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issue: May 2003 APPLIANCE Magazine

Engineering Medical Devices
Taking Tooling to the Edge


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By tooling what some deemed impossible, patients are now able to recover more quickly after having an arterial puncture.


It can be stressful to undergo a diagnostic angioplasty or other procedure in which the femoral artery is punctured. Once the procedure is complete, patients often want to be up and moving as soon as possible, but the most commonly used methods to stop bleeding can be slow and uncomfortable. Traditional techniques include manual or mechanical pressure, such as a clamping device, and 4-8 hr of lying flat without moving the affected leg. St. Jude Medical, Incorporated developed the Angio-Sealâ„¢ vascular closure device to seal arterial punctures created during these procedures, helping patients hit the road to recovery faster and more comfortably.


The top of the letter "A" on the locking tensioner cap was trapping gas, and resin couldn't flow into that area. This problem was solved by thinning out the area around the top of the letter and adding some venting, which allowed trapped gas to escape.

The Angio-Seal uses a very small anchor, collagen sponge, and suture to stop the bleeding almost immediately. An added advantage is that the human body absorbs all device components within 90 days. Although St. Jude has been using this technology for 5 years, design enhancements - made with the assistance of Phillips Plastics Corporation - have made the current Angio-Seal device easier to use and more reliable. Phillips and St. Jude worked together to make improvements for ease of use and to incorporate multi-shot soft-touch features. In the process, the injection molder designed and built a multi-shot tool to address specific Angio-Seal requirements.

Complex Components

The redesigned Angio-Seal components have proven challenging due to their part designs, which require complex multi-shot molds. St. Jude chose multi-shot technology to give the updated Angio-Seal better aesthetic appeal and contrasting graphics. Although St. Jude has in-house injection molding capabilities, it selected Phillips because of its responsiveness, expertise in designing cutting-edge tooling, and a history of successful multi-shot molding programs.

"These are very difficult parts - multi-functional and tight toleranced," says St. Jude Medical's Design Engineer Jack White. "We have our own tool shop here, but we were overloaded and unable to build tools. We also don't have multi-shot capability at this time."

Although functional, the former Angio-Seal assembly was not as intuitive as the company desired. The new design, which simplifies how the Angio-Seal is used, incorporates a host of complicated features, resulting in a far more complex set of components than the previous design. To better understand the program's requirements, Phillips' project team met with St. Jude to learn how the Angio-Seal works and to determine critical features.

During this initial discovery phase, Phillips garnered support from disciplines as far reaching as design, prototyping, processing, and post-molding operations to provide the services St. Jude required. Based on information gathered, stereolithography (SL) and selective laser sintering (SLS) were employed to verify that proposed revisions remained within the parameters of the Angio-Seal's U.S. FDA-approved design. To change the functional aspects of the design would result in added cost and time to retest the components for regulatory approval.


St. Jude's Angio-Seal allows physicians to stop the bleeding instantly during diagnostic angioplasty and other procedures.

Seesaw Design

One of the greatest program challenges came with the locking tensioner cap, which snaps into its mating part with precision slots. To form the slots, a collapsible core was required, which at the time was deemed impossible by some injection molders. Phillips' tool designers devised a concept using pins and slides in a deceptively simple seesaw-type action.

By developing this new tooling concept, a design that was considered nearly impossible is producing parts today. If the parts couldn't be molded in this fashion, the solution would have been to mold two parts and either glue or sonic weld them together. Because of the difficulty of the desired design, St. Jude was initially dubious of the success of the proposed tool design.

In addition to the complexity of the tool design, there were traditional, yet complicated features with which to contend. One was with the graphics. The top of the letter "A" on the locking tensioner cap was trapping gas, and resin couldn't flow into that area.

"There are certain ways that the elastomer likes to fill, and we gave Phillips a carte blanche on how to achieve that," Mr. White says. "As long as the logo looked right and the part functioned the way we designed it, it was really a case of fit, form, and function. Phillips had to build the tool. We had the easy part."
This slight bump in the road was quickly resolved. Because the last place to fill is a thick section, the area was thinned out around the top of the letter. Some added venting allows trapped gases to escape.

Often, there are molding issues that cannot be avoided, but with early involvement, they are overcome with proactive solutions. For example, the Angio-Seal locking tensioner cap requires a valve gate that leaves a small mark on a visual surface. This was addressed by adding design elements to camouflage the gating mark. The dimples on the end of the part were designed to mask a valve gate. Without the dimples, there would only be the gate mark. Instead, a series of depressions were made and the valve gate was hidden in one of them.

The Angio-Seal components are molded in Phillips Plastics Corporations' class 100,000 clean room. Equally important to St. Jude is Phillips' ability to provide validation assistance. "Phillips validated the process because the parts are shot in-house," says Mr. White. "We supplied the data we needed, and Phillips set up the validation parameters."


Moldflow images were created to determine fill-time for the Angio-Seal device.

(Click here for a larger image.)

 

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