Manufacturing for the Human Body
The medical market is growing
By Robert B. Aronson
While much of the manufacturing community has watched sales figures slump, or plummet, over the last few years, many companies with products for the medical industry not only survived but had record sales. And it is one of the few industries in which significant growth is predicted for the next few years.
Restore and relieve are two goals for this industry's products. Examples of those items used to "restore" a function include spinal fixation devices, replacement joints, particularly hip and knee joints, and cardiac-related devices, chiefly pacemakers and defibrillators.
Products that relieve pain or the adverse symptoms of various body malfunctions are also seeing greater application. At the same time the use of these products requires specialized surgical instruments. In addition there is a need for products used in the patient's recovery and post-surgery therapy.
Some of the physical problems treated are due to accidents or birth defects. But the aging "baby boomers" are major clients with ailments keyed to natural body deterioration.
Quality assurance. The standard for medical devices is probably the highest of any product made in the US. For example, according to Rick O'Brien, technology development manager, Biomedical Sensors, Medtronic (Minneapolis, MN), "A heart-assist device must survive 400,000,000 cycles. That is the estimated number of heartbeats a person would experience over 10 years of normal living." A large portion of the equipment and personnel used to manufacture medical products is related to quality control.
Design. From what, and by what process a medical product can be made has limitations, particularly the materials that can be used. The body can be a very hostile environment when it comes to any intrusion. It has a very effective protection system. Anything identified as unacceptable may be attacked in two ways: the body tries to dissolve it or encapsulate it.
The body's defenses "tolerate" only a limited number of materials such as refractory metals, ceramics, and certain plastics. One of the problems with joints can be the breakdown of the plastic joint linings. Even a small bit of lining can trigger the defenses and a reaction may start.
Miniaturization. Size is a major driver in all these products. First, the amount of "extra space" within the body cavity is limited. So the products that are implanted and the instruments used in the surgery have to be minimal in size.
Intrusiveness is a related issue. Much of the discomfort and infection associated with surgery is caused by large incisions. Surgeons, therefore, want the smallest possible devices. Through advances in equipment, surgeons can both view and operate on an area through a very small incision. This is due largely to fiber-optic viewing systems and miniature instruments.
Research advances. Researchers at Medtronic, the world's largest medical technology company, list a number of successes, but also emphasize the broad challenges still unresolved.
Among the major successes of this industry has been the development and acceptance of cardiac defibrillators and pacemakers. "We have a reliable product that both the surgeons and patients are comfortable with," says Dr. Sarah Audet, director, Biomedical Sensors Group and Advanced Concepts, Medtronic Cardiac Rhythm Management. "But improvements are still being made.
"For now, downsizing is not an issue. There is a trade-off between performance and size. If we made a smaller product, it would be easier to implant, but the size change might influence product life. The leads that go from the unit to the heart are also an optimum size to have the required life, current carrying ability, and flexure strength.
Another area of success for Medtronic is relieving chronic pain and the adverse symptoms of some diseases. Among the systems available are:
- Pain reliever. It is a programmable pump that delivers morphine. Because of the site-specific delivery, patients can achieve pain control with a fraction of the dose required for oral medication, thereby reducing side effects. The delivery pump and catheter are inserted surgically under the skin. The reservoir is refilled using a syringe through a septum in the pump.
- Spinal stimulus. An implanted device delivers neurostimulation to certain areas of the spine that blocks the body's pain signals to the brain. "It may somehow jam or override the body's own pain signals," says O'Brien.
- Tremor stopper. Many Parkinson's Disease patients suffer from debilitating tremors. With this device, electrodes deliver a current to the brain to help patients attain greater control over their body movements.
- Electrodes are surgically implanted in the area of the brain involved in motor control. While it is unclear how the system works, it appears to block tremor signals. Leads run under the skin to a neurostimulator implanted in the chest.
- No more needles. Currently under feasibility study is a totally implanted insulin pump for diabetics called an artificial pancreas. It has a sensing system that automatically checks the body's sugar level and delivers an insulin dose when required.
According to O'Brien, "A major area of research is diagnostic work rather than relieving chronic symptoms. For example, the heart degenerates in defined stages. Ideally, if the heart's specific problems could be diagnosed and treated before chronic conditions develop, the patient's life would be prolonged and treatment costs would be much lower.
