A Mathematical Approach to Consider Solid Compressibility in the Compression of Pharmaceutical Powders

A modified Kushner-Moore approach to characterising small-scale blender performance impact on tablet compaction

Continuous Direct Compaction (CDC) has emerged as a promising route towards producing solid dosage forms while reducing material, development time and energy consumption. Understanding the response of powder processing unit operations, especially blenders, is crucial. There is a substantial body of work around how lubrication via batch blender operation affects tablet critical quality attributes such as hardness and tensile strength. But, aside from being batch operations, the design of these blenders is such that they operate with low-shear, low-intensity mixing at Froude number values significantly below 0.4 (Froude number Fr being the dimensionless ratio of inertial to gravitational forces). The present work explores the performance of a mini-blender which has a fundamentally different mode of operation (static vessel with rotating blades around a mixing shaft as opposed to rotating vessel with no mixing shaft). This difference allows a substantially wider operating range in terms of speed and shear (and Fr values). The present work evaluates how its performance compares to other blenders studied in the literature. Tablet compaction data from blends produced at various intensities and regimes of mixing in the mini-blender follow a common trajectory. Model equations from literature are suitably modified by inclusion of the Froude number Fr, but only for situations where the Froude number was sufficiently high (1 < Fr). The results suggest that although a similar lubrication extent plateau is eventually reached it is the intensity of mixing (i.e. captured using the Froude number as a surrogate) which is important for the lubrication dynamics in the mini-blender, next to the number of revolutions. The degree of fill or headspace, on the other hand, is only crucial to the performance of common batch blenders. Testing using alternative formulations shows the same common trend across mixing intensities, suggesting the validity of the approach to capture lubrication dynamics for this system.

Tableting behavior of freeze and spray-dried excipients in pharmaceutical formulations

Most of biopharmaceuticals, in their liquid form, are prone to instabilities during storage. In order to improve their stability, lyophilization is the most commonly used drying technique in the pharmaceutical industry. In addition, certain applications of biopharmaceutical products can be considered by oral administration and tablets are the most frequent solid pharmaceutical dosage form used for oral route. Thus, the tableting properties of freeze-dried products used as cryo and lyoprotectant could be a key element for future pharmaceutical developments and applications. In this study, we investigated the properties that might play a particular role in the specific compaction behavior of freeze-dried excipients. The tableting properties of freeze-dried trehalose, lactose and mannitol were investigated and compared to other forms of these excipients (spray-dried, commercial crystalline and commercial crystalline milled powders). The obtained results showed a specific behavior in terms of compressibility, tabletability and brittleness for the amorphous powders obtained after freeze-drying. The comparison with the other powders showed that this specific tableting behavior is linked to both the specific texture and the physical state (amorphization) of these freeze-dried powders.

A Metformin-Ferulic Acid Salt with Improved Biopharmaceutical Parameters

Though ferulic acid presents great hypoglycemic potential, it possesses limited aqueous solubility, and low oral bioavailability. When associated with metformin, the first-choice drug in Type 2 diabetes treatment, FA demonstrates synergistic hypoglycemic effects, however, it also causes certain undesirable dose-related effects. This study aimed to develop a new ferulic acid - metformin multicomponent system, and incorporate it into a solid dosage form with improved biopharmaceutical parameters. A novel metformin: ferulate (1:1) salt (MFS) was produced, which was properly characterized using differing analytical techniques, including single crystal analysis. Also during the course of the study, a new polymorph of the metformin free base was observed. The MFS was obtained using solvent evaporation methods, which achieved high yields in reproducible process, as well as a 740-fold increase in ferulic acid aqueous solubility. The MFS tablets developed met quality control requirements for this dosage form, as well as revealing excellent performance in vitro dissolution tests, presenting dissolution efficiency values of 95.4 ± 0.5%. Additionally, physicochemical instability was not observed in a study at 40 °C for 3 months for both MFS powder and its tablet form. The MFS product developed is a promising candidate for further Type 2 diabetes clinical study.

