Surface treatments and coatings are engineered to functionalize medical device surfaces for a variety of medical applications. They provide useful physical properties that may not exist in the underlying substrate, like enhanced electrical stimulation or sensing, improved mechanical properties, biocompatibility, and the ability to elute drugs to selected parts of the anatomy.

Advances in medical technologies, including imaging equipment, ultrasonic and other sensor-based tools, and delivery systems all require specialized coatings.

“Neurovascular device growth and innovation is driving surface treatment progress,” said Kevin Guenther, methods development manager at Harland Medical Systems, an Eden Prairie, Minn.-based provider of medical device coatings, equipment, and manufacturing services to healthcare product manufacturers. “Ultra-thin diameters are desired for micro-diameter catheters and guidewires. Ultra-soft substrate materials like Neusoft, Chronoprene, and Polyblend are also impacting coating innovation.”

“Another trend is a single coating and process must be sufficient for multi-material device constructions,” Guenther went on. “Coatings are also evolving along with structural heart devices’ large diameters and distal tip shapes—post-coating forming is needed to accommodate shaped distal tips.”

Ever-present broader regulatory considerations—as always—are also impacting the medical device surface treatment market.

“We primarily see desire for coatings with increased durability and coatings which are compliant with increased regulations coming down in numerous regions, which will limit use of PFOA (perfluorooctanoic acid) and other chemicals in medical applications,” said Mario Gattuso, senior business development manager at Aculon, a San Diego, Calif.-based provider of surface nanocoating technology.

In recent years, the demand for portability and miniaturization of medical devices has increased even more. Once the form-factor of a device shrinks, the same expectation comes for its cost. Although, function and performance need to remain on par to replace large lab equipment.

“This trend brings both challenges and opportunities to makers of optical systems, components, and coatings,” said John Freiermuth, VP of business development at Materion Balzers Optics, a Mayfield Heights, Ohio-based optical thin-film coating solutions provider. We are working on new manufacturing technologies with our partners that enable coatings on new materials and smaller components without compromising spectral performance. One of our favorite approaches combines a system of filters into a monolithic block that can be attached directly to a detector, sample interface, and light source. This could be an array, a linear variable filter, or a beam-splitting prism assembly to separate fluorescence signals into different channels.”

The miniaturization trend has also resulted in the use of more electropolishing. Machining—especially for smaller parts—can leave parts with a wide array of imperfections. Electropolishing eliminates surface defects by removing a microscopically precise layer of surface material.

“As medtech products have become smaller and more intricate, the use of electropolishing as the final step in finishing critical metal parts has grown,” said Pat Hayes, vice president of business development at Able Electropolishing, a Chicago, Ill.-based provider of metal electropolishing, passivation, and titanium anodizing services. “Electropolishing’s ability to remove a microscopically precise amount of surface material and leave parts ultrasmooth and pathogen-resistant is a key attribute as medical device manufacturers seek to incorporate cleanability and pathogen-resistance into the design process. The use of more exotic metal alloys in medical manufacturing, because of the flexibility and memory they impart, is another continuing trend.”

Medical device manufacturers are also seeking thinner coatings and perpetually tighter tolerances to meet their customers’ enhanced performance and quality specifications. It’s so ubiquitous in the industry that every manufacturer anticipates the coated tolerance conversation.

“The need to apply increasingly thinner coating layers, ultra-thin at very tight tolerancing—as low as 0.0001 inch—is a current trend requiring newer application methods, including advanced automation to meet the requirements,” said David Dibiasio, vice president of sales and marketing at Precision Coating Company, a Woonsocket, R.I.-based provider of coating technologies to the medical industry, especially single-use devices, as well as reusable instruments and tools.

Typically while developing advanced catheter systems, a design engineer will leverage a variety of surface treatments to allow them to design a process that is optimal for their application. Platforms like transcatheter valve replacement need engineered coatings that allow excellent dielectric properties, low friction, and other beneficial characteristics typically provided by polytetrafluoroethylene (PTFE). Advanced tight-tolerance masking capabilities are also a usual requirement for this type of device.

“Surface treatments can directly correlate to PTFE coating durability and mold release, resulting in a low coefficient of friction with various manufacturing benefits,” said Michael Brown, vice president of sales and marketing at Applied Plastics, a Norwood, Mass.-based supplier of PTFE-coated products for use in the design and manufacturing of advanced catheter systems. “Our PTFE Natural® coating application features proprietary equipment and a custom surface treatment process that create a uniform, non-flaking coating to provide a lubricious surface, which is incredibly durable and withstands up to 550°F operating temperatures.”

