Characterising the surface adhesive behavior of tablet tooling components by atomic force microscopy

The aim of this study is to develop an atomic force microscopy (AFM) based approach to study the adhesive forces between tabletting punches and model formulation ingredients, that can ultimately be used to understand and predict issues such as sticking during tabletting compression.

Adhesive interactions were studied between single lactose particles and coated tablet punches. The adhesion was measured at varying relative humidities (RHs) and the influence of surface roughness was investigated. Roughness parameters were measured with AFM imaging and a modeling approach used to predict the influence of roughness on adhesion.

Surface roughness was found to play a significant role in the observed lactose-punch adhesion and the variation of this adhesion across the punch surface. Such differences between punches can be correlated to observations from industrial use. Adhesion forces were spatially mapped to identify "hot spots" of high adhesion. A modeling approach can predict the relative adhesion of different surfaces from roughness data. The adhesion was also significantly affected by RH, for one type of punch causing a greater than 3? increase in adhesion between 30 and 60% RH. Interestingly, different punches showed different RH-adhesion behavior, relating to their hydrophilicity.

The work introduces a new method for screening tablet punch materials and tabletting conditions. Important factors to be considered when evaluating adhesive interactions in tablet compression have been highlighted. Correlations are observed between AFM adhesion results and tabletting behavior during manufacture. This provides a promising basis for a predictive approach toward combating tabletting issues.