The Influence of Wet Granulation Parameters on the Compaction Behavior and Tablet Strength of a Hydralazine Powder Mixture

The aim of this paper was to describe the influence of high-shear wet granulation process parameters on tablet tensile strength and compaction behavior of a powder mixture and granules containing hydralazine. The hydralazine powder mixture and eight types of granules were compacted into tablets and evaluated using the Heckel, Kawakita and Adams analyses. The granules were created using two types of granulation liquid (distilled water and aqueous solution of polyvinylpyrrolidone), at different impeller speeds (500 and 700 rpm) and with different wet massing times (without wet massing and for 2 min). Granulation resulted in improved compressibility, reduced dustiness and narrower particle-size distribution. A significant influence of wet massing time on parameters from the Kawakita and Adams analysis was found. Wet massing time had an equally significant effect on tablet tensile strength, regardless of the granulation liquid used. Granules formed with the same wet massing time showed the same trends in tabletability graphs. Tablets created using a single-tablet press (batch compaction) and an eccentric tablet press showed opposite values of tensile strength. Tablets from granules with a higher bulk density showed lower strength during batch compaction and, conversely, higher strength during eccentric tableting.

Tableting of Fluidized Bed Granules Containing Living Microorganisms

Tablets are the favored dosage form for numerous active pharmaceutical ingredients, among others because they are easy to take, ensure safe dosing and allow cost-effective production on a large scale. This dosage form is also frequently chosen for the administration of viable probiotic microorganisms. Saccharomyces cerevisiae cells granulated in a fluidized bed process, with dicalcium phosphate (DCP), lactose (LAC) and microcrystalline cellulose (MCC) as carrier materials, were tableted using a compaction simulator, varying the compression stress. The tablets were analyzed regarding physical properties, e.g., porosity and tensile strength, as well as microbial survival. Carrier material and compression stress showed a significant influence on survival rate and physical tablet properties. The dependencies were related to material specific deformation characteristics and linked to mechanistic approaches to explain the different sensitivities.

Enhanced multi-component model to consider the lubricant effect on compressibility and compactibility

Modeling of structural and mechanical tablet properties consisting of multiple components, based on a minimum of experimental data is of high interest, in order to minimize time- and cost-intensive experimental trials in the development of new tablet formulations. The majority of commonly available models use the compressibility and compactibility of constituent components and establish mixing rules between those components, in order to predict the tablet properties of formulations containing multiple components. However, their applicability is limited to single materials, which form intact tablets (e.g. lactose, cellulose) and therefore, they cannot be applied for lubricants. Lubricants are required in the majority of industrial tablet formulations and usually influence the mechanical strength of tablets. This study combines the multi-component compaction model of Reynolds et al. (2017) with a recently published lubrication model (Puckhaber et al. 2020) to describe the impact of multiple components on a formulation consisting of two diluents and a lubricant. By that, this model combination displays a meaningful extension of existing compaction models and allows the systematic prediction of properties of lubricated multi-component tablets.

Evaluation of alternative methods to derive particle density from compression data

The determination of particle density is a critical part of material characterization regarding compression analyses. Helium pycnometry as the most commonly used method is criticized for different aspects. Most prominent is the susceptibility to errors when measuring water-containing powders. Alternative methods for determining particle density using compression data have already been described. However, a systematic investigation and evaluation is still missing. In this study, the methods by Sun and Krumme were investigated in detail regarding their robustness against variations in tableting settings. Twelve pharmaceutical excipients were tableted at five different settings to verify the applicability and sensitivity to changes in the experimental set-up. Both methods were found to be robust against influencing parameters from the experiments. A sufficiently high compression pressure to approach a constant density value of the corresponding material during tableting was considered to be an essential requirement for the performance of the methods. Brittle materials with high yield pressure were found to be unsuitable for the application of both methods. The method of Krumme gave small deviations to measurements of helium pycnometry for water-free materials. By using the tablet density after in-die elastic recovery, Krumme's method could be used for water-containing materials as well. The method of Sun was found to give significantly smaller values for particle density due to inclusion of slow elastic recovery.

