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Engineers Adjust Molecular Weight Of Polymer For Heart-Repair Device

Engineers Adjust Molecular Weight Of Polymer For Heart-Repair Device

By modifying the molecular weight of an existing polymer, engineers at Swiss medican-device manufacturer Bioring (www.bioring.com) developed a fishhook-shaped device that could eliminate repeated surgeries on children with defective hearts.

The so-called Kalangos Ring (named after the inventor) 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 clinching so the valve can open enough to allow free flow of blood, and then close completely to prevent blood leakage. Eventually, the scar tissue itself takes on the structural function.

By allowing the body to heal itself, the ring could replace the traditional procedure of implanting a device to hold the artery rigid. Children who underwent that traditional procedure required periodic surgeries as their bodies outgrew the ring.

To develop the Kalangos Ring, engineers 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 it takes for a material to degrade and the slower the material absorbs water. The goal was to adjust the molecular weight just enough so that the material would desolve at an even rate.

FDA approval of the polymer for other medical uses was critical in the engineers' decision to use it for the ring. The reason: the time savings. The material is nearing European CE approval too.

The tensile modulus for the material is 1.5 GPa. Tensile strength is 36MPa. Tests have shown that the material retains 50 percent of its tensile strength after eight weeks. The human body totally absorbs the material in seven months.

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 (below).
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