A gastric banding device contains an expandable material. The expandable material may include, for example, a hydrogel material that expands when hydrated. The hydrogel material may include a single or multiple monolithic components, and/or may include hydrogel material in particulate form, such as hydrogel beads, microspheres, or powder. The gastric banding device includes an elongate gastric band having an expandable lumen that forms a stoma opening in the stomach by encircling and partitioning the stomach into an upper stomach and a lower stomach. The hydrogel material is positioned in the lumen and expands when hydrated to at least partially expand the lumen, thus decreasing the size of the stoma opening.