Pharmaceutical & medical V


alidation causes more headaches for medical device manufacturers than almost any other stage of the


production process. For companies certified to ISO 13485, validation is always a costly and time-consuming undertaking – no matter whether a new process is being set up or an existing process is being transferred. To add to the challenges, manufacturers are confronted with new and stricter regulatory requirements such as the European Medical Device Regulation (MDR) which comes into force this year. Regulatory requirements for qualification


and validation focus on two goals: supplying faultless medical devices, and keeping patients safe. The regulations aim to guarantee product quality based on process quality – in other words, by ensuring that processes are controlled and stable. Consistent process analysis and end-to-end proof of the quality of every single step in the process are therefore essential requirements. However, it can take several months to validate the machinery and the process, and the procedure also involves uncertainties for the manufacturer. This is because the regulatory texts do not specify exactly how validation has to be performed. Nevertheless, several points are clear: medical device manufacturers must make sure that the quality requirements are met, and they must also guarantee complete transparency and documentation throughout the entire value chain. These requirements apply not only to material producers and suppliers but also to manufacturers of injection-molded products, and ultimately to legal manufacturers as well. In the absence of clearly specified requirements, several questions remain open. For example: is the data adequately


documented for all parties involved? And will the various measures, when viewed together, be able to pass an audit?


limitations of machine validation


With conventional process validation methods, the focus is on investigating the machine. The objective here is to find a process window that allows a stable injection molding process so that parts are manufactured in line with specifications. Machine-specific settings are defined with the help of downstream tests that investigate the influence of individual machine settings on the test material and the part-specific attributes of manufactured components. The drawback of this approach is that the knowledge gained is only valid for the machine that is to be qualified – and as a further disadvantage, mapping of conditions in the cavity is usually inadequate. This shortcoming has an unfortunate consequence: when an existing process is transferred to a new machine, it is usually impossible to reproduce the part quality identically. Even though the machine settings are the same, deviations occur in the molded part that will then lead to inconsistent part quality. The result is that every change of machine or location confronts manufacturers with the question of revalidation – and if revalidation is required, there is a lack of clarity regarding its scope.


cavity pressUre: the key to crystal-clear visibility


The sensible way to reduce outlay and effort on multiple revalidations is to apply a machine-independent approach that allows


end-to-end monitoring in the mold – including the manifold and the cavities. Monitoring of this type requires sensors in all the cavities: the most informative process variable here is cavity pressure. It describes the conditions under which the plastic parts are formed throughout all phases of the process – and it also provides insights into the mold where the plastic part is gradually taking shape. Pressure conditions in certain phases of the process correlate to specific attributes of the molded part: during the injection phase, for instance, it is mainly the surface characteristics that are influenced. Likewise, the progression of the compression phase determines factors such as flash and, therefore, possible damage to the mold. And finally, it is the holding pressure phase that has the most critical influence on the part's dimension and weight.


Using reference cUrves to assist process baseline


A stable curve is used as the process baseline. With the help of the baseline curve, the settings on the new machine are optimised in a multi-step process. Credit: Kistler Group


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Inline process monitoring systems such as ComoNeo from Kistler capture the pressure in the cavity throughout the entire molding process, and they document the values measured by piezoelectric sensors in the form of a profile (curve). As well as ensuring complete transparency, this approach plays a key part in process baselining: once a stable process has been defined, its profile can be used as a reference – and this is a major factor in ensuring that parts can quickly be produced with the usual quality after a change of machine or location. To achieve this, the ComoNeoRECOVER Restart Assistant accesses the reference curve for an existing optimal process that already yields a product of perfect quality. It compares this curve to the measurement curve for the new process, so any deviations in the characteristic phases of the process become clearly visible. On this basis, the system suggests that the operator should change specific machine settings to approach the ideal profile for the baseline curve. Part quality is determined by a number of different parameters such as injection speed, holding pressure time and


June 2021 Instrumentation Monthly


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