The objective of this study was to investigate the impact of polymer type on polymeric microparticle blends designed for controlled drug delivery. Microparticle blends containing a single drug (propranolol HCl [Pro] or carbamazepine [CBZ]) and blends with drugs of differing solubilities (Pro and CBZ) were prepared using the solvent evaporation method. The first emulsion and second oil phase were prepared by the water-in-oil-in-water and oil-in-water methods. The three different first emulsions were a solution of ethyl cellulose (EC), poly(lactic-co-glycolic acid) (PLGA) and poly(ε-caprolactone) (PCL) in dichloromethane (7.5% w/v). The three different second oil phases were 7.5% w/v solution of EC, PLGA and PCL in dichloromethane. The first Pro emulsion (water-in-oil) and second Pro emulsion (water-in-oil) were dispersed in an external aqueous phase (for the same drug), while the first Pro emulsion (water-in-oil) and second CBZ oil phase (for different drugs) were dispersed in an external aqueous phase, with a dispersion time interval (DTI) of 0 and 60 min for the same and different drugs. The morphology of the microparticle blends was characterized by SEM. The mean particle size was measured with a particle size analyzer. The encapsulation efficiency and in vitro drug release in phosphate buffer (pH 7.4) were also investigated. Microparticle blends containing a single drug exhibited slower release rates of Pro compared to conventional microparticles and microparticle blends (DTI of 0 min). Conversely, blends with different solubilities showed similar release rates for both Pro and CBZ (DTI of 60 min). In vitro drug release studies after 28 days showed that the Pro release from EC microparticle blends with DTI 60 min (61%) was slower than from EC microparticle blends with DTI 0 min (83%); the Pro release from PCL microparticle blends with DTI 60 min (48%) was slower than from PCL microparticle blends with DTI 0 min (75%); and the Pro release from PLGA microparticle blends with DTI 60 min (74%) was slower than from PLGA microparticle blends with DTI 0 min (88%). The size of the microparticle blend prepared as a water-in-oil-in-water (Pro) and oil-in-water (CBZ) system with DTI of 60 min and stirring time 4 h was larger than those prepared with a DTI of 0 min. In vitro drug release studies from EC microparticle blends after 28 days revealed that the CBZ release (69%) was faster than Pro release (53.5%). Drug release from PLGA microparticle blends after 28 days revealed that the CBZ release (92.5%) was faster than Pro release (81%). Drug release from PCL microparticle blends after 28 days revealed that the CBZ release (60%) was faster than Pro release (33%). This observation may be attributed to interactions between the secondary emulsion or oil phase and the solidified microparticles from the primary emulsion, wherein the secondary emulsion or oil phase blocked and coated pores on the surface of the solidified microparticles. In conclusion, polymer type significantly influences the drug release profile from microparticle blends prepared by the solvent evaporation method.
