a compound Taylor cone (three flow streams) through a spinneret and charged liquid at the nozzle orifice is drawn out by electric field to form a liquid jet. As the solvent of spinning solution evaporates, the jet solidifies and a polymer core-shell is formed.  Reasons for these modifications include i) increasing the surface area to deliver important molecules, ii) improving the mechanical properties, and iii) enhancing the structural morphology.  In this study, designing and fabrication of triaxial electrospinning spinneret capable of electrospun multi wall core-shell fibers.  We investigated the effect of solvent system properties and molecular weight on the fabrication of  core shell hollow nanofibers made of polycaprolactone (PCL), cellulose acetate (CA), and polyvinyl  alcohol (PVA).  The effects of the solvent mixture properties on the electrospinability of polymer solution were investigated.  Switching the configuration of polymers in some systems led to a failure in obtaining fibers due to the rapid solvent evaporation (volatility) of the inner shell liquid which caused phase separation during electrospinning process.  SEM images of the fabricated fibers indicated the formation of a multi layered hollow core-shell microfibers of hydrophobic hollow PCL/CA, PCL/PVA and hydrophilic CA/PCL.  The obtained results showed that solvent properties include solvent ratio solvent boiling point and solvent miscibility are critical factors that are key to jet stability and fibers uniformity. Hollow microfibers of PCL, CA and PVA were successfully produced by triaxial electrospinning.  While switching the configuration of polymers in these systems, rapid solvent evaporation (volatility) of the inner core caused phase separation, leading to failure in obtaining fibers.  Selection of solvents with appropriate boiling points relative to the outer shell is critical: outer shell should have a boiling point less than that in the inner cores. Inner core MW should be smaller or comparable to that of the outer shell.  Endothelial Cells attached and spread on these fibers suggesting no toxicity from the solvents.