Sensors for biomanufacturing process development: facilitating the shift from batch to continuous manufacturing

Control strategy for biopharmaceutical production by model predictive control

The biopharmaceutical industry is rapidly advancing, driven by the need for cutting-edge technologies to meet the growing demand for life-saving treatments. In this context, Model Predictive Control (MPC) has emerged as a promising solution to address the complexity of modern biopharmaceutical production processes. Its ability to optimize operations and ensure consistent product yields has made it an attractive option for manufacturers in this sector. Furthermore, MPC's alignment with the Process Analytical Technology (PAT) initiative provides an additional layer of assurance, facilitating real-time monitoring and enabling swift adjustments to maintain process integrity. This comprehensive review delves into the various applications of MPC, ranging from robust control to stochastic model predictive control, thereby equipping biotechnologists and process engineers with a powerful toolset. By harnessing the capabilities of MPC, as elucidated in this review, manufacturers can confidently navigate the intricate bioprocessing landscape and unlock this approach's full potential in their production processes.

Current challenges and recent advances on the path towards continuous biomanufacturing

Continuous biopharmaceutical manufacturing is currently a field of intense research due to its potential to make the entire production process more optimal for the modern, ever-evolving biopharmaceutical market. Compared to traditional batch manufacturing, continuous bioprocessing is more efficient, adjustable, and sustainable and has reduced capital costs. However, despite its clear advantages, continuous bioprocessing is yet to be widely adopted in commercial manufacturing. This article provides an overview of the technological roadblocks for extensive adoptions and points out the recent advances that could help overcome them. In total, three key areas for improvement are identified: Quality by Design (QbD) implementation, integration of upstream and downstream technologies, and data and knowledge management. First, the challenges to QbD implementation are explored. Specifically, process control, process analytical technology (PAT), critical process parameter (CPP) identification, and mathematical models for bioprocess control and design are recognized as crucial for successful QbD realizations. Next, the difficulties of end-to-end process integration are examined, with a particular emphasis on downstream processing. Finally, the problem of data and knowledge management and its potential solutions are outlined where ontologies and data standards are pointed out as key drivers of progress.

A novel approach to noninvasive monitoring of dissolved carbon dioxide in small-scale cell culture processes

Disposable small-scale vessels are commonly used in cell culture studies in academia as well as early stages of bioprocess development. These types of research are crucial for our understanding about cells and bioprocesses as they provide important information regarding different parameters affecting cells. Dissolved carbon dioxide (DCO₂) is one main parameter affecting cell metabolism. It is also an indicator of cell culture well-being. Despite CO₂ being a critical process parameter, there is a lack of appropriate monitoring system for CO₂ in small-scale vessels. Here, we present a membrane-based noninvasive method for measuring DCO₂ in cell culture medium. The idea was achieved by modifying a T-flask and replacing a small area of it with CO₂ permeable silicone membrane. In the proposed method, the concentration of CO₂ dissolved in the cell culture medium is determined by measuring the initial diffusion rate of CO₂ through a silicone membrane attached to the bottom wall of the T-flask. The measurement method was validated previously, and the efficacy of the noninvasive method was evaluated by growing E.coli, Pichia pastoris, and CHO cells in the proposed prototype. The results obtained from this method were verified with other quantitative data obtained from the process such as optical density (OD), cell density, dissolved oxygen (DO) and pH. The results show that the proposed membrane-based method is an effective way for completely noninvasive monitoring of DCO₂ in small-scale cell culture processes. Additional diffusing species such as oxygen could also be measured using the same approach.

