A comparative study on the sticking tendency of ibuprofen and ibuprofen sodium dihydrate to differently coated tablet punches

In the present study, the sticking tendencies of ibuprofen and ibuprofen sodium dihydrate as model substances for a lipophilic and a hydrophilic sticky API to differently coated punches were investigated. Increased sticking was observed with the more polar ibuprofen sodium dihydrate than with the less polar ibuprofen. Interestingly, the anti-sticking performance of the punch coatings proved to be independent of the APIs' polarity. To understand this phenomenon, key properties of the punches were investigated. The AFM adhesive forces of both APIs to the differently coated punches as well as the surface free energies and the surface texture of these punches were determined. Separately evaluating these properties revealed only a partial correlation with the sticking observed during tableting. Consistent results with the tableting data could only be achieved if evaluating the surface texture in context with the chemical composition of the respective punch surfaces. It was concluded that each punch tip coating represents an entirely different system, which were described in detail as a result of the performed investigations. Particularly, chromium nitride-coated punches resulted in excellent anti-sticking performances because of a low chemical interaction with the APIs combined with a smooth and homogeneous surface texture.