Quantification of swelling characteristics of pharmaceutical particles

Particle swelling is a crucial component in the disintegration of a pharmaceutical tablet. The swelling of particles in a tablet creates stress inside the tablet and thereby pushes apart adjoining particles, eventually causing the tablet to break-up. This work focused on quantifying the swelling of single particles to identify the swelling-limited mechanisms in a particle, i.e. diffusion- or absorption capacity-limited. This was studied for three different disintegrants (sodium starch glycolate/SSG, croscarmellose sodium/CCS, and low-substituted hydroxypropyl cellulose/L-HPC) and five grades of microcrystalline cellulose (MCC) using an optical microscope coupled with a bespoke flow cell and utilising a single particle swelling model. Fundamental swelling characteristics, such as diffusion coefficient, maximum liquid absorption ratio and swelling capacity (maximum swelling of a particle) were determined for each material. The results clearly highlighted the different swelling behaviour for the various materials, where CCS has the highest diffusion coefficient with 739.70 μm²/s and SSG has the highest maximum absorption ratio of 10.04 g/g. For the disintegrants, the swelling performance of SSG is diffusion-limited, whereas it is absorption capacity-limited for CCS. L-HPC is both diffusion- and absorption capacity-limited. This work also reveals an anisotropic, particle facet dependant, swelling behaviour, which is particularly strong for the liquid uptake ability of two MCC grades (PH101 and PH102) and for the absorption capacity of CCS. Having a better understanding of swelling characteristics of single particles will contribute to improving the rational design of a formulation for oral solid dosage forms.