Application of a chromatic confocal measurement system as new approach for in-line wet film thickness determination in continuous oral film manufacturing processes

Abstract

The key parameter of the oral film production process is the wet film thickness since it regulates the active pharmaceutical ingredient (API) content of the finished product. There is no general recommendation on how to adjust the gap height of the coating knife during the film manufacturing process to obtain the target content. Therefore, trial and error approaches are common to determine the surplus of drug for every newly developed formulation. This wastes resources, money and time and calls for an adequate in-line tool for wet film thickness measurement during the film manufacturing process to ensure consistent quality. In this work, a chromatic confocal optical probe was implemented into a continuous oral film manufacturing process on a pilot-scale coating bench. The optical probe allows a non-destructive and contactless wet film thickness measurement. The validation of the method showed good results. Linearity was demonstrated over a wide range of film thicknesses (R² = 0.999). A good precision between different films was revealed by a coefficient of variation smaller than 2%. The robustness investigations showed that the method is applicable for transparent and non-transparent film forming masses. Furthermore, coloring agents, particles in the polymer mass and different viscosities do not influence the thickness measurement.

Keywords: Continuous film manufacturing; In-line thickness; Oral film; Orodispersible film; Process analytical technology; Wet film thickness.