Issue link: https://www.e-digitaleditions.com/i/1287521
20 September 2020 Tablets & Capsules Another case study was performed that used atomic force microscopy (AFM) to measure the adhesion force of a specific API (API X) when it came into contact with various tool coating solutions (Figure 3). AFM works by moving a probe functionalized with a single particle of either the API or excipient to the surface of a variety of punch tips and anti-stick solutions. The probe is then removed and measures the force needed to detach the particle from the surface of the punch tip. Because of its moderately hydrophobic elemental composition, Phar- maCote CN, a chromium-nitride tool coating, had a very low adhesion force that stayed low even when the rela- tive humidity (RH) increased from 10 to 60 percent. For the diamond-like carbon coating, on the other hand, as the RH increased, the adhesion force also increased quite dramatically, making the coating unsuitable for this API. Interface chemistry and spatial heterogeneity. There are several different instruments used to understand the chemistry at the interface between the formulation and the punch and the formulation's spatial heterogeneity. Scanning electron microscopy can magnify a section of a coating up to 3,000 times to look at its chemical struc- ture. X-ray photoelectron spectroscopy can also be used to examine the chemical composition and structure of either the steel or the tool coating. Time of flight sec- ondary ion mass spectrometry can identify why a particu- lar formulation might only stick on a certain area of a punch tip. By etching away the adhered formulation and chromium is applied to tooling, hydrogen penetrates the steel making it more brittle and prone to unpredictable fracture, decreasing the working load by 20 percent. The green columns represent more advanced coatings (ECxtra, CN, CN+, and CT), which have been developed in recent years to decrease sticking without causing hydro- gen embrittlement and which are rapidly replacing the low tech hard-chromium-type coatings. The orange bar represents hard diamond-like carbon coating (DN). Figure 3 AFM case study for API X 10% RH 30% RH 60% RH HPG-S HPG-P HPG-SS HC HC+ ECxtra CN CN+ CT DN 600 500 400 300 200 100 0 API X adhesion force (nN) Steel and coating type