78 TABLETING
logics with model predictive control on platforms such as Matlab.2
Customised control When it comes to customising the control strategy for a new product, rapid prototyping platforms provide a valuable advantage in the early phase. For each product, the process chain implies constraints such as material properties, valid design spaces and critical control parameters, which are identified theoretically or empirically. Finally, the overall control strategy in the production line automation must take into account these constraints, leading towards customised implementations. In such implementations, the entire toolset of controls engineering must be available, reaching from simple decision trees over regular PID control loops towards non- linear, adaptive and model based control algorithms. Especially on rapid prototyping platforms, such implementation of complex control strategies is realised in a reduced time frame, speeding up the process development. Of course, the development and implementation of a control strategy does not suffice without a full understanding of the interrelations and restrictions of each process, sensors and
machinery. For instance, one might consider using NIR spectroscopy to control the continuous feeding and blending of API and excipients. A commonly seen proposal is to use the NIR measurement as a feedback signal into an internal control loop to adjust the gravimetric feeder for the API, while keeping the other (excipient) feeders constant. In such a scenario, it is crucial to ensure that the resolution of the NIR system in conjunction with the applied chemometric model is high enough to provide a stable control system. Unfortunately, although this control loop makes perfect sense from a controls engineer perspective, it will introduce a discrepancy between the product definition in the recipe and the recorded feed rates (mass flow) of all raw material streams. Instead, from a practical and regulatory perspective, the alternative solution is to rely on the accuracy of the gravimetric feeders, dispensing the pre- defined combination of raw material, but to use the NIR signal to identify temporary variations in the final blend in order to reject them if needed. As can be seen from this example, it is important to assess each element of the control strategy from different angles before taking a final decision.
Te good news is that the technologies are readily available. Model predictive control, multi- layered control architectures and rapid prototyping platforms are state of the art, commonly used in related industries to the pharmaceutical field. Similarly, we can quantify the performance and reliability of process and sensory equipment, providing valuable input for the definition of control strategies. Te greater challenge lies in the acceptance of these technologies and in the sharing of knowledge. Pharmaceutical companies, regulatory agencies, equipment suppliers and academia have to collaborate to pave the way for continuous processing in secondary manufacturing and improved quality for solid dosage forms. For this purpose, Bohle has built its Technology Center with the entire continuous processing line as a centre for education and knowledge exchange. Bohle invites pharma companies to contact and join the Technology Center.
For more information ✔ at
www.scientistlive.com/eurolab
Dr Hubertus Rehbaum is manager, Scientific Operations at L.B. Bohle.
www.lbbohle.com
REFERENCES: 1
https://iscmp.mit.edu/white-papers/white-paper-6 2
https://doi.org/10.1016/j.compchemeng.2014.02.029
Tablet press used for academic research
GTP-1 for both tablet compression research and undergraduate teaching. Dr Petr Zámostný, Associate
T
Professor, Department of Organic Technology, explains how the tablet press is now being used in current research programmes at the University: “The GTP helps us to speed up tablet compression screening in reformulation projects aimed at
www.scientistlive.com
he University of Chemistry and Technology, Prague, is now using the Gamlen Tablet Press
replacing the wet granulation by roller compaction and I am looking forward to the GTP-1 helping us in our research project involving the study of glidant action during the secondary compression of dry-granulated product.”
A small machine, with a footprint
similar to an A4 sheet of paper, the Gamlen Tablet Press is safe to use and less complex than a full-scale tablet press; properties that are beneficial in an educational environment.
“I find the GTP-1 very useful for
teaching undergraduate students the principles of tablet compression because of its easy operation and favourable size for bench-top placement”, added Zámostný. The tablet press is designed to
operate in three easy steps; the user simply weighs the powder into a die using a conventional balance, compresses the tablet and then ejects the finished product ready for use.
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