Fig. 4

Features of the Infasurf^® surface structures at various surface pressure values before and after exposure to e-cigarette vapor (unflavored) and cigarette smoke as determined by atomic force microscopy: (a) average height and (b) average surface area covered by the structures. Cigarette smoke resulted in an increase in area fraction, which was significantly increased compared to control (shown by *), and in some cases to surfactant exposed to e-cigarettes vapor (shown by $). A p-value of 0.05 was used for all analysis