Medical instrument

A medical instrument comprising:

• at least one first hollow fiber membrane layer comprised of a plurality of integrated first hollow fiber membranes, the first hollow fiber membrane layer being configured as a cylindrically-shaped body, and possessing an outer circumferential side and a central axis extending along an axial length of the cylindrically-shaped body of the first hollow fiber membrane;
• and at least one second hollow fiber membrane layer disposed at the outer circumferential side of the first hollow fiber membrane layer concentric with the first hollow fiber membrane layer, the second hollow fiber membrane layer being comprised of a plurality of integrated second hollow fiber membranes, the second hollow fiber membrane layer being configured as a cylindrical-shaped body,
• wherein each of the first hollow fiber membranes and each of the second hollow fiber membranes is wound around the central axis of the cylindrical body;
• wherein each of the first hollow fiber membranes sequentially begins at a starting point set at one site at one end of the cylindrically-shaped body, continues to a midpoint, and ends at an endpoint set at one site in the same position as the starting point or in a position deviating from the starting point around the central axis;
• wherein each of the first hollow fiber membranes is wound in a first winding pattern from the starting point to the endpoint, the first winding pattern defined by the first hollow fiber membranes being wound at least once in the circumferential direction around the central axis of the cylindrical body in an outward path from the starting point towards the midpoint, and being wound by the same number of turns in a same direction as in the case of the outward path in a homeward path from the midpoint towards the endpoint;
• wherein each of the second hollow fiber membranes sequentially begins at a starting point set at one site at an end of the cylindrically-shaped body, continues to a midpoint, and reaches an endpoint set at one site at the same position as the starting point or in a position deviating from the starting point around the central axis;
• wherein each of the second hollow fiber membranes is wound in a second winding pattern from the starting point to the endpoint, the second winding pattern being defined by each of the second hollow fiber membranes being wound by one half a circumference in the circumferential direction around the central axis of the cylindrical body in an outward path from the starting point towards the midpoint, and being wound by a same number of turns in a same direction as in the case of the outward path in a homeward path from the midpoint towards the endpoint;
• and
• whereby the first winding pattern of the first hollow fiber members around the central axis of the cylindrical body is different from the second winding pattern of the second hollow fiber membranes around the central axis of the cylindrical body.