Continuous Twin Screw Granulation: A Review of Recent Progress and Opportunities in Formulation and Equipment Design

An Advanced Twin-Screw Granulation Technology: The use of Non-Volatile Solvents with High Solubilizing Capacity

PURPOSE

Twin-screw wet granulation (TSWG) is a manufacturing process that offers several advantages for the processing of water-insoluble active pharmaceutical ingredients (APIs) and has been used for increasing the solubility and dissolution rates. Here we introduce a novel TSWG approach with reduced downstream processing steps by using non-volatile solvents as granulating binders.

METHODS

Herein, TSWG was carried out using Transcutol a non-volatile protic solvent as a granulating binder and dissolution enhancer of ibuprofen (IBU) blends with cellulose polymer grades (Pharmacoat® 603, Affinisol™, and AQOAT®).

RESULTS

The physicochemical characterisation of the produced granules showed excellent powder flow and the complete transformation of IBU into the amorphous state. Dissolution studies presented immediate release rates for all IBU formulations due to the high drug-polymer miscibility and the Transcutol solubilising capacity.

CONCLUSIONS

Overall, the study demonstrated an innovative approach for the development of extruded granules by processing water-insoluble APIs with non-volatile solvents for enhanced dissolution rates at high drug loadings.

Critical review on the role of excipient properties in pharmaceutical powder-to-tablet continuous manufacturing

INTRODUCTION

The pharmaceutical industry is gradually changing batch-wise manufacturing processes to continuous manufacturing processes, due to the advantages it has to offer. The final product quality and process efficiency of continuous manufacturing processes is among others impacted by the properties of the raw materials. Existing knowledge on the role of raw material properties in batch processing is however not directly transferable to continuous processes, due to the inherent differences between batch and continuous processes.

AREAS COVERED

A review is performed to evaluate the role of excipient properties for different unit operations used in continuous manufacturing processes. Unit operations that will be discussed include feeding, blending, granulation, final blending, and compression.

EXPERT OPINION

Although the potency of continuous manufacturing is widely recognized, full utilization still requires a number of challenges to be addressed effectively. An expert opinion will be provided that discusses those challenges and potential solutions to overcome those challenges. The provided overview can serve as a framework for the pharmaceutical industry to push ahead process optimization and formulation development for continuous manufacturing processes.

Evaluation of Polyvinyl Alcohol as Binder during Continuous Twin Screw Wet Granulation

Binder selection is a crucial step in continuous twin-screw wet granulation (TSWG), as the material experiences a much shorter residence time (2-40 s) in the granulator barrel compared to batch-wise granulation processes. Polyvinyl alcohol (PVA) 4-88 was identified as an effective binder during TSWG, but the potential of other PVA grades-differing in polymerization and hydrolysis degree-has not yet been studied. Therefore, the aim of the current study was to evaluate the potential of different PVA grades as a binder during TSWG. The breakage and drying behavior during the fluidized bed drying of drug-loaded granules containing the PVA grades was also studied. Three PVA grades (4-88, 18-88, and 40-88) were characterized and their attributes were compared to previously investigated binders by Vandevivere et al. through principal component analysis. Three binder clusters could be distinguished according to their attributes, whereby each cluster contained a PVA grade and a previously investigated binder. PVA 4-88 was the most effective binder of the PVA grades for both a good water-soluble and water-insoluble formulation. This could be attributed to its high total surface energy, low viscosity, good wettability of hydrophilic and hydrophobic surfaces, and good wettability by water of the binder. Compared to the previously investigated binders, all PVA grades were more effective in the water-insoluble formulation, as they yielded strong granules (friability below 30%) at lower L/S-ratios. This was linked to the high dispersive surface energy of the high-energy sites on the surface of PVA grades and their low surface tension. During fluidized bed drying, PVA grades proved suitable binders, as the acetaminophen (APAP) granules were dried within a short time due to the low L/S-ratio, at which high-quality granules could be produced. In addition, no attrition occurred, and strong tablets were obtained. Based on this study, PVA could be the preferred binder during twin screw granulation due to its high binder effectiveness at a low L/S-ratio, allowing efficient downstream processing. However, process robustness must be controlled by the included excipients, as PVA grades are operating in a narrow L/S-ratio range.

