Colloidal stability and in vitro permeation study of poly(ɛ-caprolactone) nanocapsules containing hinokitiol

Nanocapsules containing hinokitiol (HKL) were prepared by an emulsion-diffusion method. Poly(ɛ-caprolactone) (PCL), synthesized according to a ring opening method, was used as a wall material, and HKL dissolved in octyl salicylate (OS) was use as a core material. In an emulsification step in preparing nanocapsules, three kinds of emulsifiers were employed, namely cetyltrimethylammonium chloride (CTAC), sodium lauryl sulfate (SLS), gelatin. On a transmission electron microscope, the size was hundreds of nanometers. According to the results of pH-dependent microelectrophoresis, the absolute value of the surface potential of the nanocapsules prepared using either CTAC or SLS was greater than 20 mV. In case the nanocapsules were prepared using the mixture of CTAC and gelatin, the value was between 0 mV and 20 mV. The nanocapsules prepared by using either CTAC or SLS were stable in terms of size over the pH range of 3–11. However, the nanocapsules prepared using the mixture of CTAC and gelatin was not stable in size over the same pH range. Following the results of in vitro permeation experiment, the nanocapsules enhanced the permeation of HKL. Especially, the nanocapsules prepared using SLS was prominent in promoting the permeation. This is probably because that SLS act as a permeation enhancer. However, the nanocapsules themselves hardly penetrated into hairless mouse skin, which was observed on a confocal laser scanning microscope.