Matt Van Acker/Account Manager/Able Electropolishing
Medical device manufacturing is highly regulated and so requires the utmost attention to sanitation, safety and biocompatibility. Devices, regardless of whether intended for internal or external use, must be clean, defect-free and burr-free; meet stringent demands from a variety of regulators such as the FDA; and successfully pass biocompatibility testing. A few device-use concerns can be met with the proper application of electropolishing. For example:
Common concerns in the medical community:
- pathogen spread
- implant rejection
- surface contamination
- premature failure
Benefits of electropolishing
- enhanced corrosion resistance
- clean, sanitary, easy-to-clean surface
- improved microfinish – smoother surface
- enhanced biocompatibility
- fatigue life improvement
- burr-free surface
- decorative finish
- consistent/repeatable finish
How electropolishing works
Because it’s electrochemical in nature, electropolishing uses a combination of rectified current and a blended chemical electrolyte bath to remove flaws from the surface of a metal part. Parts are fixtured on a rack and submerged into the electrolytic bath. As the current is applied, the electrolyte acts as a conductor to allow metal ions to be removed from the part. While the ions are drawn toward the cathode, the electrolyte maintains the dissolved metals in the solution. Gassing in the form of oxygen occurs at the metal surface, furthering the cleansing process.
A skilled electropolisher can remove a precise amount of material per customer instructions. Material removal via electropolishing may be as little as 0.0001 in. per surface or up to 0.002 in. per surface depending on what the application requires. On a stainless steel part, for example, electropolishing removes the embedded contaminants and creates a chromium-rich passive layer that is 30 times more corrosion-resistant than a passivated surface.
Why electropolishing is necessary for finished medical components
Although electropolishing is marked by the bright polish left on a surface, more functionality-related benefits include deburring, endurance, microfinish improvement, increased biocompatibility and corrosion resistance, as well as removal of recast layer, discoloration from heat, and other surface flaws. Fabrication processes such as stamping, grinding, machining and heat-treating all are employed to transform a metal bar, casting or sheet into a finished part. As metal is bent, ground, heated and altered, the metal surfaces alter significantly. These alterations take the form of burrs, surface irregularities, scale and embedded particulate, which need to be removed before use in surgery. In many cases, these surface imperfections can be a focal point for infection or metal contamination for the patient. In addition, the imperfections may inhibit the functionality of the component, such as a blade with an edge that doesn’t cut as it should. Sometimes engineers look to coating processes to hide or mask a contaminated surface. The chief weakness of coatings is delamination. Depending on the application (implant, tissue insertion, multiple-use or single-use surgical tools), chipping, peeling or delaminating coatings pose unique and potentially dangerous conditions for the patient. While the coating itself may not be dangerous, exposing the poor metal surface underneath can be. Exposed burrs could break off in surgery, microscopic surface irregularities could harbor dangerous bacteria and embedded contamination can cause rust or corrosion under repeated chemical sterilization procedures. Most metalworking processes leave a metal surface porous and spongy, a condition called an “amorphous layer” of smeared metal which can be observed under 100X-300X magnification. This amorphous layer has significant air space that is perfect for trapping bacteria, water and chemicals. Research in other fields has proven that electropolished surfaces are highly resistant to biofilm production.
Not all electropolishers are the same
Electropolishing is not a commodity as some may assume – it’s also typically the last step in a sequence of manufacturing operations, so there is a lot of time and money at stake. The process takes years to master; lots of trial and error and good record-keeping are required to discover how different part configurations, material types and sizes react to the process. Electropolishing is not a one-size-fits-all process: Though it is highly scientific, there is an art to tailoring the process to a specific part – each part is unique and the process needs to be set up for the specific part and the application or engineer’s goals. Some important things to look for when finding an electropolisher you can trust with your medical parts: ISO 9001:2008 and ISO 13485 certification; amount of experience and history electropolishing parts; ability to work with materials or alloys other than the standard 300 series stainless steels including titanium and nitinol; and ability to control the process and hold tight tolerances. Properly electropolished parts will function better as a result of a smoother, more corrosion-resistant, burr-free and biocompatible surface that is uniform and in tolerance.