Medical Device Link.

Originally Published EMDM May/June 2001

Product Update

Katherine Sweeny and Norbert Sparrow

Cold ablation allows consistent, repeatable drilling without provoking thermal damage to surrounding areas.

The electronics industry used to be a bellwether for stimulating innovation among suppliers of industrial lasers, according to Mike Regan, managing director–Europe for Preco International (Canterbury, Kent, UK), a developer and supplier of laser systems. "But that has changed, at least for our company," he notes. "Today, the device industry is the front-runner. Device OEMs are the ones telling us 'here's what we want to do, now go figure out a way to do it with a laser.' "

Exitech supplied a micromachining workstation equipped with a 193-nm excimer laser to meet the application requirements of a sensor used in a blood-gas monitor.

An application developed by Exitech Ltd. (Long Hanborough, Oxon, UK) for the fabrication of a probe used in a blood-gas monitor system is a case in point. One of the production challenges involved drilling miniature, consistently sized holes in the device's optical-fibre sensors. According to an engineer familiar with the project, an excimer laser operating in the UV range was critical to the success of the project. The paragraphs that follow discuss this application in greater detail.

Product announcements from a range of suppliers of industrial lasers and related items are also included in this section. If you are or will be sourcing laser systems, begin your search by contacting these companies and telling them what it is that you want to do. Chances are that one or more of them will have a solution.

The Specification Drill

A multiparameter blood-gas monitor system combines fibre optics with specific chemical probes to directly measure blood chemistry and blood gasses. The key component in the instrument is a small invasive probe fitted with three optical-fibre sensors, which simultaneously measure CO^₂, O^₂, and pH, and a conventional thermocouple for temperature measurement. The sensors are fabricated from acrylic optical fibre measuring 175 µm in diameter.

A primary challenge faced by Diametrics Ltd. (High Wycombe, Bucks, UK), which developed the system, was to find a way to repeatably drill consistently sized holes in the fibre. The firm settled on an excimer laser that was able to perform the exacting task without straining the production budget. The blood-gas monitor is marketed by Agilent Technologies and Johnson & Johnson.

"The probe had to be as small as possible to minimize insertion trauma, and maintain existing monitoring modes," according to Diametrics operations engineering manager Malcolm Jones. "It also had to be fabricated from biocompatible polymers that could withstand at least one cycle of sterilization." The plastics had to have suitable physical properties to support the micromachining of small holes and encapsulation of appropriate chemistries, he adds, and lastly, manufacturing costs had to remain low to meet market conditions for the disposable device.

Preventing Thermal Damage

Light from an LED source is launched into the probe from a control unit and then reflected back by a small stainless-steel mirror encapsulated in the end of each optical fibre. The light passes through a series of transverse holes drilled into the fibres in a helical formation. Light passing along the fibres interacts with the chemistry in the holes before returning to the control unit, where the return light intensity is measured.

Light passes through holes drilled into the device's optical-fibre sensors in a helical formation.

Micromachining the small holes represents a critical step in the manufacturing process because the hole dimensions must be consistent to provide repeatability. Diametrics originally subcontracted the task to Exitech Ltd., a company that offers turnkey laser workstations and a range of laser processing services.

After testing, Exitech determined that an argon fluoride excimer laser was the best choice for machining acrylic fibres. When sales of the device increased, Diametrics brought the job in-house, using a laser micromachining workstation supplied by Exitech. The laser outputs at a wavelength of 193 nm, in the deep-UV range. "This is a perfect job for UV excimer lasers," says Nadeem Rizvi, principal development engineer at Exitech. "UV light can machine polymers with ultrahigh precision by directly removing the material without causing thermal damage to the surrounding areas," explains Rizvi.

To form the holes, a spool of optical fibre is loaded into the workstation that automatically feeds a 1-m-long piece of fibre to the laser drilling head. Mechanical tension and a vacuum chuck rigidly hold the fibre. The laser beam is split using a set of mirrors so that all five holes can be drilled simultaneously without moving or rotating the fibre. This streamlines the process and ensures the holes' identical dimensions: each one has a rectangular shape with a 100 x 50-µm cross section that tapers to about 50% at the opposite side of the fibre. After drilling, a new section of fibre is automatically cut by means of a metal blade and stacked for further processing.

