Capsule-forming polymers

A capsule is an oral medication that is usually swallowed. This medication is surrounded by an outer shell, often made of gelatin. Capsules come with hard or soft shells, which contain powder, miniature pellets, liquid, mini tablets, and films inside. Due to their simplicity, ease of manufacturing, ability to load various forms of medication, and patient compliance, capsules are widely used as an oral dosage form. Standard pharmaceutical capsules are made to disintegrate in the acidic environment of the stomach, thereby releasing the encapsulated therapeutic drug for absorption. However, capsules can also be coated with pH-sensitive polymers which enable the passage of the drug-loaded capsule to disintegrate at the desired site in the gastrointestinal tract. To this end, polymers are widely used for the manufacturing of capsules to enable controlled drug release, site-specific delivery, and improving drug stability, among others. The choice of polymers plays an essential role in the manufacturing of oral capsules. Several factors such as molecular weight, polydispersity, viscosity, blend composition, functional groups, glass-transition temperature, melting point, polymer-polymer interactions, or polymer-excipient interactions depend on the type of polymer forming capsules. The first-generation hydroxypropyl methylcellulose (HPMC) capsules were manufactured in combination with two added polymers, that is, carrageenan and gellan gum. The gelling of the capsule was achieved by varying the concentration of carrageenan and gellan, based on the HPMC level, by the dip-molding process. Second-generation HPMC capsules have now been developed without any requirement for a gelling agent. In this case, the gelation is induced by using heated molding pins (thermogelling process). The capsules prepared by the thermogelling process are not only expensive but also sensitive to environmental temperature and moisture. Thereafter, various blends of polymers including HPMC-gellan gum, HPMC-carrageenan, HPMC-HPMC-acetate succinate, carrageenan-modified starch, and gelatin-methacrylic acid copolymer A among others are used for the manufacturing of capsules, which are also available in the current market as Quali-V hard capsules (Shionogi Qualicaps), Vcaps hard capsules (Capsugel), DRcaps hard capsules (Capsugel), Vcaps enteric hard capsules (Capsugel), Vegesoft vegetarian softgels (Eurocaps), VersagelTM (Procaps), and EntericareTM softgels (Patheon). Emerging technologies such as 3D printing have achieved the designing and filling of capsules using fused deposition modeling. Taken together, this book chapter focuses on the classification, designing, and manufacturing of capsules using different polymeric materials. It also provides advances in capsule technologies along with the challenges and opportunities for the encapsulation of therapeutic molecules within a capsule for oral administration.