D. POPESCU*,**, C. N. ZAHARIA***, S. ION**, MARIA-LUISA FLONTA*

*Department of Neurobiology and Biophysics, Faculty of Biology, University of Bucharest, Spl. Independenţei nr. 91–95, Bucharest, Romania
**Institute of Statistical Mathematics and Applied Mathematics, Calea 13 Septembrie, nr. 13, Bucharest, Romania
***”Ștefan S. Nicolau” Institute of Virology, Șos. Mihai Bravu, nr. 285, Bucharest, Romania

Abstract. The increase of pressure inside a cell determines the stretch of its membrane. In such conditions either the cellular membrane may be ruptured and the cell dyes, or one pore may appear through its lipid matrix and the membrane becomes unstretched. It was found that only one pore can appear in a lipid vesicle at one time, but a succession of pores can form in the same vesicle. The membrane recovery happens only if a part of the intracellular material comes out of the cell through these transmembrane pores. In this paper we have analyzed the pore formation in a streatched vesicle after application of an osmotic stress. If we see the successive pores appearance as a periodic process, then the time interval between the appearance of two successive pores is a characteristic of the cyclic process, and, as usually, is named period. In the case analyzed here it is the sum of the swelling time of the vesicle and the life time of the pore formed on the vesicle. If the solvent (as water) has a low viscosity, the pore life is very short, the period is equal to swelling time. The swelling time between any two successive pores in a vesicle was calculated. At the beginning of the process the swelling time decreases with the cycle’s rank, but later it reaches a constant value. For this reason the liposome may be regarded as a time controller of drug administration at the ill place were the liposomes had been placed.
Key words: Stretched vesicle, pores, swelling time, time biocontroller, drug release.

Corresponding author’s e-mail: popescu@bio.bio.unibuc.ro

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