Engineers at the Georgia Institute of Technology are poised to deliver an innovative new valve, designed to function as a back flow prevention device for patients suffering from chronic venous insufficiency. Whether such a system translates into clinical benefit is, of course, a million dollar question.
“Blood flows to the toes because of gravity, but the body uses vein valves to pump blood in one direction back to the heart,” said David Ku, the Lawrence P. Huang Endowed Chair in Engineering and Entrepreneurship and Regents’ Professor in the George W. Woodruff School of Mechanical Engineering at Georgia Tech. “However, sometimes a vein valve dissolves away after a blood clot. The loss of the valve leaflets allows blood to flow the wrong way, causing swelling in the legs and ankles.”
Ku is leading a research team that has developed a prosthetic vein valve to replace damaged, non-functioning valves. The prosthetic vein valve design and results from laboratory studies were presented at the Society for Biomaterials Fall Symposium in Atlanta on September 12. The research – under way for the past five years – is funded by the Wallace H. Coulter Foundation and the National Collegiate Inventors and Innovators Alliance…
Ku and his collaborators believe the valve they have developed will overcome previous difficulties. The one-way flap is made of poly(vinyl alcohol) cryogel, a material patented by Georgia Tech in 1999. The material has many useful attributes, including its biocompatibility with body tissue because of its attraction to water; the ability to adjust its mechanical strength; flexibility comparable to that of natural body tissue; and composition of organic polymer, rather than silicone.
The researchers will begin conducting preclinical animal trials at Emory University in October to test the in vivo biocompatibility and performance of the prosthetic vein valve prototype in sheep. Sheep were chosen because their cardiovascular geometry and physiology are similar to those of humans.
In each animal trial, two prosthetic vein valves will be implanted by Milner. [Dr. Ross Milner is an assistant professor of surgery at Emory University.] The researchers will test the biocompatibility and performance of the devices for four weeks, using imaging techniques to check that the valves remain in the proper location, are open and allow blood to pass through the vein.
The animal trials will be conducted after several years of optimizing the valve design and testing it in the laboratory. When the Georgia Tech researchers started designing the valve, they wanted it to be as similar as possible to normal, anatomic venous valves. They focused on two major design criteria: the valve had to withstand high pressures without leaking and the valve had to open with small pressure gradients, even after 500,000 cycles of opening and closing, which is equivalent to a half year…
Sathe conducted the initial laboratory tests and found that the valve met the mechanical design criteria – it could withstand pressures of more than 500 millimeters of mercury and opened with a pressure gradient of 2.6 millimeters of mercury, which matched physiologic vein valve function. Detailed laboratory testing procedures and results were described in the June 2007 issue of the Journal of Medical Devices.
Next, Farrell developed a laboratory method to test whether blood clots would form inside the prosthetic valve. Results showed that the new generation of valves remained open with no clot formation after 120 minutes of blood flow, whereas control valves lined with polyester closed up after approximately six minutes of perfusion and showed blood cells adhering to the valves.
The laboratory tests showed that the prosthetic vein valve exhibited low flow resistance, strong competency, fatigue-resistance, low clot formation probability and material flexibility, which allowed the researchers to move forward to the animal studies.
The next step after conducting the animal studies will be human clinical trials.
Press release: Prosthetic Vein Valve Designed to Improve Venous Blood Flow…
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