Blood vessel cover

1 . A cylindrical blood vessel cover that is continuous around the entire circumference and to be placed on an outer circumference of a vein that is anastomosed to an artery or to an artificial vessel, comprising a portion (A), wherein

the portion (A) has a 20% elastic index of 1.2 N or less when an inner diameter of the blood vessel cover is expanded in a radial direction by 20% from its natural state, and

the 20% elastic index is measured by

preparing a cylindrical sample that has a length of 5 mm in an axial direction and is continuous around the entire circumference over the entire axial direction by cutting the blood vessel cover perpendicular to the axial direction along a circumferential cut line of the blood vessel cover;

inserting a first pin and a second pin each having a diameter d of 0.75 mm into a lumen of the cylindrical sample so that each of the first pin and the second pin is parallel to the axial direction of the cylindrical sample;

fixing the first pin;

pulling the second pin towards outside of a radial direction of the cylindrical sample;

measuring a pulling force F 1.2 when πd+2L becomes 1.2 times a perimeter of the cylindrical sample in its natural state given that a distance between the first pin and the second pin is L; and

dividing the pulling force F 1.2 by a strain [(1.2−1.0)/1.0] to obtain the 20% elastic index.

2 . The blood vessel cover according to claim 1 , wherein the 20% elastic index of the portion (A) is 0.1 mN or more.

3 . The blood vessel cover according to claim 1 , wherein

in the axial direction, the blood vessel cover has a first end and a second end; and the blood vessel cover has a first part from the first end to a midpoint between the first end and the second end, and a second part from the midpoint to the second end; and

the portion (A) is located in the first part.

4 . The blood vessel cover according to claim 3 , wherein the blood vessel cover has a first end part from the first end to a midpoint of the first part in the axial direction, and the portion (A) is located in the first end part.

5 . The blood vessel cover according to claim 1 , wherein the entire blood vessel cover is the portion (A).

6 . The blood vessel cover according to claim 1 , wherein

in the axial direction, the blood vessel cover has a first end and a second end; and the blood vessel cover has a first part from the first end to a midpoint between the first end and the second end, and a second part from the midpoint to the second end; and

the 20% elastic index in the second part is smaller than the 20% elastic index in the first part.

7 . The blood vessel cover according to claim 1 , wherein

in the axial direction, the blood vessel cover has a first end and a second end; and the blood vessel cover has a first part from the first end to a midpoint between the first end and the second end, a second part from the midpoint to the second end, a first end part from the first end to a midpoint of the first part, a middle part from the midpoint of the first part to a midpoint of the second part, and a second end part from the midpoint of the second part to the second end; and

the blood vessel cover satisfies the relationship Ea>Ec>Eb given that the 20% elastic index in the first end part is Ea, the 20% elastic index in the middle part is Ec, and the 20% elastic index in the second end part is Eb.

8 . The blood vessel cover according to claim 1 , a length of the portion (A) in the axial direction is 50% or longer of an outer diameter of the artery or artificial vessel to which the vein is anastomosed.

9 . The blood vessel cover according to claim 1 , wherein an inner diameter of the blood vessel cover is expandable by at least 100% in the radial direction from its natural state throughout the axial direction.

10 . The blood vessel cover according to claim 1 , having a length in the axial direction of 5 mm or longer.

11 . The blood vessel cover according to claim 1 , comprising at least one of knitted fabric, woven fabric, and nonwoven fabric as a partial or whole component.

12 . The blood vessel cover according to claim 1 , having a bellows structure with periodically repeating peaks and valleys in the axial direction, wherein

in the axial direction, the blood vessel cover has a first end and a second end; and the blood vessel cover has a first part from the first end to a midpoint between the first end and the second end, a second part from the midpoint to the second end, and a first end part from the first end to a midpoint of the first part; and

in the axial direction, a distance between adjacent peaks in the second part is longer than a distance between adjacent peaks in the first end part.