Lasers are producing medical parts in many ways, including joining, marking, cutting and additive manufacturing
Lasers — well-established tools in the manufacture of medical devices—are continuing to break ground by producing smaller, more precise and more functional parts thanks to faster pulse speeds at lower cost, new applications and the marriage of laser processing to Swiss-style machining.
As more plastics are used in medical devices, lasers are being used not only to process transparent materials but to join plastics and metals. And the need for quality assurance has led laser process monitoring to evolve to handle ever-smaller parts and welds.
Whether producing polymer catheters and other tubes, metal medical tools or implantable devices, laser processing executes features impossible or inefficient via other manufacturing methods.
Custom Systems Raise the Bar
Custom laser system specialist Innovative Laser Technologies (ILT), purchased by fiber laser giant IPG Photonics Corp. (Oxford, MA) in June, opened in Minneapolis in 1998 with Medtronic as its first customer. It has since grown to produce unique micromachining systems of all varieties.
ILT produces “standard laser systems, custom designs, custom tooling, custom software and application pieces, and incorporates process control important to the medical device industry,” according to sales manager Jim Jacklen. ILT has extensive experience with systems making catheters and other guide wire assemblies, as well as hermetically sealed implantable devices like pacemakers and defibrillators. ILT systems also process Nitinol, titanium, stainless steel and other metals with IPG fiber lasers in the IR regime.
Among their capabilities, ILT’s machines can create features in polymers ranging from 0.003″ (0.076 mm) up to 0.020″ (0.508 mm). “In some cases, we are [cutting] just through a single layer of polymer. In some cases, the holes have to go through an outer layer of polymer, then a middle layer of a metallic braid that holds that assembly together and then another internal polymer layer.”
ILT machines also create features under 0.003″, including openings in glass. “The accuracy required for some of those features for placement on the part is in some cases under 5 µm.”
The trend toward smaller components is clear and is shaping a new field of high-accuracy laser systems. “We are moving to more granite-based platforms and air-bearing stages, where you have motion system accuracy down in one or under one micron,” he said. With motion and beam delivery devices in action, “there are some inaccuracies with every system element.”
With longer beam paths, “the beam can sometimes wander a bit. It’s minute, but if the beam path is long enough and there are enough elements in the beam path, that can cause part inaccuracies.” All inaccuracies must be included in the overall error budget.
Part of ILT’s repertoire is secondary calibration of motion systems and galvo scanners via repeated testing of beam position and entering new data into their systems. In some cases, the environment must be controlled by ±1 degree F to minimize thermal effects.
Offering customization and the capability to produce complex parts, laser-based additive manufacturing continues to mature as a technology, with newer multibeam systems producing patient-specific implants.
For example, Trumpf Inc. (Farmington, CT) presented a multibeam version of its compact TruPrint 1000 3D printer at this year’s International Dental Show in Cologne and again at June’s Laser World of Photonics show in Munich. With a pair of 200-W lasers, this powder-bed system can generate up to 80% more parts in about half the time. The system produces parts with a maximum of 100-mm diam and 100-mm height.
The Ultrafast Revolution
Fast and precise, the ultrashort pulse lasers in the picosecond and femtosecond regime are becoming indispensable in manufacturing for medical devices.
“The femtosecond laser is driving a lot of new business for us for micromachining medical devices,” said Geoff Shannon, manager of advanced technology for Amada Miyachi America (Monrovia, CA). “We’re doing a lot of plastics and a lot of plastic-metal combinations that other lasers or technologies struggle to do,” including catheter applications, drilling and material removal.
Femtosecond cutting of metal tubes and stents is another growth area, he noted. “Fiber laser technology gives you a burr on the bottom edge of the cut that must be removed by postprocessing. With femtosecond lasers, you don’t get that burring; for delicate parts, that is a real benefit. If you have a tubes with a large wall thickness, deburring is relatively straightforward. However, for tubes with less than 0.01″ (250 µm) wall thickness it is problematic, as either the part can be damaged or the part dimensions are compromised. All of these postprocessing headaches disappear when using femtosecond lasers, which only require the part to be cleaned using an ultrasonic bath.”
Ultrafast lasers are becoming more affordable, with some in the $100,000 range. In fact, exhibit space at June’s Laser World of Photonics was awash in ultrafast systems, said Ron Schaeffer, founder of high-end contract manufacturer PhotoMachining (Pelham, NH).
“If you had asked me even three years ago what the status of those lasers was, I would have said developing rapidly, mostly with respect to higher power and the number of photons per dollar, ” he said. “The technology of those lasers is becoming pretty mature, so instead of people buying on the basis of some new and wonderful thing this laser does, they’re buying based on a specification sheet and price of delivery.”
Whereas many of his medical clients had been satisfied with the quality of nanosecond processing, some are switching to the better quality of pico and femto as they become more cost-effective.
Selective Laser Etching
One novel application for ultrafast lasers is selective laser etching (SLE) from German firm LightFab. It is particularly useful for producing microfluidic devices used in diagnostic tests of bodily fluids. The technology was developed at the Fraunhofer Institute of Laser Technology (ILT) in Aachen, Germany. LightFab, which is commercializing the process, is represented in the US by PhotoMachining.
SLE uses femtosecond lasers to expose transparent material, like glass. “Every place the laser hits the workpiece, it changes the internal molecular structure,” Schaeffer explained. “Then you put the piece in a vat of acid or some caustic material.” Material touched by the laser dissolves. “It is essentially 3D printing in reverse.”
Microfluidic devices have traditionally been made by structuring two pieces of material as mirror images of one another, then sandwiching them together to create flow patterns within the material. SLE “allows you to do all the laser machining inside the bulk of the material so there are no alignment issues,” said Schaeffer.
