Reliability is vital for medical device manufacturers. To accommodate such high levels of dependability, device makers use quality process control and before- and after-market traceability to ensure the highest level of integrity and compliance for their devices and instruments. This article will address challenging medical device marking concerns for device makers and show how ultrashort pulse laser marking systems can solve this critical issue.
 
There are many well-established laser marking approaches such as carbon dioxide (CO2) lasers, nanosecond-pulsed diode-pumped solid-state lasers, and continuous-wave fiber lasers to name a few. No matter the laser type, all use photoablation to produce a color change to the surface, a texturing of the surface, or even an engraving into the surface, depending on the material and the desired effect. The process is photo thermal whereby a precisely focused laser beam produces intense heat in a highly centralized manner, increasing the material temperature and thereby producing some sort of change to the material. For example, a CO2 laser marks various substrates by actually melting and boiling off the material, creating surface relief. Ultrashort pulse (USP) lasers such as picosecond and the faster femtosecond laser have some impressive results over nanosecond lasers. This makes all the difference in medical device marking.
 
Picosecond, Femtosecond, Nanosecond
Picosecond lasers produce impressive results and have become instrumental to medical device manufacturers for maintaining compliance. The advantage of producing permanent identifying marks on such devices includes counterfeit prevention, product traceability, advanced quality control, return fraud prevention, and distribution regulation.
 
The most common non-invasive black marking approach is using nanosecond lasers to create photothermal radiation-matter interactions, which can result in macroscopic implications that constrain its use in the medical device market. For instance, thermal stresses can deform fragile and sensitive areas such as sheets and tubes as well as sometimes cause unsatisfactory color or contrast changes in imprinted labels. Also, the processing window is quite narrow when creating passivation-resistant black marks on stainless steel components. Marking with picosecond and femtosecond laser systems have a much wider operating window. This is because the USP laser acts to modify the surface of the material at the nanoscale, creating an effect that essentially traps light, causing the exposed area to appear perfectly black even when viewed from all angles.
 
As a result, ultrashort pulse widths and high repetition rates enable femtosecond lasers and picosecond lasers to excel in applications where nanosecond lasers were traditionally utilized. They depend less on the wavelength than nanosecond lasers for marking materials, and this aligns with increasingly-stringent FDA requirements to favor the use of ultrashort-pulsed laser marking.
 
FDA Medical Device Mandates
Whether surgical tools; pacemakers; reusable, non-implantable devices; or joint replacements, the medical device industry will continue to rely on laser system manufacturers for their expertise in marking to ensure compliance.
 
Over the last few years, the FDA has mandated that Class II devices and those intended for repeat use or reprocessed before each use, as per 21 CFR § 801.45, must be marked with a unique device identifier, or UDI. This is because these latter devices will inevitably become separated from their original labels and device packaging. This regulation applies to one-time and multi-use stainless steel instruments and devices and when the term reprocessing is referenced, which typically refers to autoclaving (a sterilization method that uses high-pressure steam).
 
There are a few ways these required laser markings can be inadvertently removed during subsequent cleaning processes. However, marks produced using the picosecond or femtosecond lasers are far more robust and survive the passivation process more reliably than other laser types.
 
The FDA instilled such UDI regulations to guarantee hospital staff can access the data encoded in these identifying marks, and any failures at reading these codes would generate records within the FDA database. If the FDA finds there are numerous reports generated for a given device or instrument, they can initiate the shutdown of production while they investigate.
 
UDI on Devices
Marking UDIs on devices and instruments is needed to follow devices on the market and provides a straightforward way to document and track device use in electronic health records (EHR), clinical information systems, claim data sources and registries. Additionally, UDIs support post-market surveillance systems and support pre-market approval or clearance of new devices as well as any new uses of existing devices already on the market.
 
More specifically, the marking of UDIs on devices enables better reporting, reviewing and analyzing of adverse events so that problematic issues can be quickly uncovered and corrected. It can reduce medical errors because it permits healthcare professionals to act more quickly and accurately in identifying a device and allow access to any and all vital information concerning device requirements. Additionally, the use of a standardized UDI enables manufacturers, distributors and healthcare facilities to more effectively manage medical device recalls and to act more quickly in locating where the device is in use. This makes the use of picosecond and femtosecond ultrashort pulse lasers a significant benefit for medical device makers.
 
