Roundtable: Evolution, Not Revolution, Drives Biomaterials Development

Recently, MPMN assembled a panel of biomaterials experts to discuss the exciting developments in the field over the past 25 years and to predict what lies ahead. Moderated by MPMN editor-in-chief Shana Leonard, the roundtable included panelists Marcus Jarman-Smith, technology leader at Invibio (West Conshohocken, PA); Andrew Nield, director of sales and marketing at C5 Medical Werks (Denver, CO); and Robert Raess, medical market manager and Midwest regional manager at Titanium Industries Inc. (Rockaway, NJ). They specialize in biocompatible polymers, ceramics, and metal alloys, respectively.

MPMN: In honor of MPMN's 25th anniversary, what do you cite as the most significant breakthrough in biomaterials for medical device applications in the past 25 years?

Jarman-Smith: What constitutes something significant? You can consider things like the size of the patient population, or how widespread the benefits of something would be, or what clinical advancement the material development would bring and, ultimately, what the impact is for the patient. Two things come to my mind immediately: The Medtronic Infuse bone graft being used in combination with things like PEEK-Optima polymer cages has had a significant impact. There are now more than 2.5 million devices with PEEK Optima in them, so it's pretty significant. Another example would be the arrival of drug-eluting stents over the past 25 years. Metal stents in combination with drug-eluting polymers have really been a massive breakthrough.

Nield: The most important breakthrough that I've seen in the last 25 years is ceramic being used in hip joints. If you go back 20 years, you'd typically see a patient getting a hip joint replaced when they were maybe 65 or older and being happy to just walk again. But what we're seeing now is ceramic being used in maybe a 31-year-old cyclist that wants to be able to do the Tour de France again. The shift is in these lifestyle changes--people wanting to lead an active life again after they've had the surgery. They want to be able to do an Ironman, cycling, skiing. If you just look at the success rate of ceramics in hip joints, there is a less than 0.1% revision rate for fracture on these surgeries.

Raess: For me, it's what has happened since Type 316 stainless steel was developed to be implantable in the body and how it has progressed through all of the other materials mentioned.  I've seen the natural progression of metals and polymers and ceramics over the years, but I guess it all comes down to biocompatibility. Is the material compatible with the body? Is it corrosion resistant? What kind of strength does it have? What kind of modulus of elasticity does it have? In certain applications, a basic Type 316 implantable-grade stainless steel might be the right choice. In other cases, titanium might be the right material where it gives you the right strength-to-weight ratio. In certain applications, PEEK and ceramics might be the right fit. It's just an ongoing natural progression of medical technological advances and materials science developments.

MPMN: A number of medical device designs have replaced metal with other materials, including polymers such as PEEK, for example. Do you think medical device design engineers will continue to find alternatives to metal, or do you think that metal alloys will always have a prominent place in medical device design?

Raess: I think there will always be a place for metal, especially titanium. Its physical properties, as well as its density, strength, and serviceability characteristics, are so closely matched with that of bone. There will always be a place for the mainstays, but there will be unique and new applications. There's still a growing population, and there will always be new procedures, but I think there's a market for everything.

Jarman-Smith: I would echo all of Bob's points. Metals make a phenomenal contribution to medical devices and they're always going to have a place. In trauma, metal has been in use for over a century and continues to be excellent in patient care. As we look at more-specific patient populations and their particular needs, it may be that new materials bring with them new benefits that outweigh those of metals or indeed other existing material solutions. From experience, we've seen instances in younger patients where minimal stress shielding at the bone is desirable. This could benefit from a material that can connect to a structural bearing material but can still also transfer the stresses through to the acetabulum. I suppose it's bringing something new that isn't present at the current time for a particular niche application. Sometimes, it might not just be about the mechanicals, but other benefits as well. Polymers can bring their own benefits, ceramics others, and metals others. Really, we have to just consider the best solution for a patient and offer more high-quality choices to the engineers to hopefully encourage them to innovate either with a different material that allows them more freedom or with combinations of materials. I think we're going to see more combinations of materials coming in the future as well.

Nield: And I would echo that last point: The most important thing I see is integrating different materials together. There is no device that only uses a ceramic; it is integrated with polymer or a metal. That becomes much more important as you start to get smaller and smarter devices and you want to increase their reliability. You need to get more out of a material and get synergistic materials by putting two materials together.

MPMN: Materials have been at the center of an escalating controversy in terms of growing concern over metal-on-metal bearing materials for hip implants. As a medical materials supplier, what is your take on this hot-button issue?

Nield: I can really only look at it from the ceramic perspective, but we're still learning a lot there. The benefits of ceramic in that application are low wear compared to a polymer or metal alloy and you also get smaller particles. Ceramic materials that are used in orthopedic implants are bioinert, so the body doesn't react to the particles. We've seen applications for ceramic where it can be used in a total disc replacement in the spine and as a bearing surface in the hip joint and the knee joint. It's a really good material that lasts longer and causes less or no harm to the patient than perhaps other materials.

