Intelligent Materials Design for Heart Valves, by Peter D Gabriele and Ryan Heniford
The future of biomaterials is an investment in understanding the physiological, economic and bioengineering constraints of materials. When assessing the development of heart valve devices, most of those that have synthetic components at the device or native tissue interface use polyester or PTFE because, along with a proven history, these materials have been deemed biocompatible by the FDA. However, current materials are limited by low durability and long-term degradation (leading to premature device failure), calcification, and cusp stiffening (Seifalian, A M, et al, “Current Developments and Future Prospects for Heart Valve Replacement Therapy,” Journal of Biomedical Materials Research Part B: Applied Materials (pp. 290-300). doi: 10.1002/jbm.b.31151).
These limitations can impact the long-term performance of heart valve replacements and may require that patients take anticoagulants daily due to the risk of clotting.
When exploring the future of cardiovascular engineering materials, it is important to develop materials that promote long-term indigenous physiological activity. On average, the heart pumps an estimated 2,000 gallons (7,570 litres) of blood each day. As a result, materials that are used in heart valve replacements undergo a tremendous amount of haemodynamic stress.
Heart valves of the future need to be biologically smart, meaning that they must incorporate polymers that are biomimetic. The new material must be able to perform its service function while surviving in the body without causing a shift in homeostasis. Through intelligent materials design, such a polymer will be engineered to provide early-stage mechanical and performance properties while gradually allowing the body to regenerate the anatomical part.
Other properties that must be considered for a next-generation polymer include:
- Mechanical strength: elastogenicity, burst strength, haemodynamic adaptation, fatigue strength and durability, and suturability;
- Compliance/compressibility;
- Vasoactivity;
- Low thrombogenicity;
- Degrees of freedom in fatigue;
- Resistance to infection, inflammation and hyperplasia;
- Promotion of healing;
- Minimisation of capsule formation; and
- Flexibility.
Fabrics or textile components could be made out of next-generation polymers for use in the heart valve leaflet and the stent. Achieving the right loading conditions while the valve is working, along with the optimal degradation times and proper cell growth, could lead to the creation of an all-fabric valve that degrades over time in the body and thus creates a new valve, enabling the valve to heal itself.
Regenerative medicine technologies will provide materials with the ability to degrade over time and be replaced by functional tissue. To meet this promise, however, a serious mechanical challenge with resorbable materials must be addressed: Can a valve construct be designed to manage the mechanical stress of life support while at the same time promote the remodeling as a regenerative process? This truly is the barrier to the development of future heart valve polymers.
Peter D Gabriele is vice president, emerging technology, at US medical textile manufacturer Secant Medical and Ryan Heniford is that company’s director, business development.