Replacing the surgeon's scalpel

One portion of the Hippocratic Oath physicians take is a vow to do no harm to the patient. Paradoxically, surgical procedures often require large incisions to allow surgeons access to specific organs. Much of the patient's recovery time is spent in healing these large cuts. Medical device designers are trying to minimize invasive procedures by developing endoscopic instruments that require only a tiny incision that heals quickly. These same designers are choosing injection molded plastic to house and support endoscopic equipment.

A recent entry in this field, the Ancure Endograft system from Guidant Corp. (Menlo Park, CA), exemplifies the trend toward less invasive surgery and offers a window on the need for teamwork in designing these devices. The Ancure system won a gold (first place) award in the 2002 Medical Design Excellence Awards competition presented by Canon Communications in June at the Medical Design & Manufacturing East show.

Deploying the Implant
Before we delve into the design and molding of this device, let's take a quick look at what it does. It is used to treat abdominal aortic aneurysm, a condition in which weakened walls of the aorta expand and threaten to explode. Without the device, a surgeon must make a large incision in the patient's abdomen to attach a blood-diverting sheath to the aortic wall.

Instead, the Ancure device requires only a 5-mm incision in the femoral artery (located in the leg) and is used in a stepped procedure. A catheter is inserted into the artery, and the sheath, or graft implant, is delivered to the aorta. It is remotely positioned, deployed, and fastened, and is used with a fluoroscope, along with markers on the product, that allow the doctor to see where the catheter and graft implant are located.

A relatively large-diameter graft and attachment system, up to 26 mm, is needed for the aorta. It collapses to less than 5 mm for delivery into the body. The delivery system handle includes numbered controls for manipulation and deployment of the implant, and clearly numbered safety tabs prevent out-of-sequence deployment. Benefits are said to include lower mortality, reduced complication rates, shorter hospital stays, and faster recovery.

Call for Design
When its in-house design engineers finished the functional engineering for the Ancure system, Guidant called Stirling Design to work on the housing, appearance, and user interaction issues. Other members of the design team included molder and tool designer Phillips Plastics, as well as resin supplier Bayer.

Loren Stirling, an industrial designer with more than 30 years of experience in plastics design, explains why the human interface portion of endosurgical devices is so critical. "In-house designers often deal with the total function and intent of the product. They must be focused on that part of it. Often, however, the rest of the human interface portions lose out to functionality. There is a balancing act that takes place between industrial designers and engineers to create the best product without losing functionality."

For one, this product had to be easy to use. "It's not what the surgeon is doing, but how they are doing it," says Stirling. "This instrument is essentially the handle for the puppeteer." The method of having a stepped process, a major part of the user interface, came out of meetings with Guidant's marketing group, which in turn interviewed doctors regarding their preferences. To add to ease-of-use, Stirling also minimized the overall size of the product after early prototype testing.

Another consideration was the material selection. The resin had to meet FDA requirements, structural requirements, and appearance standards. Says Stirling, "There is a brake that is under load constantly in the instrument's freestanding position. A surgeon releases the brake to place the catheter. Since this area is always under pressure, we needed a material that would not creep under load." Bayer provided material samples and documentation, and the team finally decided on an FDA-approved ABS blend.

Comfort was yet another target. "We made sure that the device felt comfortable in a surgeon's hand, and that any user could get a good grip on the pull rings, brake handle, and balloon actuator. We also eliminated sharp edges and flat parting lines to minimize flash," Stirling says.

Team Effort
Phillips Plastics' designers worked on design for manufacturability and assembly, adding draft and shutoff angles and determining nominal wall thicknesses. In addition, Phillips suggested P-20 tooling to meet the low volume requirements and time-to-market goals. Most tools were ready in four to six weeks, according to Steve Schultz, Phillips' project engineer.

Today, Phillips supplies Guidant with 21 molded parts, many of which have a sequence number printed on them to assist the surgeon in correctly deploying the implant.

All team members agree that the success of this breakthrough device required input from each party. "The only way to achieve the optimum product is to collaborate," says Stirling. Paul Bell, Guidant's design engineer adds, "We always strive to work cooperatively with our suppliers, but on this program, it went to new levels."