Efficiency of sildenafil encapsulation in poloxamer micelles

The purpose of this study is to prepare and investigate the physicochemical and thermodynamic evidence of sildenafil (SIL) encapsulated poloxamer 188 (P188) micelles. The micelles were prepared by the thin-film hydration technique and investigated by pendant drop tensiometry and dynamic light scattering techniques. The closed association model was used to determine the micelle-monomer equilibrium parameters. The standard Gibbs free energy of the micelle formation was calculated from the partition coefficient. The change in the pattern of the surface tension, particle count rate, and particle size of the SIL encapsulated P188 micelles was observed. The corresponding critical micelle concentration (CMC) was approximately 0.04 mM. The hydrodynamic Z-average size of the micelles ranged from 6 to 9 d. nm. The encapsulation efficiency (EE) of SIL in the micelles was up to 54.3 +/- 0.2%. The obtained equilibrium constant was 0.67. The standard Gibbs free energy of the formation of SIL encapsulated micelles at 25 degrees C was -32.9 kJ/mol. The formation of SIL encapsulated P188 micelles was confirmed by the change in the pattern of the surface tension, particle count rate and size of the micellar solution. The standard Gibbs free energy of the formation indicated the spontaneous partition process in the micellar systems.