Research and Markets predicts the global orthopedic device market will reach $44 billion by 2022. Much of this demand is driven by the need for implants, especially for the aging boomer generation. Surface coatings and modifications continue to be a major part of both the implant and instrument business for orthopedic OEMs. To improve functionality and performance, forward-thinking companies seek out advancements in the design, functionality, and manufacturing of devices, tools, and instruments, including the use of additive manufacturing and 3D printing.
A significant amount of research and development is focused on surface modifications and coatings, with the goal of improving wear resistance and osseointegration. Plasma-sprayed titanium surfaces or calcium phosphate/hydroxyapatite (HA)-based coatings are currently considered to be the standard methods for improving bone growth and integration.
With increased scrutiny from the FDA and other regulatory bodies, OEMs are paying more attention to the performance of their devices, especially how the coatings on reusable devices hold up during real-life cleaning and sterilization. As the FDA focuses on how to prepare reusable medical devices for re-use and to ensure cleanliness and sterility, many companies are making more of an effort to gain first-hand knowledge about how their coatings perform in the end-use environment.
“Typically, surgical equipment companies are investing in in-house capabilities to simulate the real-life product conditions seen by their products in respect to cleaning and sterilization, to evaluate how their products perform,” said Tim Cabot, president of Precision Coating Company, a Boston, Mass.-based provider of fluoropolymer and anodic coatings for medical manufacturers.
Supporting trends, he noted, include the desire by major OEMs to have global vs. regional product lines, which requires the ability to meet the very aggressive, high alkaline (> pH 10) cleaning chemistries commonly used in Europe and elsewhere, even if these are not the approved methods in legacy markets. “This is in part based on the perceived risk of prion diseases in these markets,” said Cabot.
What OEMs Want
Although there is plenty on their wish lists, most OEMs, regardless of the surface treatment or the coating being provided, want shorter lead times.
“More times than not, the surface treatment and coating provider is the final supplier in the production plan, and pressure is always there to provide parts quicker to the market,” said Michael Venturini, president and CEO of DOT America, a Columbia City, Ind.-based provider of surface treatments for the orthopedic industry.
One way to shorten lead time is by providing multiple options and treatments, thereby eliminating the amount of travel for parts between multiple suppliers. “Also, having the ability to blast, polish, passivate, anodize, laser mark, physical vapor deposition [PVD] coat, and titanium plasma spray coat allows customers to send the parts to one location for many of their outsourcing needs, greatly reducing the time it takes to see a finished part back in their hands,” said Venturini.
“Cost and high-quality deliverables seem to be the biggest challenges right now for pad printers,” added Eric Purviance, sales manager for TouchMark, a Hayward, Calif.-based provider of medical and electronic device pad printing. “OEMs feel the pressure from health organizations to decrease time on the supply chain and lower costs when possible. Also, due to the expansion of materials used in various types of procedures, printers must be savvy in the ways of surface modifications, to maximize print adhesion.”
In addition to high quality, OEMs also desire long-lasting performance. OEMs and end users expect their reusable devices to last three to five years in the field in a high-volume setting. “There can’t be any significant deterioration to the coating or the printing/marking over this time period,” said Cabot. “Printing is also a high-priority issue, as the FDA requires all Class II devices to have full lifetime traceability. As a result, many companies are evaluating unique device identification [UDI] and other forms of serialization for traceability.”
Although the standard coating processes and surface modification technologies have been used for decades, orthopedic companies continue to look for ways to enhance the osseointegration process. Advances in surface treatments include lubricious coatings and polytetrafluoroethylene [PTFE] blends. Even though orthopedic OEMs and their contract manufacturers are reluctant to alter a proven process unless there is a strong business need, some emerging technologies for surface modifications are gaining traction, such as using cutting-edge lasers to replace bead blasting and knurling.
“This is an exciting development, because many of these methods will likely improve yields and reduce fallout, while allowing for more selective surface modifications,” said Cabot.
Although 3D-printed implants have been successful, many companies still have doubts about the purity of the process, or the evenness of the coatings/anodizing. “3D-printed implants create new processing concerns for metal finishing, such as the potential for chemical entrapment,” said Tim Zentz, general manager for Danco Anodizing, a Warsaw, Ind.-based provider of surface finishing for the orthopedic industry.
To counter contamination and/or rejection issues, researchers from RMIT University in Australia have successfully coated 3D-printed titanium implants with a diamond surface. Implant rejection can be caused by chemical compounds on the titanium, which interfere with tissue and bone growth around the implants. “To work around this, we have used diamond on 3D scaffolds to create a surface coating that adheres better to cells commonly found in mammals,” said lead researcher Kate Fox. “The diamond enhances the integration between the living bone and the artificial implant and also reduces bacterial attachment over an extended period of time. Not only could this diamond coating lead to better biocompatibility for 3D-printed implants, it could also improve their wear and resistance. It's an exceptional biomaterial.”
Relevant research regarding implant materials, surface treatments, and coatings can often be found in the field of dental science. Compared to dentistry, the orthopedic industry is much more conservative when it comes to introducing new surface technologies for improving osseointegration. As a result, there may be much to learn from the dental implant research.
