Some day, doctors will be able to tap into vast warehouses for virtually every human body replacement part - or create custom-made tissue and organs as needed. As part of that effort, engineers at Georgia Institute of Technology (Atlanta) are working to develop what may be a more obscure, if not necessary part of the human inventory: prosthetic vein valves for patients suffering from chronic venous insufficiency (CVI).
CVI is a condition which affects more than seven million people in the U.S. that occurs when valves in a person's veins can no longer ensure a one-way flow of blood back to the heart.
Valves in the veins usually push the flow of blood up toward the heart. But when they're damaged, blood leaks and pools in the legs and feet and results in CVI. Compression stockings and devices – along with anticoagulants and bed rest – are the most advanced treatments available today.
While it's not life threatening for most people unless infection ensues, "CVI makes their lives miserable," David Ku, MD, 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, told Medical Device Daily.
With a background in vascular surgery, Ku said he saw a lot of patients with this condition and current treatments don't fix the problem.
"Most people get compression stockings and they provide symptomatic relief, but often there's still skin breakdown and infection that can be pretty nasty," he said. "The skin tends not to heal without good blood flow."
Blood normally flows to the toes because of gravity, but the body uses vein valves to pump blood in one direction back to the heart. Problems with these little valves start when they dissolve 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.
Symptoms can also include dull, aching, heaviness, or cramping in legs, itching and tingling, pain that's worse when standing, redness of legs and ankles, skin color changes around the ankles, superficial varicose veins, thickening of the skin on legs and ankles and ulcers on the legs and ankles.
Some surgical options are available to repair or replace damaged vein valves, including valve transplantation. But Ku believes that replacing the valve with a prosthetic one is likely to be a better option because finding a suitable donor valve in one of the patient's legs can be challenging to difficult.
Ku and his collaborators are developing a valve made of poly cryogel, a material patented by Georgia Tech in 1999. The material is biocompatible 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.
Georgia Tech retains the rights to use the material for research purpose, but commercial uses are licensed to SaluMedica (Atlanta), a company that uses the material called Salubria in two products: SaluCartilage is a synthetic implant developed to replace worn-out cartilage surfaces, restoring mobility and relieving joint pain, and the SaluBridge nerve cuff is intended to provide a protective environment for peripheral nerve repair after injury.
Classified as a hydrogel, Salubria contains water in similar proportions to human tissue and can be processed to be similar in its mechanical and physical properties. The organic polymer-based biomaterial is known to be biocompatible. Although it is soft and compliant like human tissue, it has been formulated to be wear-resistant and strong.
To date, Ku and team have implanted the valves in sheep cadavers. They are now launching into live animal studies. Sheep were chosen because their cardiovascular geometry and physiology are similar to those of humans.
Lab 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.
Assuming the animal studies go well, Ku envisions licensing the technology to a company.
"To my knowledge there are no prosthetic valves in clinical studies or on the market today," he said. "The makers of heart valves have designed similar valves and described them in the literature. Most have been made of metal or hard plastic, but they tend to erode over time and the vein is very thin."
The prosthetic vein valve design and results from laboratory studies were presented at the Society for Biomaterials Fall Symposium in Atlanta earlier this month. Ku's research is being funded by the Wallace H. Coulter Foundation and the National Collegiate Inventors and Innovators Alliance.