Sentence:  Similar studies of rats have employed four different intracranial resorbable, slow sustained release systems&mdash;surgical foam, a thermal <WSD>gel</WSD> depot, a microcapsule or biodegradable polymer beads. 
Meaning of the word marked with <WSD> tags:  A semi-solid to almost solid colloid of a solid and a liquid, such as jelly, cheese or opal.