48. Biodegradable Hydrogels for Controlled Drug Delivery

Hydrogels are three-dimensional cross-linked polymeric networks that can imbibe large amount of water or biological fluids. The ability of hydrogel to absorb water appears due to the presence of hydrophilic groups such as –OH, –CONH, –CONH₂, –COOH, and –SO₃H, along the polymer chain. Depending on the pendant functional groups, hydrogels have the ability to respond to their environmental changes such as pH, ionic strength, or temperature. The high water content and soft texture of these hydrogels translate them into a biocompatible material. This property renders the hydrogel similar to biological tissues and consequently minimizes inflammation once implanted or injected in the body. Biodegradable hydrogels are further adding advantages of degradation of the matrix into innocuous biocompatible products that can be eliminated after serving, thus eliminating the necessity of their removal. The degree of biodegradation can be controlled by manipulating the cross-linking with suitable precursors. Their mechanical property can also be tailored to have structural stability followed by extended release of cargo molecules. Their flexibility and minimally invasive administration are useful characteristics for their increased application in biomedical fields. Biodegradable hydrogels as controlled release systems are investigated to improve the temporal and spatial presentation of drug in the body, to protect drug from physiological degradation or elimination and to improve patient compliance. Hence the author has made an attempt to discuss biodegradable polymers of natural and synthetic origin, the biodegradation mechanisms, hydrogel engineering strategies, drug-hydrogel interactions, and release kinetics and mechanisms of such hydrogels to attain controlled delivery of drugs to different site of action in this chapter.