Simultaneous electrospinning and electrospraying: a straightforward approach for fabricating hierarchically structured composite membranes.

We present here for the first time a simple method for micropatterning nonwoven composite membranes. The approach is based on the simultaneous electrospraying of microparticles and electrospinning of nanofibers from different polymer solution feeds (polyethylene glycol and poly(D,L-lactide)) on a common support. The mechanism of self-organization between fibers and particles into hierarchical honeycomb-like structures, as well as the evolution of the later as a function of the thickness of the composite, is investigated. We demonstrate that aggregates of particles, leading to a nonuniform distribution of the electrostatic field near the collector, are necessary to form the self-organized composite. Furthermore, it is shown that the specific dimensions of the generated patterns can be controlled by tuning the flow rate of electrospraying. The obtained composite mat exhibits a multilevel porous structure, with pore sizes ranging from few up to several hundreds of micrometers. Finally, it is shown that the microparticles can be selectively leached, allowing the production of a monocomponent membrane and retaining the hierarchical organization of the nanofibers suitable for biomedical and filtration applications.