Growth areas for femtosecond lasers in medical device manufacturing
Stent manufacturing is one of the biggest applications of laser technology in medical device manufacturing (Image: Shutterstock/Christoph Burgstedt)
The use of lasers in the medical industry for diagnostics and procedures such as eye surgery, tattoo removal and treating varicose veins is well known.
In these applications, it is often the laser itself that is the workhorse, however this is far from being the whole story when it comes to the medical implementation of laser technology.
In recent years, lasers have increasingly been used in medical device manufacturing, for example to machine components – often on the micro-scale – or to mark them with tracking data to ensure they comply with the latest regulations.
In particular, it is ultrafast lasers – those emitting pulses in the order of picoseconds (10-12s) and femtoseconds (10-15s) in duration – that are becoming the lasers of choice for such micromachining and marking tasks. In this article we will focus on the applications of femtosecond lasers, due to them seeing particularly healthy, increasing adoption in this sector.
Burr-free, micron-level structures in stents
Neuro and cardiovascular stents are an excellent example of medical devices now routinely manufactured using femtosecond lasers.
Such was shared by Dr Husain Imam, Director of Strategic Marketing for Ultrafast at international fibre laser manufacturer NKT Photonics. He explained that femtosecond lasers enable the precise machining of burr-free, micron-level structures on the stents, which is extremely important for preventing adverse effects when inserting them into the body. He added that some stents are made from nitinol, a nickel-titanium alloy that does not readily lend itself to being processed with mechanical techniques, hence why femtosecond lasers have proven so effective here.
Stents and other medical devices can also be made from biodegradable polymers, which also require precision machining. According to Imam, although such materials have typically been processed using nanosecond UV lasers and excimer lasers, manufacturers “are now moving to shorter-pulsed femtosecond processes”.
One of the main advantages of using femtosecond pulses, as opposed to nanosecond (10-9s) or even picosecond pulses, is that the beam is in contact with the workpiece for the shortest possible time. This minimises the heat-affected zone on the workpiece and thereby reduces any detrimental effects caused by excess heating. For certain medical devices – including stents – this is absolutely critical for maintaining the biocompatibility of materials destined for implanting.
Dr Dariusz Świerad, Sales and Marketing Director of Polish ultrafast laser manufacturer Fluence Technology, explained that stent manufacturing is one of the primary target markets for the firm’s Jasper X0 range of 1,030nm high-power femtosecond lasers. These lasers deliver pulse energies of up to 100µJ and average power up to 60W depending on the model, and via harmonic generation modules can operate at three additional wavelengths: 515nm (green), 343nm (UV) and 258nm (UV).
Fluence’s femtosecond lasers can be used to cut commonly used medical materials such as bioresorbable polymer (polylactide) with negligible kerf (<1um) and no taper, ensuring their biocompatibility. (Image: Fluence)
“In the case of vascular stents, if you use a continuous-wave laser or a pulsed nanosecond/picosecond laser, rather than a femtosecond laser, then the biopolymer material can become biotoxic as it heats up and changes chemical composition,” says Świerad. “So if you want to limit these thermal effects, one of the ways is to use a femtosecond laser. This provides athermal micromachining capabilities in which minimal heat will be transferred to the material.”
“Secondly, femtosecond lasers are attractive because you can create very precise features,” he continues. “As you can imagine, stents are tiny, being around 2.5 - 4mm in diameter and 8 - 48mm in length. There are manufacturers of stents who use nanosecond or picosecond lasers. While those are cheaper than femtosecond lasers, if you want top quality with very good details and edges, and you don’t want to risk biopolymers becoming toxic or metals experiencing oxidation, then you need a femtosecond laser.”