Process Simulation of Twin-Screw Granulation: A Review

Twin-screw granulation has emerged as a key process in powder processing industries and in the pharmaceutical sector to produce granules with controlled properties. This comprehensive review provides an overview of the simulation techniques and approaches that have been employed in the study of twin-screw granulation processes. This review discusses the major aspects of the twin-screw granulation process which include the fundamental principles of twin-screw granulation, equipment design, process parameters, and simulation methodologies. It highlights the importance of operating conditions and formulation designs in powder flow dynamics, mixing behaviour, and particle interactions within the twin-screw granulator for enhancing product quality and process efficiency. Simulation techniques such as the population balance model (PBM), computational fluid dynamics (CFD), the discrete element method (DEM), process modelling software (PMS), and other coupled techniques are critically discussed with a focus on simulating twin-screw granulation processes. This paper examines the challenges and limitations associated with each simulation approach and provides insights into future research directions. Overall, this article serves as a valuable resource for researchers who intend to develop their understanding of twin-screw granulation and provides insights into the various techniques and approaches available for simulating the twin-screw granulation process.

Assessing Abuse-Deterrent formulations utilizing Ion-Exchange resin complexation processed via Twin-Screw granulation for improved safety and effectiveness

Opioid misuse is a public health crisis in the United States. In response, the FDA has approved drug products with abuse-deterrent features to reduce the risk of prescription opioid abuse. Abuse-deterrent formulations (ADFs) typically employ physical or chemical barriers or incorporate agonist-antagonist combinations as mechanisms to deter misuse. This study aims to assess the impact of abuse-deterrent properties, specifically ion-exchange resin complexation as a chemical barrier, on a model drug, promethazine hydrochloride (PMZ) tablets. Various formulations were developed through twin-screw wet granulation (TSWG) followed by twin-screw melt granulation (TSMG). In the TSWG process, the drug interacts with the resin through an exchange reaction, forming a drug-resin complex. Additionally, the study explored factors influencing the complex formation between the drug and resin, using the drug loading status as an indicator. DSC and ATR studies were carried out to confirm the formation of the drug-resin complex. Subsequently, hot melt granulation was employed to create a matrix tablet incorporating Kollidon® SR and Kollicoat® MAE 100P, thereby enabling sustained release properties. The drug-resin complex embedded in the matrix effectively deters abuse through methods like smoking, snorting, or parenteral injection, unless the drug can be extracted. In order to assess this, solvent extraction studies were conducted using an FDA-recommended solvents, determining the potential for abuse. Further investigations involved dissolution tests in change-over media, confirming the extended-release properties of the formulation. Results from dissolution studies comparing the ground and intact tablets provided positive evidence of the formulation's effectiveness in deterring abuse. Finally, alcohol-induced dose-dumping studies were conducted in compliance with FDA guidelines, concluding that the formulation successfully mitigates dose dumping in the presence of alcohol.

Hot-Melt Extrusion: from Theory to Application in Pharmaceutical Formulation-Where Are We Now?

Hot-melt extrusion (HME) is a globally recognized, robust, effective technology that enhances the bioavailability of poorly soluble active pharmaceutical ingredients and offers an efficient continuous manufacturing process. The twin-screw extruder (TSE) offers an extremely resourceful customizable mixer that is used for continuous compounding and granulation by using different combinations of conveying elements, kneading elements (forward and reverse configuration), and distributive mixing elements. TSE is thus efficiently utilized for dry, wet, or melt granulation not only to manufacture dosage forms such as tablets, capsules, or granule-filled sachets, but also for designing novel formulations such as dry powder inhalers, drying units for granules, nanoextrusion, 3D printing, complexation, and amorphous solid dispersions. Over the past decades, combined academic and pharmaceutical industry collaborations have driven novel innovations for HME technology, which has resulted in a substantial increase in published articles and patents. This article summarizes the challenges and models for executing HME scale-up. Additionally, it covers the benefits of continuous manufacturing, process analytical technology (PAT) considerations, and regulatory requirements. In summary, this well-designed review builds upon our earlier publication, probing deeper into the potential of twin-screw extruders (TSE) for various new applications.