"There are two challenges: on the medical side: knowing what the therapy should be, and on the technical side, knowing how to administer that therapy.
"We need long-term monitoring to make those decisions; a form of statistical process control similar to that used on factory machinery to use on the human body," explains O'Brien. "When the doctor takes your blood pressure, he gets a kind of 'snapshot' of the heart's performance. In our research we monitor over long periods to know more of what is happening."
The knowledge gained from long-term monitoring will also better determine the best therapy. "For example, we have a number of drugs that can help the heart, but the problem is knowing how much to deliver and when. A low dose may be ineffective, a high dose may be dangerous or cause the patient to become insensitive to the drugs.
"There are a great many variables to consider. For example, you can change the blood characteristics so it's easier for the heart to pump. But that may adversely influence blood pressure and cause fainting.
"One of our biggest design challenges is supplying electric power. We are working both to increase the power of our batteries and to cut the current use by the devices to the microamp level. Wire design is another concern. Wire size is 0.0013" [0.033-mm] diam at this time. But we must also consider the wire's electronic performance and its chemical reactivity."
Fighting friction. Two issues manufacturing engineers at Wright Medical Technology (Arlington, TN) are actively working on are friction reduction and process control. It is not uncommon for those with replacement joints to have a second and even third re-replacement. "The main reason for this is joint wear due to metal-on-plastic friction," explains David Barnett, senior director, operations engineering.
"We have a superfinishing process that improves roundness and surface finish," he says. "There is a match between mating surfaces that allows metal-to-metal and ceramic-to-ceramic contact that provides longer wear than the metal-to-plastic designs formerly used."
The other area is process control. "We have significantly improved our production by using more mill-turn machines. Being able to do multiple processes in one setup has cut wait time for machining operations and accelerated overall productivity. In addition, the mill-turn machines save valuable floor space.
"Utilizing lean principles for each production line has also helped us reduce shop-floor inventory, and allowed us to predict production more accurately," Barnett concludes.
Another development is an alternative to total knee replacement. The version developed by Wright is called Uni-Knee. In some cases, it is possible to relieve problems by only replacing part of the deteriorated knee. Knee pain is usually caused by bone-on-bone friction. The Uni-Knee replaces the wearing surfaces. Through a small incision, the surgeon saws away part of the affected area then places a cobalt-chrome casting in the femur; the tibia bone gets a plastic section.
Big backup. Rarely is a medical device made totally by the supplier. A great many subcontractors are part of the manufacturing chain. Here are a few examples.
Kanthal Palm Coast, a Sandvik Materials Technology Co. (Palm Coast, FL) has used its experience in the manufacture of stainless wire to move into the medical market by making catheter braiding wire. Currently typical dimensions for this wire are 0.001 X 0.003" (0.03 X 0.08 mm) but thicknesses down to 0.00075" (0.02 mm) can be produced. Key features of the wire are that it must be able to withstand high torque, be kink-resistant, and have "pushability."
Sandvik Bioline (Scranton, PA) supplies a large quantity of material, chiefly stainless steels, to orthopaedic implant and surgical tooling manufacturers. This division is part of Sandvik Materials Technology, specifically working with materials for the medical device industry.
"There are many industry standard medical grade alloys available which cover the majority of our customers needs--if you look at about 80 to 85% of their overall demand," says Stephen Cowen, Global Technical Manager. "For the remainder, we look to supply tailor-made alloys. It's a matter of balancing the volume needed with the research and development investment. This is a growing market as existing products are improved and new ones introduced. For example, we have developed some new wire materials and a new grade of stainless steel for hips. Plus we are working with a number of titanium alloys.
"Often the requests are not for new materials, but new forms. So we supply a wide range of sizes of wire, tubes, bars, plates and custom shapes. By providing the stock material in custom forms nearest to the desired shape, we can minimize the customer's machining and forming operations and improve yields.
