We put filters in our coffeemakers in order to allow the small water molecules flow through while holding back the gritty grounds we don’t want to drink in our morning cup of java. But in a new study, published in Science, researchers turned the purpose of a filter upside down. They created a membrane that allows larger objects to pass through but holds back smaller particles. For example, the filter can hold back gases but allow solids to flow through.
The researchers got their inspiration from nature. Membranes that allow large particles to pass through while retaining small ones must possess the ability to “self-heal,” similar to liquids. Plunge a stick into a puddle of water and the water will automatically close as soon as you remove the stick—the hole in the water does not remain. The new membrane retains objects based on their speed, not size. Bigger objects move slower, so they readily go through, and then the filter self-heals and retains smaller, faster objects.
The researchers envision many applications for their new filter, such as an invisible barrier to contaminants in surgical procedures. It could keep bacteria and dust particles out of an open surgical site while allowing instruments to go through, as well as allowing surgeons to pull tissue back out. The filter could also act as a barrier to insects and pollens or to trap odors in a waterless toilet. —J.B.