Engineering News

By Design News Staff -- Design News, June 7, 1999

Medical adhesives join safety, reliability

Bonding parts of a device used in or near the human body poses some sticky problems. Here's how special adhesives and dispensers helped two companies do it right

By Christine M. Ferrara, Associate Editor

Newton, MA--The old expression says different strokes for different folks, and never is this more true than in specifying adhesive and dispensers for critical medical applications. But no matter what the bonding method, gluing together a medical device presents special challenges. FDA regulations also require process validation.

Core Dynamics (Jacksonville, FL) manufactures surgical devices in a clean room that are used to drain body fluids or administer medication. The two-piece assembly consists of a flexible tube called a cannula with a pointed instrument called a trocar attached at one end. To bond the two pieces, Core Dynamics uses Dymax Corp.'s (Torrington, CT) Ultra Light Weld 1191-M UV/visible light-curing fluorescing adhesive and MediCure MC4000 UV light-curing system.

The urethane acrylate adhesive is 100% solids, with no solvent to flash off, says Kyle Rhodes, medical technical services representative for Dymax. The adhesive is USP Class VI and ISO-10993 certified, ensuring biocompatibility with complete cure. The MediCure MC4000 light-cure system is for high-intensity light spot curing, emitting 3 to 4W of intensity in a spectral output of 300 to 500 nm. The adhesive's ability to cure with visible light dramatically increases cure speed, and also permits curing through UV-blocked plastics, Rhodes adds.

"The speed of cure is seconds," Rhodes says. "It bonds on demand. When you expose it to UV light, the adhesive cures immediately, creating a hermetic seal."

Rapid cure was one reason Core Dynamics chose the adhesive to assemble the cylindrical outer diameters of the trocar and cannulas, says Mike Ontiveros, project engineering manager. The adhesives also fluoresce under black light, which allows the company to pre-inspect for imperfections such as air bubbles or voids in the bond.

Core Dynamics applies the Dymax UV adhesives using a pneumatic dispenser with an anodized steel housing from Ventrex Inc. (Ventura, CA). Measuring 23.9 × 17.3 cm, the compact unit uses a submerged piston pump. Through timing circuits and air pressure, the dispenser pumps adhesive from a primary to a secondary reservoir. Each time the pump strokes, it delivers about 1 to 1.5 cc's of adhesive to the custom applicator, in this case a polyethylene wick.

Model UV8350's polyurethane wick is constantly saturated with adhesive. "As long as the wick is saturated, the excess gets recirculated through a reservoir," says Jim Callegari, director of operations for Ventrex.

Many manufacturers use a needle and syringe dispenser to assemble medical applications that use UV adhesive, Callegari adds. This method's inherent drawbacks are its operator dependence and inconsistency. "On a cylindrical part, it is very hard to be consistent, operator to operator, part to part, to dispense this adhesive along the entire I.D. or O.D," he says.

The UV8350 dispenser provides the manufacturer with the advantages of better consistency, controllability, and ease of use, as well as high speed, Callegari says. The dispenser's controlled beads of UV adhesive help the company meet FDA regulations on manufacturing process documentation and validation. "We have to show that the equipment will consistently deliver enough adhesive to give a good bond," Callegari adds. "Through the process validation, you are validating that the process works."

To further help in the process validation, Core Dynamics wanted to come up with a way to validate the UV light intensity in the manufacturing process. Dymax introduced a radiometer into the process for this purpose, says Core Dynamics' Mike Ontiveros.

Ventrex's dispenser isn't just for medical applications. Callegari points out that it can be used in high-volume industries using any type of bonding that can benefit from repeatable, controlled processes. Specific applications include automotive and retrofitter automation.

Manufacturing monitors. Nonin Medical Inc. (Plymouth, MN) manufactures pulse oximeters, non-invasive medical monitors that measure pulse rate and blood oxygen saturation. The monitor consists of a pulse oximeter and a separate sensor that plugs into it. Nonin also makes Onyx^TM, a self-contained finger pulse oximeter and sensor that measures 2 inches long and weighs less than 3 oz with batteries.

Nonin formerly used UV adhesives to install LED windows into the Onyx line. However, the company discovered the UV adhesive would not work with its plastics, says Katy Green, production supervisor for Nonin. The company switched to Sicomet® 63 adhesive from Henkel KGaA (Dusseldorf, Germany), a cyanoacrylate applied at up to 80C targeted for use in bonding small metal and plastic parts. Clear Scotch-Grip^TM plastic adhesive from 3M's Adhesives Div. (St. Paul, MN) is used to hold the pulse oximeters together. Scotch-Grip works on flexible vinyl, polyethylene, and polypropylene substrates, 3M says.

For moisture protection, important for pc-board protection, Nonin uses Dow Corning® 739 black plastic adhesive from Dow Corning Corp. (Midland, MI). The one-part, nonslumping paste adhesive provides an alcohol cure at room temperature upon exposure to water vapor. Nonin also uses 128 silicone rubber clear adhesive sealant from GE Plastics (Pittsfield, MA) on the pulse oximeters, Green says.

The Scotch-Grip plastic adhesives, Sicomet, and RTV sealants bond well, Green says. However, they present longer cure times than UV adhesives--anywhere from five to 90 minutes. Also, Nonin has to use clamps to hold the oxidimeters, rather than have an instant cure. In addition, Sicomet blooms, which presents aesthetic problems, she adds.

The company uses EFD Inc.'s (East Providence, RI) Model 1500XL adhesive dispenser to apply both the RTV sealant and the plastic adhesive that holds the two halves of the device's case together. "It is an efficient way for us to dispense adhesives," Green says.

