(Surgeon+chemist) X designer=medical innovation

Noted Wilmington, DE, breast-cancer specialist Ruben Teixido's "boyhood curiosity" was getting the best of him. A well-experienced surgeon, he had decided to do something about a long-standing annoyance in many surgical procedures.

The result: a plastic surgical retractor that eliminates the problems of electrical and heat conductivity during operations.

Conventional retractors--stainless steel, clawlike devices--spread tissue to reach an area of interest. Assistants often pull on these for long periods during an operation.

That's not the only problem. "In some types of surgery," Teixido notes, "an electrical scalpel or needle, with a precisely controlled current, is used to cut and seal tissue with heat." This heat is generated by a current passing from the device into the patient. In breast surgery, despite care on the part of a surgeon, slim 2-mm blades and needles often mean "operating in narrow canyons where the scalpel can come close to the metal retractor, electrically discharging through it. The resulting burns add time to the healing process," says Teixido.

He figured a non-conductive plastic retractor could solve the problem, as well as not conduct heat where it was not wanted, such as into a tumor being removed for biopsy. "Heat can distort the tissue architecture, affecting a pathologist's diagnosis," says Teixido. And such distortions may not ensure that a narrow, clear margin is cut around the tumor--as in lumpectomies, where a surgeon removes only small, 10- to 20- mm blocks of tissue.

To get his idea off the ground, Teixido called Ruskin Longworth, a life-long friend in Wilmington and a retired Dupont chemist. After hearing of the surgeon's desire for a plastic retractor, Longworth decided that General Electric's Ultem(reg) 1000 polyetherimide resin would be the appropriate non-conductive material that could withstand sterilization and still keep its strength. With a processing temperature range of 640 to 800F, Ultem was already accepted for other autoclavable surgical applications.

The two friends formed a partnership and, in Teixido's words, "to get it out of the 'garage stage', "took it to a patent attorney. By mid-1997, he in turn led them to product-development specialist Paramount Industries (Langhorne, PA). The firm was experienced in design of hand-held surgical devices, keying on ergonomic factors. Its previous designs included toothbrushes and hand-held instruments.

Within 10 days of the initial meeting, Paramount produced 18 retractor concept sketches and hand-carved foam mockups. Thus began what Teixido calls "a trip to discovery. The collaboration became a very pleasant experience. We were talking to people eager to understand and interpret our ideas."

Jim Williams, Paramount CEO, says the two inventors conveyed their objectives regarding the use of plastic, ergonomics, and light weight. He adds that Teixido also wanted to mount an air evacuation tube on the retractor. This draws off any smoke produced by electro-cutting. OSHA regulations were now dictating its use to prevent the airborne spread of viruses, including AIDS and hepatitis. Such tubes were being mounted directly on scalpels, which was awkward and cumbersome for the surgeon, or were held by an assistant.

Paramount design and engineering manager Rich Upcavage says, "After talking about the pros and cons of the first foam study model, we created a 3D CAD solid model using SDRC's (Milford, OH) I-deas Master Series(TM)." For further ergonomic evaluation, they then made an exact physical model in plastic from the digital data set using the Selective Laser Sintering process from DTM (Austin, TX).

"This gave us confidence to machine Ultem 1000 for prototypes to use in clinical trials," notes Upcavage. "Because the prototypes would be sterilized for use within the body, no other material could have been used in the trials," he strongly emphasizes. "We had to use the actual material. It couldn't have been done with conventional rapid prototyping, or cast materials from rubber molds." And Jim Williams adds, "By direct CNC machining Ultem blocks, we didn't have to build tools to get prototypes into trials, saving about 12 weeks in the process. Time to market has always been [critical to] the way we operate." Upcavage concludes, "With CNC, the horse is back in front of the cart" when material properties are crucial.

By the time this is read--in well under a year from drawing approval last August--conventionally machined injection molding dies should be turning out production Ultem 1000 retractors and similar larger hooks for working deeper in tissue. In summing up, surgeon and inventor Teixido says, "This is not the discovery of America--it's just a refinement--but an extremely important one."

Non-conductive retractor enabling technologies

- Sterilization-resistant resin materials

- CAD solid modelling of ergonomic designs

- Laser sintering rapid prototyping

- Precision CNC machining of production resin

Medical-equipment engineering hurdles

Devices engineered to work inside the human body have to be made of stern stuff to meet several design objectives:

- Biocompatibility: Equipment in and near the body must not cause chemical and allergic reactions, nor cutting and destructive heating of tissue. Materials cannot leach in presence of body fluids and electrolytes.

- Strength: In doing the job safely, nothing can break inside the patient.

- Sterilization: One of several cleaning methods must be survivable without deterioration or color changes. These include exposure to a sterilizing gas; gamma rays; or autoclave heating in dry air (375F) or steam (275F).

- Ergonomics and biomechanics: Any device should be comfortable to use and functional.