Terahertz pulsed imaging as an advanced characterisation tool for film coatings—A review

International Journal of Pharmaceutics
Available online 6 April 2013
http://dx.doi.org/10.1016/j.ijpharm.2013.03.053

Authors: Miriam Haaser^{a, b, c}, Keith C. Gordon^d, Clare J. Strachan^e, Thomas Rades^f
a School of Pharmacy, +University of Otago, P.O. Box 56, Dunedin, New Zealand
b Cavendish Laboratory, +Cambridge University Press Education , Cambridge CB3 0HE, UK
c +TeraView Ltd., St. John's Innovation Park, Cambridge CB4 0WS, UK
d Department of Chemistry, MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago, Dunedin, New Zealand
e Division of Pharmaceutical Technology, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland
f Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark

Abstract

Solid dosage forms are the pharmaceutical drug delivery systems of choice for oral drug delivery. These solid dosage forms are often coated to modify the physico-chemical properties of the active pharmaceutical ingredients (APIs), in particular to alter release kinetics. Since the product performance of coated dosage forms is a function of their critical coating attributes, including coating thickness, uniformity, and density, more advanced quality control techniques than weight gain are required. A recently introduced non-destructive method to quantitatively characterise coating quality is terahertz pulsed imaging (TPI). The ability of terahertz radiation to penetrate many pharmaceutical materials enables structural features of coated solid dosage forms to be probed at depth, which is not readily achievable with other established imaging techniques, e.g. near-infrared (NIR) and Raman spectroscopy. In this review TPI is introduced and various applications of the technique in pharmaceutical coating analysis are discussed. These include evaluation of coating thickness, uniformity, surface morphology, density, defects and buried structures as well as correlation between TPI measurements and drug release performance, coating process monitoring and scale up. Furthermore, challenges and limitations of the technique are discussed.


... The imaging unit in TPI instruments such as the TPI imaga 2000 system (TeraView, Cambridge, UK), therefore comprises a six-axis robotic arm, the probe and a separate optical laser operating at 670 nm. ...

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