The dielectric study of insulin-loaded reverse hexagonal (HII) liquid crystals

Abstract

The dielectric behavior of the insulin-loaded H_II mesophase (containing GMO–TAG–water–glycerol–insulin) was studied using two empty reference systems (GMO–TAG–water and GMO–TAG–water–glycerol) at a frequency range of 10⁻²–10⁶ Hz, and a temperature range of 290–333 K. Three clearly defined relaxation processes were observed and assigned to the reorientation of GMO polar heads, the tangential movement of counterions at the interface, and the movements of TAGs through the lipid tail. Upon addition of glycerol, a heterogeneous inner structure was formed within the H_II cylinders: the water–glycerol core surrounded by a water rigid layer. Upon heating, two critical points were detected referring to the dehydration of the GMO heads (at 304 K, similar to the water-filled H_II system) and to energetic modifications (at 316 K), resulting in breaking of the water layer allowing on-demand controlled release. Insulin incorporation combined the features of both reference H_II systems. Yet, unlike the empty H_II systems, insulin perturbed the GMO–water interface while decreasing the movement of the GMO headgroup, and reducing T₀ (296 K). No interactions were formed between the dipole of each counterion at the interface region and the matrix (the GMO), fitting the Debye process. Dynamic behavior was observed, pointing to mobility between the hexagonal rods themselves, enabling controlled release from the H_II carrier.