AN INVESTIGATION INTO THE ROLE OF WATER-MOVEMENT AND MUCUS GEL DEHYDRATION IN MUCOADHESION

Water transfer between mucoadhesive formulations and mucus gels was investigated. The water uptake by compacts and gels, measured in terms of weight gain, was evaluated at 37-degrees-C by placing each onto a section of dialysis membrane which was then placed in contact with a sample of porcine gastric mucus. Water transfer occurred for all the dry (and concentrated gel) formulations and was evident after only 1 min, with anionic polymers dehydrating the mucus gel more than the neutral polymer. As the concentration of gels containing Carbopol 934P decreased, so the extent of water uptake decreased, with water being lost from the 4% gels. The effect of dehydration on the physical properties of the mucus gel was evaluated using a modified tensiometer and dynamic oscillatory rheology. The adhesive and cohesive nature of the mucus gel was seen to increase when the water content decreased, which would be predicted to result in the strengthening of the weakest component of a mucoadhesive joint. It was concluded that water movement would be a significant factor in mucoadhesion involving dry and partially hydrated dosage forms, and this may be more important than molecular interpenetration.