Influence of the drug deformation behaviour on the predictability of compressibility and compactibility of binary mixtures

Various studies investigate the predictability of the compressibility and compactibility of tablet formulations based on the behaviour of the pure materials. However, these studies are limited to a few materials so far probably because of the complexity of the powder compaction process. One approach preventing the excessive increase in complexity is the extension of the investigations from pure materials to binary powder mixtures. The focus of this study is on the predictability of the compressibility and compactibility of binary mixtures consisting of an active pharmaceutical ingredient (API) and the excipient microcrystalline cellulose. Three APIs with markedly different deformation behaviour were used. The API concentration and type are systematically varied. For all three material combinations it is found that the in-die compressibility of the binary mixtures can be precisely predicted based on the characteristic compression parameters of the raw materials using the extended in-die compression function in combination with a volume-based linear mixing rule. Since the tablet porosity (out-of-die) also follows a linear mixing rule, the predictability can be further extended using the method of Katz et al. In contrast, the influence of the API concentration on compactibility or rather on tablet tensile strength is non-linear and strongly dependent on the deformation behaviour of the API, making the predictability more difficult. Neither the approach of Reynolds et al. nor this of Kuentz and Leuenberger are able to predict the compactibility when clear deviations from a linear mixing rule appear.

Improved Pharmaceutical Properties of Honokiol via Salification with Meglumine: an Exception to Oft-quoted ∆pKa Rule

Honokiol (HK), a BCS class II drug with a wide range of pharmacological activities, has poor solubility and low oral bioavailability, severely limiting its clinical application. In the current study, incorporating a water-soluble meglumine (MEG) into the crystal lattice of HK molecule was performed to improve its physicochemical properties. The binary mixture of HK and MEG was obtained by anti-solvent method and characterized by TGA, DSC, FTIR, and PXRD. The SCXRD analysis showed that two HK^- molecules and two MEG⁺ molecules were coupled in each unit cell via the ionic interaction along with intermolecular hydrogen bonds, suggesting the formation of a salt, which was further confirmed by the XPS measurements. However, the ∆pK_a value between HK and MEG was found to be less than 1, which did not follow the oft-quoted ∆pK_a rule for salt formation. After salification with MEG, the solubility and dissolution rate of HK exhibited 3.50 and 25.33 times improvement than crystalline HK, respectively. Simultaneously, the powder flowability, tabletability and stability of HK-MEG salt was also significantly enhanced, and the salt was not more hygroscopic, and that salt formation did not compromise processability in that regard. Further, in vivo pharmacokinetic study showed that C_max and AUC_0-t of HK-MEG salt were enhanced by 2.92-fold and 2.01-fold compared to those of HK, respectively, indicating a considerable improvement in HK oral bioavailability.

Compression Modulus and Apparent Density of Polymeric Excipients during Compression-Impact on Tabletability

The present study focuses on the compaction behavior of polymeric excipients during compression in comparison to nonpolymeric excipients and its consequences on commonly used Heckel analysis. Compression analysis at compaction pressures (CPs) from 50 to 500 MPa was performed using a compaction simulator. This study demonstrates that the particle density, measured via helium pycnometer (ρpar), of polymeric excipients (Kollidon®VA64, Soluplus®, AQOAT®AS-MMP, Starch1500®, Avicel®PH101) was already exceeded at low CPs (<200 MPa), whereas the ρpar was either never reached for brittle fillers such as DI-CAFOS®A60 and tricalcium citrate or exceeded at CPs above 350 MPa (FlowLac®100, Pearlitol®100SD). We hypothesized that the threshold for exceeding ρpar is linked with predominantly elastic deformation. This was confirmed by the start of linear increase in elastic recovery in-die (ERin-die) with exceeding particle density, and in addition, by the applicability in calculating the elastic modulus via the equation of the linear increase in ERin-die. Last, the evaluation of “density under pressure” as an alternative to the ρpar for Heckel analysis showed comparable conclusions for compression behavior based on the calculated yield pressures. However, the applicability of Heckel analysis for polymeric excipients was questioned in principle. In conclusion, the knowledge of the threshold provides guidance for the selection of suitable excipients in the formulation development to mitigate the risk of tablet defects related to stored elastic energy, such as capping and lamination.

An update on microcrystalline cellulose in direct compression: Functionality, critical material attributes, and co-processed excipients

Microcrystalline cellulose (MCC) is one of the most popular cellulose derivatives in the pharmaceutical industry. Thanks to its outstanding tabletability, MCC is generally included in direct compression (DC) tablet formulations containing poor-tabletability active pharmaceutical ingredients. Nowadays, numerous grades of MCC from various brands are accessible for pharmaceutical manufacturers, leading to variability in MCC properties. Hence, it seems to be worthy and urgent to evaluate the influences of MCC variability on tablet quality and to identify critical material attributes (CMAs) based on the idea of Quality by Control. Besides, MCC-based co-processed excipients can effectively combine the functions of the filler, binder, disintegrant, lubricant, glidant, or flavor, and thus have drawn extensive interest. In this review, we focused specifically on the recent advances and development of MCC on DC tableting, including the functions in tablet formulations, potential CMAs, and MCC-based co-possessed excipients, therefore providing a reference for further studies.

