hydrogels that expand volumetrically in response to a change in their environment and their methods of manufacture and use . generally , the hydrogels are prepared by forming a liquid reaction mixture that contains a ) monomer and / or polymer at least portion of which are sensitive to environmental changes , b ) a crosslinker and c ) a polymerization initiator . if desired , a porosigen may be incorporated into the liquid reaction mixture to create pores . after the hydrogel is formed , the porosigen is removed to create pores in the hydrogel . the hydrogel may also be treated to cause it to assume a non - expanded volume in which it remains until a change in its environment causes it to expand . these hydrogels may be prepared in many forms including pellets , filaments , and particles . biomedical uses of these hydrogels include applications wherein the hydrogel is implanted in the body of a patient and an environmental condition at the implantation site causes the hydrogel to expand in situ .