Investigations Concerning the Residence Time Distribution of Twin-Screw-Extrusion Processes as Indicator for Inherent Mixing

Enhancing Process Control and Quality in Amorphous Solid Dispersions Using In-Line UV-Vis Monitoring of L* as a Real-Time Response

Background: This study demonstrates the application of the sequential design of experiments (DoE) approach within the quality by design (QbD) framework to optimize extrusion processes through screening, optimization, and robustness testing. Methods: An in-line UV-Vis process analytical technology (PAT) system was successfully employed to monitor critical quality attributes (CQAs) of piroxicam amorphous solid dispersion (ASD) extrusion products, specifically lightness (L*). Results: L* measurement proved highly effective for ensuring the quality and uniformity of ASDs, offering real-time insights into their physical appearance and process stability. Small variations in L* acted as early indicators of processing issues, such as phase separation or bubble formation, enabling timely intervention. This straightforward and rapid technique supports real-time process monitoring and control, allowing automated adjustments to maintain product consistency and quality. By adopting this strategy, manufacturers can minimize variability, reduce waste, and ensure adherence to quality target product profiles (QTPPs). Conclusions: Overall, this study highlights the value of in-line UV-Vis spectroscopy as a PAT tool in hot melt extrusion, enhancing CQA assessment and advancing the efficiency and reliability of ASD manufacturing.

UV/Vis spectroscopy as an in-line monitoring tool for tablet content uniformity

Continuous manufacturing provides advantages compared to batch manufacturing and is increasingly gaining importance in the pharmaceutical industry. In particular, the implementation of tablet processes in continuous plants is an important part of current research. For this, in-line real-time monitoring of product quality through process analytical technology (PAT) tools is crucial. This study focuses on an in-line UV/Vis spectroscopy method for monitoring the active pharmaceutical ingredient (API) content in tablets. UV/Vis spectroscopy is particularly advantageous here, because it allows univariate data analysis without complex data processing. Experiments were conducted on a rotary tablet press. The tablets consisted of 7- 13 wt% theophylline monohydrate as API, lactose monohydrate and magnesium stearate. Two tablet production rates were investigated, 7200 and 20000 tablets per hour. The UV/Vis probe was mounted at the ejection position and measurements were taken on the tablet sidewall. Validation was according to ICH Q2 with respect to specificity, linearity, precision, accuracy and range. The specificity for this formulation was proven and linearity was sufficient with coefficients of determination of 0.9891 for the low throughput and 0.9936 for the high throughput. Repeatability and intermediate precision were investigated. Both were sufficient, indicated by coefficients of variations with a maximum of 6.46% and 6.34%, respectively. The accuracy was evaluated by mean percent recovery. This showed a higher accuracy at 20000 tablets per hour than 7200 tablets per hour. However, both throughputs demonstrate sufficient accuracy. Finally, UV/Vis spectroscopy is a promising alternative to the common NIR and Raman Spectroscopy.

Material Transport Characteristics in Planetary Roller Melt Granulation

Melt granulation for improving material handling by modifying particle size distribution offers significant advantages compared to the standard methods of dry and wet granulation in dust reduction, obviating a subsequent drying step. Furthermore, current research in pharmaceutical technology aims for continuous methods, as these have an enhanced potential to reduce product quality fluctuations. Concerning both aspects, the use of a planetary roller granulator is consequential. The process control with these machines benefits from the enhanced ratio of heated surface to processed volume, compared to the usually-applied twin-screw systems. This is related to the unique concept of planetary spindles flowing around a central spindle in a roller cylinder. Herein, the movement pattern defines the transport characteristics, which determine the energy input and overall processing conditions. The aim of this study is to investigate the residence time distribution in planetary roller melt granulation (PRMG) as an indicator for the material transport. By altering feed rate and rotation speed, the fill level in the granulator is adjusted, which directly affects the average transport velocity and mixing volume. The two-compartment model was utilized to reflect these coherences, as the model parameters symbolize the sub-processes of axial material transport and mixing.

