Roller compaction process development and scale up using Johanson model calibrated with instrumented roll data

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.

Implementation of mechanistic modeling and global sensitivity analysis (GSA) for design, optimization, and scale-up of a roller compaction process

The pharmaceutical industry has been shifting towards the application of mechanistic modeling to improve process robustness, enable scale-up, and reduce time to market. Modeling approaches have been well-developed for processes such as roller compaction, a continuous dry granulation process. Several mechanistic models/approaches have been documented with limited application to high drug-loaded formulations. In this study, the Johanson model was employed to optimize roller compaction processing and guide its scale-up for a high drug loaded formulation. The model was calibrated using a pilot-scale Minipactor and was validated for a commercial-scale Macropactor. Global sensitivity analysis (GSA) was implemented to determine the impact of process parameter variations (roll force, gap, speed) on a quality attribute [solid fraction (SF)]. The throughput method, which estimates SF values of ribbons using granule production rate, was also studied. The model predicted SF values for all 14 Macropactor batches within ± 0.04 SF. The throughput method estimated SF with ± 0.06 SF for 7 out of 11 batches. GSA confirmed that roll force had the largest impact on SF. This case study represents a process modeling approach to build quality into the products/processes and expands the use of mechanistic modeling during drug product development.

Determining the Impact of Roller Compaction Processing Conditions on Granulate and API Properties: Impact of Formulation API Load

Previous work demonstrated that roller compaction of a 40%w/w theophylline-loaded formulation resulted in granulate consisting of un-compacted fractions which were shown to constitute between 34 and 48%v/v of the granulate dependent on processing conditions. The active pharmaceutical ingredient (API) primary particle size within the un-compacted fraction was also shown to have undergone notable size reduction. The aim of the current work was to test the hypothesis that the observations may be more indicative of the relative compactability of the API due to the formulation being above the percolation threshold. This was done by assessing the impact of varied API loads in the formulation on the non-granulated fraction of the final granulate and the extent of attrition of API particles within the non-granulated fraction. The influence of processing conditions for all formulations was also investigated. The results verify that the observations, both of this study and the previous work, are not a consequence of exceeding the percolation threshold. The volume of un-compacted material within the granulate samples was observed to range between 34.7 and 65.5% depending on the API load and roll pressure, whilst the API attrition was equivalent across all conditions.

Elucidating the Impact of Material Properties on Tablet Manufacturability for Binary Paracetamol Blends

PURPOSE

Although the mechanical properties of paracetamol and MCC are extensively described in literature, there still is a need for a better understanding of the material properties impacting them. Thus, this study systematically analyzed material properties of paracetamol-MCC blends to elucidate their influence on the mechanical tablet properties in roller compaction and direct compression with special focus on surface properties.

METHODS

Multiple material characteristics of binary mixtures of paracetamol and MCC with varying drug loads were analyzed, with particular emphasis on specific surface area and surface energy. Subsequently, mechanical tablet properties of the materials in direct compression and after roller compaction were examined.

RESULTS

It was demonstrated that the impact of the initial material properties on mechanical tablet properties prevailed over the impact of processing route for paracetamol-MCC blends, underlining the importance of material characterization for tabletability of oral solid dosage forms. By applying bivariate as well as multivariate analysis, key material properties influencing the tabletability of paracetamol, MCC and its mixtures such as surface area, surface energy, effective angle of internal friction and density descriptors were identified.

CONCLUSIONS

This study highlighted the importance of comprehensive assessment of different material characteristics leading to a deeper understanding of underlying factors impacting mechanical tablet properties in direct compression and after roller compaction by the example of paracetamol-MCC mixtures with varying drug loads. Furthermore, it was shown that multivariate analysis could be a valuable extension to common bivariate analysis to reveal underlying correlations of material properties.

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.

