Just as we can find polyurethane in our everyday lives, so too can we find it throughout many of the medical procedures we probably don’t care to think too much about. Many of these applications in the medical realm are a result of the attractive properties of polyurethane, which can be attributed to the chemical structure of this polymer.
In the synthesis of polyurethane, a flexible polyol that makes up the polyurethane backbone, reacts with an isocyanate to generate the cross-linked polymer and the ‘soft’ segment of the material, as well as a low molecular weight hydroxyl- or amine-based chain extender that also reacts with the isocyanate to form, due to the additional presence of intramolecular hydrogen-bonding interactions, the ‘hard’ segment of the resultant polyurethane. The generation of this block co-polymer, whereby the soft and hard segments alternate, leads to a unique material that is elastomeric, as well as tough and tear resistant in nature.
These properties of polyurethane lead to its advantages in medical devices over other types of polymers, such as polyvinyl chloride or polyethylene, as the material is able to withstand continual bending and rubbing during its use, without becoming weakened or breaking.
Read on to learn more about some of the medical applications and recent advancements that rely on the benefits of polyurethane.
If we consider the use of polyurethane in medical applications, one of the first things that surely comes to mind is its compatibility with the body. Luckily, much work has been carried out in the fields of chemistry, engineering, and medicine to ensure that the materials used today have sufficient structural, chemical, and mechanical integrities, so we can rest assured that implants will maintain their shapes and desired functions, and will not be degraded by biological attack while in the body.
Historically, polyurethane can be commonly found in a range of medical tubings, for example in catheters and feeding tubes, as well as in surgical gloves and other medical garments, and in bedding. More recently, however, a more diverse range of applications are being realised.
One such application is a polyurethane-based heart valve reported by South African scientists, which offers the advantage, through 3D printing of a titanium frame and dip moulding to introduce the polyurethane valve, of being constructed specifically for each patient. This particular valve offers an exciting alternative treatment to the traditionally utilised biological valve, which degenerates fairly quickly in younger patients, or mechanical valve, which requires life-long anti-coagulation therapy – this development is thus ideal for younger patients in developing countries, such as those in sub-Saharan Africa, where rheumatic heart disease is unfortunately prevalent. Animal and further mechanical testing of the valve is currently underway, so keep an eye out for future progress in this field!
Image courtesy of Central University of Technology, Free State
Patient comfort is an integral part of healthcare and treatment, and one particular polyurethane, thermoplastic polyurethane, offers a significant advantage over other plastics due to its ability to respond to heat due to the presence of transient cross-links between hard segments in the copolymer. The subsequent flexibility of the polyurethane imparted by this property allows for the material to act more as a rubber than a plastic, and adapt to movement in the patient’s body, which makes it much less cumbersome and annoying for the patient.
As such, these thermoplastic polyurethanes have a range of applications in a variety of tubings, oxygen masks, and wound dressings, as well as in a range of intravenous and intra-aortic balloon catheters, all of which are subject to much motion, and which patients appreciate for their flexibility.
When we think of polyurethane foams, their incorporation into medical devices may not be the first thing that comes to mind. Their rigid structure as a result of extensive cross-linking between the hard and soft segments of the co-polymer, is a bonus when support and inflexibility are required, however.
One such example of a rigid support comes in the form of a suture alternative, known as the Zip, which uses an adjustable ladder-type structure to close evenly an incision in places of stitches or staples. The polyurethane the Zip is made of facilitates the dynamic nature and conformability of the device, so the precision is also protected from the forces of patient movement, which aids in healing and recovery, and, perhaps most importantly for patients, also minimises scarring and track marks left by more traditional methods, so also offers cosmetic benefits.
Video courtesy of ZipLine Medical
For those who have suffered the ill-fate of broken bones and wearing a cast, the hassles of showering, the perpetual and unreachable itch, and the general discomfort can be appreciated. Luckily for any of our future breaks, a new company, Cast21, hailing from the University of Illinois at Urbana-Champaign has developed a means of addressing these issues. The cast, while still maintaining the rigidity required to repair a broken bone, is also hollow (so no itching!) and waterproof (showerproof!). To achieve this remarkable feat, the cast is based around a flexible network of silicon tubes into which the two components of polyurethane are injected, react, harden, and form a rigid foam exoskeleton that distributes force evenly across the limb in need of repair. Simple!