Assessment of the Thickness Variation and Surface Roughness of Aqueous Film Coated Tablets Using a Light-Section Microscope

Abstract

The Light-Section Microscope measures the thickness and surface roughness of transparent film coats without contacting them. It enables the determination of tablet film coat thickness at different regions on a tablet surface and analysis of coat thickness variation. Examination of aqueous film coated tablets using a Light-Section Microscope has shown that the coat application conditions can influence the film density and thickness, film thickness variation and film coat surface roughness. Coat application conditions which give rise to smoother surfaces are shown to produce more dense, thinner coats which may exhibit a more even thickness on smooth substrates but larger variations in film thickness on rough substrates. The potential for film thickness and surface roughness to vary at different positions on the substrate surface has also been demonstrated, with film coats tending to be smoother and thinner at the periphery of tablet faces.The thickness of polymer films applied to tablets is often determined using a micrometer after film removal from a tablet, or by extrapolation from knowledge of the amount of polymer/coat applied. The former method is destructive and measurements reflect the thickest part of the film. Adhesion of substrate particles may also lead to artificially high thickness values being obtained. With the latter method, accurate values for film density and coating eficiency are required for meaningful thickness calculations to be made. Both methods yield a single value for film thickness and give no indication of thickness variation. 161 1 Copyright 0 1995 by Marcel Dekker, Inc. Drug Dev Ind Pharm Downloaded from informahealthcare.com by University of Otago on 01/03/15 For personal use only.

Characterization of the coating and tablet core roughness by means of 3D optical coherence tomography

“…On the contrary, the coating is slightly rougher than the core towards the end of the process. The roughness of the coating surface strongly depends on the coating application conditions, as was shown by Twitchell et al, 1995. The authors stated, on the basis of light section microscope measurements, that increasing the spray gun-to-bed distance, changing the spray shape from a narrow cone to a wide flat spray or decreasing the atomizing air pressure produce rougher surfaces.…”

Spatially resolved characteristics of pharmaceutical sprays

“…Twitchell et al,10 Ruotsalainen et al,6, 11 and Tobiska et al,12 all of whom confirmed that increasing atomizing air pressure decreased intratablet film thickness variations.…”

“…In addition to finish defects, spray characteristics can also contribute to inter/intratablet coating nonuniformities. Relevant literature includes that by: Twitchell et al,10 Ruotsalainen et al,6, 11 and Tobiska et al,12 all of whom confirmed that increasing atomizing air pressure decreased intratablet film thickness variations. Rege et al13 and Porter et al,14 who noted that a greater intertablet film thickness variation resulted when atomizing air pressure,13, 14 liquid viscosity, or liquid supply rate was increased 14 …”

The Influence of Film Coating on the Surface Roughness and Specific Surface Area of Pellets

“…Visual assessment and SEM can only provide a qualitative impression on the surface roughness, but they are very popular and simple techniques [9 ± 11]. Light-section microscopy is a non-destructive technique that can be used on transparent films [12]. It provides quantitative data such as the surface rugosity, but the calculation of these values from the observations made is rather difficult.…”