Multiscale treatment of theoretical mechanisms for the protection of hydrogel surfaces from adhesive forces

Abstract

One role of a lubricant is to prevent wear of two surfaces in contact, which is likely to be the result of adhesive forces that cause a pair of asperities belonging to two surfaces in contact to stick together. Such adhesive sticking of asperities can occur both for sliding surfaces and for surfaces which are pressed together and then pulled apart. The latter situation, for example, is important for contact lenses, as prevention of sticking reduces possible damage to the cornea as the lenses are inserted and removed from the eye. Contact lenses are made from both neutral and polyelectrolyte hydrogels. It is demonstrated here that sticking of neutral hydrogels can be prevented by repulsive forces between asperities in contact, resulting from polymers attached to the gel surface but not linked with each other. For polyelectrolyte hydrogels, it is shown that osmotic pressure due to counterions, held at the interface between asperities in contact by the electrostatic attraction between the ions and the fixed charges in the gel, can provide a sufficiently strong repulsive force to prevent adhesive sticking of small-length-scale asperities.

Spatially dependent diffusion coefficient as a model for pH sensitive microgel particles in microchannels

“…The MG have found use in medical applications as potential cartilage replacement 18 and as friction and antiwear modifiers. 19,20 Dispersions of MG exhibit the characteristics of colloids in general, such as an increase of viscosity with volume fraction, progressing eventually at sufficiently high densities to a jammed or glassy nonequilibrium state with non-zero shear modulus and a yield stress required to initiate flow. 21,22 Biomolecular systems in solution have been modelled numerous times using the computer simulation technique of Brownian Dynamics (BD), which is based on the Langevin formulation of Brownian motion.…”

Contact mechanics for poroelastic, fluid-filled media, with application to cartilage

“…In particular the tribology of soft matter, such as rubbers or gels, has drawn increasing attention, but is a very complex topic. [5][6][7][8][9][10][11][12][13] One important class of soft tribology problems refers to the tribology of biological matter (i.e., material of living bodies). Thus, human body possesses exquisite systems of lubrication that can withstand thousands of work cycles per day without fatigue.…”