The LED window was another reason Nonin switched from UV adhesives. "When we applied the UV adhesive from the EFD dispenser, the adhesive wouldn't cure," Green adds. "We finally figured out the LED lens was made from a plastic that wouldn't allow UV light to pass through it."

The 1500XL uses an adjustable air pulse to dispense material and a microprocessor-based timer to control the dispensing cycle. Dispense times range from 0.001 to 99.9 sec, with 0.00005-sec repeatability.

After adjusting the time and pressure controls, the operator simply holds the dispensing tip in position on the part and taps an electric foot pedal to make consistent deposits. Benefits include better process control, less rework and fewer rejects, and more benchtop workspace.

Sticking in the future. So what do both medical manufacturers and suppliers hope to see in the way of future medical adhesives developments? The ability to change color, for one thing. "Along the same lines as the fluorescing adhesives, it would be great to have an adhesive that would change colors after curing,"says Core Dynamics' Ontiveros.

Dymax's Rhodes agrees. "Adhesives that change colors to ensure complete cure are the holy grail of UV technology. No one has been able to come up with it yet commercially, but who knows what the future may hold?"

In the near future, however, expect to see an increase in the use of UV-curable gaskets and UV-curable opaque black conformal coatings, says Rhodes, as well as a wider range of high temperatures and more substrates. "The ability to cure through UV-blocked substrates with adhesives such as 1191-M is also a major breakthrough."

Medical adhesives should also withstand more and more technical requirements, especially as applications get smaller and more complicated, Rhodes says. "Customers want to be able to work smarter and faster, while obtaining higher-quality products."  

What this means to you

• Bonding medical equipment requires medically certified adhesives.

• Adhesive dispensing systems can help document manufacturing processes.

• Constant monitoring of the bonding process is critical for production efficiency.

3D printer cuts surgical time

Houston, TX--In reconstructive surgical procedures accuracy is crucial. To ensure success, surgeons are looking past 2D CT scans and x-rays to diagnose and plan surgery. Instead, they are looking to 3D imaging and modeling, thanks to specialized imaging software and rapid prototyping tools.

This technology helped Dr. John Teichgraeber, a pediatric plastic and reconstructive surgeon in Houston, TX, when he began working with a 9-month-old patient who suffered from craniosynostosis. This term refers to premature closure of one or more of the sutures that separate the seven bones of a baby's skull. If the sutures don't develop properly, the brain may not expand normally within the skull, resulting in increased brain pressure that can cause brain damage or sight loss.

To correct this, a surgeon must release the fused structure and reshape the skull. The procedure, which can take from two to five hours, depending on the surgeon's expertise and the case severity, presents many challenges.

The surgeon must decide where to make new bone cuts so the skull develops properly. Without careful planning, the new cuts could expand too much or asymmetrically, making for a misshapen head. Not to mention, the window of time between when this problem is diagnosed and when surgical intervention must take place is between six and 12 months of age.

Dr. Teichgraeber performs many of these procedures in a typical month. Recently, he began working with Medical Modeling Corp. (MMC; Golden, CO) to assist in accuracy and reduce surgery time and associated costs.

MMC uses different rapid prototyping machines for jobs of this category. In addition to its 3D Systems (Valencia, CA) SLA- 250 and SLA-350 machines, MMC is using a Z402^TM 3D printer from Z Corp. (Somerville, MA) to produce physical models of internal biologic data derived from medical imaging modalities such as computed tomography (CT) or magnetic resonance imaging (MRI). The resulting plastic model replicates patient bone structures.

The company has been using the Z Corp. machine for about five months. As for the difference between the two machines, Andy Christensen, general manager for MMC, foresees cost as a big advantage.

"Cost has always been a factor. The average RP medical model costs anywhere from $1,000 to $3,000. The Z Corp. model is one-third that," says Christensen. "Since cost is the major factor in why more surgeons are not using these models, this provides a great new solution to this situation."

However, Teichgraeber acknowledges that each of these machines has its own advantages depending on the application.

"Some applications don't require as much accuracy as others. Those where surgeons want to see bone or tissue structure, and may want to do some surgical simulation, that's where the Z Corp. machine is beneficial," said Christensen. "In those cases where surgeons are dealing with small, thin pieces of bone, that's where other RP methods like stereolithography come into play."

Using 2D CT scan data provided by Dr. Teichgraeber, MMC imported the data into the MIMICS software package from Materialise (Ann Arbor, MI). The software was then used to threshold the data from the scan to provide MMC's CT technologist with the needed bone data. The technologist then exports the STL file from MIMICS to the Z402. Once imported into Z Corp's build software, the file is sliced and prepared for modeling.

The machine created a model out of a proprietary starch-based material from Z Corp., with 0.007-inch layers, in less than four hours. This saved more than 12 hours when compared with rapid prototyping techniques.

Dr. Teichgraeber used the model in preparation for the surgery, and also took it into the operating room (non-sterile) for reference during surgery.

According to him, using this $650 model reduced this five-plus hour surgery by one hour, which cut thousands of dollars of surgery costs. Furthermore, MMC was able to provide Teichgraeber with a true 3D model at about 1/3 the cost of a stereolithography model.

"This repair was done in the least amount of time possible, while providing the patient with a great outcome," says Teichgraeber. "The model provided more than enough accuracy and allowed for communication before the surgery between myself and the neurosurgery team."

