Swelling characteristics of hydrophilic matrices for controlled release New dimensionless number to describe the swelling

Drug release mechamsms of swellable systems for controlled drug administration were investigated The variations of the matrix relaxation and drug diffusion rates were quantified, by measuring the surface area exposed during matrix swelling and drug release as a function of impermeable coating coverage and location. Four different types of matrices, partially coated on various sides, were investigated in order to elucidate the role of the swelling behavior on the release from such delivery systems, especially m view of the three-dimensional nature of the swelling phenomenon. Dependence of the release kinetics on the matrix surface area was assesed. A new dimensionless number, the swelling area number, Sa, was defined for evaluating the significance of the relative rate of matrix swelling variation and drug diffusivity. The systems stu&ed were produced by partial coverage of the release area of tablets by an impermeable coating.