Evaluation of mechanical strength of granules from compression data

Jan. 1, 2018, midnight - by Milan Decorte

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Defining granule characteristics is a critical aspect of tablet formulation. However, there are limited methods available for determining the strength of individual granules. Adams et al. proposed a method to deduce the single agglomerate failure force from a uniaxial confined compression test, and this project aims to validate and optimize that method. Granules were produced using five pure excipients and mixtures of each excipient with one of four APIs via roll compaction/dry granulation, employing four specific compaction forces. The Styl’One Evolution was used for compression. The method assumes spherical, monodisperse granules with equally strong bonds and a uniform failure load in each granule column. Spatial rearrangement under load was checked through bulk and tapped density measurements, confirming the validity of this assumption. Wall friction between the die and granules was addressed by investigating bed height and external lubrication. Compression tests were executed with external lubrication to meet the assumptions. Plastic deformation was ruled out by compressing granule beds at different speeds, revealing no significant speed-dependent effects on failure forces. Besides validating the method, measurements on pure excipients and mixtures were performed to optimize the process. Results indicated that the method is developed enough to compare different excipients and showed that the API did not influence the failure force, though the API amount in the mixtures was insufficient for a notable impact. While the research validated the method's core assumptions, it also highlighted the need for further development to establish a standardized approach for determining granule strength.