Christensen believes there is a need for both system types. "The SLA is a great system, the key has been to find something to supplement it. The Z Corp. machine does that, it opens doors."

Laser welds tiny medical devices

Santa Clara, CA--Lasers--concentrated light waves--can guide missiles, move information, or entertain. Although the technology has been applauded for its accuracy and cleanliness, a big drawback has always been the laser's bulkiness and cumbersome size.

Now one Silicon Valley-based company, Equilasers (Santa Clara, CA), has developed a laser system which is not only highly reliable, but rugged, compact, and adaptable enough for use in an increasing number of medical applications. In fact, the EDWS system, which consists of the laser, workstation, video camera, and computer, comes in a desktop package and fits into a 3 × 5-ft-space.

With laser spot sizes of 25 to 550 microns, the EDWS system is used for spot and seam welding of minimally invasive medical devices. The 25-micron spot size (1.0 mil or 1/4 the diameter of a human hair) is the smallest spot size attained for a fiber coupled laser welder--allowing seam welding of a circle with a 5-mil diameter. The small spot size enables extremely tight welds with excellent structural integrity.

"We envision that this and next generation products will replace resistant welding in some applications," says Richard Sam, president. "We are perfecting smaller and smaller spot sizes and wider dynamic ranges--from a fraction of a joule to tens of joules." Sam established the company in 1994 after managing several major government laser projects. His expertise is matched by co-founder Max Eagleson's 40 years of military laser design.

At the core of this system is a 15 or 25W laser welder. This new laser system is an advanced version of the highly successful Equilasers medical OEM laser. The EDWS system is computer-controlled; the self-contained laser is approximately the same size as a typical PC tower case. Laser power is delivered via an optical fiber to a precision focusing and viewing assembly. The system is equipped with a video camera to view the welding area. The focusing assembly is attached to a set of X, Y, & Z axes, which are servomotor-driven and computer-controlled to offer a linear resolution and repeatability to ±0.0001 inch. A joystick enables easy remote control of the X and Y stages. A stepper-motor-driven lathe is included for precision circumferential welds.

The video system features a miniature, high-resolution color camera and monitor. Camera lighting is provided through a fiber-optic light guide joined to a high-intensity illuminator. The combined video camera/lens configuration has a magnification up to 80X and clearly displays features as small as 1 mil. A visible, red aiming light, co-located with the welding spot, serves as a guide to accurately focus the beam to a small spot.

The system runs on 20A/110V ac household current, is semi-automatic, and has a graphical user interface which makes it easy to operate.

In addition to laser welding, Equilasers supplies OEM laser subsystems to medical companies. In cardiology, Equilasers supplies Holmium laser heads for use in transmialcardial revascularization, a therapy in which tiny 1-mm-diameter holes are drilled in a person's heart to reduce angina or chest pain. These holes in the heart wall enable new blood vessels to form and revitalize diseased heart tissue. The procedure is being pioneered by Eclipse Surgical Technology.

"In an operating room, a highly reliable laser with a small footprint is important," says Sam. The company also markets a Nd:YAG laser for dental soft tissue applications.

INTERBUS streamlines drug production

By Rick DeMeis, Senior Editor

Tonawanda, NY--BOC Edwards Pharmaceutical Systems was looking to reduce installation costs while maintaining the reliability of its pharmaceutical freeze dryers. Drug manufacturers use the units to process and preserve antibiotics, vaccines, and blood fractions. The dryers may contain up to $3 million dollars worth of product during a 24-hr or longer batch run. Thus reliability is paramount.

"BOC Edwards also builds high-speed filling lines for pharmaceutical manufacturers in our Dutch facility," adds engineering manager Ivan Lanaway. "We were looking for a protocol that would serve both facilities' needs. Our colleagues there used INTERBUS in a new range of in-line filling equipment where high-speed communication is critical, and were pleased with its performance."

Based on a joint decision with the Dutch operation, the company recently introduced the INTERBUS protocol to its U.S. customers because of its flexibility in communicating with a wide variety of PLCs--including those from Siemens, Allen-Bradley, Modicon, and Mitsubishi. The protocol also enhanced the company's global market presence (it exports around two-thirds of its freeze dryers). Specifically, Lanaway notes, "As an international supplier of custom-built equipment, we're driven by the type of PLCs our customers use. After examining various systems, we settled on INTERBUS protocol as the most universal."

BOC Edwards selected the Phoenix Contact (Harrisburg, PA) INTERBUS ST I/O System for its medium-sized Lyomax®11 freeze dryer. A dryer system is a series of separate skid- or frame-mounted components, a process chamber, condenser, refrigeration unit, and control cabinet housing an Allen-Bradley PLC-530. The skids may be located adjacent to each other or on separate floors in a plant. INTERBUS ST links the PLC (via an IBS PLC-5 DSC/I-T interface module) and 300 input/output points that monitor limit, temperature, and pressure switches. The system also uses Phoenix Contact smart terminal blocks for connections. The skids are also linked by process piping for freezing, heating, and vacuum.

Using INTERBUS ST modules, with fault detecting and compensating BK interfaces at key points, BOC Edwards reduced the hard wiring assembly necessary with cumbersome parallel wiring and wiring loom architectures. "We estimate we will now save one week's worth of work during installation," says Lanaway. "We have already experienced time savings of one day during our in-plant test process. The field bus installation makes it easy to change installation configuration and make future updates. In addition, with less wiring, we anticipate a reduction in the amount of wiring errors. Depending on the scale of an installation, from 50 to 70% of wiring can be saved."