In terms of looking at the stent manufacturing process as a whole, another advantage of femtosecond lasers is that “post processing after cutting the stent is minimised,” adds Aivaras Urniežius, Key Account Manager for Light Conversion, a Lithanian femtosecond laser manufacturer. He explained that using pulse durations exceeding the femtosecond range can cause structural damage when processing stents made from nitinol, stainless steel and magnesium materials. “This structural debris then has to be removed in some way either by cleaning it or using acid,” he says. “Whereas if you use a femtosecond laser, you cut the stent, put it in an ultrasonic bath and can almost immediately put it in the human body.”
Femtosecond lasers therefore remove a lot of processing steps and thereby save production time, Urniežius continues: “While a femtosecond laser is up to five-times more expensive compared to nanosecond lasers, the steps that you save in production are worth the additional cost.”
Laser machining of fluid delivery devices
Femtosecond lasers are also an ideal choice for fabricating medical devices that deliver fluids very precisely, such as annulae, catheters and needles. As explained prior, when these devices are made from metals, the femtosecond pulses prevent re-melting of the surface and consequent changes in structure. In the case of polymers, it avoids issues with potential toxicity as well as structural damage.
“A lot of challenges are coming from plastic materials,” remarks Urniežius. “So you can have specific tubes where you need to create slots or holes for drug delivery. They have to be of highly controllable and repeatable dimensions if you want to create a specific flow of gas or drugs through these tubes. So you drill a tiny hole and if you have specific pressure, the flow from one tube to another will be highly controllable.”
Drilling tiny holes in microfluidic medical devices is an application where femtosecond lasers have been shown to excel. (Image: Fluence)
For example, glass biopsy probes, with diameters from 12µm to over 20µm, require the drilling of ports – holes with sharp edges through the sidewall near the probe’s tip – ranging from 5µm to over 10µm in size. Light Conversion has two femtosecond lasers, Pharos and Carbide, suited to such an application. Pharos offers 100fs - 20ps tunable pulse duration, 4mJ maximum pulse energy and 20W maximum average power, while Carbide offers 190fs - 20ps tunable pulse duration, 2mJ maximum pulse energy and 80W maximum average power. Both lasers can be used across a range of different materials and devices due to their ability to offer wavelengths of 1,030nm, 515nm, 343nm and 257nm via harmonic generation modules.
Collaborating with customers on medical laser solutions
For Light Conversion, supplying lasers for medical component manufacturing makes up “a significant amount” of its revenue, according to Urniežius, who explained that new ideas for this sector are constantly coming from interactions with customers.
“When you have a company that is manufacturing something specific, they don't always think about a laser as a solution,” he says. “So you meet with their engineers, speak with people who are responsible for their R&D, show them pictures and listen to what kind of problems they have. Then you offer a laser as a possible solution.”
Fluence has established a dedicated applications lab in order to work more closely with its customers – showcasing the capabilities of its lasers and developing bespoke processes. This allows the firm to demonstrate the manufacture of sample components, or carry out research on specific laser parameters in collaboration with industrial or academic partners.
The micromachining station at Fluence's applications lab is comprised of positioning stages, galvoscanners, and various fixed and beam-shaping optics. (Image: Fluence)
“If they’ve had an idea of how to solve a problem in a particular way and come to us and ask ‘can we manufacture this sample this way so we don’t have these effects?’ or ‘do you have this precision?’ then we can test this in our applications lab,” explains Świerad. “We also develop new micromachining processes. For example, if a company came to us and said they wanted to weld plastic for a medical device, or microdrill some holes for microfluidics, then we can develop a process to do that.”
Every material is different in terms of what laser parameters are required to machine it, he continues: "You need to find the right pulse energy, wavelength, repetition rate, and overlap of the pulses – the so-called pitch. Then you can also temporally shape the pulse, and use either a single pulse or burst mode.” This latter mode generates a burst of femtosecond pulses, where each pulse can have the optimal fluence to maximise the ablation efficiency and increase the process speed while improving quality. For any given material “it requires a lot of knowledge and experience to find the optimal set of parameters”, remarks Świerad.
NKT Photonics also works closely with its customers for applications development, says Imam: “We can develop custom processing techniques that are specific to the design and materials of their device. However, there are now demands for higher precision machining and better selectivity when processing different materials in the same medical device.”
