A Laser’s Role in Medicine
The use of lasers in the development of medical devices through to their actual usage in the devices themselves has been a steadily growing trend. The capabilities and functionality they offer to both design engineers as well as healthcare professionals is varied and beneficial. This article looks at the advantages lasers offer in the development of medical devices.
Lasers have always played an important role in material processing of devices used in hospitals and doctors’ offices, from surgical tools and implantable devices to part identification that is permanent, non-corrosive, safe, and non-toxic. Medical technology continues to advance, procedures become less invasive, and economic pressures demand reduced costs. These changes put lasers in the spotlight. Cutting, welding, drilling, ablation, and marking are all possible with the laser. As a fast and flexible tool, lasers are also able to process a wide range of materials, including polymers, stainless steel, titanium, many metal alloys, and specialty metals, such as Nitinol—a shape-memory alloy common in stent manufacturing.
So why are lasers so important? Even before the miniaturization of medical devices, it was critical to control thermal and mechanical stresses on the material. Today, this is even more important. Since there is no contact with the material, minimal thermal input (low HAZ), and excellent precision and repeatability, lasers offer the unique ability to process extremely small components with speed and accuracy. Whether cutting stents and bone saws; welding endoscopes, batteries, or pacemaker components; or marking surgical tools or implantable devices, lasers are found in countless applications.
Advantages of the Laser Types
Although a veteran technology, CO2 lasers are still a very important tool in material processing. Since surgical tools or metal enclosures are cut from large flat sheets of metal or expensive alloys, CO2 lasers can maximize yield for reduced scrap. Cost-effective part production is achieved with limited or no damage from thermal or mechanical stress. In addition, unlike the wavelength of solid state lasers that pass through clear plastics, the 10.6 µm wavelength emitted by a CO2 laser is well absorbed by clear or colored plastic, allowing it to be cut or welded effectively.
For over 25 years, pulsed Nd:YAG lasers have also delivered exceptional performance in medical device manufacturing. Although newer laser technologies are available, in some cases the Nd:YAG is still the best or only laser for a specific job. Traditionally Nd:YAG laser applications, such as cutting small, intricate parts from thin and exotic metals, is now often done with fiber lasers. However, since pulsed Nd:YAG lasers can deliver extremely high peak powers with pulses in the millisecond and nanosecond range, they are still the best choice for highly reflective materials. The pulsed Nd:YAG laser also excels in welding intricate and heat sensitive parts such as arthroscopic shavers, pacemakers, small batteries, or any sensitive electrical device that is implanted in the body and, therefore, must be hermetically sealed. For these types of applications, a tailored-shaped, high peak-energy pulse is specifically designed to weld without damaging the part. Pulsed Nd:YAG lasers also drill holes in hypodermic needles, drug delivery devices, and precision flow valves.
In the last seven years, developments in laser technology have taken material processing to new heights. Faster and more precise results are achieved with less material damage and in new materials. The best known are fiber and disk lasers, which are diode pumped of an active medium and deliver a 1,030- to 1,100-nm wavelength through an optical fiber as small as 11-µm diameter. These lasers boast electrical efficiencies around 30% and deliver extremely high beam quality through a fiber to the work piece. System design and maintenance are less complex, which has enabled large market growth. Lasers under 1,000 W cut thin gauge metals for stents; enable new, smaller surgical devices and tools; or achieve precise and narrow welds for many medical devices.
One of the most innovative developments in material processing is the short or ultrashort pulsed laser. Instead of peak pulse energies in the 1,000s of watts, which melts metals as in the case of the pulsed Nd:YAG lasers, the pulse energy in picosecond or femtosecond lasers are in megawatts. These high-energy short pulses occur so fast, they vaporize the material to achieve “cold cutting” or “cold processing” and are more precise than the pulsed lasers discussed previously.
Fusion cutting with a typical laser requires precision gas nozzles to blow molten metal from the cut area. This molten material deposits around the cut, which can lead to small imperfections on the edge as it cools. Since imperfections are breeding grounds for bacteria, the implantable device must undergo very elaborate and expensive secondary processing to minimize the risk of serious infections in a patient. This usually results in a lower yield of usable parts. With “cold cutting,” simple air pressure blows away the vaporized material particles such that surface imperfections are minimal. This drastically reduces post processing and costs while making the implant safer for the patient.
These short and ultrashort pulse lasers are found in many micro applications, such as cutting metal and polymer stents, drilling precisely tapered holes, micro welding, and ablation. By adding non-linear crystals to these lasers, green and deep UV wavelengths can be created, which expand the types of materials that can be processed and allows for the laser to be tailored to a customer’s specific requirements. This opens the door to countless new possibilities.
Many of the emerging technologies mentioned—disk, fiber, and short pulse lasers—use diodes to create the laser light. Diode technology continues to advance at a rapid pace, especially in ways to use the light directly from the diodes. The beam of this “diode laser” is still delivered via an optical fiber, but with higher beam quality and greater efficiency. These exciting lasers open new possibilities in plastic and thin metal welding.
With all the medical devices mentioned, laser marking is used with most. The FDA requires implantable devices to be marked so they can be tracked to see when, where, how, and by whom they were manufactured. A laser mark is permanent and non-toxic, and causes no damage to the material surface that could otherwise lend itself to bacteria growth or corrosion. For surgical instruments, which withstand countless sterilization procedures and heavy use, laser marking is critical. As surface areas become smaller, miniaturized parts will require lasers to mark them, especially to eliminate mechanical or thermal stresses to the tiny surface area.
Lasers have played an important role in medical device manufacturing. Looking forward, the laser will become an even more important tool as new technology enables the concepts dreamed of today to help save lives in the future.
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