Medical Device Manufacturing by
Laser Micromachining Technology

Introduction

Since the invention of lasers in 1960, many laser applications in the medical field have been found. Today, it is difficult to name a field of medicine in which lasers have not found an application.

People started to use lasers in clinical treatment in the early years. In 1961, a unique medical application was found for lasers: retinal photocoagulation. Ophthalmologists found that they could use the ruby laser to treat the retina. The laser light, tightly focused by the lens of the eye was absorbed and converted to heat in the retinal tissues, leading to coagulation and formation of a localized scar. Many other medical applications stemmed from this first medical application.

Today, laser technology has been successfully applied to processes like angioplasty and corneal sculpting, as well as to potential clinical applications of treating cartilage and nerves that would not be possible with conventional techniques. However, beyond the widely publicized clinical applications, laser technology has made major contributions to medicine in the industrial and scientific arenas. In fact, many patients are probably unaware of how lasers have helped them by increasing the precision and the reliability of industrial processes, and thus, of medical devices and instrumentation.

Medical devices are generally quite small for two basic reasons. They often must fit into small spaces, or they are made of expensive materials, thus the need for miniaturization to be cost effective. Lasers, which can work in areas that require tolerances of a few microns, are often ideal solutions for cost-effective manufacturing of miniaturized devices.

Lasers and Basics of
Laser Micromachining

Lasers have unique temporal and spatial characteristics. They can generate very short pulses of light of a single wavelength. These characteristics allow the precisely controlled deposition of a great amount of energy into a selected region of material. Of many types of medical lasers now in use (CO2, YAG, excimer, dye, argon ion, diodes, etc.,), each has its own unique characteristics and capabilities suited to a particular application. Factors that determine the type of laser to use for a particular application include laser wavelength, laser energy and power, temporal and spatial mode characteristics, material type, feature sizes and tolerances, processing speed and cost.

Through the use of focusing optics to produce a well-defined spot at the work piece, if the necessary energy/power density can be achieved to melt or to vaporize the material, the laser energy is transformed into thermal energy to perform the specific process. This is normally called a "thermal process". Processes performed using CO2, and Nd:YAG lasers belong to this category. Another mechanism, which is nonthermal and referred to as photo-ablation, occurs when organic materials are exposed to ultra violet (UV) radiation generated from excimer, harmonic YAG, or other UV sources. In medical device manufacturing, both types of processes can be found.

Technology Match

When one thinks of contract manufacturing in the medical device industry, lasers and laser micromachining may not immediately come to mind. Instead, manufacturing engineers tend to look toward contract houses to out-source medical microelectronics, plastic extrusions, specialty coating services, precision machining of surgical tools or offshore turnkey assembly. In many situations, this makes a lot of sense.

After all, medical microelectronics is an offshoot of traditional PC microelectronics that utilizes similar technologies such as multi-chip modules(MCM) employing thick film or BGA substrates. Plastic extrusions for catheters, and classic drug and gas delivery products borrow technologies from the traditional plastic molding industry. Specialty coating services tend to be sub-contractors to the component manufacturers, and use similar spin coating, vapor deposition or injection technology of other industries. Precision machining of surgical tools is a natural niche for metal machine shops employing stamping, wire EDM, and grinding machines. And lastly, offshore turnkey assembly houses have long been an established resource for high volume and low cost manufacturing, where labor represents a significant portion of the overall product cost.

So where do contract manufacturing of medical devices using lasers and laser micromachining fit together?

Applications

Today, a wide range of laser applications can be found in medical device manufacturing where laser micromachining technology offers specific advantages.

Processing Catheters

Catheters are used in a wide range of medical procedures and come in a variety of sizes. New developments are constantly arising, and laser welding, cutting, and drilling are required in the production of many current designs.

A classical welding application is fixing the hollow catheter tip to the spiral wound coil at the end of a catheter. The end of the spiral is cut to prepare it for spot welding. The welds must provide a strong connection without penetrating into the bore of the tip. The spot size required is often in the range of 100 to 115 microns.

Another potential cutting application is catheter stents. These are made primarily from three materials that satisfy requirements for biocompatibility: stainless steel, titanium, and tantalum. The diameters range from several millimeters down to less than one millimeter. The manufacture of these stents calls for a cut width (kerf) of around 35 microns in 100 to 150 micron thick material, and kerf of 15 microns in thinner sections.

It is well known that lasers are utilized in the medical device industry. When facing a challenging manufacturing problem, manufacturing engineers always evaluate a variety of solutions available to them, including lasers. Not only do they have to look at the technical feasibility, often they have to make a decision on whether to bring the technology in house or to outsource. The decision is based on a number of factors. We would like to address some of these issues associated with laser contract manufacturing in an attempt to assist production managers and manufacturing engineers in their decision making process.

To begin, we need to understand how laser micromachining technology can be used for medical device manufacturing and more importantly, why one would use such technology if more traditional technologies were available.

The answers lie hand in hand. Primarily, laser micromachining applications are developed because traditional manufacturing technologies can not meet the product requirements and specifications. If one needs to micro drill a side hole in a F2 catheter for a specific cardiovascular or neurological application with a hole size less than 0.004", there are not very many options available. Laser micromachining technology, which can approach a factor of 100 times smaller, is a natural fit. (See figure 1 - photo of 6 holes drilled in a catheter.)

However, the real growth of laser micromachining technology for production outsourcing has very little to do with simply exceeding the limits of the traditional technology spectrum. Instead, the real advantage lies with reaching the original goal of outsourcing - finding a way to manufacture a product at an acceptable target cost, with high quality and yield, without having to invest in capital equipment. If these goals can be met, then the operations manager, having a tacit interest in the technology, will measure the performance of the outsource partner as a function of delivery, quality and the overall business relationship - not the manufacturing technology itself.

Skiving slots or holes with dimensions below 0.020" is a natural fit for lasers. Traditionally, the medical device industry has employed techniques such as manual cutting with razor blades, where the skill of the operator will often determine the yield. Alternatively, if a laser beam is used, tubes can be skived without worrying about repeated tool replacement, unacceptable yield losses or positioning inaccuracies (see figure 1). In some cases, operation managers will choose to free up their valuable clean room space and let laser contract manufacturers offer timely skiving services with automated QC control. Others will prefer to bring the laser skiving technology to their own facilities.

Very precise holes that are less than 0.004" in diameter are often required in F1-F4 catheters. These are necessary for several different areas of application. The primary purpose of such holes is venting of a delivery system, where air is expelled by squeezing the saline bag while viscosity and surface tension prevent the saline from escaping. Precise micro holes also allow for precisely metered and distributed drug delivery to locations within the body. Another example is a catheter complete with electrical sensors that can be used to monitor oxygenation of blood in premature babies. Blood is sucked into the catheter through a 700-micron diameter hole machined by an excimer laser.