Studies on the release of CMC and PEO from gels were
performed with PBS used as the release medium. Membranes
of porcine intestine were mounted on the bottoms of petri
dishes (diam 50 mm) with double-sided adhesive tape. Gels
were prepared with fluorescein-labeled PEO. An aliquot of
5.0 ml of each gel was evenly spread over the surface of the
membrane. PBS (10 ml) was carefully loaded on the top of
the gel layer, followed by incubation at room temperature
under gentle shaking. At the time periods of 3 min, 10 min,
20 min, 1 h, and 2 h the dish was tipped to one side and 1.0
ml of PBS was pipetted from the solution above the gel and
analyzed for the amount of PEO and CMC released.
The released PEO was quantified by measuring the absorbance
of the fluorescein moiety attached at the PEG chain at
500 nm. The CMC released into the incubation medium was
determined by measuring hexose content, by the method of
phenol-sulfuric acid reaction, where the absorbance at 480
nm is measured after the CMC is incubated with phenol and
sulfuric acid at 30 °C for 20 min.