Experimental studies on the effect of moisture content and volume resistivity on electrostatic behaviour of pharmaceutical powders

Prediction of the Effective Work Function of Aspirin and Paracetamol Crystals by Density Functional Theory-A First-Principles Study

Crystals of active pharmaceutical ingredients (API) are prone to triboelectric charging due to their dielectric nature. This characteristic, coupled with their typically low density and often large aspect ratio, poses significant challenges in the manufacturing process. The pharmaceutical industry frequently encounters issues during the secondary processing of APIs, such as particle adhesion to walls, clump formation, unreliable flow, and the need for careful handling to mitigate the risk of fire and explosions. These challenges are further intensified by the limited availability of powder quantities for testing, particularly in the early stages of drug development. Therefore, it is highly desirable to develop predictive tools that can assess the triboelectric propensity of APIs. In this study, Density Functional Theory calculations are employed to predict the effective work function of different facets of aspirin and paracetamol crystals, both in a vacuum and in the presence of water molecules on their surfaces. The calculations reveal significant variations in the work function across different facets and materials. Moreover, the adsorption of water molecules induces a shift in the work function. These findings underscore the considerable impact of distinct surface terminations and the presence of molecular water on the calculated effective work function of pharmaceuticals. Consequently, this approach offers a valuable predictive tool for determining the triboelectric propensity of APIs.

Study of Diminutive Granules as Feed Powders for Manufacturability of High Drug Load Minitablets

The maximal amount of drug contained in a minitablet is limited. To reduce the total number of minitablets in a single dose, high drug load minitablets can be prepared from high drug load feed powders by various pharmaceutical processing techniques. Few researchers have however examined the influence of pharmaceutical processing techniques on the properties of high drug load feed powders, and consequently the manufacturability of high drug load minitablets. In this study, silicification of the high drug load physical mix feed powders alone did not yield satisfactory quality attributes and compaction parameters to produce good quality minitablets. The abrasive nature of fumed silica increased ejection force and damage to the compaction tools. Granulation of fine paracetamol powder was crucial for the preparation of good quality high drug load minitablets. The diminutive granules had superior powder packing and flow properties for homogenous and consistent filling of the small die cavities when preparing minitablets. Compared to the physical mix feed powders for direct compression, the granules which possessed higher plasticity, lower rearrangement and elastic energies, yielded better quality minitablets with high tensile strength and rapid disintegration time. High shear granulation demonstrated greater process robustness than fluid bed granulation, with less discernment on the quality attributes of feed powder. It could proceed without fumed silica, with the high shear forces reducing interparticulate cohesivity. An in-depth understanding on the properties of high drug load feed powders with inherently poor compactability and poor flowability is important for the manufacturability of high drug load minitablets.

Effects of adding methods and modification types of cellulose on the physicochemical properties of starch/PBAT blown films

This study revealed the relationship between cellulose types/adding methods and film properties, in which sodium carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose (HPMC), and microcrystalline cellulose (MCC) were added into starch/PBAT blown films in powder, aqueous solution, and emulsion forms, respectively. Cellulose interacted with starch networks via hydrogen bonds, and those added in emulsion form made more homogeneous film morphologies. MCC emulsion enhanced the film strength (40%) and modulus (149%) to the greatest extent, while comprehensively, HPMC emulsion possessed better reinforcement effects on the films, which increased mechanical properties (31% ~ 100%), moisture barrier (20%), oxygen barrier (93%), surface hydrophobicity (20%), as well as water resistance (12% ~ 76%). Findings supported the application of cellulose in high-throughput biodegradable films, and the high-content starch/PBAT blown films reinforced by HPMC emulsion had great potential in commercial packaging fields.

