Sustained Release from Lipid-Core Nanocapsules by Varying the Core Viscosity and the Particle Surface Area

Based on the structure of polymeric nanocapsules containing a lipid-dispersed core composed of caprylic/capric trygliceride (CCT) and sorbitan monostearate (SM), we hypothesized that varying the core component concentrations the drug release kinetic could be modulated. Our objective was also to determine the parameters which were responsible for controlling the drug release kinetics. The nanocapsules were prepared by interfacial deposition of poly(epsilon-caprolactone). Interfacial hydrolysis of indomethacin ester (IndOEt) was used to simulate a sink condition of release. Mathematical modeling showed that the IndOEt half-lives increased (198 to 378 and 263 to 508 min) with the increase in the core lipid concentrations, and that the release mechanism was the anomalous transport. By increasing the SM concentration, the diameters were constant (around 250 nm) and the surface areas increased (from 1.06 × 10⁴ to 1.51 × 10⁴ cm² ⋅ ml^–1), while by increasing the CCT concentration, the diameters increased (215 to 391 nm) and the surface areas reduced (1.46 × 10⁴ to 1.06 × 10⁴ cm² ⋅ ml^–1). The presence of SM increased the viscosity of CCT and the IndOEt apparent permeability decreased from 4.26 × 10^–7 to 2.54 × 10^–7 cm ⋅ s^–1, while for CCT series, the apparent permeability was constant around 3.0 × 10^–7 cm ⋅ s^–1. A mathematical correlation was established and the IndOEt apparent permeability can be estimated by the SM concentration. In conclusion, varying the CCT and SM concentrations the IndOEt release was controlled by the nanocapsule surface area and by the viscosity of the core, respectively.