Formulation Effects on the Thermomechanical Properties and Permeability of Free Films and Coating Films: Characterization of Cellulose Acetate Films

The authors investigate the effects of a polyethylene glycol plasticizer and water on cellulose acetate film properties.
Mar 02, 2009

Cellulose acetate (CA) is a polymeric excipient widely used in pharmaceutical dosage forms for controlled release (1–5) and taste masking (6–8). CA also is one of the most suitable materials to serve as a semipermeable membrane for osmotic drug delivery systems (9–10).

Although osmotic drug delivery systems have many designs and configurations, they generally consist of a tablet core surrounded by a semipermeable membrane (11). When designing an osmotic drug delivery system, many factors could affect the release rate of an active needed to be delivered. Selection and design of the semipermeable membrane remain one of great challenges for formulation scientists.

Knowing the relationship between a formulation and its film properties is crucial for designing a membrane to control release rate. Yuan et al. have investigated the effects of solvent systems (acetone and acetone/water), polyethylene glycol (PEG) molecular weight and level on the properties of CA-free films (12). In that study, water as a cosolvent in the formulation definitely affected morphology, and ultimately, the properties of the films. The films prepared from acetone were transparent, flexible, stronger, but less permeable to water vapor compared with those films containing water as a cosolvent. Meier et al. published similar results when they studied the influence of the plasticizer content and film preparation procedure on the morphology, thermal, and mechanical properties of CA films plasticized with poly(caprolactone triol) (PCL-T) (13). They demonstrated that the addition of water, a nonsolvent, during the membrane-casting process was a simple and effective way to change membrane porosity and consequently the drug-permeation profile. When small quantities of nonsolvent were used to obtain low-porosity membranes, the presence of a plasticizer agent could be used to better modulate drug permeation (14).

In general, as the acetyl content in CA increases, the CA film permeability decreases, solvent resistance increases, and the glass transition temperature increases (15). However, for the small variation within the specification of CA-398-10NF-EP, no study has been found to address the effect of the acetyl content on CA film properties. Although free film properties would provide insights for predicting permeability of the films, applying CA polymer onto a substrate is a final step to ensure the release profile as designed. The objectives of this study were to investigate the acetyl content in CA polymer on the film properties, particularly the permeability of free films and coating films, and to study the effects of plasticizer level (polyethylene glycol 3350) and water level on the properties of free films and coating films.