Medical Device Link.

Originally Published EMDM January/February 2002

SPECIAL REPORT

Making it Smaller: Manufacturing Minimally Invasive Devices

The demand for minimally invasive device components is growing nearly as rapidly as the parts themselves are shrinking. To fulfill these requests economically, metal fabricators have developed several novel techniques.

Zachary Turke

Manufacturing these specialty-metal pinchers required a smooth, high-speed mill.

It has become increasingly difficult over the last decade for anyone associated with the medical industry to ignore the dramatic rise in popularity of minimally invasive surgery (MIS). From coronary bypasses to nephrectomies to fundoplications, more and more surgical procedures are being performed with the aid of endoscopes, arthroscopes, and other tools that allow surgeons to operate through smaller incisions than ever before. Take, for example, the case of sinus surgeries. According to Frost & Sullivan (London), a market consulting firm, 90% of the 551,000 sinus surgeries performed in the US during 1999 were done using minimally invasive techniques. Gall bladder removals and joint operations have also shown a similar reliance on MIS technology.

One of the driving forces behind this shift is a practical one: cost. MIS reduces expenses for both the healthcare provider and the patient by decreasing the need for patient sedation and monitoring, often allowing even complicated procedures to be performed on an outpatient basis. But while MIS translates into savings for hospitals and patients, it often leads to higher expenses for device manufacturers. Due to their small size and complicated nature, minimally invasive devices (MIDs) generally cost more to make than traditional surgical instruments. With the use of MIS procedures expected to continue its expansion throughout this decade, it is becoming increasingly important for OEMs to develop economical manufacturing practices.

Sidebars: Increasing Functionality on the Surface MEMS: Making Everything Much Simpler

Much of this challenge will have to be met in the field of metal forming. Though there is a growing trend towards the use of plastics, metal remains the material of choice for the majority of MID components and, as such, is a major contributor to device costs. The ability of OEMs to produce MIDs economically will depend in large part on their ability to find metal fabricators that can produce such increasingly complex parts in the required volumes and at reasonable costs. But producing such components is forcing suppliers to confront many unique challenges. In this article, several industry-leading metal fabricators talk about how their firms are creating cost-effective solutions that may help to reduce the cost of MIDs.

CNC Machining Meets New Challenges

CNC machining is a common method for producing many kinds of products and one that experts say will figure prominently in future production of MIDs. Though the technology has been around for years, suppliers of machining services are encountering a range of problems that accompany the production of miniature medical parts. A case in point is the firm Kern Micro- und Feinwerktechnik GmbH (Murnau, Germany). Approached to make an arthroscopic tissue-removal pincher for a Japanese company, the full-service CNC milling and drilling firm had to find an economically feasible solution to a problem that is becoming increasingly common with such devices: the use of specialty materials.

"There is definitely a trend towards the use of titanium and other special materials for these kinds of devices," says Kern's managing director Burkhard Rother. "The pinchers we were trying to make were to be constructed from a unique surgical steel that was very hard." Specialty materials like these are often used to give finished devices strength, light weight, and other physical properties. But while they benefit the end-user, these kinds of materials can often lead to higher manufacturing costs, explains Rother. "It was important that the pinchers have a sharp cutting surface with an extremely smooth surface finish to operate properly," he adds. "To cut the material, however, we had to [run] our machines at a very high milling speed, which can produce vibrations that detract from the quality of the finish." If the vibrations did damage the surface finish, a secondary finishing operation would have to be employed that would raise manufacturing costs.

Kern solved this problem by changing the way in which its milling machines are constructed. Instead of using a cast-iron base, the units rest on a frame of polymer concrete. "This material has dampening properties that are up to 10 times better than standard cast iron," says Rother.

The company also isolated the spindle movement from the rest of the machine to further reduce the effect of vibration. Kern mills use a spindle that is mounted on the z-axis; it only travels vertically to limit negative effects of high operating speeds. These modifications have allowed the company to produce the pinchers with a smooth surface finish that reduced the need for costly secondary operations.

A different type of challenge faced by metal formers is the increased call for value-added features on MID components. More and more, these parts require screw holes, coined edges, or other special features that improve performance. Each feature often requires additional machining, however, thus increasing manufacturing costs and lessening quality. "Each time you have to unclamp a part and move it to another machine to add a feature, it decreases accuracy and increases the likelihood for human error," explains Moses Feldman, president of Aeromed Inc. (Hatfield, PA, USA), a CNC machining firm specializing in medical components.

