Medical Manufacturing for the Golden Agers
Preventing, repairing, and easing the problems of aging
By Robert B. Aronson
Manufacturing serving the medical market continues to enjoy almost constant growth. The expansion of that market has created a number of opportunities for manufacturers in all areas. Much of this is due chiefly to an aging population as "baby boomers" reach retirement age and experience normal physical deterioration. They need hearing aids, replacement teeth, and eyeglasses. At the same time there is a need for products that assist conventional living and mobility such as automatic wheel chairs, and special devices for the home. This growth market for manufacturers requires new levels of precision and quality.
Hip and knee replacements, once complex and rare operations, are common. At the same time researchers are generating a constant stream of new products to prevent, repair, and assist many of the maladies that were accepted as the penalties of aging. Medical products are quite competitive, and for some time manufacturers of those products tried to keep the production inside their own plants. Now success is forcing many to reach out, thereby creating opportunities for a number of suppliers.
Keep it small. With many devices implanted in the body, small size is critical. The device has to be small enough to be placed without causing any or very limited damage. Because the body is very good at attacking substances it determines are not wanted or dangerous by dissolving or neutralizing the offending substances, the implant must be made of something that does not activate the body's defense mechanisms. This selection is currently limited to a few metals and plastics.
One pioneering technology in the area of miniature medical devices are the MEMS (miniature electromechanical systems). MEMS products are essentially grown, not formed or cut. One of the companies active in this is Microfabrica (Burbank, CA), which uses the EFAB technique. It is similar to that used by rapid prototyping systems, but it produces three-dimensional devices, components, and machines that are typically the size of a grain of sand. They are made by depositing one planar layer of metal at a time until the entire product is fabricated. Each layer consists of a structural metal, which remains in the final product, and a sacrificial metal, which serves as a "scaffolding" during the fabrication process and is dissolved away once all layers are formed. The technology fabricates multiple devices simultaneously in batches, much like computer chips are produced.
According to Microfab CEO Adam Cohen, "EFAB technology allows medical devices and instruments to be scaled down to much smaller sizes than is feasible using conventional machining technology, while offering the cost benefits of batch fabrication and reduced assembly cost [complex devices having multiple, independently-moving components can be produced without the need for assembly in most cases]. For example, it's possible to fabricate small instruments that enable surgeons performing minimally-invasive surgery to further reduce trauma to the patient and access regions of the body that would be difficult or impossible with larger tools. These devices are normally implanted by surgery, by inserting them using a catheter [e.g., for a stent], or by injecting them through a needle. They may be powered when needed by tugging on cables from outside the patient, by pressurized fluid, or electrically."
On the electronic side, when powered, the implanted device has to have minimal current draw to transmit its signals to some receiver. This can be done by conductors through the body wall. This arrangement sends the clearest signals, but is least desirable because of infection danger.
Transmitting through the body to a receiver on the outside is medically safer, but it takes more power and can be less accurate.
Pill camera. For a medical device to function within the human body it must not only be very small but must require very little power. One of the more impressive devices that meets these requirements is the capsule-size camera called the Pillcam made by Given Imaging (Yoqneam, Israel; Given is short for gastro intestinal video endoscopy imaging). This sensing system, which is actually no bigger than a large vitamin pill, is swallowed by the patient. As it moves through the body's plumbing, like any piece of food, it takes photos at rates up to 16 frames per sec. Using a radio frequency transmitter chip, the pill relays images to a data recorder worn by the patient.
About 12 hours later the doctor downloads the recording system and can generate full-color 300 X 300-pixel photos of the patient's innards. The camera is used only once.
The PillCam video capsule for the small bowel (PillCam SB) takes images at a rate of two frames per second over its entire eight-hour journey, a total of about 50,000 images. The PillCam video capsule for the esophagus. It takes 14 frames per second during the 20-min procedure. That said, the PillCam video capsules record these images regardless of their positioning within the small bowel or esophagus. The Pillcam may replace the more intrusive and uncomfortable processes that have been used for some years. The patient needs no preparation--unlike procedures using an endoscope that require a short hospital stay.
