Purpose: The double emulsion (w/o/w or o/w/o) solvent evaporation method has been widely used for the fabrication of polymeric drug particles. In the w/o/w emulsion, the encapsulation of hydrophilic drugs is challenging due the rapid partitioning of the hydrophilic drug from the inner aqueous phase to the outer one causing poor encapsulation efficiency. Several studies were performed to mitigate the low encapsulation efficiency of hydrophilic drugs by varying different process and/or formulation variables in the w/o/w systems. The evaluation of influence of each of these process and formulation variables and their interactions allows for the engineering of polymeric drug particles with higher encapsulation efficiency and of the desired physical properties. While some variables, such as polymer to drug ratio, have been extensively studied, other basic process and formulation variables were overlooked. The aim of this study was to investigate the influence of the three variables of 1) primary emulsion dispersion method (sonication versus vortexing 2) surfactant (PVA) concentration in inner water phase as well as 3) drug: polymer ratio in a w/o/w emulsion on the fabricated polymeric particles encapsulating metformin hydrochloride, a model hydrophilic drug. A 23 full factorial design was employed to evaluate the influence of such variables on the yield %, encapsulation efficiency and loading % and the physicochemical properties of the fabricated polymeric particles.
Methods: The w/o/w double emulsion was prepared as following: the inner aqueous solution of metformin HCl was emulsified into the middle organic phase of dichloromethane containing poly (lactic-co-glycolic acid) (PLGA 50:50) to form primary emulsion. Prior studies were performed to optimize the concentration of PLGA in the organic phase. The primary emulsion was then emulsified into outer water phase with 1% PVA. The w/o/w was stirred for 2 h to allow for organic solvent evaporation and the PLGA particles were collected by filtration then lyophilized for 24 h for further characterization. The 23 full-factorial design (table 1) was performed using the Stat-Ease Design-Expert software. The factors studied were: (1) dispersion method of the primary emulsion (sonication for 30 seconds versus vortexing for 150 seconds), (2) PVA concentration in inner aqueous phase (0 and 1 % w/v) and (3) drug: polymer ratio (1:4, 1:10) in which the amount of polymer was kept constant. The selected responses were: yield%, encapsulation efficiency, loading % and particle size. The loading and encapsulation efficiency of the particles were determined by dissolving 10 mg of particles in DCM water (5:2) mixture followed by HPLC analysis of metformin concentration in the water phase. The morphology and the size of the particles were determined using scanning electron microscopy (SEM) (Fig.1). Thermal analysis of the particles was done using DSC. Finally, the release profile of the particles was determined by adding 10 mg particles in 1 ml phosphate buffer solution (pH=6.80±0.05) at 37°c with continuous stirring at 200 rpm for 7 days.
Results: Higher concentration of PLGA in the organic phase showed significant increase in both loading and encapsulation efficiency of metformin hydrochloride in PLGA particles. The PLGA concentration of 400 mg/ml was set as the optimum polymer concentration to be used in the DoE study. No significant difference was observed between the yields obtained from the 8 DoE runs. In contrast, there were noticeable differences between the encapsulation efficiency and loading % between the different DoE runs depending on the dispersion method of the primary emulsion and the drug: polymer ratios. Sonication of the primary emulsion resulted in encapsulation efficiency of 27.7 (9.47) compared to 5.9 (2.34) after vortexing. Similarly, the lower drug: polymer ratio (1:10) increased the encapsulation efficiency to 20.5 (16.54) compared to 13.1 (10.05) for the 1:4 drug to polymer ratios. The addition of 1% PVA to the inner water phase didn’t have a significant impact on any of the studied responses. The 8 DoE runs resulted in spherical particles with average size of 335 µm and varying degrees of surface smoothness and porosity. The DSC analysis of the metformin loaded PLGA particles revealed an endothermic peak corresponding to the melting of crystalline metformin solely in the thermograms of the runs with higher loading. Lastly, the release profile of the metformin PLGA particles of runs 2, 6, 7 and 8 was slower than the profiles of the rest of the runs owing to their higher metformin loading %.
Conclusion: In this work, PLGA particles of the hydrophilic drug of Metformin HCl were fabricated using double emulsion solvent evaporation technique. The design of experiment study revealed the significant influence of the primary emulsion dispersion method and the drug to polymer ratio on the encapsulation efficiency and the loading percentage of metformin which consequently affected their release profile. Thus, process as well as formulation variables in w/o/w double emulsion solvent evaporation method should be carefully selected to fabricate hydrophilic drug loaded polymeric particles with high drug loading % and the desired physicochemical properties.
Mariam Ibrahim– Postdoctoral Fellow, Virginia Commonwealth University, Richmond, Virginia
Abu Badruddoza– Research Assistant Professor, Virginia Commonwealth University
James Ferri– Professor, Virginia Commonwealth University
Thomas Roper– Professor, Virginia Commonwealth University