Materials
Researchers are racing to develop a polymer heart valve that can replace mechanical and bioprosthetic valves.
biocompatible, hemocompatible, calcification resistant, and possess the proper biostability properties. “The heart valve must also be rubbery, soft and durable, just like SIBS. But these key biological properties are all surface properties.” The surface coating, however, wasn’t quite enough for the heart valve design. A polymer heart valve would have to exhibit the surface properties of SIBS while possessing the strength for structural and dynamic applications.
artificial valves have been used to replace failing valves for over 50 years, they have significant disadvantages. Mechanical valves require lifelong anticoagulation and bioprosthetic valves are prone to structural degeneration, requiring reoperation to replace the original replacement valve. As valvular disease continues to be one of the leading causes of cardiovascular morbidity, mortality and functional disability worldwide, a solution that would overcome the limitations of current valve replacements remains top of mind for researchers, who continue to test different polymer compounds and materials for long-term durability, hemocompatibility, and other essential qualities that prove they can be the future valve replacement solution. Dr. Joseph Kennedy, professor of polymer science and chemistry at The University of Akron, author of more than 700 original scientific publications, and inventor of over 130 issued US patents on polymer science and technology, has devised a design using a polymer material he believes is far superior to any other polymer heart valve material currently being researched or tested. The path to a successful, fully synthetic polymer heart valve began with Kennedy’s patented Poly (Styrene-block-IsoButylene-block-Styrene) (SIBS) polymer, used as a coating for cardiac stents. However, SIBS was only the beginning of his work toward creating a polymer that could function as a heart valve. “For SIBS, the surface was everything,” Kennedy says. Like the stent coating, the heart valve must be
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“After examining many possibilities, we combined the polyisobutylene polymer that is part of the SIBS structure and polyurethanes,” says Kennedy. The combination created what Kennedy calls PIB-PU (polyisobutylene-polyurethane), a new polymer with strong biocompatible rubbers suitable for heart valves and other medical devices. “Strength ensures shape retention, durability, and other properties needed in a polymer heart valve,” he says. “PIB-PU is also highly fatigue-resistant, a critical property for a beating heart whose valves constantly open and close.” Importantly, PIB-PU is designed for the crimping necessary for transcatheter aortic valve replacement (TAVR) procedures. TAVR is quickly becoming the preferred procedure for heart valve replacement because it is minimally invasive and results in much less downtime than surgical valve replacement. “This is a thermoplastic elastomer,” says Kennedy, “which is the same material as existing TAVR valves because they have to be squeezed together through the catheter.” According to Kennedy, the heart valve is only one of the many possibilities for PIB-PU in medical devices: “We have started investigating other uses, including meshes and anti-adhesion barriers. There is a whole landscape of possibilities, but it started with the heart valve.”
Kennedy adds now that they have the material needed for the valve, they need animal studies to further the research. “We have only done in vitro studies,” he says. “Rodents aren’t good for these studies. We need larger animals like sheep, dogs, or cows.” Polymer science and medical device engineering present complex challenges. Polymers must be safe for the body and maintain their performance for an extended or designated amount of time. Despite these challenges, polymers offer pragmatic solutions that continue to redefine healthcare by providing innovative tools that can improve patients’ lives across a broad spectrum of disease and medical problems. There is no end in sight for the crucial role polymers play in medical device engineering as they pave the way for the future of healthcare. ●
Medical Device Developments /
www.nsmedicaldevices.com
Sebastian
KaulitzkiShutterstock.com
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