Hydrostatic and osmotic pressure gradients facilitate filtration across a semipermeable membrane. Cell membranes are essentially lipid bilayers which form a semipermeable membrane. Note that a semipermeable membrane is not the same as a selectively permeable membrane. Another example of a semipermeable membrane is dialysis tubing. The fiber wall acts as the semipermeable membrane. Diffusion of solvents, such as water, through a semipermeable membrane is classified as osmosis. This solution is separated from pure solvent by a semipermeable membrane. Chemiosmosis is the movement of ions across a semipermeable membrane, down their electrochemical gradient. Commercial applications for ionomers include golf ball covers, semipermeable membranes, sealing tape and thermoplastic elastomers. Osmosis is a vital process in biological systems, as biological membranes are semipermeable. These are semipermeable membranes manufactured principally for use in water purification or desalination systems. Part of the capillary in each vessel is replaced by a semipermeable membrane. The semipermeable membrane is pertinent to cellular communication. Particle unharness would then occur upon fusion of the MVB with the semipermeable membrane. A process of osmosis through semipermeable membranes was first observed in 1748 by Jean-Antoine Nollet.