A Novel Approach for Non-Invasive Continuous In-Line Control of Perfusion Cell Cultivations by Raman Spectroscopy

Continuous manufacturing is becoming more important in the biopharmaceutical industry. This processing strategy is favorable, as it is more efficient, flexible, and has the potential to produce higher and more consistent product quality. At the same time, it faces some challenges, especially in cell culture. As a steady state has to be maintained over a prolonged time, it is unavoidable to implement advanced process analytical technologies to control the relevant process parameters in a fast and precise manner. One such analytical technology is Raman spectroscopy, which has proven its advantages for process monitoring and control mostly in (fed-) batch cultivations. In this study, an in-line flow cell for Raman spectroscopy is included in the cell-free harvest stream of a perfusion process. Quantitative models for glucose and lactate were generated based on five cultivations originating from varying bioreactor scales. After successfully validating the glucose model (Root Mean Square Error of Prediction (RMSEP) of ∼0.2 g/L), it was employed for control of an external glucose feed in cultivation with a glucose-free perfusion medium. The generated model was successfully applied to perform process control at 4 g/L and 1.5 g/L glucose over several days, respectively, with variability of ±0.4 g/L. The results demonstrate the high potential of Raman spectroscopy for advanced process monitoring and control of a perfusion process with a bioreactor and scale-independent measurement method.

Knowing more from less: miniaturization of ligand-binding assays and electrophoresis as new paradigms for at-line monitoring and control of mammalian cell bioprocesses

Monitoring technologies for Process Analytical Technology (PAT) in mammalian cell cultures are often focusing on the same hand full parameters although a deeper knowledge and control of a larger panel of culture components would highly benefit process optimization, control and robustness. This short review highlights key advances in microfluidic affinity assays and microchip capillary electrophoresis (MCE). Aiming at the miniaturization and integration of PAT, these can detect at-line a variety of metabolites, proteins and Critical Quality Attributes (CQA's) in a bioprocess. Furthermore, discrete analytical components, which can potentially support the translation of increasingly mature microfluidic technologies towards this novel application, are also presented as a comprehensive toolbox ranging from sample preparation to signal acquisition.

Process Analytical Technologies and Data Analytics for the Manufacture of Monoclonal Antibodies

Process analytical technology (PAT) for the manufacture of monoclonal antibodies (mAbs) is defined by an integrated set of advanced and automated methods that analyze the compositions and biophysical properties of cell culture fluids, cell-free product streams, and biotherapeutic molecules that are ultimately formulated into concentrated products. In-line or near-line probes and systems are remarkably well developed, although challenges remain in the determination of the absence of viral loads, detecting microbial or mycoplasma contamination, and applying data-driven deep learning to process monitoring and soft sensors. In this review, we address the current status of PAT for both batch and continuous processing steps and discuss its potential impact on facilitating the continuous manufacture of biotherapeutics.

Portable Analytical Techniques for Monitoring Volatile Organic Chemicals in Biomanufacturing Processes: Recent Advances and Limitations

It is essential to develop effective analytical techniques for accurate and continuous monitoring of various biomanufacturing processes, such as the production of monoclonal antibodies and vaccines, through sensitive and quantitative detection of characteristic aqueous or gaseous metabolites and other analytes in the cell culture media. A comprehensive summary toward the use of mainstream techniques for bioprocess monitoring is critically reviewed here, which illustrates the instrumental and procedural advances and limitations of several major analytical tools in biomanufacturing applications. Despite those drawbacks present in modern detection systems such as mass spectrometry, gas chromatography or chemical/biological sensors, a considerable number of useful solutions and inspirations such as electronic or optoelectronic noses can be offered to greatly overcome the restrictions and facilitate the development of advanced analytical techniques that can target a more diverse range of key nutritious components, products or potential contaminants in different biomanufacturing processes.