Scale-up in twin-screw wet granulation: impact of formulation properties

The focus of this study was to investigate the sensitivity of different drug formulations to differences in process parameters based on previously developed scale-up strategies. Three different formulations were used for scale-up experiments from a QbCon® 1 with a screw diameter of 16 mm and a throughput of 2 kg/h to a QbCon® 25 line with a screw diameter of 25 mm and a throughput of 25 kg/h. Two of those formulations were similar in their composition of excipients but had a different API added to the blend to investigate the effect of solubility of the API during twin-screw wet granulation, while the third formulation was based on a controlled release formulation with different excipients and a high fraction of HPMC. The L/S-ratio had to be set specifically for each formulation as depending on the binder and the overall composition the blends varied significantly in their response to water addition and their overall granulation behavior. Before milling there were large differences in granule size distributions based on scale (Earth Mover's Distance 140-1100 µm, higher values indicating low similarity) for all formulations. However, no major differences in granule properties (e.g. Earth Mover's Distance for GSDs: 23-88 µm) or tablet tensile strength (> 1.8 MPa at a compaction pressure of 200 MPa for all formulations with a coefficient of variation < 0.1, indicating high robustness for all formulations) were observed after milling, which allowed for a successful scale-up independent of the selected formulations.

Validation of model-based design of experiments for continuous wet granulation and drying

This paper presents an application case of model-based design of experiments for the continuous twin-screw wet granulation and fluid-bed drying sequence. The proposed framework consists of three previously developed models. Here, we are testing the applicability of previously published unit operation models in this specific part of the production line to a new active pharmaceutical ingredient. Firstly, a T-shaped partial least squares regression model predicts d-values of granules after wet granulation with different process settings. Then, a high-resolution full granule size distribution is computed by a hybrid population balance and partial least squares regression model. Lastly, a mechanistic model of fluid-bed drying simulates drying time and energy efficiency, using the outputs of the first two models as a part of the inputs. In the application case, good operating conditions were calculated based on material and formulation properties as well as the developed process models. The framework was validated by comparing the simulation results with three experimental results. Overall, the proposed framework enables a process designer to find appropriate process settings with a less experimental workload. The framework combined with process knowledge reduced 73.2% of material consumption and 72.3% of time, especially in the early process development phase.

T-shaped partial least squares for high-dosed new active pharmaceutical ingredients in continuous twin-screw wet granulation: Granule size prediction with limited material information

This work presents a granule size prediction approach applicable to diverse formulations containing new active pharmaceutical ingredients (APIs) in continuous twin-screw wet granulation. The approach consists of a surrogate selection method to identify similar materials with new APIs and a T-shaped partial least squares (T-PLS) model for granule size prediction across varying formulations and process conditions. We devised a surrogate material selection method, employing a combination of linear pre-processing and nonlinear classification algorithms, which effectively identified suitable surrogates for new materials. Using only material properties obtained through four characterization methods, our approach demonstrated its predictive prowess. The selected surrogate methods were seamlessly integrated with our developed T-PLS model, which was meticulously validated for high-dose formulations involving three new APIs. When surrogating new APIs based on Gaussian process classification, we achieved the lowest prediction errors, signifying the method's robustness. The predicted d-values were within the range of uncertainty bounds for all cases, except for d90 of API C. Notably, the approach offers a direct and efficient solution for early-phase formulation and process development, considerably reducing the need for extensive experimental work. By relying on just four material characterization methods, it streamlines the research process while maintaining a high degree of accuracy.

Drying capacity of a continuous vibrated fluid bed dryer - Statistical and mechanistic model development

The drying capacity of a continuous vibrated fluid bed dryer was studied using a DoE by varying microcrystalline cellulose content in the formulation, water amount in the twin-screw granulation, inlet air temperature, air flow rate and the acceleration of the horizontal fluid-bed. Temperature and humidity profiles were measured along the dryer using wireless sensors. For the parameter space explored in this study, acceleration was the most influential process parameter of the dryer regarding the resulting granule moisture content. An empirical model was developed that allowed for fast and accurate moisture content prediction that could be incorporated into an enhanced control strategy. In addition, a mechanistic model was formulated that allow for prediction of temperature and moisture profiles, and most importantly the moisture content of the granules inside the dryer. The mechanistic model can be integrated to other unit operation models to provide overall understanding of an integrated continuous process line. The mechanistic model also makes it possible to define the equipment design requirements (e.g., length of the dryer) to meet the specific needs in terms of drying capacity, temperature and moisture profile.