Zarlink Semiconductor (Ottawa, Canada) developed the chip responsible for collecting and transmitting the data. The pill camera may have a significant market in the US according to Steve Swift, senior vp and general manager, ultra-low-power division, if it replaces the approximately 20-million investigative procedures done annually in the US. The company also makes the ultralow-power chips used in pacemakers, cochlear implants, and hearing aids.
"When developing chips for advanced medical applications, ultra-low-power design techniques are critical to ensure minimal power use and longer operating time," says Swift. "For example, by lowering the power demands for the transmitter chip, we have been able to help significantly extend the capabilities of Given Imaging's Pillcam."
"What's That?" Hearing loss is another problem that comes with advancing years. Hearing aids have been the staple answers ranging from tin horns to today's miniature amplification devices. The manufacturing problems are the same as for most powered medical assists: Size and current draw. The smallest of today's hearing aids are self-contained units in which both the battery and amplifier units fit into the ear cavity. When more power is needed, the battery pack fits behind the ear.
External noise has always been a problem. Normally the user wants to hear a conversation or a speaker, but ambient noise is also amplified. In earlier units, all sound was amplified equally. Modern units have filters and programming that selectively amplify sound, so the aid wearer gets a more useful input.
For more drastic hearing problems, the cochlear implant has shown a lot of promise.
A main element that translates vibrations into sound signals is a spiral section of the ear that looks something like a sea shell. It's called the cochlea. It is a coil-like device containing hair-like sensors. Vibrations strike these sensors and generate signals that the brain identifies as various sounds.
When these hair-sensors no longer send signals, or send them poorly, that portion of the sound spectrum is no longer heard. With aging, normally, the higher frequencies drop out first, then the failure progressively influences the lower sounds.
Some of this hearing can be recovered with a cochlear implant. With this device fine wires are placed in the cochlea. In the case of a unit provided by Cochlear Americas (Englewod, CO) there are 22 sets of wires or channels. Each wire rests on a different area of the cochlea.
In operation, sound is detected by an implanted unit. This unit then sends small electric signals to the wire resting next to the appropriate natural sensor and activates it, restoring some hearing capability. The implant does not restore natural hearing but does provide hearing clues, particularly to help understand conversation. At first, the patient may hear a sound something like a poorly tuned radio. In time, many patients can use the phone on enjoy listening to music.
"Key to the success of this device is its installation," explains Dr. Chris Van dan Honert, vice president of research and development for Cochlear Americas (Enlgewood, CO). The initial problem was getting the wires into the curved cochlea, in particular, getting the wire to lay against the outer curve of the cochlea where the hair sensors are. This was achieved by a proprietary casting method that introduced a bend in the wires. Initially, the wires are held in a straight position by a sleeve. As the unit is inserted, the sleeve is pulled back, allowing the wire to curve as needed.
"Another manufacturing problem was developing a set of wires that curved properly, and the sleeve to initially hold the wires," Van Dan Honert concludes.
Another mechanical hearing improvement has been to replace the small bones that transmit vibration to the ear drum. With aging, these elements begin to lock In place. In some cases, they can be replaced by plastic "bones" that duplicate the function of the natural parts.
Backup pump. A total mechanical heart has been a goal of surgeons and medical researchers for some time. There were a couple of attempts to keep patients alive with mechanical implants that were modestly successful. In the earlier designs, first, there was the problem of size. The designs were too large for general use and could only fit into the chest of an adult male. Another issue was that the mechanical heart could not handle all the variables of a natural organ. A heart can adapt to a variety of changes: exercise, resting, stress, sleep, food, medication. But a mechanical device has problems handling these many changes.
But a design that is working well is a system called a ventral assist. This is a small implanted pump that assists a natural heart. Mostly they have been used to keep a patient alive until a donor heart can be found, or until repairs can be carried out on the natural heart.
