Nature as a Model: Lizard Airways Help JKU Researchers Create Air Filters

Researcher and JKU scientist Anna Stadler was inspired by studying lizards that can spend long periods under the sand without suffocating.

The sandfish lizard ‘swims’ through the desert sands. According to researchers in Linz, the lizard’s airways are aerodynamically filtered, keeping grains of sand from entering their airways which could cause them to otherwise suffocate. Researchers used 3D models to explain just how the animal filters the air to remove sand and subsequently applied for a patent modeled after the lizard’s particle-filtering respiratory system. The study and article have been published in the journal "Bioinspiration and Biomimetics".

Also known as the common skink (Scincus scincus), the sandfish lizard was used by healers in ancient times. Believed to have healing and aphrodisiacal properties, the sandfish lizard was killed, burnt, pulverized, and then sold at pharmacies. The ancient Egyptians embalmed the lizards to resemble their pharaohs and placed them into the pharaoh’s last resting place as a burial gift.

Spending most of their lives buried in the fine desert sand and able to grow up to 20 centimeters in length, the sandfish’s respiratory physiology allows it to breathe down to a depth of a half of a meter without getting sand into its lungs. A team led by Anna Stadler and Werner Baumgartner (Institute of Biomedical Mechatronics, JKU) has discovered that fine particles are aerodynamically filtered when they enter the nasal cavity.

Model from the 3D printer
The researchers created a 3D printed model of the sandfish’s respiratory tract and used the model to study airflow and observe what happens to inhaled sand. During an interview with APA, Anna Stadler explained, "At the beginning there is a round channel, followed by a chamber that is wide at the top and narrow at the bottom."  There, the larger cross-section causes a drop in pressure and slows the airflow down. The particles are forced to the wall, where they are trapped by mucus.

The depot is emptied by a kind of sneeze. The lizard inhales leisurely for an average of two seconds, but exhales very strongly in only 40 milliseconds.

The aerodynamic filter system works for a certain particle size up to a half of a millimeter in diameter. Computer simulations show, however, that the sandfish can also separate inhaled particles up to 70 micrometers in size.

Researchers at the University of Linz have applied for a patent for a "device for filtering particles" based on the sandfish lizard’s respiratory tracts. A "new filter system based on the lizard’s nasal cavity" would make it possible to filter out tiny particles, even those that are five micrometers in diameter. The device would contain a good self-cleaning mechanism by imitating the sandfish’s exhalation technique. Compared to other filter systems, it would make less noise and would not require sensitive membranes. [JKU/APA]