Hydrogels are materials whose use has been extensively researched recently, especially in the fields of pharmacy and biomedicine. The main reason for this is their ability to carry and release drugs. The drug release rate is of utmost importance in many applications. Therefore, many models have been developed to describe the rate and mechanism of drug release. The properties of the loaded drug have a big influence in the drug release. The size of the drug is an essential factor that can help reduce the drug release rate. Interactions between the drug molecules and hydrogel network can also have a major impact on the release rate. They, just like the drug size, inhibit the drug release, but the formation of interactions can also be used to increase the absorption rate of mainly hydrophobic drugs. The hydrophilicity or hydrophobicity of the drug also has an indirect influence on the release rate, as it affects the water absorption rate and the maximum possible amount of water the network can absorb.
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