Medical Device Link.

Originally Published EMDM March/April 2004

ENGINEERING INSIGHT

Connectors that are moulded directly into medical equipment can resolve sterilization and design issues associated with conventional cable harnesses.

Mobile phones, laptop computers, and digital cameras all contain electrical connectors moulded into their enclosures. Cables are hidden inside hinges and shells, and behind displays, to save space, weight, and money. For similar reasons, electromedical instruments are increasingly adopting this technology.

The medical industry has seen a rapid rise in the use of electronics and sensors in catheters, defibrillators, monitors, and related products. More devices are transmitting and/or receiving electrical signals to and from the patient than was perceived possible just a few years ago. New medical chip sets are capable of handling multiple data channels; they also process a wide range of display information, machine orders, and pump signals. To perform these tasks, many probes, sensors, and detectors integrate the requisite wiring, cables, and connectors.

“Our built-in connectors are designed to be moulded directly into medical equipment,” says Robert Stanton, director of technology at Omnetics Connector Corp. (Minneapolis, MN, USA). The connector insulators are first assembled with pins or sockets that have been prewired or have solder lugs on the back, he explains. Mechanical assembly drawings are used to size and specify the internal fit of the overmoulded housings, handles, or probes that contain the connectors. The final probe or assembly is then moulded over the component. “Based on the application, customers can choose among a number of materials—from soft silicones to the hard glossy white plastics used in tool handles—for the outer shell,” adds Stanton.

Built-In Connectors Enhance Perfusion Monitor Probe Assembly

A perfusion monitor with built-in connectors in the probe assembly is one example of how this technology can optimize medical equipment. The product couples an instrument designed to withstand rigorous cleaning and sterilization with a disposable part in the electronic probe assembly.

“The insert portion of the miniature connector is overmoulded onto a part that serves as a connector and handle for the small electronic probe,” says Stanton. “In this case, the end of the probe contains a thermistor that changes electrically with variations of temperature.” A surgeon inserts the probe into a patient’s body to monitor blood and tissue temperature during a procedure. After the procedure, the patient end of the cable assembly can be discarded and the instrument cable disinfected for reuse.

Miniature circular connectors enable the design of quick-change probes and sensors for a number of medical diagnostics applications. The standard building sets of circular insulators have alignment keys in the insulators to provide error-free mating and easy attachment, explains Stanton. Socket shrouds protect the pin and socket elements. “We begin the integration process using these standard sets,” says Stanton. The internal fit of the overmoulded housing, handle, or probe is sized, and the outer portion of the equipment is then configured to suit the application.

The connectors are made with military-grade materials that meet the quality and reliability standards required by medical device manufacturers. The pins and sockets are fabricated from annealed beryllium-copper and are spring-tension controlled before being plated with nickel and gold. Circular insulators are moulded from a glass-filled liquid-crystal polymer that exceeds most temperature and chemical requirements required by industry. The Teflon-insulated wires are preassembled or supplied with solder cups to allow attachment during equipment configuration.

Omnetics engineers have extensive experience in the use of USP Class VI materials, adds Stanton, and they routinely offer assistance to customers seeking regulatory approval in the United States and Europe. Indeed, many of the assemblies have already passed reliability and quality tests needed to achieve US FDA approval. “Specific application testing and certification is all that remains for the OEM to ensure that the final design meets the new application needs,” says Stanton.

Medical applications in which built-in connectors are currently used include laser tool handles, probes, sensors, electronic catheters, extended optical inspection devices, and even robotic instruments. Bone-conduction hearing aids are good candidates, because they require tiny, lightweight, easy-to-mount parts. Surgical tools and ultrasound equipment use integrated connectors to enable rapid tool and head replacement.

Omnetics offers built-in circular connectors in three diameters and up to 27 positions in mated pairs at a 0.050-in. pitch. Standard wiring includes Teflon-insulated 26-gauge stranded wire to achieve maximum cable flexibility. Solder-cup connector shells are also available. The company routinely supplies custom wire and mechanical assemblies to the medical device and other industries.

To learn more about Omnetics Connector’s products and services, select #7 on the bound-in reader service card, or go to RequestLink at www.devicelink.com/emdm. 

Copyright ©2003 European Medical Device Manufacturer