Micro-dosing of powders into capsules using a new automated micro-dosing system: effect of powder characteristics and operating conditions on the filling of 0.5 mg-100 mg weights.

OBJECTIVE: To demonstrate the applicability of a novel micro-dosing system for precisely filling low powder doses (down to a few mg) into capsules along with weighing the filled powder mass accurately. METHODS: Ten commonly used pharmaceutical powders, ranging from cohesive to free-flowing, were selected and filled at three target fill weights (0.5, 1, and 10 mg), to investigate the effect of distinct powder properties on the filling performance. The fill weight and variability, filling speed and yield (% and number of conforming capsules out of all capsules collected), as well as the system's long-term performance were assessed. RESULTS: The filling accuracy was found to be good for all investigated powders. In particular, the results demonstrate that the tested powders, including the challenging cohesive ones, could be dosed at standard deviations within 0.23 mg at a 10 mg target weight, within 0.07 mg at a 1 mg target weight, and within 0.05 mg at a 0.5 mg target weight. In all cases, free-flowing powders showed lower standard deviations. Intermediate and cohesive powders had slightly higher standard deviations but were still within an acceptable range. CONCLUSION: The study shows the suitability of the tested micro-dosing system for filling low powder doses into capsules, which is of particular importance for dosing active pharmaceutical ingredients (APIs) directly in capsules, i.e. an API-in-capsule (AIC) approach for clinical trials (often in conjunction with highly potent APIs), and for low-dose powder filling for inhalation applications.

Modeling the coating layer thickness in a pharmaceutical coating process.

Although mechanistic numerical simulations can offer great insights into a process, they are limited with respect to resolved process time. While statistical models provide long-term predictability, determining the underlying probability distributions is often challenging. In this work, detailed CFD-DEM simulations of a pharmaceutical Wurster coating process for microspheres are used to evaluate the input parameters for a novel Monte-Carlo simulation approach. The combined strengths of both modeling approaches make it possible to predict the coating mass and thickness distributions over the entire process time. It was observed that smaller beads receive a thicker coating layer since they pass the spray zone closer to the nozzle. Moreover, it was established that, in contrast to the airflow rate, the spray rate has a great impact on the inter-particle coating variability. A stochastic model was developed to investigate the relative contribution of coating layer variability and fill weight variability to the product non-uniformity in a capsule filling process of Multiple Unit Pellet Systems (MUPS).

How to measure coating thickness of tablets: Method comparison of optical coherence tomography, near-infrared spectroscopy and weight-, height- and diameter gain.

Film coating of pharmaceutical dosage forms, such as tablets and pellets, can be used to tailor the drug release profile. With that regard, a uniform coating thickness of a single tablet (intra-tablet), all tablets (inter-tablet) and subsequent batches (inter-batch) is crucial. We present a method comparison between in-line (optical coherence tomography and near-infrared spectroscopy) and well-established off-line (height-, weight- and diameter-gain) approaches to determining the coating thickness of tablets. We used single tablets drawn during a commercial coating process. Comparing the low intra- and high inter-tablet coating variability indicated that the tablets had a broad distribution of spray zone passes but at a random tablet orientation. Even at the end of the coating process at a mean coating thickness of about 70 µm, the inter-tablet standard deviation was about 9 µm or 13% relative standard deviation. Determining correlations between the methods identified the factors that contribute to the measurement uncertainty and bias for each method. Ultimately, we aimed to establish that in-line methods match or even surpass the conventional off-line reference methods in terms of accuracy and precision of coating thickness measurement.

Sensitivity of a continuous hot-melt extrusion and strand pelletization line to control actions and composition variation.

