Effect of liposomes on suspension stability.

The effect of positively charged liposomes on the stability of negatively charged indomethacin particle suspensions was investigated by adsorption, microelectrophoresis, sedimentation volume, and redispersibility. It was found that flocculation occurred in the neighborhood of the zero point of charge of the liposome:indomethacin suspensions. This resulted from the operation of van der Waals attraction under the condition of nil electrostatic repulsion. Correlation among the results of adsorption, microelectrophoresis, sedimentation volume, and redispersibility was good. The mixing effect of the suspension was examined by microelectrophoresis and confirmed by sedimentation volume and redispersibility. Results indicate that there was no difference between the method of dilution of the liposome:indomethacin concentrated suspension after mixing and the method of dilution of liposomes prior to mixing with the indomethacin suspension. This was due to interaction depending on the charge density of the particles.