Breath-figure polymer films with local microporosity controlled via spatio-thermal templating

Porous structures offer a vast range of important industrial applications. In the context of medicine, and specifically in the area of controlled drug delivery, spatial [and temporal] control over local porosity has a significant influence on net molecular flux through [membrane-based] controlled release platforms. Such systems may be formulated as oral, transdermal, or even implantable entities, and address chronic infusion needs covering such ailments as diabetes, cancer and hypertension [1]. In all the aforementioned situations, a facility to spatially control porosity could offer significant advantage, such as safer controlled release over extended durations. Here, we describe a novel route to engineering-in such flexibility within polymeric thin films by modifying spin-coating protocols to accommodate breath film patterning, that is, the spatially controlled condensation of pore forming droplets onto a liquid-polymer film. Upon film solidification, characterization via optical- and scanning probe microscopy revealed that local variations in porosity, as inferred from topographic measurements, could be effectively controlled through provision of an embossed vacuum holding chuck that effectively retains intimate thermal contact with the film substrate during forming. Parallel measurements using real time thermography support the hypothesis that porosity is controlled by local solvent evaporation rates.