Jarman-Smith: It's important to get perspective on any of these headline-grabbing stories. Metal-on-metal implants have been in use since the 1950s and continue to work well in certain applications. We're still learning about the impact of the correct positioning and how metal-on-metal constructions work in certain applications and patient types. It's probably clear that we need to be more selective in its use, but I don't think the entire story is in yet. From the polymer side, Invibio has helped to provide alternative options for certain applications. We try to evidence this through screening, simulating studies, wear-particle-debris analysis, that kind of thing. Consequently, we're seeing certain hip, knee, and spine applications come through using PEEK Optima materials. But I guess it's horses for courses and understanding where the best fit is for the purpose. We're seeing FDA asking more and new questions and requiring new data on wear particulates, and we're even seeing that in nonarticulating applications. The only thing to do is keep providing the research and clinical data. Invibio is lucky in that we have an extensive Master File and a decade of clinical data, but there are still so many unknowns. So, we keep doing development work and hopefully choose the right materials for the right applications.

Raess: The other factor you must keep in mind is the design of the implant. There have also been issues with squeaky hips, for example, and sometimes it's material selection, sometimes it's design, and sometimes it's installation techniques. All materials have limitations, and if you take them past what they can perform or do, problems can't be prevented by the materials themselves. Design and installation are major factors.

MPMN: There's also a lot of buzz around bioabsorbable materials and their future in a variety of implantable devices, including stents. Do you think that bioabsorbable materials can live up to the hype in implantable devices, and what does this mean for more-traditional materials?

Jarman-Smith: It's about need, really. The current PLLA resorbables are good in certain areas--sports medicine, suture anchors, and those sorts of things--but they lack high strength for more-demanding applications. There are concerns about the resorption profile, the consistency, and the degradation of the materials. Creating resorbables that can serve some of the more-critical application areas is quite a steep technical climb. Probably lesser known, Invibio is currently looking beyond PEEK Optima polymers and has been conducting R&D into a high-strength resorbable with a surface-degradation profile that strives to address the gap in needing something with high strength and surface degradation. We've recently published two studies at the European Society of Biomaterials. But again, I would say it's about selecting the right materials for the device. Rather than viewing it as a question of displacement, resorbables are widening the choice in the medical device designer's toolkit, but I don't think they're going to be the answer to everything. They've been around for some time now, but the technology is limited with the existing materials that are out there.

MPMN: I'm noticing a theme in all of your diplomatic answers that there's a place for everything. As emerging, optimized, and composite materials enter the market, are you seeing opportunities dwindle or are you creating new opportunities?

Nield: I think it comes back to that integration. When something like bioresorbable materials comes into the picture, it's figuring out how to use that along with the device we have now to make a better device that capitalizes on the synergistic benefits of both materials.

Jarman-Smith: I totally agree. As we're getting into new sectors and application areas, it's definitely about being complementary. Whether a new material's benefit is manufacturability or a difference in cost or bigger head sizes or thinner parts or bone conservation, the end device still needs those other biomaterials as components in the bigger picture. Things are becoming more complementary as you step into new application areas.

MPMN: It seems like every day there's an announcement from university research labs and companies about a superlative new material that could revolutionize the medical device industry. What do you think will be the 'next big thing' in terms of materials for medical applications?

Raess: I think stem cells will be the biggest breakthrough if they can ever figure them out.

Jarman-Smith: When medical device development news hits the headlines, you always hope the product will be out a few months later, but it never works out that way. I come from a tissue-engineering background originally, and we're still looking at tissue engineering 25 years after it was touted as the next big thing. I suppose stem cells are the next significant area, and these sorts of innovations will require, in some cases, biomaterial delivery vehicles to localize them. One of the great things about polymers is that you can combine them with compounds or coatings, so there are opportunities there. Another key clinical problem to address would be infection, and in our sector, we've seen silver-based technologies picking up momentum and being incorporated into PEEK and metal biomaterials. But we should look at things that are evolutionary rather than revolutionary--improvements that are more incremental and shorter term. The gulf I noticed when I stepped into this marketplace was the gulf between blue-sky developments and the actual reality of there being a metal or ceramic or polymer part in your body. There's going to be buzz about these longer-term blue sky things, but I think there's a technical challenge to just doing the incremental improvements.

Nield: I agree that evolution is the way to go in the medical market. If I go to one of our customers and say that we've got something groundbreaking, I hear a few murmurs of interest and a promise that they might take a look at it. But if I say we have something that is an incremental improvement that will improve the reliability, improve the life, reduce the cost, or reduce time to market on an existing device, then there's a lot of excitement around that. About 10 or 20 years ago, for example, ceramic started to be used in medical devices, and what you started to see was a migration and evolution in using specific materials for specific applications. Certain ceramics were developed for hips and knees, others for spinal, and others for pacemakers or dental applications, and you start to see evolutions.

Jarman-Smith: Referring back to what we just talked about with evolution rather than revolution, I would say a lot of that approach is made even more real by the regulatory environment that has changed over the past year and the diligence and scrutiny that has come in from the FDA. I think certainly in terms of the risk, the room to bring revolutionary products to market is limited, or the number of people willing to tackle that hurdle is reduced. So, it's about incremental stuff, making sure the product is safe, proven, evident, and secure.