To address these challenging demands, NKT also offers green (515nm) and UV (343nm) wavelengths between its Origami and AeroPulse femtosecond laser series via harmonic generation modules (in addition to standard infrared wavelengths). “Processing at shorter wavelengths increases the resolution of the processing and also further reduces any unwanted thermal effects,” Imam explains.
Laser marking medical devices for traceability
Currently, according to Urniežius, producing stents is the biggest medical device manufacturing application for laser technology. However, he added that the use of femtosecond lasers to microweld other types of medical devices, or to open and clean metal wire contacts on implantable devices, is also growing.
Overall though, for Urniežius, it is the marking of medical components with unique identifying codes that will likely prove the biggest growth area for femtosecond lasers in the future. Such codes will be required to comply with existing and forthcoming regulations from several countries, so it will soon be mandatory during the manufacture of many medical devices.
Femtosecond lasers are increasingly being used to mark medical devices such as kidney dishes (left) and syringes (right) with anti-corrosive traceability codes and other key information. (Image: NKT Photonics)
“Everything that's going into the human body will need traceability,” confirms Urniežius. “If you have a pacemaker, for example, some of the components in the pacer, such as tiny micromechanics, might need to be marked in a specific way. So for a lot of these applications, only something as precise as a femtosecond laser can create such marks and not affect the functioning of the device or the component part.”
In the case of stainless-steel surgical instruments “femtosecond lasers are being slowly accepted as the only solution” for marking, continues Urniežius. This is because other types of laser would change the composition and the surface shape of the metal, leading to the potential for corrosion occurring at the mark site during sterilisation procedures.
Fluence’s Świerad added that femtosecond lasers’ ability in particular to both machine components and mark them with unique identifying codes will be what leads to their more widespread adoption in medical device manufacturing.
Manufacturing lab-on-chip devices
In addition to devices used within healthcare settings, there are of course a whole host of medical monitoring devices used within homes. This is a growing market – with many of us striving to improve our health, and with the population getting older, we are increasingly turning towards technology to help us manage health conditions and fitness. NKT Photonics’ Imam thinks this general trend will lead to a growth in laser processing within the next five years.
“There is a drive for more personalised health testing and monitoring,” he says. “We can already see today that there are sensors for continuous glucose monitoring, blood oxygen content, blood pressure, etc. These biosensors will become increasingly important, as health service providers will rely on continuous, realtime data for the patient’s wellbeing.”
Furthermore, there is significant development of ‘lab-on-chip’ sensors, which enable local testing and diagnosis at healthcare providers or even at the home – rather than sending blood samples to a centralised lab facility, which is both expensive and time-consuming. “These sensors require multi-modal functions on one miniature chip platform: microfluidics, chemical mixing, and light guiding,” Imam continues. “As these different functions require different structures and different materials on the one chip, it is envisaged that laser processing of these chips will become increasingly important.”
“We can already see that medical companies prefer prototyping these complicated sensors with laser-based technologies,” adds Imam. “This is because prototyping using traditional mechanical techniques requires a minimum quantity of samples, and if a sensor requires several different techniques due to different functions on the chip, then a high number of samples will need to be purchased in the development phase, making the process expensive and time consuming. Laser-based processes have the capability of processing a multiple of materials by changing laser parameters or laser sources, making prototype turnaround faster and less expensive.”
About the author
Science writer and broadcaster Dr Sharon Ann Holgate studied defects in crystals at university. Her credits include writing for Science and New Scientist, presenting on BBC Radio 4 and the BBC World Service, authoring a popular science book on nuclear fusion and four undergraduate textbooks, and writing case studies and brochures for both the Institute of Physics and the Institute of Physics and Engineering in Medicine. A former Young Professional Physicist of the Year, in 2022 Dr Holgate was awarded the William Thomson, Lord Kelvin Medal and Prize from the Institute of Physics for her work in communicating science.