The purpose of this work was to develop a robust hot-melt extrusion and strand pelletization process for manufacturing pellets with an immediate release (IR) of a poorly water-soluble active pharmaceutical ingredient (API), nimodipine. The robustness of pharmaceutical continuous manufacturing processes and of its control strategy is vital for competitiveness to traditional batch-manufacturing. Therefore, first the sensitivity of product quality, process stability, and process monitoring tools to i) parameter changes due to control actions and ii) typical process deviations, i.e., feeding errors, was investigated in a design of experiments (DoE). Thereby, die melt pressure was found to be highly sensitive to composition deviations, i.e. a limiting factor for process stability. Especially critical were deviations to increased HPMC content, since it behaved as a filler in the melt. Pelletization, or pellet size and size distribution respectively, were found to be sensitive to an increased throughput, due to the resulting insufficient strand cooling before the pelletizer. API dissolution in contrast, was found to be robust across the entire investigated range of formulation and process settings. Second, a design space for the production of IR pellets for subsequent tableting was established, and finally, a technical control strategy was developed to ensure a robust process. Near-infrared (NIR) spectroscopy was applied to monitor API content and the sensitivity of the residence time distribution (RTD) was investigated by means of tracer measurements. NIR-based API content monitoring and RTD models for material tracking were found to be at risk after processing melt with high HPMC content, due to a lack of purging by less viscous formulation compositions.

Formulation performance and processability window for manufacturing a dual-polymer amorphous solid dispersion via hot-melt extrusion and strand pelletization.

This work evaluates several compositions of an amorphous solid dispersion (ASD) comprising nimodipine (NMD) as poorly soluble model API in a dual-polymer carrier system. HPMC E5 and Eudragit E were used for the two polymeric carriers. The formulation was designed for hot-melt extrusion (HME) and subsequent strand pelletization. The aim was to identify a formulation window with desired functional ASD performance, i.e. physical stability and immediate API release, as well as processability in strand pelletization. Samples were prepared using small-scale methods, such as vacuum compression molding (VCM) and benchtop extrusion. Miscibility and phase studies were performed for a wide range of polymer ratios and three levels of API content (10-30% w/w). Ternary ASD formulations were phase-separated, yet physically stable upon exposure to elevated temperature/humidity. A study of phase composition showed that the drug molecules were predominantly solubilized in the Eudragit E fraction of the formulation. The miscibility study and Fourier-transform infrared spectroscopy indicated hydrogen (H)bond interactions between NMD and Eudragit E. In HPMC, the amorphous API was dispersed in polymeric matrix and stabilized due to anti-plasticization and the disruption of intermolecular Hbonding between API molecules. Concerning processability in strand pelletization the formulation is limited at high Eudragit E content. NMD and EE-rich phases exhibit low mixture glass transition, low melt stability and brittle breaking behavior upon strand cutting. The high viscosity and yield point of HPMC contributes to the mechanical robustness of the strand at temperatures relevant for processing. Formulation-intrinsic dissolution rates in VCM ASDs developed as an irregular function of polymer ratio, associated with diverse and competitive dissolution mechanisms in the polymers. With regard to the binary system of NMD with HPMC E5, surface crystallization was observed in VCM ASDs. For extruded pellets this was not the case, and a steady trend of formulation-intrinsic dissolution rate across different polymer ratios was observed. These discrepancies indicated a major influence of shear stress during sample preparation on HPMC-based ASD performance. Finally, a feasible formulation window within a polymer ratio of 1:2-2:3 Eudragit E:HPMC was identified in which Eudragit E acts as a dissolution rate enhancer and ASD stabilizer during dissolution.

RTD-based material tracking in a fully-continuous dry granulation tableting line.

Continuous manufacturing (CM) offers quality and cost-effectiveness benefits over currently dominating batch processing. One challenge that needs to be addressed when implementing CM is traceability of materials through the process, which is needed for the batch/lot definition and control strategy. In this work the residence time distributions (RTD) of single unit operations (blender, roller compactor and tablet press) of a continuous dry granulation tableting line were captured with NIR based methods at selected mass flow rates to create training data. RTD models for continuous operated unit operations and the entire line were developed based on transfer functions. For semi-continuously operated bucket conveyor and pneumatic transport an assumption based the operation frequency was used. For validation of the parametrized process model, a pre-defined API step change and its propagation through the manufacturing line was computed and compared to multi-scale experimental runs conducted with the fully assembled continuous operated manufacturing line. This novel approach showed a very good prediction power at the selected mass flow rates for a complete continuous dry granulation line. Furthermore, it shows and proves the capabilities of process simulation as a tool to support development and control of pharmaceutical manufacturing processes.

