Company insight Laser marking for
disposables and reusables
A laser marker for medical devices and products can now be optimised to permanently mark plastic disposables or stainless steel reusables without compromising the device surface. Coherent is one of the world’s leading photonics manufacturers and innovators, and offers a unique and distinct product portfolio that touches many different markets and industries.
Black marks before and after a 20-minute Citrisurf passivation process – the mark is neither faded nor corroded. T
here is a growing mandatory requirement for labelling reusables with permanent Unique Device Identifier (UDI) marks that don’t fade with repeated sterilisation (autoclaving). Many of these devices are fabricated from stainless steel and it is vital that the UDI marks do not degrade the natural passivation of the stainless steel surface, for example, its corrosion resistance. Traditional engraving compromises the passivation. Plus, it creates surface features that can irritate tissue while also potentially trapping contamination. Alternatively, traditional dark marks produced by laser oxidation of the metal surface compromise the passivation and will quickly fade/ corrode with repeated sterilisation.
Black marking for reusable UDIs Fortunately, a newer method based on ultrashort pulse (USP) lasers called ‘black marking’ now creates high-contrast marks suitable for human and machine viewing without compromising passivation. Here the high peak power and short pulse duration of USP lasers causes a permanent nanoscale change in the surface and subsurface structure of stainless steel
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products. This has a strong light-trapping (anti-reflection) effect that makes the marks appear black with very high contrast. Because this is a nanostructural change in the steel, it does not corrode or fade during repeated autoclaving – see example above. By adjusting the USP laser output, black marking can be applied to certain anodised alloys, where it produces a light-trapping nanostructure in the aluminium that’s smooth and doesn’t compromise the outer clear anodised surface.
Subsurface marking of plastic disposables
Manufacturers of plastic disposables also need an advanced laser marking technique for devices and/or the device packaging, because of the limitations of traditional methods. Specifically, labels can be damaged or removed, inks can be contaminated, and infrared lasers will cause charring, surface roughness and other unwanted thermal effects. The latest ultraviolet lasers meet this need, since their high energy photons directly break the molecular bonds in plastic polymers. This can be used to cause a photochemical transformation that changes the colour of
the plastic, without removing material or causing any damage to the surface. The most common photochemical transformation is to bleach a coloured material, creating a pale mark. But some materials are designed to produce other types of colour change. For example, ultraviolet lasers can create dark, high- contrast marks on nylon and polyurethane that are white due to titanium dioxide doping. Examples include UDI marks on disposable catheters as well as QR codes on pharmaceutical bottle caps. Ultraviolet lasers can also mark transparent plastics, for example, inhalation masks and coated coloured plastics, without damage to overlaying transparent anti-allergen coatings, as used in hearing aids. For any laser application, service and support are also vitally important. Coherent now runs 17 service centres and multiple applications labs, strategically located around the world and all coordinated from the company’s centre of excellence near Munich, Germany, which acts as a single, centralised hub for all Coherent marking resources. ●
www.coherent.com Medical Device Developments /
www.nsmedicaldevices.com
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