Fact Sheet: ChronoFlex® AR: Biodurable Medical Grade Polyurethane
[In pdf format]

Introduction

We manufacture and market a solution-grade, segmented, aromatic, polycarbonate-based polyurethane designed for use in solvent casting and dipping applications. This elastomer may be evaluated for use in the fabrication of blood contact surfaces, pump diaphragms, and other medical devices.

Typical physical properties of ChronoFlex® AR films are shown below:

ChronoFlex® AR is a medical-grade polyurethane, meaning that we are committed to maintaining lot quality control, lot traceability, product certification, and lastly that physical properties are audited periodically in conjunction with a ninety (90) day sample retention. ChronoFlex® AR films have been tested by an independent laboratory, and have passed or exceeded all requirements specified in the USP Class VI biocompatibility tests.

Applications
ChronoFlex® AR is ideal in applications requiring exceptional flexure endurance, such as artificial heart diaphragms or vascular grafts. We only supply materials and do not supply finished devices.

Fabrication
ChronoFlex® AR is processed by traditional solvent casting techniques. Removal of Dimethyl Acetamide (DMAC) solvent leaves a polymeric film that is best attained in a forced hot air oven. We recommend temperatures between 60°Cand 80°C.

Depending upon the size of the component being manufactured, the duration of heating time may vary between 2 and 24 hours. It is essential that dry air be used during DMAC evaporation, because this solvent is highly hygroscopic, and water absorption into the solvent will cause the film to become cloudy, with reduced physical properties.

Both viscosity and percent solids may be reduced by addition of DMAC. Analytical-grade DMAC is recommended for these purposes, since this grade of solvent has minimal moisture content.

Composition
Synthesis of ChronoFlex® AR is carried out by the addition of MDI (diphenylmethane 4,4'-diisocyanate) to polycarbonate diol, followed by addition of a mixture of chain extenders and a molecular weight regulator, with the reaction carried out in DMAC solvent.

ChronoFlex® AR is thus supplied as a 22% solids solution, ready for solution casting.

Most medical-grade polyurethanes are clear to slightly yellow in their original state. However, aromatic-based polyurethanes turn dark yellow to amber as a result of processing, sterilization or exposure to UV light. While this discoloration (which is caused by the formation of chromophoric groups in the MDI portion of the molecular chain) does not affect the physical properties of the product, it may nevertheless influence the aesthetics of the device.

Biodurability
Biodurability means freedom from biologically-induced Environmental Stress Cracking (ESC) during the intended period of implantation (1). In general, it refers to the unwanted action of macrophagic enzymes onto polyether-based polyurethanes, which results in surface fissures. ESC may lead to catastrophic device failure. ESC susceptibility is tested by the "Stokes" test.

ChronoFlex® AR elastomers are polycarbonate based, and are thus believed to be resistant to ESC. However, we strongly recommend that customers test the suitability of this product in their specific application.

References
1. Szycher, M. "Biostability of Polyurethane Elastomers: A Critical Review" J. Biomat. Appln., 3(2):299-402, (1988).

2. Stokes, K.B., et al. "New Test Methods for the Evaluation of Stress Cracking and Metal Catalyzed Oxidation in Implanted Polymers," in PU in Biomedical Engineering, H. Planck et al, eds,. Amsterdam: Elsevier, 109-127 (1987).

FDA Status
The use of ChronoFlex® AR in medical devices is not covered by any specific FDA regulation. It is the responsibility of the user to establish safety with the FDA through submission of an individual application. We have submitted an MAF to the FDA and will approve FDA access as required in processing a customer's application. The MAF contains proprietary information on the base polymers, the manufacturing process, product release specifications, and other relevant data to assist FDA personnel in the approval process.

Technical Service
Our technical personnel stand ready to assist you with processing, product availability, or pricing.

This information has been gathered from standard reference sources and is believed to be accurate and reliable. CardioTech makes no other warranty, express or implied, that the results obtained from the use of this product or information contained herein shall be merchantable or fit for any particular purpose, or that the use of this product will not infringe any patent. it is offered solely for your consideration, investigation, and verification.
[In pdf format]