Moisture Transport Coefficients Determination on a Model Pharmaceutical Tablet

In this work, a novel methodology to determine moisture transport coefficients for MMC PH101 tablets is presented. Absolute permeability, moisture diffusion, moisture transfer, and water vapor permeability coefficients were estimated on compressed powder tablets produced with different compression pressures (20 MPa to 200 MPa with an interval of 20 MPa). The ASTM D6539 standard test was used to measure the absolute permeability. The moisture transfer coefficient was determined from measured absolute permeability. The moisture diffusion coefficient was obtained with the tablet average pore radius, which was determined with the water droplet penetration method. Descriptive and phenomenological models derived from the measurements were confronted with existing and adopted models, and a good agreement was found. The obtained models are of the function of the microstructural properties of the tablet (average pore radius and average porosity). The tablet average porosity was found to be the principal parameter that governs the behavior of the moisture transport coefficients. The findings of this study might be applicable to obtain a series of input parameters for modelling software, such as COMSOL Multiphysics®, to infer delamination, sticking, and failure propensity from the effect of moisture.

Three-dimensional compaction of soft granular packings

This paper analyzes the compaction behavior of assemblies composed of soft (elastic) spherical particles beyond the jammed state, using three-dimensional non-smooth contact dynamic simulations. The assemblies of particles are characterized using the evolution of the packing fraction, the coordination number, and the von Misses stress distribution within the particles as the confining stress increases. The packing fraction increases and tends toward a maximum value close to 1, and the mean coordination number increases as a square root of the packing fraction. As the confining stress increases, a transition is observed from a granular-like material with exponential tails of the shear stress distributions to a continuous-like material characterized by Gaussian-like distributions of the shear stresses. We develop an equation that describes the evolution of the packing fraction as a function of the applied pressure. This equation, based on the micromechanical expression of the granular stress tensor, the limit of the Hertz contact law for small deformation, and the power-law relation between the packing fraction and the coordination of the particles, provides good predictions from the jamming point up to very high densities without the need for tuning any parameters.

Modeling of High-Density Compaction of Pharmaceutical Tablets Using Multi-Contact Discrete Element Method

The purpose of this work is to simulate the powder compaction of pharmaceutical materials at the microscopic scale in order to better understand the interplay of mechanical forces between particles, and to predict their compression profiles by controlling the microstructure. For this task, the new framework of multi-contact discrete element method (MC-DEM) was applied. In contrast to the conventional discrete element method (DEM), MC-DEM interactions between multiple contacts on the same particle are now explicitly taken into account. A new adhesive elastic-plastic multi-contact model invoking neighboring contact interaction was introduced and implemented. The uniaxial compaction of two microcrystalline cellulose grades (Avicel^® PH 200 (FMC BioPolymer, Philadelphia, PA, USA) and Pharmacel^® 102 (DFE Pharma, Nörten-Hardenberg, Germany) subjected to high confining conditions was studied. The objectives of these simulations were: (1) to investigate the micromechanical behavior; (2) to predict the macroscopic behavior; and (3) to develop a methodology for the calibration of the model parameters needed for the MC-DEM simulations. A two-stage calibration strategy was followed: first, the model parameters were directly measured at the micro-scale (particle level) and second, a meso-scale calibration was established between MC-DEM parameters and compression profiles of the pharmaceutical powders. The new MC-DEM framework could capture the main compressibility characteristics of pharmaceutical materials and could successfully provide predictions on compression profiles at high relative densities.

