GE’s Lexan* HPM Resin Raises the Benchmark for Hemocompatibility and Reduced Protein Binding in Medical Devices

BERGEN OP ZOOM, THE NETHERLANDS — November 15, 2006 — GE Plastics’ advanced Lexan* HPM polycarbonate resin is representative of GE Plastics’ response to the changing needs of the healthcare industry. It provides a major step-advance in hemocompatibility with substantially improved performance relative to platelet retention, leukocyte and C3a protein activation, and reduced Fibrinogen protein surface binding characteristics. All of which are innovations that may mean greater safety for patients undergoing surgery and with higher levels of care throughout recovery as well as during blood collection and donations.

Importantly, these improvements have been achieved without any major compromises in the key properties for which polycarbonate is well known and appreciated by design engineers and end users alike. These include transparency, ductility, durability and processability, as well as sterilizability with good property retention following gamma or EtO sterilization or autoclaving at 121°C and resistance to chemicals common to the healthcare environment.

Available in two grades, Lexan HPM1944 and HPM1914 resins, offering medium flow and high flow respectively, this next-step material exhibits better flow and higher ductility than a traditional polycarbonate; giving the possibility of thinner wall sections essential for many of today’s medical device designs. Better inherent mold release, without the use of fatty acid derivatives or other release agents of animal origin, is also a positive addition to the material’s processibility and productivity.

Central to the development of Lexan HPM resin is the optimization of GE’s standard polycarbonate formula to create physical properties that render the surface of the material less likely to have affinity for either blood or proteins. While in general some of these characteristics may be achieved with other types of plastics, it can be challenging to achieve the balance of mechanical properties, clarity and advanced biocompatible performance expected by customers in the healthcare sector.

Statistically measurable improvements

In tests based on a range of blood components and proteins, conducted by third party universities and independent laboratories, Lexan HPM resin has been shown to outperform other injection moldable polymers, including standard polycarbonate. This serves to make Lexan HPM resin a unique and enhanced polycarbonate material solution for diagnostic equipment and blood handling devices, as well as the surgical instruments used in cardio-vascular and orthopedic surgery, among other procedures.

Like GE’s traditional Lexan polycarbonate, Lexan HPM has been tested for biocompatibility¹; testing was conducted according to ISO 10993. However, Lexan HPM resin has been designed to reach beyond the basic qualifying standard and deliver measurably improved performance values that may reduce the safety concerns of end-users.

Medical devices in contact with or handling blood for re-circulation into the human body seek to reduce the initiation of any change in the blood’s components. However, blood contact with foreign environments may trigger platelet response, the blood’s primary clotting mechanism, therefore the material selected for a device should seek to reduce this response rate. Lexan HPM resin advances the capability of biocompatible polycarbonates to offer potential reduction in blood/plastic interaction thereby helping to preserve the nature and component level of the patient’s blood in an attempt to improve both surgery and recovery outcomes.

In support of this, tests² have shown that in contact with Lexan HPM resin blood retains up to 50% more of its original platelet content than it does when it is in contact with standard polycarbonate. Moreover, this higher factor of retention may result in greater platelet yield and contribute to the preservation of original blood composition. Given that the human body has limited reserves of platelets their retention is central to patient well-being.

Leukocyte activation provides another biomarker for material performance comparison. Leukocytes are an intrinsic part of the body’s immune system and help defend it against infections and foreign matter. Because of this it is highly desirable that they not be activated by a medical device as they may form leukocyte–platelet aggregates which have the potential to instigate the clotting process.

This is particularly unwelcome in respect of donor blood handling. Where standard polycarbonate may stimulate a four-fold increase in leukocyte activation above the normal level for resting blood, the superior performance of Lexan HPM resin provides for significantly less bio-interaction resulting in 50% lower activation of leukocytes than regular polycarbonate technology².

C3a is one of a number of related proteins that are part of the blood clotting process. Therefore, an elevation in the concentration of C3a protein in blood also indicates an increase in other proteins and the activation of a cascade effect in blood clotting. The exposure of blood to standard polycarbonate may raise the concentration of C3a by as much as 70%. Whereas Lexan HPM resin has minimal influence on C3a activation and its level of concentration remains similar to that recorded for resting blood, indicating less clotting and a reduction of other protein interactions².

Typically used by medical device OEMs in their own tests, Fibrinogen is also a good indicator for other protein complexes that may bind to a material’s surface. Measured using standard adsorption criteria for plastics, Lexan HPM resin exhibits 60% lower adsorption to its surface than that of similarly tested standard polycarbonate². Consequently, its use for blood management devices may result in a higher protein content remaining in the blood or drug solution.

In in-vitro diagnostics and biopharmaceutical treatments for which a specific yield of a protein is required, it is desirable that the protein neither binds to, nor interacts with, a plastic device and passes freely over its surface to enhance the effectiveness of diagnostics, or optimization of patient drug dosage and benefit. To validate the adsorption characteristics of Lexan HPM resin, Fibrinogen was selected as it is commonly used within the healthcare industry as a benchmark protein for diagnostics, biopharmaceuticals and blood care management devices.

First applications commercialized

While GE may share performance data of its product grades with customers, customers are responsible for conducting their own device validation testing, in addition to those required by regulatory protocols, as the final performance of an application may be influenced by factors such as design, specific in-use interaction with bio-fluids, whether blood or complex protein-based fluids and contact time.

Since its introduction to healthcare and medical device OEMs in mid-2005, advanced hemocompatible Lexan HPM resin has attracted wide interest. This has resulted in a progressively strong trial of the material by GE customers for the validation in applications with blood and protein-based fluid contact. ESTECH, a maker of cardiac surgery devices, selected the GE material for the paddle of its single-use ClearView MV™ Atrial Depressor to help achieve a high level of device reliability and biocompatibility¹ in minimally invasive mitral valve repair and replacement procedures. For ESTECH, GE’s Lexan HPM resins offered the typical strength of PC as well as the new capabilities offering improved hemocompatibility², reduced protein binding, improved low temperature ductility, and the potential for improved flow and release. Companies in the in-vitro diagnostics segment have noted improvements in reduced protein binding as well as value from animal-free composition, as also noted by biopharmaceutical device makers. Other customers, designing devices with blood contact, have indicated an improvement in blood/plastics performance. Completions of end users’ own testing, together with regulatory approvals in progress have led to a number of early adoptions for marketable use pending device commercialization.

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