air for 30 min. The electrical conductivity of CMCS-AP hydrogel
was determined by a Pocket Conductivity Meter (HANNA8733).
80 mg of the model molecule diclofenac sodium was dissolved
in 10 mL water. 10 mg of dry hydrogel of CMCS and CMCS-AP20
was then submerged into the above solution for 60 h until the
swelling equilibrium was reached. The hydrogel was taken out
and dried at 37 C in an oven until reaching a constant weight.
For the release experiment, the dried hydrogel with loaded-drug
was placed into conical flask containing 100 mL buffer solution
(pH 7.4). The flask was then place into a shaking incubator at
37 C with a rotation speed of 100 rpm. At predetermined time
intervals, 1 mL of solution was taken out and replaced with equal
volume of the same release media. The amount of drug loaded
and released from the hydrogel was spectrophotometrically determined
at 276 nm using a UV–Vis spectrophotometer (PerkinElmer
Lambda 35) with a standard linear curve of diclofenac sodium.
The rheological properties of the CMCS-AP hydrogels were evaluated
with a TA rheometer (DHR-2) at 25 C with the parallel-plate
geometry (plate diameter of 20 mm, gap of 1000 lm). The measurement
was performed using a dynamic frequency sweep test,
which covered a range of frequencies from 1 to 100 rad/s at a constant
shear amplitude of 0.1%.