Scratching the Surface: Experts on Medical Device Coating Trends

It began with a chance encounter.

Ernst Werner von Siemens and Johann Georg Halske met through a mutual acquaintance who recognized a rare complementarity of mechanical ingenuity and technological foresight.

Turns out that acquaintance was not mistaken.

Shortly after meeting, Siemens and Halske launched a company in October 1847 to build the pointer telegraph, a groundbreaking invention that enabled messages to be transmitted letter by letter from one device to another. One week after founding Telegraphen-Bauanstalt von Siemens & Halske, Siemens received a telegraph design patent in Prussia; the following year, the new firm was awarded a government contract to install a telegraph line between Berlin and Frankfurt, Germany. The startup completed the telegraph line in time for the Prussian king’s election as German emperor.

That early triumph set Telegraph-Bauanstalt von Siemens & Halske—and Siemens himself—on a course that would cement their respective legacies.

Telegraph-Bauanstalt von Siemens & Halske, of course, evolved from its humble beginnings in telecommunications and electrical engineering into a global developer of industrial and building automation, rail transport, and health technology (including medical imaging, laboratory diagnostics, and advanced therapy solutions). The company’s name also underwent a few changes and is now known simply as Siemens AG.

Aside from the pointer telegraph and copper wire insulation, Siemens’ most significant scientific discovery was the dynamo-electric principle, a revolutionary advancement that enabled electric machines to convert mechanical motion into electricity through electromagnetism. The discovery set the stage for modern electrification and laid the technological foundation for reliable motion in industry.

In addition to the dynamo-electric principle, Siemens invented the world’s first passenger train, the first electric elevator, the first electric tram service, and the trolleybus (the Electromote). Another patented invention—a moving coil transducer—was adopted as a loudspeaker in the Bell telephone system in the 1920s, three decades after his death.

Siemens is also credited with developing the first technical plasma application in 1857 with his dielectric barrier discharge tube, originally used as an ozone generator.

Considered the fourth state of matter, plasma forms when sufficient energy, such as heat or an electric field, is applied to a gas. The added energy causes electrons to speed up and collide with gas atoms or molecules, and these collisions can knock electrons free, creating more charged particles. When this process becomes self-sustaining, plasma forms.

First coined (as a term) nearly a century ago, plasma has evolved from early gas-discharge research into a precise, dry-processing technology that can modify the surface characteristics of materials for various industrial applications. Plasma treatment systems generate a plasma cloud that cleans, activates, etches, or coats surfaces, improving wettability and promoting stronger bonding and adhesion

In healthcare, plasma technology is used to modify implant and medical device surfaces to boost their biocompatibility and overall performance. Plasma surface modification techniques enhance osseointegration, promote soft tissue integration, provide microbial protection, improve corrosion resistance, and enable localized drug delivery.

Plasma, however, is one of several methods medtech manufacturers use to modify device surfaces. Other approaches include coatings (antimicrobial and hydrophilic, the latter of which adds useful properties like lubricity, thromboresistance, and drug-eluting capabilities), physical alterations such as sandblasting and laser blasting, and chemical treatments like acid etching, which removes surface layers.

As healthcare systems demand safer, more durable, and minimally invasive medical devices, surface engineering has emerged as a critical area of innovation. From cardiovascular interventions and orthopedic implants to catheters, guidewires, and surgical instruments, specialized coatings are helping manufacturers improve clinical performance while meeting increasingly stringent regulatory requirements.

To better understand the significance of surface modification techniques and the market forces driving their adoption, MPO spoke to more than a half-dozen industry experts over the last several weeks. Those providing input included:

• Niall Cullen, vice president of marketing at Integer Holdings Corporation 
• Maria Holm, chief operating officer; Eric Guire, chief innovation officer; and Kristin Taton, chief scientific officer at Innovative Surface Technologies Inc. (ISurTec)
• Dr. Jason McNary, research scientist at Comco Inc.
• James Morris, president/CEO; and Dr. Craig Morris, clinical innovation advisor, member, at Surgical Coatings LLC
• Todd Paulsen, vice president at Formacoat LLC

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Michael Barbella: What key surface properties influence biological response?

