Characterization and in vitro Permeation Study of Poly(ϵ‐caprolactone) Nanocapsules Containing Hinokitiol

Abstract

Nanocapsules containing hinokitiol (HKL) were prepared by an emulsion‐diffusion method. Poly(ϵ‐caprolactone) (PCL), synthesized according to a ring‐ opening method, was used as a wall material, and HKL dissolved in octylsalicylate (OS), was used as a core material. Under a microscope, submicron‐sized microcapsules were observed. The apparent shape was either spherical or amorphous. According to the image analyzer analysis, the size ranges from tenths of a nanometer to one micron, and more than 50% in number were less than 300 nm. In a calorimetric study, HKL exhibited an endothermic peak around 52°C, but no peak for the melting of HKL was observed when it was encapsulated in microcapsules. This suggests HKL remained dissolved in the nanocapsule cores but did not exist as a solid crystalline. In an in vitro permeation study, the flux of HKL encapsulated in the nanocapsules was somewhat higher than that of HKL dissolved in either propylene glycol or ethanol. This is probably because that PCL is hydrophobic, so the nanocapsules would readily interact with skin lipid.