"Medical devices offer unique challenges to the material producer. For example, most conventional applications want an austenitic stainless with a certain inclusion content, because it's easier to machine. The medical industry requires a totally clean material without inclusions, because such grades offer better resistance to corrosion and additionally, in some cases, enhanced mechanical properties. With such requirements machining becomes more challenging, and at Sandvik Bioline we have the advantage of being able to work with our tooling division, Sandvik Coromant, so that we can supply cutting data and tool recommendations to the customer to support their use of our steels.
"For permanent prostheses such as replacement joints, stainless steel, titanium, or cobalt- chromium alloys are usually supplied. But there are a number of semi-permanent or disposable items that use different materials. Single-use items include dental drills and burrs, bone saws, suture needles, and scalpel blades. In one case we use a special precipitation hardening, heat-treatable steel specifically for dental screwdrivers. They are used to insert the metal posts to which crowns are attached. Because of the material's high strength and ductility, it is also used in suture needles.
"For the future, we are keeping a close watch on non-metals in case the industry shifts that way. We can bring the same R&D, materials and product development expertise as we currently have in metals," Cowen concludes.
Cataract care. With an estimated 4.4 million surgical procedures conducted worldwide each year (1.3 million in the US), cataract surgery is one of the most common operations. Considering the continued aging of the population, it's also one of the fastest growing. In the US alone, 25% of those 65 or older and 50% of those 80 or older will likely develop a cataract.
Alcon (Sinking Spring, PA) is a major manufacturer of ophthalmic surgical products. The company primarily manufactures sterile, single-use disposable devices used in ophthalmic surgery. One of those products is an ultrasonic needle used in cataract treatment called phacoemulsification. Eye surgeons apply the hollow ultrasound tip (which looks like a miniature version of an inflation needle for a basketball) directly to the cataract to break it into small pieces and remove it from the eye.
As an example of how software is being developed specifically for this industry, Alcon began using a system from Rockwell Automation (Milwaukee) to track machine performance to identify ways to improve the overall process at the company. It uses data from the plant's existing control system and programmable controllers to gather data from production equipment and store it in a central database.
Called RSBizWare PlantMetrics, the package allows Alcon to run and view detailed equipment efficiency and event reports, to help identify which machines, parts, and shifts cause efficiency problems.
Another development at Wright Medical Technology is the Conserve Total Hip system that mimics the natural kinematics of the hip by replacing the body's natural head with a large diameter femoral head implant. The design is a liner-less, high-carbon, cast cobalt-chrome cup, with a large diameter high-carbon, cast cobalt-chrome femoral head anchored by either press-fit or cemented stems. This provides a low-wear, metal-on-metal articulation.
Seco-Carboloy (Warren, MI) is a company that is focusing its product line and marketing plans to take advantage of the medical industry. The company currently has cutting tools specifically designed to work in this area, and their R&D department is developing tooling to further extend this range.
"One of the issues to consider when appealing to the medical market is the ability to cut different materials and cutting tools that can handle smaller, intricate parts," says the company's Bob Goulding. "We know we will be working with materials such as cobalt- chrome, titanium alloys, and stainless steels, as well as other exotics that the industry uses.
"We will introduce a line of Swiss-machine tool products that will include tools for turning, milling, drilling and threading, and through the recent acquisition of the Jabro Tools company we have added a line of solid carbide end mills."
Many components used in replacement joints begin as a forging or casting made to near net shape. " This means using tooling that can take small depths of cut at high metal removal rates and support, providing the expertise in applying these techniques," says Goulding.
"In particular, micrograin carbides with sharp edges perform well in these materials. A potential future demand may come in the form of ceramic replacement joints, in which case we would recommend using PCD grades as a solution.
"We have solid carbide drills with geometries specifically designed for these difficult materials, and offer inserts with small nose radii and sharp, high positive rakes for turning. Another of our products is an indexable milling cutter called a NanoTurbomill. It is designed for small depths of cut at high table feeds. This tool takes 6-mm indexable inserts and as such has a very close pitch. For example the 1" (25-mm) diam tool has seven teeth, which translates into a very high feed rate capability, typically twice the feed of many normal products. Our new end mills are engineered with substrates and edge conditions to specifically suit these materials while having the capability to remove material quickly. The market also requires reliable tooling, so our carbide grades have tough micrograin substrates with wear and heat-resistant TiAlN PVD coatings."
