Viscoelastic Parameterization of Human Skin Cells to Characterize Material Behavior at Multiple Timescales

Abstract

Countless biophysical studies have sought distinct markers in the cellular mechanical response that could be linked to morphogenesis, homeostasis, and disease. Here, a novel iterative-fitting methodology is used to investigate the viscoelastic behavior at multiple relaxation times of human skin cells under physiologically relevant conditions. Past investigations often involved parameterizing linear elastic relationships and assuming purely Hertzian contact mechanics. However, linear elastic treatment fails to capture and properly account for the rich temporal information available in datasets. We demonstrate the performance superiority of the proposed iterative viscoelastic characterization method over standard open-search approaches. Our viscoelastic measurements revealed that 2D adherent metastatic melanoma cells exhibit reduced elasticity compared to normal counterparts—melanocytes and fibroblasts, whereas are significantly less viscous than only fibroblasts over timescales spanning three orders of magnitude. Interestingly, melanocytes are stiffer than melanoma cells, while being the less viscous cells measured. The measured loss angle indicates clear differential viscoelastic responses across multiple timescales between the measured cells. We propose the use of viscoelastic properties at multiple timescales as a mechanical biomarker of diseases. Altogether, this method provides new insight into the complex viscoelastic behavior of metastatic melanoma cells relevant to better understanding cancer metastasis aggression.

Power Laws Describe Bacterial Viscoelasticity

“…Additionally, at these low frequencies, the frequency dependent behavior of storage and loss modulus is similar to what one would expect from both a maxwell element, a standard linear solid as well as a generalized maxwell model, as published in an investigation of the dynamic mechanical behavior of bacterial surfaces and for measurements of eukaryotic cells. 21,44 Stress Relaxation Can Be Described by Power Laws at Different Loads. In a next step, we performed nanomechanical stress relaxation measurements on the bacteria by keeping a constant deformation at 1, 2, 4, and 8 nN for 2 s making use of the AFM feedback mechanisms.…”