Hybrid modeling of roll compaction processes with the Styl'One Evolution

An evaluation of six techniques for measuring porosity of ribbons produced by roller compaction

Ribbon porosity is a critical parameter to monitor in the roller compaction process. In this study, six techniques for measuring the porosity of solid compacts, i.e., manually by caliper (Caliper), X-ray microtomography (µCT), off-line near-infrared spectroscopy (NIR), laser triangulation (Laser), mercury intrusion porosimetry (MIP), and GeoPyc, were compared using a set of rectangular ribblets of microcrystalline cellulose (MCC). These ribblets, which were compressed at 8-130 MPa on a compaction simulator, exhibited porosities over the range of 0.09 - 0.52. Subsequently, porosities of MCC ribbons made on a roller compactor at specific roll forces of 1.8 kN/cm and 8.8 kN/cm were measured. The Caliper method is convenient for samples with a simple shape but not suitable for real ribbons. The accuracy of GeoPyc measurement relies on accurate conversion factor (unit in cm3/mm), sample shape and size, and sufficient sample volume percentage in the medium. The µCT data is more accurate at lower porosities (< 0.2), while the MIP data is more accurate at higher porosities (> 0.4). The Laser method has good accuracy and is more reproducible compared to other methods in the ribblets measurement. The NIR method is fast, which makes it suitable for in-line monitoring of changes in ribbon quality, but porosity quantification is sensitive to sample presentation, such as surface curvature and roughness. These insights could assist in the choice of the most appropriate method for monitoring ribbon porosity to guide the development and optimization of a roller compaction process for a given formulation.

Accelerating pharmaceutical tablet development by transfer of powder compaction equipment across types and scales

Roller compaction is a key unit operation in a dry granulation line for pharmaceutical tablet manufacturing. During product development, one would like to find the roller compactor (RC) settings that are required to achieve a desired ribbon solid fraction. These settings can be determined from the compression profile of the powder mixture being compacted and a mathematical model that interprets it. However, establishing compression profiles in an RC requires relatively large amounts of powder, which are expensive and may not be available during drug development. As a cost-effective alternative to an RC, a compactor simulator (CS) can be used, which is a small-scale equipment that uses minimal amounts of powder to build the compression profile. However, since the working principles of a CS and an RC are different, the compression profiles obtained from the two devices for a given powder are also different. In this study, we propose a transfer learning approach that allows the RC compression profile of a given powder to be easily predicted from the compression profile obtained in a CS for the same powder. Based on the well-known Johanson model and on the mass correction factor theory, we examine the compaction behavior of six formulations, two of which including active ingredients, and we find that the mass correction factor does not depend significantly on the powder being compacted. We develop a simple, generalized correlation (transfer model) that allows the mass correction factor to be predicted solely as a function of the pressure at which the compaction is carried out. By using the proposed transfer model, the prediction of the RC compression profiles for the validation powders is significantly improved over the case where a constant value of the mass correction factor is used.

Modeling of Styl'One Evolution Correction Factors for Multicomponent Mixtures Scaling-up to Roller Compaction

Roll compaction (RC) is a cost-effective dry granulation method, widely implemented in the pharmaceutical industry. In early formulation development however, when the material availability is limited, being able to predict the most important parameters in RC, like gap width and specific compaction force (SCF), to obtain a target ribbon solid fraction (SF) would significantly improve the formulation development efficiency as it would avoid the need of performing experiments on the roller compactor itself. However, at the present state of things, experiments on RC mechanical simulators present an overestimation of the target SF, when compared to roller compactor SF values. Although numerous correction approaches have been developed to improve the predictive performance of different mathematical models applied to the simulation experimental results, no study has collected a database wide enough to demonstrate the validity of a correction factor that allows to accurately simulate the compaction behavior of multicomponent mixtures. Here, 25 different formulations at 40 % drug load are compacted at different SCFs, both on a RC mimicking device (Styl'One Evolution) and on an actual roller compactor (Gerteis Mini-Pactor): following a similar approach as Reimer et al. and implementing a simplified version of the Johanson's mathematical model, 4 different correction factors are calculated, depending on how their material properties and pressure dependencies are considered. In conclusion, one correction factor is identified as the optimal trade-off between the SF prediction accuracy on the Gerteis Mini-Pactor and its applicability to a wide range of formulations, as it is independent of the material properties. This finding is particularly relevant when applied to scale-up to this specific roller compactor or early development processes of new formulations that have not been mechanically characterized yet.