Machining Multiple Parts

Excimer lasers have been in use in industrial settings since the 1980s. They emit photons in the UV region without frequency conversion. Because of the incoherent and highly divergent nature of the beam, excimer lasers are suitable for multiple, simultaneous feature machining; splitting the main beam enables multiple part processing.

While excimer lasers can be configured to produce 308-, 248-, or 193-nm wavelengths, the most popular models are in the 248-nm range and use a combination of krypton and fluorine. They are highly reliable and can be used to machine most plastics. The 193-nm laser used by Diametrics is more expensive to operate, but its manufacturer claims it is the only laser of its kind that can directly break the strong chemical bonds of biocompatible materials such as Teflon and acrylic fibres. "In this case, laser micromachining is truly an enabling technology," notes Jones. "This task simply could not be performed by any other means."

Lasertec B.V.

Incorporating a diode-pumped solid-state UV laser, the Compendium-M system marks a range of materials without requiring the use of additives. The laser creates markings by acting on the titanium dioxide that is already present in many polymers. Developed by Lasertec B.V. (Barendrecht, Netherlands), the device is used to mark hearing aids (pictured), dialysis equipment, and related medical products.

The Compendium-M immediately found acceptance in the device and food industries, according to managing director Marco Bak, because it eliminates the need to use so-called laser-grade materials. "Conventional laser marking systems require the presence of an additive in the material to produce the desired result," says Bak, which can have an appreciable effect on production costs. Those systems also typically have a narrower processing window than the Compendium-M, he adds. "You have to make adjustments depending on the materials and additives that are being used, and then you have to control the process," he says. Lasertec's system employs a cold marking process that is not subject to those limitations: the laser beam simply renders select titanium dioxide particles dark grey by initiating an oxygen reduction. Other benefits of the cold marking process include a lack of thermal stress and an absence of surface degradation. Bak adds that the technology is well suited for marking polypropylene and polyethylene, materials routinely used in the device industry that cannot be easily marked with ink.

The Compendium-M works only with materials containing titanium dioxide, which is typically used to whiten polymers. The company is currently conducting research on adapting the process to mark transparent or virgin materials, according to Bak.

Lasertec supplies both OEM marking engines, suited for integration into existing production lines, and custom stand-alone units.

Preco International

Using an Nd:YAG laser operating in the 355-nm UV spectrum, a laser system that performs ablation cutting is suited for use in medical applications. Supplied by Preco International (Canterbury, Kent, UK), the PL355 system relies on a cold rather than burn-through process.

In addition to fine-line marking of miniature parts, the laser has been used in various types of cutting. "We have put small holes in adhesive tapes, for example," says Mike Regan, managing director for Europe. "That can't be done with a tool because the holes are too small," he says. The medical industry demands a clean cut, he adds, and Preco's equipment can help to achieve that. "If something is going to be used as a dressing, we can process the material without any scorching or browning in surrounding areas."

The company is currently working with a client to develop a lamination line that will incorporate conventional die-cutting and laser cutting. "It's an on-the-fly system," says Regan. "We will be reading the material as it comes toward the lamination system, and based on the information we are reading off that material, we will be able to laser cut a liner, for want of a better description, that will marry up perfectly in position." On-the-fly laser heads will work within a certain area, he adds. "They will be performing different functions: some will be cutting, others will be making openings and removing the slugs by incineration," says Regan. The alternative would be to perform some of those tasks separately off-line, he notes. "With this system, we can do them together on-line and speed up those areas of application."

TUI Laser AG

Incorporating an innovative tube design, compact excimer lasers are suited for cleanroom micromachining applications. Developed by TUI Laser AG (Gräfelfing, Germany), the ExciStar S-Series lasers can be used to ablate a variety of devices including catheters, stents, and microfluidic systems.

The company's proprietary FutureTube design enables the lasers to meet accelerated production cycles and achieve elevated repetition rates, according to vice president of applications and sales Heinz Huber. The ExciStar S-Series notably features corona preionization, which results in a homogeneous beam that ensures pulse-to-pulse stability. Electrode erosion has been minimized, thus extending the tubes' life cycle, and solid-state switching enables the lasers to reach 1000-Hz repetition rates without delays caused by warm-up procedures. The 65 x 46 x 27-cm³ unit delivers 18-mJ pulse energy in continuous operation at a 248-nm wavelength.

