A cylindrical body is produced which is composed of a fiber structure with a basis weight of 1-50 g/m2 and having a diameter of 0.5-50 mm and a bellows-shaped section, wherein the crest-to-crest spacing of the bellows-shaped section is no greater than 2 mm and the crest-to-valley depth of the bellows-shaped section is 0.01-1 mm collagen is added to the cylindrical body to produce a composite including the cylindrical body and collagen.