Laser applications in medical device manufacturing
Stent manufacturing is one of the biggest applications of laser technology in medical device manufacturing
The medical device manufacturing sector is one of the fastest growing application areas of laser materials processing.
It is also a growing sector in itself, with the global medical devices market projected to increase from its 2022 figure of $495.5 billion to $718.9 billion by 2029, according to Fortune Business Insights. This growth is despite a decline in demand during 2020, due to the disruption to normal healthcare services through the first phases of the Covid-19 pandemic.
Lasers are now regularly used in medical device manufacturing both for micro-scale machining – including welding, cutting, surface structuring and drilling holes – and for marking components and devices with tracking data to make sure current and forthcoming regulations on traceability are adhered to. Devices and components machined via lasers include catheters, endoscopes, heart pacemakers, meshes, stents, and needles.
Ultrafast lasers, which emit pulses in the order of picoseconds (10-12s) and femtoseconds (10-15s) long are often used for these tasks, with femtosecond lasers fast becoming the laser of choice. In the case of cutting procedures, for instance, this is because femtosecond lasers reduce the number of post-processing steps needed and also minimise thermal effects that in some cases can make materials bio-toxic. Femtosecond lasers can also process almost every type of material, enabling coated and laminated structures to be machined in one single step.
Medical device machining
The types of welds required to join parts of surgical blades, endoscopes, implantable batteries and pacemakers are less than 1mm in diameter. This micro-welding is of two main types: spot welding and seam welding. Spot welding is used in the manufacture of medical components such as the electrical contacts for fine springs, guidewires, and tubes. Depending on the spot size required and the material being welded, it can be carried out by continuous wave (CW), quasi-continuous-wave (QCW), or nanosecond-pulsed lasers. The seam welding used to seal up implantable devices can also be performed using such lasers.
Nanosecond fibre lasers and, increasingly, femtosecond lasers are routinely used for machining both neuro and cardiovascular stents. These stents are often made from nitinol, a nickel-titanium alloy that cannot be easily processed via mechanical techniques. Since stents are inserted into the body, they must not have rough edges that could injure the patient. So the ability of femtosecond lasers to machine burr-free, micron-level structures is extremely important.
Ultrafast laser manufacturer 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)
Stents can also be made from biodegradable polymers, which can also be processed effectively by femtosecond lasers, particularly those in the UV wavelength. Using femtosecond pulses instead of nanosecond or even picosecond pulses ensures that the laser beam contacts with the piece being machined for the shortest time possible. This minimises the heat-affected zone on the workpiece, resulting in a reduction in any detrimental effects caused by excess heating. For certain medical devices – including stents – reducing heating effects is absolutely critical for maintaining the biocompatibility of materials destined for implanting.
If vascular stents are machined via a continuous-wave laser or a pulsed nanosecond or picosecond laser, the biopolymer material can become bio-toxic as it heats up and its chemical composition alters. By contrast, femtosecond lasers limit such thermal effects as they transfer minimal heat to the material.
Another advantage of femtosecond lasers is that post processing after cutting the stent is minimised. This is because using lasers with pulse durations longer than a femtosecond can cause structural damage when cutting stents made from nitinol, stainless steel and magnesium. The structural debris must then be removed via various cleaning steps. In comparison, stents cut using femtosecond lasers – which give very good details and edges – only need to be put in an ultrasonic bath before use, thereby removing multiple processing steps and saving production time.
Ultrafast laser manufacturer Fluence’s femtosecond lasers can be used to drill tiny holes in microfluidic medical devices (Image: Fluence)
For fabricating medical devices that need to deliver fluids very precisely such as annulae, catheters (some of which are made from polyether ether ketone (PEEK)) and needles, femtosecond lasers are also a favoured tool. For metal versions of these devices the rapid femtosecond pulses prevent re-melting of the surface and consequent changes in structure, while their use avoids toxicity and structural damage in polymers. The latter is particularly important for devices containing laser machined slots or holes through which drugs need to be delivered; these must be extremely accurate and repeatable to enable the required high controllability of flow needed for drug delivery.
Component and implant manufacturing
Femtosecond lasers are also increasingly being used to open and clean the metal wire contacts on implantable devices, and micro-weld medical device components. They are equally ideal for machining holes known as ports into glass biopsy probes with diameters from 12µm to over 20µm. These ports are between 5µm and 10µm in size, and have sharp edges that need to be drilled through the sidewall near the probe’s tip.
Laser additive manufacturing of bone implants is another application in which the use of lasers is being investigated. Such lasers could enable implants to be readily tailored to individual patients, and allow shapes to be made that are impossible to fabricate using standard manufacturing techniques.