Kristin Taton: Three primary factors are surface roughness/topography, substrate stiffness, and surface chemistry, including surface energy (wettability). Surface roughness can affect biological response in macroscopic ways, for example, tissue damage due to a rough catheter insertion, and in microscopic ways. Surface roughness and porosity can have a profound influence on cellular integration with the substrate material. Cells may even align along surface microarchitecture, forming specific geometries. Smoother surfaces are generally called for in short-term device applications, but roughness has major advantages for long-term implants that require cell and tissue integration, such as orthopedics, implant meshes, or devices needing endothelialization.

Substrate stiffness can affect cellular adhesion and proliferation through specialized mechanosensory organelles present in the cellular plasma membrane. The degree of local tissue damage and inflammatory response surrounding long-term implants can be reduced when the mechanical properties of the device are tuned to match those of the tissue in which they are implanted.

Surface chemistry can be broken down further. Surface energy is one component, including wettability, which is a kind of old-school way of looking at it. Both hydrophilic and hydrophobic materials can be very biocompatible.  Protein binding is probably the biggest factor, since protein absorption is the first step in the biological cascade for clotting, foreign body response, and fibrosis or gliosis.  The interesting thing is that this first step of protein binding induces denaturation of the protein on the surface, which the body recognizes as being awry and initiates an immune attack, recruiting macrophage and other immune cells through cellular communication via soluble growth factors, cytokines, and other proteins. Controlling that initial protein adsorption is a sort of a holy grail among surface scientists. Researchers have examined polyethylene glycol, zwitterions, fluorochemicals, and many biological molecules like hyaluronic acid to reduce protein adhesion, but no perfect solution exists.  Alternately, you can engineer surface chemistry to have specific cellular interactions, using a cell-binding peptide sequence like RGD or a biomolecule like heparin, which either promotes or inhibits binding. You can also immobilize antibodies to recognize specific cell types for selective recruitment to the surface. The key surface properties are the chemical functionality (whether protein or synthetic), texture and porosity, and the substrate stiffness, along with whatever specific biological response is actually being targeted.

Dr. Jason McNary: Two key surface properties that influence biological response are mean surface roughness (Ra, Sa) and developed surface ratio (Sdr). Mean surface roughness (Ra in 2D, Sa in 3D measurements) is the average height and depth of peaks and valleys from a mean surface height. On implantable items (bone screws, dental implants, artificial hip joints), a high surface roughness provides friction between the implant and the tissue, allowing time for the tissue to heal around and fuse with the implant. Furthermore, a rough surface can inhibit bacterial growth, as it is more difficult for large microbial mats to form on highly uneven surfaces.

Developed Surface Ratio (Sdr) is the percentage of additional surface area that a rough surface has compared to a flat/smooth surface of the same dimensions. The increased surface area allows more contact between the implant and the tissue for bonding. Finally, abrasive blasting will remove the oxide layer from metallic implants and stents, exposing a fresh surface for the tissue to bond to.

How this relates to microblasting technology:

1. Creating a specified Ra finish—The surface texture of a dental implant determines how quickly and smoothly the implant integrates into a jaw bone. Studies indicate that the surface of a dental implant needs to be more than just “rough.” Several surface characteristics impact the rate of integration. Microblasting controls two of these characteristics: Ra, the size of the surface peaks and valleys; and the developed surface, or the amount of surface area created through the texturing process. 

Automated systems produce the most consistent and repeatable surface textures on dental implants. Automated systems are capable of creating surfaces as smooth as 10 µin or as rough as 200 µin. Comco technology in particular allows for careful control over particle velocity and coverage to create a consistently uniform surface.

Maintaining a smooth surface on the apex of the implant helps prevent bacterial growth where the implant sits at the gum line. Any method used to roughen the surface of the threads must not affect this area. Comco’s automated microblasting platforms achieve full coverage with a transition zone of 0.007″. 

2. Contaminant removal—Laser machining or stamping of nickel-titanium alloys (Nitinol) create surface defects, like oxide layers, heat-affected zones (HAZ), and pulse marks. If left untreated, these imperfections will adversely affect the performance as well as the lifespan of the device. Microblasting is an effective means of eliminating these possible source of problems.