For example, “numerous surface modifications based on processes as diverse as the grit blasting, anodization, and chemical surface modifications are currently used in the dental field to enhance osseointegration,” indicated Jodie Gilmore, global orthopedics director for Elos Medtech and managing director for Onyx Medical, Elos Medtech’s Memphis, Tenn.-based manufacturer of wires, guide pins, half pins, drills, and screws for the orthopedic industry. “While many of these systems still pose challenges when it comes to bacterial infections, the risk of coating delamination is low or nonexistant, compared to classic HA coatings, for example.”
With bacterial infections being of high concern, a key consideration is the porosity and texture of the surface coating. Research shows that rough surfaces facilitate bacterial adhesion, making it more difficult to treat these infections with systemic antibiotics. On the other hand, roughness in the micrometer range is beneficial for stimulating osteogenesis and ensure fixation of the implant in the bone. “Considering these factors, a turned surface with a roughness in the nanometer range, would be desirable for reducing the risk for bacterial infections. This, however, requires that other means than micrometer roughness, for stimulating osteogenesis, are introduced,” said Gilmore.
Another potential solution for eliminating bacterial infections is coating implants with antibiotics. Jennifer Baker, a physician at the University of Cincinnati’s College of Medicine, has developed a way to use thin films of antibiotics to prevent surgical implant infections. “Our coatings on surgical implants demonstrate marked reduction of implant infection,” she stated. “Implants can be coated with ethanol, doxycycline, erythromycin, chloramphenicol, and levofloxacin using a unique dip-coating method we have developed.”
Another group of products prone to infection is percutaneous devices (devices penetrating the skin). Although significant advances have been made within this field over the last decade, these devices are still associated with high failure rates resulting from bacterial infections at the implant/skin interface. “While such implant systems are still a small part of the orthopedic segment, they hold great promise for certain patient groups, such as amputees,” said Gilmore. “Therefore, development of surface technologies that further increase the stability of the implant/skin interface are paramount for bringing these technologies into broader use.”
Printing capabilities continue to advance—for example, printing on curved or complex surfaces. As devices become more complex, and utilize unique blended materials, ink adhesion becomes more challenging. Ink chemistries continue to evolve, such as conductive and radiopaque inks. Ultimately, it is a bit of an art form, finding the perfect combination of surface modifications and ink type to do the job.
“With the great variety of design types, it can be challenging to find a way to print on these materials,” said Purviance. “Sometimes it’s as simple as a little tweak to the plasma treatment, improving the ink adhesion on the substrate. Other times, it is developing a better print process that allows us to pass along cost reductions so we can more closely meet a client’s target price.”
Printing adhesion greatly depends on the surface texture. For example, printing on PTFE only works with properly modified surfaces. “Many companies can print on PTFE, but getting the ink to adhere after more than an isopropyl alcohol [IPA] wipe is another conversation,” said Purviance.
This is often because of the chemistry blends used to create ultra-lubricious tubing. These materials are produced by after-coating companies, which print on one surface and then coat over it with something more lubricious—an alternative approach to directly printing on PTFE.
Just as it is important for bone growth, surface porosity also affects printing and ink. For example, Precision Coating Company has introduced a new permanent and high-resolution printing method in full color, direct from file (Sanford Print DFF). “Printing into the open anodic pores before sealing allows for indestructible print and images over the life of the article,” said Cabot.
New Coatings, New Materials
OEMs prefer titanium and titanium alloys for orthopedic implants because of their mechanical properties, biocompatibility, corrosion resistance, and low electronic conductivity. However, metal materials, because of their low bioactivity, do not effectively induce osseointegration. Therefore, researchers tend to focus on new ways to enhance integration between the bone and titanium implants. This typically involves modifying the surface structure or developing advanced coatings that can be applied to the device. For example, Elos Medtech has developed a surface technology that accelerates the process of osseointegration for titanium implants with smooth surfaces. The product is a titanium oxide-based PVD coating that releases small amounts of the bone-stimulating element strontium. “This release does not compromise the stability of the coating and therefore the integrity of the deposited surface coating is maintained throughout the lifetime of the implant,” said Ole Zoffmann Andersen, research manager for Elos Medtech. “We have benchmarked this technology against leading dental implant surfaces and it outperforms these surfaces for early-stage (two-week) peri-implant bone volume.”
Based on previous experiences with thick hydroxyapatite coatings, some OEMs might fear coating delamination. This risk, however, is greatly reduced by determining the right type of substrate adhesion and the correct thickness of the applied coating. “For our titanium-strontium technology, adhesion is ensured by including a graded binding layer and applying a very thin coating in the one to two micrometer range,” said Andersen.