3D bioprinting using hollow multifunctional fiber impedimetric sensors

3D bioprinting is an emerging biofabrication process for the production of adherent cell-based products, including engineered tissues and foods. While process innovations are rapidly occurring in the area of process monitoring, which can improve fundamental understanding of process-structure-property relations as well as product quality by closed-loop control techniques, in-line sensing of the bioink composition remains a challenge. Here, we report that hollow multifunctional fibers enable in-line impedimetric sensing of bioink composition and exhibit selectivity for real-time classification of cell type, viability, and state of differentiation during bioprinting. Continuous monitoring of the fiber impedance magnitude and phase angle response from 102 to 106 Hz during microextrusion 3D bioprinting enabled compositional and quality analysis of alginate bioinks that contained fibroblasts, neurons, or mouse embryonic stem cells (mESCs). Fiber impedimetric responses associated with the bioinks that contained differentiated mESCs were consistent with differentiation marker expression characterized by immunocytochemistry. 3D bioprinting through hollow multifunctional fiber impedimetric sensors enabled classification of stem cells as stable or randomly differentiated populations. This work reports an advance in monitoring 3D bioprinting processes in terms of in-line sensor-based bioink compositional analysis using fiber technology and provides a non-invasive sensing platform for achieving future quality-controlled bioprinted tissues and injectable stem-cell therapies.

A Geometric Observer-Assisted Approach to Tailor State Estimation in a Bioreactor for Ethanol Production

In this work, a systematic approach based on the geometric observer is proposed to design a model-based soft sensor, which allows the estimation of quality indexes in a bioreactor. The study is focused on the structure design problem where the set of innovated states has to be chosen. On the basis of robust exponential estimability arguments, it is found that it is possible to distinguish all the unmeasured states if temperature and dissolved oxygen concentration measurements are combined with substrate concentrations. The proposed estimator structure is then validated through numerical simulation considering two different measurement processor algorithms: the geometric observer and the extended Kalman filter.

Cavity-Enhanced Raman and Helmholtz Resonator Photoacoustic Spectroscopy to Monitor the Mixed Sugar Metabolism of E. coli

We introduce and compare two powerful new techniques for headspace gas analysis above bacterial batch cultures by spectroscopy, Raman spectroscopy enhanced in an optical cavity (CERS), and photoacoustic detection in a differential Helmholtz resonator (DHR). Both techniques are able to monitor O₂ and CO₂ and its isotopomers with excellent sensitivity and time resolution to characterize bacterial growth and metabolism. We discuss and show some of the shortcomings of more conventional optical density (OD) measurements if used on their own without more sophisticated complementary measurements. The spectroscopic measurements can clearly and unambiguously distinguish the main phases of bacterial growth in the two media studied, LB and M9. We demonstrate how ¹³C isotopic labeling of sugars combined with spectroscopic detection allows the study of bacterial mixed sugar metabolism to establish whether sugars are sequentially or simultaneously metabolized. For E. coli, we have characterized the shift from glucose to lactose metabolism without a classic diauxic lag phase. DHR and CERS are shown to be cost-effective and highly selective analytical tools in the biosciences and in biotechnology, complementing and superseding existing conventional techniques. They also provide new capabilities for mechanistic investigations and show a great deal of promise for use in stable isotope bioassays.

The Microenvironment in Immobilized Enzymes: Methods of Characterization and Its Role in Determining Enzyme Performance

The liquid milieu in which enzymes operate when they are immobilized in solid materials can be quite different from the milieu in bulk solution. Important differences are in the substrate and product concentration but also in pH and ionic strength. The internal milieu for immobilized enzymes is affected by the chemical properties of the solid material and by the interplay of reaction and diffusion. Enzyme performance is influenced by the internal milieu in terms of catalytic rate (“activity”) and stability. Elucidation, through direct measurement of differences in the internal as compared to the bulk milieu is, therefore, fundamentally important in the mechanistic characterization of immobilized enzymes. The deepened understanding thus acquired is critical for the rational development of immobilized enzyme preparations with optimized properties. Herein we review approaches by opto-chemical sensing to determine the internal milieu of enzymes immobilized in porous particles. We describe analytical principles applied to immobilized enzymes and focus on the determination of pH and the O₂ concentration. We show measurements of pH and [O₂] with spatiotemporal resolution, using in operando analysis for immobilized preparations of industrially important enzymes. The effect of concentration gradients between solid particle and liquid bulk on enzyme performance is made evident and quantified. Besides its use in enzyme characterization, the method can be applied to the development of process control strategies.