The medical sector continues to innovate and bring the best treatments to patients for a range of ailments. One of the biggest areas of growth is minimally invasive surgery, which is helping patients spend less time in hospital and undergo less risky surgical procedures that have much shorter healing times. Switching many surgeries to minimally invasive procedures (where applicable) has reduced clinical costs associated with the surgery and yielded better patient outcomes. Successfully implementing minimally invasive surgical procedures requires the very small medical devices that often have complex shapes and surface features, for which lasers are required.
Medical-related laser technology is continually improving – leading to lasers that have high power and performance but are not cost-prohibitive for clinical settings. This has led to laser micromachining – a method that continues to grow in technological capabilities for creating medical devices with very intricate patterns and complex geometries – being the preferred choice over mechanical methods for the fabrication of minimally invasive devices.
What is laser micromachining?
Laser micromachining is a non-contact precision manufacturing method that uses a focused laser beam to create small and intricate features on the surface of medical implants. It is a high-precision technique that creates accurate features on a range of materials at much smaller scales than other fabrication techniques. It also has the added benefit of no tool wear because it uses light, unlike mechanical system that degrade over time and lose their resolution.
Depending on the resolution and size of the focused beam of the laser micromachine technique, the features created can be between a few microns to a few hundred microns. It should be noted that laser micromachining is used on both small and large medical devices, but the features it creates are always small regardless of the implant’s size.
Laser micromachining is now performed with ultrashort pulse (USP) lasers. These emit ultrashort pulses of light that contain short wavelengths and short pulse widths from the picosecond (ps) to femtosecond (fs) timescales. USPs are known as fast lasers, because of the speed at which the laser pulses on and off, not the speed of light propagation. Short pulses enable high optical intensities to be achieved, while using less power. While this may seem counterintuitive, it is because they form more tightly focused beams that reduce energy loss during beamforming and beam propagation.
Unlike other lasers – such as nanosecond (10-9) lasers, which have wavelengths in the ultraviolet (UV) regions – the materials absorb less of the energy due to the short pulse with a USP laser. This means that the material can be vapourised from the implant with minimal heat transfer, leading to negligible heat affected zones (HAZs) on the implant’s surface (as a high HAZ can produce inaccurate features that affect implant performance). For this reason, laser micromachining with a USP is known as a ‘cold ablation’ process.
The latest technological breakthrough
For many years, nanosecond lasers have been widely used. This was followed up by picosecond USP lasers. More recently, femtosecond (10-15) USP lasers have become the gold standard for minimally invasive devices. There are many types of femtosecond laser technologies being applied to medical devices, including fibre lasers, semiconductor lasers and solidstate lasers. The shorter pulses enable less material to be removed from the surface of medical devices with a much higher precision due to a narrower laser beam, which has led to even smaller and more intricate features being possible.
For many years, laser pulses with very high peak power intensities were difficult to use because they exhibit complex non-linear optical properties. So, it was very difficult to create femtosecond lasers that were suitable for small devices – as the only applications were on very large devices that could handle the complex optical properties of the laser.
This all changed when a Nobel-prize winning technology called chirped pulse amplification (CPA) was developed that made ultrashort laser pulses with high peak powers compatible with compact laser systems. CPAs contain a short pulse oscillator and diffraction gratings that stretch the pulse by a factor of thousands. This is followed by raising the peak power massively before a diffraction grating reverses the stretching process. This allows pulses to be stretched, amplified and recompressed, so that they can be used with smaller laser systems but still have produce safe high-energy USPs of laser light.
Femtosecond lasers produce very little heat because the pulse time is shorter than electron relaxation times. This prevents electrons in the material from transferring heat energy when excited by the laser (from the emission of photons), leading to a cold ablation of material in a very small target region on the medical device. The thermal transfer properties vary from nanosecond lasers that have been used in the past. Nanosecond lasers produce a HAZ thickness of around 20–50μm, whereas the thickness of the HAZ in a femtosecond laser is less than 1μm. Exact HAZ values depend on the material being machined and the specific laser parameters used, such as pulse energy, repetition rate and focus. Therefore, these figures should be considered indicative rather than absolute.
Femtosecond lasers are also compatible with many of the advanced materials and metal alloys that are being used today to create medical implants using traditional manufacturing and metal additive manufacturing methods. These include nitinol alloys, bioresorbable polymers and cobalt-chromium (cobalt chrome) alloys. The properties of femtosecond laser beam pulses preserve shape memory characteristics in nitinol alloys, prevent molecular chain degradation in bioresorbable polymers, and prevent micro-cracking in cobalt-chromium alloys.
“Laser micromachining has no HAZ for preserving material properties, is very versatile for use with a range of implant materials, provides a high design agility for adapting to new geometries without retooling, and ensures that there is no contamination risk due to no tool wear – something which is critical for medical devices being implanted into the body,” says Dr Nazeer Basha, senior mechanical engineerlaser technology/joining process at GE Healthcare.
Smaller and more advanced
Femtosecond lasers are enabling the next generation of medical devices that have feature resolutions lower than 5μm. Because performance-enhancing features can now be made smaller, it means that the overall device can be miniaturised compared with other fabrication techniques.
