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Hydroforming Eases Production of Titanium Housings for Infusion Pumps

Originally Published MPMNMarch 2002

PROFILE

Hydroforming Eases Production of Titanium Housings for Infusion Pumps

The raised septum on Arrow International's pump housing enables reservoir refill to occur with a changing of needles. (click to enlarge)

Titanium has become the material of choice for implantable devices because of its strength, weight, and inertness to body fluids. There is a trade-off, however: the material can be difficult to work with, particularly when the application involves a small product with intricate parts. That was the challenge faced by a company developing a titanium housing for an implantable drug-delivery system. It found a solution in a technology that uses hydraulic pressure to impart a form to titanium blanks.

The Model 3000-series implantable infusion pumps were developed by the Implantable Drug Delivery System division of Arrow International Inc. (Walpole, MA) to treat patients who are undergoing chemotherapy, in need of chronic pain management, or suffering from spasticity. The constant-flow pumps have fully contoured circular titanium housings that provide smooth, sloping edges between surfaces. Titanium is "ideal for devices that will remain in a person's body for the rest of his or her life," says operations manager Daniel Krebs. But it can be a difficult material to process, he adds. Arrow turned to Hudson Tool & Die Co. (Ormond Beach, FL), whose hydroforming technique proved to be a valuable asset in the development and production of the housings.

Under Pressure

Arrow International's implantable pump housings were developed using Hudson Tool & Die's hydroforming process.

The hydroforming process forms a heated metal blank into a desired shape by means of hydraulic pressure. Basic system components are a lower die, guides, a rubber diaphragm, and an upper ram-punch. The metal blank is placed on the lower die and held in place by guides. The rubber diaphragm is placed on top of the blank and the punch compresses the diaphragm against the blank, which then flows into the lower die to form the desired shape. Changing the hydraulic pressure allows the fabricator to form extreme profiles that are not economically achievable with conventional forming techniques. "Hydroforming allows us to produce highly precise parts typically needed for medical applications," says Hudson engineer Jim Wagner. "It also eliminates one side of the tooling, significantly reducing cost."

Hudson Tool has an in-house facility dedicated solely to metal stamping and heat-treating. According to the company, the integrity of the furnace is maintained because it is used only for stainless-steel and titanium parts. "We were extremely impressed with Hudson's dedicated 'plant within a plant' for medical parts," Krebs explains. "In the medical industry we are always concerned with quality and contamination issues, and Hudson has taken the necessary steps to address these critical concerns."

For the Arrow project, Hudson Tool has developed special baskets to hold the pump housings during the heat-treating process to ensure that the parts are treated uniformly. Also, the baskets are used only for titanium parts to eliminate the possibility of cross-contamination.

Housing Starts

The pump housings consist of a can, or bottom body, and top, or upper cover. The can has four small suture loops attached to it and ranges from 61.2 to 86.4 mm diam and 19.7 to 27.4 mm in height, depending on pump capacity. The upper cover ranges in height from 10 to 12.3 mm. A small recess along the top lip of the can ensures a tight seal with the upper cover.

The upper cover has a palpable raised silicone septum that is 10.2 mm diam on all models. Single-septum access makes reservoir refill a matter of changing needles rather than searching for injection ports, as on conventional pumps. For bolus injections, a special needle is used that has a side hole to allow the medication to bypass the drug reservoir and flow into the patient's body.

"We needed a supplier that could produce the pump housings quickly to meet product introduction schedules," Krebs continues. "We were fortunate to find a metal parts producer that could improve the housing economics while maintaining close tolerances and high quality."

Katherine Sweeny

Copyright ©2002 Medical Product Manufacturing News

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