Development and optimization of solid lipid nanoparticles coated with chitosan and poly(2-ethyl-2-oxazoline) for ocular drug delivery of ciprofloxacin

Many formulation strategies have been employed to improve ocular bioavailability of topical eye drops. The aim of this study was to develop and evaluate a series of solid lipid nanoparticles coated with poly(2-ethyl-2-oxazoline) and chitosan for ocular delivery of ciprofloxacin. Ciprofloxacin-loaded poly(2-ethyl-2-oxazoline) (PSLN) formulation was prepared by a combination of melt-emulsion sonication and low-temperature solidification methods. A Box-Behnken design, was employed to statistically optimize the effects of the amount of drug (X1), lipid:polymer ratio (X2) and surfactant concentration (X3) on particle size (Y1) and entrapment efficiency (Y2). Analysis of variance was used to validate the optimization design; and regression equations and response surface plots were generated. The optimized formulation was selected through numerical point prediction approach. These nanoparticles were characterized using dynamic light scattering, transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and powder X-ray diffractometry (PXRD). In vitro drug release and corneal permeation studies were carried out, while the mucoadhesive properties were evaluated ex vivo using porcine corneal tissue. The particle size and zeta potential of the optimized formulations ranged from 141 to 213 nm and +24.6 to −35.6 mV, respectively. PSLN possessed higher encapsulation efficiency than chitosan-coated solid lipid nanoparticles (CSLN). The in vitro drug release from all the formulations showed an initial burst release followed by prolonged release over 24 h. The release mechanism followed Korsemeyer-Peppas model and Fickian diffusion (n < 0.5). DSC revealed lower enthalpy and crystallinity of the formulations as also detected by PXRD, while TEM showed spherical particles in the lower nanometer range with a layer of polymer coating. The results of this study demonstrated that CSLN exhibited higher mucoadhesion and retention on corneal tissues compared with PSLN and also showed higher flux and apparent permeability, but with lower entrapment efficiency.