Provided is a medical substrate suitable for reproduction of a circulatory system, the medical substrate being suitable for a blood vessel in which a clot readily forms, e.g., a relatively narrow artificial blood vessel that has a lumen diameter of 6-8 mm or less and is exposed to high pressure from the lumen, such as venous system blood vessel or an artery. The medical substrate according to the present invention is sheet-shaped, tube-shaped, or a combination of these shapes, and is transplanted into a body and used to reproduce a circulatory system, the medical substrate having a multilayer structure provided with at least an inner layer disposed on an inner membrane side of a circulatory system, and an outer layer disposed further toward an outer membrane side of the circulatory system than the inner layer, the layer disposed further toward the outer membrane side of the circulatory system than the inner layer being formed in a porous shape so that a feeding blood vessel reaches the inner layer or can penetrate to the vicinity of the inner layer, and with regard to a rigidity index a determined by a specific method, the ratio of the rigidity index a of the outer layer of the tube-shaped medical substrate to the rigidity index a of a transplanted blood vessel being 7.5 or less.La présente invention concerne un substrat médical adapté à la reproduction dun système circulatoire, le substrat médical étant adapté à un vaisseau sanguin dans lequel un caillot se forme facilement, par exemple, un vaisseau sanguin artificiel relativement étroit qui a un diamètre de lumière de 6-8 mm ou moins et est exposé à une haute pression à partir de la lumière, tel quun vaisseau sanguin de système veineux ou une artère. Le substrat médical selon la présente invention est en forme de feuille, en forme de tube ou une combinaison de ces formes, et est transplanté dans un corps et utilisé pour reproduire un système circulatoire, le substrat médical ayant une structure multicouche comport
