Study of viscoelasticity and adhesion of human alveolar epithelial cells by atomic force microscopy. The importance of probe geometry

Abstract

[eng] During the last century, cellular biology has been mostly assessed from the biochemical point of view: studying how biochemical stimuli modify the biochemical composition of living cells. However, most of the cells that form our body constantly exert or are subjected to mechanical forces. Muscle cells exert forces during contraction, vascular endothelial cells are subjected to shear forces due to blood stream, and pulmonary cells resist cyclic deformations due to spontaneous breathing. Therefore, it appears reasonable that mechanical forces play an important role in determining cell structure, composition, and function. The continuous increase in works relating mechanical properties of cells with cellular function has shown that mechanics are as important as biochemistry at the cellular level. Even the high development of nanotechnology, techniques such as atomic force microscopy (AFM) still present important limitations when applied to biological systems. The general aim of this thesis was to improve and apply AFM methods to the measurement of mechanical properties of living cells, laying especial emphasis on the probe geometry. The studies presented in this thesis are part of the work I carried out during the last four years in the Biophysics and Bioengineering Unit at the University of Barcelona School of Medicine. The thesis can be divided into four main sections: Introduction, Aims, Experimental studies, and Conclusions. The introduction (Chapter 1) attempts to make a brief review of cellular mechanics. The specific aims are presented in Chapter 2. The first work (Chapter 3) describes the design and set-up of an AFM based system to measure the mechanical properties (viscoelasticity and adhesion) of living cells under physiological conditions. The second work (Chapter 4) describes the development and validation of a blunted pyramidal elastic model used to determine the viscoelastic properties of soft gels and living cells. The third study (Chapter 5) validates the use of FIB modified flat-ended cylindrical tips to study the mechanical properties of biopolymer gels and living cells. The last work (Chapter 6) applies the modified cylindrical cantilevers and the developed AFM system to measure elastic and adhesive properties of living cells under inflammatory conditions.