The two types of gels used in capillary electrophoresis are permanently coated gels and dynamically coated gels.
Permanently coated gels are prepared inside the capillary by polymerization of monomers. One example of such a gel is a cross-linked polyacrylamide. This type of gel is usually bonded to the fused-silica wall and cannot be removed without destroying the capillary.
Dynamically coated gels consist of hydrophilic polymers such as linear polyacrylamide, dextran or cellulose derivatives. These polymers are soluble in aqueous separation buffers, creating a separation medium that serves as a molecular sieve. Unlike permanently coated gels, dynamically coated gels are simpler to prepare because they don't require cross-linking. They can be prepared in a vial and then introduced into a capillary without generating electroosmotic flow, using pressure to fill the capillary walls.