Fig. 11.

The electrostatic restoring force mechanism which acts on fibrils to maintain the lattice organization. The mechanism is illustrated for the case where all fibrils in the lattice are held fixed in their lattice positions and a single fibril is displaced relative to its lattice position. (a) Shows a set of fibrils in a regular lattice arrangement with their associated GAG chains and a distribution of mobile ions. In this situation, which corresponds to normal physiological conditions, the osmotic pressure is essentially uniform. (b) Depicts the osmotic pressure in each subcell around the undisturbed fibril. The osmotic pressure in each subcell exerts a force on the fibril but because the osmotic pressure is uniform, all six forces balance and the net force is zero, as indicated by the red dot. (c) Shows a fibril displaced from its lattice position. The GAG chains attached to the fibril move with the fibril and the GAG fixed charge density and mobile ion concentration increase in advance of the fibril displacement and reduce behind it. (d) Indicates the resulting osmotic pressure in each of the subcells, which is higher where GAG fixed charge density has increased and lower where it has reduced. The forces exerted by each of the subcells now has changed magnitude with the result that a net force acts on the fibril with a direction oriented towards the original lattice position. This restoring force is shown as a red arrow. Figure and caption reproduced from Cheng and Pinsky (2013) with permission of the copyright holder.