Improving the longevity of passive microfluidic systems through plasma polymer films with a vertical chemical gradient

Abstract

Capillary driven microfluidic devices rely on hydrophilic surfaces to facilitate and control the fluid flow inside microchannels. This can be accomplished through the deposition of a highly functional plasma polymer film (PPF) on the surface of the device. Highly functional plasma polymer films exhibit ageing effects characterized by oxidation, degradation, swelling, dissolution, and restructuring at the surface to minimize the surface energy. The application of plasma polymer films in microfluidics is, therefore, limited by this instability. To overcome this limitation, plasma polymer films in the form of a vertical chemical gradient structure were deposited on the surface of microfluidic devices designed to perform immunodiagnostics for use during space missions. The vertical chemical gradient PPFs were composed of a highly cross-linked base layer with gradually less cross-linked and more functional surface layers. The highly cross-linked base layer of the gradient structure effectively hindered restructuring at the surface of the film, resulting in a more stable surface composition and surface wettability than that of the more traditional non-gradient structure. In addition, the microfluidics prepared using a gradient structure showed more stable chip runtimes. The stability of the gradient plasma polymer films will allow for their implementation in microfluidics, as well as a diverse range of biomedical applications such as drug delivery and the generation of antibacterial coatings.