In-vitro evaluation of bioadhesion in particulate systems and possible improvement using interactive mixtures

The bioadhesion of tablet components was tested using the fracture method (maximum tensile stress in detaching the sample from mucus membrane) and comparing traditional tablet specimens with powder monolayers. Both nonadhesive excipients and established mucoadhesive materials were investigated. Some nonadhesive materials showed unexpectedly good adhesive properties when tested as tablets but not as powders. Conversely, some bioadhesive materials had unexpectedly low adhesive properties when tested as tablets. Thus, powder specimens of some materials appear to give more realistic results than tablet specimens in this respect. The use of powder specimens seems particularly applicable for testing dispersible tablets intended for transmucosal absorption. Potential for increasing the bioadhesive properties of coarse, nonadhesive carrier particles by coating them with fine particles of bioadhesive materials during dry mixing (forming interactive mixtures) was also studied. The tensile strength of the adhesive bond between the mucosa and the nonadhesive excipients was improved when fine cross-linked carboxymethyl cellulose sodium (Ac-Di-Sol) particles were added. The addition of increased proportions of Ac-Di-Sol initially improved the bioadhesive properties until a plateau was reached. A standardised test of bioadhesive capacity could therefore involve the addition of fine bioadhesive powders to coarse carriers in proportions close to those providing monoparticulate surface coverage. Interactive mixtures such as these may also offer potential as a tool for use in the development of bioadhesive drug formulations.