Challenges in the transfer and scale-up of mini-tableting: Case study with losartan potassium

Mini-tablets (MTs) with losartan potassium were developed to treat the rare disease Epidermolysis Bullosa. The focus was placed on transfer and scale-up of a direct compressible formulation from the compaction simulator STYL'One Evo (CS) to the rotary tablet press Korsch XM 12 (RP). Transfer of tabletability and compactibility profiles from CS to RP did not show good agreement, e.g. at a tableting pressure of 125 MPa mean tensile strengths (TS) of 4 MPa on CS and 1-1.5 MPa on RP were reached. These results highlight the impact of the feed frame on final product qualities depending on process and material factors. In the scale-up studies the critical quality attributes (CQAs) mass variation, content uniformity, TS and disintegration time were investigated. After an appropriate run-up time, most CQAs reached a plateau, after reaching a balance between influx, efflux and distribution of lubricant in the feed frame. TS values of 1-2 MPa, disintegration times of max. 50 s, mass variation of 0.9-2.2 % (CV) and acceptance values below 15.0 were reached depending on chosen process parameters.

Simulation of roller compaction by combination of a compaction simulator and oscillating mill - A material sparing approach

This study investigates the feasibility of a compaction simulator and oscillating mill to mimic a roller compactor as a material sparing approach for process development. Microcrystalline cellulose and dicalcium phosphate dihydrate were selected to represent soft and hard materials, respectively. The relative density of ribbons and riblets was determined using a pycnometer and granules size distribution was determined by laser diffraction. Tablet tensile strength and relative density were determined using a hardness tester and pycnometer, respectively. This study showed that the relative density of riblets and ribbons were similar between 1 and 12 kN/cm, which indicates that the compaction simulator adequately mimics the compaction of the roller compactor using a Kp of 1. The size distribution of granules produced by the oscillating mill and roller compactor were similar, which indicates that the oscillating mill adequately mimics the roller compactor when using a similar gap and sieve design. Finally, the tablet tensile strength and relative density were similar independent of the applied granulation method and deformation behaviour of the material. In conclusion, the use of a compaction simulator and an oscillating mill in combination adequality mimics the roller compactor, which ultimately can save large amounts of material and time during process development.

Influence of Roll Speed during Roll Compaction and Its Effect on the Prediction of Ribbon Solid Fraction

Influence of the roll speed (RS) during roll compaction on ribbon, granule, tablet properties and its effect on the prediction of the ribbon solid fraction at-gap is often neglected or controversially discussed. The aim of this study was to investigate the effect of the RS systematically. Microcrystalline cellulose (MCC) and lactose were compressed at several maximum roll pressures (Pmax) and RS combinations using a gap-controlled roll compactor. The ribbon solid fraction after elastic recovery (SFribbon), granule size distribution and tabletability of the granules as well as the ribbon solid fraction at-gap (SFgap) were measured. The Midoux number (Mi), derived from the Johanson model, was used to predict the ribbon solid fraction at-gap (SFMi). The measured SFgap and the predicted SFMi&nbsp;lead to a prediction accuracy (PA) of the Midoux number. The results are highly dependent on the material used and the applied Pmax. Higher plasticity of the material leads to a reduction in SFribbon and granule size with increasing RS. However, this effect can be overcome or reduced by adjusting Pmax&nbsp;above the yield pressure of the used material. These results allow for higher roll speeds as a potential upscaling method in roll compaction. On the other side, the PA of the Midoux number was also reduced with increased RS for MCC and had no effect for lactose. Thus, RS seems to be an important factor in the prediction of roll compaction processes and prediction models should include RS as a parameter to improve their accuracy.

