Medical Manufacturing Supplement: Medical Manufacturing Frontiers
This article is the first of two covering new and renewed products developed for producing medical devices. Part 2 will appear in our October issue.
By Robert B. Aronson
The Advanced Medical Technology Association (Washington, DC) says the medical device industry grew to nearly $220 billion worldwide in 2006, and is predicted to grow by yet another 10% in 2007. The manufacturing technology enabling this expansion comes from two types of manufacturers—those who modify existing products or processes to meet a need, and those making something totally new. Here's a sampling of both types.
Following the trends of the auto industry in going to second and third-tier suppliers, the micro industry is also going the same way. One example is Gateway Laser Services (Maryland Heights, MO), a large contract manufacturer that specializes in laser microcutting and welding. Most of their work is as a subcontractor to manufacturers of medical devices. Their lasers are made to their own specification from supplied components.
Company business manager Mario Vaenberg explains, "There is no such thing as a typical order. Our assignments range from a few prototypes to thousands. More often there is a cut or special feature on a product that the customer can't handle. A typical job would be making 0.001" [0.025-mm] holes in a medical catheter with a precision of 0.0002" [0.005 mm], or a part for a device that functions within the body, such as a pacemaker.
"Very often, when a company is content with what we do on a small order, the big orders come in. The main goal is consistency. Anyone can make a prototype, but to hold quality when you are doing thousands takes special talent," he concludes.
Morgan Advanced Ceramics (Rugby, UK) has a history of involvement with medical manufacturing, with a long list of established and new products. "We find customers come to us because of our ceramics expertise, after they have tried other materials that didn't work," says Keith Ferguson, business development manager of the company's San Mateo, CA office.
At Morgan, injection molding of ceramics is a growing area in their manufacturing. "It is drawing in more manufacturers of medical products because ceramics are safe to use within the body, and essential for electro-surgical tools that need nonconductive elements," says Ferguson. "In some cases their product was originally made from a plastic. Then a requirement for increased operating temperatures made the plastic impractical."
Injection molding can be costly. Dies are usually complex, and because ceramics are abrasive, wear is higher than for conventional molding. Usually a run of 10,000 or more is needed to make it economically practical. Also, part size is critical. "A part two inches across would be considered big," explains Ferguson. "Design economics play a bigger part because of shrinkage issues, but this process can handle complicated shapes including threads, blind holes, internally intersecting holes, and the need for multiple parts. Currently we can mold walls less than 0.008" [0.2-mm] thick," he says.
"For products fist-size and bigger, we can braze ceramics to a metal after first coating the ceramic with a chemical bond that allows the metal to adhere. This process is sometimes used for analytical instrumentation or medical instruments that are too costly to dispose of and must be sterilized," says Ferguson.
System 3R USA (Elk Grove Village, IL) offers numerous cutting reference systems and machine accessories. One of their specialty product lines is for micromanufacturing that is used for manufacturing within the medical market.
The majority of the company's work at EDM Department Inc. (Bartlett, IL) is devoted to small, precision EDM electrodes. For example, they manufacture electrodes for making holes as small as 120 µin. with a depth of 1700 µin. in M2 steel. "Prints are more commonly specified in microns," says Mark Raleigh, president.
"We are capable of micro work and pursuing nano. We make micro parts with nano features, although getting below 1 µin. is still a challenge."
One of 3R's most difficult jobs was a needle with submicron features. The customer wanted a 500-nm radius tip. This sharpness was delivered using a combination of nano-pulse technology and VDP (vibration-damped pallet system) technology. Finding ways to hold the part was one of the biggest challenges.
One of the ways that System 3R can achieve its micro accuracy is its VDP. A special dampening capability filters out error-causing vibration while cutting electrodes.
VDP retains static stiffness while providing high dynamic stiffness. This is difficult to control while in operation because cutting forces change when machine axes move, and the part changes shape as material is removed. A vibration-damping mechanism using polymer-metal composite is built into the chucking units. Benefits include longer tool life, improved surface finish, higher removal rate, and lower machining forces.
The EDM Department Inc. has improved aspect ratio from 14:1 to 37:1 by using System 3R VDP chucks.
