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BAYER PLASTICS' MAKROLON® POLYCARBONATE RESINS ARE THE CLEAR CHOICE FOR COMPACT HEART-LUNG BYPASS SYSTEM
A Non-conventional Approach The CORx System, manufactured by CardioVention Inc. of Santa Clara, Calif., consists of a CORx IOS (Integrated Oxygenation System), which integrates air handling, oxygenation, and pumping into a single compact unit. A separate disposable tubing system (CORx A/V Loop) is used to carry blood to and from the heart. Compared to the blood circuitry of today's much larger heart-lung bypass machines, the small unit - about the size of a soda can - is able to function with one-tenth the amount of surface area exposed to blood and with minimal to no priming volume required for activating the system. The effect of priming, known as hemodilution, thins a patient's blood, reducing its oxygen carrying capacity and potentially compromising other body functions. By reducing hemodilution and the surface area exposed to blood, CardioVention believes the new system will play a critical role in minimizing patient platelet loss, blood damage, blood transfusions and systemic inflammation. Makrolon Polycarbonate: The Correct Material for the CORx System The CORx System is made of two grades of polycarbonate - Bayer Plastics' Makrolon 2558 and DP1-1452 resins. These grades meet the requirements of the FDA-modified ISO 10993, Part 1 'Biological Evaluation of Medical Devices' tests with human tissue contact time of 30 days or less. This is key since only products that meet these requirements may be considered for applications - like the CORx System - requiring biocompatibility. Another important aspect of these resin grades are their ability to be sterilized using radiation, ethylene oxide, or steam autoclaving. The core of the CORx System, a 4-inch-long, 1.42-inch-diameter cylinder, is injection molded by Delta Pacific Products Inc. of Santa Clara, Calif., in a clean room environment using Bayer's Makrolon 2558 resin. Makrolon 2558 resin provides outstanding impact strength, excellent dimensional stability and glass-like transparency. The core was challenging to mold due to the part's geometry, which included zero draft, and some thick and thin sections - from 0.125 inches to 0.028 inches thick - that create an adhesive groove on the cylinder, according to Delta Pacific Products President Fred Betke. 'Because of these design challenges, material melt flow was an important criteria for this part,' said Betke, who said Bayer Makrolon polycarbonate was up to the challenge. 'We understand this material - we've used it before in other medical applications and it performs well,' he continued, adding that Bayer personnel provided valuable technical support for the project. Following molding and degating, the component is double bagged and shipped to CardioVention for assembly. Six other CORx system components - VFT cover, VFT top, upper gas manifold, shell, pump housing and pump base - are injection molded from Bayer's Makrolon DP1-1452 polycarbonate resin by Pacific Plastics and Engineering of Soquel, Calif. Makrolon DP1-1452 resin exhibits improved flow and easy release characteristics over other polycarbonates. It features an internal mold release (IMR) technology that can, in many cases, eliminate the use of mold-release sprays. The resin's properties also include an outstanding balance of high strength, toughness, clarity and processibility. The resin offers increased design flexibility for complicated medical products with difficult-to-fill molds and parts with shallow drafts. Two of these six components - the VFT top and shell - proved to be particularly challenging from a tooling and molding standpoint, according to Ratan Bajaj, Pacific Plastics & Engineering's Director of Sales. For example, the top, which measures 3 inches tall with a 3-inch diameter, featured complex geometries, including undercuts. The shell - the outer casing of the CORx System - measures 4inches tall with a 3 inch diameter. Ray Scherer, engineering manager, explains that the part's complex geometry and minimal draft contributed to the tooling challenge, as did the requirement for a full diamond finish. To ensure there are no drag marks on the part, cores and slides were treated with a special PVD chemical. 'It was important to use a coating that wouldn't inhibit the diamond finish and would, at the same time, have good wear resistance for the components inside the tool,' explained Scherer. CardioVention utilized Bayer's expertise when selecting a material to form the shell, according to Ben Bobo, Vice President, Marketing and Business Development for CardioVention. 'Bayer provided technical assistance in selecting an engineering resin that would help us produce the shell, which does not lend well to molding because of the minimal draft and undercut conditions,' Bobo explained. 'The Bayer technical personnel are extremely knowledgeable and thei r input has been very beneficial.' http://www.bayermaterialscience.com
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