Surface Treatments and Coatings for Microfluidic Channels

Why surface chemistry matters

As channels shrink, the ratio of surface area to volume becomes very large, so interactions at the walls strongly influence behaviour. Surface properties affect capillary filling, droplet formation, electro-osmotic flow, bubble retention, and the non-specific adsorption of proteins and cells.

Hydrophilic vs hydrophobic surfaces

• Hydrophilic (water-loving) walls help aqueous liquids wick in by capillary action — useful for pump-free filling in point-of-care devices.
• Hydrophobic (water-repelling) walls are needed to make stable water-in-oil droplets, and to create capillary stop-valves.

The right choice depends entirely on the application — and native materials are often not ideal as supplied, so the surface is modified.

Common treatments and coatings

• Oxygen-plasma treatment — makes surfaces (especially PDMS) temporarily hydrophilic; also used to activate surfaces for bonding.
• Chemical silanisation — grafts molecules onto glass or oxidised surfaces to make them durably hydrophobic or to add specific chemistry.
• Polymer / PEG coatings — reduce non-specific protein and cell adsorption (anti-fouling).
• Surfactants — added to fluids to modify interfacial tension, important in droplet work.

The challenge of stability

A recurring problem is that treatments do not last. Plasma-treated PDMS, for example, gradually recovers its hydrophobicity over hours to days as mobile polymer chains migrate to the surface. Durable performance often needs covalent coatings or a material chosen with the right native surface — a factor to weigh when moving from prototype to production.

Designing with surfaces in mind

Consider wettability alongside material and geometry from the start. The interplay of surface, material and process is part of design-for-manufacture; our team can advise when you upload a design.

Frequently asked questions