Temperature-Sensitive Permeation of Methimazole through Cyano-biphenyl Liquid Crystals Embedded in Cellulose Nitrate Membranes

Abstract

ABSTRACT In this study, the application of thermotropic liquid crystals (TLCs) embedded in cellulose nitrate membranes as binary thermosensitive drug barriers in response to temperature changes is described. Liquid crystals are physically observed to flow like liquids, but they have some properties of crystalline solids. Two kinds of low-molecular nematic liquid crystals, n-pentyl-cyanobiphenyl (K15) and n-heptyl-cyanobiphenyl (K21), with nematic to isotropic phase-transition temperatures (T n-i) of 36.3°C and 43.3°C, respectively, were chosen to modulate drug release. Triple-layer membranes (TLMs), composed of K15 and K21 as TLCs sandwiched between two layers of cellulose-nitrate (CN) films, were prepared. No TLC leakage was observed through this hydrophilic membrane. TLMs successfully acted as rate-controlling systems, which may also be regarded as time-controlling systems. The transport of methimazole as a low-molecular-weight drug model through the membranes was examined. It was found that changing the environmental temperature below and above the T n-i of TLCs could modulate methimazole permeation through these composite membranes. These experiments were also repeated with thermal cycling between 30°C and 46°C. The permeation profiles were reversible and followed zero-order kinetics.