The Body Synthetic
  Winter 2008

  Dr. D. Jaron
  Dr. P. Lelkes
  Dr. R. Seliktar

  Shuk-Man Charli Hon
  Richard Gerbino
  Natalie Gostola

The key to improving any technology is continued research.  Below are some current research initiatives relating to artificial heart valves.

http://www.medgadget.com/archives/img/1cfrwe1.jpgIn order it improve heart valve design first researchers must have a reliable way to detect potential flaws.  Several scientists at the University of Edinburgh in Scotland have devised cheap and efficient method for predicting areas prone to clot formation in replacement valves.  They have discovered that the use of curdled milk effectively simulates blood flow and clotting characteristics.  Existing methods for testing heart valves, including using large mammals like sheep, are expensive and sometimes fail to detect problems that have later appeared in human clinical trials. After repeated trials with multiple valve, including Starr-Edwards caged ball valves, Bjork-Shiley and Medtronic Hall tilting disc valves, and St. Jude and Medtronic Parallel valves, it was confirmed that milk clots appeared in the same locations as reported thrombus locations of valves in situ.(Martin) This includes a clot found in the Medtronic Parallel hinge pockets, which was not detected as a potential in animal trials, but later proved thrombogenic in clinical trials.(Martin)  This technique should allow researchers to indentify problem areas before undertaking clinical trials, thus saving money and reducing patient risk.  This work was funded in part by the National Science Foundation (NSF).

One of the major drawbacks of the mechanical heart valves is the risk of thrombosis and the need to receive lifelong doses of anti coagulant drugs.  As such, research is underway to create new materials to line the valves which will create non adhesive surfaces, reducing the ability of platelets or proteins to aggregate on the implant.  Dr. Anja Mueller, a researcher at the University of Clarkson in New York is working with a polymerization process that utilizes a compound known as horse radish peroxidase (HRP) as a catalyst.  The scientists have found that HRP can make aromatic polymers that are similar in structure to pyrolytic carbon, and flexible hydrophilic polymers, needed for a non adhesive outer coating. 

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The next generation of mechanical valves is the tri-leaflet which more closely mimics natural heart valve function and has improved hemodynamics over even the bi-leaflet design and the potential for greatly reduced thrombosis risks.  This has been demonstrated in calves with the Triflo MHV implanted in the mitral position without the use of anticoagulant drugs.  The results were promising although one calf was terminated on day 25 of the study due to complications with the valve. (Sato)

Triflo tri-leaflet valve

Much of the current research however involves tissue engineering and attempts to grow replacement valves outside the body on tissue scaffolds.  This project at the University of Michigan is one example.  Researchers there are attempting to create chitosan based scaffolds in order to grow bio synthetic tri-leaflet valves.  This technology has the potential to be sized to a specific individual then, seeded with the patient’s own cells for a completely autologous implant.

Created: February 17, 2008