ENHANCED ERYTHROCYTE SUSPENSION LAYER STABILITY ACHIEVED BY SURFACE TENSION LOWERING ADDITIVES

ABSTRACT

An electrostatic repulsion - van der Waals attraction mechanism was used to explain the stability of erythrocyte suspensions layered on a D₂O cushion. By lowering the surface tension of D₂O to values around 65 ergs/cm² by admixture of varying concentrations of dimethyl sulfoxide (DMSO), the van der Waals attraction between cells was reduced to zero. The zeta potentials, as measured by microelectrophoresis, were reduced also by DMSO but at a slower rate than for the surface tensions as shown by total interaction energy calculations. In the presence of low van der Waals attraction and at large negative surface potentials, high cell concentrations were supported on a D₂O cushion without the suspension layer becoming unstable. Reduction in the electrostatic repulsion while maintaining low van der Waals attraction significantly reduced the suspension layer stability. Clearly defined secondary minima varying in depths from 3.9kT to 7.8BkT at separation distances varying from 55Å to 65Å were obtained from the energy curves for the cells in the absence of OMSO. Addition of OMSO of varying concentrations decreased the secondary minima to very low values or zero at DMSO concentrations between 11% and 14% (v/v). It was concluded that maximum stability of erythrocyte suspension layers could be attained in the absence of cross-linking ions, at high zeta potentials and low van der Waals attraction, and that the technique of the determination of the maximum stability with respect to droplet sedimentation could serve as another alternative method for the study of surface tensions of biological particles. The surface tension values obtained via the droplet sedimentation technique were confirmed independently by means of freezing front exclusion. The values obtained by the two methods agree well confirming the feasibility of using the droplet sedimentation method.