This was the problem faced by Aeromed when it was called upon to produce a rotor for the clearing of arterial blockages. Spinning at more than 200,000 rpm, the rotor had to be completely balanced, leaving little room to deviate from specifications. The company had no problem milling the 3Ž16-in.-diam part within tolerances, but the screw hole and other special features the part also required raised the risk of a high price tag. "To produce a part like that in the past, you used to have to take it to three, four, or five machines," says Feldman. "Each machine brought a new chance to decrease quality and increase costs."

The solution to this problem comes from the multifunctional milling machines now finding use within the industry. Aeromed produced the rotor on a 13-axis machine that was also able to perform a variety of secondary operations without operators having to unclamp the part. "We were able to turn the part, drill a very small hole, trepan it, and mill the blade, all on the same machine," says Feldman.

Stamping and Metal Injection Moulding Offer Alternative Solutions

While some manufacturing challenges can be met with existing technologies, others require the development of new production methods or the adaptation of existing equipment to new uses. The advent of single-use devices presented one such challenge. "More and more, MIDs are designed to be disposable," says Randy Palmer, vice president of business development at Micro Stamping Corp. (Somerset, NJ, USA). "Disposable products must be less expensive to produce and are often required in greater numbers than reusable devices, something that is difficult to achieve with many of the established production methods," he notes.

Micro Stamping, a metal stamping firm, was faced with this challenge when it was asked to produce a 15-in. disposable endoscopy tube. "Our client had been producing the tube using a continuous drawing process that was too expensive," says Palmer. "The company wanted to see if we could do it using metal stamping." According to some industry experts, this was an unusual request. Although metal stamping is not commonly thought to maintain a sufficient level of accuracy to produce these kinds of products, the results were encouraging.

"We were able to produce the 0.169-in.-OD tube with a tolerance of 0.0015 in., well within the required specifications," says Palmer. Company officials estimate that the switch to metal stamping reduced tubing costs for the customer by as much as 75%, savings that added up to US$7.5 million annually. This decreased cost was accompanied by an increase in the rate of production. "With drawing, the company was able to produce about 300 parts per hour. We can produce 60 parts per minute and add as many features as desired at the same time," says Palmer. The previous production method required as many as 10 secondary operations.

The need for parts with increasingly complex shapes is a manufacturing challenge that may require the use of a developing technology. Traditional solutions have included constructing complex components as assemblies of simpler individual parts or putting the piece through a series of expensive multistage machining operations, but these methods may no longer be viable. "Surgical tools have always had complex shapes," states Phillip Booker, senior metallurgist for Smith Medical Products (Lindstrom, MN, USA), "but as the overall dimensions of these parts gradually shrink, manufacturers are being forced to look for new ways to produce them economically." According to Booker, metal injection moulding may be the solution.

"It's possible to produce many of the difficult parts required for MIDs using conventional methods, but they may be cost-prohibitive," says Booker. "With metal injection moulding, you can produce a part with almost unlimited complexity in a single stage without a lot of secondary operations." Take, for example, the distal wrist clevis the company produced for the da Vinci surgical system marketed by Intuitive Surgical (Mountain View, CA, USA). This innovative machine that allows doctors to perform MIS remotely using robotic controls required a complex part that could securely hold the operating tools and mimic the motion of the human wrist. Not only did these requirements demand a clevis with a difficult multifaceted oval shape, but they also called for posts for attaching pulleys and blank grip pivot holes. Using metal injection moulding, Smith Metal Products produced the component in one step that required only minimal surface finishing before the product was ready for use.

Frost & Sullivan predicts that the conversion of standard medical procedures to minimally invasive techniques will be a major driving force for the European device industry for at least the next seven years. Valued at US$1.05 billion in 1998, this sector is expected to increase by a compound annual growth rate of 4.2% to US$1.40 billion in 2005. Continued gains like these are likely to attract new competition to the MID market, and OEMs will have to find ways to minimize the cost of device production to stay viable. Metal fabricators that can produce high-quality complex components at competitive rates and in the required volumes can represent a key ally in this struggle.

Copyright ©2002 European Medical Device Manufacturer