Bioadhesion (also known as mucoadhesion) refers to the ability of a drug delivery system to adhere to biological tissues.
In the context of mucosal drug delivery, mucoadhesion ensures that the formulation remains in contact with the mucosal surface for an extended period, enhancing drug absorption and efficacy.
Mechanisms of Mucoadhesion
Electronic Interactions:
Hydrogen Bonding: Formation of hydrogen bonds between the polymer and mucin glycoproteins.
Van der Waals Forces: Weak attractions contributing to overall adhesion.
Mechanical Interlocking:
Surface Roughness: Polymer chains interpenetrate the mucosal surface irregularities, creating a physical bond.
Fracture Adhesion:
Energy-Based Adhesion: The energy required to detach the adhesive from the mucosal surface contributes to the overall adhesion strength.
Diffusion Theory:
Interpenetration of Polymer and Mucin Chains: Polymer chains diffuse into the mucosal surface, creating entanglements that enhance adhesion.
Wetting Theory:
Spreadability: Adequate wetting of the mucosal surface by the formulation allows for better contact and adhesion.
Factors Influencing Mucoadhesion
Physiological Factors
Mucin Structure: Affects mucoadhesive interactions.
pH of Mucosa: Alters ionization, impacting adhesion.
Mucus Turnover: Influences the duration of adhesion.
Mucosal Hydration: Affects material swelling and adhesive strength.
Biological Factors
Epithelium Type: Different structures at sites like buccal or nasal influence adhesion.
Cell Turnover: Faster turnover reduces adhesion time.
Enzymes: Mucosal enzymes can degrade mucoadhesive materials.
Disease State: Conditions like inflammation impact adhesion.
Mucus Thickness: Thicker layers affect penetration and adhesion.
Role of Mucin in Adhesion
Viscoelastic Properties: Influence interaction with delivery systems.
Barrier Function: Provides a protective layer for prolonged adhesion.
Binding Sites: Functional groups on mucin aid in adhesion.