Stratasys Inc., an RP company from Eden Prairie, MN, owes its early existence to the medical market with some original sales to medical facilities. Currently they offer two RP methods, fused deposition modeling (FDM) and electron beam melting (EBM). With FDM the part is created by building up thermoplastic layer by layer. The finished product can be used as a visual aid communicating a concept or to cast an actual part.
The EBM process creates a fully dense metal part from titanium or cobalt chrome, and may be then machined for use as an in-body part (implant). In this method, metal powder is melted with an electron beam to build up successive layers. This develops a fully-dense, porosity-free part layer by layer.
Both methods, particularly EBM, have a growing popularity in the medical market, particularly in reconstructive surgery. The patient may have been injured or deformed by an accident, disease, or genetic fault.
There are three areas of application. The first is preoperative analysis, in which a model is used to explain to the medical staff what is to be done. For example, in a tumor operation, the data from a CAT scan can be converted to an STL file for input to an RP machine. This will make a model of the tumor to guide the surgeon.
Second, for in-theater work, the actual part can be made. Most joint replacements done today use off-the-shelf joints and fittings that are selected by size. Although adequate in most cases, the life of the prosthetic could be greater and more comfortable if it were custom-made for more accurate reconstruction.
When making one-off skeletal parts such as when repairing accident damage, it is often necessary to build in fastening elements, such as screw holes for pins to keep the implant in place. This is done by modifying the computer program.
Another medical application for these systems is in the design and testing of surgical instruments and medical devices. There is nothing like a functional prototype to test designs out before the product goes into full scale production.
"At present, there are surprisingly few technical impediments to greater usage of these systems by the medical field," says Fred Fischer of Stratasys. "The two largest obstacles are awareness and cost. Today, many physicians are still unaware of this technology and what can be done."
Translume (Ann Arbor, MI) is a good example of how manufacturing technologies developed for other applications are finding a new home in the biomedical industry. The company specializes in micromachining fused silica. Using proprietary laser-writing technology, Translume creates complex 3-D optical waveguides in the interior of fused silica substrates. By combining this capability with proprietary etching processes, Translume also selectively, and precisely, removes material to accuracies of a few microns, to create microfluidic elements such as holes, grooves, channels, tunnels, etc., in fused-silica substrates. This combined capability leads, for example, to the ability to create small instruments where a fluid sample is delivered by microfluidic elements to a work/analytical area.
The company, which initially specialized in optical components for the telecommunications industry, got into the medical industry when the US Army contacted them about a pressing need for a number of microfluidic devices. One of these devices was for a biological application—a flow cytometer, a device commonly used for counting cells in fluids that has promising applications as a lab instrument for cancer detection.
Many pathological examinations of thoracentesis and paracentesis samples fail to detect the presence of metastasized breast, lung, and ovarian cancer tumors due to cell concentrations below those needed for reliable detection. Translume's unit would help pathologists perform analyses that locate cancer cells in low-concentration samples that ordinarily would have been misclassified.
In addition to creating new products, companies involved in medical manufacturing are often given the task of improving existing products.
In one product, GE Plastics was able to replace a metal laryngoscope blade with a disposable plastic one to facilitate use of the device and reduce potential health hazards.
For a transportable hospital ultrasound device redesign, GE Plastics offered a new polymer to support the needs of 30 different plastic component parts to provide rigidity, resistance to certain chemicals, and improved appearance. And on the manufacturing side, the plastic had to be easily molded with particular attention to thin-wall parts.
To assist healing of wrist fractures/injuries this plastic support was developed by Rigid fx Orthopedics Corp. with plastic provided by GE Plastics (see supplement cover photo). It replaces traditional metal fixators. It holds the hand stationary while the bones mend, yet offers light weight and slim design for patient comfort with transparency for easy monitoring of bone. The design balances strength and light weight with a polymer not visible to X-rays.