Predicting Residence Time and Melt Temperature in Pharmaceutical Hot Melt Extrusion

Hot-melt extrusion is increasingly applied in the pharmaceutical area as a continuous processing technology, used to design custom products by co-processing drugs together with functional excipients. In this context, the residence time and processing temperature during extrusion are critical process parameters for ensuring the highest product qualities, particularly of thermosensitive materials. Within this study, a novel strategy is proposed to predict the residence time distribution and melt temperature during pharmaceutical hot-melt extrusion processes based on experimental data. To do this, an autogenic extrusion mode without external heating and cooling was applied to process three polymers (Plasdone S-630, Soluplus and Eudragit EPO) at different specific feed loads, which were set by the screw speed and the throughput. The residence time distributions were modeled based on a two-compartment approach that couples the behavior of a pipe and a stirred tank. The throughput showed a substantial effect on the residence time, whereas the influence of the screw speed was minor. On the other hand, the melt temperatures during extrusion were mainly affected by the screw speed compared to the influence of the throughput. Finally, the compilation of model parameters for the residence time and the melt temperature within design spaces serve as the basis for an optimized prediction of pharmaceutical hot-melt extrusion processes.

Conformational changes and physicochemical attributes of texturized pea protein isolate-konjac gum: With a new perspective of residence time during extrusion

The present study aimed to investigate the effects of different extrusion temperatures (110, 130 and 150 °C) and konjac gum addition (0.1 %, 0.2 %, and 0.3 %) on the flow behavior, physicochemical properties and microstructure of extruded pea protein isolate (PPI). The results showed that the textured protein could be improved by enhancing the extrusion temperature and adding konjac gum during extrusion. The water/oil holding capacity of PPI decreased and the SH content increased after extrusion. With temperature and konjac gum content increased, the β-sheet of extruded proteins transformed to other secondary structural components, and Trp residue transformed to a more polar environment, illustrating the changes in protein conformation. All extruded samples presented as yellow hue with little green and higher lightness, while excessive extrusion process reduced the brightness and promoted more formation of browning pigments. Extruded protein showed more associated layered with some air pores, and its hardness and chewiness increased with the increase of temperature and konjac gum concentration. Cluster analysis showed that the addition of konjac gum could effectively improve the quality characteristics of pea protein under low temperature extrusion, and the effect was similar to that of high temperature extrusion product. With the increase of konjac gum concentration, the flow pattern of protein extrusion gradually converted from plug flow to mixing flow, and the disorder degree of polysaccharide protein mixing system was enhanced. Moreover, Yeh-jaw model showed better fitting effect in F(θ) curves compared to Wolf-white.

Soft sensor for content prediction in an integrated continuous pharmaceutical formulation line based on the residence time distribution of unit operations

In this study, a concentration predicting soft sensor was achieved based on the Residence Time Distribution (RTD) of an integrated, three-step pharmaceutical formulation line. The RTD was investigated with color-based tracer experiments using image analysis. Twin-screw wet granulation (TSWG) was directly coupled with a horizontal fluid bed dryer and an oscillating mill. Based on integrated measurement, we proved that it is also possible to couple the unit operations in silico. Three surrogate tracers were produced with a coloring agent to investigate the separated unit operations and the solid and liquid inputs of the TSWG. The soft sensor's prediction was compared to validating experiments of a 0.05 mg/g (15% of the nominal) concentration change with High-Performance Liquid Chromatography (HPLC) reference measurements of the active ingredient proving the adequacy of the soft sensor (RMSE < 4%).

