From Cellulose\nSolutions to Aerogels and Xerogels:\nControlling Properties for Drug Delivery

A cheap and easy-to-recycle\nsolvent, namely, aqueous\nNaOH with\nno additives, was used to dissolve cellulose and make cross-linker-free\nmaterials with varying porosity, testing them as drug delivery devices.\nCellulose solutions were gelled, coagulated in a nonsolvent (water,\nethanol), and dried either using supercritical CO<sub>2</sub> (aerogels)\nor low-vacuum evaporation (named “xerogels”). Aerogels\nhad densities of around 0.1 g/cm<sup>3</sup> and specific surface\nareas (SSAs) of 200–400 m<sup>2</sup>/g. A significant influence\nof the first nonsolvent and drying mode on material properties was\nrecorded: when the first nonsolvent was ethanol and low-vacuum drying\nwas performed from ethanol, aerogel-like xerogels were obtained with\ndensities of around 0.2 g/cm<sup>3</sup> and SSAs of 200–260\nm<sup>2</sup>/g. Other conditions (under evaporative drying) resulted\nin cellulose with much lower porosity and SSA. All materials were\nevaluated as drug delivery devices in simulated gastrointestinal fluids;\ntheophylline was used as a model drug. Materials of high porosity\nexhibited shrinking and rapid drug release, whereas denser materials\nswelled and showed slower release. Two release mechanisms were suggested:\ndiffusion through aqueous media in pores and diffusion through swollen\npore walls. The results demonstrate a large spectrum of options for\ntuning the properties of porous cellulose materials for drug release\napplications.