Amoeboid swimming in a channel.

Area of Science:

• Biophysics
• Microbial Locomotion
• Fluid Dynamics

Background:

• Microorganisms utilize flagellar, ciliary, or amoeboid motion for propulsion.
• Eukaryotic cells, including immune cells, are increasingly recognized for their ability to migrate without substrate adhesion.
• Amoeboid movement involves shape deformation for crawling or swimming.

Purpose of the Study:

• To analyze amoeboid swimming in confined fluids using a model of an inextensible membrane with active forces.
• To investigate how confinement affects the trajectory, nature (pusher/puller), and velocity scaling of amoeboid swimmers.
• To analyze the efficiency of amoeboid swimmers under varying confinement conditions.

Main Methods:

• Modeling a swimmer as an inextensible membrane with zero net force and torque.
• Simulating movement in a confined fluid channel.
• Analyzing the scaling of swimmer velocity (V) with force amplitude (A) and fluid viscosity (η).

Main Results:

• Swimmer trajectory depends on confinement, ranging from straight paths to wall-navigating behavior.
• The swimmer's nature (pusher vs. puller) is influenced by confinement, not an intrinsic property.
• Velocity scaling differs from flagellar swimmers: V∼A²/η² at low forces and becomes force-independent at high forces.

Conclusions:

• Confinement significantly alters amoeboid swimming dynamics and characteristics.
• The velocity scaling and nature of amoeboid swimmers are distinct from flagellar/ciliary swimmers.
• Efficiency analysis reveals confinement-dependent optima for one efficiency definition.