The series was designed for troublefree installation into cleanroom manufacturing environments. "The air suction system, and gas and security management systems have all been optimized for cleanroom use," says Huber. "We sell a version of this laser for semiconductor applications, which, as you know, have even more stringent standards than the device industry," he notes.

ExciStar S-Series lasers can drill holes measuring up to 300 µm in plastics and up to 100 µm in ceramics and metals, according to Huber. They are offered as a turnkey system, and specialized staff are available to assist customers who wish to integrate a unit into their production process.

Coherent Laser Div.

Compact diode-pumped industrial UV lasers have been introduced to complement a company's 355-nm Q-switched line of lasers. Developed by Coherent Laser Div. (Santa Clara, CA, USA), the lasers are designed for applications such as marking and materials processing where high repetition rates are required.

The Avia Ultra 355-400 and 355-250 "exhibit the stability, reliability, and ease of integration of the company's 1.5- to 4.5-W lasers," says product line manager Paul Somerville, "but in a lower-power platform. They have a 50% smaller footprint than comparable UV lasers," he adds.

The new Ultra series lasers produce 355-nm output power of 400 and 250 mW at 40 kHz. Like all of the Avia lasers, these devices are equipped with an automatic pulse-energy equalization feature that ensures process consistency. The 355-250 has a pulse width of <15 nanoseconds, while the 355-400 has a pulse width of <10 nanoseconds.

In printing applications, the laser employs a cold marking process that produces high-resolution marks by effecting a colour change on the surface of plastic components without degrading the component material. "Typically when you use laser marking, you melt the surface of a part by creating pits or decomposition materials," says Paul Crosby, vice president of Coherent. "With cold marking, the reaction takes place underneath the surface or right at the surface, so the component is not degraded. This can be very useful from a regulatory standpoint and can be done in a sterile environment." Crosby notes that this technology, which has actually been available for five or six years, is still just starting to be deployed by the medical manufacturing industry.

Lasirvis Optoelectronic Components Ltd.

Two visible-red 650-nm laser diodes offering 5- and 10-mW power output have been introduced. The components can convert current to laser output at threshold currents as low as 13 mA. Developed by Lasirvis Optoelectronic Components Ltd. (Bedford, UK), the diodes reportedly have the potential to enable new applications because they cost no more than high-power light-emitting diodes and consume less power at equivalent optical-energy outputs.

"This development makes the cost versus performance comparison between lasers and LEDs almost indistinguishable," says sales and marketing manager Ian Bulavs. "Portable items and limited-life disposable products will benefit" from this product, he adds, citing home-care products and medical sensors as two promising applications.

Both diodes feature high slope efficiency: a small increase in the drive current to the laser diode produces a larger expansion in optical output. Typical slope efficiency is quoted as 1.0 mW/mA. The products are packaged in TO-18 style (5.6-mm) headers and metal cans.

Lambda Physik GmbH

A diode-pumped solid-state Nd:YAG laser is designed for precision micromachining of metal, ceramic, and diamond. Developed by Lambda Physik GmbH (Göttingen, Germany), the Gator 2000 rapidly and accurately drills holes smaller than 100 µm. Features include a 10-kHz repetition rate, high peak power at 15 nanoseconds per pulse, and an optimized beam profile. Measuring 330 x 122 mm, the laser can be easily integrated into most production environments.

Lambda Physik recently announced a new addition to its Gator laser systems with the introduction of PowerGator IR, which delivers 28 W average power. The unit delivers short 15-nanosecond pulses to optimize plasma penetration while minimizing heat-induced effects. The laser was specifically developed for micromachining small features in ceramics, silicon, and metal alloys in thicknesses between 0.75 and 1.5 mm. All Gator Series lasers are equipped with a hermetically sealed head and RS-232–based function controls. They also feature hands-free operation and a removable supply unit.

Exitech Ltd.

Laser systems are designed and manufactured to suit specific application needs by a company founded in 1984. The turnkey systems designed by Exitech Ltd. (Long Hanborough, Oxon, UK) typically incorporate pulsed lasers, beam-delivery optics, beam shapers, multiaxis motion controllers, dose controllers, autofocus systems, vision diagnostics, and full safety interlocks. In the biomedical arena, the lasers are routinely used to process catheters, biochips, and sensors.

The company boasts extensive on-site laboratory facilities and a Class 10,000 cleanroom in which personnel and customers can conduct basic research, applications development, and production work.

Copyright ©2001 European Medical Device Manufacturer