Tablets are the most widespread dosage form because of low production cost, convenient administration, good patient compliance, and long shelf life (Paul and Sun, 2017, Zhao et al., 2021). The tableting process includes two fundamental steps: the volume reduction of granules and the generation of inter-granule bonds (Persson et al., 2022). Compression is commonly used to describe the first step, and it enables rearrangement, deformation, or fragmentation for the original granules, and thereby enhances the density of materials (Xiao et al., 2022). The term “compressibility” represents the tendency of compression and it is generally quantified by obtaining parameters from various compression models (Persson et al., 2022), such as Heckel and Walker equations. The second important step in the tableting process reflects the capacity of granules to form tablets with the expected hardness under a certain compression pressure, which is typically considered the term “tabletability” (Sun and Himmelspach, 2006). A comprehensive understanding and systematic evaluation of granules’ compressibility and tabletability before the production of tablets are highly required for formulation development in solid formulations.

It has been proved that granules’ physical properties are important for the tableting process (Liu et al., 2023, Silva et al., 2022, Wünsch et al., 2021). The quality of tablets could be impacted by granules’ moisture content (Shi et al., 2011), porosity (Liu et al., 2023), and particle size (Mawla et al., 2023). Recently, the granules’ shape has also been reported to play a vital role in the tableting process (Wünsch et al., 2021). It was proposed that irregular paracetamol granules had better compressibility than traditionally spherical ones (Simek et al., 2017). In another study, it was reported that tetrahedral granules had poorer compressibility than their spherical counterparts due to reduced granule rearrangement and higher resistance to deformation (Talat and Khan, 2023). Thus, it is worth studying the shape of granules for the development of tablets.

Recently, cylindrical granules attracted more and more attention in the pharmaceutical field (Korkerd et al., 2022, Li et al., 2023, Niegodajew et al., 2022). The aspect ratio (AR) was considered a critical property of cylindrical granules. In manufacturing, cylindrical granules’ filling rate, random loose packing (Zhang et al., 2021), fluidization in fluidized bed (Ma et al., 2017), and mixing situation (Iniyatova et al., 2022) were significantly associated with the AR. In addition, Boribayeva et al. simulated the compact formed by cylinders under gravity deposition using the discrete element method (Boribayeva et al., 2021). It was found that the median local packing density decreased for compacts composed of cylinders with a high AR. However, in practice, the relationships between AR and the tableting process are still unclear.

This study aims to elucidate the effects of cylindrical granules’ AR on the tableting process. At first, mesalazine (MSZ) cylindrical granules with different AR were prepared by extrusion. Then, their length, width, AR, morphology, bulk and tapped densities, crushing strength, and specific surface area (SSA) were characterized. Besides, various mathematical models and X-ray microtomography were adopted to study the tableting process. Finally, the dissolution tests of MSZ tablets were conducted. This study clarified the role of AR in the tableting process and had significant guidance for the actual production and application of cylindrical granules.