At the University of Michigan (Ann Arbor, MI) some pioneering work is being carried out in Biomedical Manufacturing. Headed by Albert Shih, who has a joint appointment in Mechanical Engineering and Biomedical Engineering, researchers are working on solving medical and healthcare problems in a way that has a close parallel to conventional manufacturing. For example, those involved in biomedical manufacturing often use a hospital/factory analogy in which the tissue/patient corresponds to a conventional manufacturer's workpiece, the surgical instrument matches the machine tool, the hospital bed is like a fixture, and the doctor corresponds to the operator. This way, the scope of manufacturing is broadened to have direct impact to the cost, quality, and service of healthcare.
Traditionally, most invasive surgery uses a scalpel. But some of the major projects in the biomanufacturing department involve efforts to make smaller, less damaging incisions in the body. Therefore, this old technology is being replaced by modern energybased electrosurgery and ultrasonic surgery. Key reasons are faster healing, less chance of infection, less pain for the patient, and minimized cosmetic problems such as scarring.
The basic principle of electrosurgery is the same as electrical discharge machining (EDM) or electrical resistance heating. The "cutting" instrument generates a spark that jumps from an electrode to the flesh and burns away a small amount of tissue. The "coagulation" instrument uses the RF current to resistively heat the tissue, which eliminates bleeding from the surgical site once the heated tissue is cut.
Because human nerve and muscle stimulation cease at frequencies over 10 kHz, the electrical energy in radio frequency alternating current can be delivered safely to generate the spark for cutting or the heat for coagulating.
However, heat has the significant side effect of damaging local tissue and, more importantly, the nerves or the tissue underneath the surgical site. This is particularly important in three types of surgery: prostatectomy, hysterectomy, and neurosurgery. Tissue machining is defined as the coagulation and cutting of tissue in surgery.
A nerve-sparing surgical thermal management system based on advanced machining technology to minimize thermal spread and nerve damage problems in surgery is being developed at the University of Michigan. It is analogous to minimizing the thermal damage to the workpiece in machining.
The new surgical procedure, with better thermal management, can reduce morbidity and preserve postoperative quality of life for patients. Tissues are very sensitive to temperature. The threshold temperature for tissue damage is also time-dependent, but can be as low as 43°C.
Methods for minimizing collateral damage to the patient are being developed by Robert Dodde, a PhD student. The goal is to minimize and localize the heat generated in the wound. This may be done by cooling the cutting tip, imposing pressure gradients around the cutting tip to focus the electrical energy, and by controlling the waveform's size and current.
The Robot's Medical Roles
Robots used in medical applications have an entirely different set of needs than those significant to industry, where one of the primary concerns is cycle time. In many medical-device assembly applications, the primary difference is the amount of activities involved in meeting various regulatory requirements and process validation.
In other areas in the health and life sciences (HLS), speed is often not a concern or even desirable. In laboratory automation, for example, because most processes involve liquid handling, quick starts and stops are something to be avoided. There is some level of fear that industrial robots are more robust (and therefore more dangerous) than HLS needs to move the light payloads at the slow speeds required. As a result, robots tend to be on the smaller side.
Another difference is human-robot proximity. In industry, robots are segregated, are usually placed behind hard guarding, and are safeguarded by a slew of safety interlocks, safety mats, and light curtains. In contrast, many applications involving robots in hospitals take place in the operating room, where they are very close to humans. Robots are being used more to position devices used in various therapies or in diagnostics. Consequently, new developments in robot safety are being designed and implemented.
Robotic assistance in surgical procedures is another application. Currently, these are primarily master-slave-type arrangements where the robots are linked to human operators. The primary benefits are to reduce surgeon fatigue, provide additional articulation, and to dampen hand trembling.
That market is still determining what is needed in terms of robots. However, it appears that trying to design a single, general-purpose robot is not the way to go. The more likely answer is purpose-built robots designed to perform a set task or range of tasks. The reason is that different procedures will require different robot capabilities.
High accuracy will most likely be a common denominator, but some procedures may require higher rigidity—such as in driving screws in orthopedic procedures. Others may simply call for positioning a cutting guide or endoscope.
One thing for certain is that, at least for the foreseeable future, robots used in surgery will be either transmitting human movements, or assisting the surgeon. We are still many years away from totally automated surgery.
Director of Medical Products Business
This article was first published in the September 2007 edition of Manufacturing Engineering magazine.