{Reference Type}: Journal Article {Title}: Swelling and penetration of fatty acid vesicles under ion-competitive environment. {Author}: Chen L;Huang Y;Zhao H;Xue S; {Journal}: Colloids Surf B Biointerfaces {Volume}: 236 {Issue}: 0 {Year}: 2024 Apr 15 {Factor}: 5.999 {DOI}: 10.1016/j.colsurfb.2024.113800 {Abstract}: The physicochemical characteristics of fatty acid (FA) vesicles and their ion sensitivity as drug delivery vehicles in an ion-competitive environment have received much attention. Here, we show that in a Na+/K+ competitive ionic environment, FA vesicles undergo a cascade of periodic expansion and selective ion retention in response to osmotic attack. When the Na+/K+ ratio is altered, the expansion and volume of vesicles are affected and the ions in vesicles mix with the hyperosmotic fluid to produce a stable transmembrane potential, consistent with the Donnan effect and iontophoresis theory. Furthermore, osmotic swelling experiments suggest that FA vesicles are more easily maintained in a single Na+ or K+ solution than in a multicomponent ion competition system. As a theoretical basis for the utilization of FA vesicles in multicomponent ionic environments, we developed a core theoretical model to characterize the basic features of the volume fluctuations of FA vesicles in ion-competing environments.