Optical Vortex Tracking Microrheology: A Novel Technique for Evaluating Viscoelastic Properties of Soft Materials

In this paper, we present a novel technique called optical vortex tracking microrheology (OVTM) that allows us to assess the viscoelastic properties of soft scattering materials. We achieve this by tracking the movement of optical vortices in random speckles generated by the media. By analyzing the trajectories of these vortices, we are able to calculate the mean square displacement (MSD) of the vortices.

We observe that the MSD of the vortices varies significantly depending on whether the viscoelastic sample behaves more like a liquid or a solid. Furthermore, we establish an inverse linear relationship between the MSD of the vortices and the viscoelastic modulus of the scattering material. This relationship holds over a wide range of frequencies and moduli.

By analyzing the diffusive exponent of the optical vortices, we are also able to extract the phase angle of the material. This enables us to measure both the elastic modulus and the viscous modulus of the media.

Additionally, we demonstrate that our technique can distinguish between homogeneous and inhomogeneous materials. Homogeneous materials exhibit a relatively uniform diffusive pattern of the optical vortex, while inhomogeneous materials display a more erratic diffusive behavior.

The optical vortex tracking microrheology technique offers several advantages. It provides sensitive and non-destructive evaluation of the mechanical properties of scattering soft materials without the need for exogenous tracers or large sample volumes. This makes it highly suitable for investigating the physical characteristics of viscoelastic materials such as tissues, gels, and polymers. Furthermore, it has potential applications in scientific and clinical settings, such as material fabrication, pathological tissue identification, and blood coagulation monitoring.