Thermo-Responsive Core−Sheath Electrospun Nanofibers from Poly (N-isopropylacrylamide)/Polycaprolactone Blends

Core−sheath nanofibers with biodegradable polycaprolactone (PCL) as the core and thermo-responsive poly( N -isopropylacrylamide) (PNIPAAm) as the sheath were prepared by single-spinneret electrospinning of blends of the two polymers. The morphology of the composite fibers with different proportions of PNIPAAm to PCL was determined using scanning electron microscopy (SEM). Surface enrichment of PNIPAAm was confirmed by both x-ray photoelectron spectroscopy (XPS) quantification and time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging. It was found that the phase separation was driven by both thermostatic/kinetic factors and electric-field-orientation effects. The combination of appropriate choice of miscible solvents with large parameter differences (solubility of the two polymers, dielectric constant, and evaporation speed during jet traveling) and difference in molecular weight/viscosity of the two polymers contributed to the core−sheath self-assembly. The thermo-responsive wettabilites of the PNIPAAm dominant fibrous surfaces were demonstrated using contact angle (CA) measurements and a microcontact printing (μCP) method.