3. Preventing corrosion defects—The environment where medical implant devices are placed makes them highly susceptible to corrosion. Three critical issues include: discoloration and oxide layers, laser pulse marks, and laser slag. To reduce the vulnerability of the devices to corrosive elements, it is important for their surface areas to have a smooth finish. Blasting the devices with micro-abrasives removes the oxide layers and discoloration, smooths pulse marks, and removes remelt, restoring the device to uniformity, thus ensuring the effectiveness of the electro-polishing process.

4. Decreasing stress-failure caused by micro-cracking—Both stamping and laser machining leave small cavities or micro-cracks on the base material. The cracks will corrode with time, becoming larger and eventually weakening the structural integrity of the implant device. The impact nature of the microblasting process specifically targets weak, brittle regions of the Nitinol device. The abrasive removes the brittle oxide layer and smears the more ductile base layers. This works to create a more uniform surface ideally suited to resist the harmful effects of cyclic fatigue.

James Morris, Dr. Craig Morris: The most important properties influencing biological response are the leaching factors of a surface coating. Leaching is the release of compounds and chemicals from the coating material to the surrounding or exposed environment. Successfully completing biological leach testing is what most often determines whether a coating material is safe for patient contact. Leach testing for plastics is critical to investigate and demonstrate the safety of the tissue type and the duration the coating material may be exposed to the patient.

Todd Paulsen: It really depends on the desired functionality of the device. The ones Formacoat tends to focus on are surface chemistry, biological interactions, surface topography and design, as well as surface energy. These are the big ones to focus on when selecting a coating for a medical device. It’s the reason we employ six full-time chemists on staff. Just like in real estate—where it’s all about location, location, location—with substrate properties, it’s all about chemistry, chemistry, chemistry.

Barbella: What role do specialty coatings play in enhancing medical device durability, usability, and reliability? 

Niall Cullen: Coatings often need to perform several functions at once, and those requirements can compete.  For example, there’s durability, which is resisting abrasion, wear, and corrosion, so a part holds up over its service life. There’s usability, which really comes down to how the device feels and performs, whether that’s dry or wet lubricity or just a smoother, more consistent surface. And there’s reliability: does the coating perform the same way on part one thousand as it did on part one, because that’s what shows up in an OEM’s design and regulatory data. Most coating chemistries are good at one or two of those, not all three. That’s the real case for working with a partner that has several coating platforms under one roof instead of picking a single coating and hoping it stretches to cover everything.

Barbella: What clinical needs are driving demand for advanced surface engineering?

Eric Guire: At a higher level, the clinical needs driving demand for advanced surface engineering fall into three segments: access and deliverability, tissue and blood compatibility, and long-term performance. Lubricious coatings have greatly reduced trauma associated with insertion and navigation, enabling the field of minimally invasive surgery. As the lubricity and durability of hydrophilic lubricious coatings continue to improve, surgeons are gaining minimally invasive therapeutic and interventional access to increasingly distal vasculature, particularly in the brain. Surfaces that can improve blood compatibility result in higher procedural safety for patients and fewer reinterventions. Long-term performance often boils down to maintaining a sensor, electrode, or drug depot function over time, as well as stable tissue integration at the chosen implant location. We’re always trying to improve medical devices, and the interface with the body is a top concern, especially with a longer-term implant.

At the center of this is the need to control cell attachment, one way or another. The main levers available are texture and surface chemistry. In some places in the body, you want a device to stay long term, held in place in a specific spot where the surgeon implants it, so the device and surface are designed for a porosity allowing cell infiltration. In other cases, you want to minimize response as much as possible and avoid clotting, which calls for a passivated surface.

Biological passivation is one of the largest clinical challenges. This includes anti-fouling coatings, which help with clogging as well as foreign body response, and keeping sensors functional. There’s also work being done on texturing, for example with aneurysm devices, where texture is applied to the metal to minimize foreign body response and clotting.

On the flip side, there are cases where you want cells to attach strongly to the device, without initiating a foreign body response, so the device integrates with the tissue. With stents, for example, you want re-endothelialization. The same is true with something like a hernia mesh, where the architecture of the mesh is controlled to promote healthy integration of cells into the scaffold. There is also the texture of a fabric that is used to induce healing or clotting when you want a device to stay in place.

