Control of the surface properties of micro-fluidic devices for external power-free biochip application

Abstract

Micro-fluidic or nano-fluidic devices have been received a great attraction in chemical and biological applications. Due to the increase of the surface/volume ratio, control of the surface properties of these devices is highly important. Polymer-based materials have been newly developed in micro-fluidic or nano-fluidic devices due to the great needs of easy processing, cost-effectiveness and clarity for the material. However, it is still challenging to control of the surface properties of these devices on demand. Most of the current materials in use for micro-fluidic devices are relatively hydrophobic; therefore, they usually need an extra assistance to transport aqueous samples within the microfluidic chip, such as micro-pump or any relevant mechanical or electrical apparatus. This makes the micro-fluidic device bulky and difficult to be portable. Polyelectrolyte multilayer (PEM) films assembled by layer-by-layer are very practical coatings to modify surfaces of various substrates. Layer-byLayer deposition (LbL) is a versatile technique whereby ultrathin films are assembled from the repetitive, sequential adsorption of oppositely charged polyelectrolytes from dilute aqueous solution. Moreover, the functional groups which remained reactive after the film deposition allow further chemical reactions such as polymer micro-contact printing, selective photo-crosslinking and controlled nanoparticle synthesis. In this paper, we utilized this method to modify the surface of the micro-channel of the device in order to control cellular interactions inside of the channel. We have been studied cellular interactions on various polyelectrolyte multilayer films on open surfaces. Multilayer films comprised of weak polyelectrolytes exhibit different surface properties as they were assembled at different pH conditions. Therefore, the wettability of the PEM-coated surface also can be tuned by changing the assembly condition. We applied various PEM films on the channel surface of microfluidic device and tested the wetting property and capillary force build-up in the micro-channel. Considering biological applications, weak polyelectrolytes including biocompatible polymer such as poly(hyaluronic acid) (HA) were investigated for this purpose. And the preliminary results were obtained in the study of surface-cell interaction using these coatings.