INTERBUS ST not only eliminates extensive freeze-dryer parallel wiring looms but provides fault detection and compensation.

Flex sensor to investigate sleep disorder

By Rick DeMeis, Senior Editor

Costa Mesa, CA--Since Design News last visited the topic of band-aid-like wearable sensors (1/5/98, p. 71), the National Institute of Neurological Disorders and Stroke (part of the National Institutes of Health), in April, awarded developer Irvine Sensors an approximately $750,000 Small Business Innovation Research (SBIR) grant to develop a prototype of and demonstrate an untethered sensor to diagnose sleep disorders. The device will measure electromyogram (EMG) signals that control the eyelid.

The first year of the 24-month grant will see an advanced ASIC/flexible substrate breadboard prototype built. Scheduled after the second year is a fully miniaturized flexible silicon-circuit pre-production prototype with a final form factor. Another six months to a year development after that should result in a refined prototype optimized for manufacturing, says Irvine Sensors' Manager of Technology Development Volkan Ozguz, "We are pulling our technology solutions in flexible silicon off the shelf and learning biomedical applications. But waiting for funding, not technology, is the key pacing factor."

Thin is in. Ozguz notes the company's patent-pending silicon thinning technology is fast and cost effective to realize practical results. "You start with a standard, 25 mil (625 µ) thick silicon wafer, six or eight inches in diameter. The process is based on 90% mechanical thinning and maintains electrical and mechanical integrity of the silicon. A wafer and all the dies on it are processed in a couple of minutes."

The dies are then mounted on a 2-mil (50 µ) flexible Kapton substrate. A compliant, low-temperature epoxy holds the two. He adds, "The epoxy is anisotropically conductive, like a series of small wires, it conducts in only one direction." The face-down-mounted chip is mechanically and electrically mated.

Irvine Sensors is partnering with Altec (Boston, MA) for the electrode/skin interface experience this biomedical sensor company has. The team envisions an EMG sensor about 15×30 mm that can be worn on the temple area for eight hours sleep duration. Available flexible batteries will power the device.

Ozguz says the data retrieval mechanism is not yet set. Options include removing the flash-memory equipped sensor and taking it to a doctor or clinic; transferring via modem; or downloading into a PC in the patient's home for several days of data storage. He notes patient computer literacy will be a factor in what method is used. The flash memory allows for power-free data storage.

Lifetime testing will also be part of the SBIR program. The sensor will have to be durable to withstand repeated sterilizing, much like electrocardiogram sensors. A matching $200,000 grant from the State of California funds concurrent production-device engineering development .

Under its Silicon Brain^TM Initiative, Irvine Sensors is expanding flexible-silicon technology to electronically mimic the human central nervous system. The company stacks silicon layers in modules such as for a wearable computer being developed by Boeing. Ozguz notes that these stacks, made up of layers of highly integrated processors, are physically much like the human brain, which is nerve-cell layers folded upon one another.

Fiber-optic transducer aids heart monitoring

Walled Lake, MI--Fiber optics has fueled the growth of the world's communication networks--and is finding increasing use in medical imaging, diagnosis, and therapy.

Although still in development, a new application for sensor technology is emerging that uses fiber optics for intravascular pressure measurement. It has the potential to exceed the performance and cost effectiveness of any pressure measurement system in cardiovascular applications, claims developer Sentec Corp. (Walled Lake, MI).

A prototype fiber optic MEMS pressure transducer has been developed with a diameter of 0.8 mm (small enough to be inserted into blood vessels--arteries, veins or the heart chamber itself) and designed to measure pressures of 0 to 300 mm Hg.

Researchers hope that the new sensor will be placed on the tip of guidewires used in angioplasty surgeries to measure pressures during the procedure to unclog arteries. The system could find use in monitoring after heart surgery, when pressures within the heart chamber must be taken continuously for 72 hr to make certain the heart is recovering properly.

The design is based on a movable, metallic ribbon which works as a reflector to transform the pressure into a light signal. In laboratory tests conducted by Baylor College of Medicine in Houston, TX, the sensor showed high sensitivity and low noise of about 1 mm Hg over the 0 to 300 mm Hg pressure range.

Underwritten by a grant from the National Institutes of Health Small Business Innovative Research Program, Sentec Corp. has worked on development of the fiber optic pressure catheter for three years, says researcher Takeo Sawatari, manually assembling prototypes which have been tested through Baylor College of Medicine.

"The original application," says Sawatari, "was a monitoring probe instead of a fluid filled catheter--a device which is accurate and disposable without the fluidic lumen which can create calibration problems. Our goal is to produce something which is superior and more cost effective.

"The trick is to make a small and highly accurate pressure sensor which is also stable," says Sawatari. The sensor must also enable pressure readings, which are independent of temperature changes in the range of 30 to 50C.

A fiber-optic pressure sensor holds the benefits of safety with no electrical connection to the body. Since its primary signal is optical, it is not subject to electrical interference. The optical leads, very small and flexible, can be included in catheters for multiple sensing. Materials suitable for long-term implantation, such as plastic, can be used in their fabrication. These sensors are sufficiently simple in their design to be disposable.

The sensor operates using white light from an illuminator which passes through a coupler, connector, and a fiber to reach the other end of the fiber, where the sensor head generates "white light fringes." The fringe information is reflected back through the fiber, the connector, and the coupler to spectroscopic detectors. The detectors read the spectroscopic fringes and a computer determines the contrast of the fringes and converts the contrast into a pressure measurement. The contrast varies as the pressure changes and thus the measured pressure is obtained.

