Bubble-patterned films by inkjet printing and gas foaming

The micropatterning of thin films represents a challenging task, even for additive manufacturing techniques. In this work, we introduce the use of inkjet-printing technology coupled with a gas-foaming process, to produce patterned porosities on polymeric thin films, to develop a bubble-writing method. Inkjet printing of an aqueous solution of poly (vinyl alcohol) (PVA), a well-known gas-barrier polymer, allows the selective coating of a thin poly (lactic acid) (PLA) film, which is, successively, exposed to a gas-foaming process. The foaming of the thin PLA film is effective, only when PVA is printed on top, since the PVA barrier hinders the premature loss of the gas, thus allowing the formation of cavities (bubbles) in the covered areas; then, removing the PVA coating by water washing forms a bubble pattern. As a proof of concept, the surface-morphology features of the patterned porous PLA films have been proven effective at driving endothelial cell growth. A new technological platform is, hence, introduced in the field of tissue engineering and, in general, in fields involving thin films, where a patterned porous structure may add value.