| Bioadhesive approach to prolong residence time of a drug delivery system in stomach to achieve local treatment for gastric ulcers and cancer, to increase the relative bioavailability of drugs and patient compliance, through controlled or sustained drug release was not successful due to poor understanding of stomach surface property. It is hypothesized that the gastric mucosa lining in humans is hydrophobic because of the presence of phospholipids, which acts as a bioadhesion barrier to hydrophilic bioadhesives and allows bioadhesion of polymers with a degree of surface hydrophobicity.; We examined the surface of a pig stomach using contact angle measurements, alcian blue staining, proton permeability, and morphological studies. It was found that the pig gastric mucosal surface is relatively hydrophobic due to the presence of a hydrophobic phospholipid layer on the surface of the mucus layer. With this crucial information, a simplified in vitro gastric mucus model, which can mimic the hydrophobic surface of an animal stomach, was developed and validated by contact angle measurements, alcian blue staining, proton permeability, and stability assay for the phospholipid lining. Using this validated in vitro model, we investigated the effect of functional groups of polymers on adhesion to the hydrophobic phospholipid lining of the model and various control gel surfaces using fluorescent polystyrene microspheres with three different functional groups ( -COOH, -NH2, and plain polystyrene). It turned out that the hydrophobic phospholipid lining of the in vitro model did not allow adhesion of microspheres with -COOH and -NH2 functional groups, whereas it did allow adhesion of microspheres with hydrophobic attributes. In addition, the effect of the surface hydrophobicity of polymers on adhesion was studied using diblock copolymers of polystyrene and polyacrylate. The results showed that the in vitro adhesive force between the hydrophobic phospholipid lining of the in vitro model and the polymer increased when the surface hydrophobicity of the polymer increased.; The conclusion from our in vitro studies is that the hydrophobic phospholipid lining of the in vitro gastric mucus model acts like an adhesion barrier to hydrophilic bioadhesive polymers. Conversely, it allows adhesion of hydrophobic polymers with a certain degree of surface hydrophobicity. |