The sensor uses a ribbon reflector, which is underneath a polyurethane window, as the key sensing element that translates its mechanical motion, due to pressure, to an optical intensity variation of the return beam. The end of the fiber is coated with a thin film which works as a Fabry-Perot interferometer. It sends back a fixed "white light fringe pattern," which is not affected by the measurement variable (pressure), in addition to the reflected light beam from the reflector, which is modulated by pressure.

The contrasts of these fringes, which are observed through the spectrometer, vary as a function of the amount of light reflected from the ribbon. Since the fringe contrasts are independent of the first order spectrum change, or source fluctuation, one can measure pressure without being influenced by fiber bending or source fluctuation. To further reduce the fiber bending effect, a fiber connector is devised in such a manner that inside the connector, the fiber is sharply bent, curved, or looped, so that the higher order modes of the fiber leak out. Temperature drift is eliminated by the creation of a vent from the sensor head to the outside atmosphere to keep the inside pressure stable at atmospheric pressure.

According to Craig J. Hartley, Professor of Medicine and Cardiovascular Sciences at Baylor College of Medicine, who has conducted animal tests on the catheter for over a year and a half, "we are encouraged by the process and its potential." Hartley has used the 1.4 French microtip pressure catheter to obtain pressure readings in mice hearts.

The Sentec fiber-optic blood pressure monitoring system includes a sensor catheter, computer with data acquisition board, and optical components.

Classroom design creates innovative ideas for emergency care

Pasadena, CA--Students at Art Center College of Design recently developed concepts for products that will be used in pre-hospital emergency medical care as part of a 14-week educational project sponsored by a non-profit Advanced Technology for Emergency Medical Services consortium, or EMSAT.

The quality of emergency medical care has emerged as a crucial issue as hospitals look for ways to down-size their trauma units and restructure pre-hospital care. The EMSAT project brought together healthcare providers and product designers to find innovative solutions for the improvement of future pre-hospital care. Human, environmental, mechanical, and electronic factors were taken into consideration by the student designers. The students also researched the emergency medical equipment market and defined the manufacturing viability of their concepts.

After students developed a half dozen ideas, EMSAT members gave them feedback and direction on final product design. "The goal was to let them run with their creativity rather than restrain them in their development," says Bruce Jackson, EMSAT President.

As part of their research, students took ride-alongs with actual trauma patients in ambulances and a medical evacuation helicopter. Emergency medical care providers such as paramedics, trauma center nurses, and physicians guided students and provided them with additional information on the particular needs of the field.

"The students' designs were innovative and well within the realm of current technological possibility at the same time," commented Tom Scott, medical transportation consultant.

Dr. Bill Koening, director of the Emergency Department at Long Beach Memorial Medical Center noted the potential applicability of many designs. "The work clearly illustrates how the prehospital care industry can provide more patient friendly and cost-effective medical care in the future."

"Bioscan," a compact, hand-held portable imaging device and scanning unit for use in a wide variety of field conditions. Using radar technology to image both soft and hard tissue, this device computes an image that can be viewed in 3D, thereby ensuring quick and more accurate patient diagnosis. The interactive LCD touch screen also allows the user to select and transmit visual images via satellite to the base hospital for diagnosis.

An ergonomically designed laryngoscope with a specially textured rubber handle grip. The frontal area of the die-cast aluminum blade is made of an elastomeric material to provide protection for the patient's teeth. A small light in the base of the handle provides general illumination to the patient's mouth. Fiber optics route light directly on the throat cavity, providing the physician with a clear view of possible obstructions during entubation.

"Scorpio," a compact intravenous (IV) tube administration system composed of a flexible, easy to clean polypropylene arm-guard attached to a disposable splint. The splint serves to stabilize the patient's arm as well as the IV tubing during transport to the hospital. A built-in container on the splint itself provides a secure area for needle storage and disposal. The arm guard contains infrared lights to assist with IV insertion. Also included are devices that monitor oxymetry, pulse, and IV flow rate.

A compact, self-contained life-support system that attaches to a patient's leg to allow emergency medical technicians maximum patient access. The "Extracorporeal Mechanical Circulatory Support System" is a portable, disposable bypass system that acts as the patient's heart and lungs in a catastrophic emergency. A catheter shunts blood from the patient's femoral artery to a centrifugal pump that reoxygenates, then recirculates it. This device would be used en route to the hospital and into surgery.

Prosthetics get a composite assist

Poulsbo, WA--Strength and durability prove essential ingredients for prosthetic components that act as the structural connection to a prosthetic foot. For instance, the amount of force and weight applied to a prosthesis can equal up to three times a person's body weight.

Finding the right material for such an application that also would reduce manufacturing costs led Seattle Orthopedic Group to a long-glass, fiber-reinforced nylon 6/6 composite for the design of its ankle blocks and laminating cores. These components attach the prosthetic foot to the residual limb. For this project, Seattle Orthopedic engineers selected Verton® RF from LNP Engineering Plastics (Exton, PA).

The company originally machined the ankle blocks and laminating cores out of unfilled nylon 6/6 rod stock. "In a cost-saving move, we made the decision to injection-mold these components instead," says Stewart Atkinson, engineer, research and development. "We soon discovered, however, that the molded nylon 6/6 lost some of its required properties. To increase the strength, we went to the glass-filled composite. It not only absorbs the shock loads, but enhances endurance."

Such lower-extremity prostheses are referred to as exoskeletal--all of the structural strength is obtained through the outer surface. "It's an old-fashioned way to make a prostheses," Jennifer Dowell, staff prosthetist at Seattle Orthopedic, explains, "but such products are still employed about 20% of the time."