Areas of the material touched by the laser will, when subjected to a caustic bath, “etch 1000 to 10,000x faster than the unexposed area,” he explained. Making the first piece usually requires several iterations, but subsequent parts are highly reproducible.
The “lab on a chip” devices produced via SLE indicate to clinicians the presence of cancer or harmful bacteria, even diabetes or high blood pressure.
As part of developing SLE, LightFab also created specialized beam-scanning hardware. One such system resides in the US, Schaeffer said, and initial agreements and testing are in the works after inquiries from roughly two dozen potential customers.
Laser Marking for Passivation Resistance
Because stainless steel medical tools undergo rigorous repeated sterilization in autoclaves, giving them identifying marks that conform to FDA regulations and resist corrosion at super high heat requires processing only lasers can achieve, says Amada’s Shannon.
“Getting a solution for laser marking parts for passivation resistance has been an ongoing problem in the medical device area,” he explained. “You laser mark the parts and put them through a passivation process, which removes iron particles from the surface and makes them impervious to rust. But by doing so, you end up removing the laser mark. We’ve come up with a number of strategies to avoid that.”
The range of stainless steel used in medical tools, including 304, 316, 17-4 and 17-7, requires a variety of laser sources like nanosecond fiber or UV and picosecond IR—and the understanding of their heat input parameters. “A universal marking solution for every part and mark does not exist,” Shannon wrote in a 2016 article. Choosing the right laser for the job means considering the material used, surface finish desired and the speed at which the mark is made.
Lasers Join Traditional Machining
Companies like GF Machining Solutions, Marubeni Citizen-Cincom and Tsugami/Rem, well-known for Swiss machining and other micromanufacturing methods, have begun adding lasers to their repertoire.
For example, Tsugami/Rem Sales LLC (Windsor, CT), introduced its S206 LaserSwiss in 2014 as a one-system setup for producing small tubular medical parts. The system is used for “more extreme micro components and complex part geometries,” said Stefan Brusky, Midwest regional sales manager.
With parts getting smaller as surgeries become less invasive, “we focus almost exclusively on integrating femtosecond lasers,” says Onik Bhattacharyya, director of sales and business development for the Microlution line at GF Machining Solutions (Lincolnshire, IL). Ultrafast lasers produce medically ideal surface quality and burr-free edges with no post-processing for tools and implantable devices. Microlution machines are accurate to ±1 µm with submicron repeatability, he said. Beam-steering equipment controls tapering on the sidewalls of part features like holes or slots.
Comparing Microlution systems to wire EDMs, Bhattacharyya said that while both processes can produce burr-free parts, laser micromachining offers higher quality and faster cycle time. While wire EDM lets manufacturers stack parts, laser micromachining is a better option for one-off medical parts, which are often cylindrical or round. A hole that would take a wire EDM 30 seconds to drill can be lasered in under five seconds.
Microlution’s latest successes have been producing measurement devices, end effectors on small surgical devices and ablation catheter tips used to cauterize heart cells that trigger arrythmia. The catheters require machined holes smaller than the diameter of human hair to regulate the irrigating saline solution passing through the catheters to cool the area for the procedure.
At Marubeni Citizen-Cincom Inc. (Allendale, NJ), “we take one of the stations that we can use for a milling station on a screw machine and attach a laser head,” said Glen Crews, Western regional sales manager. Producing the part in one process instead of blanking out a part first and then transferring to a laser cutter removes throughput inefficiencies and positioning errors. MCC’s Laser System L2000 uses a 400-W IPG fiber laser with a 10-µm delivery fiber. With an optional quasi continuous wave optical head, “near endless” geometric shapes and kerf widths down to 20 µm can be achieved. The system is able to cut a 72-diamond pattern stent in 92 seconds, or a bone cutter in 6.04 seconds.
Three key areas of laser manufacturing, fairly well-established in general industrial manufacturing, are undergoing notable change in the medical sector:
–Welding: With catheters and tubes for medical applications decreasing in diameter, weld sizes are down to about 100 μm and smaller, compared to 300 or 400 µm a few years ago, said Amada’s Shannon.The growing range of available lasers “has allowed us to access areas where we couldn’t weld before, with much smaller spot sizes with the fiber laser,” said Shannon. “The nanosecond fiber laser is arguably a more cost-effective solution for certain types of welds, so that is opening more doors, too.”
–Plastics: While not a new process, welding of plastics has had “slow traction in medical for various reasons”—partly because many parts were designed for adhesives. Shannon predicts a steady uptick in laser processing of transparent materials “in a few years time” thanks to a greater availability of lasers in various wavelengths, coupled with the learning curve design engineers are undergoing. At present, the ideal wavelengths for processing of transparent welding are 1.5–2 µm using thulium fiber lasers, he said.
Amada is having success with joining plastic and metal parts. The company also focused on catheter operations that involve drilling and material removal.
At ILT, “we started to see more customers processing polymers, which transitioned into micromachining,” Jacklen recalled. “Customers had soft materials—catheter-type products—that they needed to drill holes in or remove material from or open slots in to expose other substrates. That’s where we got into some of the other laser wavelengths—green, UV—and the ultrafast pico and femto lasers, as well as galvo scanning controls for positioning the beam on the parts and generating small features. IPG has a presence in all these regimes.”
–Process monitoring: Quality assurance with 100-µm diameter welds can be challenging. “You’ve got a very small signal and a lot of signal is lost—particularly at the start of the weld,” said Shannon. With smaller medical welds that could be under 4 milliseconds, an off-the-shelf process monitoring solution does not exist, he said.
Small-scale process monitoring “is really where the holy grail is residing right now. That’s something we’re working on; it’s not necessarily ready for prime time,” said Shannon.