Best Practices for Medical Device Material Selection

Medical device design and development has evolved over the years, notably influenced by market demands and regulatory requirements. Traditional design practices, beginning with a reliance on generic material specifications, are ill equipped to keep pace with these changes.

Material science expertise alongside regulatory and market knowledge is crucial for the success of a medical product, argues Gavin Braithwaite, CEO of Cambridge Polymer Group. While companies may have some of that expertise in house, groups often exist in silos and it may be more expedient, and ultimately cost-effective, to bring in a fresh set of eyes and avoid delays in the all-important time to market. Braithwaite will talk to this at Advanced Manufacturing Minneapolis on Oct. 17 during his session titled, “Getting Material Selection Right the First Time.” He shared some of his thoughts on the parameters of an effective material selection process with PlasticsToday. 

Based in Woburn, MA, Cambridge Polymer Group has provided materials-related contract testing, research, and development services to global customers since 1996. Braithwaite holds degrees in physics and electrical engineering, a PhD in chemical engineering, and was a post-doctoral fellow at Harvard and MIT, where he designed and tested a micro-shear rheometer.

At what stage of the development process should material selection come into play?

Gavin Braithwaite: Obviously material selection is usually done very early on. However, it is often the case — particularly in smaller organizations or groups — that material selection is not thought through sufficiently at that stage. It is easy to design a prototype concept with off-the-shelf materials, and then the natural inclination is to evolve the design from there. This process can lead the engineer down blind alleys or wasteful detours. But even putting aside the engineering aspect, thinking about market forces is just as important. For example, in recent years there has been a push for onshoring of suppliers as well as second sources, all in the name of supply chain robustness. Being aware of that pressure and taking it into account when selecting materials is vital for the longevity and future of a device.

What primary factors should be taken into consideration when selecting a material?

Braithwaite: Performance is the obvious one, and the one that almost every engineer can solve. But my point is that the engineer needs to think beyond that, particularly in relation to medical devices. Within the concept of their device, they should consider early on what additional forces may intrude on their elegant concept. Sterilization, for example, needs to be considered up front — not after the prototype has been made — because different modalities impact polymers differently. Deciding that terminal radiation sterilization is the only path forward can completely rule out specific materials. Other examples are apparently even more tangential. Currently there is a lot of discussion about fluorinated polymers: Medical devices are largely exempt at the moment . . . but that is likely to change. So, an engineer in the here-and-now might design a perfectly adequate device that only has a limited product life because of regulatory changes completely outside of the engineer’s control.

What are some common errors medical device OEMS make when specifying a material for their device?

Braithwaite: As noted before, sterilization is one we keep seeing. There are a host of manufacturing pressures that drive the choice of sterilization processes — not thinking that through early can be costly and time consuming. Another aspect is additive packages and equivalence. Using off-the-shelf materials for early-stage development can cause a host of issues if the additives are not well understood, or are problematic for the tightening regulatory safety pathway. 

Is there a particular “horror story” you can share illustrating the consequences of ill-advised material selection?

Braithwaite: The one that comes to mind is almost an evolution of a class of devices, rather than a specific product. In orthopedics the first hip replacement by Sir John Charnley was based on PTFE (fluoropolymers again!). This made sense from an engineering design perspective, because PTFE has very low friction. But — as we now know — wear is not the same as friction: The PTFE liners suffered terrible wear, and the devices failed. Obviously now there might be extensive testing to confirm wear properties, and a device could not be implanted without that validation, but the point here is that a simple engineering solution required more material insight than reading the specification sheet for the material. 

If a company does end up having to use a different material than initially planned and development is already well underway, what is the best course of action?

Braithwaite: Collaborating with your vendors is key, and bringing in expertise early can help. Understanding what forces are driving the change, and how they impact the design and materials is key, and getting support to select alternatives, or advise on mitigation strategies, is often the most cost-effective strategy. We have found that companies often have a strong engineering and regulatory staff, but what they are missing is the ability to look beyond their immediate skill set.  This is rarely needed for long, but that input can be vital.

Tell us a bit about how the materials science expertise of Cambridge Polymer Group can help medical device OEMs in the material selection process.

Braithwaite: Cambridge Polymer Group has been working in medical devices, and beyond, for almost 30 years. We have collectively seen many changes in the industry, and our staff has worked on 510(k) and investigational device exemption (IDE) submissions for testing through to biological risk assessment. As a company, we run the analytical tests as well as publish on, and develop, new materials. We, therefore, have a breadth of experience “vertically” through the product lifecycle and “horizontally” across market segments, and even industries. It is this breadth of experience that allows us to act as a resource to development teams and groups. Those companies don’t need someone to replace their skills — they know their product and design and are experts in that regard — but frequently they are too “silo’d” and don’t have the experience outside of their immediate needs. Given time, they could determine what information they have to worry about and how to mitigate it, but usually it is more efficient to bring in targeted support to ease them over specific roadblocks.

What about smaller companies? Is there a return on investment (ROI) case to be made?

Braithwaite: Although there is no simple ROI calculation in that regard, it is a balance between spending their own time solving a problem, or getting help early to solve that issue more efficiently. Often that timing gain is at least an order of magnitude, and the personnel that would have been reassigned are free to continue their core responsibility.

Braithwaite’s session — “Getting Material Selection Right the First Time” — is scheduled for 2:15 p.m. on Oct. 17 as part of the Medical Device R&D & Implementation track at the Advanced Manufacturing Minneapolis event, which includes co-locates Plastec, MD&M, ATX, MinnPack, and D&M. The trade show and conference returns to the Minneapolis Convention Center on Oct. 16 and 17, 2024, and is organized by Informa Markets – Engineering, which also produces PlasticsToday.