Use of an ankle block or laminating core component depends on how much clearance you have. For example, if the amputation is closer to the ankle where there isn't a lot of room between the top of a prosthetic foot and the bottom of the residual limb, a laminating core works best, since it can be cut to any height. An ankle block serves the same purpose when the clearance is greater. The block's composite core gets a coating of rigid polyurethane foam for added strength.

By switching to injection-molded components, Seattle Orthopedic realized an added benefit--lower manufacturing costs. "It has eliminated washing," says Atkinson. "When we machined the components, coolant helped prevent the nylon from building up on the cutting tool. The coolant then had to be scrubbed off or the rigid foam wouldn't adhere. Injection molding also reduced the time it takes to process the components."

Solid-state cooling shapes operating room mattress

By Charles J. Murray, Senior Regional Editor

Charleston, SC--Employing solid- state cooling instead of a conventional refrigeration system, engineers have designed a new thermal mattress that incorporates more features and uses less floor space in the operating room.

Designed by engineers at the Hill-Rom Co. Inc., a subsidiary of Hillenbrand Industries, the new mattress includes features that heat, cool, and help position a patient on the operating room table. In the past, hospitals have used two or three separate products to accomplish all that. At the same time, however, the new mattress's cooling system takes up less than half the floor space of conventional compressor-based refrigeration systems.

Known as the contOR^TM table surface, the new product incorporates the features of a heating/cooling system, a vacuum bag, and polyurethane foam. The vacuum bag and foam help relieve pressure on anesthetized surgical patients, who, in some cases, do not move for more than three hours at a time. The heating/cooling system helps to keep patients warm during long operations, or cool in cases such as open heart surgery. Previously, all of those systems were independent and separate.

One of the keys to the creation of the new product was the development of a liquid chiller for the heating/cooling feature. To minimize the size of the liquid chiller and enhance its reliability, Hill-Rom engineers employed a novel approach: They used a solid-state cooling system.

Designed by engineers at Chicago-based ThermoElectric Cooling America (TECA), the system chills the coolant liquid in the channels of the mattress. It measures about 8 inches square by 10 inches deep.

Had it used a conventional compressor-based system instead of solid-state cooling, it would have been roughly the size of a window unit air conditioner, engineers say. "The solid-state cooler eliminates a lot of bulk and size," notes Karl Caldwell, senior project engineer specialist for Hill-Rom. "It also eliminates the potential risk of Freon leakage, which you don't want in the operating room."

Solid-state cooling:

How it works

Most engineers are familiar with the traditional forms of refrigeration: The refrigerator's condenser transmits heat; the evaporator cools.

But what's solid-state cooling? "Many engineers aren't familiar with it," notes Andy Brecklin, vice president of engineering for ThermoElectric Cooling America (TECA) Corp.

Solid state--also known as thermoelectric--cooling has much in common with traditional refrigeration. Only the means is different. Instead of a refrigerant, such as Freon, the thermoelectric cooler employs two dissimilar semiconductors. As electrons pass from one semiconductor to another, the junction between them grows cold. In that sense, the junction behaves like an evaporator. And a dc power source, which pumps electrons into the device, plays the same role as a conventional compressor, which pumps refrigerant.

Heat or cold is then transmitted to associated devices through a heat sink, instead of conventional condenser fins.

The result is largely the same as a traditional system--without the bulk and chemicals. "When you put current through them, you create a temperature differential, and then you transfer heat from one surface to another," Brecklin says. "In that sense, it's no different than a conventional refrigerator."

CAD increases design trials

Oxford, CT--Bone cement--a dangerous and unsophisticated, yet vital, part of implant surgery.

Seeing the need to improve the cumbersome process, Jay Seaton, president of Immedica (Chatham, NJ), approached Donald Barker and James Gleason of Creative Product Development, Inc. (CPD, Oxford, CT), about developing an easy-to-use bone cement mixer. "The product originated because of surgeon concerns for both operating room safety and material consistency from patient to patient," says Seaton.

Barker and Gleason spent four years asking such questions as: "What is the safest and most effective way of mixing the liquid and powder?" "At what speed?" and "How can it best be inserted into the bone cavity?"

By experimenting with gears, materials, shapes of paddles and augers, mixing and dispensing speeds, they developed the twistOR^TM. This hand-held, disposable power mixer and dispenser looks deceptively simple. But the group developed more than 20 designs using 2D and 3D CADKEY products from Baystate Technologies (Marlborough, MA) before arriving at just the right helix pitch and distance, the optimum rotating speeds and direction.

Doctors use cement to secure implants in the body. A doctor must first drill and ream the bone, add cement, and then the implant, which the doctor holds in place until the cement sets up. A young person usually doesn't require cement because the bone quality is good and will quickly regenerate to encase the implant naturally, says Barker, president of Creative Product Development. Older people, on the other hand, need this process.

Physicians commonly make bone cement by mixing a toxic liquid (methyl methracrylate) and powder (polymethyl methacrylate methyl methacrylate ) in an open bowl with a spoon or with a hand-crank device. Due to the toxicity of the monomer or liquid portion of the mixture, if the cement accidentally spills, the operating room must be cleared immediately. After mixing, the cement is placed into a caulking gun and inserted into the bone cavity. Another method is to slide a cartridge of cement into the gun chamber after the cartridge has been put through a centrifuge to pull the air out. The least amount of air makes the best cement mantle, or adherent for the implant.