Lasers can also be used to roughen the surfaces of some implantable devices to help them integrate within the body via improving the bone ingrowth (osseointegration). In particular, it is ultrafast lasers that are holding promise for modifying the surfaces of implants to enhance osseointegration. Currently, grain blasting followed by acid etching is used to create a surface that bones cells can grow more readily on. But these techniques are not optimal, as they can leave behind residues and impurities which reduce the overall gain in the amount of osseointegration. Ablating using ultrashort pulsed lasers leave no residue – and, unlike other types of laser, ultrafast lasers minimise surface melting and vapourisation effects because they interact with the material for such a short timeframe.
The stripping of wires is another requirement during some medical device manufacturing processes. Femtosecond green lasers, for instance, can be used for this as they can ablate polyurethane coatings of up to 20 micrometres thick without any risk of damage to the wire inside.
Marking devices for traceability
With several countries recently instigating or set to bring in new labelling regulations, marking devices and components with unique identifying codes will be the biggest growth area for laser use in medical device manufacturing over the coming few years.
For example the European Medical Device Regulation (MDR), which came into force in 2020, specifies the corrosion-resistant labelling of all medical device products with Unique Device Identification (UDI).
The UDI contains information on the manufacturer, product and batch numbers of devices and their components, and consists of human-readable characters together with a machine-readable two-dimensional data matrix code. This label must be clearly readable throughout the entire lifecycle of the medical device.
Components requiring laser marking include bone screws and other metal implants, stainless-steel surgical instruments, the outer cases for heart pacemakers, endoscopes and dental tools.
Firms such as NKT Photonics and Foba offer laser technologies for producing high-contrast traceability markings on medical equipment such as kidney dishes (right) and surgical scissors (left) (Images: Foba and NKT Photonics)
Laser marking originally began in the mid- to late-1980s, using pump flash Nd:YAG lasers, which had large power consumptions compared with current fibre lasers. Today, lasers working in the infrared, UV and green wavelengths are used for marking – the choice of laser source being dictated by whatever material the laser needs to mark.
Prior to the latest regulations, marking on the selected medical devices which previously required traceability was done via ink, or mechanical engraving or etching. One of the main advantages for laser marking is that it does not require the use of solvent-based inks. Also, although lasers produce the mark by changing the material’s characteristics, they do not make physical contact with the device or component.
The number of medical items that now require marking is vast, simply because it is every individual component of a medical device that needs traceability. So, for instance, within a pacemaker, all of its internal components, including all the micromechanical parts, need to be marked in a specific way. A femtosecond laser is perfectly suited to marking parts such as these because unlike other types of laser, it minimises heat damage and consequent adverse effects on the functioning of the device or component.
Femtosecond lasers are also set to become the laser of choice for marking stainless-steel surgical instruments, which are subject to exposure to blood and other body fluids, wear and mechanical stress, as well as repetitive cleaning processes. Other types of laser would alter the composition and surface shape of the stainless steel, which can lead to corrosion at the mark site during the routine sterilisation procedures that surgical instruments undergo.
Prototyping and continued innovation
According to Grand View Research, in 2021 the patient monitoring devices market size was valued at $47.0 billion worldwide. This figure is expected to grow substantially with a rise in the use of monitoring devices driven partly by an ageing population and increasing numbers of us seeking to improve our own health and fitness. Healthcare providers moving towards using remote monitoring of patients, in order to provide care at home rather than in hospital, will also fuel this growth.
Existing types of devices include sensors for continuous glucose monitoring, blood oxygen level monitors, and home blood pressure monitors. But the current range of home monitoring devices available to individuals and healthcare providers looks set to increase as companies are using laser-based technologies to prototype complex ‘lab-on-chip’ sensors. The aim of these devices is to enable localised testing and diagnosis of blood samples either at the surgeries of healthcare providers or even in the patient’s home.
Currently, blood samples need to be sent to a centralised lab facility, which costs more and takes longer than a home test would. Since these lab-on-chip sensors have multi-modal functions – namely microfluidics, chemical mixing, and light guiding – on a single chip, each of which are made from different materials and have different structures, laser processing is promising to become increasingly important in their manufacture.
In the meantime, laser machining is being used to create prototypes of these home monitoring devices. Unlike using traditional mechanical techniques, fabricating with lasers avoids the need to order a minimum quantity of samples, which can be costly. Lasers also make prototype turnaround faster and cheaper, thanks to their ability to process multiple materials through their adjustable parameters and range of wavelengths.
Lead image: Shutterstock/Christoph Burgstedt