![]() ![]() To do so, two distinct strategies are adopted. In Section 8.3 we show that the same propulsion principle can be applied to achieve movement in non-Newtonian media. The microrobots consist of a rigid helical micro-structure that is rotated in the fluid by a torque applied by an external magnetic field. Microrobots moving in Newtonian fluids similar to bacterial flagella are considered in Section 8.3. ![]() In Section 8.2, the mechanism of propulsion based on cilia is further described, along with the development of a soft microrobot that swims in a Newtonian fluid by a mechanism inspired by ciliary propulsion found in unicellular protozoa – microorganisms called ciliates. The eukaryotic flagellum, a flexible appendage whose beat in solution generates a traveling-wave-like non-reciprocal motion ■Ĭilia, short appendages that beat in an asymmetric and self-coordinated fashion. The bacterial flagellum, a rotating helical propeller, whose chiral shape leads to symmetry-breaking and non-reciprocity ■ The main strategies adopted by microorganisms and cells to swim in such conditions rely on three different kinds of propellers and appendages: ■ In other words, small scale organisms and devices must perform complex non-reciprocal motions to effectively swim in Newtonian fluids. This means that reciprocal motions, such as the opening and closing of a single-hinge mechanism, lead to no net displacement, no matter how fast or slow the different phases are (which is known as the scallop theorem ). At such a small scale, the characteristic Reynolds number Re, which represents the ratio between inertial and viscous forces, is lower than unity, thus inertia is negligible and time-reversibility applies (low- Re regime). Newtonian fluids as simple as water already present their own considerable challenges for micro-scale swimmers. ![]()
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