Roller Compaction Scale-Up Made Simple: An Approximate Analytical Solution to Johanson's Rolling Theory

Modified Roller Compaction Model to Account for Roll Speed Effect on Powder Compaction in Dry Granulation Process

This study introduces a modification to the roller compaction model proposed by Sousa et al.1 to account for the effect of roll speed on powder compaction in the dry granulation process. The proposed model enhances the prediction accuracy, particularly at higher roll speeds, which are often overlooked in existing models. The modified model is validated using literature data, demonstrating improved performance compared to the original model. Additionally, the model is applied to a pharmaceutical formulation, showing its applicability in an industrial context. The integration of the model into gPROMS allows for global sensitivity analysis and design space exploration, providing valuable insights for process optimization and scale-up. The study contributes to the understanding of roller compaction dynamics and offers a practical tool for decision-making in pharmaceutical manufacturing.

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.

Laser Triangulation Based In-Line Elastic Recovery Measurement for the Determination of Ribbon Solid Fraction in Roll Compaction

Process Analytical Technology (PAT) plays a crucial role in the design of today's manufacturing lines as continuous manufacturing becomes more important. Until now PAT tools to measure the ribbon solid fraction (SFribbon) in-line are not commonly used in roll compaction. The aim of this study was therefore to establish a new approach as PAT for in-line ribbon solid fraction determination. Different placebo formulations with different binders and one formulation containing active pharmaceutical ingredient were investigated using in-line laser triangulation measurement to detect the ribbon thickness after compaction. With this the ribbon elastic recovery was determined in-line (ERin-line) while the ribbons are attached to the roll surface. It was found that the ratio (ERratio) between the total elastic recovery and ERin-line is formulation specific and not influenced by any process parameters. This enables ERratio as prediction tool for SFribbon, if the solid fraction at gap (SFgap) width is known. SFgap was determined with ribbon mass flow measurement or based on the Midoux model, a simplified Johanson model, gaining two prediction models for SFribbon. Both models showed good agreement of the predicted SFribbon and the measured one.

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 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 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.

Modelling of the Fine-Grained Materials Briquetting Process in a Roller Press with the Discrete Element Method

By using the Altair® EDEM™ software, which implements the discrete element method, modelling and further study of the processes occurring in the roller press’s deformation area were carried out. It was shown that the discrete element method makes it possible to accurately describe the phenomena occurring in the area of roller press deformation compared with the finite element method. Models of material compaction in a roller press are developed using calcium hydroxide (slaked lime) and copper ore concentrate. The developed model makes it possible to determine the process’s energy parameters and the material’s compaction characteristics, taking into account the characteristics of its constituent particles. It was shown that discrete element modelling could be used effectively to create roller presses that provide rational characteristics of the briquetting process, taking into account the properties of the material being briquetted and the operating modes of the equipment. The results of the studies provided the basis for the applicability of the development of the discrete element method for describing the phenomena occurring in roller presses and accelerating the design of press equipment and briquetting technological processes.

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.

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.

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.