A review of emerging technologies enabling improved solid oral dosage form manufacturing and processing

Tablets are the most widely utilized solid oral dosage forms because of the advantages of self-administration, stability, ease of handling, transportation, and good patient compliance. Over time, extensive advances have been made in tableting technology. This review aims to provide an insight about the advances in tablet excipients, manufacturing, analytical techniques and deployment of Quality by Design (QbD). Various excipients offering novel functionalities such as solubility enhancement, super-disintegration, taste masking and drug release modifications have been developed. Furthermore, co-processed multifunctional ready-to-use excipients, particularly for tablet dosage forms, have benefitted manufacturing with shorter processing times. Advances in granulation methods, including moist, thermal adhesion, steam, melt, freeze, foam, reverse wet and pneumatic dry granulation, have been proposed to improve product and process performance. Furthermore, methods for particle engineering including hot melt extrusion, extrusion-spheronization, injection molding, spray drying / congealing, co-precipitation and nanotechnology-based approaches have been employed to produce robust tablet formulations. A wide range of tableting technologies including rapidly disintegrating, matrix, tablet-in-tablet, tablet-in-capsule, multilayer tablets and multiparticulate systems have been developed to achieve customized formulation performance. In addition to conventional invasive characterization methods, novel techniques based on laser, tomography, fluorescence, spectroscopy and acoustic approaches have been developed to assess the physical-mechanical attributes of tablet formulations in a non- or minimally invasive manner. Conventional UV-Visible spectroscopy method has been improved (e.g. fiber-optic probes and UV imaging-based approaches) to efficiently record the dissolution profile of tablet formulations. Numerous modifications in tableting presses have also been made to aid machine product changeover, cleaning, and enhance efficiency and productivity. Various process analytical technologies have been employed to track the formulation properties and critical process parameters. These advances will contribute to a strategy for robust tablet dosage forms with excellent performance attributes.

Tableting model assessment of porosity and tensile strength using a continuous wet granulation route

This paper presents a comprehensive assessment of the most widely used tablet compaction models in a continuous wet granulation tableting process. The porosity models, tensile strength models and lubricant models are reviewed from the literature and classified based on their formulations i.e. empirical or theoretical and applications, i.e. batch or continuous. The majority of these models are empirical and were initially developed for batch tabletting process. To ascertain their effectiveness and serviceability in the continuous tableting process, a continuous powder processing line of Diamond Pilot Plant (DiPP) installed at The University of Sheffield was used to provide the quantitative data for tablet model assessment. Magnesium stearate (MgSt) is used as a lubricant to investigate its influence on the tensile strength. Whilst satisfactory predictions from the tablet models can be produced, a compromise between the model fidelity and model simplicity needs to be made for a suitable model selection. The Sonnergaard model outperforms amongst the porosity models whilst the Reynolds model produces the best goodness of fitting for two parameters fitting porosity models. An improved tensile strength model is proposed to consider the influence of powder size and porosity in the continuous tableting process.

Process Modeling and Simulation of Tableting-An Agent-Based Simulation Methodology for Direct Compression

In pharmaceutical manufacturing, the utmost aim is reliably producing high quality products. Simulation approaches allow virtual experiments of processes in the planning phase and the implementation of digital twins in operation. The industrial processing of active pharmaceutical ingredients (APIs) into tablets requires the combination of discrete and continuous sub-processes with complex interdependencies regarding the material structures and characteristics. The API and excipients are mixed, granulated if required, and subsequently tableted. Thereby, the structure as well as the properties of the intermediate and final product are influenced by the raw materials, the parametrized processes and environmental conditions, which are subject to certain fluctuations. In this study, for the first time, an agent-based simulation model is presented, which enables the prediction, tracking, and tracing of resulting structures and properties of the intermediates of an industrial tableting process. Therefore, the methodology for the identification and development of product and process agents in an agent-based simulation is shown. Implemented physical models describe the impact of process parameters on material structures. The tablet production with a pilot scale rotary press is experimentally characterized to provide calibration and validation data. Finally, the simulation results, predicting the final structures, are compared to the experimental data.

How can single particle compression and nanoindentation contribute to the understanding of pharmaceutical powder compression?

The deformation behaviour of a powder and, thus, of the individual particles is a crucial parameter in powder compaction and affects powder compressibility and compactibility. The classical approach for the characterization of the deformation behaviour is the performance of powder compression experiments combined with the application of mathematical models, such as the Heckel-Model, for the derivation of characteristic compression parameters. However, the correlation of these parameters with the deformation behaviour is physically often not well understood. Single particle compression and nanoindentation enables the in-depth investigation of the deformation behaviour of particulate materials. In this study, single particle compression experiments were performed for the characterization of the deformation behaviour of common pharmaceutical excipients and active pharmaceutical ingredients (APIs) with various, irregular particle morphologies of industrial relevance and the findings are compared with the results from powder compression. The technique was found useful for the characterization and clarification of the qualitative deformation behaviour. However, the derivation of a quantitative functional relationship between single particle deformation behavior and powder compression is limited. Nanoindentation was performed as complementary technique for the characterization of the micromechanical behavior of the APIs. A linear relationship between median indentation hardness and material densification strength as characteristic parameter derived by in-die powder compression analysis is found.