Integrated Continuous Wet Granulation and Drying: Process Evaluation and Comparison with Batch Processing

The pharmaceutical industry is in the midst of a transition from traditional batch processes to continuous manufacturing. However, the challenges in making this transition vary depending on the selected manufacturing process. Compared with other oral solid dosage processes, wet granulation has been challenging to move towards continuous processing since traditional equipment has been predominantly strictly batch, instead of readily adapted to material flow such as dry granulation or tablet compression, and there have been few equipment options for continuous granule drying. Recently, pilot and commercial scale equipment combining a twin-screw wet granulator and a novel horizontal vibratory fluid-bed dryer have been developed. This study describes the process space of that equipment and compares the granules produced with batch high-shear and fluid-bed wet granulation processes. The results of this evaluation demonstrate that the equipment works across a range of formulations, effectively granulates and dries, and produces granules of similar or improved quality to batch wet granulation and drying.

On the influence of raw material attributes on process behaviour and product quality in a continuous WET granulation tableting line

Continuous manufacturing of oral solids is a complex process in which critical material attributes (CMAs), formulation and critical process parameters (CPPs) play a fundamental role. However, assessing their effect on the intermediate and final product's critical quality attributes (CQAs) remains challenging. The aim of this study was to tackle this shortcoming by evaluating the influence of raw material properties and formulation composition on the processability and quality of granules and tablets on a continuous manufacturing line. Powder-to-tablet manufacturing was performed using four formulations in various process settings. Pre-blends of different drug loadings (2.5 % w/w and 25% w/w) and two BCS classes (Class I and II) were continuously processed on an integrated process line ConsiGmaTM 25, including twin screw wet granulation, fluid bed drying, milling, sieving, in-line lubrication and tableting. The liquid-to-solid ratio and the granule drying time were varied to process granules under nominal, dry and wet conditions. It was shown that the BCS class and the drug dosage influenced the processability. Intermediate quality attributes, such as the loss on drying and the particle size distribution, directly correlated with the raw material's properties and process parameters. Process settings had a profound impact on the tablet's hardness, disintegration time, wettability and porosity.

Application of I-Optimal Design for Modeling and Optimizing the Operational Parameters of Ibuprofen Granules in Continuous Twin-Screw Wet Granulation

The continuous twin-screw wet granulation (TSWG) process was investigated and optimized with prediction-oriented I-optimal designs. The I-optimal designs can not only obtain a precise estimation of the parameters that describe the effect of five input process parameters, including the screw speed, liquid-to-solid (L/S) ratio, TSWG feed rate, and numbers of the 30° and 60° mixing elements, on the granule quality in a TSWG process, but it can also provide a prediction of the response to determine the optimum operating conditions. Based on the constraints of the desired granule properties, a design space for the TSWG was determined, and the ranges of the operating parameters were defined. An acceptable degree of prediction was confirmed through validation experiments, demonstrating the reliability and effectiveness of using the I-optimal design method to study the TSWG process. The I-optimal design method can accelerate the screening and optimization of the TSWG process.

Pharmaceutical Application of Process Understanding and Optimization Techniques: A Review on the Continuous Twin-Screw Wet Granulation

Twin-screw wet granulation (TSWG) is a method of continuous pharmaceutical manufacturing and a potential alternative method to batch granulation processes. It has attracted more and more interest nowadays due to its high efficiency, robustness, and applications. To improve both the product quality and process efficiency, the process understanding is critical. This article reviews the recent work in process understanding and optimization for TSWG. Various aspects of the progress in TSWG like process model construction, process monitoring method development, and the strategy of process control for TSWG have been thoroughly analyzed and discussed. The process modeling technique including the empirical model, the mechanistic model, and the hybrid model in the TSWG process are presented to increase the knowledge of the granulation process, and the influence of process parameters involved in granulation process on granule properties by experimental study are highlighted. The study analyzed several process monitoring tools and the associated technologies used to monitor granule attributes. In addition, control strategies based on process analytical technology (PAT) are presented as a reference to enhance product quality and ensure the applicability and capability of continuous manufacturing (CM) processes. Furthermore, this article aims to review the current research progress in an effort to make recommendations for further research in process understanding and development of TSWG.

