Viscoelasticidade de células em substratos macios

Abstract

The study of cells on soft substrates is relevant because they mimic the natural conditions of \textit{in vivo} cells, allowing analyzes in cells with full control of their environment. It is already known that cells react to the stiffness of their underlying substrate, but there is no consensus on the functioning of their internal mechanisms. The objective of this work is to analyze how fibroblasts (lineage L929) have their biomechanics altered according to the stiffness of the substrate they are in, in order to understand how the stiffness of the substrate affects internal mechanisms of viscoelastic relaxation and its morphology, with the measurement of its viscoelastic parameters by Atomic Force Microscopy, and by the quantified determination of their morphology by Confocal Fluorescence Microscopy. The mechanical properties of individual cells are obtained in the time and frequency domains (between 1 Hz to 1 kHz), and the morphological properties are obtained by calculating the fractal dimension of the filamentous actin network present in the cell skeleton. Soft substrates are polyacrylamide hydrogels whose stiffness can be controlled according to the concentration of the crosslinking agent used in their fabrication (0.01%, 0.1%, and 1+%). Atomic force microscopy results show an increase in cellular stiffness correlated with a decrease in substrate stiffness, and the viscoelastic parameters reveal that the cellular relaxation follows a double power law model, in which a regime of rapid viscoelastic relaxation is observed in very short times (below tens of milliseconds), and a slow relaxation regime in long observation times (hundreds of milliseconds to tens of seconds). Confocal microscopy data revealed an increase in the fractal dimension of the cytoskeleton images with increasing substrate stiffness, which could be visually correlated with the growth of long actin fibers through the cell body.