Pharmaceutical application of multivariate modelling techniques: a review on the manufacturing of tablets

The tablet manufacturing process is a complex system, especially in continuous manufacturing (CM). It includes multiple unit operations, such as mixing, granulation, and tableting. In tablet manufacturing, critical quality attributes are influenced by multiple factorial relationships between material properties, process variables, and interactions. Moreover, the variation in raw material attributes and manufacturing processes is an inherent characteristic and seriously affects the quality of pharmaceutical products. To deepen our understanding of the tablet manufacturing process, multivariable modeling techniques can replace univariate analysis to investigate tablet manufacturing. In this review, the roles of the most prominent multivariate modeling techniques in the tablet manufacturing process are discussed. The review mainly focuses on applying multivariate modeling techniques to process understanding, optimization, process monitoring, and process control within multiple unit operations. To minimize the errors in the process of modeling, good modeling practice (GMoP) was introduced into the pharmaceutical process. Furthermore, current progress in the continuous manufacturing of tablets and the role of multivariate modeling techniques in continuous manufacturing are introduced. In this review, information is provided to both researchers and manufacturers to improve tablet quality.

Determining the Impact of Roller Compaction Processing Conditions on Granule and API Properties

The attrition of drug particles during the process of dry granulation, which may (or may not) be incorporated into granules, could be an important factor in determining the subsequent performance of that granulation, including key factors such as sticking to punches and bio-performance of the dosage form. It has previously been demonstrated that such attrition occurs in one common dry granulation process train; however, the fate of these comminuted particles in granules was not determined. An understanding of the phenomena of attrition and incorporation into granule will improve our ability to understand the performance of granulated systems, ultimately leading to an improvement in our ability to optimize and model the process. Unique feeding mechanisms, geometry, and milling systems of roller compaction equipment mean that attrition could be more or less substantial for any given equipment train. In this work, we examined attrition of API particles and their incorporation into granule in an equipment train from Gerteis, a commonly used equipment train for dry granulation. The results demonstrate that comminuted drug particles can exist free in post-milling blends of roller compaction equipment trains. This information can help better understand the performance of the granulations, and be incorporated into mechanistic models to optimize such processes.

Model-Based Scale-Up Methodologies for Pharmaceutical Granulation

In the pharmaceutical industry, it is a major challenge to maintain consistent quality of drug products when the batch scale of a process is changed from a laboratory scale to a pilot or commercial scale. Generally, a pharmaceutical manufacturing process involves various unit operations, such as blending, granulation, milling, tableting and coating and the process parameters of a unit operation have significant effects on the quality of the drug product. Depending on the change in batch scale, various process parameters should be strategically controlled to ensure consistent quality attributes of a drug product. In particular, the granulation may be significantly influenced by scale variation as a result of changes in various process parameters and equipment geometry. In this study, model-based scale-up methodologies for pharmaceutical granulation are presented, along with data from various related reports. The first is an engineering-based modeling method that uses dimensionless numbers based on process similarity. The second is a process analytical technology-based modeling method that maintains the desired quality attributes through flexible adjustment of process parameters by monitoring the quality attributes of process products in real time. The third is a physics-based modeling method that involves a process simulation that understands and predicts drug quality through calculation of the behavior of the process using physics related to the process. The applications of these three scale-up methods are summarized according to granulation mechanisms, such as wet granulation and dry granulation. This review shows that these model-based scale-up methodologies provide a systematic process strategy that can ensure the quality of drug products in the pharmaceutical industry.

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.

Parameter estimation for roller compaction process using an instrumented vector TF mini roller compactor

Using instrumented roll technology, statistical models relating process parameters such as hydraulic pressure, roll speed and screw speed of Vector TF mini roller compactor to ribbon normal stress and density were developed for placebo blends. Normal stress was found to be directly proportional to hydraulic pressure, roll speed and inversely to screw to roll speed ratio. A power-law relationship between ribbon density and normal stress was observed for placebo blends. Models developed for placebo were found to predict ribbon densities of active blends with good accuracy. Standard optimization of roller compaction process parameters involves the investment of a large amount of time and active ingredient. These models can, therefore, be utilized to predict starting instrument settings required to generate a ribbon of desired solid fraction during early-stage development where material availability & time is limited.

