An ultrasound measurement system was employed as a non-destructive method toevaluate its reliability in predicting the tensile strength of tablets andinvestigate the benefits of incorporating it in a continuous line,manufacturing solid dosage forms. Tablets containing lactose, acetaminophen,and magnesium stearate were manufactured continuously and in batches. Theeffect of two processing parameters, compaction force and level of shear strainwere examined. Young's modulus and tensile strength of tablets were obtained byultrasound and diametrical mechanical testing, respectively. It was found thatas the blend was exposed to increasing levels of shear strain, the speed ofsound in the tablets decreased and the tablets became both softer andmechanically weaker. Moreover, the results indicate that two separate tabletmaterial properties (e.g., relative density and Young's modulus) are necessaryin order to predict tensile strength. A strategy for hardness prediction isproposed that uses the existing models for Young's modulus and tensile strengthof porous materials. Ultrasound testing was found to be very sensitive indifferentiating tablets with similar formulation but produced under differentprocessing conditions (e.g., different level of shear strain), thus, providinga fast, and non-destructive method for hardness prediction that could beincorporated to a continuous manufacturing process.
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