DLS Microrheology

Material behavior can tell us a lot about how it functions, but to quantitatively characterize material behavior is still a challenge. Rheology is the study of how fluids flow and is often the most common way to understand the physical behavior of a material. Current rheology techniques are great for understanding bulk material behavior but are unable to derive smaller length-scale physics. Even particle-based rheology methods are often invasive or limited in their frequency range of measurement. In the field of cellular biophysics, in particular, it is important to use a technique that can capture the material behavior within a composite material of cells and extracellular matrix. One facet of my work is to development new characterization techniques for precious biological samples to better understand the nuanced physics within. One important contribution I have made thus far is dynamic light scattering microrheology (DLSµR). This method characterizes the mechanical properties of biological materials, both with and without living cells, is noninvasive for time-lapse measurements, and requires only small volumes (~12μL) of sample.

Articles

PC Cai, BA Krajina, MJ Kratochvil, L Zou, A Zhu, EB Burgener, PL Bollyky, CE Milla, MJ Webber, AJ Spakowitz, SC Heilshorn. “Dynamic light scattering microrheology for soft and living materials.” Soft Matter.

We present a method for using dynamic light scattering in the single-scattering limit to measure the viscoelastic moduli of soft materials. This microrheology technique only requires a small sample volume of 12 μL to measure up to six decades in time of rheological behavior. We demonstrate the use of dynamic light scattering microrheology (DLSμR) on a variety of soft materials, including dilute polymer solutions, covalently-crosslinked polymer gels, and active, biological fluids. In this work, we detail the procedure for applying the technique to new materials and discuss the critical considerations for implementing the technique, including a custom analysis script for analyzing data output. We focus on the advantages of applying DLSμR to biologically relevant materials: breast cancer cells encapsulated in a collagen gel and cystic fibrosis sputum. DLSμR is an easy, efficient, and economical rheological technique that can guide the design of new polymeric materials and facilitate the understanding of the underlying physics governing behavior of naturally derived materials.

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