Оbstructed osmosis

Osmosis is a fundamental physical process, which plays a major role in various biological processes, such as the fluid exchange in animal cells and the water transport in plants. This process has found clinical application in the drug delivery systems1. Osmotic pressure of the (blood) plasma is one of the essential characteristics of the blood.

New theoretical and simulation models, applicable under different conditions, have been developed during the recent years for the study of the osmotic phenomena.

In the present paper, we consider the obstructed osmosis. In more general terms we speak of obstructed diffusion of fluids through a membrane. This is diffusion of the solvent through a semi-permeable membrane, at which the natural volume expansion of the solution is blocked by means of external mechanical action, which leads to an increased pressure in the confined volume. It explains the well-known natural phenomenon, where the skin of some fruits and vegetables, like grapes, cherries, tomatoes and others, starts to rip open after several rainy days. The phenomenon results from the so-called endosmosis, at which the water enters the cells and when the internal pressure exceeds certain critical value, the skins-barriers of the fruits burst.

In mechanics there are two types of motion (of the mechanical system), imposed onto the system: in the absence and in the presence of mechanical bonds2. In the case of obstructed osmosis there is a mechanical bond imposed on the solution, which obstructs the free rise in its level. Thus, under the same other conditions, pressure upon the membrane would be different at obstructed and unobstructed osmosis, which is of significance in the investigation of its permeability and strength.

Obstructed osmosis occurs in every normal living cell: whether vegetal or animal one. The cell wall acts as a barrier and of a semipermeable membrane. The pressure exerted in the osmotic process on the wall of a plant cell or bacterial cell by the water entering the cell is called turgor pressure or turgidity. It is in fact a partial case of the treated in the present paper obstructed osmotic pressure. When a cell reaches maximal turgor, its wall may burst and the so-called plasmoptysis occurs. 3, 4



  1. Verma, R. K., Arora, S., Garg, S. Osmotic pumps in drug delivery. Crit. ReV. Ther. Drug. 21, 2004, p. 477-520.
  2. Meller K. Theory of Relativity. Moscow, Atomizdat, 1975.
  3. Salisbury, F. B. and C. W. Ross. Plant physiology. 4th ed. Belmont, California, Wadsworth publishing, 1992.
  4. 4. Tachev, A. S. Physiology of human and animals. Smoljan, Ed. PPI, 1995.