Robots. For both product and patient "assembly," robots are being called into action in a number of ways to assist the medical manufacturer and surgeon. In one example Becton Dickinson, a company that provides diagnostic instruments to the health care industry, had a problem with sample preparation. One process involved dispensing precise amounts of fluids on a repetitive basis. Traditional manual methods were tedious and caused worker fatigue, resulting in inaccuracies and errors. To resolve this problem the company developed an automated sample processor. The system automates the sample handling associated with high-volume testing. A key element in the design was a Cobra 600 from Adept Technology. It allows the system to perform pipetting transfers without the use of syringe pumps and tubing. Technicians have fewer repetitive motions and process errors were reduced.
Robots are also being tried as "surgeon's assistants" in some procedures.
The positioning accuracy a robot can provide may be used to insert and position some elements in joint replacement operations.
This article was first published in the May 2004 edition of Manufacturing Engineering magazine.
| The Medical Side of Design
Micromanufacturing is a fairly new term or buzzword that describes a type of machining that has been going on behind the scenes for years. Now it is emerging as an industry of its own. It hadn't been given its own classification before, even though many companies have been micromachining for some time.
In the medical-device arena we are micromachining a wide range of parts and products. We use both sinker and wire EDM technology to burn small, intricate features on dies and molds. We also build many parts and fixtures with miniature features that require tight tolerances and fine surface finishes.
We machine many 3D models and parts on high-speed CNCs using end mills as small as 0.004" (0.1-mm) diam. Our work often entails drilling miniature holes to challenging depths.
The materials being machined can create an incredible challenge. Obviously, if you are working with stainless or other metals, EDM machines can be utilized in most applications. However, the majority of our parts and fixtures consist of different types of plastics. This forces toolmakers to be more creative when micromachining, because the plastics aren't as stable as metals.
Historically, our company has had to build our own machines to carry out our unique jobs. In the future, I believe machine manufacturers will have more equipment available to meet the needs of the micromachining industry. They are beginning to understand the requirements for equipment capable of producing micromachined parts. This will include not only machine tools but tooling, inspection equipment, and even deburring equipment.
The major change that I see is the entry of rapid-prototyping equipment. Guidant has a stereolithography (SLA) machine built by 3D Systems (Valencia, CA) that is able to build parts within ± 0.001" (0.025 mm) out of resin. In the future, I hope to see more accuracy and maybe the possibility of producing microparts using selective laser sintering (SLS) out of materials such as stainless, aluminum, and Delrin. If this happens, it could completely change the way we produce parts.
Model Shop Group Leader
St. Paul, MN
| Parts from Puerto Rico
One of Puerto Rico's manufacturing specialties is medical products, both pharmaceuticals and hardware. Several of the major US "spare part" makers are there, including giants such as Medtronic and Guidant.
CNC 2000 Inc. (Caguas, PR) is an example of such a second-tier supplier. It's one of a handful or large-size job shops on the island. Among the company's clients is Zimmer Caribe, for which CNC 2000 does the front-end step in the manufacture of replacement hip joints.
In the production process the company chiefly uses lathes and machining centers such as Okuma-Howa lathes, and Seiki machines. Initially the joint shape is cut from round bars of titanium to a surface finish of Ra 32 or better.
According to company president Johnny Ramos, "The most difficult part of this job is maintaining constant surface finish on a sphere, outside the hip cup. We achieve that using a CNC Fanuc code called Constant Surface Feed. All critical dimensions are made using a CMM. The parts then go back to the manufacturer for a proprietary final finishing.
The Zimmer company, along with a number of other medical equipment manufacturers, takes advantage of the tax and shipping advantages Puerto Rico offers to have subcontractor work done. In fact, notes Ramos, "There has recently been a significant trend among medical part manufacturers to subcontract their work to companies in Puerto Rico. Medical device companies are finding Puerto Rico is a major player in the manufacture of high-precision components. This ability, coupled with our domestic relationship with the continental US, positions us to better service this market.
"The variety of components could go from simple nails and screws, to sophisticated bone screws, back-bone plates, heart valves, and complete medical products. I expect these contracts might range from $0.5 to $20 million annually for components, with a potential for $50 million for turnkey medical contracts delivering completed products.