August 30, 2010
By Michael Salame, Mechanical Engineer
If you have taken science (or Latin) classes, you can probably infer the meaning of the terms hydrophobic and hydrophilic. Beads of water resting on a plant leaf, for example, exemplify the leaf’s hydrophobic surface - it resists the ingress of water. On the other hand, the makers of Bounty brand paper towels probably take great pride in their product’s hydrophilic quality, in that it will soak up almost anything.
These properties are also useful in the world of medical devices. When a product needs to allow air to flow through an opening but can’t let liquids such as blood or water in, putting in a single piece of hydrophobic membrane could solve the problem. It allows air to flow through but repels liquids.
Yet there are some liquids that even hydrophobic membranes have difficulty blocking, such as oils and soap. It all has to do with surface tension: the lower the surface tension of a liquid, the harder it is to repel. See this list of the surface tensions of common liquids (notice how high the surface tension of water is compared with other liquids – it’s a pretty easy liquid to repel!).
Fortunately, a recent technology has been developed to tackle this issue: oleophobic membranes. These oil phobic membranes can repel liquids of much lower surface tension than a regular hydrophobic membrane can. Medical membrane manufacturer Gore explains the background and science behind the oleophobic membrane in a recently published article.
If you’re developing a medical product, you might ask why you would want to use an oleophobic membrane, when the most common liquids a medical membrane sees are water and blood – which a hydrophobic membrane can easily handle. While that is certainly true, having an oleophobic membrane instead of a hydrophobic membrane could open up doors to new opportunities for your product.
For example, in wound care devices, where air circulation is needed to promote healing of the wound, a membrane is commonly used to allow airflow but block out any potential liquids that may come in contact with the device. With an oleophobic membrane, the user now would not have to worry about soap from their shower wetting out the membrane and ruining their device. This would not have been possible with a hydrophobic membrane. Talk about making a wound care product user-friendly!
In conclusion, hydrophobic membranes are pretty phenomenal pieces of technology that can be used as vents and filters to prevent liquid ingress but still allow airflow. Yet keep in mind that hydrophobic membranes do not work against all liquids; in such cases, an oleophobic membrane could be your solution.