Orthopedics is another area with a lot of surface engineering, where porous hydroxyapatite stimulates bone integration and antibiotic cement all work together to minimize infection risk while promoting cell ingrowth to heal. There’s also an ongoing need for antimicrobial technologies.

Morris: When interacting directly with clinical needs, the demand often differs significantly. One of our owners is a cardiac electrophysiologist, and the clinical demands often drive novel approaches to increasing device and procedure effectiveness and efficiency. Increasing visibility in imaging of the position of tools relative to the patient’s imaged and actual anatomy has been continually driven by clinical demand.  Other demands have shed light on poor surface coating quality and poor applications, resulting in underperforming or unreliable medical device function. 

Dr. Craig Morris: Surgery and procedures are moving toward smaller incisions, more energy-based tools, and more robotics, and each shift raises the bar for instrument surfaces. Surgeons and proceduralists need insulation that prevents stray energy from injuring tissue outside of the intended field, coatings that minimize glare under bright scope lighting, and smooth, durable surfaces that pass-through ports with minimal trauma and survive repeated reprocessing. Looking ahead, surfaces may also help imaging and navigation systems track instruments precisely in space. From the proceduralist’s perspective, the ideal surface is one we never have to think about. It should simply perform the same way every time, in every case, because a coating failure is often invisible until a patient is harmed. 

Morris: Given our position in the medical device manufacturing supply chain, we are less involved in clinical and surgeons’ needs and more engaged with medical device engineers and the design issues they face. The medical device engineers’ requirements and problems become our problems. Regulatory constraints can often limit the scope of true novelty that a clinical demand may imagine or desire. The biggest driver of demand from our customers is RF isolation for devices, or even for adjacent devices, in a procedure. 

Paulsen: It is all very use- and function-dependent, but there are some big ones that always just stand out. Recently we’ve seen an increased interest in lowering infection rates, longer durability and device lifetime, and as a lover of all things hydrophilic, my favorite is improved device deliverability. If you can’t get it where it needs to go, it can’t do its job. With that comes a reduction in foreign body exposure, which is why we love HA-based formulas. The most exciting one is application in complex geometries. The majority of coating companies only focus on the easy stuff, such as catheters and guidewires but we’ve seen more complex designs and substrate variants coming through our doors that no one can coat. 

Barbella: What role does biocompatibility play alongside mechanical performance evaluation? 

Cullen: Biocompatibility and mechanical performance should be evaluated together for coated devices. A coating might give you lubricity or thromboresistance, but everything about it, from the materials, what leaches out, what degrades, the particulates it sheds, and how sterilization changes it, has to be judged against how long and how closely it’s going to touch blood or tissue. 

That’s why mechanical testing needs to sit next to the biological testing, not after it: adhesion, abrasion, lubricity retention, simulated use, particulates, corrosion. You’re checking that before and after simulated use, and comparing it against acceptance criteria set ahead of time, especially once sterilization and aging are factored in.

Barbella: What recent breakthroughs in surface modification have the greatest commercial potential?

Eric Guire: From academic literature, hybrid coatings that combine antifouling (for long-term implants) or lubricious hydrogels (for procedural access) with antibacterial or antibiofilm properties. These have the potential to greatly improve safety and tolerability for patients by combining multiple mechanistic approaches. Externally activated coatings (e.g., near-IR-triggered thrombolysis and biofilm disruption using spiky silver nanoparticles) hold potential for orthogonal approaches.

Morris: The biggest breakthroughs we see are in understanding and control of the necessary application methods for surface coatings, and in the increasing integration of automation, process control, and quality management to meet the quality and precision required by medical device applications. It is often more important to control the process beyond Six Sigma validation to meet the economic and quality constraints our customers face. Quality, supplier management of the coating manufacturers and their processes, and the application of the coating must be 100%. Several issues with poor quality and performance have helped promote surface coatings over pultruded composite and other heat-shrink solutions.

Other potential areas we see are more novel copolymers and chemical solutions in the polymer chains that address our growing understanding of the effects of leaching and exposure to chemical compounds in patient contact. 

