Investigation into powder tribo-charging of pharmaceuticals. Part II: Sensitivity to relative humidity

Reviewing the Impact of Powder Cohesion on Continuous Direct Compression (CDC) Performance

The pharmaceutical industry is undergoing a paradigm shift towards continuous processing from batch, where continuous direct compression (CDC) is considered to offer the most straightforward implementation amongst powder processes due to the relatively low number of unit operations or handling steps. Due to the nature of continuous processing, the bulk properties of the formulation will require sufficient flowability and tabletability in order to be processed and transported effectively to and from each unit operation. Powder cohesion presents one of the greatest obstacles to the CDC process as it inhibits powder flow. As a result, there have been many studies investigating potential manners in which to overcome the effects of cohesion with, to date, little consideration of how these controls may affect downstream unit operations. The aim of this literature review is to explore and consolidate this literature, considering the impact of powder cohesion and cohesion control measures on the three-unit operations of the CDC process (feeding, mixing, and tabletting). This review will also cover the consequences of implementing such control measures whilst highlighting subject matter which could be of value for future research to better understand how to manage cohesive powders for CDC manufacture.

Assessment of Tribo-charging and Continuous Feeding Performance of Direct Compression Grades of Isomalt and Mannitol Powders

Tribo-charging is often a root cause of mass flow deviations and powder adhesion during continuous feeding. Thus, it may critically impact product quality. In this study, we characterized the volumetric (split- and pre-blend) feeding behavior and process-induced charge of two direct compression grades of polyols, galenIQ™ 721 (G721) for isomalt and PEARLITOL^® 200SD (P200SD) for mannitol, under different processing conditions. The feeding mass flow range and variability, hopper end fill level, and powder adhesion were profiled. The feeding-induced tribo-charging was measured using a Faraday cup. Both materials were comprehensively characterized for relevant powder properties, and their tribo-charging was investigated for its dependence on particle size and relative humidity. During split-feeding experiments, G721 showed a comparable feeding performance to P200SD with lower tribo-charging and adhesion to the screw outlet of the feeder. Depending on the processing condition, the charge density of G721 ranged from -0.01 up to -0.39 nC/g, and for P200SD from -3.19 up to -5.99 nC/g. Rather than differences in the particle size distribution of the two materials, their distinct surface and structural characteristics were found as the main factors affecting their tribo-charging. The good feeding performance of both polyol grades was also maintained during pre-blend feeding, where reduced tribo-charging and adhesion propensity was observed for P200SD (decreasing from -5.27 to -0.17 nC/g under the same feeding settings). Here, it is proposed that the mitigation of tribo-charging occurs due to a particle size-driven mechanism.

Recent developments in the computational simulation of dry powder inhalers

This article reviews recent developments in computational modeling of dry powder inhalers (DPIs). DPIs deliver drug formulations (sometimes blended with larger carrier particles) to a patient's lungs via inhalation. Inhaler design is complicated by the need for maximum aerosolization efficiency, which is favored by high levels of turbulence near the mouthpiece, with low extrathoracic depositional loss, which requires low turbulence levels near the mouth-throat region. In this article, we review the physical processes contributing to aerosolization and subsequent dispersion and deposition. We assess the performance characteristics of DPIs using existing simulation techniques and offer a perspective on how such simulations can be improved to capture the physical processes occurring over a wide range of length- and timescales more efficiently.

Insights into the Impact of Nanostructural Properties on Powder Tribocharging: The Case of Milled Salbutamol Sulfate

The impact of the crystallinity of organic solid materials on their tribocharging propensity is well reported. However, no unequivocal explanation about the potential underlying mechanism(s) could be found so far in the literature. This study reports the effect that different degrees of crystalline disorder has on the tribocharging propensity of a small molecular organic material, salbutamol sulfate (SS). Ball-milling was used to induce structural transformations in the crystalline structure of SS. Particles with different nanostructures were produced and analyzed for their solid-state, particle properties, and tribocharging. It was found that differences in the amorphous content among the processed particles and related moisture levels had an impact on powder tribocharging. A correlation between the latter and the nanostructural properties of the particles was also established. The presence of interfaces between nanodomains of different densities and shorter average lengths within the phases seems to lead to a mitigation of charge. This suggests that undetected, subtle nanostructural differences of materials can affect powder handling and processability by altering their tribocharging. The present findings demonstrate the nanostructural implications of powder triboelectrification, which can help toward the rational design of a wide variety of organic solids.