Micro-scallop that swims in biological media
Building and operating microdevices that can navigate in biomedical fluids and tissue is one of the ultimate goals of microrobotics. Realising artificial microswimmers is, however, extremely challenging, as this is the realm of low Reynolds number hydrodynamics where the laws of physics are reciprocal, and a symmetric swimmer, such as a scallop that only opens and closes its shells, cannot propel. This is known as the Purcell’s scallop theorem, but it only applies to Newtonian fluids such as pure water. In biological (non-Newtonian) fluids the scallop theorem no longer holds, and this has allowed us to build the first microswimmer, a microscallop, that can move wirelessly with symmetric body shape changes. The significance is that this opens new possibilities in designing biomedical micro-devices, as most actuators give rise to reciprocal shape changes. [Nature Communications 5, 5119, (2014)].