With the twistOR, the liquid and powder are mixed in an enclosed container that converts to a cement dispenser. The CPD design is basically a plastic bowl with a mixer or paddle. The powder is poured into the bowl through a funnel. The doctor adds the liquid, screws on the top, and attaches a vacuum hose to remove the air. Next, the mixture is mixed. A power tool resembling a drill without the bit sits at every implant workstation so the doctor can drill and ream the bone to the right fit. The physician attaches the power tool with a Hudson fitting at one end of the twistOR.

After approximately one minute, the substance is completely mixed. Next, the doctor places the 7- to 8-inch nozzle on the other end of the bowl and the cement mixer becomes a dispenser. Again, the physician squeezes the trigger on the power tool and the helix blade forces the cement into the cavity. Because the mixer is made out of plastic, it is completely disposable and inexpensive.

The helix. One of the challenges for the bone cement mixer was designing the auger and mixer paddle. "We must have had at least 20 different versions over a four-year- period before we came up with the right design," says Gleason, project manager. "Originally, we had a very simple paddle and auger design. The first paddle was flat. But this didn't work because it didn't force the material to the auger for dispensing."

They began the auger in CADKEY Wireframe to visualize what they wanted but soon switched to solid modeling. "We've found that when a design requires a lot of plastic parts, we can work best in solids. If a project involves designing a machine, we do quicker sketches in 2D," says Gleason.

In this case, "we quickly realized that we couldn't machine the part so we designed it in CADKEY Solids and FastSURF instead. We drew different pitches and every time we redid the solid model. This was one of the nicest things about CADKEY. It has a built in Helix Spline function so that changing pitches, lengths, and spacings was easy. All I would have to do is extrude a helix path. This allowed us to experiment with all types of designs. We looked at other CAD systems. But when I asked them to make a helix, they just snickered."

An important consideration was how fast the auger and mixing paddle needed to spin. "We experimented a lot with different drill speeds," says Barker. After much experimentation, they decided the auger and the paddle must move in opposite directions and at different speeds. The paddle needed to move slowly so it wouldn't whip the material and add air, while the auger needed to move fast enough to create a quick dispensing speed with the correct pressure. When doctors use the cordless power tool to spin the auger, this becomes a direct drive. Different-sized gears in the top of the cap of the cement mixer spin the paddle in the opposite direction and at a different speed.

Beginning in wireframe. The group started in 2D and then moved to solids for later designs. "In the beginning, we were still in the experimental stage," says Gleason, project manager. "We were thinking of mixing cement only. The quickest way for us to think about mixing cement was in 2D. It is so much quicker for people to think in 2D because that is the way they are used to thinking."

And this is how people at Creative Product Development produce their projects. "Most of our jobs are inventions," says Barker. "So even if we have an idea where we're heading, the product always changes." For this reason, they create and design in 2D, do a prototype, then go to solids if needed.

"We've had CADKEY since version 2 came out. We think it's made for what we do. We train people on it as a side business. It's so easy to learn," says Gleason. "We've had a dozen or so people start with our company saying the CAD system they used at their previous employer was the greatest. Within a week of working with CADKEY, they are claiming that CADKEY is the greatest."

So far, the bone cement mixer has received an overwhelming response. In the two shows where it has debuted, "doctors love it," Barker says. "This simplifies the process and makes it easier and safer." Creative Product Development Inc. expects to have the patented twistOR on the market later this year. Immedica is currently taking the device through U.S. FDA approval process and sterilization testing.

MRI bearings have non-magnetic personality

Santa Monica, CA--Magnetism, as far as personality goes, is usually a good thing. But bearings used in magnetic resonance imaging (MRI) machines require something more subdued.

Toshiba America (San Francisco, CA) manufactures MRI machines, which use strong magnetic fields to make images of the body's soft tissues. The machines feature a table bearing that has a 360° range of motion. Because of the machine's magnetic fields, the bearing had to be nonmagnetic so as not to interfere with the fields.

Toshiba needed a supplier who had been making nonmetallic bearings, a relatively new technology compared to metal bearings, for use in the MRI machines. Busak+Shamban provided Toshiba with custom Durobal® bearings constructed of thermoplastic and glass, which can move in any direction on the MRI machine bearing surface.

Busak used standard acetal thermoplastics, along with glass, to create the bearings, which the company buys from the manufacturer and blends in their own ingredients. "In this way, we custom-formulate our own bearing compounds," says V. Eric Long, product manager for Busak+Shamban bearing products.

Typical metal ball bearings consist of an outer and inner race, a ball, and a retainer cage. The Durobal thermoplastic bearings used in the MRI machines, in contrast, feature smooth sides and two rolls, or wheels, underneath. This allows the bearing to move in all different directions, as opposed to regular bearings which move on an X-Y axis, forward and sideways.

Other advantages of using the Durobal bearing, Long says, include self-lubrication, zero maintenance, elimination of the corrosion found in metal bearings, and noise-free operation. "The low noise factor is important when you work with patients," Long adds.

While the initial cost of thermoplastic bearings can be higher, the cost over time is lower due to reduced maintenance, Busak+Shamban can custom-design and manufacture bearings to fit the needs of individual MRI equipment, or can modify off-the-shelf products. The company injection-molds the bearings and can automate their production. "Sixty to 80% of our bearings business is customs," Long says. "We work with design engineers to design and custom-fit our bearings with their applications."

CAD combines many instruments into one

Tarrytown, NY--Daily, hundreds of blood samples pass through large blood analyzers. Each analytical instrument examines the sample for separate parameters. This process is time consuming, labor intensive, and requires many instruments for one sample.

