PROBLEM TO BE SOLVED: To provide a medical base material which is suitable for a blood vessel on which clot easily occurs, for example, a venous system blood vessel or a relatively thin artificial blood vessel which is exposed to high pressure from a lumen and whose lumen diameter is 6-8 mm or smaller, such as an artery, the medical base material being suitable for reproduction of a circulatory system.SOLUTION: A medical base material is formed into a sheet shape, a tube shape or a shape combining the sheet shape and the tube shape, and is used for reproduction of a circulatory system by being implanted into a body, and the medical base material comprises a multi-layer structure comprising at least an inner layer provided in an inner membrane side of the circulatory system, and an outer layer provided in an outer membrane side of the circulatory system relative to the inner layer, and the layer provided on the outer membrane side of the circulatory system relative to the inner layer is formed into a porous shape so that a nutrient blood vessel reaches the inner layer, or can enter the vicinity of the inner layer, and about an index a of rigidity determined by a specific method, a ratio of an index a of the rigidity of the outer layer of the tube shape medical base material and an index a of the rigidity of the blood vessel to be implanted is within 7.5.SELECTED DRAWING: Figure 1【課題】循環器系の再生に好適な医療用基材であって、血栓の出来易い血管、例えば静脈系血管や、動脈のように内腔からの高い圧力に曝され、内腔直径が6～8mm以下の比較的細い人工血管に好適な医療用基材を提供する。【解決手段】医療用基材は、シート形状、管形状、又はこれらを組み合わせた形状をしていて、体内に移植して循環器系の再生に使用される医療用基材であって、循環器系の内膜側に配置される内層と、内層より循環器系の外膜側に配置される外層と、を少なくとも備える複層構造をしており、内層よりも循環器系の外膜側に配置される層が、栄養血管が内層に達するように又は内層近傍まで入り込めるように、多孔質形状に形成されているとともに、特定の方法で決定される剛性の指標ａについて、管形状の医療用基材の外層の剛性の指標ａ/移植される血管の剛性の指標ａの比が7.5以内である医療用基材である。【選択図】図１