On-Line Optical Monitoring of the Mixing Performance in Co-Rotating Twin-Screw Extruders

The use of real-time techniques to evaluate the global mixing performance of co-rotating twin-screw extruders is well consolidated, but much less is reported on the specific contribution of individual screw zones. This work uses on-line flow turbidity and birefringence to ascertain the mixing performance of kneading blocks with different geometries. For this purpose, one of the barrel segments of the extruder was modified in order to incorporate four sampling devices and slit dies containing optical windows were attached to them. The experiments consisted in reaching steady extrusion and then adding a small amount of tracer. Upon opening each sampling device, material was laterally detoured from the local screw channel, and its turbidity and birefringence were measured by the optical detector. Residence time distribution curves (RTD) were obtained at various axial positions along three different kneading blocks and under a range of screw speeds. It is hypothesized that K, a parameter related to the area under each RTD curve, is a good indicator of dispersive mixing, whereas variance can be used to assess distributive mixing. The experimental data confirmed that these mixing indices are sensitive to changes in processing conditions, and that they translate the expected behavior of each kneading block geometry.

Using residence time distribution in pharmaceutical solid dose manufacturing - A critical review

While continuous manufacturing (CM) of pharmaceutical solid-based drug products has been shown to be advantageous for improving the product quality and process efficiency in alignment with FDA's support of the quality-by-design paradigm (Lee, 2015; Ierapetritou et al., 2016; Plumb, 2005; Schaber, 2011), it is critical to enable full utilization of CM technology for robust production and commercialization (Schaber, 2011; Byrn, 2015). To do so, an important prerequisite is to obtain a detailed understanding of overall process characteristics to develop cost-effective and accurate predictive models for unit operations and process flowsheets. These models are utilized to predict product quality and maintain desired manufacturing efficiency (Ierapetritou et al., 2016). Residence time distribution (RTD) has been a widely used tool to characterize the extent of mixing in pharmaceutical unit operations (Vanhoorne, 2020; Rogers and Ierapetritou, 2015; Teżyk et al., 2015) and manufacturing lines and develop computationally cheap predictive models. These models developed using RTD have been demonstrated to be crucial for various flowsheet applications (Kruisz, 2017; Martinetz, 2018; Tian, 2021). Though extensively used in the literature (Gao et al., 2012), the implementation, execution, evaluation, and assessment of RTD studies has not been standardized by regulatory agencies and can thus lead to ambiguity regarding their accurate implementation. To address this issue and subsequently prevent unforeseen errors in RTD implementation, the presented article aims to aid in developing standardized guidelines through a detailed review and critical discussion of RTD studies in the pharmaceutical manufacturing literature. The review article is divided into two main sections - 1) determination of RTD including different steps for RTD evaluation including experimental approach, data acquisition and pre-treatment, RTD modeling, and RTD metrics and, 2) applications of RTD for solid dose manufacturing. Critical considerations, pertaining to the limitations of RTDs for solid dose manufacturing, are also examined along with a perspective discussion of future avenues of improvement.

Novel Cleaning-in-Place Strategies for Pharmaceutical Hot Melt Extrusion

To avoid any type of cross-contamination, residue-free production equipment is of utmost importance in the pharmaceutical industry. The equipment cleaning for continuous processes such as hot melt extrusion (HME), which has recently gained popularity in pharmaceutical applications, necessitates extensive manual labour and costs. The present work tackles the HME cleaning issue by investigating two cleaning strategies following the extrusion of polymeric formulations of a hormonal drug and for a sustained release formulation of a poorly soluble drug. First, an in-line quantification by means of UV–Vis spectroscopy was successfully implemented to assess very low active pharmaceutical ingredient (API) concentrations in the extrudates during a cleaning procedure for the first time. Secondly, a novel in-situ solvent-based cleaning approach was developed and its usability was evaluated and compared to a polymer-based cleaning sequence. Comparing the in-line data to typical swab and rinse tests of the process equipment indicated that inaccessible parts of the equipment were still contaminated after the polymer-based cleaning procedure, although no API was detected in the extrudate. Nevertheless, the novel solvent-based cleaning approach proved to be suitable for removing API residue from the majority of problematic equipment parts and can potentially enable a full API cleaning-in-place of a pharmaceutical extruder for the first time.

