The Role of Particle Surface Area and Adhesion Force in the Sticking Behavior of Pharmaceutical Powders

UV-VIS imaging-based investigation of API concentration fluctuation caused by the sticking behaviour of pharmaceutical powder blends

Surface powder sticking in pharmaceutical mixing vessels poses a risk to the uniformity and quality of drug formulations. This study explores methods for evaluating the amount of pharmaceutical powder mixtures adhering to the metallic surfaces. Binary powder blends consisting of amlodipine and microcrystalline cellulose (MCC) were used to investigate the effect of the mixing order on the adherence to the vessel wall. Elevated API concentrations were measured on the wall and within the dislodged material from the surface, regardless of the mixing order of the components. UV imaging was used to determine the particle size and the distribution of the API on the metallic surface. The results were compared to chemical maps obtained by Raman chemical imaging. The combination of UV and VIS imaging enabled the rapid acquisition of chemical maps, covering a substantially large area representative of the analysed sample. UV imaging was also applied in tablet inspection to detect tablets that fail to meet the content uniformity criteria. The results present powder adherence as a possible source of poor content uniformity, highlighting the need for 100% inspection of pharmaceutical products to ensure product quality and safety.

Uncovering the mechanism of Tenofovir amibufenamide fumarate punch sticking by combining direct compression experiment and computational simulation

Punch sticking during tablet manufacturing is a prevalent issue for many active pharmaceutical ingredients (APIs) encountered by the pharmaceutical industry. Tenofovir amibufenamide fumarate (TMF), a heavyweight drug for the treatment of hepatitis B, was selected as a model drug due to its tendency to punch sticking during tablet compression. In this study, the cause of sticking was explored by investigating crystal habits, excipients and structure characteristics. The difference in sticking of three crystal habits can be visually represented through direct compression experiments on powdered samples and analysis of crystal surfaces. The excipients play a direct role in decreasing the probability of sticking, and the extent of sticking can be assessed by measuring the tensile strength of the tablet. Additionally, the plasticity index was utilized to theoretically analyze the potential enhancements of four excipients. These experimental results indicate that the block-shaped crystals have superior ability of anti-sticking and that suitable excipients can significantly improve the sticking situation of TMF. Ultimately, the phenomenon of punch sticking was additionally examined through computational calculations, focusing on the mechanical characteristics of TMF molecules and intermolecular interactions. The strategy of combining experiments and simulation calculations has broader significance for the study of drug production.

Worsened punch sticking by external lubrication with magnesium stearate

External lubrication of tooling with magnesium stearate (MgSt) is a common strategy to eliminate punch sticking when compressing powders with a high sticking propensity, such as many pure active pharmaceutical ingredients (APIs). We found that it actually led to aggravated punch sticking at low compaction pressures. This counterintuitive phenomenon was explained based on interplay of forces among the punch tip, MgSt, and API. The explanation is supported by the observed effects of pressure and mechanical properties of APIs on this phenomenon.

Effects of tableting process parameters and powder lubrication levels on tablet surface temperature and moisture content

Punch sticking is a recurrent problem during the pharmaceutical tableting process. Powder moisture content plays a key role in the buildup of sticking; it evaporates due to increased tablet temperature, accumulates at the punch-tablet interface, and causes sticking through capillary force. This study investigated the effects of compaction pressure (CP), compaction speed (CS), and lubrication level (magnesium stearate (MgSt) ratio) on tablet surface temperature (TST) and tablet surface moisture content (TSMC). TST and TSMC were measured with an infrared thermal camera and near-infrared sensor, respectively. Microcrystalline cellulose was used as the tableting powder and MgSt as the lubricant. The low range of CS values (16-32 mm/s) considered in this study did not have significant effects on TST and TSMC. MgSt ratio had a significant positive effect on TST; this may be explained by the increase in powder blend effusivity with the addition of MgSt. However, MgSt ratio did not have a significant effect on TSMC. CP had a significant positive effect on both TST and TSMC. Increased CP induced higher heat generation through particle deformation and friction during the compaction phase, leading to increased TST. Furthermore, the water vapor diffusion rate through the powder bed might have increased due to the rise in thermal energy and led to further moisture accumulation at the tablet-punch interface, causing the significant positive effect of CP on TSMC. This result may explain the occurrence of sticking regardless of the CP applied during the tableting process.