For years, the medical community has requested an easy-to-maintain analytical system that would perform more than a single analysis. "We've made analytical blood systems and instruments before, but each would perform a certain type of test and that was all," says Wallace McLeod, manager of CAD and documentation at Bayer Business Group Diagnostics. "Our customers were looking for something more." They will soon have their wish. Bayer plans to release the ADVIA® Integrated Modular System (IMS) late in 1999.

The ADVIA IMS combines clinical chemistry and immunoassay testing in a single instrument. It has more than 3,000 parts and is 8 to 10 ft in length. It may sound big, but is significantly smaller than what is currently offered, as the ADVIA IMS combines two large systems into the footprint of a single unit of equivalent size.

Everyone wants to do more in less space. The medical community is no exception. To put several testing procedures into one unit, Bayer decided on a modular design approach. "We can insert Module A or Module B depending on which test the customer wants to run," says McLeod. "The modularity of the system is different than anything else offered today. This makes it easy to service and puts some redundancy into the system so there is less downtime."

Engineers designed the ADVIA IMS to include a single sample transport and processing system that uses built-in robotics to move samples individually from the loading area to the modular processing engines. These analytical engines can perform clinical chemistry plus homogeneous immunoassay testing, or heterogeneous immunoassay testing. Each 22-inch-long module can accommodate up to 36 different reagents in individual reagent storage areas, as well as pipetting stations, incubation, and measurement capabilities.

Tubes of blood collected by a phlebotomist are labeled with a patient ID number and sent to the lab for analysis. Before the ADVIA IMS, each sample would likely end up being analyzed by a different instrument, each handled by a separate lab scientist. Now robots do much of the manual work. The chemistry module and the immunoassay module sit side by side. The system automatically sends each sample to the proper module for the test requested.

At the beginning of the project, Bayer Diagnostics Lab Testing Business Segment had just standardized on I-DEAS from SDRC (Milford, OH). "We had a lot of different CAD programs before," says McLeod. "But we wanted to use just one where we could do full solid modeling."

Bayer chose I-DEAS because it had all the tools the company needed. The company particularly liked I-DEAS' Team Data Management (TDM) feature. Design teams working simultaneously can use TDM for reviewing or revising engineering documents. "TDM organizes engineering data the way Metaphase organizes documentation for every aspect of a project," says McLeod.

McLeod also appreciated how SDRC came to Bayer Diagnostics to help train. "This way our employees used I-DEAS in our environment, learning it in context the way we do things," he says. "This gave them a jump in what was needed." To run I-DEAS, Bayer Diagnostics chose SGI Unix workstations.

Because space was such a factor, Bayer Diagnostics allocated a certain amount of real estate to each engineer. All parts of the unit were developed simultaneously. "This made it critical for everyone to communicate with each other and see the other's part of the project," says McLeod. Each person had to ask, "Who is working on components next to my design? Will my components interfere with their design or vice-versa?" It could be as simple a process as passing a cable through two different modules. But communication was key. "This was also a challenge," says McLeod. "Most people were used to working independently. It took a while for engineers and designers to talk to each other."

After the design was finished, Bayer Diagnostics used I-DEAS to produce a virtual prototype. "This saved a lot of time in our schedule, because we could do all the modeling on the computer," McLeod says. "However, it is hard to quantify the amount of time saved because we have never run an equivalent project without using modeling," he adds. Now that Bayer Diagnostics is up and running with I-DEAS, the Lab Testing Segment plans to implement SDRC's Metaphase project data management technology. "This is the best way to handle I-DEAS documents," says McLeod. "Plus its management is compatible with the worldwide Bayer AG plan." Once in, Metaphase, with its certified SAP interface, will be integrated with a SAP system.

Polymer breathes new life into medical device

Corby Northants, UK--Dubois Ltd. has developed what it refers to as a breakthrough in a medical breathing system design. The new disposable breathing system, used on patients in operating rooms and intensive care units, promises greater patient comfort and lower supply costs for medical purchasing agents.

In Dubois' new design, the Gaunt "Swivel Y," aliphatic polyketones provide the right combination of strength, flexibility, and resilience that allow the use of lips and undercuts for snap-fit assembly--without the risk of damage or distortion to the finished product. Also, the polymer's relatively high lubricity lets the Swivel Y joint move easily, while ensuring a tight fit to minimize leakage. The material specified by Dubois engineers: CARILON supplied by Shell Chemicals (Houston).

Prior to the introduction of the Swivel Y circuit, Y piece connectors were either fixed, rigid plastic components or heavy metal and rubber devices that often restricted airflow due to poor internal design. Before investigating CARILON, the product evolved through numerous redesigns and was in a total stop-sell situation. "If we had not been able to fix the design, we would have had to completely withdraw from the market, writing off about $300,000 in tooling costs," says Anthony Fraser, Dubois' sales and marketing director.

Shell worked with Dubois engineers to help establish the material's optimum molding characteristics. Keith Stone, Shell's development engineer, reports that CARILON reduced cycle time on the tools. It also earned for Dubois an exclusive distribution agreement with Pall Medical, a large medical-device manufacturer.

"Our final design is a cost-effective, disposable component with the functionality of a heavy, reusable Y piece, but at the cost of a disposable, fixed Y," notes Fraser. "We claim that our disposable Y circuit is the best on the European market, possibly in the world."

Swivel Y connector made of an aliphatic polyketone replaced a heavy metal and rubber joint in a disposable breathing system that won the designer an exclusive medical-device contract.