The engineering of a functional blood vessel substitute has for a quarter of a century been a "holy grail" within the cardiovascular research community. Such a substitute must exhibit long term patency, and the critical issues in this area in many ways are influenced by biomechanics. One of the requirements is that it must be non-thrombogenic, which requires an "endothelial-like" inner lining. It also must have mechanical strength, i.e. a burst pressure, sufficient to operate at arterial pressures. Ideally, however, it must be more than this. It also must have viscoelastic properties that match those of the native vessel being replaced. Finally, if it is to be able to adapt to changing blood flow conditions, it must exhibit vasoactivity, a function which in and of itself can be viewed as biomechanical in nature. To achieve this requires having, as part of the construct, vascular smooth muscle cells, which are contractile in nature and oriented in a circumferential direction. Only if an engineered blood vessel substitute possesses all of these functional characteristics, can one say that the functionality exhibited by a native vessel is being mimicked.