mucoadhesion

Mucoadhesion is the phenomenon by which a material adheres to a mucosal surface, such as those lining the gastrointestinal, nasal, buccal, ocular, vaginal, or pulmonary pathways. The interaction occurs at the mucus layer overlying the epithelium and can extend residence time, improve local drug delivery, or enable rapid systemic uptake through mucosal tissues.

Adhesion arises from hydration and wetting of the mucoadhesive, interpenetration of polymer chains with mucin glycoproteins, and non-covalent interactions such as hydrogen bonding, electrostatic forces, and van der Waals interactions. In some systems, covalent bonding or disulfide exchange can strengthen attachment. The principal explanatory models include diffusion (interpenetration of polymer and mucus chains), adsorption (interfacial bonding), electronic (interfacial charge interactions), and cohesive (mechanical interlocking).

Mucoadhesive materials include natural and synthetic polymers such as chitosan, starches, cellulose derivatives (carbomers, hydroxypropyl cellulose), polyacrylates, alginates, and thiolated polymers that form stronger bonds by introducing reactive groups. Formulations take the form of gels, films, tablets, and nanoparticles designed to maximize contact with mucus and to maintain a hydrated, flexible contact surface.

Mucoadhesion depends on mucus properties (turnover rate, thickness, mucin composition), tissue pH, ionic strength, and hydration, as well as polymer molecular weight, chain length, degree of substitution, hydrophilicity, and chain mobility. Adhesion is typically evaluated by detachment force, work of adhesion, or rheological/ex vivo mucosal tests.

Applications span buccal and sublingual drug delivery, nasal and ocular administration, and topical GI therapies. Benefits include prolonged residence time and improved bioavailability, while challenges include variability in mucus properties, mucociliary clearance, potential irritation, and safety concerns with certain functional groups. Ongoing work seeks smarter, stimuli-responsive and bioinspired mucoadhesives.