Toward Predicting Tensile Strength and Characterizing the Acoustic Properties of Pharmaceutical Tablets on Continuous Manufacturing Platforms

Purpose. An ultrasound measurement system was employed as a non-destructive method to evaluate its reliability in predicting the tensile strength of tablets and investigate the benefits of incorporating it in a continuous line, manufacturing solid dosage forms.

Methods. Cylindrical tablets were prepared either continuously or in batch. The formulation was kept constant, while the compaction force and level of shear strain varied. Ultrasound testing was used to evaluate the strength of tablets by measuring the time of flight. The tensile strength of the same tablets was then determined using a mechanical hardness tester.

Results. The effect of two processing parameters, compaction force and level of shear strain were examined. Ultrasound speed of sound was found to be sensitive to the relative density and the level of shear strain. Ultrasound testing could detect even small differences between tablets that a hardness tester failed to do so.

A strategy for hardness prediction is proposed that uses the existing models for Young’s modulus and tensile strength of porous materials. A clear correlation between Young’s modulus and tensile strength at zero porosity is presented.

Conclusions. Ultrasound testing is a good candidate to be placed on/at-line to measure the mechanical integrity of tablets non-destructively. These results provide information about the behavior of processing parameters on the performance of tablets and the ability to engineer product properties.