Abstract
One of the major hurdles in the development of biocompatible/biodegradable EWOD (Electrowetting-on-dielectric) devices is the biocompatibility of the dielectric and hydrophobic layers. In this study, we address this problem by using reactive ion etching (RIE) to prepare a super-hydrophobic film combining fluorinated cellulose triacetate (CTA) and poly (lactic-co-glycolic acid) (PLGA). The contact angle (CA) of water droplets on the proposed material is about 160°. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) characterizations indicate that a slight increase in the surface roughness and the formation of CFx (C-F or CF2) bonds are responsible for the super-hydrophobic nature of the film. Alternating Current (AC) static electrowetting and droplet transportation experiments evidence that contact angle hysteresis and contact line pinning are greatly reduced by impregnating the CTA/PLGA film with silicon oil. Therefore, this improved film could provide a biocompatible alternative to the typical Teflon® or Cytop® films as a dielectric and hydrophobic layer.
Highlights
In recent years, microfluidics has found numerous applications in the biomedical and environmental monitoring fields, for instance, in ecotoxicology [1,2], cell analysis [3,4,5,6], fertilization in vitro (IVF), cell culture [7,8], food detection [9] and soil analysis [10,11]
A typical EWOD device consists of a substrate layer, a driving electrodes layer (ITO, Al, Cu, etc.), a dielectric layer (Su-8, SiO2 etc.) and a hydrophobic/super-hydrophobic layer (e.g., Teflon® or Cytop® ) on top of it
When the voltage difference V is applied between a droplet and the electrode, the droplet surface becomes charged and is pulled towards the electrode, reducing the contact angle (CA) of the droplet
Summary
Microfluidics has found numerous applications in the biomedical and environmental monitoring fields, for instance, in ecotoxicology [1,2], cell analysis [3,4,5,6], fertilization in vitro (IVF), cell culture [7,8], food detection [9] and soil analysis [10,11]. It shows great potential to become one of the key components in future biological systems for sustainable development, such as real time analysis of water and soil quality [17,18], continuous monitoring for agricultural production [19,20,21] and point-of-care medical applications [22,23,24]. For a droplet of non-conducting liquid at mechanical equilibrium and at moderate electric voltage, this phenomenon can be described by the Lippmann-Young (L-Y)
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