Chemically inert coatings create a non-reactive surface so the user can get the most out of device or instrument performance. Even stainless steel degrades and threatens product safety, especially when harsh materials are used for cleaning. Proteins, blood, and other biomaterials also readily adsorb onto metal surfaces.

Dielectric coatings, also called thin-film coatings or interference coatings, consist of thin layers of transparent dielectric materials deposited on a substrate. Their function is to modify the surface’s reflective properties by exploiting interference of reflections from multiple optical interfaces. Dielectric coatings are applied to medical devices that require electrical insulation, for example electrosurgical or robotic surgical equipment.

“Inert properties able to handle a diverse array of more aggressive sterilization environments are increasing requirements of coatings this year,” said Dibiasio. “Dielectric properties are a key component in newer platforms in growing segments of the industry like robotic surgery, and FFR (fractional flow reserve) platforms.”

Of course, coatings can’t be applied to a part uniformly if the device’s surface texture isn’t adequately prepared. In some cases, this causes a disconnect between medical device manufacturers and their coating partners.

“Regardless of the type of coating we are seeing a similar problem: variation in how well the coatings are sticking to the part,” noted Colin Weightman, director of technology at Comco Inc., a Burbank, Calif.-based designer, builder, and seller of micro abrasive blasting (MicroBlasting) equipment and supplies. “Customers are finding that their specification for how to prep the surface isn’t working consistently. We are finding a disconnect between their specifications and what they are actually trying to achieve. They are looking for better ways to specify how to create the surface they need.”

Medical devices with surface enhancements that are able to perform minimally-invasive surgery have become the gold standard for efficient and low-risk surgeries. These surgeries satisfy the desire for a speedy recovery and shortened hospital stay, and respond to the pressures to minimize healthcare costs and boost outcomes.

For example, catheters and guidewires used in a slew of minimally invasive procedures may be coated in a hydrophilic (water-repellant) polymer that binds to its surface. The hydrophilic coating uptakes water to make the surface smooth and slippery, which remains intact on insertion. Low friction characteristics (pull forces as low as three grams and coefficient of friction values as low as 0.01) help these devices navigate winding anatomical paths. Using the coatings also helps lower tissue irritation.

“We have invested in coating solutions and processes that enable application of hydrophilic coatings to metals, specialty substrate materials like polyimide, silicone elastomers, and ultra-soft polymers,” said Guenther.

Conversely, hydrophobic (water repellant) and oleophobic (oil repellant) are other coating options. When combined with hydrophilic surface treatments, some truly innovative devices can be realized.

“Our repellency technologies (hydrophobic and oleophobic) and water attracting technologies (hydrophilic) can be utilized independently or in conjunction to create microfluidic pathways without physical barriers,” noted Gattuso. “In addition, they can be utilized to selectively modify channels and pathways in a variety of sequencing and lab-on-a-chip applications.”

Coatings can also imbue medical devices and equipment with antimicrobial properties. Antibiotic-resistant pathogens that cause healthcare-associated infections (HAIs) increasingly challenge hospitals during clinical treatment and in preventing cross-transmission. Healthcare workers and patients are exposed to additional risk, valuable resources are consumed, and additional expenses are incurred. Antimicrobial medical device coatings employ polymers that can be applied to anything from catheters to medical electronics and implants to help reduce HAI risk.

Harland Medical’s Bacticent coating, for example, utilizes a heat-cured copolymer matrix infused with the antimicrobial chlorhexidine diacetate.

“Bacticent is typically applied to PICC catheters, dialysis catheters, central venous catheters, and orthopedic devices,” said Guenther. “Bacticent coatings provide active antimicrobial performance by eluting an anti-infective drug into the tissue surrounding an implanted device. Customers specify the anti-infective drug and the duration of the activity. We then prepare a drug/excipient formulation that will satisfy the device requirements.”

Polytetrafluoroethylene (PTFE) coatings are used for more than just non-stick pans—from surgical instruments to guidewires and catheters, the coating ensures the device’s surface doesn’t gather any matter during a procedure. A PTFE coating with a non-acid formulation is also applied to medical wires, which are necessary for a variety of devices and mandrels required to stay sterile and protected from the elements.