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.

Impact of roll compaction design, process parameters, and material deformation behaviour on ribbon relative density

Ribbons from microcrystalline cellulose (MCC), mannitol, and their 50:50% mixture were produced using the roll compactors AlexanderWerk BT120, Hosokawa Alpine Pharmapaktor C250, L.B. Bohle BRC 25, and Gerteis Mini-Pactor in the frame of multilevel full factorial experimental plans. The specific compaction force (SCF)/hydraulic pressure (HP), gap width (GW), roll speed, and fraction of MCC were analyzed as quantitative factors, whereas the roll surface and sealing system were examined as qualitative factors. Ribbon relative density was investigated as response of the models. The SCF/HP is found to be the most significant factor in each model. A significant inverse effect of the GW is obtained in the models of AlexanderWerk BT120, Pharmapaktor C250, and BRC 25 roll compactors, using smooth rolls. The principle of the establishment of a conversion factor (c_f) is introduced based on the obtained data sets of AlexanderWerk BT120 and Mini-Pactor. This can facilitate the transfer of a roll compaction process between different types of roll compactors.

Determination of the Nip Angle in Roller Compactors With Serrated Rolls

In roller compaction, the nip angle defines the critical transition interface between the slip and nip regions which is used to model material densification behavior and the properties of compacted ribbons. Current methods to determine the nip angle require either sophisticated instrumentation on smooth rolls or input parameters that are difficult to obtain experimentally. In this study, a practical method to determine nip angles for serrated rolls was developed based on mass balance considerations established around the nip region. Experimental input relating to roll geometry, powder density, and mass output from the compactor were required and they could be obtained reliably. The calculated nip angles were validated against those obtained from physical measurements during actual roll compaction. These nip angles were in agreement for various powder formulations containing plastic and brittle materials. The nip angles ranged from 4° to 12° and decreased significantly when the proportion of brittle material increased. Nip angles were also calculated using the widely used Johanson model. However, wall friction measurement on serrated roll surfaces could be impractical. The Johanson model-derived nip angles could differ by 3°-8° just by altering the roughness of the reference wall and this had compromised their reliability.

MCC-mannitol mixtures after roll compaction/dry granulation: percolation thresholds for ribbon microhardness and granule size distribution

In roll compaction, the specific compaction force, the gap width and the roll speed are the most important settings as they have a high impact in the products obtained. However the mechanical properties of the mixture being compacted are also critical. For this reason, a multilevel full factorial design including these parameters as factors plus three repetitions of the center point was performed for microcrystalline cellulose, mannitol and five binary mixtures (15, 30, 50, 70 and 85% MCC). These two reference excipients were chosen in order to investigate the plastic/brittle behavior of mixtures for the roll compaction process. These materials were roll compacted in a 3-W-Polygran^® 250/50/3 (Gerteis) and the ribbons obtained were collected and milled into granules which were characterized regarding granule size distribution. After statistical evaluation, it was found that the most critical factors affecting the D10, D50, D90 and the fines fraction from the granules were the gap width and the specific compaction force, as well as the proportion of MCC together with its quadratic effect and the interaction between force and proportion of MCC. The microhardness of the ribbons from the center point as well as the D10, D50, D90 and the fines fraction from the granules produced at these same conditions were characterized. In all the cases, the proportion of MCC, i.e. the composition of the mixture, showed also an important effect on these properties measured. In this sense, the percolation theory was applied in order to study further the importance of the plastic/brittle ratio by calculating the percolation threshold or the limit over which the behavior of the system changes. This resulted in values of 34% for the HU (expression of microhardness), 27% and 28% for the D10 and fines, respectively (percolation of MCC) and 84% and 85% for the D50 and D90, respectively (percolation of mannitol).