Partial least squares regression to calculate population balance model parameters from material properties in continuous twin-screw wet granulation

In the pharmaceutical industry, twin-screw wet granulation has become a realistic option for the continuous manufacturing of solid drug products. Towards the efficient design, population balance models (PBMs) have been recognized as a tool to compute granule size distribution and understand physical phenomena. However, the missing link between material properties and the model parameters limits the swift applicability and generalization of new active pharmaceutical ingredients (APIs). This paper proposes partial least squares (PLS) regression models to assess the impact of material properties on PBM parameters. The parameters of the compartmental one-dimensional PBMs were derived for ten formulations with varying liquid-to-solid ratios and connected with material properties and liquid-to-solid ratios by PLS models. As a result, key material properties were identified in order to calculate it with the necessary accuracy. Size- and moisture-related properties were influential in the wetting zone whereas density-related properties were more dominant in the kneading zones.

Evaluation of the influence of material properties and process parameters on granule porosity in twin-screw wet granulation

In recent years, continuous twin-screw wet granulation (TSWG) is gaining increasing interest from the pharmaceutical industry. Despite the many publications on TSWG, only a limited number of studies focused on granule porosity, which was found to be an important granule property affecting the final tablet quality attributes, e.g. dissolution. In current study, the granule porosity along the length of the twin-screw granulator (TSG) barrel was evaluated. An experimental set-up was used allowing the collection of granules at the different TSG compartments. The effect of active pharmaceutical ingredient (API) properties on granule porosity was evaluated by using six formulations with a fixed composition but containing APIs with different physical-chemical properties. Furthermore, the importance of TSWG process parameters liquid-to-solid (L/S) ratio, mass feed rate and screw speed for the granule porosity was evaluated. Several water-related properties as well as particle size, density and flow properties of the API were found to have an important effect on granule porosity. While the L/S ratio was confirmed to be the dictating TSWG process parameter, granulator screw speed was also found to be an important process variable affecting granule porosity. This study obtained crucial information on the effect of material properties and process parameters on granule porosity (and granule formation) which can be used to accelerate TSWG process and formulation development.

Towards the Continuous Manufacturing of Liquisolid Tablets Containing Simethicone and Loperamide Hydrochloride with the Use of a Twin-Screw Granulator

Continuous manufacturing is becoming the new technological standard in the pharmaceutical industry. In this work, a twin-screw processor was employed for the continuous production of liquisolid tablets containing either simethicone or a combination of simethicone with loperamide hydrochloride. Both active ingredients present major technological challenges, as simethicone is a liquid, oily substance, and loperamide hydrochloride was used in a very small amount (0.27% w/w). Despite these difficulties, the use of porous tribasic calcium phosphate as a carrier and the adjustment of the settings of the twin-screw processor enabled the optimization of the characteristics of the liquid-loaded powders and made it possible to efficiently produce liquisolid tablets with advantages in physical and functional properties. The application of chemical imaging by means of Raman spectroscopy allowed for the visualization of differences in the distribution of individual components of the formulations. This proved to be a very effective tool for identifying the optimum technology to produce a drug product.

Model-Guided Development of a Semi-Continuous Drying Process

INTRODUCTION

With an increased adoption of continuous manufacturing for pharmaceutical production, the ConsiGma® CTL25 wet granulation and tableting line has reached widespread use. In addition to the continuous granulation step, the semi-continuous six-segmented fluid bed dryer is a key unit in the line. The dryer is expected to have an even distribution of the inlet air between the six drying cells. However, process observations during manufacturing runs showed a repeatable pattern in drying time, which suggests a variability in the drying performance between the different cells of the dryer. The aim of this work is to understand the root-cause of this variability.

