TAVR valves are built from three main components: a metal frame, animal tissue leaflets, and synthetic fabric skirts. The metal frame acts as the skeleton, the leaflets open and close with each heartbeat to control blood flow, and the fabric skirts seal the valve against the surrounding tissue to prevent leaks. Each component uses different materials chosen for specific mechanical and biological properties.
The Three Parts of a TAVR Valve
Every TAVR valve shares the same basic architecture. The stent frame provides structural support and anchors the valve in place. Inside, three leaflets mimic the function of your natural aortic valve, opening to let blood through and closing to prevent backflow. Surrounding the frame, inner and outer skirts made of synthetic fabric help create a tight seal against the walls of your aorta so blood doesn’t leak around the edges.
Metal Frames: Nitinol vs. Cobalt-Chromium
The frame material determines how the valve gets deployed during the procedure. The two most common metals are nitinol (a nickel-titanium alloy) and cobalt-chromium, and each behaves differently inside the body.
Nitinol is a “shape-memory” metal. It can be compressed into a narrow catheter for delivery, then springs back to its original shape once released at body temperature. This makes it the material of choice for self-expanding valves. The Medtronic Evolut family (Evolut R, Evolut PRO, Evolut PRO+) and many other designs use nitinol frames. Because self-expanding valves open on their own, the procedure doesn’t always require the rapid heart pacing needed with other valve types. The tradeoff is that nitinol frames tend to be taller, which can press against nearby electrical pathways in the heart and sometimes cause rhythm disturbances.
Cobalt-chromium is used in balloon-expandable valves, most notably the Edwards SAPIEN 3 and SAPIEN 3 Ultra. These valves are crimped onto a balloon, threaded into position, and then expanded by inflating the balloon. Cobalt-chromium frames sit lower in profile, which makes it easier for doctors to access the coronary arteries later if needed. The original SAPIEN valve used stainless steel, but newer generations switched to cobalt-chromium for a thinner, stronger frame. A newer balloon-expandable option, the Myval, uses a nickel-cobalt alloy called MP35N.
Leaflets: Treated Animal Tissue
The leaflets in virtually all commercially available TAVR valves are made from animal pericardium, the thin, tough sac that surrounds the heart. Most current valves use bovine (cow) pericardium, though some designs use porcine (pig) pericardium instead.
Bovine pericardium is thicker and stronger. It holds up better under the repeated stress of being crimped into a catheter and then expanded, and it has a higher load-bearing capacity overall. Porcine pericardium is thinner with finer, looser fiber bundles. Research comparing the two found that porcine tissue calcifies less but is also less durable under mechanical stress, which has led some researchers to suggest it may be better suited for lower-pressure positions like valves on the right side of the heart rather than the high-pressure aortic position.
The Edwards SAPIEN 3 Ultra RESILIA valve uses bovine pericardium treated with a proprietary process called RESILIA, designed to reduce calcium buildup over time. Calcification is the main long-term threat to any tissue valve. It happens because the chemical used to preserve the tissue, glutaraldehyde, leaves behind reactive molecules that attract calcium from the bloodstream. Over years, calcium deposits stiffen the leaflets and eventually impair valve function.
How the Tissue Gets Preserved
Raw animal tissue would break down quickly in the body, so it must be chemically fixed before implantation. Glutaraldehyde is the standard preservative. It cross-links the collagen fibers in the tissue, making them resistant to degradation by the immune system. The problem is that leftover glutaraldehyde molecules become nucleation sites for calcium crystals. Manufacturers use various anti-calcification treatments to neutralize these leftover molecules. Techniques include washing the tissue with citric acid, treating it with enzymes that break down residual aldehydes, or applying specialized coatings. The goal is to keep the structural benefits of glutaraldehyde fixation while minimizing the chemical residue that triggers calcification.
Fabric Skirts: Synthetic Sealants
The skirts that wrap around the frame are made from polyethylene terephthalate, commonly known as PET. This is the same type of polyester used in many medical implants. According to FDA documentation, the SAPIEN 3 uses PET for its fabric skirt, and the SAPIEN 3 Ultra uses PET for both inner and outer skirts. PET is biocompatible, flexible enough to conform to irregular anatomy, and durable over time. The outer skirt is particularly important because it fills gaps between the valve frame and the native tissue, reducing paravalvular leaks, one of the more common complications after TAVR.
How Long These Materials Last
A study tracking first-generation TAVR valves over a decade found that structural valve deterioration was relatively uncommon. At 10 years, severe deterioration occurred in only about 4.3% of patients overall, and complete bioprosthetic valve failure was seen in 9%. There were notable differences between valve types: the balloon-expandable SAPIEN had a 10-year deterioration rate of 8.9% compared to 2.2% for the self-expanding CoreValve. These numbers come from early-generation devices implanted in elderly, high-risk patients (average age around 80), and current-generation valves with improved tissue treatments are expected to perform at least as well.
It’s worth noting that only 10.3% of these patients were still alive at 10 years, largely because of how old and sick the original TAVR population was. As TAVR expands to younger, healthier patients, long-term valve durability becomes a much bigger question, and it’s the primary reason researchers are working on alternatives to animal tissue.
Polymer Valves in Development
Several companies are developing TAVR valves that replace animal tissue leaflets entirely with engineered polymers. The potential advantage is significant: synthetic leaflets wouldn’t calcify the way biological tissue does, could be manufactured more consistently, and might last longer in younger patients who need decades of valve function.
The most advanced effort comes from Foldax, whose Tria Heart Valve platform uses a silicone-based polyurethane material they call LifePolymer. It’s the first polymeric valve platform designed for aortic, mitral, and tricuspid positions. Other polymer TAVR valves in development include the Triskele valve (using a silicone-polycarbonate-polyurethane nanocomposite), the SAT valve from South Africa (using a thermoplastic silicone-polycarbonate-urethane), and the SIKELIA valve from Shanghai Yixin Med (a self-expanding nitinol frame with polyurethane nanocomposite leaflets). PECA Labs is developing the STEALTH polymer aortic valve using ePTFE, and the TaurusApex valve takes a different approach with a five-layer bionic polymer fiber braid as leaflet material.
None of these polymer valves have reached widespread clinical use yet, but they represent the clearest path toward TAVR valves that could outlast the biological tissue versions currently on the market.