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Surgeon Touts Benefits of Molybdenum-Rhenium in Spinal Applications

Kornelis Poelstra, M.D., Ph.D., believes that new materials will bring the next wave of innovation in spine. His belief spurred him to send FDA a letter asking for a list of acceptable materials to study in animals with the intent of future commercialization. It also spurred a partnership when he crossed paths with Jay Yadav, M.D., an entrepreneurial cardiologist working to introduce molybdenum-rhenium (MoRe) to orthopaedics. 

At the North American Spine Society Annual Meeting, Dr. Polestra presented research on the use of MoRe in spinal applications. The data will be used as MiRus, a startup spine company, launches a platform of technologies using MoRe. 

We spoke with Dr. Poelstra, an orthopaedic and neural spine surgeon and founder of The Spine Center of Excellence at Sacred Heart Hospital in Pensacola, Florida, asking him to explain the alloy’s benefits. 

What is molybdenum-rhenium alloy?

Dr. Poelstra: Molybdenum-rhenium is an alloy that’s been used for a long time to make stents in cardiology. The beauty of the material is, compared to what’s commonly used in spine—cobalt-chrome, titanium and stainless steel—it has characteristics that are a lot stronger. MoRe uses a lot less metal to achieve the same strength and durability and is two to three times stronger and four times more durable than cobalt-chrome or titanium. MoRe-based stents for the heart can be made with material that’s as thin as hair, which allows us to weave them. Before, stents looked like a chicken wire-kind of material; a lot more metal was needed to keep the stent open. MoRe showed favorable characteristics with that process.

The thought was, “Where else can we use this?” Spine seems to be the perfect world, because we put all of this hardware in people with large architecture, since it needs to have certain strength. Because of the strength, we need a lot of metal and fairly significantly-sized rods (5.5 or 6.0mm). So, with the uptick of MIS applications, if we had a material that was stronger and therefore would allow us to achieve the same thing with a lot less metal, we could make smaller implants. We’re in the infancy of seeing what this metal can do. 

During standard tests so far, it outperforms cobalt-chrome and titanium in every aspect we’ve looked at. That makes it exciting.

Even with osteointegration?

Dr. Poelstra: Yes. So, some implants are friendlier with bone than others. This has a lot to do with hydrophilic (attract water) versus hydrophobic (expel water) materials. The plastics we use in spine are hydrophobic, meaning bone has a hard time attaching to them. The more hydrophilic a material is, the more favorable it is for bone growth. MoRe is about 60%more wettable than titanium. We’ve done studies in which we’ve put small pieces of MoRe on rods in a rabbit femur and made it flush with the surface of the cortex. The cap of the bone that grows over top of it is a sign that MoRe is friendly to bone-forming cells. The bone formation looked to be better—or at least equivalent—than what we see in titanium. 

As a surgeon, what would you say to device companies that are thinking about new product creation, in terms of what your needs are?

Dr. Poelstra: We tend to become myopic and just look at what’s in front of us. As an industry, for the past 20 years, we’ve maximized what we can get out of cobalt-chrome, titanium, stainless steel and a couple of plastics. Our industry isn’t good at looking beyond what’s available. MoRe could be a tremendous revolution for our industry, and it may not stop at MoRe. Maybe there are other, different materials we need to look at instead of just continuing to use what has worked well for 20 years. We can’t continue to stare at the table in front of us, not looking beyond. 

MoRe is well-tolerated within the body. This is allowing us to make materials and do things either with additive or subtractive manufacturing. 

It might lead to a lot of innovations. We can break through this glass ceiling we’re under and who knows what we may be able to do next, in terms of creating implants we may not have even thought of before.

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