Classes/types of polymers used in oral delivery (natural, semisynthetic, synthetic), their chemical structure and general functionalities

The oral route is the most preferred route of drug delivery as it is patient-friendly, painless, and easy for self-medication. However, proteins and peptides are difficult to administer orally since they are hydrolyzed easily and have poor bioavailability. Polymers have emerged as a promising materials for oral drug delivery. There are several advantages to polymers, including protecting against chemical degradation, responding to a stimulus, conjugating with antibodies and biomarkers for molecular target detection, drug delivery devices, optimizing drug loading and release properties, and crossing the blood-brain barrier. As a result of the availability of a wide range of polymers (natural, synthetic, or semisynthetic) with unique chemical structures and surface characteristics, these functions have been significantly expanded. There have been some studies showing that natural polymers such as chitosan, alginate, dextran, starch, and pectin can deliver insulin to the body orally. Pectin-based systems were used to achieve colon-specific delivery of indomethacin. Among all the other reported synthetic polymers, pegylated polymers have been extensively studied for tissue engineering. They have also been used as stimuli-responsive polymers in anticancer drug delivery systems. The most explored semisynthetic water-soluble cellulose derivatives including hydroxypropyl methylcellulose, methylcellulose, and hydroxypropyl cellulose were used in the fabrication of amorphous solid dispersions, thereby increasing the bioavailability of poorly water-soluble drugs. Polymers forming micelles such as polyethylene glycol and polylactic acid have been used as vehicles to enhance the permeability of drugs across the gastrointestinal mucosa in chronic therapies. In combination with lipid-based systems, polymers such as chitosan, methylcellulose, and hydroxypropyl cellulose have been shown to increase the therapeutic activity of the molecules by overcoming biological barriers. Taken together, this book chapter focuses firstly on polymer classification, along with their chemical structure and functional properties. In addition, it provides a comprehensive overview of its applications and recent advances in oral drug delivery.