“Ultrashort-pulse lasers make it possible to miniaturise devices without compromising performance or putting them under mechanical stress or degradation,” says Basha. “In minimally invasive devices, this translates to ultra-smooth edges, microchannels, and perforations that enhance functionality while maintaining structural and biocompatible integrity.”
Femtosecond lasers bring a higher design freedom to medical devices by allowing many different patterns, holes and grooves – including advanced surface features such as 3D pore structures and variable material stiffnesses – to be introduced to ultrasmall medical devices intended for minimally invasive surgery. These features are introduced to improve performance or bio-integration in some way by altering the surface features of the device. So, having a better control over the surface properties of small implant devices is helping to create more effective minimally invasive devices that last for longer in the body post-surgery and cause fewer complications.
Many types of minimally invasive devices can be improved using laser micromachining. These include stents, electrophysiology devices, embolic protection devices, intraocular lenses, prosthetics, catheters, biomedical filters, heart valve components and pacemaker components. All these devices are shrinking and becoming more complex because laser micromachining can introduce smaller features, which allows the overall device size to be minimised.
Of all the smaller implantable medical devices now possible with laser micromachining, the area that has benefitted the most is stents. Stents have been getting increasingly complex as more procedures are performed each year. Many early stents used to end up covered in scar tissue, rendering them ineffective. Efforts since have used biodegradable polymer coatings to prevent this, but now laser micromachining is being used to create stents that are inherently biocompatible based on their surface features – which reduces the risk of arterial narrowing after surgery (restenosis).
It is important to note that biocompatibility is also influenced by material selection and any coatings applied; laser micromachining enhances surface characteristics but works alongside these other factors to improve overall performance.
Devices enabled by micromachining
Many stents – especially drug-eluting stents – need to be smaller to be placed in smaller blood vessels. Laser micromachining is not only helping to create stents with smaller tube diameters and more complex features, but its versatility is enabling stents to be made from a wider range of materials. For enabling smaller stents, other techniques have struggled due to the induced HAZ causing damage, but that’s no longer an issue.
Basha states that “laser micromachining can introduce micro-perforations for drug delivery or fluid control in stents and catheters, while fabricating surface nanotextures in metal and polymer stents enhances cell adhesion, drug retention and biocompatibility, while reducing bacterial colonisation”. On top of the stents themselves, laser micromachining can be used to fabricate very small and structurespecific membranes that act as an arterial filter to stop any broken pieces from entering the vessels during surgery and causing further complications (such as a potential stroke).
But it’s not just stents, various catheters are being improved by laser micromachining. It is being used to introduce micro-perforations into fibre-optic catheters, which helps with regulating fluid delivery and embedding sensing features (something that is a future direction for catheters). These micro-perforations are carefully designed to control fluid flow or enable sensing functions, ensuring precise delivery of therapeutic agents or accurate measurement of physiological parameters. For the surgical procedures themselves, photonic-bandgap fibres can be used in flexible surgical instruments to enable minimally invasive cutting with minimal thermal damage, which can then be followed up by the cauterisation of tissue using laser micromachined cryogenic catheters.
While they are not a minimally invasive device per se, laser micromachining is also helping to create sharper surgical tools used during these procedures by introducing sharper contours that enable a cleaner cutting of the skin. On the diagnostic and testing side that runs alongside minimally invasive surgery, microfluidics and lab-on-chip diagnostic platforms are also being improved because smaller channels can be made smooth and burr-free with more precise cutting, leading to smaller diagnostic platforms being created and lab-on-a-chip platforms that have more channels per area.
The future of laser micromachining
There are already many examples of laser micromachined minimally invasive devices in use today. “Laser-cut stents, micro-perforated catheters and microfluidic diagnostic chips are already in global clinical use,” says Basha. “More advanced devices – such as bioresorbable laser-textured implants and sensor-integrated catheters – are progressing through trials. Regulatory approvals are stringent, but the reproducibility and cleanliness of laser processes facilitate compliance.”
It’s also likely that the future of laser micromachining will involve some level of artificial intelligence (AI) integration for real-time optimisation of the fabrication process. “The next evolution will combine ultrafast laser micromachining with AI-driven process control and inline inspection. This integration will enable scalable, high-throughput production of complex, patient-specific devices,” states Basha, concluding that “we’re moving towards a future where the laser system doesn’t just machine – it thinks, inspects and validates every feature in real time”.
While the developments in laser micromachining are now widely implemented, it is not the only new manufacturing innovation that is being used to create minimally invasive devices. 3D printing has now become a widely used manufacturing technique for making small implants with complex geometries and optimised surface properties (such as a specific surface roughness to promote cell adhesion and osseointegration). However, it is seen as a complementary technique – not a competitive technique.
Basha captured the interplay between 3D printing (additive manufacturing) and laser micromachining very well, “Additive manufacturing can form the complex 3D structure of a medical device, and laser micromachining refines and functionalises it. Think of additive manufacturing as building the house – laser micromachining is the precision interior finishing.”