Impact breakage of single pharmaceutical tablets in an air gun

Milling is commonly used for controlling the size distribution of granules in the pharmaceutical dry granulation process. A thorough understanding of the breakage of single compacts is crucial in unravelling the complex interactions that exist between different pharmaceutical feed materials and the mill process conditions. However, limited studies in the literature have examined the impact breakage of single pharmaceutical compacts. In this study, pharmaceutical powders including the microcrystalline MCC 101, MCC 102 and MCC DG were compressed at different pressures and tablets with different porosities and thicknesses were produced. Impact breakage tests were conducted in an air gun and the tablet impact velocities and breakage patterns were analysed using a Phantom ultrahigh-speed camera. It was observed that the tablet breakage rate and the amount of fines reduced as the tablet porosity decreased. In addition, thin tablets with low porosity exhibited semi-brittle fracture and less intense crack propagation while thick tablets with high porosity primarily disintegrated into fine fragments. Thus, this study provides a better understanding of the breakage behaviour of different pharmaceutical materials and can potentially be used to describe the breakage modes of compacts in the ribbon milling processes.

Comparison of the performance of two grades of metformin hydrochloride elaboration by means of the SeDeM system, compressibility, compactability, and process capability indices

Quality by design, applied to the development of a pharmaceutical drug, demands scientific methodologies, representing a source of information that will allow for a complete understanding the production process and the materials used for its manufacturing. Although the SeDeM system is a tool that enables a rational development of a product, result does not assure that an assessed material or mixture will be successful in terms of compression, hence, further research will be necessary on these features. The objective of this study was to assess and compare two grades of metformin hydrochloride elaboration: crystalline and direct compression using PXRD, the SeDeM expert system, the Heckel and Ryshkewitch-Duckworth models, as well as process control tools such as control charts and process capability indices to characterize and predict the performance of the materials in a direct compression process. The assessment identified that in spite of dealing with two different technical grades of a material with specific critical quality attributes for each one, PXRD analysis showed we dealt with the same crystalline structure, while the SeDeM system profiles obtained have very close values, and the main differences in materials were observed when subjecting them to conditions that simulate a compaction process with the Ryshkewitch-Duckworth model, in which a 46-times higher mechanical resistance was observed in the direct compression material compared with the crystalline one. The statistical control analysis revealed that only the direct compression material could be used to elaborate tablets whose weight variation was always maintained within the specification and control limits.

The influence of particle size on the application of compression and compaction models for tableting

The physical characteristics of raw materials determine powder compression and compaction performance as relevant in pharmaceutical processes. For instance, the influence of initial particle size on powder compression and the resulting strength of specimen are highly complex and are still not sufficiently understood. Existing studies are often limited to materials with well-defined deformation behaviour, such as purely brittle or ductile. However, the deformation behaviour of active pharmaceutical ingredients (APIs) is often more complex. In this study, the influence of initial particle size on powder compressibility and compactibility is systematically characterized by consideration of in-die compressibility, specific energies, quick elastic recovery, tablet porosity and, tensile strength for the binder microcrystalline cellulose and three APIs. The decrease of particle size leads to an increase of the resistance against compression by trend and probably to a different contribution of the acting deformation mechanisms. The compactibility is increased with decreasing particle size because of the increasing number of bonds in a cross-sectional area of the tablet, as found by the application of the model of Rumpf. Furthermore, it is found that the model of Rumpf combined with the JKR model provides a meaningful property function to estimate tablet tensile strength.

Grain size effect on the compression and relaxation of a granular column: solid particles vs dust agglomerates

We studied experimentally the effect of grain size and maximum load on the compaction and subsequent relaxation of a granular column when it is subjected to vertical uniaxial compression. The experiments were performed using two different types of grains: 1) solid glass beads, and 2) porous beads that consist of agglomerates of glass powder. We found that the compression force increases non-linearly with time, with sudden drops for the case of glass beads and periodic undulations for dust particles. Whereas the grain size effect is small in the average force load, the fluctuations become larger as the grain size increases. On the other hand, the relaxation process is well described by the Maxwell model with three different relaxation time scales.

