In-situ Internal Study of Liquid Binder Penetration and Nucleation Dynamics in Wet Granulation of Pharmaceutical Powders using Synchrotron X-ray Imaging

Wet granulation is a common form of granulation with a liquid binder, having broad applications in the chemical and pharmaceutical industries. In order to produce high-quality granules, it is essential to continuously monitor the granule's microstructure during the granulation process. Wet granulation is a fast process and pharmaceutical powders are typically opaque in nature. So conventional methods cannot capture wet granulation internally. In contrast, synchrotron X-ray imaging techniques allow for visualization of the internal fast process due to higher photon flux, compared to lab-based X-ray imaging. This study employed the synchrotron X-ray imaging technique to examine the internal characteristics of powder beds and how they influence the dynamics of single droplet penetration and the microstructure of the dry granule. The single-drop impact method was used to obtain in-depth knowledge of the process of wet granulation. In this study, the liquid binders were deionized water and isopropanol, and the powders were binary mixtures of acetaminophen (APAP) as the active pharmaceutical component, with lactose monohydrate (LMH) and microcrystalline cellulose (MCC), two common excipients. An internal analysis of powders revealed that, for particles of various sizes, increasing the excipient led to the presence of more void spaces and thereby increased the porosity. It is essential to understand the powder's mixing quality before granulation. A higher mixing quality was obtained by increasing the APAP component. In general, MCC mixtures exhibited fewer aggregations and more uniform pore distribution than those from LMH ones. The spreading and vertical imbibition of an isopropanol droplet during penetration exhibited competing behaviors, demonstrating that penetration in coarse MCC powders followed a more linear vertical movement, mostly because of aligned pore distribution. For the first time, the internal rapid nucleation with liquid binders was studied. Granules in more uniformly distributed, coarser, and homogeneous powders experienced a faster rate of pore evolution during the nucleation. Wetting investigations revealed that the non-uniform pore distribution in powder beds was responsible for the Crater mechanism for the majority of the 50% of excipients. For MCC with the largest droplet diameter growth, the Spreading mechanism was observed, and for 90% of fine LMH with the longest penetration length, the Tunneling occurred. The spreading and Tunneling mechanisms produced final granules with the highest and lowest porosity, respectively. In-situ monitoring of the wet granulation process using synchrotron X-ray imaging was demonstrated in this work, and for the first time, data on pore studies throughout the nucleation and growth stages were provided. This study revealed how wet granulation and the resulting granules were affected by liquid-powder interactions. The new information gained from this research will be highly helpful for choosing the desirable powders and process conditions for granulation processes in the chemical and pharmaceutical industries