Background

Coronary Artery Disease

Coronary artery disease (CAD) is one of the major reasons for morbidity and mortality in western countries. CAD does not only affect the quality of life of the patients, but also puts a major strain on healthcare systems.

Available Treatments

The symptoms of CAD, like chest pain (angina), can be kept at bay pharmacologically in many patients. However, as the disease progresses, invasive methods must be applied to avoid heart attacks. Basically, there are two approaches. Balloon angioplasty, often combined with stenting, dilates the obstructed region of the coronary arteries by inserting a special catheter. Stents are hollow tubes built from a mesh which keeps the dilated region open mechanically. The second approach is coronary artery bypass grafting (CABG), which uses a conduit to bypass the obstructed region. CABG is considered the method of choice especially for multivessel disease if judged by long-term survival rates.

Graft Sources

Autologous (i.e. the patient's own) vessels are an excellent source of grafts as they are not rejected by the body. The greater saphenous vein (one of the superficial veins of the leg) is the most commonly used graft source. However, other vessels like the radial artery (taken from the lower arm) are used too.

Removing one of these vessels always carries a risk of wound healing problems and sepsis, and leaves scars on the affected limbs. Additionally, an increasing number of patients does not have suitable autologous vessels due to prior removal, varicosis, or limb loss.

Tissue Engineered Vessels

Tissue Engineering means to create a replacement tissue or organ employing the patient's own cells. Vascular tissue engineering is supposed to provide vessel grafts which are equal or superior to autologous vessels. Several properties are required:

• antithrombogenic surface: the graft surface must not cause platelets to adhere or to aggregate. The best possible surface is the patient's own endothelium, the innermost layer of all blood vessels.
• compliance: the viscoelastic properties (roughly speaking, the "stiffness") must match the patient's own vessels
• burst pressure: the graft must withstand the pressure in the coronary circulation, with a sufficient safety margin
• contractile function: the graft should respond to constricting and dilating signalling substances in an appropriate way
• suturability: the graft must be suitable for common surgical procedures and materials
• kink resistance: the graft wall should be flexible enough to not kink when sutured into place

There are many approaches to develop artificial vascular grafts. Some groups build vessels from individual layers of cells, whereas others, like the Viskograft team, use some kind of scaffold to seed cells.