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Coatings Support Early Integration, Infection Prevention

After combing through company product launches, university research findings and surgeon-led discussions at meetings, and receiving requests for supplier partner referrals, it’s clear that implant coatings are of great interest to orthopaedic professionals all along the supply chain.
Naturally, these interests align with the way that coatings are developed, the problems they solve and the outcomes they produce. Further, these findings uncover current trends, like spine companies coating PEEK with titanium, the search for the holy grail to end postsurgical infection and the focus on ease of manufacturing and cost. (To the latter point, Jason Mansell, Ph.D., whom you’ll hear more from, ended our conversation with, “Suffice to say, you could make this new coating in your kitchen using water as the solvent in a matter of hours!”)
Coating technology is exciting and provides a means for innovation and even just incremental improvements. We spoke with three individuals, all professors and one a surgeon, all at different stages of coating research. 
We asked about the basics behind the technology they seek to advance, what role coatings play in the implant, what level they perceive their colleagues’ understanding of coatings science to be, what they would share with device companies commercializing new technologies. And, what will be the dialogue around coatings five years from now. Here's what they're excited about.



Orthopaedic Problem: Total Joint Aspetic Loosening

Coating Research: Lysophosphatidic Acid

Jason Mansell, Ph.D., University of the West of England Associate Professor in Biomedical Sciences within the Department of Applied Sciences, speaks about his research initiative to make titanium implants bond better through a coating that interacts with Vitamin D to enhance bone-forming cell function.

Approximately 10% of total joint replacements (TJRs) fail within the lifetime of the patient through a process known as aseptic loosening, i.e., no bacterial involvement. Here in England and Wales alone, the cost incurred to replace these failures is around £300 million (~US $360 million) per annum—ouch! My priority has been to find a way to promote TJR longevity by coating primarily titanium (Ti) with simple agents that I discovered could enhance bone forming osteoblast formation and maturation. The agents in question, the lysophosphatidic acid (LPA) family, were chosen because of their small size, their natural affinity to strongly bind to Ti and their ability to promote or bolster the actions of vitamin D, which we all know is key to a healthy skeleton.

Our LPA-Ti coating promotes human osteoblast responses conducive to supporting bone formation. The coating is stable to prolonged storage at room temperature (at least 12 months); it can survive gamma irradiation, the preferred choice of implant sterilization, and the LPA coating can survive washing and abrasion as would be expected during implant insertion into the body.

In terms of overall cost, our LPA modification is certainly below the costs incurred for hydroxyapatite (HA) coatings of Ti, which is a popular implant coating choice. Because the LPA family members have a natural affinity for Ti, this means that the route to implant modification is facile, whereas HA coating is a far more costly and involved process.

[What we will be saying about coatings in five years] depends upon whether industry wants to embrace change; after all, 90% of their devices will survive the lifetime of the patient. That said, if we can find a bona fide coating that is simple to generate, enhances early integration into host bone and is antibacterial, this will be a game-changer. So long as the antibacterial agent can remain firmly bound and has capacity to kill bacteria at the implant surface, this will be the new technology that companies look for. Cost is everything; for the time taken to make the modification, the process needs to be facile and without the need for unusual operating conditions, onerous procedures and specialized personnel. If the devices can be developed within the company, this will be very important.

Orthopaedic Problem: Large Bone Defect Healing

Coating Research: Nanostructured Mineral

William L. Murphy, Ph.D.’s titles include University of Wisconsin’s Harvey D. Spangler Professor, Biomedical Engineering and Orthopedics; Co-Director, Stem Cell and Regenerative Medicine Center; and Director, Human MAPs Center. He is also a Founder and Board Member at Tissue Regeneration Systems, which recently sold its bioresorbable, 3D-printed technology to DePuy Synthes to treat orthopaedic and craniomaxillofacial deformities and injuries. He spoke about his research and the important role of a coating.

Our recent focus has been on using high throughput approaches to identify coatings with unique characteristics. We have for some time been able to generate coatings that are osteoconductive and have osteostimulatory characteristics. Our more recent work shows that coatings can also have other very attractive attributes, including the ability to reduce bacterial adhesion and reduce inflammation. We have used high throughput screening to identify coatings that simultaneously embody many of these attractive attributes.

