Hydrogels that expand volumetrically in response to a change in their environment (e.g., a change in pH or temperature) and their methods of manufacture and use. Generally, the hydrogels are prepared by forming a liquid reaction mixture that contains a) monomer(s) and/or polymer(s) at least portion(s) of which are sensitive to environmental changes (e.g., changes in pH or temperature), 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 it situ.