One of the latest developments of this type was developed with the help of hydraulic engineers at NASA's Johnson Space Center. It's an axial flow device that is easily implanted and can work with children. It supplements the pumping power of either the left or the right ventricle and requires only 8 W. It's powered by a battery pack and controller worn by the patient with the power leads passing though the abdominal wall.
The device has already been accepted by the medical community in Europe and is currently undergoing FDA trials in the US. So far, a 300-patient test group is using it, some for over two years. The ventral assist is also being considered for "destination therapy" in which the patient keeps the assist permanently.
According to Dr. Michael Debaky, professor of surgery, Baylor College of Medicine and Chancellor Emeritus, Baylor School of Medicine (Baylor, TX), "We try to minimize the negative affects on the patient. This implant requires less surgical manipulation, causes less tissue damage, and has a very low incidence of infection. In this country we do about 2300 transplants of natural hearts, but there are 50,000 potential candidates that might benefit from our design."
My aching back. Disk degeneration is a major source of back pain for many, particularly the Golden Agers. As the spinal disks deteriorate, the vertebrae may press on the spinal column nerves, causing pain and numbness.
A common operation for this problem is fusion. In this procedure, the damaged natural disk is removed and the two adjoining vertebrae are fused together. The main disadvantage of this operation is that the patent loses some mobility because the spine no longer has its original freedom of motion.
One of the latest developments to alleviate this problem is the civet disk developed by DePuy Div., Johnson and Johnson. The concept is rather simple, a replacement disk is made as a sandwich consisting of two metal disks and a plastic core. In the operation, the deteriorated disk is removed and the mechanical replacement inserted. The two caps, made of chromium, have spurs on their outward surfaces that help anchor it to the adjacent vertebra. The polymer disk allows the vertebrae to move relative to each other and maintains the spacing without pressure on the spinal nerves.
There are limitations on this device relative to the type of deterioration, age of the patient, and other medical factors.
It's a bearing problem. Longer life is the goal of all implant makers. And they have achieved this by improvements in design and machining practices. Not too long ago, a hip replacement would last from eight to 10 years. Now the average can be 20 or more. The extended life means younger people are being encouraged to have the operation.
Replacement joint design continues to mature. The bearing within the joint has to survive an average of two million cycles per year.
But many have heard the story--or experienced--a situation where there have been two or more hip or knee replacements. The problem is often a bearing issue. Usually something breaks down, possibly the plastic element in the joint fails or something, such as a bone fragment, scratches the metal surface of the joint and sets up a part failure due to excessive wear.
Makers of replacement joints are concentrating their efforts on improving bearing life. According to Richard Tarr, vice president world wide research and emerging technology DePuy Inc. (Warsaw, IN), a Johnson & Johnson company, his company is looking at several possible design improvements.
- Improve the wear characteristics of existing materials, usually cobalt chromium alloys riding on an ultra-high molecular weight polymer.
- A metal-on-metal design fitted with a precision that captures a fluid film kind of lubricant between the mating parts. A main concern with the metal-on-metal idea is the release of metallic ions that could potentially cause the body to react negatively to these ions. Researchers are looking at some of the coatings developed for cutting tools to improve mating-part hardness and resist abrasion.
- A ceramic-on-ceramic joint possibly made of alumina or zirconia. This design would avoid the metallic ion problem. The parts would be cast, then fired and polished.
- Borrowing an idea from hybrid bearings, they might use a metal on ceramic design. This version has shown good results in lab tests.
"We have been working more on product improvements than on expanding our line," explains Tarr. "Two areas of activity are joint design and new instrumentation. One goal is to make the operation less intrusive, so the patient has less pain, a shorter healing time, and less chance for infection. Before, a hip joint would require an 8 - 10" [203 - 254-mm] incision. Now it can be done with a 3 - 4" [76 - 102-mm] incision. However, this has required us to develop a new set of smaller instruments to work in a more-limited area."