Paulsen: The one that we’ve been chasing of late is multi-functional coatings. For example, we have seen the benefits of collagen coatings when applied to wound dressings. But what if we combine a collagen coating with antimicrobial or antibacterial agent? Now we are fighting infection while promoting healing, and this kind of cross-functionality can be applied to so many different platforms. In the hydrophilic market alone, there is a lot that we can do to elevate a coating from just being slippery to being so much more.

Barbella: How are regulations evolving as new materials and technologies enter the market? 

Cullen: Regulatory expectations are becoming more detailed as new coatings, materials, and technologies enter the market. Reviewers increasingly expect clear links between design inputs, risk analysis, material characterization, process validation, test methods, acceptance criteria, and intended clinical use, rather than separate evidence points that stand on their own.  

For coated vascular devices, e.g., cardiovascular, neurovascular, structural heart, etc., that usually means going deeper on composition, adhesion, and sterilization compatibility, with durability data that reflects how the device is actually used, advancing it through a vessel model, exposing it to guidewires, checking for coating loss afterward. We’re seeing the same expectation show up for reusable orthopedic instruments now too: proof that the coating still holds up, adhesion included, after real-world cleaning and sterilization rather than just a lab simulation.

Barbella: What validation challenges do manufacturers face?

Maria Holm: If development is executed properly, validation should be a very simple part of the process. You produce the product, confirm it was made according to spec through quality review, and release it after it passes all QC testing. If the product does not pass, challenges show up in a few specific areas. When there’s a validation failure, you have to investigate why, and it could be a multitude of things: a raw material issue, or the fact that the batch record wasn’t consistently executed. People need to be trained well, because if they’re not executing the spec laid out, that can easily impact the product quality and validation outcome.

Raw material suppliers can be a source of challenges. If suppliers send materials that vary batch to batch, contain contaminants, or are not cleaned properly, that creates challenges for product consistency, and in turn your production process may fail validation, so having a reliable supplier and supplier management program is critical. 

It’s important to really understand your process. If you don’t understand what’s going on, it can be difficult to validate, because when you are designing the validation, you’re not necessarily looking at all the variables. There may be hidden variables that need to be uncovered, requiring root cause analysis that can be very time-consuming.

It is critical that everyone executing commercial functions in the supply chain has proper work materials and is trained. A new team member isn’t going to know every in and out of how the process should work, so making sure they have the right support in place is essential so they can execute to spec, down to the product-based requirements. When there’s a validation failure, you have to investigate why, and it could be a multitude of things: a raw material issue, or the fact that the batch record wasn’t consistently executed. People need to be trained well, because if they’re not executing to the spec laid out, that can easily impact validation. Adequate control of the environment is another factor, since that introduces hidden variables, something seen when not controlling the environment well.

Morris: I feel that most coating application providers in the medical device industry find that validation is a nightmare. This is all due to how difficult it is to control your coating application process. Coating is not easy. However, we are on the opposite end of the spectrum. We have continually improved our automated systems and process controls to the point where process validation is fun. Our most recent process validation for coating thickness has a CPK of 4.98. Our latest Virtual Masking™ (laser ablation) process validation was a CPK of 13.37.  For context, those values are 14.94 and 40.11 Sigma qualifications. We strive for process control and automation, and our Senior Automation Engineer, Peter Taenzer, has helped us build our next-generation automated powder coating line, which has uniquely raised the eyebrows of every quality and manufacturing engineer in the industry. We are extremely fortunate to have people who care about the business and put their work-life balance and well-being on the line to ensure patients receive the highest-quality, most repeatable, validated surface coating possible. To reference our owner, Dr. Craig Morris, the best coating is the one the doctors don’t know exists. 

Paulsen: Validation has evolved from a final quality check to a risk-based, lifecycle process that hopefully begins early in product development and continues through commercial production. The trick is to design for validation in a manner that can reduce development timelines, improve manufacturing yields, and streamline regulatory submissions. In the world of coating application and design, a successful validation depends on a combination of factors: coating chemistry, process engineering, analytical testing, quality systems, and regulatory. It’s important to really do the first four properly, as it will make the final process much easier, particularly with more complex devices and with regulatory expectations continuing to rise.