Computer simulations of the mechanical response of brushes on the surface of cancerous epithelial cells.

A Gama Goicochea,S J Alas Guardado

doi:10.1038/srep13218

A Gama Goicochea, S J Alas Guardado

Open Access

https://doi.org/10.1038/srep13218

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Journal: Scientific Reports	Publication Date: Aug 28, 2015
Citations: 12	License type: CC BY 4.0

Affiliation: Autonomous University of San Luis Potosí

Abstract

We report a model for atomic force microscopy by means of computer simulations of molecular brushes on surfaces of biological interest such as normal and cancerous cervical epithelial cells. Our model predicts that the force needed to produce a given indentation on brushes that can move on the surface of the cell (called “liquid” brushes) is the same as that required for brushes whose ends are fixed on the cell’s surface (called “solid” brushes), as long as the tip of the microscope covers the entire area of the brush. Additionally, we find that cancerous cells are softer than normal ones, in agreement with various experiments. Moreover, soft brushes are found to display larger resistance to compression than stiff ones. This phenomenon is the consequence of the larger equilibrium length of the soft brushes and the cooperative association of solvent molecules trapped within the brushes, which leads to an increase in the osmotic pressure. Our results show that a careful characterization of the brushes on epithelial cells is indispensable when determining the mechanical response of cancerous cells.

Highlights

Of the brush layer is accounted for separately from that of the cell’s surface
To represent normal and cancerous cell surfaces, we used a soft model that allows for the deformation of the surfaces upon compression, while the brushes were modeled as chains of uniform length, as well as non—uniform length, motivated by the experiments of Iyer and collaborators[17]
The simulation model used, known as dissipative particle dynamics (DPD)[23,24], is a coarse—grained method that involves the grouping of several microscopic units into beads, which interact with each other according to simple rules

Summary

Results and Discussion

The surfaces of cancerous epithelial cells are known to be different from the surfaces of normal cells[29]. Both types of soft brushes on cancerous cells (liquid and solid) exert a larger force on the AFM probe to be deformed the same distance h/rc than their stiff brush counterparts. The motion of the chains that make up the so called liquid brushes on the surface of the cell can be considerable, as Fig. 3 shows, where the meandering of a given brush “molecule” on the surface of the cell is followed Such motion does not change the force profile with respect to the case when the brush molecules are fixed on the surface of the cell (solid brush) because the tip of the AFM covers the entire brush regardless of the type (liquid or solid), and the number of chains per unit area is the same for both types of brushes[34]. This argument can be clearly seen from an analysis of the Alexander—de Gennes scaling law for the osmotic pressure, from which the force acting on the brush can be derived[35]: Fsoft (h) F stiff (h)

Lsoft Lstiff exp

Methods

Additional Information