Understanding the Tabletability Differences between Indomethacin Polymorphs Using Powder Brillouin Light Scattering

Abstract

Purpose: The unconventional tabletability of the indomethacin polymorphs – α and γ – are investigated from a topological and mechanical perspective using powder Brillouin light scattering (p-BLS) to identify the specific structure-performance relationship in these materials. Method: Indomethacin (γ-form) was purchased and used to prepare the α polymorph. Powder X-ray diffraction was used to confirm phase identity, while p-BLS was used to obtain the mechanical properties. Energy frameworks were determined with Crystal Explorer to visualize the interaction topologies. Using a Carver press and a stress-strain analyzer, the tableting performance of each polymorph was determined. Results: Polymorph-specific acoustic frequency distributions were observed with distinct, zero-porosity, aggregate elastic moduli determined. The p-BLS spectra for α-indomethacin display a population of low-velocity shear modes, indicating a direction of facilitated shear. This improves slip-mediated plasticity and tabletability. Our p-BLS spectra experimentally indicates that a low-energy slip system is available to α-indomethacin which supports ours and previous energy framework calculations. Despite a 2d-layered crystal motif favorable for shear deformation, the γ-form displays a higher shear modulus that is supported by our hydrogen-bonding analysis of γ-indomethacin. Conclusion: Our experimental, mechanical data is consistent with the predicted interaction topologies and these two inputs combined permit a comprehensive, molecular understanding of polymorph-specific tabletability.