Evaluation of the Reproducibility and Robustness of Extrusion-Based Bioprinting Processes Applying a Flow Sensor

Bioprinting is increasingly regarded as a suitable additive manufacturing method in biopharmaceutical process development and formulation. In order to manage the leap from research to industrial application, higher levels of reproducibility and a standardized bioprinting process are prerequisites. This said, the concept of process analytical technologies, standard in the biopharmaceutical industry, is still at its very early steps. To date most extrusion-based printing processes are controlled over penumatic pressure and thus not adaptive to environmental or system related changes over several experimental runs. A constant set pressure applied over a number of runs, might lead to variations in flow rate and thus to unreliable printed constructs. With this in mind, the simple question arises whether a printing process based on a set flow rate could improve reproduciblity and transfer to different printing systems. The control and monitoring of flow rate aim to introduce the concept of PAT in the field of bioprinting. This study investigates the effect of different processing modes (set pressure vs. set flow rate) on printing reproducibility occurring during an extrusion-based printing process consisting of 6 experimental runs consisting of 3 printed samples each. Additionally, the influence of different filling levels of the ink containing cartridge during a printing process was determined. Different solutions based on a varying amount of alginate polymer and Kolliphor hydrogels in varying concentrations showed the need for individual setting of printing parameter. To investigate parameter transferability among different devices two different printers were used and the flow was monitored using a flow sensor attached to the printing unit. It could be demonstrated that a set flow rate controlled printing process improved accuracy and the filling level also affects the accuracy of printing, the magnitude of this effects varies as the cartridge level declined. The transferability between printed devices was eased by setting the printing parameters according to a set flow rate of each bioink disregarding the value of the set pressure. Finally, by a bioprinting porcess control based on a set flow rate, the coefficient of variance for printed objects could be reduced from 0.2 to 0.02 for 10% (w/v) alginate polymer solutions

Automated and dynamic extrusion pressure adjustment based on real-time flow rate measurements for precise ink dispensing in 3D bioprinting

Extrusion-based printing relying on pneumatic dispensing systems is the most widely employed tool in bioprinting. However, standardized and reliable methods for process development, monitoring and control are still not established. Suitable printing parameters are often determined in a trial-and-error approach and neither process monitoring nor real-time adjustments of extrusion pressure to environmental and process-related changes are commonly employed. The present study evaluates an approach to introduce flow rate as a main process parameter to monitor and control extrusion-based bioprinting. An experimental setup was established by integrating a liquid flow meter between the cartridge and nozzle of a pneumatically driven bioprinter to measure the actual flow of dispensed ink in real-time. The measured flow rate was fed to a Python-based software tool implementing a proportional-integral-derivative (PID) feedback loop that automatically and dynamically adapted the extrusion pressure of the bioprinter to meet a specified target flow rate. The performance of the employed experimental setup was evaluated with three different model inks in three application examples. a) Continuous dispensing: Several runs of continuous dispensing showed that the PID-based pressure control was able to generate a steady flow rate more consistently and precisely than constant pressure settings. b) Adaptation to ink inhomogeneities: Deliberately created ink inhomogeneities were successfully compensated for by real-time pressure adjustments which profoundly enhanced the printing quality compared to printing without adaptive pressure. c) Process transfer to other nozzle types: Experiments with different nozzle types demonstrated the potential of the established setup to facilitate and accelerate process transfer and development. The present study provides an alternative approach for process design, monitoring and control by introducing flow rate as a main process parameter. We propose bioprinting processes to be based on flow rate specifications instead of constant pressure settings. This approach has the potential to save time by avoiding tedious parameter screenings and to introduce an active, real-time control over the printing process. Subjective influences by individual users during process development can be reduced and the process transfer between different devices and experimental setups can be facilitated and accelerated

Analytics in Extrusion-Based Bioprinting: Standardized Methods Improving Quantification and Comparability of the Performance of Bioinks

Three-dimensional bioprinting and especially extrusion-based printing as a most frequently employed method in this field is constantly evolving as a discipline in regenerative medicine and tissue engineering. However, the lack of relevant standardized analytics does not yet allow an easy comparison and transfer of knowledge between laboratories regarding newly developed bioinks and printing processes. This work revolves around the establishment of a standardized method, which enables the comparability of printed structures by controlling for the extrusion rate based on the specific flow behavior of each bioink. Furthermore, printing performance was evaluated by image-processing tools to verify the printing accuracy for lines, circles, and angles. In addition, and complementary to the accuracy metrics, a dead/live staining of embedded cells was performed to investigate the effect of the process on cell viability. Two bioinks, based on alginate and gelatin methacryloyl, which differed in 1% (w/v) alginate content, were tested for printing performance. The automated image processing tool reduced the analytical time while increasing reproducibility and objectivity during the identification of printed objects. During evaluation of the processing effect of the mixing of cell viability, NIH 3T3 fibroblasts were stained and analyzed after the mixing procedure and after the extrusion process using a flow cytometer, which evaluated a high number of cells. It could be observed that the small increase in alginate content made little difference in the printing accuracy but had a considerable strong effect on cell viability after both processing steps

On the reproducibility of extrusion-based bioprinting: round robin study on standardization in the field

