mucoadhesion

Mucoadhesion is the science of making a dosage form stick to a wet, slippery internal surface, the way a wet sticky note clings to a steamed-up bathroom mirror. The aim is to hold the medicine in place long enough to release its drug where you want it.

Mucosal surfaces line the mouth, nose, gut, eye, and reproductive tract, and they are coated by mucus, a viscous gel rich in glycoproteins. A mucoadhesive material first makes intimate contact with this layer (helped by wetting and swelling), then forms bonds with it: polymer chains interpenetrate and entangle with the mucus, and form hydrogen bonds and electrostatic attractions. Polymers such as chitosan, carbomers, and certain cellulose derivatives are common mucoadhesives.

The benefit is longer residence time and closer contact, which can improve absorption and allow less frequent dosing. The catch is that mucus is constantly being shed and renewed, so adhesion is temporary, and the surface conditions, pH, and water content vary between sites and individuals. Bonds that are too strong can also be uncomfortable or damage the tissue, so formulators aim for a balance.