Study of a low-dose capsule filling process by dynamic and static tests for advanced process understanding.

Precise filling of capsules with doses in the mg-range requires a good understanding of the filling process. Therefore, we investigated the various process steps of the filling process by dynamic and static mode tests. Dynamic tests refer to filling of capsules in a regular laboratory dosator filling machine. Static tests were conducted using a novel filling system developed by us. Three grades of lactose excipients were filled into size 3 capsules with different dosing chamber lengths, nozzle diameters and powder bed heights, and, in the dynamic mode, with two filling speeds (500, 3000 caps/h). The influence of the gap at the bottom of the powder container on the fill weight and variability was assessed. Different gaps resulted in a change in fill weight in all materials, although in different ways. In all cases, the fill weight of highly cohesive Lactohale 220 increased when decreasing the gap. Furthermore, experiments with the stand-alone static test tool indicated that this very challenging powder could successfully be filled without any pre-compression in the range of 5 mg-20 mg with acceptable RSDs. This finding is of great importance since for very fine lactose powders high compression ratios (dosing-chamber-length-to-powder-bed height compression ratios) may result in jamming of the piston. Moreover, it shows that the static mode setup is suitable for studying fill weight and variability. Since cohesive powders, such as Lactohale 220, are hard to fill, we investigated the impact of vibration on the process. Interestingly, we found no correlation between the reported fill weight changes in dynamic mode at 3000 cph and static mode using similar vibration. However, we could show that vibrations during sampling in the static mode dramatically reduced fill weight variability. Overall, our results indicate that by fine-tuning instrumental settings even very challenging powders can be filled with a low-dose dosator capsule filling machine. This study is a further step towards a scientific qualification of dosator nozzles for low-fill weight (1-45 mg) capsule filling.

Mechanistic modeling of a capsule filling process.

Filling a dosator nozzle moving into a powder bed was investigated using the Discrete Element Method (DEM). Various particle diameters and contact properties were modeled. The simulations qualitatively showed the influence of powder properties on the amount of dosed powder. Two factors that influence the dosed mass were observed. First, the ratio between the particle and dosator diameters affects the packing of particles inside the dosator chamber. Second, the flow behavior of the powder significantly modifies its filling and compression behavior. Cohesive powders pack less densely inside the powder bed, which could lead to a lower amount of dosed powder. In contrast, cohesive powders are compressed more during dosing and the density inside the dosator chamber increases during the dosing process. Since the simulation of fine cohesive powders is numerically impossible due to a high number of particles and small simulation time steps, we applied a simple method for particle scaling to acquire a qualitative understanding of the filling behavior of coarse and fine powders.

Comparison of video analysis and simulations of a drum coating process.

Tablet coating is a common unit operation in the pharmaceutical industry. To improve currently established processes, it is important to understand the influence of the process parameters on the coating quality. One of the critical parameters is the tablet velocity. In this work, numerical results are compared to results obtained experimentally. Tablet movement in the drums was simulated using the Discrete Element Method (DEM). The simulation parameters were adapted to fit the simulation to the experimental data. A comparison of the experimental and simulation results showed that the simulation correctly represents the real tablet velocity. A change in the velocity over time and its dependence on the rotation rates and the baffle position in the simulation were similar to the experimental results. In summary, simulations can improve the understanding of tablet coating processes and will thus provide insights into the underlying process mechanics, which cannot be obtained via ordinary experiments.

Micro-feeding and dosing of powders via a small-scale powder pump.

Robust and accurate powder micro-feeding (<100mg/s) and micro-dosing (<5 mg) are major challenges, especially with regard to regulatory limitations applicable to pharmaceutical development and production. Since known micro-feeders that yield feed rates below 5mg/s use gravimetric feeding principles, feed rates depend primarily on powder properties. In contrast, volumetric powder feeders do not require regular calibration because their feed rates are primarily determined by the feeder's characteristic volume replacement. In this paper, we present a volumetric micro-feeder based on a cylinder piston system (i.e., a powder pump), which allows accurate micro-feeding and feed rates of a few grams per hours even for very fine powders. Our experimental studies addressed the influence of cylinder geometries, the initial conditions of bulk powder, and the piston speeds. Additional computational studies via Discrete Element Method simulations offered a better understanding of the feeding process, its possible limitations and ways to overcome them. The powder pump is a simple yet valuable tool for accurate powder feeding at feed rates of several orders of magnitude.

