The effects of humidity on the adhesion of pharmaceutical excipients to steel surfaces

The adhesion between powders and surfaces is influenced by their topography. We investigate the relationships between the topography on stainless steel, the humidity, and the adhesion of three pharmaceutical powders. These relationships are captured within 'effective' work of adhesion parameters tuned using the enhanced centrifuge method (ECM). The parameters describe the effects of the size, shape, humidity, and topography on the adhesion. The powders' ability to nestle into features on the steel drove the work of adhesion. When the powders absorbed moisture, the balance of moisture -driven deformation and increased mass dictated the powder removal from the surface. The irregularly shaped hypromellose (HPMC) adhered more strongly to the stainless steel at low humidity than at high. The lactose monohydrate and ABT-089 showed the opposite behavior. The HPMC adhered more strongly to the rough steel than to the smooth or untreated steel. The lactose monohydrate and ABT-089 again showed the opposite behavior.