Euler buckling in red blood cells: An optically driven biological micromotor

TL;DR

This study explores how red blood cells behave under optical trapping, revealing buckling and rotation phenomena driven by laser intensity, and models these effects to understand their physical mechanisms.

Contribution

The paper introduces a model based on buckling instabilities to explain RBC folding and rotation in optical traps, supported by experimental validation.

Findings

RBCs fold into rod-like shapes in optical traps.

Rotation occurs when circular polarization is used.

Critical laser intensity causes large shape fluctuations.

Abstract

We investigate the physics of an optically-driven micromotor of biological origin. A single, live red blood cell, when placed in an optical trap folds into a rod-like shape. If the trapping laser beam is circularly polarized, the folded RBC rotates. A model based on the concept of buckling instabilities captures the folding phenomenon; the rotation of the cell is simply understood using the Poincar\`e sphere. Our model predicts that (i) at a critical intensity of the trapping beam the RBC shape undergoes large fluctuations and (ii) the torque is proportional to the intensity of the laser beam. These predictions have been tested experimentally. We suggest a possible mechanism for emergence of birefringent properties in the RBC in the folded state.