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Abstract
In many applications, usefulness of conventional hydrogels is limited by their slow
swelling. To improve the swelling property of the conventional hydrogels, we have
synthesized superporous hydrogels (SPHs) which swell fast to equilibrium size in minutes
due to water uptake by capillary wetting through numerous interconnected open pores.
The swelling ratio was also large in the range of hundreds. The mechanical strength
of the highly swollen SPHs was increased by adding a composite material during the
synthesis. The composite material used in the synthesis of SPH composites was Ac-Di-Sol((R))
(croscarmellose sodium). The gastric retention property of the prepared SPH composites
was tested in dogs both in fasted and fed conditions. The SPH composites were placed
in a hard gelatin capsule (size 000) for oral administration. All dogs tested were
fasted for 36 h before experiments. Under the fasted condition, the SPH composite
remained in the stomach for 2-3 h after before breaking into two pieces and being
emptied. When food was given before the experiment just once following 36 h of fasting,
the SPH composite remained in the stomach for more than 24 h, even though the fed
condition was maintained only for the first few hours. Our study indicated that SPH
composites possessed three properties necessary for gastric retention: fast swelling;
superswelling; and high mechanical strength. While more improvements need to be made,
the SPH composites provide the basis for the development of effective long-term gastric
retention devices.