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Optimisation of polyurethanes for specific biomedical applications
Release time:
2023-09-06
Polyurethanes for implantable devices can be selected from commercially available biomedical polymers, i.e. catalogue items, or they can be custom synthesised for specific applications. The latter may be necessary when complex, highly constrained property specifications must be met.
Even when studying available polymers, factors other than the polymer properties listed in the datasheets, which are typically measured dry at room temperature, need to be considered. These include changes in properties immediately after implantation due to heating to body temperature, and absorption of water from the body. The role of water as a solvent/plasticiser is an important consideration in material selection, particularly in hydrogen bonded polymers such as PU and PUU. For example, the oxidative stability of poly (carbonate polyurethane) and its silicone-containing copolymers has led to its evaluation as an alternative to poly (ether polyurethane) (PEU) in many medical devices. The ether moiety increases equilibrium water content during implantation, resulting in varying degrees of softening, creep and permanent deformation of poly(ether urethanes) relative to their polycarbonate-containing analogues.
Meeting Volume and Surface Property Requirements
The composition and concentration of the soft chain segments affect not only the overall properties, but also the surface because of their ability to migrate and concentrate in the surface area. The movement from the bulk to the surface is "surface activation". The spontaneous ordering of similar molecules in a surface is known as self-assembly. When using surface activity and self-assembly to modify polymer surfaces, it can be very useful to have even less restriction on the mobility of the polymer end-groups.
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