Quality control is an important element in any manufacturing process but when the products are components for use in medical devices, it is more than important, it is critical. Many medical device components are manufactured using medical-grade plastics, as the material has excellent biocompatibility, is both lightweight and durable, and can withstand the sterilization process.

When creating a quality management protocol for these types of components, there are particular concerns that must be taken into consideration, not only around characteristics native to the materials but also because these parts can be intricate and are often very small. In general, the quality control process may involve any of the following; inspection, measurement, and documentation in order to provide proof of compliance.

In addition to developing quality control protocols within a manufacturing process, it may also be necessary to have protocols in place for any supply chain vendors. Protocols can be shared with these vendors, or inspection processes can be put in place to ensure that incoming components meet specific requirements.

Automated inspection systems placed on production lines improve productivity and workflow. However, it is still necessary to have human interaction through random checks to safeguard against any changes that may occur during an automated routine.

A quality management process is critical to that ensure products meet customer’s specifications as well as industry standards such as ISO 13485, FDA regulations, and a company’s own quality benchmarks. Below are points to consider when creating a quality protocol.

Volume. The volume of parts that need to be inspected, such as the barrel of a hypodermic needle syringe, will vary according to whether random sample inspections are sufficient or whether every single component needs to be checked. In cases where a device has many components, each of these may need inspecting or measuring, increasing the workload of the inspection team. In such instances, the equipment used will influence the speed of the quality control process; therefore, this needs to be taken into consideration when planning inspection protocols and production timetables.

Component Characteristics. When designing an inspection process for plastics, the protocol needs to include assessing the component for the effects of residual stress, warping, sink marks, or short shots, as well as ensuring there are no residual fragments left behind from the molding process. Often there is also the need to ensure that the parts comply with color and surface finish specifications.

The miniature size of the components used in medical devices, together with the strict quality specifications, means that microscopic inspection is an essential part of the quality control regimen. The design and size of the components being inspected dictates the magnification necessary along with the type of microscope required.

Visual Inspection Requirements. Components need to be inspected at agreed discrete levels of magnification to ensure that quality checks are verifiable and repeatable. For example, initial checks could be undertaken at 8x magnification. However, in instances where there are concerns and parts needs a closer look, 15x magnification could be specified to assess any fault. This prevents operators inspecting at slightly different magnification levels, such as 6x or 20x, possibly impacting compliance.

A quality control protocol should include microscopes that offer a variable magnification range. The range of magnification detailed in the inspection procedure document affects the choice of equipment. For example, if the determined magnification levels were 8x and 15x, a microscope with fixed magnification would be an ideal choice, whereas a requirement for greater magnification levels or the ability to have a range of magnification options would dictate the need for a zoom microscope with the maximum magnification limit to suit.

A protocol needs to ensure that there are no residual fragments left behind from the molding process. (Credit: Vision Engineering)

Additionally, the ability to control depth of field and contrast makes the inspection process far easier, especially when the color or transparency of a plastic part makes it difficult for operators to gain a clear view of edges. Any microscope should provide iris control within the zoom unit. Inspection of parts with hard-to-view edges or features is also helped by the use of an optical system where a 3D, stereo view is achieved.

A digital inspection microscope can display depth of field with the help of a focus stacking feature that layers multiple images, each focused at a slightly different position, providing an image with excellent depth of focus, ensuring intricate details are easily viewed, giving the user all the benefits of high quality optical viewing.

A visual inspection protocol may also need to include processes for quality assessments of cylindrical or multifaceted shapes. In such cases, specifying the use of a microscope that offers a 3D view of the component, together with a 360° rotating viewer option, allows a part to be accurately assessed from all angles. A 360° viewer is great for looking around a raised feature or at the inside edge of a sunken feature. This is useful as the point of connection between surfaces is viewed so that both sides of the surface can be seen. In direct-down views, a vertical surface can’t be seen so the view of the intersection is not as clear.

Metrology Requirements. Apart from visual inspection, there are many instances where components for medical devices need to be measured in order to meet product specifications. The quality control management process should list appropriate measurement routines, together with the degree of accuracy specified by the design team or customer.

The degree of measurement accuracy required can range from basic comparison against a reticule to extremely stringent tolerances, with compliance being measured in microns. Efficiency and accuracy are both important considerations in any quality control process and achieving the right balance between the two can be challenging. In the case of medical devices, it is critical that accuracy is maintained.

Video measurement is fast and accurate, ensuring an efficient process where edges are obvious. However, in the case of plastics, edges or intricate details can be difficult to detect. When this is an issue, the use of an optical measurement system provides better accuracy but may affect the repeatability and reproducibility.

When measuring a variety of components with a range of features, a system that combines both optical and digital measuring capabilities is ideal. When creating any quality control protocol with measurement specifications, quality managers should also consider measurement range in order to assess whether a two or three-axis measurement system is the appropriate choice.

In cases where only the x and y axis of a component need to be measured, a 2D measurement system is specified as part of the quality control guidelines. In such instances, a rapid measurement system is a good choice because it allows several pieces to be placed within the field of view where they can be measured accurately within seconds.

Where large volumes of clear or black plastic components need to be measured across x, y, and z axes, introducing a measurement system that allows operators to switch between noncontact and probe measurement greatly improves the speed of checks without affecting accuracy. A touch probe option allows operators to include both noncontact and contact measurement in a single measurement routine, manually or automated. The routine measures defined features via a digital camera, while concealed or poorly defined features are measured with a touch probe.

Documentation Requirements. The level of detail required for quality assurance documentation is dictated by customer requirements and industry standards. The quality management process may only require that a record be kept showing that the component was inspected and passed the required checks. In other instances, a visual record needs to be stored alongside any written records, meaning image capture becomes a part of the inspection regime, or if reports are required for measurement inspection, choosing the right software with the ability to export reports should be considered.

Whatever the extent of the documentation required, when creating quality assurance methodology, it is important to assess whether specified systems can capture and record relevant information quickly and easily.

There is a lot to consider when creating a quality management protocol, particularly where compliance is critical. With a range of inspection and measurement systems available in the marketplace, developing a quality protocol first helps identify the unique and specific criteria needed for a system to meet the quality protocol requirements.

This article was written by Nili Walp, Marketing Manager, Vision Engineering, New Milford, CT. For more information, visit here .


Medical Design Briefs Magazine

This article first appeared in the December, 2020 issue of Medical Design Briefs Magazine.

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