Continuous monitoring of API content, API distribution and crushing strength after tableting via near-infrared chemical imaging.

Near-infrared chemical imaging (NIR-CI) with high-speed cameras based on the push-broom acquisition principle is a rapidly-evolving and can be used for a variety of purposes, from classification (and sorting) of products to mapping spatial distribution of materials. The present study examined if NIR-CI is suitable for tablet manufacturing. To that end, the tablets were introduced into the CI system via a flat belt conveyor. A formulation, which consisted of 4wt.%-6wt.% caffeine, 5wt.% crospovidone as a disintegrant, 88wt.%-90wt.% lactose as a filler and 1wt.% magnesium stearate as a lubricator, was tableted at compression forces ranging from 5kN to 30kN. The intra- and inter-tablet homogeneity of caffeine and the tablet's hardness were analyzed via NIR-CI. For the homogeneity evaluation, two methods were applied: standard deviation (SD) and distributional homogeneity index (DHI). The results showed that the SD of caffeine in a single tablet increased with an increase in the caffeine content. This was attributed to natural variations in a binary mixture of caffeine and excipients. Overall, the chosen NIR-CI setup has strong potential to be transferred to the production scale to monitor all tablets in a production stream.

The effect of material attributes and process parameters on the powder bed uniformity during a low-dose dosator capsule filling process.

The objective of this work was to assess the effect of process parameters of a dosator nozzle machine on the powder bed uniformity of inhalation powders with various characteristics during a low-dose dosator capsule filling process. Three grades of lactose excipients were extensively characterized and filled into size 3 capsules using different dosing chamber lengths (2.5, 5mm), nozzle diameters (1.9, 3.4mm), powder bed heights (5, 10mm) and filling speeds (500, 3000capsules/h). The fill weight and the weight variability of Lactohale 100 (large particles, good flowability, low cohesion) remained almost the same, regardless of the process parameters throughout the capsule filling run time. Moreover, for this powder an increase in the fill weight at a higher filling speed was observed in all cases. Fill weight variability was significantly higher for lower dosing chamber volumes at a filling speed of 3000 capsules per hour. Lactohale 220 (small particles, poor flowability, high cohesion) delivered entirely different results. After a certain run time, depending on instrumental settings, a 'steady-state' with constant fill weights and low weight variability was achieved. For this highly cohesive powder, a high dosing chamber volume requires a low filling speed in order for the powder to completely fill the dosator nozzle. Moreover, it was established that a dosing chamber length of 2.5mm and a powder bed height of 10mm were required due to the powder's high fill weight variability over time, while the dosator size had no effect on it. In summary, the layer uniformity, the fill weight and the weight variability strongly depend on the powder characteristics and the instrumental settings. The results indicate that Lactohale 220 requires special attention during low-dose capsule filling. The study presents excellent insights into the effect of material attributes and process parameters on the layer uniformity and the quality of end product.

Multi-methodological investigation of the variability of the microstructure of HPMC hard capsules.

The objective of this study was to analyze differences in the subtle microstructure of three different grades of HMPC hard capsule shells using mechanical, spectroscopic, microscopic and tomographic approaches. Dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), vibrational spectroscopic, X-Ray scattering techniques as well as environmental scanning electron microscopy (ESEM) and optical coherence tomography (OCT) were used. Two HPMC capsules manufactured via chemical gelling, one capsule shell manufactured via thermal gelling and one thermally gelled transparent capsule were included. Characteristic micro-structural alterations (associated manufacturing processes) such as mechanical and physical properties relevant to capsule performance and processability were thoroughly elucidated with the integration of data obtained from multi-methodological investigations. The physico-chemical and physico-mechanical data obtained from a gamut of techniques implied that thermally gelled HPMC hard capsule shells could offer an advantage in terms of machinability during capsule filling, owing to their superior micro- and macroscopic structure as well as specifically the mechanical stability under dry or humid conditions.

