August, 2018
www.us-tech.com
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s the medical device industry continues to grow rapidly, manufacturers must contend with a variety of challenges as they differen-
Functional PVD Coatings Improve Medical Device Performance
By Jeff Elliott
tiate their products in a highly competitive mar- ketplace. Greater emphasis is being placed on the functional coatings that are applied to stainless steel, titanium and other substrates of critical medical devices from implants to scalpels, needle drivers, bone saws, and reamers. When manufacturers first began coating
instruments, the primary purpose was to improve the aesthetics of instruments and improve identifi- cation during surgery. Titanium nitride, with its easily recognizable gold color, quickly became the coating of choice for this purpose. However, OEMs are now looking to move
beyond aesthetics by applying titani- um nitride and other innovative PVD coatings to improve wear resistance, reduce galling between sliding com- ponents, increase lubricity, and even help retain sharp edges on cutting instruments.
Coatings for Medical Devices These same coatings can also
deliver other important functional benefits, such as providing anti- glare surface for bright operating rooms, antimicrobial properties and anti-fouling in the presences of blood and tissue. In some cases, it can even potentially turn devices into multiple re-use items, for example with laparoscopic instruments. Another alternative is anodiza-
tion, an electrolytic process that coats the metal substrate. Unfortunately, it is impossible to effectively anodize stainless steel without losing wear resistance and durability, which is a significant disadvantage. Moreover, anodization can form
a layer of rust on the stainless steel, causing it to corrode. For this reason, anodization is typically only used on aluminum or titanium. This limits the range of medical devices that can utilize this type of coating.
Physical Vapor Deposition To overcome these challenges,
medical device manufacturers are increasingly turning to physical vapor deposition (PVD), a process that describes a variety of vacuum deposi- tion methods that can be used to pro- duce extremely hard, thin coatings on stainless steel, titanium, ceramics and other advanced materials. These coatings provide a unique
combination of extreme surface hard- ness, low friction coefficient and anti- corrosion properties. The coatings also have the advantage of being thin, typically 0.04 to 0.2 mil (1 to 4 µm). This feature, in conjunction with close tolerancing, means that the component retains its form, fit and dimensions after coating without the need for re-machining. Introduced into the medical
device industry nearly 20 years ago, PVD coatings, such as titanium nitride (TiN) are extremely hard (2,200 to 2,400 Vickers) and provide excellent wear resistance. Despite its functional properties the first med- ical instruments used the coating as a decorative, high-end finish. “Initially, the industry was look-
ing for ways to differentiate instru- ments aesthetically and for identifica- tion purposes, and titanium nitride was as a solution for that. To this day, it is the highest volume PVD coating used in the medical device industry,”
explains Matt Thompson, Oerlikon Balzers’ North American business development manager. Oerlikon Balzers offers coating services at more than 140 coating centers worldwide, including 16 locations throughout the United States and has been produc- ing coatings for more than 70 years. Given its widespread use, titanium nitride is
well-established in the medical device industry. This is supported by a vast quantity of litera-
ture and testing that supports the biocompatibility of the coating, and many precedents with the FDA. As a result, other PVD coatings like diamond-
like-carbon (DLC) and aluminum titanium nitride (AlTiN) have gained widespread acceptance — par-
PVD-coated medical tools. Continued on page 63
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