Low Permeability Biomedical Polyurethane Nanocomposites for Cardiac Assist Devices

Introduction Biomedical polyurethanes generally possess good biocompatibility and mechanical properties but, due to the low Tg and relatively high concentration of soft segments, are relatively permeable to air and water vapor. The ‘traditional’ approach to the permeability problem is to modify the chemistry of the copolymer, particularly that of the soft segment. For example, replacement of polytetramethylene oxide (PTMO) soft segments with aliphatic polycarbonate segments results in about a factor of two reduction in water vapor transmission rate. Recently, a more efficient approach for reducing the permeability of elastomers has received widespread attention. The basic idea is to disperse an organically-modified layered silicate (OMS) in the polymer, creating a more tortuous path for diffusion of gas molecules through the resulting composite. In a recent publication we demonstrated the utility of this approach for a generic poly(urethane urea) [PUU], resulting in as much as a 5× reduction in water vapor permeability at modest OMS loadings. The current paper represents an extension of this work to commercial PUUs that are used in cardiac assist devices.