Stretching and heating cells with light—nonlinear photothermal cell rheology

Constantin Huster,Julian Thiele,Nicolas Hauck,Saeed Ahmed,Gheorghe Cojoc,Jochen Guck,Klaus Kroy,Devavrat Rekhade,Adina Hausch

doi:10.1088/1367-2630/aba14b

Abstract

Stretching and heating are everyday experiences for skin and tissue cells. They are also standard procedures to reduce the risk for injuries in physical exercise and to relieve muscle spasms in physiotherapy. Here, we ask which immediate and long-term mechanical effects of such treatments are quantitatively detectable on the level of individual living cells. Combining versatile optical stretcher techniques with a well-tested mathematical model for viscoelastic polymer networks, we investigate the thermomechanical properties of suspended cells with a photothermal rheometric protocol that can disentangle fast transient and slow ‘inelastic’ components in the nonlinear mechanical response. We find that a certain minimum strength and duration of combined stretching and heating is required to induce long-lived alterations of the mechanical state of the cells, which then respond qualitatively differently to mechanical tests than after weaker/shorter treatments or merely mechanical preconditioning alone. Our results suggest a viable protocol to search for intracellular biomolecular signatures of the mathematically detected dissimilar mechanical response modes.

Highlights

A common difficulty in medical diagnosis and therapy of intracellular malfunctions is that symptoms may manifest themselves on a much higher level of organization, such as organs or larger parts of the body
While the optical stretcher (OS) has been, in the past, used quite extensively to study more applied biological questions, and to lay the basis for potential future medical applications of cell mechanics, in this study we investigate the thermomechanical properties of suspended cells with a photothermal rheometric protocol that can disentangle fast transient and slow ‘inelastic’ components in the nonlinear mechanical response
We varied the laser wavelength and stretching power and compared the peak compliance defined as the ratio of strain at the end of the stretching phase and global geometrical factor (GGF) [34,35,36], which is a measure of stress which takes into account the several parameters characterizing the experimental conditions

Summary

Introduction

A common difficulty in medical diagnosis and therapy of intracellular malfunctions is that symptoms may manifest themselves on a much higher level of organization, such as organs or larger parts of the body. We propose that an important first step in this direction can be taken, by applying prototypical physiotherapeutic protocols to individual isolated cells and by quantitatively comparing and interpreting their effects onto the mechanical state of the cells. To this end, we employ two different optical stretcher (OS) setups that allow stretching forces with and without concomitant heating to be applied to a large number of identically prepared individual cells. We can explore experimental conditions that transcend the framework of (linear) thermorheology previously successfully applied in cell mechanics [7, 8]

Methods

Results

Conclusion