Addressing potent single molecule AFM study in prediction of swelling and dissolution rate in polymer matrix tablets

Abstract

Our goal was to understand and thus be able to predict the swelling behavior of xanthan matrix tablets in media of various pH and ionic strengths using data obtained from single xanthan molecules and films with atomic force microscopy. Imaging was performed in 1-butanol using contact mode AFM in order to characterize single xanthan chains prepared from various solutions. Image analysis was used to calculate the molecular contour, persistence length, and radius of gyration. Nanoindentation measurements of xanthan films were carried out to evaluate their mechanical properties. Increasing the ionic strength of solutions induced reductions in chain parameters such as molecular contour, persistence length, and radius of gyration. Nanomechanical measurements demonstrated that Young’s moduli of xanthan films prepared from solutions with higher ionic strengths are twice as large as those prepared at lower ionic strengths. This may help explain xanthan matrix tablets’ reduced degree of swelling and faster dissolution rate in the presence of salts or ions. We successfully come to conclusion that microscopic polymer properties such as radius of gyration and persistence length are responsible for the macroscopic polymer behavior. For instance, longer persistence lengths and radius of gyration of xanthan’s chains result in a higher degree of swelling, corresponding to softer polymer films, increased gel layers in matrix, and a slower release rate of the incorporated drug from the tablets.