Simulation of a tablet coating process at different scales using DEM.

Spray coating of tablets is an important unit operation in the pharmaceutical industry and is mainly used for modified release, enteric protection, better appearance and brand recognition. It can also be used to apply an additional active pharmaceutical ingredient to the tablet core. Scale-up of such a process is an important step in commercialization. However, scale-up is not trivial and frequently, at manufacturing scales the required coating quality cannot be reached. Thus, we propose a method where laboratory experiments are carried out, yet scale-up is done via computational methods, i.e., by extrapolating results to larger scales. In the recent years, the Discrete Element Method (DEM) has widely been used to simulate tablet behavior in a laboratory scale drum coater. Due the increasing computational power and more sophisticated DEM algorithms, it has become possible to simulate millions of particles on regular PCs and model industrial scale tablet coating devices. In this work, simulations were performed on the laboratory, pilot and industrial scales and DEM was used to study how different scale-up rules influence the bed behavior on larger scales. The material parameters of the tablets were measured in the laboratory and a glued sphere approach was applied to model the tablet shape. The results include a vast amount of qualitative and quantitative data at the different scales. In conclusion, the evolution of the inter-tablet coating variation for the different scales and process parameters is presented. The results suggest that keeping the Froude number constant during the scale up process leads to faster processes as the cycle time is shorter and the spray residence time is more uniform when compared to keeping the circumferential velocity constant.

Continuous feeding of low-dose APIs via periodic micro dosing.

Precise and effective feeding of small powder quantities remains a challenge in many fields, including pharmaceutical development and production. This paper demonstrates that a simple feeding principle can be applied to accomplish stable micro feeding (<100mg/s) and describes a gravimetric powder feeding system with a vibratory sieve mounted on a chute. Feeding was induced via vertical vibrations that can be adjusted within a broad range of frequencies and amplitudes. The feeding system was studied using different frequencies, amplitudes, sieves and powder properties. Feeding was characterized by means of a dynamic scale and high-speed camera recordings. The feeding system provided effective powder feeding even in a range of 1-2mg/s. It was shown that powder properties require special attention when the vibratory sieve-chute system operates at higher feed rates (or feeding times >30min), i.e., feeding at a higher throughput. A combination of discrete element method (DEM) simulations and compartment population balance model (PBM) was used to incorporate the proposed micro feed system into a continuous powder mixer (Gerike GCM250; Gerike Holding LTD., Regensdorf, Switzerland). It illustrates how oscillating feeding rates (the latter is a characteristic of the studied micro feeding system) affect the content uniformity of low dose blends, i.e., powder mixtures with a relatively low fraction of active pharmaceutical ingredient.

Injection molding as a one-step process for the direct production of pharmaceutical dosage forms from primary powders.

The objective of the present study was to develop a one-step process for the production of tablets directly from primary powder by means of injection molding (IM), to create solid-dispersion based tablets. Fenofibrate was used as the model API, a polyvinyl caprolactame-polyvinyl acetate-polyethylene glycol graft co-polymer served as a matrix system. Formulations were injection-molded into tablets using state-of-the-art IM equipment. The resulting tablets were physico-chemically characterized and the drug release kinetics and mechanism were determined. Comparison tablets were produced, either directly from powder or from pre-processed pellets prepared via hot melt extrusion (HME). The content of the model drug in the formulations was 10% (w/w), 20% (w/w) and 30% (w/w), respectively. After 120min, both powder-based and pellet-based injection-molded tablets exhibited a drug release of 60% independent of the processing route. Content uniformity analysis demonstrated that the model drug was homogeneously distributed. Moreover, analysis of single dose uniformity also revealed geometric drug homogeneity between tablets of one shot.

Analysis of large-scale tablet coating: Modeling, simulation and experiments.

