Table 4.

Summarized mechanisms of the various GRDDS.

Gastroretentive Approach	Mechanism	References
Low-density systems/ floating systems	System causes buoyancy in gastric fluid. Density of pellets/tablets is lower than the density of stomach fluid.	[1,17,20,47]
High density systems	Uses the density of dosage form as a strategy to produce the retention mechanism. Sinking system remains at the bottom of the stomach, where the density of the dosage form is greater than the gastric fluid.	[1]
Expandable systems	Expansion of the dosage form occurs by swelling or unfolding in the stomach. Swelling usually occurs because of diffusion. Unfolding takes place due to mechanical shape memory.	[6,12,61]
Bioadhesive systems	A very complex process with several mechanisms, including electrical theory, adsorption, wetting, diffusion, and fracture theories. The interaction between the negatively charged mucosal surface and positively charged polymers might facilitate the bioadhesive process.	[12,45]
Raft forming systems	The polymer in presence of mono or di valent cations, absorbs water, swells and forms in situ gel layers, which float above gastric fluid and termed as raft.	[62,63]
Super-porous hydrogel systems	Swells up to 100 times due to water update by capillary wetting through numerous pores.	[12,64]
Magnetic systems	Consists of the small internal magnet mixed with the drug. Its position inside the stomach is controlled by an extracorporeal magnet.	[16]
Ion-exchange resin systems	Drug is loaded into the resin to form the resin loaded drug complex, which can be combined with floating delivery or bioadhesive systems.	[16]