Device Traceability
The markings help with tracking and recordkeeping that device manufacturers need to not only comply with government mandates but also to address and correct production errors, decrease costs, and even, at times, defend against any potential lawsuits. To maintain traceability on tools and devices as they are produced, distributed, or in use by the patient, device makers can either permanently mark via a unique number, bar code, 2D symbol, or logo on ceramics, composites, metals, and/or polymers used to make and package products. This is done using a picosecond laser to produce a clear, corrosion-resistant laser mark.
 
The picosecond and femtosecond laser system delivers a unique laser mark that survives multiple passivation, autoclaving cycles, and repeated sterilization. These devices, often made from various stainless steels need to be marked with high contrast, high resolution black marks so operators or machines can easily read them—all for the sake of traceability. Achieving high contrast is key because after many cycles of autoclaving, the high contrast can eventually pass below threshold for certain automated readers, which is problematic. It is critical these marks are fade-proof, and the USP lasers do a very good job at this.
 
Understanding the Role of Passivation
Picosecond laser systems are able to produce marks on contoured surfaces. The marking process, most importantly, does not compromise the natural passivation, the process of treating or coating stainless-steel surfaces in order to reduce its the chemical reactivity of its surface. The need for re-passivation can be greatly decreased or even eliminated, which is a major benefit as well as a cost saver.
 
For generating black marking, the laser processing procedure, which causes extremely dark, high-contrast markings on a surface without material ablation, the picosecond laser system uses ultrashort pulse durations that impart energy to a steel surface with almost no thermal effect. Unlike heat-generated annealed marks produced from other lasers, black marks created by a picosecond laser system provide substantially high contrast periodic nanostructures with anti-reflective properties. This makes marking appear deep black against its background.
 
As opposed to an oxide layer, the restructured surface is greatly resistant to bacteria forming, passivation, corrosion, and autoclaving. In addition, this laser system offers a much wider processing window for marking stainless steel, aluminum, and titanium than standard lasers. If devices and instruments are too heavily cleaned during the passivation process, any disappearance of the laser mark could cause the device to be out of compliance. It is also critical that a groove isn’t made where bacteria could cling and potentially infect the patient.
 
Medical device designers may not know all that is involved with UDI, especially in terms of passivation. For instance, many stainless-steel alloys commonly used in medical devices have a natural outer surface of chromium oxide that stops corrosion during repeated sterilization. Natural passivation can be compromised by machining, grinding, polishing, or other mechanical processes during device fabrication. If there is a need for re-passivation using a citric or nitric acid, it can remove the unoxidized iron particles from the surface.
 
Picosecond Laser System Advantages
With picosecond lasers, the pulse duration is shorter than the time for heat to flow out of the laser interaction zone, even in metals, so peripheral thermal effects are greatly reduced compared to nanosecond lasers. This means a much higher portion of the total laser power is used to create the mark, rather than producing unwanted heating. Second, the high peak power of picosecond pulses enables unique interactions between the laser and the substrate, including multiphoton absorption, where material is directly atomized in a relatively cold process, rather than heated to vaporization. Picosecond laser systems do not melt the material and leave no burrs after engraving, resulting in a very smooth surface.
 
While picosecond lasers are considered quite an investment, these lasers can more than pay for themselves within the medical device community where failures can ruin a company. The areas treated with the picosecond laser absorb light to appear as unreflective dark marks on stainless steel devices. As opposed to oxide-made marks that differ in appearance depending upon the angle at which they are viewed, a black subsurface marking produced by a picosecond laser system will appear the same from all angles.

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David Locke is technical sales manager for ASCYS Lasertechnik US, where he advises customers on their line of customizable laser systems for cutting, marking, welding, and engraving. He has been in the industrial laser industry since 1984. Locke has a degree in physics from St. Michael’s College.