S. Narisawa et al., POROSITY-CONTROLLED ETHYLCELLULOSE FILM COATING .4. EVALUATION OF MECHANICAL STRENGTH OF POROUS ETHYLCELLULOSE FILM, Chemical and Pharmaceutical Bulletin, 42(7), 1994, pp. 1491-1495
The mechanical characteristics of porous ethylcellulose (EC) film as a
barrier in a controlled release dosage form were investigated. Spraye
d EC films with various porosities were prepared by changing the ethan
olic concentrations in the EC spraying solution, and their film porosi
ties (epsilon) and tensile strength (T-s) were measured. It was found
that the T-s of EC films decreased with an increase in epsilon, and th
at the quantitative relationship between both parameters was considera
bly adapted to the equation proposed by Bal'shin. By using the permeab
ility-epsilon and T-s-epsilon relations, the mechanical strength of tw
o EC films with different porosities were estimated under the assumpti
on that the drug permeation rate through the two films was equal. The
result suggested that, when the permeation rate was equal, a film with
higher porosity would have higher mechanical strength. This was also
proved by a high-shear dissolution test for theophylline beads coated
with EC film. The in vivo drug release behavior from porous EC film-co
ated heads agreed well with the in vitro drug release, indicating that
the porous EC film-coated beads had sufficient strength to withstand
the mechanical stress of the gastrointestinal tract, and that the poro
us EC film coating could be used as a barrier for controlled release p
reparations.