Plant cell adhesion to polymer surfaces as predicted by a thermodynamic model and modified by electrostatic interaction

Abstract

A thermodynamic model of particle adhesion from a suspension onto a surface considers the roles of the solid surface tension (γ sv), the liquid surface tension (γ lv) and the cellular surface tension (γ cv). The model was used to describe the initial phases of adhesion of cultured plant cells of Catharanthus roseus maintained in suspending-liquids of various surface tension to the polymer substrates fluorinated ethylene propylene (γ sv=16.4 mJ m −2), polystyrene (γ sv=25.6 mJ m −2), polyethylene terephthalate (γ sv=47.0 mJ m −2) and sulphonated polystyrene (γ sv=66.6 mJ m −2). The extent of adhesion decreased as a function of increasing γ sv when γ lv>γ cv; however, adhesion increased with increasing γ sv when γ lv<γ cv. In essence, adhesion is more extensive to hydrophobic surfaces (i.e. polymers with a low surface tension) than to hydrophilic surfaces when the surface tension of the cells is less than the surface tension of the suspending-medium. These results are consistent with theoretical predictions. The cellular surface tension was determined, by contact angle measurements and adhesion experiments, to have a value of approximately 53 (±3) mJ m −2 and was modulated as determined by sedimentation volume analysis during the growth cycle of the plant cells. An electrostatic repulsion-van der Waals attraction mechanism explains the initial adhesion of suspension cultured plant cells to polymers immersed in liquids of various surface tension and ionic strength. The surface tension of distilled water was lowered from 72.5 to 44.5 mJ m −2 by addition of 1-propanol; at some γ lvintermediate between these two values this is expected to reduce the van der Waals attraction between cells to zero. Adhesion to surfaces was reduced in the presence of low van der Waals attraction and relatively high negative cell surface potentials. The negative cell surface potential was reduced and neutralized by addition of plurivalent cations. The influence of suspending-liquid ionic strength in solutions of NACl, CaCl 2 and AlCl 3 was examined. The electrophoretic mobilities of the cells, as determined by microelectrophoresis, were reduced by increased ionic strength of the suspending-liquid, and the electrophoretic mobility was reduced increasingly as a function of increasing cation plurivalence. Increased cellular adhesion was recorded in response to decreased electrophoretic mobility induced by increased ionic strength. Adhesion was most extensive when the cells were bathed in a solution of 0.1 M AlCl 3; adhesion decreased with further increases in ionic strength until the negative cell surface potential was neutralized and charge reversal occurred. Suspending-liquids of up to 1.0 M CaCl 2 also resulted in increased cellular adhesion to all surfaces but charge reversal was not observed. These results conform to predictions of the DLVO theory. Adhesion in all test solutions demonstrated the paramount influential role of γ sv, γ lv, and γ cv in controlling the initial phases of the plant cell adhesion process in accordance with thermodynamic model predictions; electrostatic repulsive interactions serve to modify the extent of plant cell adhesion to the surfaces. The process of plant cell adhesion is controlled by the interaction between interfacial tensions and electrostatic phenomena in the system.