Enhancing Microfluidic Device Performance with COC Hydrophilic Coatings

Cyclic Olefin Copolymer (COC) is a popular material in the development of microfluidic devices due to its transparency, biocompatibility, and resistance to a variety of chemicals. However, COC is inherently hydrophobic, which means it repels water. This characteristic can be problematic in microfluidics, where control over fluid flow is crucial. To enhance COC's suitability for microfluidic applications, a hydrophilic (water-attracting) coating is often applied. This coating improves the flow properties of fluids within the microchannels by reducing surface tension, thus facilitating faster and more reliable fluid movement. Without such a coating, fluid flow might be too slow or even stall. A cutting-edge method for applying this hydrophilic coating involves plasma-enhanced chemical vapor deposition (PECVD). This technique allows for the precise application of a PEG-like (polyethylene glycol-like) coating on both polymer and glass surfaces used in microfluidic chips, such as COC, polystyrene, polycarbonate, and PMMA.

Improved Surface Coating with Plasma-Enhanced Vapor Deposition (PECVD)

Recently, a new type of hydrophilic coating has been developed. In this process, the surface is modified using a PEG-like coating. Both exposed glass and polymer surfaces (COC, polystyrene, polycarbonate, PMMA) can be coated with this substance. The coating is applied using the plasma-enhanced chemical vapor deposition (PECVD) technique. In this method, the surface is covered with a very thin film that transforms from a gas state (vapor) to a solid state. 

The effectiveness of this coating is measurable through the "contact angle" of a water droplet on the surface. A lower contact angle indicates a more hydrophilic surface; typically, the treated surfaces achieve contact angles between 50° to 55°, significantly lower than those of uncoated, hydrophobic surfaces.

Advancements in Anti-Fouling Technology for Polymer Consumables

Additionally, this hydrophilic coating offers anti-fouling properties. Polymers in their original (uncoated, hydrophobic) state, are subject to a lot of fouling of biological material. For glass materials, fouling through electrostatic interactions is a concern. Fouling could interfere with the function of the device, which in turn might affect test results. Coating decreases the unwanted adsorption of biological material, but can’t completely prevent it. The anti-fouling capabilities of the modification have been tested using BSA (Bovine Serum Albumin) as the fouling agent. Adsorption of BSA was reduced to around 20% when compared to its adsorption on the original polymer surface. This is critical in preventing contamination and ensuring the accuracy of experiments.

Optimizing COC Device Assembly with PECVD Coatings

However, there are some limitations to vapor deposition method. The vapor deposition method with which the coating is applied can only be used on the outside of a structure and not in an enclosed microfluidic system. This means the surface modification has to be performed before the bonding of the device. The coating is compatible with the thermal bonding process that is generally used for COC devices. In tests performed thus far, the hydrophilic and anti-fouling properties of the coating weren’t affected by the bonding procedure. This technique is still being tested and tuned, and in doing so we hope to find out more, for example, if this process can also be applied to other polymer materials.