The effects of spray drying, HPMCAS grade, and compression speed on the compaction properties of itraconazole-HPMCAS spray dried dispersions

Spray dried dispersions (SDDs) have the potential to dramatically improve the oral bioavailability of drugs with poor water solubility. However, SDDs tend to have material attributes, such as small particle size, low bulk density, and poor flowability, which are undesirable for downstream processing such as tableting. The objective was to perform a comprehensive compaction characterization of both physical mixtures and SDDs consisting of itraconazole (ITZ) and hypromellose acetate succinate (HPMCAS) to elucidate process and material influences on compressibility and compactibility. We fabricated SDDs with 20% ITZ as a model BCS Class 2 drug and 80% HPMCAS as a polymer carrier. Results indicate that SDDs, as well physical mixtures of ITZ and HPMCAS, were easily deformable with similar compressibility profiles across all compression speeds. Analysis of Heckel plots revealed that yield pressures were fairly low for both physical mixtures and SDDs (43.97-59.75 MPa), indicative of ductile materials. SDDs had a much greater propensity to laminate, especially at higher compression speeds, compared to physical mixtures. This difference is likely due to the higher elastic recovery of SDDs. However, for intact tablets, the mechanical strength of compacts from SDDs tended to be higher than those produced from physical mixtures, likely due to the much smaller particle size of the SDDs. Importantly, examination of the compacts with differential scanning calorimetry did not detect any drug crystallization as a result of compaction. In conclusion, while spray drying did not significantly alter the compressibility of binary mixtures ITZ and HPMCAS, it dramatically impacted compactibility and tabletability, increasing elastic recovery, and making the mixtures more prone to lamination. However, at low compression speeds, SDDs produced tablets with higher tensile strength than physical mixtures.

Impact of feed material properties on the milling of pharmaceutical ribbons: A PBM analysis

Dry granulation is commonly used in the pharmaceutical industry for compressing heat and moisture sensitive feed materials into compacts, subsequently followed by milling. Population balance models (PBMs) are often used to explore the effects of milling conditions on the granule size distribution (GSD) but limited studies have investigated the effects of the feed material and ribbon properties on the resulting GSD. In this work, a variety of feed materials and ribbons with different mechanical properties were used to validate a mass-based bi-modal breakage function developed in a previous study (Olaleye et al., 2019). Ribbon like tablets (referred to as ribblets) with a range of precisely controlled porosities were produced using an Instron machine and pharmaceutical excipients including the microcrystalline cellulose MCC 101, MCC DG and a DCPA/MCC mixture. Roll compacted ribbons were also produced using MCC 102 and MCC DG excipients. The ribblets and ribbons were milled in an impact-dominated cutting mill and PBM parameters were obtained from the ribblet milling data. Mechanistic models related to the feed ribbon property were then developed. It was found that the PBM with the mass-based bi-modal breakage function can accurately predict the GSDs of both the milled ribblets and roll compacted ribbons. The model developed was successfully linked to ribbon properties such as porosity for the first time and the model parameter a that reflects the fines mode in the bi-modal breakage function increased linearly with ribblet porosity. This work demonstrates the versatility of the developed PBM and provides a systematic approach for describing the ribbon milling process.

Compaction of mixtures of rigid and highly deformable particles: A micromechanical model

We analyze the isotropic compaction of mixtures composed of rigid and deformable incompressible particles by the nonsmooth contact dynamics approach. The deformable bodies are simulated using a hyperelastic neo-Hookean constitutive law by means of classical finite elements. We characterize the evolution of the packing fraction, the elastic modulus, and the connectivity as a function of the applied stresses when varying the interparticle coefficient of friction. We show first that the packing fraction increases and tends asymptotically to a maximum value ϕ_{max}, which depends on both the mixture ratio and the interparticle friction. The bulk modulus is also shown to increase with the packing fraction and to diverge as it approaches ϕ_{max}. From the micromechanical expression of the granular stress tensor, we develop a model to describe the compaction behavior as a function of the applied pressure, the Young modulus of the deformable particles, and the mixture ratio. A bulk equation is also derived from the compaction equation. This model lays on the characterization of a single deformable particle under compression together with a power-law relation between connectivity and packing fraction. This compaction model, set by well-defined physical quantities, results in outstanding predictions from the jamming point up to very high densities and allows us to give a direct prediction of ϕ_{max} as a function of both the mixture ratio and the friction coefficient.

