Preparation and Characterization of Cellulose Acetate Membrane for Monolithic Osmotic Tablet

Cellulose acetate (CA) is one of the most popular membrane materials for osmotic pump coat. The influences of nature and amount of plasticizers on properties of CA membrane including drug release profiles, thermal properties, microporosity and mechanical properties have been studied. It has been found that hydrophilic plasticizer poly(ethylene glycol) (PEG) increases drug release of monolithic osmotic tablet system, whereas hydrophobic plasticizer triacetin decreases drug release of the system. All dry CA membranes showed a dense morphology. Originally PEG plasticized CA membrane developed wholly porous structure after 24 hrs leaching. In contrast, originally triacetin plasticized CA membrane retained dense structure, though only it showed porosity on the surface. The glass transition temperature (T_g) and melting point (T_m) of unplasticized CA were found to be at 189.6 and 213.0°C , respectively. At low plasticizer level of 0 to 5 (w/w CA) %, it was found that both ultimate tensile strength (σ_u) and elastic modulus (E) of dry CA membrane increased as the plasticizer level increased, and that no significant difference resulted from plasticizer nature. At high plasticizer level of 5 to 40 (w/w CA)%, however, it was observed that both σ_u and E of dry CA membrane decreased as plasticizer level increased and that those of triacetin plasticized were higher than those of PEG plasticized at the same plasticizer level. Also, it has been observed that both σ_u and E of CA membrane reduced significantly after 24 hrs contacting with water. Osmotic tablet shell such as CA membrane could be considered as a small container with thin walled cylinder sustaining inner hydrostatic pressure. It has been estimated that the inner pressure of the monolithic osmotic tablet system could sustain was in range of 0.123∼2.81 MPa (1.25∼28.6 atm) in our monolithic osmotic delivery system.