Charge Reduction Assisted Production of Diminutive Fluid Bed Granules for High Drug Load Minitablets

Micronized drug powders are generally unsuitable as tableting feed to produce minitablets due to their cohesivity and poor flow. The silicification of fine paracetamol powder (PCM_F) with an optimal concentration range of fumed silica (fSi) [0.7 - 0.9 %, w/w] reduced the net negative charge of PCM_F and improved powder flow. The optimal fSi concentration range suitable was established through the measurement of charge and flowability of the silicified powders. Silicification of PCM_F by physical mix did not satisfactorily overcome the cohesive forces between the PCM_F crystals and improve powder flow sufficiently such that it will feed consistently into the smaller die orifices during tableting. Using a specialized fluid bed system with swirling air and side spray, controlled granulation of silicified PCM_F packed and agglomerated the interlocking-prone needle shaped PCM_F crystals into diminutive granules that are more spherical and free flowing. With optimized fSi concentration (≈ 0.8 %, w/w) and granulation process parameters, high drug load diminutive granules (D₅₀≃ 90 μm) were successfully prepared from PCM_F as starter seeds (D₅₀≃ 30 μm). Minitablets prepared from the diminutive granules had low weight variation, and were mechanically strong with disintegration time of less than 30 s. This study demonstrated the feasibility of producing high drug load minitablets from a cohesive, electrostatic-prone fine drug powder.

Discrete Element Modeling (DEM) based investigation of tribocharging in the pharmaceutical powders during hopper discharge

Triboelectric charging is defined as the phenomenon of charge transfer between two different material surfaces when they are brought into contact and separated. The focus of this research is the development of a Discrete Element Method (DEM) based simulation model to predict tribocharging during hopper discharge. Due to decreased particle-wall interactions and reduced particle wall contact times, net charges generated during hopper discharge are low. The simulation model confirmed this effect and was implemented to predict the triboelectric behavior of glass beads and MCC particles during hopper flow, along with the prediction of percent charged and uncharged particles. Approximately one-third of the particles were predicted to remain uncharged during the hopper discharge simulations for mono-dispersed particles, thus rendering a comparatively high amount of charge distribution into a small concentration of materials. The DEM model acted as a tool to predict charges that can be generated during hopper discharge at a specified geometry, with a potential to mitigate particle charging, when used for appropriate selection of hopper angles, and hopper wall materials.

A Simplex Centroid Design to Quantify Triboelectric Charging in Pharmaceutical Mixtures

The present study focuses on the implementation of a modified simplex centroid statistical design to predict the triboelectrification phenomenon in pharmaceutical mixtures. Two drugs (Ibuprofen and Theophylline), 2 excipients (lactose monohydrate and microcrystalline cellulose/MCC), and 2 blender wall materials (aluminum and poly-methyl methacrylate) were studied to identify the trends in charge transfer in pharmaceutical blends. The statistical model confirmed the excipient-drug interactions, irrespective of the blender wall materials, as the most significant factor leading to reduced charging. Also, lactose monohydrate was able to explain the charge variability more consistently compared with MCC powders when used as secondary material. The ratio of the individual components in the blends explained almost 80% of the bulk charging for Ibuprofen mixtures and 70% for Theophylline mixtures. The study also explored the potential lack of efficacy of lactose-MCC as a combination in ternary systems when compared with binary mixtures, for impacts on charge variability in pharmaceutical blends.

Quantification of Moisture-Induced Cohesion in Pharmaceutical Mixtures

Moisture-induced flow variabilities in pharmaceutical blends lead to multiple impediments during manufacturing of solid dosage formulations. Processing and storage humidity conditions both govern the moisture contents of the pharmaceutical mixtures and bear significant impact on the final product quality. In this study, experimentally validated discrete element method-based computational models along with statistical formalism have been implemented to develop a predictive tool for moisture-induced cohesion in binary and tertiary mixtures. V-blending was applied to prepare the pharmaceutical blends, and mixing characterization was performed using a Raman PhAT probe. Optimum fill volume was established for the mixing conditions to minimize static charging due to blender wall interactions on the pharmaceutical powders. A simplex-centroid (augmented) design for 3-component system was implemented to predict and quantify the nonlinear behavior of moisture-induced cohesion between the pharmaceutical powders based on their systematic hopper discharge studies (experiments and simulations). A methodical implementation of these quantification tools was hence performed to validate a design space that enables an approach to the appropriate selection of blend concentrations that achieve minimum mixture flow variability across different humidity conditions.