Use of 2-hydroxypropyl-β-cyclodextrin as adjuvant for enhancing encapsulation and release characteristics of asiaticoside within and from cellulose acetate films

The inclusion complex between asiaticoside (AC), an active substance from the medicinal plant Centella asiatica L., and 2-hydroxypropyl-β-cyclodextrin (HPβCD) was investigated. The phase solubility profiles of AC in distilled water and 90:10 (v/v) mixture of 80 vol.% acetic acid and N,N-dimethylacetamide (DMAc) both in the absence and the presence of HPβCD were classified as AL-type and indicated a 1:1 molar ratio of the AC/HPβCD complex. The 1:1 stoichiometric molar ratio of the complex was confirmed by both the 1D and the 2D 1H-nuclear magnetic resonance spectrometry. Unlike the highly crystalline nature of the native AC, the stoichiometric AC/HPβCD complex powder was amorphous in nature. The average diameters of the self-assembling aggregates of the AC/HPβCD complex, a priori prepared at various HPβCD to AC molar ratios of 0.5, 1, and 2, in the solution state, were about 2.4, 3.3, and 3.8 μm, respectively. The solvent-cast CA films containing these complexes showed strong evidence of the aggregates on their surfaces. The maximal cumulative released amounts of AC, a sparingly water-soluble substance, from the CA films containing a mixture of AC/HPβCD of varying molar ratios (i.e., 1:0.5, 1:1, and 1:2) in the phosphate buffer saline solution (PBS) containing 10% (v/v) methanol (i.e., P/B/M medium) were 2.2, 3.9, and 5.8% (based on the actual weights of the film specimens), respectively, which were clearly an increasing function of the HPβCD content in the films.