Confined Bed Breakage of Fine Iron Ore Concentrates

High-pressure grinding rolls (HPGR) have gained great popularity in the mining industry in the last 25 years or so. One of the first successful applications of the technology has been in iron ore pressing prior to pelletization. Piston-and-die tests can provide good insights on the material response in an HPGR. This work analyzed confined bed breakage of four iron ore concentrates under different conditions. Saturation in breakage of particles contained in the top size in the tests was observed to occur at specific energies of about 2 kWh/t, whereas full saturation in breakage, with no additional increase in specific surface area of the material, occurred at energies above about 6 kWh/t. An expression was proposed to characterize the propensity of a material to break under confined bed conditions. The phenomenology involved in confined bed breakage of such materials was then analyzed in light of the results.

A Spray-Dried, Co-Processed Rice Starch as a Multifunctional Excipient for Direct Compression

A new co-processed, rice starch-based excipient (CS) was developed via a spray-drying technique. Native rice starch (RS) was suspended in aqueous solutions of 10%–15% cross-linked carboxymethyl rice starch (CCMS) and 0.5%–6.75% silicon dioxide (in the form of sodium silicate), before spray drying. The resulting CSs were obtained as spherical agglomerates, with improved flowability. The compressibility study revealed an improved plastic deformation profile of RS, leading to better compaction and tensile strength. The presence of CCMS also ensured a rapid disintegration of the compressed tablets. CS-CCMS:SiO₂ (10:2.7), prepared with 10% CCMS, 2.7% silicon dioxide, and 40% solid content, was found to exhibit the best characteristics. Compared to the two commercial DC excipients, Prosolv^® and Tablettose^®, the flow property of CS-CCMS:SiO₂ (10:2.7) was not significantly different, while the tensile strength was 23%: lower than that of Prosolv^® but 4 times higher than that of Tablettose^® at 196 MPa compression force. The disintegration time of CS-CCMS:SiO₂ (10:2.7) tablet (28 s) was practically identical to that of Tablettose^® tablet (26 s) and far superior to that of Prosolv^® tablet (>30 min). These results show that CSs could potentially be employed as a multifunctional excipient for the manufacturing of commercial tablets by DC.

Compaction Model for Highly Deformable Particle Assemblies

The compaction behavior of deformable grain assemblies beyond jamming remains bewildering, and existing models that seek to find the relationship between the confining pressure P and solid fraction ϕ end up settling for empirical strategies or fitting parameters. Using a coupled discrete-finite element method, we analyze assemblies of highly deformable frictional grains under compression. We show that the solid fraction evolves nonlinearly from the jamming point and asymptotically tends to unity. Based on the micromechanical definition of the granular stress tensor, we develop a theoretical model, free from ad hoc parameters, correctly mapping the evolution of ϕ with P. Our approach unveils the fundamental features of the compaction process arising from the joint evolution of grain connectivity and the behavior of single representative grains. This theoretical framework also allows us to deduce a bulk modulus equation showing an excellent agreement with our numerical data.

Along the Process Chain to Probiotic Tablets: Evaluation of Mechanical Impacts on Microbial Viability

Today, probiotics are predominantly used in liquid or semi-solid functionalized foods, showing a rapid loss of cell viability. Due to the increasing spread of antibiotic resistance, probiotics are promising in pharmaceutical development because of their antimicrobial effects. This increases the formulation requirements, e.g., the need for an enhanced shelf life that is achieved by drying, mainly by lyophilization. For oral administration, the process chain for production of tablets containing microorganisms is of high interest and, thus, was investigated in this study. Lyophilization as an initial process step showed low cell survival of only 12.8%. However, the addition of cryoprotectants enabled survival rates up to 42.9%. Subsequently, the dried cells were gently milled. This powder was tableted directly or after mixing with excipients microcrystalline cellulose, dicalcium phosphate or lactose. Survival rates during tableting varied between 1.4% and 24.1%, depending on the formulation and the applied compaction stress. More detailed analysis of the tablet properties showed advantages of excipients in respect of cell survival and tablet mechanical strength. Maximum overall survival rate along the complete manufacturing process was >5%, enabling doses of 6 × 108 colony forming units per gram (CFU gtotal−1), including cryoprotectants and excipients.