MATERIALS AND METHODS

In a first step, the variability in the air temperature and air flow velocity between the dryer cells was measured on an empty dryer. In a second step, the experimental data were interpreted with the help of results from computational fluid dynamics (CFD) simulations to better understand the reasons for the observed variability.

RESULTS

The CFD simulations were used to identify one cause of the measured difference in the air temperature, showing the impact of the air inlet design on the temperature distribution in the dryer.

CONCLUSIONS

Although the simulation could not predict the exact temperature, the trend was similar to the experimental observations, demonstrating the added value of this type of simulation to guide process development, engineering decisions and troubleshoot equipment performance variability.

Faster to First-time-in-Human: Prediction of the liquid solid ratio for continuous wet granulation

In early development, when active pharmaceutical ingredient (API) is in short supply, it would be beneficial to reduce the number of experiments by predicting a suitable L/S ratio before starting the product development. The aim of the study was to decrease development time and the amount of API needed for the process development of high drug load formulations for continuous twin-screw wet granulation (TSWG). Mixer torque rheometry was used as a pre-formulation tool to predict the suitable L/S ratios for granulation experiments. Three different values that were based on the MTR curves, were determined and assessed for their ability to predict the suitable L/S ratio for TSWG. Three APIs (allopurinol, paracetamol and metformin HCl) were used as model substances in high drug load formulations containing 60% drug substance. The MCC-mannitol ratio was varied to assess the optimal composition for the high-dose formulations. The API solubility affected the mixer torque rheometer (MTR) curves and the optimum L/S ratio for TSWG. The highly soluble metformin needed a much lower L/S ratio compared with allopurinol and paracetamol. A design space was determined for each API based on granule flowability and tablet tensile strength. The flowability of the granules and tensile strength of the tablets improved with an increasing L/S ratio. The MCC-mannitol filler ratio had a significant effect on tabletability for paracetamol and metformin, and these APIs having poor compaction properties needed higher MCC ratios to achieve the 2 MPa limit. The MCC-mannitol ratio had no effect on the granule flow properties. Instead, API properties had the largest influence on both granule flow properties and tensile strength. Based on this study, both the L/S ratio and MCC-mannitol ratio are crucial in controlling the critical quality attributes in high drug load formulations processed by TSWG. The optimum flow and tablet mechanical properties were achieved when using 75:25 MCC-mannitol ratio. Both start of the slope and 2/3 of the L/S ratio at the maximum torque in MTR provided a solid guideline to aim for in a TSWG experiment.

Analysis of the Effects of Process Parameters on Start-Up Operation in Continuous Wet Granulation

Toward further implementation of continuous tablet manufacturing, one key issue is the time needed for start-up operation because it could lead to lower product yield and reduced economic performance. The behavior of the start-up operation is not well understood; moreover, the definition of the start-up time is still unclear. This work investigates the effects of process parameters on the start-up operation in continuous wet granulation, which is a critical unit operation in solid drug manufacturing. The profiles of torque and granule size distribution were monitored and measured for the first hour of operation, including the start-up phase. We analyzed the impact of process parameters based on design of experiments and performed an economic assessment to see the effects of the start-up operation. The torque profiles indicated that liquid-to-solid ratio and screw speed would affect the start-up operation, whereas different start-up behavior resulted in different granule size. Depending on the indicator used to define the start-up operation, the economic optimal point was significantly different. The results of this study stress that the start-up time differs according to the process parameters and used definition, e.g., indicators and criteria. This aspect should be considered for the further study and regulation of continuous manufacturing.

Review: Continuous Manufacturing of Small Molecule Solid Oral Dosage Forms

Continuous manufacturing (CM) is defined as a process in which the input material(s) are continuously fed into and transformed, and the processed output materials are continuously removed from the system. CM can be considered as matching the FDA's so-called 'Desired State' of pharmaceutical manufacturing in the twenty-first century as discussed in their 2004 publication on 'Innovation and Continuous Improvement in Pharmaceutical Manufacturing'. Yet, focused attention on CM did not really start until 2014, and the first product manufactured by CM was only approved in 2015. This review describes some of the benefits and challenges of introducing a CM process with a particular focus on small molecule solid oral dosage forms. The review is a useful introduction for individuals wishing to learn more about CM.