TeraView (Cambridge, UK; www.teraview.com) has conducted successful proof-of-principle testing for high-speed measurements of coating thickness on tablets applicable to on-line tablet inspection. The noncontact, nondestructive technique may also be extended to on-line measurement of other key product attributes, such as coating or core density tablet delamination and many other parameters characterizing the performance of drugs that TeraView has identified with its products and collaborators.
Terahertz light (30 μm--3 mm) is useful for pharmaceutical applications because of its lower frequencies and longer wavelengths relative to mid-infrared radiation. In particular, terahertz radiation is sensitive to vibrations of noncovalent bonds but not to those of discrete bonds. The former correspond to intermolecular vibrations or vibrations of large units in a molecule.
When used in spectroscopic techniques, terahertz radiation provides information on phonons in crystalline semiconductors and in molecular systems.
Thus, in the pharmaceutical industry, terahertz technology can be used to identify particular molecules.
In addition, longer wavelengths result in little scattering, which, when combined with low absorption in dry solids, renders terahertz radiation important for imaging. Researchers Louise Ho, Michael Pepper, and Phil Taday at TeraView describe the use of terahertz pulsed spectroscopy for solid-state analysis and terahertz pulsed imaging for tablet coating analysis in an article published by SPIE (see spie.org/x20175.xml). This development represents a step toward addressing one of the most difficult problems to be overcome in on-line pharmaceutical inspection--measuring product attributes such as coating thickness accurately and rapidly while the tablets are in random motion in a coating pan. This capability opens up the opportunity for deployment of terahertz sensors in rapid, nondestructive tablet inspection to ensure that pharmaceutical products remain within the specifications necessary to maintain therapeutic efficacy and drug performance.
Ultimately, these sensors could also be used in feedback systems to control production parameters (for example, coating spray rates, tablet compression force for single and multiple layer tablets) in real time. The technique could also support the pharmaceutical industry's future plans to implement continuous process systems in drug manufacture.