Promimic, a Mölndal, Sweden-based provider of biomaterials, has a strategic partnership with Danco Anodizing to market its HAnano Surface production line in the U.S. This coating enhances implant stability and promotes bone growth into porous materials and 3D structures by combining high wettability and optimal surface chemistry with optimized nano-roughness. The 20-nm surface helps new bone grow directly into the micrometer topography on the implant surface, providing mechanical stability. HAnano Surface is compatible with a variety of substrates, including metals, ceramics, and polymers such as polyetheretherketone (PEEK). Studies show this coating can increase the anchoring of titanium implants by up to 35 percent and PEEK implants by over 80 percent during the first critical period of healing.
Bioglass, a non-crystalline amorphous solid that contains 45 weight percent of SiO2 with lesser amounts of calcium, sodium, and phosphorus, has potential as a coating material for bone integration. When implanted in the body, bioactive glass triggers a specific biological activity that forms a layer of material similar to hydroxyapatite on the glass surface. This layer enables the bioactive glass to form a strong bond with both soft and hard tissues. Within hours, blood proteins and collagen are incorporated into this layer, which then crystallizes into hydroxycarbonate apatite. Researchers have applied bioglass coatings to titanium implants with promising results.
Inspired by the composition of adhesive proteins in mussels, a group of Chinese scientists have tested dopamine as a possible surface coating for orthopedic implants. A layer of polydopamine (PDA) was applied to the surface of a titanium implant using a simple dip-coating process. The PDA layer improved the hydrophilicity and corrosion resistance of the implant. “The simple dip-coating process, accompanied by the oxidative polymerization of dopamine under alkaline conditions, proved to be a facile approach for creating a tightly adherent PDA layer,” stated lead researcher Yanxian Zhang of the University of Science and Technology in Beijing, China. “Additionally, PDA has been successfully used to support a variety of organic reactions and create functional organic layers as bioactive surfaces for cell adhesion.”
PEEK, of course, is still in high demand for implants, despite some key concerns regarding poor integration with surrounding bone. Osseointegration can be improved when a surface coating of osteoconductive material such as hydroxyapatite is applied to the PEEK implant. Although composite titanium-PEEK implants show promise, they are susceptible to wear and delamination. A new patented PEEK material by Vertera Spine (now owned by NuVasive) optimizes both the surface modification and porosity of PEEK.
“Our porous PEEK Scoria technology features a porous architecture that seamlessly transitions to solid PEEK,” said Chris Lee, CEO of Vertera Spine, an Atlanta, Ga.-based provider of spinal products and materials. “The porous structure promotes bone formation on the cellular level and allows for tissue infiltration into the pores, effectively creating a strong mechanical interlock between implant and bone, to ensure good implant stability and fusion. The solid PEEK base allows the mechanical and imaging properties of regular PEEK to be retained.”
The depth of surface porosity and the size of the pores in PEEK Scoria are precisely controlled by extruding PEEK through a porous template under heat and pressure. Varying the template geometry during this process can reliably control surface pore morphology.
BIOSTEM, an EU-funded research organization, has recently successfully modified collagen for coating PEEK to facilitate bone apposition. Found naturally in bones, muscles, and skin, collagen forms a scaffold that provides strength and structure for cell growth. The hybrid PEEK-collagen material increased the attachment of mesenchymal stem cells and supported osteogenic differentiation. The goal is to use the hybrid PEEK material as a coating to create biologically active implants that improve osseointegration after joint arthroplasty procedures.
In addition, the plasma device used for coating the implants can be easily housed in hospitals for on-site fabrication. The coating process bombards the outer surface of PEEK with a gas containing the collagen. The molecules of collagen react with the destabilized outer area and become incorporated into the PEEK. Because it is portable, the machine fits on a lab bench and can therefore be used directly in the hospital where the surgery is taking place. “PEEK wears well and producing biologically active PEEK will increase osseointegration of joint implants to decrease the need for costly revision surgeries,” said research scientist and project leader Mary Murphy.
One of the biggest challenges ahead for coating and surface modification providers is regulatory scrutiny. For example, biocompatibility tests that were acceptable and inclusive just a few years ago require more in-depth analysis today. Within the increasingly regulated medical device market, it has become more time consuming and costly for OEMs to obtain approval for devices that carry new surface technologies. Depending on the specific technology, there is little to no possibility for claiming similarity to predicate devices already on the market, which adds time and cost to the process.
“It is always important to ensure patient safety,” stated Gilmore. “However, with the increased regulatory pressure, the risk of ‘killing’ new and innovative solutions that could benefit patients is a real concern, especially for smaller startup companies that do not have the regulatory competences in-house.”
As regulations become tougher, more OEMs are re-evaluating how their products perform. Some companies discover their legacy coatings do not hold up as well as they had expected—forcing them to consider newer surface coatings and treatment methods.
As the orthopedic implant market continues to evolve and shift due to changing demographics and regulatory expectations, the demand for higher-performing implants will increase. To meet these market demands, OEMs and their supply chain partners must find new and innovative ways to improve implant functionality by investing in advanced coatings and surface modifications—ultimately delivering a better patient experience.
Mark Crawford is a full-time freelance business and marketing/communications writer based in Madison, Wis. His clients range from startups to global manufacturing leaders. He also writes a variety of feature articles for regional and national publications and is the author of five books.