The other area of improvement is computer-aided surgery to help the surgeon implant the joint. Currently, much of the placement is dependent on the surgeon's skill. An assist developed by DePuy uses markers placed on the bone after the initial incision. The position of these markers is then compared to a computer image of the leg made before the operation. By matching the markers with the computer image, the surgeon can more readily position implants properly. The process brings a new acronym: CAS (computer-aided surgery).
Chairs and scooters. Mobility is a major problem for the Golden Ager. Part of the tremendous growth of mobility devices, chiefly manual and powered wheelchairs, is the fact that the government often pays part or the entire purchase price through Medicare and Medicaid.
The market is changing and growing; a number of companies have entered the markets. Drivers include an aging population with diseases that limit mobility and the fact that as people age they are more likely to have falls or accidents that will limit mobility.
Invacare (Elyria, OH), a $1.4 billion company, makes a number of devices for the Home Healthcare market with powered wheelchairs a big part of their product line. They started manufacturing with manual wheelchairs, then added power chairs around the mid-1980s.
"Through the years we have constantly improved our product," explains Tom Tuckowski, Invacare's director of rehab engineering. "A big move was the change from belt-drive power wheelchairs to direct-drive, gear-motor power wheelchairs. We have also done a lot of work on suspensions, to improve patient comfort. Microprocessors have been another advance. They have been a big help in increasing capabilities and product flexibility.
"The market has gotten more sophisticated. The 'K' codes from the government that regulate wheelchair specifications have grown from four to 49. This has been necessary to cover the range of designs now available. They (49 codes) were developed by the Center of Medicare and Medicaid Services (CMMS) with the goal of ensuring chair design and performance specifically aligns with patients' needs."
Power wheelchairs have a wide range of designs beginning with basic units for those who need only partial help--for example, someone who needs an assist for a few hours a day for a trip round the neighborhood or to a shopping mall. At the other end of the spectrum are chairs for those with permanent injuries such as quadriplegics. "For those needs, we have power wheelchairs that can accommodate a number of electronic options. For example, those with limited body control may be only able to use head motion or a "sip and putt" straw-like sensor to control chair motion.
"Ordering a chair is usually a two-step process. First a therapist or physician will determine the patient's needs. When that order is called in our customer service people rely upon a computerized customer service order entry tool, called the "Configurator," that helps establish the specific options that patient will need. Features to consider include basics like dimensions, color, and seat size as well as special needs such as type of armrest, legrest, and other positioning components. Normally, a chair is built and shipped within five days.
"Our manufacturing philosophy allows for customized mass production. We have two basic forms of assembly. Low-volume units are assembled by a team using a stationary stand. Higher - volume chairs are built on an assembly line. In all situations it is important to maintain commonality of components to enable customized mass production."
Scooters have become more popular for those patients who need assistance in moving around the house or on short trips such as shopping.
The Ranger (George, IA) offers units from $1595 to $4995 depending on the model, with the most popular units selling for $2550 and $2650. Top speeds range from 4 to 5 mph (6.4 - 8 km/h). The scooters are powered by two 12-V batteries. Normally a unit operates all day on a full charge. Charging time is usually 6 - 8 hr.
The design features an easily operated adjustable tiller and simple disassembly for transporting. It can be taken apart in less than a minute. The scooter's frame is light-weight extruded aluminum, and the body is vacuum-formed ABS plastic with the color impregnated in the plastic, not painted.
Ouch! Possibly the most familiar medical device is the hypodermic needle. Not too much has changed in their design and manufacture. They are made from tubing cut into lengths, then the points are ground. There have been experiments with needle points to determine what type of point creates a wound that most easily heals.
Because of high-volume production that keeps cost down, the cost of sterilization, and the liability potential for reuse, the majority of needles are now disposable. Some use a silicone coating which makes insertions easier.
High-cost needles used for certain testing or special administration procedures, such as those requiring multihole shafts are often sterilized and reused.
This article was first published in the May 2005 edition of Manufacturing Engineering magazine.