A New Computer-Aided Apparatus for Simultaneous Measurements of Water Uptake and Swelling Force in Tablets

Water uptake and disintegrating force development have frequently been related to tablet disintegration properties. Water penetration into compressed tablets has been studied by many authors using modified Enslin apparatus. Meanwhile, in previous papers by our group, a great deal of attention has been paid to the measurements of disintegrating force and to the kinetics of force development. Given the fact that water penetration and swelling force development are related to each other, a new apparatus was set up which allows simultaneous measurements of water penetration and force development. It consists of a modified apparatus for force measurements, integrated with a modified Enslin apparatus. Both force and water uptake data were collected by a computer and stored for subsequent analysis. Fitting of both water penetration and force development curves was performed with a commercially available software package for non-linear regression analysis. This enables an examination of the relationships between force development and water penetration on the basis of homogeneous rate parameters. The apparatus was validated on a model tablet formulation based on dicalcium phosphate dihydrate with carboxymethylstarch. Besides application in fast disintegrating tablets, this approach could be useful to study the behaviour of swelling-controlled release systems, in which the release mechanism (swelling force) is triggered by water penetration.