Using a Model-based Material Sparing Approach for Formulation and Process Development of a Roller Compacted Drug Product

The present work details a material sparing approach that combines material profiling with Instron uniaxial die-punch tester and use of a roller compaction mathematical model to guide both formulation and process development of a roller-compacted drug product. True density, compression profiling, and frictional properties of the pre-blend powders are used as inputs for the predictive roller compaction model, while flow properties, particle size distribution, and assay uniformity of roller compaction granules are used to select formulation composition and ribbon solid fraction. Using less than 10 g of a model drug compound for material profiling, roller compacted blend in capsule formulations with appropriate excipient ratios were developed at both 1.4% and 14.4% drug loadings. Subsequently, scale-up batches were successfully manufactured based on the roller compaction process parameters obtained from predictive modeling. The measured solid fractions of roller compaction ribbon samples from the scale-up batches were in good agreement with the target solid fraction of the modeling. This approach demonstrated considerable advantages through savings in both materials and number of batches in the development of a roller-compacted drug product, which is of particular value at early development stages when drug substance is often limited and timelines are aggressive.

Laser triangulation as a fast and reliable method for determining ribbon solid fraction; focus on accuracy, precision, and measurement time

Roller compaction and dry granulation represent well-established unit operations in the pharmaceutical industry. The ribbon solid fraction is classified as a critical quality attribute, that directly impacts final product quality and performance. The development and evaluation of novel methods measuring ribbon solid fraction represent a subject of current research, since novel analyses strategies need to be established for at-, on-, or in-line process monitoring to overcome limitations of end product testing and to set the course for continuous manufacturing. In this study, a novel analytical device, using the principle of laser triangulation, was investigated to asses its potential being used as at-line process analytical technology tool during a roller compaction process. To this end, the laser triangulation device was compared with X-ray micro-computed tomography and powder based volume displacement measurement techniques using different statistical evaluation methods. Special focus was given to accuracy, precision, and total measurement time. The laser triangulation device was confirmed as highly accurate and precise, enabling the shortest total measurement time compared to the other methods. The findings of this study support the idea of implementing the laser triangulation device as a novel at-line process analytical technology tool into a roller compaction process.

Improving Process Understanding in Roll Compaction

Roll compaction/ dry granulation is gaining importance. Numerous papers have been published and many attempts to model the process are available in the meantime. Johanson published a model in 1965, which is the basis for many further modifications until today. The aim of the paper is to improve process understanding in roll compaction, which can be used to setup a roll compaction process, to design a scale-up strategy or to help in process transfer between different types of roll compactors. Based on some assumptions, simple considerations help to estimate a required densification factor and to visualize the relations between roll diameter, gap width and nip angle. Two recently published papers based on simplified Johansen models are used to visualize the relations between specific compaction force and the maximal pressure experienced by the material. The influence of roll diameter, gap width and compressibility constant are discussed. This helps to estimate, if a scale-up or process transfer is reasonable. The recently introduced dimensionless Midoux-number can also be used to design scale-up or process transfer of roll compaction without knowledge about the maximal pressure. Exploring the simple concepts can help to improve process understanding even without a background in engineering.

