At the "heart" of the new Visionª Blood Cardioplegia (VBC) System from Gish Biomedical, Inc., is the clear plastic VBC device. It is used in cardiac surgery to cool and warm blood, and is about the size of a human fist.

"The small size of the VBC unit and thus the need for much less blood to prime the system is a breakthrough," said Daniele Ghidoli, project engineer at Gish Biomedical, Inc. "The unit provides complete visibility of the blood path and excellent heat exchange efficiency."

The VBC device requires only about 45 ml to prime, handles blood flow up to 600 ml/min, and has an integral bubble trap, particulate filter and temperature port.

The structural strength, biocompatibility and clarity - it is critical for the perfusionist to be able to see how the blood is flowing and to see if there are any bubbles in the blood - are provided by a medical grade of Makrolon¨ polycarbonate from Bayer Polymers.

The Vision Blood Cardioplegia was displayed by Bayer's exhibit at the International Plastics Exhibition (NPE), June 23-27, 2003, in Chicago.

Resin Properties are Critical

Gish Biomedical and its molder, Ambrit Engineering Corp., selected Makrolon polycarbonate for its combination of clarity, dimensional stability, and ease of processing. It also met the requirements of the FDA-modified standard ISO 10993, Part 1 Biological Evaluation of Medical Devices.

Only products that meet these requirements may be considered for applications Ð like the VBC Ð requiring biocompatibility. Another important aspect of the Makrolon resin grade is its ability to be sterilized using radiation, ethylene oxide, or steam autoclaving. The resin's physical and molding properties also made it ideal for the application.

"We have very tight requirements with regard to dimensional stability," Daniele Ghidoli said. "For example, the inside surface has to be very close to the heat exchanger to reduce the likelihood of shunting and to assure the most efficient cooling or warming of the blood."

Molding Process

The VBC unit is molded in two parts.

One part is shallow, and is molded with a blood inlet port, blood outlet port, and pressure relief port. The part also has a temperature port connected to the blood outlet port; a stainless steel part is insert molded in the temperature port.

The second part is deeper, forming the housing for the heat exchanger, and has two half-inch universal water connectors, as well as the integrated bubble trap on the top, which has a pressure monitoring and vent port. Both parts are formed in a single family mold.

During assembly of the VBC, the stainless steel heat exchanger and the blood filter are installed, and the two plastic parts are joined using UV bonding. The resulting unit is just 5 in high, 3 in wide and 2 in deep.

"The whole unit is basically four pieces - the two polycarbonate parts, the blood filter, and the heat exchanger," Daniele Ghidoli said. The VBC units are sterilized using ethylene oxide and supplied in sterile packs with various configurations of tubing attached, to meet the needs of a particular surgery.

Consistency and Ease of Use

Ambrit Engineering has worked with Gish for many years and is experienced with Makrolon resins.

"Gish asked us to participate in development of the VBC when it was in the design stage, evaluating the different kinds of materials that could be used," said John Mattimoe, Ambrit's president. "We build the tooling and do the molding, so we also worked with Gish on the design of the parts, since that would affect the design of the mold and the way it would fill."

Mr. Mattimoe said his company recommended Makrolon polycarbonate because the configuration of the parts is non-uniform Ð an upper and a lower housing that are quite different in shape.

"Even though the two parts are non-symmetrical, they have a tongue-and-groove joint that has to match up perfectly, so polycarbonate is the ideal candidate," Mr. Mattimoe said. "We knew that with Makrolon we would be assured of a reliable shrinkage factor. The material also has a wide processing window, which allows us to have more latitude in molding a complex part like this."

Mr. Mattimoe said the VBC project was completed on a tight deadline, but with excellent results. "The project was done in just under ten weeks, which for a mold of this complexity was pretty fast," he said. "It worked right off the bat."