A novel mixing rule model to predict the flowability of directly compressed pharmaceutical blends

In the pharmaceutical industry, powder flowability is an essential manufacturability attribute to consider when selecting the suitable manufacturing route and formulation. The selection of the formulation is usually based on the physical and chemical properties of the Active Pharmaceutical Ingredient (API) under consideration. Current industrial practice heavily relies on experimental work, which often results in significant labor and API consumption that results in higher costs. In this study we describe the development of a mixing rule to predict powder blend flowability from the flow properties of the individual components for industrial formulations manufactured via Direct Compression (DC). The mixing rule assumes that the granular solids' interactions are dominated by cohesive forces but are pragmatic to calibrate from the perspective of the typical data collated in an industrial environment. The proposed model was validated using a range of different APIs and the results show that the model can effectively predict the flowability properties of any formulation across the space of DC-relevant formulation compositions. Finally, a connection between the model and APIs properties (shape and size) was investigated via a linear correlation between the API particle properties and interparticle forces.

Sticking Detection by Repeated Compactions on a Single Tablet

"Sticking" during tablet manufacture is the term used to describe the accumulation of adhered tablet material on the punch over the course of several compaction cycles. The occurrence of sticking can affect tablet weight, image, and structural integrity and halt manufacturing operations. The earlier the risk of sticking is detected during R&D, the more options are available for mitigation and the less potential there is for significant delays and costs. The detection osf sticking, however, during the early stages of drug development is challenging due to the limitations of available material quantity. In this work, single tablet multi-compaction (STMC) and a highly sensitive laser reflection sensor are used to detect the propensity of sticking with ibuprofen powder blends. STMC can differentiate the various formulations and replicates the trends of sticking at different punch speeds. The results demonstrate the potential for STMC to be used as an extremely material sparing (requiring very few tablets) methodology for the assessment of sticking during early-stage development.

Understanding the role of magnesium stearate in lowering punch sticking propensity of drugs during compression

The sticking of active pharmaceutical ingredient (API) to the surfaces of compaction tooling, frequently referred to as punch sticking, causes costly downtime or product failures in commercial tablet manufacturing. Magnesium stearate (MgSt) is a common tablet lubricant known to ameliorate the sticking problem, even though there exist exceptions. The mechanism by which MgSt lowers punch sticking propensity (PSP) by covering API surface is sensible but not yet experimentally proven. This work was aimed at elucidating the link between PSP and surface area coverage (SAC) of tablets by MgSt, in relation to some key formulation properties and process parameters, namely MgSt concentration, API loading, API particle size, and mixing conditions. The study was conducted using two model APIs with known high PSPs, tafamidis (TAF) and ertugliflozin-pyroglutamic acid (ERT). Results showed that PSP decreases exponentially with increasing SAC by MgSt. The composition of material stuck to punch face was also explored to better understand the onset of punch sticking and the impact of possible MgSt-effected punch conditioning event.

Predicting lubricants effect on tablet sticking using ketoprofen as model drug and evaluating sticking propensity using different metals and powder rheology

Tablet sticking occurrence is a persistent, costly, and time-consuming problem that needs to be resolved. Predicting the sticking tendency of a new formulation has been very difficult during the development batches because of short runs and limited data. A model formulation comprising ketoprofen and microcrystalline cellulose was used to predict the effect of magnesium stearate and sodium stearyl fumarate on the occurrence of tablet sticking relative to different punch metals. Lubricant amounts were varied from 0.0% to 2.0 %w/w. Five different metal coupons were used to represent punch metals. The sticking index (SI) of each formulation relative to each metal coupon was determined by measuring angle of internal friction and angle of wall friction by performing shear cell test and wall friction test, respectively. The SI was used to predict each formulation's sticking tendency rank order relative to metal coupon. Both lubricants show a decrease in the powder blend's sticking propensity with increased lubricant concentration. The predicted sticking propensity rank order was then validated by the compression study. The result suggests that the SI can be used to predict tablet sticking, such as by changing the composition of the formulation or changing the punch metal during tablet compression.