Starch Alcogels, Aerogels, and Aerogel-like Xerogels: Adsorption and Release of Theophylline

Abstract

Starch is one of the most abundant and biodegradable natural polysaccharides; it has been widely used in pharmaceutics in tablets, as a disintegrant, or as a porous carrier. In this work, starches in different forms─alcogels, aerogels, and low-vacuum-dried materials (named xerogels)─were designed and tested as carriers of theophylline. The influence of the starch amylose/amylopectin ratio, concentration in solution, retrogradation time, and drying method (supercritical CO2 drying for aerogels, low-vacuum drying for xerogels) on materials’ density, specific surface area, and morphology was investigated. The precursors before drying were starch alcogels made by water-to-ethanol exchange in retrograded hydrogels. Starch alcogels were loaded with theophylline via impregnation. Loading capacities and efficiencies of alcogels, aerogels, and xerogels were determined, and release of the drug from xerogels and aerogels was evaluated. Two remarkable phenomena were obtained: (1) The low-vacuum drying method resulted in starch aerogel-like materials; i.e., xerogels with low densities and specific surface areas above 100 m2/g. (2) Starch alcogels adsorbed theophylline from ethanol resulting in loading efficiency as high as 250%. The results obtained show a new pathway in making aerogel-like polysaccharide materials without drying in supercritical conditions for potential use as drug carriers.