Transfer and scale-up of the manufacturing of orodispersible mini-tablets from a compaction simulator to an industrial rotary tablet press

Orodispersible mini-tablets (ODMTs) are a promising dosage form for the pediatric use showing increasing interest from pharmaceutical industry. However, a scale-up process for ODMTs from a compaction simulator to a rotary tablet press following FDA and EMA guidelines has not been performed and investigated yet. Isomalt (galenIQ™721) and Ludiflash® both excipients with proven suitability for the development of ODMTs have been investigated in transfer and scale-up from a compaction simulator to a rotary tablet press. ODMTs with isomalt and Ludiflash® were produced on the rotary tablet press monitoring the product temperature over time and assessing the properties of the residual powder in the feed shoe. Critical quality attributes like tensile strength, mass and disintegration time were evaluated. The transfer from compaction simulator to rotary tablet press succeeded as for both excipients similar disintegration times, tabletability and compactibility profiles were obtained. However, during scale-up, disintegration time significantly increases over time for both excipients. Monitoring of the product temperature revealed that with increasing batch size the product temperature increases as well having a significant impact on disintegration time. The properties of ODMTs produced with the residual powder are comparable in tabletability and disintegration time compared with ODMTs produced from fresh powder.

Simplifying Johanson's roller compaction model to build a "Virtual Roller Compactor" as a predictive tool - Theory and practical application

The purpose of the study is to build a "virtual roller compactor" as a predictive tool to assess the roll force (RF)-maximum pressure (P_max) and RF-ribbon density relationship for pharmaceutical roller compaction. We provided a theoretical basis to demonstrate that, there exists a critical nip angle for a pharmaceutical powder, beyond which the RF-P_max relationship is insensitive to wall friction angle or effective angle of internal friction. We showed that for most pharmaceutical roller compaction, the critical nip angle is lower than 17 degree, and can be exceeded via wall friction elevation, using rolls with non-smooth surface. Under this condition, the original Johanson model can be substantially simplified to a single equation requiring only one material property (compressibility). By performing manufacturing-scale roller compaction using materials with diverse compressibility, we showed that the simplified, friction angle-free model performed similar to the original Johanson model. It can predict the RF-P_max and RF-ribbon density relationship well after applying a correction factor. The predictive tool, in the form of a user-friendly graphical user interface, was created based on the simplified model. The tool was adopted for in-house, bench-scale formulation development and scale-up because of its ease-of-use, good predicting capability, and very low material demand.

The relevance of granule fragmentation on reduced tabletability of granules from ductile or brittle materials produced by roll compaction/dry granulation

Roll compaction/dry granulation often results in loss of tabletability. The two main hypotheses for this are granule hardening and granule size enlargement. The aim of this study was to investigate the effect of granule size, roll compaction force, and granule fragmentation upon tableting and its effect on tabletability of granules constituting a ductile or brittle material. Plastically deforming microcrystalline cellulose (MCC) and fragmenting lactose monohydrate (lactose) were roll compacted at five roll compaction forces ranging from 2 to 16 kN/cm. Granule size fractions of 250-355 and 500-710 µm were blended with 10% magnesium stearate (MgSt), compressed into tablets and ground to obtain compressed granules. The predominant deformation behaviour of the particles constituting the granules directly impacted granule deformation upon tableting, as lactose granules fractured extensively upon tableting, whereas MCC granules predominantly deformed by plastic deformation. Increased roll compaction force resulted in more granule hardening of both materials and thereby granules less susceptible to fragmentation upon tableting. Granule hardening accounted for the largest loss of tabletability of MCC granules upon roll compaction. Roll compaction force and granule size had no or negligible effect on tabletability of lactose tablets without MgSt, whereas increased roll compaction force and larger granules decreased tensile strength of tablets containing lactose granules blended with MgSt. This was explained by inter-particle and inter-granular bonds contributing equally to the tensile strength of lactose tablets without MgSt. However, after addition of MgSt, the decreased fragmentation tendency of larger granules compacted at higher roll compaction forces resulted in greater MgSt coverage of the granules upon tableting, thereby decreasing tabletability.

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.

