LIFE-SAVING DEVICE COMES IN SMALL PACKAGE; UTILIZES BAYER POLYMERS
08 April 2003 - Bayer MaterialScience AG

Available in both automatic and semi-automatic configurations, the LIFEPAK CR Plus defibrillator is designed to be used by people - in the event trained professionals are not available - who come to the aid of a person suffering cardiac arrest.

'CPR, in cases of cardiac arrest, is not enough,' said Richard Cardin, Senior Mechanical Engineer for Medtronic Physio-Control. 'Prompt defibrillation provides the greatest likelihood of survival, and our devices are intended to meet the need for emergency defibrillation.'

To achieve the necessary ruggedness, as well as a small, more convenient size, Medtronic Physio-Control and the molder, Accurate Molded Plastics, Inc., used Bayblend® FR 110 resin, a combination of polycarbonate and ABS (acrylonitrile butadiene styrene), to mold the case for the LIFEPAK CR Plus. Another Bayer material, Makrolon® 2405 polycarbonate, is used to make the lid of the device.

These devices are relatively small, and that's why the PC/ABS material was used. Medtronic Physio-Control was trying to keep the cost low, so these devices can be more affordable for the general public, and in doing so, they put a large number of features into one part as opposed to making several pieces and putting them together. They also needed the fire-retardant properties available in the Bayblend FR 110.

Plastic and Polyurethane: a Winning Combination

The design features of the defibrillator case were challenging. Wire routing channels and mounts for the different components that snap fit into the case are molded in. The seals and bumpers are also integrated into the case, which is a function of using the combination of Bayblend PC/ABS material and a polyurethane.

The parts that make up the case for the LIFEPAK CR Plus are molded, and then in a second step, a layer of polyurethane is molded over the Bayblend PC/ABS substrate to provide both functional and decorative features to the defibrillator. The overmolded polyurethane adheres well to the Bayblend material, so no mechanical features are needed to hold the polyurethane in place.

The 4.4-lb. LIFEPAK CR Plus is just 9.5 inches by 8 inches by 4.2 inches, and is a strikingyellow and black. The yellow is the Bayblend case and the black is the overmolded polyurethane.

The device also has a lid that protects the defibrillation pads. One push of the On/Off button opens the lid and gives the rescuer access to the pads and turns the unit on. The lid is molded in Bayer's Makrolon polycarbonate.

The combination of the Bayblend and the polyurethane provides excellent impact strength and scuff resistance, which are very important to making this field medical device more rugged.

Design and Bayblend Benefits Reduce Parts and Handling

In addition to having the right mechanical properties - including providing consistent snap fit of components - Bayblend PC/ABS has good UV resistance. Prior to using the Bayblend resin, Medtronic Physio-Control used to use a material that over time turned a sort of greenish yellow. Bayblend PC/ABS stays true to its color.

During the m oldi ng process, insert molding is used to incorporate metal parts used for connector contacts, and five other parts are insert molded into the case - four into the Bayblend PC/ABS material and the other into the overmolded polyurethane.

Because they are able to mold in the additional parts, Medtronic Physio-Control doesn't have to inventory, handle and assemble them separately. Between the combination of the polyurethane and the Bayblend PC/ABS, they were able to eliminate 59 additional parts that they would otherwise have had to find a way to assemble and incorporate into the case.

Total assembly has been cut to 37 parts. Another benefit is that the PC/ABS allows for the parts of the Charge-Pak (battery re-charger) housing to be ultrasonically welded together.

Performance Materials and Technical Support

Dave Kosanke, Senior Process Engineer for Accurate Molded Plastics, said using the Bayblend resin offered processing, cost and performance benefits. 'It's our choice of material - because of its easy moldability and excellent impact properties for field use. The case needs to be strong, and wall thicknesses are just 90/1000ths of an inch.'

Kosanke said there are several components in the finished unit. 'It has three lenses in it, and the connector for the defibrillator pads used on the patient, that are all molded into the enclosure, which is then overmolded with polyurethane,' he noted. 'The Bayblend material is pre-colored and is just a very easy-to-process material which lends itself nicely to molding in all these other features.'

Kosanke said other small components of the LIFEPAK CR Plus are molded using Bayer Polymers' Bayblend FR 110 PC/ABS resin, including the Charge-Pak enclosures.

He added that Bayer Polymers' technical service has been excellent. 'Any time I've needed any help they've always been more than willing to support me in any way I've asked,'Kosanke said.

Bayer Polymers' resins are supplied to Medtronic Physio-Control and its molder by CC+P Engineering Polymers, a Bayer Polymers distributor in the Pacific Northwest.

Notes CC+P Engineering Polymers president Tony Christler, 'We've had a long relationship with Medtronic Physio-Control, and assisted with material selection and design criteria for the LIFEPAK CR Plus.'

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