“Design engineers leverage lubricious coatings such as PTFE Natural® coated mandrels for complex catheter manufacturing processes ranging from reflow processing mandrels to forming and tipping mandrels and coated pull wires for steerable catheters,” said Brown. “A low coefficient of friction coating can offer static and dynamic benefits depending on the engineer’s performance requirements. For example, PTFE-coated reflow processing mandrels helps ease mandrel release after the reflow process, which aids in manufacturing and can reduce manufacturing cycles. Consistent, robust, and durable PTFE coatings are necessary to hold tight tolerances and ensure the catheter’s inner diameter is free from particulates.”

“Coating application options and formulations tailored for medical devices’ unique properties allow use of PTFE and other polymers on a variety of substrates and platforms,” said Dibiasio. “A range of color options and ability to apply thin coating layers are attractive qualities for R&D engineers designing next-gen products. PTFE also has a high temperature usage range allowing for use in many different medical applications. In addition to interventional devices and tooling, PTFE application on mandrels enhances performance of components used in centrifuge devices, stirring and mixing machines, blood separation, and sterilization devices.”

An anodic coating is a type of coating material that uses anodizing (or reversed electroplating) to provide increased thickness, color, and protection to aluminum or any type of substrate. The coating consists of an oxide film created on metal through electrolysis, with the metal acting as an anode or positive electrode. During anodizing, the aluminum is submerged in a water solution or acid electrolyte. The coating’s consistency will depend on the controlled temperature.

This is done because the natural coating present in aluminum and other ductile, soft metals can be quite thin, rendering it easily damaged. Therefore, building up the anodic coating offers beneficial properties to the aluminum.

“While aesthetically pleasing, anodic coatings provide a high degree of functionality to surgical instruments and accessories,” said Dibiasio. “Anodic coatings are naturally nonconductive, so they have inherent desirable dielectric properties. The anodic coating is much harder than the aluminum substrate, protecting from abrasion damage. You can easily color and—therefore, color code—anodized product. We can also provide permanent markings for traceability, CE marks, and bar coding.”

MicroBlasting, a proprietary surface treatment process from Comco, uses very fine abrasive media and a miniature nozzle to create a controllable abrasive jet that can target and remove microns of material. The result is a reliable, repeatable method for deburring, texturing, cleaning, stripping, ateching, or milling part surfaces. The company’s systems are used to process not only medical and dental implants, but also aerospace components, semi-conductor devices, machine parts, and electronics.

“MicroBlasting offers two key advantages over other methods when creating a surface texture: accuracy in creating a consistent Ra or Sdr finish, and no need for masking. Unlike conventional sandblasting, we have far greater control over the blast variables so we can create consistent surface finishes to meet tightly defined Ra, Sa, and Sdr specifications.”

As devices have become smaller and more intricate, laser machining has continued to be integral in manufacturing medical implants. Further, Nitinol, a nickel-titanium alloy with superelasticity and “shape memory” qualities, is increasingly being used for medical applications. However, laser machining nitinol creates surface defects like oxide layers, heat-affected zones, and pulse marks. The expansion process during manufacturing turns these defects into potential sites for cracks to propagate.

“MicroBlasting can effectively remove these contaminants without affecting the base material. While a matte finish may seem contrary to the goal of electropolishing, a uniform matte base speeds the polishing process. Skip the microblasting step and the electropolish will take longer, and may remove too much in some areas to get the desired finish. This makes it an excellent preparation tool for more successful electropolishing.”

Aluminum oxide has long been the standard abrasive to clean stents, valves, and other Nitinol implants prior to electropolishing. However, recently selective edge-rounding has emerged as another manufacturing method involved in making these devices because round edges decrease likelihood of catching, snagging, and other implantation risks. Unfortunately, aluminum oxide was found not to be enough.

“MicroBlasting with aluminum oxide produces a 5-15 µm radius, but the new geometries are specified closer to 25 µm. This radius can be achieved through three avenues: extending the blast cycle, using a larger size of aluminum oxide, or using a different abrasive altogether,”explained Weightman.

Through testing, Comco discovered a longer blast cycle leads to more mass removal, and a larger size of aluminum oxide creates a surface too rough to polish. An aluminum oxide particle is block-like in shape with slightly sharp edges, which left the firm with one viable option—try a different type of abrasive.

