CarboSil™  20 55D - The Polymer Technology Group - 

CarboSil® thermoplastic silicone polycarbonate urethane is a true thermoplastic urethane copolymer containing silicone as a soft segment. It is manufactured using a continuous synthesis process where polydimethylsiloxane (PSX) is incorporated into the polymer soft segment with an aliphatic, hydroxyl-terminated polycarbonate. The hard segment consists of an aromatic diisocyanate, MDI, with a low molecular weight glycol chain extender. The copolymer chains are also terminated with silicone (or other) Surface-Modifying End Groups™ (SME).

Silicones have long been known to be biostable and biocompatible in most implants, and also frequently have the low hardness and low modulus useful for many device applications. Conventional silicone elastomers can have very high ultimate elongations, but only low to moderate tensile strengths. Consequently, the toughness of most biomedical silicone elastomers is not particularly high. Another disadvantage of conventional silicone elastomers in device manufacturing is the need for cross-linking to develop useful properties. Once cross-linked the resulting thermoset silicone cannot be redissolved or remelted. In contrast, conventional polyurethane elastomers are generally thermoplastic with excellent physical properties. TPUs combine high elongation and high tensile strength to form tough, albeit fairly high-modulus elastomers. Aromatic polyether TPUs can have excellent flex life, tensile strength exceeding 5000 psi, and ultimate elongations greater than 600 %. They are often used for continuously-flexing chronic implants, such as ventricular assist devices, intraaortic balloons, and artificial heart components*. TPUs can easily be processed by melting or dissolving the polymer to fabricate it into useful shapes.

The prospect of combining the biocompatibility and biostability of conventional silicone elastomers with the processability and toughness of TPUs is an attractive approach to what would appear to be a nearly ideal biomaterial. Silicone acts synergistically with polycarbonate-based polyurethanes to improve in vivo and in vitro stability. This class of polyurethanes also has low-energy silicone surface and outstanding oxidative stability.

CarboSil thermoplastic silicone polycarbonate urethanes are manufactured using a high throughput, continuous reactor and are currently available in three standard hardness grades: 80A, 90A, and 55D with various silicone contents. These materials accept fillers well and are heat-sealable and easily post-formed. Other hardness grades or percent silicone may be custom synthesized and all grades of the polymer are available with various Surface Modifying End Groups™ (SME), such as Silicone, Fluorocarbon, PEO, etc.