Surgical devices thrive on concurrent engineering

April 30, 1997

When design teams at EES Endo-Surgery embark on new product development, members of the team are more likely to wind up in the operating room than at the drawing board. That's because EES, a Johnson & Johnson company (Cincinnati), specializes in taking current "open surgery" procedures, and converting them to endoscopic, or minimally invasive, techniques along with developing the instruments required to perform these procedures.

IMM asked Gary Knight, senior design engineer at EES, to explain what's vital for success in this market: "Our main challenges revolve around these criteria: meeting the surgeon's needs, compressing the concept-to-production cycle, and containing costs for an increasingly managed-care surgical environment. We've found that designing products concurrently with our suppliers' input helps us to tackle all three of these areas."

EES's forte is innovation, and according to Knight, it is somewhat forced into this arena due to the fast-paced world of medical technology. "We're still selling instruments we developed 10 years ago," he says, "but that's a small part of our business today." There are 250 people in the R&D group, and a total of 1000 employees at the Cincinnati plant site. Although no molding is performed inhouse, EES works with several custom molders and does assembly, packaging, and sterilization at its facilities.

Cross-functional teams are a mainstay here. These cross-functional teams consist of an entire R&D spectrum, from quality engineers to manufacturing integrators (those who move new products onto the production floor). Teams are focused on delivering a specific product in a set time, with input from marketing, a team leader, design engineers, manufacturing, quality, suppliers, and even industrial designers for ergonomic issues.

In the concept development phase, where designers are generating a new procedure and its devices, teams interact principally with one another and with material supplier Dow Plastics, says Knight. "Once we've finalized a concept and are ready to talk specifics about overall instrument design, we pull in our molders and toolmakers for their input on final part design. We explain the procedure and how the instrument will be used, then talk specifics about the way components will interact. This helps them to get a better understanding for what the critical dimensions are, and why we may need a specific shape or geometry."

In the course of development, EES conducts several pilot runs to produce molded parts for physical and functional testing. "As we get dimensions worked out and we're confident of the instrument's performance, we run the 'prototypes' through quality testing," Knight adds.

Design teams work with several key contacts at Dow Plastics - Karen Winkler, senior applications development engineer, offers input on materials options in light of design ideas and goals, helping design components and selecting materials, or modifying a design for a certain material (see sidebar); Nancy Hermanson, medical market technical leader, works directly with molders on processing issues; and Ed Haber, senior account manager, handles all commercial aspects.

Dow is part of EES's Supplier Alliance program, essentially an agreement in which Dow guarantees resin availability in return for EES consolidating the grades and colors it uses down to a select few. In addition to selecting these materials, EES also tested and characterized them according to biocompatibility protocols to help speed up product development. Now EES gets the material without having to spend several months resolving compatibility issues for a new product. "We can't afford to take six months trying to figure out if a material will meet the specs," Knight adds. If EES needs to develop a new material that's not on the standard list, its designers work with Dow apart from ongoing development projects.

Recently issued GMPs (good manufacturing practices) and pending FDA regulatory changes have altered the way EES designs its products. "One of the changes in FDA regulations that affects us more than anything else is moving the FDA's control back into our design process," Knight says. "The FDA now has the ability to question not only the manufactured product, but also how wall thicknesses, geometries, and materials were decided upon. As a result, we have made changes to the way we document our product design and development process. This may increase the level of paperwork, and does challenge us to keep the development moving at a swift pace."

What else lies in the future for endosurgical devices? Says Knight, "At EES, we're always looking at current 'open' surgical procedures to see if they can be done endoscopically, in a minimally invasive way. Size is important, and obviously the smaller the better. We've gone from instruments 12 to 15 mm in diameter to a standard today of about 5 mm in diameter. As the incision size continues to decrease, fewer stitches are required to close it."

From a materials standpoint, that means EES designers are looking for resins that offer higher stiffness and better flow into thin-wall sections. The thinner the plastic can be, the smaller the diameter of the incision. Winkler notes, "The biggest challenges right now are material-related: higher-flow materials that will process efficiently at thinner walls without trading off toughness and stiffness."

This is true across most of the molded medical device industry, according to Dow's Hermanson, who also develops new materials for the medical industry. She confirms that Dow's global product development team is currently working on a gamma-stabilized, high-flow PC. "Medical devices are going toward thinner walls and longer flow lengths that standard PCs have a hard time filling. Most medical devices today are also tending toward higher-cavitation molds, so an improved mold-release Calibre PC was recently introduced as well," she says. For more on medical materials from Dow, circle 236.

Dissection in a single shot

Designers at EES developed this vein harvester, an instrument used by physicians to extract a vein from the leg of heart patients to be used during bypass surgery. Using Isoplast polyurethane, instead of a plastics/metal combination, enabled the designers to change the vessel dissector, the trickiest part of the Harvester, into a one-piece assembly.

To illustrate the benefits of concurrent design, Gary Knight and Dow's Karen Winkler recount a recent project in which EES developed an endoscopic method for harvesting blood vessels from a patient's leg for use during coronary artery bypass surgery. The vein harvester allows physicians to make one to four 1-inch "access" incisions in the leg to extract the vein, rather than one long open incision, which would be prone to infection. A vessel dissector - part of the vein harvesting procedure - required a needle-like shape to allow surgeons to separate the vein from surrounding connective tissues. Several design and manufacturing concepts were being considered for the vessel dissector.

"My job was to help EES evaluate candidate materials," says Winkler, "including plastics, metals, or a combination of the two." The device was long and thin, potentially requiring two or three components made from different materials. EES's goal, however, was to make the dissector in one piece to shorten the development cycle. The challenge was finding a material that could do the job, yet still remain cost-competitive in the medical market. The main criteria for the instruments: ease of manipulation; thin enough to fit through the small incisions; strong enough to maintain force applied by a surgeon. Most important, the instruments could have no sharp edges that might nick, cut, or otherwise damage the vein and surrounding tissue.

Winkler realized that the tip geometry of the dissector exceeded the range of unfilled or even short-glass-filled resins. But a combination plastic/metal part brought on assembly and manufacturing hurdles. Her suggestion: a 40 percent long-glass fiber PU (Isoplast engineering thermoplastic polyurethane) for metal-like stiffness and flow rates capable of filling the single-gated tool.

"Instead of melting at processing temperatures, this amorphous material depolymerizes. Its molecular weight actually decreases as it is heated, improving flow rates. As it cools, the resin quickly polymerizes again and achieves its traditional toughness along with levels of stiffness more closely related to a crystalline resin."

Knight's group implemented the material suggestion and performed mold filling analysis before cutting the tool. "Simulation showed that we could fill the tool, but just to be safe, we inserted the last 1.5 inches of the mold so that if it didn't work, we could substitute a metal tip," he adds. "In actual mold trials, however, the polyurethane worked beautifully."

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