“Determined to overcome this hurdle, we tested several types of media and found that blasting with glass bead before aluminum oxide creates the desired radius at the corners—up to 30 µm—without removing additional mass from the device. This two-step process met all the goals: it created the desired radius and a surface finish optimized for electropolish, without removing excess material.”

Advancements are also abound to collect useful data as the coating process is taking place. Advanced software is added to the coating lines to do so—one company even created its own PID control software, where data is collected and fed through the software to adjust variables.

“Our latest advancement was PID software we developed to coating variable control on our automated coating lines,” said James Morris, president and CEO of Surgical Coatings LLC, a Sedalia, Colo.-based provider of surface coating services for medical devices and surgical equipment. “This software helps feed valuable information to our coating technicians and allows them to focus on running as fast as possible. Also, we collect a copious amount of statistical process control data, close the feedback loop, and use it to make sophisticated real-time decisions to reduce scrap and reject rates. Using the technologies we recently invested in, we realized routing times reduced by a factor of 2x while decreasing reject rates below one percent in some cases.”

The powder coating line automatically sorts parts measuring high or low for coating thickness and feeds the data back through to adjust the variables on the powder coating guns, like supplemental air or charge on the material. Data is also collected via laser micrometers and other measuring devices, tracked by the firm’s proprietary software. The statistical process control data is also delivered to customers.

“Controlling electrostatic powder coating and liquid coating applications for medical device manufacturers requires intimate knowledge of the coating chemistries and novel automation approaches to deliver a medical device level of precision and quality,” said Morris. “Coating applications automation has historically focused on solving problems associated with waste and transfer efficiency.”

The firm also utilizes a process it’s named Virtual Masking to ensure perfectly defined coating-free areas and eliminate poor edge quality, increasing overall surface quality. During this process, the company coats the whole substrate, then uses automated laser ablation systems to remove the coating in specific areas.

“We are currently developing and installing our next generation of automated coating lines and Virtual Masking technologies,” said Morris. “The next generation of our automated equipment will address challenging customer needs centered on precision and quality by removing human interaction to handle high-volume production.”

Surface treatment providers continue to invest in robotic automation as well. Robotic processes ensure consistent and repeatable results for fragile medical implants moving through the surface treatment process. In the case of electropolishing, medical device manufacturers focus on cleanability and a microsmooth finish. Able has invested in 26 robots on site to make sure automation is at the core of its services. In addition to added precision, automation drives efficiencies and speed to meet clients’ demanding specifications.

“We continue to grow our use of robotic automation to ensure precise, consistent, and repeatable results,” said Hayes. “Automation allows us to achieve repeatable results for highly customized processes. Our processes and our technology is constantly being adapted to our clients’ requirements and for each individual part. Rack makers design specialized racks for every part, chemical formulations are customized, and full production equipment is used for test runs to ensure exacting results.

As devices get smaller and more complex, surface treatment and coating providers have to stay ahead of the technology curve and integrate new technologies and materials into their processes to meet medical device manufacturers’ demands and stay on top of regulatory constraints. Device manufacturers benefit the most when experienced supply chain partners stay ahead of the game.

“We recognize a surge in robotic surgery applications,” said Morris. “These applications require tight tolerances and robust coatings to provide insulative coatings with a high factor of safety. Rising healthcare costs make other solutions in the robotic surgery space uneconomical and regulatory risky solutions. We also anticipate more electrosurgical devices and advanced energy devices used in surgeries in the next five years. Many robotic applications will begin utilizing more energy-based devices to reduce operating and patient recovery times.”

“We see a move away from complicated vacuum deposited coating technologies and materials utilizing PFOAs and other regulated chemistries,” said Gattuso. “Our focus on PFOA-free, safe, durable, and liquid applied coatings is allowing us to address the surface treatment needs of medical device manufacturers in the coming five years and beyond.”

“I believe cohabitation in new facilities or partner investments will trend in the near future,” added Dibiasio. “I also believe miniaturizing components from surgical robots to ultrasound devices and artificial intelligence capability will expand on medical device platforms in the next five years. Designing and expanding outpatient options expedited by COVID experiences in 2020 will also be a factor.”

“Additive manufacturing has dramatically broadened medical device designers’ ability to create intricate and highly customized devices, especially implants designed to work as a seamless extension of the human body,” concluded Hayes. “Electropolishing’s ability to remove a microscopically small amount of surface material will continue to be an asset in efforts to reduce these parts’ size and increase their durability.”