The outcome of three-dimensional (3D) bioprinting heavily depends, amongst others, on the interaction between the developed bioink, the printing process, and the printing equipment. However, if this interplay is ensured, bioprinting promises unmatched possibilities in the health care area. To pave the way for comparing newly developed biomaterials, clinical studies, and medical applications (i.e. printed organs, patient-specific tissues), there is a great need for standardization of manufacturing methods in order to enable technology transfers. Despite the importance of such standardization, there is currently a tremendous lack of empirical data that examines the reproducibility and robustness of production in more than one location at a time. In this work, we present data derived from a round robin test for extrusion-based 3D printing performance comprising 12 different academic laboratories throughout Germany and analyze the respective prints using automated image analysis (IA) in three independent academic groups. The fabrication of objects from polymer solutions was standardized as much as currently possible to allow studying the comparability of results from different laboratories. This study has led to the conclusion that current standardization conditions still leave room for the intervention of operators due to missing automation of the equipment. This affects significantly the reproducibility and comparability of bioprinting experiments in multiple laboratories. Nevertheless, automated IA proved to be a suitable methodology for quality assurance as three independently developed workflows achieved similar results. Moreover, the extracted data describing geometric features showed how the function of printers affects the quality of the printed object. A significant step toward standardization of the process was made as an infrastructure for distribution of material and methods, as well as for data transfer and storage was successfully established

On the reproducibility of extrusion-based bioprinting: round robin study on standardization in the field

The outcome of three-dimensional (3D) bioprinting heavily depends, amongst others, on the interaction between the developed bioink, the printing process, and the printing equipment. However, if this interplay is ensured, bioprinting promises unmatched possibilities in the health care area. To pave the way for comparing newly developed biomaterials, clinical studies, and medical applications (i.e. printed organs, patient-specific tissues), there is a great need for standardization of manufacturing methods in order to enable technology transfers. Despite the importance of such standardization, there is currently a tremendous lack of empirical data that examines the reproducibility and robustness of production in more than one location at a time. In this work, we present data derived from a round robin test for extrusion-based 3D printing performance comprising 12 different academic laboratories throughout Germany and analyze the respective prints using automated image analysis (IA) in three independent academic groups. The fabrication of objects from polymer solutions was standardized as much as currently possible to allow studying the comparability of results from different laboratories. This study has led to the conclusion that current standardization conditions still leave room for the intervention of operators due to missing automation of the equipment. This affects significantly the reproducibility and comparability of bioprinting experiments in multiple laboratories. Nevertheless, automated IA proved to be a suitable methodology for quality assurance as three independently developed workflows achieved similar results. Moreover, the extracted data describing geometric features showed how the function of printers affects the quality of the printed object. A significant step toward standardization of the process was made as an infrastructure for distribution of material and methods, as well as for data transfer and storage was successfully established

How is teaching and learning of literacy influenced by methods of text production? An exploratory study by means of Herrndorfs "Tschick"

Literarisches Verstehen von Schüler_innen im Literaturunterricht mit textproduktiven Verfahren wird bisher nur in zwei Perspektiven empirisch untersucht: Während einige nach den didaktischen Potenzialen dieser Verfahren im Literaturunterricht fragen, geht es anderen um kognitionspsychologisch gemessene Wirkungen textproduktiver Verfahren im Vergleich zu textanalytischen. Im vorliegenden Beitrag wird demgegenüber in kommunikationstheoretischer Perspektive nach der pädagogischen Formbildung von Literaturunterricht mit textproduktiven Verfahren gefragt. Dafür rekonstruieren wir ausgewählte Szenen von zwei kontrastiven Fällen des Literaturunterrichts, in dem u.a. mit textproduktiven Verfahren zu Herrndorfs Roman "Tschick" gearbeitet wird. Im Ergebnis wird ein Aussetzen des für Unterrichtsgespräche typischen Frageformats (I-R-E) gezeigt und eine damit zusammenhängende modifizierte Bedeutung der Erzeugung schriftlich fixierter Produkte als Modus der Kontingenzbearbeitung sichtbar. Herausstellen lässt sich auch, dass durch den Verzicht auf eine klassenöffentliche Diskussion der Schülertexte eine Auseinandersetzung zu moralischen Fragen des eigenen Lebens in beiden Fällen vermieden wird. Der Beitrag schließt mit Thesen zum didaktischen Diskurs textproduktiver Verfahren. (DIPF/Orig.)Literary understanding of students in literature classes that focus on processes in text production has empirically been studied from only two perspectives so far: While some ask for the didactical potential of the methods used in literature classes, others are concerned with the cognitive effects of text-productive processes, which can be measured psychologically, in comparison to text-analytical methods. From a perspective based on communication theory, this paper will examine how literary classes undergo pedagogical formation by means text-productive methods. Therefore, selected scenes from two contrasting cases of literature teaching will be reconstructed. Among other things, methods of text-production are used here while being applied to Herrndorf\u27s novel "Tschick". As a result, it is shown that the question format (I-R-E) which is typically used in classroom conversations is suspended. It is also linked to a modified importance of generating written products which becomes visible as a mode of tackling of contingency. Further, it can also be highlighted that in both cases a discussion on moral issues of one\u27s own life is avoided due to the absence of a class public discussion of student texts. The paper concludes with thesis statements concerning the didactic discourse of text-productive processes. (DIPF/Orig.