This work concerns a tablet coating process in an industrial-scale drum coater. We set up a full-scale Design of Simulation Experiment (DoSE) using the Discrete Element Method (DEM) to investigate the influence of various process parameters (the spray rate, the number of nozzles, the rotation rate and the drum load) on the coefficient of inter-tablet coating variation (cv,inter). The coater was filled with up to 290kg of material, which is equivalent to 1,028,369 tablets. To mimic the tablet shape, the glued sphere approach was followed, and each modeled tablet consisted of eight spheres. We simulated the process via the eXtended Particle System (XPS), proving that it is possible to accurately simulate the tablet coating process on the industrial scale. The process time required to reach a uniform tablet coating was extrapolated based on the simulated data and was in good agreement with experimental results. The results are provided at various levels of details, from thorough investigation of the influence that the process parameters have on the cv,inter and the amount of tablets that visit the spray zone during the simulated 90s to the velocity in the spray zone and the spray and bed cycle time. It was found that increasing the number of nozzles and decreasing the spray rate had the highest influence on the cv,inter. Although increasing the drum load and the rotation rate increased the tablet velocity, it did not have a relevant influence on the cv,inter and the process time.

Development of a design space and predictive statistical model for capsule filling of low-fill-weight inhalation products.

The objectives of this study were to develop a predictive statistical model for low-fill-weight capsule filling of inhalation products with dosator nozzles via the quality by design (QbD) approach and based on that to create refined models that include quadratic terms for significant parameters. Various controllable process parameters and uncontrolled material attributes of 12 powders were initially screened using a linear model with partial least square (PLS) regression to determine their effect on the critical quality attributes (CQA; fill weight and weight variability). After identifying critical material attributes (CMAs) and critical process parameters (CPPs) that influenced the CQA, model refinement was performed to study if interactions or quadratic terms influence the model. Based on the assessment of the effects of the CPPs and CMAs on fill weight and weight variability for low-fill-weight inhalation products, we developed an excellent linear predictive model for fill weight (R(2 )= 0.96, Q(2 )= 0.96 for powders with good flow properties and R(2 )= 0.94, Q(2 )= 0.93 for cohesive powders) and a model that provides a good approximation of the fill weight variability for each powder group. We validated the model, established a design space for the performance of different types of inhalation grade lactose on low-fill weight capsule filling and successfully used the CMAs and CPPs to predict fill weight of powders that were not included in the development set.

Accuracy of micro powder dosing via a vibratory sieve-chute system.

This paper describes a powder dosing system with a vibratory sieve mounted on a chute that doses particles into a capsule. Vertical vibration occurred with a broad range of frequencies and amplitudes. During dosing events, the fill weight was accurately recorded via a capacitance sensor, covering the capsules and making it possible to analyze filling characteristics, that is, the fill rates and their robustness. The range of frequencies and amplitudes was screened for settings that facilitated reasonable (no blocking, no spilling) fill rates for three lactose powders. The filling characteristics were studied within this operating space. The results reveal similar operating spaces for all investigated powders. The fill rate robustness varied distinctly in the operating space, which is of prime importance for selecting the settings for continuous feeding applications. In addition, we present accurate dosing studies utilizing the knowledge about the filling characteristics of each powder.

Continuous API-crystal coating via coacervation in a tubular reactor.

We present a proof-of-concept study of a continuous coating process of single API crystals in a tubular reactor using coacervation as a microencapsulation technique. Continuous API crystal coating can have several advantages, as in a single step (following crystallization) individual crystals can be prepared with a functional coating, either to change the release behavior, to protect the API from gastric juice or to modify the surface energetics of the API (i.e., to tailor the hydrophobic/hydrophilic characteristics, flowability or agglomeration tendency, etc.). The coating process was developed for the microencapsulation of a lipophilic core material (ibuprofen crystals of 20 µm- to 100 µm-size), with either hypromellose phthalate (HPMCP) or Eudragit L100-55. The core material was suspended in an aqueous solution containing one of these enteric polymers, fed into the tubing and mixed continuously with a sodium sulfate solution as an antisolvent to induce coacervation. A subsequent temperature treatment was applied to optimize the microencapsulation of crystals via the polymer-rich coacervate phase. Cross-linking of the coating shell was achieved by mixing the processed material with an acidic solution (pH<3). Flow rates, temperature profiles and polymer-to-antisolvent ratios had to be tightly controlled to avoid excessive aggregation, leading to pipe plugging. This work demonstrates the potential of a tubular reactor design for continuous coating applications and is the basis for future work, combining continuous crystallization and coating.