Coatings can be quite valuable in promoting tissue healing, and avoiding pathology, at the implant/tissue interface. Recent work from our group and others indicates that the biology of healing can often be influenced not just by complicated biologic drugs or cells, but also by physical coating properties such as topography and chemical composition. This emerging idea may allow for orthopaedic implants to mediate biologic healing without using biologics, thereby simplifying regulatory approval and clinical adoption.

Orthopaedic implants tend to be extensively optimized in terms of their structural and mechanical properties. They are also typically painstakingly designed to encourage surgeon adoption and enhance success in surgery. What is most attractive about coatings, from my perspective, is that they can allow for enhancement of biological outcomes without compromising optimized structural, mechanical, and handling properties of common orthopaedic devices. If coatings are designed and developed appropriately, they can be applied to a broad range of orthopaedic implants to provide unique improvement in efficacy without appreciably changing the surgical technique.

The coating is just as important to the success of a surgical procedure as the underlying implant itself, and therefore just as valuable.

Orthopaedic Segment: Trauma Infection Prevention
Coating Research: Antimicrobial Silver Ionization Technology

Bohdan Chopko, M.D., Ph.D., is Professor of Neurosurgery and Complex Spine, Stanford University and Founder of Silver Bullet Therapeutics. Thinking back to previous conversations with him about infection prevention, we sought his perspective on the future of what he calls “smart” coatings to prevent infections, and the perception of coatings by his surgeon colleagues.

When you look at surgeons, their exposure in general to coatings is that it’s just another add-on feature to a product line. “OK, now we have a new and improved device X.” A lot of understanding revolves around the idea that a coating is simply that, like a chocolate-covered cherry: it’s chocolate on a cherry. That is probably the greatest area of lack of information amongst surgeons and physicians, and that thinking, like drug-eluting stents or coated stents, surface technology in orthopaedics is simply “we dip the implant in whatever we want to coat it with.” What that springs from is what I call passive coating or dumb coating, because really what you’re doing is literally painting something on one way or another. Although that might sound appealing on the surface, it really is a poor way to interact with the body’s biology. A coating like that is not going to be durable, especially when you’re talking about devices that are being screwed in through soft tissue and bone or being pounded into place, tamped into place. ...The other category is smart coatings, where the coatings are complex not only in how they adhere to the surface or how the surface technology is being applied or developed or manufactured, but how it interacts with the body and the biology of the recipient. That’s where it becomes exciting.

We have a proprietary coating, a platinum silver hybrid that creates a self-sustaining battery on the surface of the screw once it’s in the aqueous or fluid environment of the human body. That turns on this battery switch, so to speak, this electric chemical reaction, and that forcefully elutes a cloud of silver ions into the system and into the surrounding tissue. Silver ions are orders of magnitude more bacterialcital than passive silver coatings. That’s an example of an inert object on the shelf, but once you take it out of the package and implant it in the human body, it becomes activated. And we have a great deal of flexibility as to how much of that coating we want to be activated: where the coating is, how long we want that silver ionic distribution to occur, how deep into the surrounding tissue and bone do we want it to extend. ...A second example of a smart coating is Titan Spine’s nanotechnology. ...A third example would be scaffolding technologies for bioengineering of tissues, where scaffolds create a Piezoelectric form of electricity across the surface. That can change how fibroblasts react. Once again, that is a very interesting use of smart technology; it’s not just simply a passive scaffolding at that point. You could theoretically turn on and off that Piezoelectric field, increase it or decrease it depending on how you want to modify those fibroblasts.

There has been a lot of interest over 20 years or more of effort, in trying to come up with antimicrobial coatings for various orthopaedic and spine implants. Obviously surgical site infection is something we all live in and have a great deal of anxiety around.

We’re still in the embryonic stages of antimicrobial coatings, because what a lot of us do now is we pour antibiotic into the wound, we irrigate with antibiotic solution. As far as actual devices that are coated with the strict purpose of antibacterial effects, they are few and far between. We’re one of the only few U.S. companies pursuing that actively; there are some in Europe also. These are only early efforts right now. As we go forward, hopefully people’s eyes will be open to the fact that this is an ongoing problem that deserves significant attention.

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