Influence of humidity and polymer additives on the morphology of hierarchically porous microspheres prepared from non-solvent assisted electrospraying

Porous polymer microspheres have attracted great interest in many potential fields of application, such as controlled drug release, catalysis, and scaffolds, due to their high surface to volume ratio, low density, permeability, etc. It is desirable to control the porous structure of the microspheres to meet their application requirements. In this study hierarchically porous microspheres were prepared by the technique of non-solvent induced phase separation (NIPS) during electrospraying. Porous and/or hollow microspheres were prepared by using different non-solvents. The influence of humidity on the surface morphology and microstructure by vapor induced phase separation and breath figure effect were investigated. Microspheres with an irregularly hollow structure was observed with the increase of humidity, when ethanol was used as the non-solvent. On the other hand, the polymer additives in the solution could also affect the NIPS and thus the surface morphology of the electrosprayed microspheres. It was found that the microstructure of both the microsphere and surface pores varied little when the polymer additives were not soluble in the non-solvent (hexanol). When polyvinyl pyrrolidone (PVP – soluble in the hexanol) was used as the polymer additive, dimples on the microsphere surface were formed.