Scaling Tableting Processes from Compaction Simulator to Rotary Presses-Mind the Sub-Processes

Compaction simulators are frequently used in the formulation and process development of tablets, bringing about the advantages of flexibility, low material consumption, and high instrumentation to generate the most possible process understanding. However, their capability of resembling general aspects of rotary press compaction and their precision in simulating or mimicking sub-processes such as feeding and filling need to be systematically studied. The effect of material deformation behavior, blend composition, and feeding on tensile strength and simulation precision as compared with rotary presses of different scales is evaluated in this study. Generally, good simulation performance was found for the studied compaction simulator. Compaction profile-sensitivity was demonstrated for highly visco-plastic materials while shear-sensitivity in feeding was demonstrated for lubricated blends of ductile particles. Strategies for the compensation of both in compaction simulator experiments are presented by careful investigation of the compaction stress over time profiles and introduction of a compaction simulator-adapted shear number approach to account for differences in layout and operation mode between compaction simulator and rotary press, respectively. These approaches support the general aim of this study to provide a more straightforward determination of scaling process parameters between rotary press and compaction simulator and facilitate a quicker and more reliable process transfer.

Elastic recovery in roll compaction simulation

Roll compaction/dry granulation is a widely used granulation method in the pharmaceutical industry. The simulation of the process is of great interest, especially in the early phase of formulation development of solid dosage forms. The hybrid modeling approach allows to predict the roll compaction process parameters to produce ribbons with a desired solid fraction. Based on the process parameters, compacts (ribblets) of the same solid fraction are produced on a single punch press. So far, the prediction accuracy for the solid fraction of the ribbons was not satisfactory. It was found that the lack in prediction accuracy was due to the elastic recovery, which was not considered in the model. In this study, the fast in-die and the slow out-of-die elastic recovery of different excipients with varying compaction properties were investigated. A method was established to compensate for the elastic recovery of compacts in roll compaction simulation and to improve the prediction accuracy of the solid fraction considerably. The results were successfully implemented into the model through an additional learning step. Moreover, the findings were transferred to the mimicking of an API containing formulation. By modeling, it was possible to accurately predict the process settings to obtain ribbons with the desired solid fraction using only a small amount of material.

Using a Material Library to Understand the Impacts of Raw Material Properties on Ribbon Quality in Roll Compaction

The purpose of this study is to use a material library to investigate the effect of raw material properties on ribbon tensile strength (TS) and solid fraction (SF) in the roll compaction (RC) process. A total of 81 pharmaceutical materials, including 53 excipients and 28 natural product powders (NPPs), were characterized by 22 material descriptors and were compacted under five different hydraulic pressures. The transversal and longitudinal splitting behaviors of the ribbons were summarized. The TS-porosity and TS-pressure relationships were used to explain the roll compaction behavior of powdered materials. Through defining the target ribbon quality (i.e., 0.6 ≤ SF ≤ 0.8 and TS ≥ 1 MPa), the roll compaction behavior classification system (RCBCS) was built and 81 materials were classified into three categories. A total of 24 excipients and five NPPs were classified as Category I materials, which fulfilled the target ribbon quality and had less occurrence of transversal splitting. Moreover, the multivariate relationships between raw material descriptors, the hydraulic pressure and ribbon quality attributes were obtained by PLS regression. Four density-related material descriptors and the cohesion index were identified as critical material attributes (CMAs). The multi-objective design space summarizing the feasible material properties and operational region for the RC process were visualized. The RCBCS presented in this paper enables a formulator to perform the initial risk assessment of any new materials, and the data modeling method helps to predict the impact of formulation ingredients on strength and porosity of compacts.

Model-based approach to the design of pharmaceutical roller-compaction processes

This work presents a new model based approach to process design and scale-up within the same equipment of a roller compaction process. The prediction of the operating space is not performed fully in-silico, but uses low-throughput experiments as input. This low-throughput data is utilized in an iterative calibration routine to describe the behavior of the powder in the roller compactor and improves the predictive quality of the mechanistic models at low and high-throughput. The model has been validated with an experimental design of experiments of two ibuprofen formulations. The predicted sweet spots in the operating space are in good agreement with the experimental results.