Applications of Polyurethanes in Medical Materials

The composition of the human body is inherently complicated in nature. Starting with the cell, it proceeds to form a collection of cells which are formed into various organs, furthermore integrating to form the whole body. It is important to note that all of these processes are interrelated and thus, no part of the body, whether it is the smallest cell or a complex body system, works in isolation from each other. It is this fine-tuned balance that results in homeostasis, essential for the maintenance of health and optimal functioning of the body, whereas disease is the disruption of this balance or homeostasis.

Medical devices made from polyurethane materials help in the diagnosis and treatment of cardiovascular, orthopedic, neurological, urinary, digestive diseases. In the cardiovascular sector, Polyurethanes, in the form of Thermoplastic Polyurethanes (TPUs), have been the focus of many studies over the years. A combination of favorable physical and chemical properties combined with its flexibility in processing techniques have been the main attractions for the use of TPUs in fabricating heart valves leaflets, conduits for left ventricle assist devices (LVAD), coating on stents, construction of the Total Artificial Heart (TAH), insulation of cardiac leads including pacemakers and defibrillators. The biggest concern with polyurethanes was their susceptibility to degradation in the body. The presence of groups that are hydrolytically unstable was addressed by the elimination of ester groups in the soft segment of the polyurethanes. The introduction of carbonate and siloxane groups in the soft segment progressively improved the oxidative stability of TPUs.

With the range of structural possibilities in polyurethanes offering a wide spectrum of physical properties, polyurethane formulations have always been of great interest in orthopedic applications. The areas of biostability and the relevant physical properties of polyurethane formulations were evaluated for suitability in orthopedic applications. They have lower modulus values than Ultra-high-molecular-weight polyethylene (UHMWPE) and have been hypothesized to operate under a micro-hydrodynamic lubrication regime, which leads to reduced wear. TPUs are considered as alternative materials for hard-on-soft bearings in artificial joints. They are seen in several studies to better substitute the mechanical properties and lubrication of cartilage.

Many fundamental design concepts of neurostimulators are very similar to cardiac pacemakers and defibrillators, owing to the similarity in the requirements of both technologies. Polyurethanes are widely used in neurostimulation devices as the insulators for leads and extenders, and in the fabrication of headers on the top of pulse generators. The polyurethanes used in cardiac pacemaker devices must meet a number of requirements, such as having superior mechanical and biostability qualities. It is common for neurostimulation devices to use the same materials as cardiac devices.

Polyurethane biomaterials have been used in medical devices in a number of other ways. There are numerous examples in the scholarly literature, and some of these polyurethane formulations are being utilized in the fabrication of commercial devices for various purposes. Devices such as intravaginal rings and polyurethane-based penile prostheses are used in the reproductive system area. The use of urethane chemistry in the production of contact lenses is one of the ophthalmologic applications.

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Author
Ajay D Padsalgikar (Ph.D. California, USA)
Trainer at Polymerupdate Academy