Microrheology of Complex Fluids and Soft Materials

Microrheology probes the mechanical behaviour of complex fluids, colloidal suspensions, polymer networks and biological soft materials by tracking the motion of embedded micro- or nano-scale probes. In contrast to classical bulk rheology, microrheological techniques access local viscoelastic properties over wide frequency ranges and at length scales comparable to microstructural heterogeneities. Passive methods exploit thermal fluctuations of tracer particles to extract frequency-dependent storage and loss moduli, while active approaches apply controlled optical, magnetic or acoustic forces to quantify non-equilibrium responses. These measurements reveal fundamental insights into the dynamics of polymer entanglements, gelation and glass transitions in synthetic materials, as well as the mechanical microenvironment within living cells, tissues and biomolecular condensates. Advances in optical tweezer designs, magnetic twisting cytometry and light-scattering methods have extended the accessible window from milli- to megahertz, enabling studies of rapid structural reorganisations and age-dependent changes in viscoelasticity. Beyond fundamental science, microrheology informs the design of drug-delivery vehicles, wound-healing hydrogels, organ-on-chip platforms and diagnostic tools that exploit mechanical biomarkers of disease.

Research from Nature Portfolio

Rotational magnetic spectroscopy has been used to interrogate the local shear viscosity and elasticity of living cell cytoplasm. Superparamagnetic micro-wires embedded within fibroblasts and cancer cells reveal a transition between synchronous and asynchronous rotation regimes, affirming that the cytosol behaves as a viscoelastic liquid rather than a solid gel. Universal glass-forming behaviour in both reconstituted cytoplasm and living cells has been demonstrated through particle-tracking experiments, showing that metabolic activity converts a fragile colloidal glass into a strong, Arrhenius-like glass former, thus maintaining fluidity under crowded conditions. A straightforward optical-tweezer-based method for measuring relative viscosity employs autocorrelation of tracer-bead position, providing rapid viscosity estimates for scarce or precious samples and validating results against bulk rheometry across synthetic polymer and biomedical fluids.

Microrheology of Complex Fluids and Soft Materials publication trend

The graph below shows the total number of articles in microrheology of complex fluids and soft materials across all publications each year (not limited to Nature Index journals).

Technical terms

Viscoelasticity: Combined viscous flow and elastic deformation exhibited by materials under applied stress.

Microrheology: Techniques that measure local mechanical properties of fluids and soft materials at micron or submicron scales using probe particles.

Optical tweezers: Highly focused laser beams that trap and manipulate micron-sized particles to apply forces and measure displacements.

Diffusing-wave spectroscopy: A light-scattering method analysing temporal fluctuations of multiply scattered light to infer microstructural dynamics.

Mean-squared displacement: Statistical measure of the average squared distance travelled by tracer particles, used to characterise diffusive or subdiffusive behaviour.

References

1. Measuring age-dependent viscoelasticity of organelles, cells and organisms with time-shared optical tweezer microrheology. Nature Nanotechnology (2025).
2. Coherent light scattering from cellular dynamics in living tissues. Reports on Progress in Physics (2024).
3. Simultaneous Nanorheometry and Nanothermometry Using Intracellular Diamond Quantum Sensors. ACS Nano (2023).
4. Local viscoelasticity of living cells measured by rotational magnetic spectroscopy. Nature Communications (2016).
5. Universal glass-forming behavior of in vitro and living cytoplasm. Scientific Reports (2017).
6. Evaluating the Viscoelastic Properties of Tissue from Laser Speckle Fluctuations. Scientific Reports (2012).
7. Microrheology with Optical Tweezers: Measuring the relative viscosity of solutions ‘at a glance’. Scientific Reports (2015).