APPLICATION FOCUS: MEDICAL DEVICE MANUFACTURING Special polymers for welding


Clariant has unveiled medical devices and components made from new variants of its Mevopur polymer material, formulated to improve laser welding performance. The chemical firm made the announcement at Medical Design & Manufacturing (MD&M) West in Anaheim, at the start of February. Increasingly, laser welding is


preferred in production of medical devices because it provides speed and reliability, can handle complex structures and avoids some of the downsides of other methods, such as solvent residues. According to Eric Rohr, however,


Clariant’s medical and pharmaceutical segment manager for North America, because medical devices are frequently


made of transparent or translucent materials, the polymer’s ability to absorb the laser energy often needs to be enhanced using additives. While Clariant has offered such


additives for many years, and in 2016 began using them in compounds used for laser marking applications, welding presents additional challenges to marking, as it involves two polymers rather than one – one polymer that is transparent to laser energy and the another that can absorb it to create the weld. The process can be complicated further by any pigments or fillers, which can change the way the plastic reacts to the laser. At MD&M West, the firm displayed welded products that appear to involve


than produce unwanted heating. Lastly, due to the pulse width being a thousand times shorter than a nanosecond laser, the peak power to average power ratio is around a thousand times higher, which enables unique interactions between the picosecond laser and the substrate, including multi-photon absorption. Here, the material is directly atomised in a relatively cold process, rather than being heated to vaporisation via boiling, as is done when using a CO2


laser for marking applications. Coherent has demonstrated that black marks


can be created on 1.4301 stainless steel, using a picosecond laser with an average power of 7W, a pulse width of less than 15 picoseconds, and a maximum pulse repetition rate of 1MHz. ‘At first glance, these marks appear similar to


the black [oxide] marks produced using nanosecond lasers. However, their actual structure is quite different,’ the firm remarked. ‘With picosecond laser marking, a major contributor to the high contrast black appearance seems to be a subsurface nanostructural change that results in efficient light trapping and light absorption, without significant change in the material composition.’ In testing, Coherent demonstrated that the


created marks are naturally resistant to corrosion during repeated autoclaving and do not require any re-passivation for this purpose. In addition, neither passivation nor autoclaving cause any appreciable fading of the marks. ‘Tis extends the lifetime of re-usable


devices, lowering the cost of ownership,’ the firm said. ‘It also simplifies and lowers the overall cost of medical device fabrication, as it puts no restriction on the order of when, and in what order, the marking and passivation


www.lasersystemseurope.com | @lasersystemsmag Laser marked dental implants


processes are performed. Te bottom line is that these picosecond laser marks are more permanent and less restrictive to use than nanosecond laser marks.’


Implant tracking While UDI-marking is currently only mandatory for non-implantable medical devices, resistant and biocompatible UDI marks could also be used to improve the traceability of medical implants, according to laser marking firm Foba, particularly due to the possibility of revision surgery taking place if an implant malfunctions. Te firm highlighted that the German


federal health minister, Jens Spahn, has recently presented a draſt law for an official nationwide implant register – based on the already existing Endoprothesenregister Deutschland (EPRD) – that is intended to provide more safety for patients when they need knee replacements, pacemakers and other implants. Te register would track where and when an implant was made, in addition to


two parts made of identical materials. However, two different formulations have in fact been developed in order to achieve laser transmission in one, and absorption in the other, enabling them to be welded together reliably. Another important factor in achieving


a good weld, according to Clariant, is the even distribution of the additive throughout the polymer matrix of the final part. In some cases, a concentrate, or masterbatch, can be dosed at the injection-moulding stage of production, where the injection-moulding machine mixes it sufficiently into the polymer melt before moulding. Injection- moulding machines, however, are not always ideal for dispersing the concentrate into the host polymer. In


some applications, the machine, the material or the part design may cause inconsistent distribution and lead to unreliable welding. Clariant addresses this by also


offering compounds where the job of distribution of the laser-absorbing additive, along with any other pigments or additives, is performed on highly efficient compounding lines. The injection moulder can use this all-in-one material without further dilution, with the formula and quality control having already been taken care of. The new laser-friendly materials are


manufactured at facilities that are certified compliant with ISO13485- 2016, the latest quality management standards for medical devices.


which patient has the implant. Tis would enable all patients who have had a particular implant installed, to be informed if a problem is discovered with their product. Hospitals and medical professionals are


requested to contribute to the current EPRD consistently, with the aim of tracking the lifespan (duration in the body) of registered implants as completely as possible. Patients are also able to report issues with implants. In 2017, Add’n solutions, a service provider


for UDI laser marking on medical devices, in close cooperation with Foba, conducted a long-term study in which laser-marked reusable surgical instruments underwent 500 sterilisation and cleaning cycles in order to prove the durability of the laser markings. Te markings were proven to withstand the


500 cycles, however the study provided evidence that only by using an additional passivation process – developed to exactly match the marking process – can long-term protection against corrosion be achieved for marks made with both short-pulsed (nanosecond) and ultrashort pulsed (picosecond) lasers.


References 1


‘Better Patient Safety due to Laser Marking on Medical Implants’ – Foba Laser Marking + Engraving


2


Laser marking of reusable surgical instruments mastering multi-process requirements – Foba Laser Marking + Engraving


3


Permanent Marking of Stainless Steel Medical Devices Without Post-Processing – Coherent


ISSUE 42 • SPRING 2019 LASER SYSTEMS EUROPE 27


Foba


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