Design breakthroughs don't always have to depend on revolutionary new components. In some cases, a little tweaking of the design may do just fine.
That's just what engineers at Swiss medical device manufacturer Bioring (www.bioring.com) did recently. By modifying the molecular weight of an existing polymer, these engineers developed a deceptively simple device that, they say, will eliminate the repeated surgeries children with defective heart valves have to undergo as their bodies grow.
Called the Kalangos Ring, the fishhook-shaped device cinches a heart valve so it will operate properly, alternately opening enough to allow free flow of blood, and closing completely to prevent blood leakage.
The standard treatment for faulty heart valves used to be replacement of the valves. More recently, surgeons have opted for repair procedures, implanting a ring to hold the artery rigid. For children, however, repair strategy required periodic surgeries as the bodies outgrew the ring.
Bioring's Kalangos Ring (named after the surgeon who developed it) exploits the body's ability to develop scar tissue. Implanted at the base of the mitral or tricuspid valve, it mimics the natural fibrous ring in the valve and performs the necessary cinching. But, the Kalangos Ring lasts only as long as it takes for scar tissue to develop. Eventually, the scar tissue takes on the structural function. "It encourages the body to heal itself," says Raymond Andrieu, Bioring chairman and CEO.
Engineers started with studies of how long it might take for the scar to form. Then, they modified the molecular weight of PDO/Polydioxanone, an FDA-approved biocompatible non-inflammatory polymer used for absorbable surgical sutures. The higher the molecular weight, the longer the time it takes for the material to degrade and the slower the material absorbs water. Engineers had to adjust the molecular weight so the material would desolve at an even rate.
The material can withstand the heart valve's mechanical constraints. Standard systolic-diastolic pressures in an artery range from 120-80 mm Hg. The ring is designed to withstand only the movement inside the natural fibrous ring (or annulus), represented by the movements of the heart occurring during the systolic and diastolic phases. It does not have to withstand any compressive forces of dynamic blood flow.
The material is non-inflammatory, and is nearing European CE approval. Bioring will shortly apply for approval by the U.S. FDA.
Given the green light
One critical factor in choice of the polymer for the ring was that it has been approved by the FDA for other medical uses, specifically tissue-engineering structures. Tissue-engineering and device companies tend to use materials that have already undergone FDA approval to minimize development barriers.
The ring is modified PDO suture material, one of the strongest materials in its class. PDO can support a wound for 60 days. The tensile modulus is 1.5 GPa. Its tensile strength is 36 MPa. It retains full properties almost six weeks after implantation. Tests showed that after eight weeks it still retains 50 percent of its tensile properties. It is totally absorbed by the body in seven months.
The ring comes in 11 different sizes and weighs 0.2g. Ring thickness in pediatric sizes is 1,30 mm; in adult sizes is 1,50 mm. Other products will include a ring for urinary incontinence.
Cinched: The Kalangos Ring, a fish-hook shaped device
used in cinching a defective heart valve, is shown (at left) implanted in
relation to the cardiac valves