Abstract

RHEOLOGICAL CHARACTERISTICS OF HINOKITIOLCONTAINING GELS

Rina Suzuki, Mizuki Tsuri, Yutaka Inoue*, Toru Tanaka, Isamu Murata, Ikuo Kanamoto

Abstract

In the present study, gels were formulated to contain a complex of hinokitiol (HT) and γ- cyclodextrin (γ-CD) and their physicochemical properties were explored. HT/γCD complexation was carried out using a co-grinding method. Xanthan gum (Xan) and κ, λ, ι-carrageenan (κ, λ, ι-Car) were used as thickeners at varying concentrations: HT/γCDXan1.5%, HT/γCD-κ-Car1.0%, HT/γCD-λ-Car1.75% and HT/γCD-ι- Car1.0%. The formation of clear gels with a good dispersion of HT was observed visually and under a fluorescence microscope. Viscosity measurements of HT/γ-CD-Xan and HT/γ-CD-ι-Car confirmed that the flexibility of the formulations was good. Furthermore, the disruption to their structures was less over the narrow stress flow curve area. The pH of HT/γCD-Xan1.5% and HT/γCD-ι-Car1.0% were weakly acidic: 5.18 and 5.78, respectively. This is thought to result in less skin irritation. The yield values serve as indicators of hardness and were 16.4 (HT/γCD-Xan1.5%), 35.1 (HT/γCD-κ- Car1.0%), 215.5 (HT/γCD-λ-Car1.75%) and 24.4 dyne/cm2 (HT/γCD-ι-Car1.0%). HT/γCDXan1.5% and HT/γCD-ι-Car1.0% spread more readily than the other formulations. The drug release tests demonstrated faster release after 5 minutes from HT/γCD-κ-Car1.0% and HT/γCD-ι-Car1.0%, whereas HT/γCD-Xan1.5% and HT/γCD-λ-Car1.75% displayed slower release rates. In the stability test (temperature 4°C, relative humidity 33%), there was at least 90% of HT present in HT/γCD-Xan1.5% for 14 days. Overall, the results of this study suggest that HT/γCD-Xan1.5% has potential as a novel gelling formulation.

Keywords: hinokitiol, gel, xanthan, xanthan, viscosity.