Tissue engineering of blood vessels and heart valves

 

Cardiovascular surgery is a one of the most quickly and successfully progressing fields of medicine, and in time operations performed in patients with heart and blood vessels disease not only prevent disability of thousands of patients, but also affect mortality rate. The gold standard for treatment of cardiovascular diseases caused by vascular occlusion is bypass surgery. In case of coronary artery disease and lower extremity arterial disease, bypass of small diameter blood vessels is required, and, as usual, autologous saphenous veins or arteries are currently used for this surgery. Synthetic prostheses with vessel diameter of more than 8 mm are well-proven, but prostheses with smaller size were unsuitable due to low patency. There is an urgent need for vascular prostheses with properties that are identical to the properties of human native arteries. Tissue engineering, a rapidly developing field in the last decade, is able to offer an alternative for synthetic grafts and autovenous shunts that are currently used. Artificial arteries obtained by tissue engineering techniques must meet all requirements for vascular substitutes today. As expected, conduits obtained by tissue engineering techniques, will regenerate and be populate by recipient cells, actually becoming the patient's own arteries. Currently, none of the developed blood vessel substitutes possess these qualities in full.

Tissue engineering of heart valves is a combination of challenges, and a key to the solution of these problems requires a full and thorough understanding of the structure and function of the valve. Heart valve obtained by tissue engineering techniques not only should adapt successfully to deformation, but also should possess the appropriate flexibility, strength, be easily implanted, durable, be resistant to infection, athrombogenic, and what is especially actual for pediatric cardiac surgery, should have the ability to remodel and grow with the growth of other structures of the host heart.

Valve testing program includes measurement of valve geometry, pulsatile flow through a valve, and static pressure loss across the valve, monitoring of pressure in the heart chambers and aorta. Synchronously with the measurement of pulsatile pressure and flow, a visualization of the movements of the valve cusps is carried out both in the axial view of the output side of the valve through an optical window by a digital video camera, and in the lateral view through a water-filled elastic shell by ultrasonic transducer of the echocardiography system. Also, several biomechanical properties of the valves (extensibility, flexion strain index, closing function) are monitored. Hydrodynamic efficiency is primarily determined by high performance index (or efficiency index) and low back flow leakage (regurgitation). Perturbing effects of the valve on blood flow, i. e., risk of mechanical damage of the formed elements of the blood and thrombus formation when blood flow passes through the valve, are evaluated.