Abstract
A rotatable central composite design (RCCD) was applied to optimize the preparation of cyclosporine-loaded poly D,L (lactide-glycolide) (PLAGA) nanoparticles (NP) and microspheres (MS) by solvent displacement and solvent evaporation techniques, respectively. The joint influence of needle gauge, polymer amount and the injection rates on the mean particle size, relative standard deviation (RSD), yield and drug encapsulation percentage in NP were evaluated. With regards to MS, the polymer amount and the stirring rate were evaluated. Scan electron microscopy of MS and NP showed spherical particles with a dense polymeric network in the first case. From the statistical analysis of data polynomial equations were generated. The mean particle size ranged from 50 to 150 nm for NP and from 1.5 to 30/pm for MS. Smallest nanoparticles (46 nm) were obtained by using the lowest polymer amounts, the highest injection rates and the lowest needle gauges ( r 2 = 0.9443). Under these conditions the drug entrapment percentage was maximum (85.2%), suggesting the drug might be entrapped and adsorbed on the nanoparticle surface. The relative standard deviation was only affected by the polymer amount ( r 2 = 0.8034) and the yield rose with the amount of PLAGA ( r 2= 0.9016). A very important increase in particle size ( r 2 = 0.9855), relative standard deviation ( r 2 = 0.9353) and encapsulation percentage ( r 2 = 0.9669 ) were observed for MS by decreasing emulsification stirring rates and increasing polymer amounts, the stirring rate being the most significant independent variable ( α < 0.0001) in all cases. The highest experimental encapsulation value (97.69 ± 0.78%) correspond to samples prepared from 150 mg of polymer and a global stirring rate of 2000 rpm. By using response surface diagrams and the mathematical models proposed, it is possible to easily deduce experimental conditions to prepare NP and MS with the desired properties.
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