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

Mechanical response of a surface of increasing hardness covered with a nonuniform polymer brush: a numerical simulation model

The compression force with indentation on a polymer brush with chains of unequal lengths is predicted with numerical simulations, as a function of increasing hardness of the grafting surface, finding that properties of the brush are distinguished from those of the surface and that its hardness propagates through the brush.

The contributions to the force on a deformable surface covered with polymer brushes can be accounted for separately.

Measuring the Elastic Properties of Living Cells

Cell's elasticity is an integrative parameter summarizing the biophysical outcome of many known and unknown cellular processes. This includes intracellular signaling, cytoskeletal activity, changes of cell volume and morphology, and many others. Not only intracellular processes defines a cell's elasticity but also environmental factors like their biochemical and biophysical surrounding. Therefore, cell mechanics represents a comprehensive variable of life. A cell in its standard conditions shows variabilities of biochemical and biophysical processes resulting in a certain range of cell's elasticity. Changes of the standard conditions, endogenously or exogenously induced, are frequently paralleled by changes of cell elasticity. Therefore cell elasticity could serve as parameter to characterize different states of a cell. Atomic force microscopy (AFM) combines high spatial resolution with very high force sensitivity and allows investigating mechanical properties of living cells under physiological conditions. However, elastic moduli reported in the literature showed a large variability, sometimes by an order of magnitude (or even more) for the same cell type assessed in different labs. Clearly, a prerequisite for the use of cell elasticity to describe the actual cell status is a standardized procedure that allows obtaining comparable values of a cell independent from the instrument, from the lab and operator. Biologically derived variations of elasticity could not be reduced due to the nature of living cells but technically and methodologically derived variations could be minimized by a standardized procedure.This chapter provides a Standardized Nanomechanical AFM Procedure (SNAP) that reduces strongly the variability of results obtained on soft samples and living cells by a reliable method to calibrate AFM cantilevers.

Fractal properties of biophysical models of pericellular brushes can be used to differentiate between cancerous and normal cervical epithelial cells

Fractal behavior is found on the topographies of pericellular brushes on the surfaces of model healthy and cancerous cells, using dissipative particle dynamics models and simulations. The influence of brush composition, chain stiffness and solvent quality on the fractal dimension is studied in detail. Since fractal dimension alone cannot guarantee that the brushes possess fractal properties, their lacunarity was obtained also, which is a measure of the space filling capability of fractal objects. Soft polydisperse brushes are found to have larger fractal dimension than soft monodisperse ones, under poor solvent conditions, in agreement with recent experiments on dried cancerous and healthy human cervical epithelial cells. Additionally, we find that image resolution is critical for the accurate assessment of differences between images from different cells. The images of the brushes on healthy model cells are found to be more textured than those of brushes on model cancerous cells, as indicated by the larger lacunarity of the former. These findings are helpful to distinguish monofractal behavior from multifractality, which has been found to be useful to discriminate between immortal, cancerous and normal cells in recent experiments.

Mesoscopic Modeling of the Encapsulation of Capsaicin by Lecithin/Chitosan Liposomal Nanoparticles

The transport of hydrophobic drugs in the human body exhibits complications due to the low solubility of these compounds. With the purpose of enhancing the bioavailability and biodistribution of such drugs, recent studies have reported the use of amphiphilic molecules, such as phospholipids, for the synthesis of nanoparticles or nanocapsules. Given that phospholipids can self-assemble in liposomes or micellar structures, they are ideal candidates to function as vehicles of hydrophobic molecules. In this work, we report mesoscopic simulations of nanoliposomes, constituted by lecithin and coated with a shell of chitosan. The stability of such structures and the efficiency of the encapsulation of capsaicin, as well as the internal and superficial distribution of capsaicin and chitosan inside the nanoliposome, were analyzed. The characterization of the system was carried out through density maps and the potentials of mean force for the lecithin-capsaicin, lecithin-chitosan, and capsaicin-chitosan interactions. The results of these simulations show that chitosan is deposited on the surface of the nanoliposome, as has been reported in some experimental works. It was also observed that a nanoliposome of approximately 18 nm in diameter is stable during the simulation. The deposition behavior was found to be influenced by a pattern of N-acetylation of chitosan.