Quality by design thinking in the development of long-acting injectable PLGA/PLA-based microspheres for peptide and protein drug delivery

Adopting the Quality by Design (QbD) approach in the drug development process has transformed from "nice-to-do" into a crucial and required part of the development, ensuring the quality of pharmaceutical products throughout their whole life cycles. This review is discussing the implementation of the QbD thinking into the production of long-acting injectable (LAI) PLGA/PLA-based microspheres for the therapeutic peptide and protein drug delivery. Various key elements of the QbD approaches are initially elaborated using Bydureon®, a commercial product of LAI PLGA/PLA-based microspheres, as a classical example. Subsequently, the factors influencing the release patterns and the stability of the peptide and protein drugs are discussed. This is followed by a summary of the state-of-the-art of manufacturing LAI PLGA/PLA-based microspheres and the related critical process parameters (CPPs). Finally, a landscape of generic product development of LAI PLGA/PLA-based microspheres is reviewed including some major challenges in the field.

Development and Validation of an In-Line API Quantification Method Using AQbD Principles Based on UV-Vis Spectroscopy to Monitor and Optimise Continuous Hot Melt Extrusion Process

A key principle of developing a new medicine is that quality should be built in, with a thorough understanding of the product and the manufacturing process supported by appropriate process controls. Quality by design principles that have been established for the development of drug products/substances can equally be applied to the development of analytical procedures. This paper presents the development and validation of a quantitative method to predict the concentration of piroxicam in Kollidon^® VA 64 during hot melt extrusion using analytical quality by design principles. An analytical target profile was established for the piroxicam content and a novel in-line analytical procedure was developed using predictive models based on UV-Vis absorbance spectra collected during hot melt extrusion. Risks that impact the ability of the analytical procedure to measure piroxicam consistently were assessed using failure mode and effect analysis. The critical analytical attributes measured were colour (L* lightness, b* yellow to blue colour parameters—in-process critical quality attributes) that are linked to the ability to measure the API content and transmittance. The method validation was based on the accuracy profile strategy and ICH Q2(R1) validation criteria. The accuracy profile obtained with two validation sets showed that the 95% β-expectation tolerance limits for all piroxicam concentration levels analysed were within the combined trueness and precision acceptance limits set at ±5%. The method robustness was tested by evaluating the effects of screw speed (150–250 rpm) and feed rate (5–9 g/min) on piroxicam content around 15% w/w. In-line UV-Vis spectroscopy was shown to be a robust and practical PAT tool for monitoring the piroxicam content, a critical quality attribute in a pharmaceutical HME process.

Scale-Up of pharmaceutical Hot-Melt-Extrusion: Process optimization and transfer

Hot-Melt-Extrusion on Twin-Screw-Extruders has been established as a standard processing technique for pharmaceutical products. A major challenge is the transfer from a lab to a production level, since the combination of several unit operations within one apparatus leads to complex conditions for such a continuous manufacturing process. Here the residence time distribution is a crucial measure, which reflects the different mechanisms, e.g. dissolution, mixing or degradation, during processing. In the first part of a Scale-Up study, a methodology for the optimization of an extrusion process with respect to the load and throughput is presented. The developed concept was applied for different extruder scales in order to compare the identified processing windows. A deviation of the dominant material heating mechanisms was observed for the different scales, while the constraints for the transfer of a process to a different scale by the developed optimization concept is demonstrated. Finally, a sufficient operating point on a reference extruder is identified and in the second part of this study, different concepts from literature are applied for the transfer of this Hot-Melt-Extrusion process to two larger scales. The focus of the investigations was on the impact of the different approaches on the residence time distribution and the comparison. The determined results revealed a change of the most sufficient approach for the two different extruder sizes. The impact on the location in the time domain and form of the distribution are discussed and additionally evaluated by the fit to a RTD-model. In conclusion, the ratio of the applied energy for transport to mixing is identified as valuable addition in this context.