Biodegradable aliphaticaromatic copolyester comprising: A) an acid component comprising repeating units of: 1) 53 to 54 mol % of an aromatic carboxylic acid; 2) 47 to 36 mol % of an aliphatic acid at least 50% of which is azelaic acid; B) a diol component selected from the group consisting of C3, C4 and C6 diols; said AAPE being disintegrated according to the Standard ISO 20200 in 90 days. The first and second test TFTs are disposed on the joint obligate region according to a regular distance. The sleeve is mounted around the housing. The SISD structure has a composition gradient wherein the percentage of the second element varies from the upper surface of the sourcedrain structure to a lower surface of the SISD structure. Further, each clamping unit is provided with a pressure cylinder the cylinder housing of which, being disposed radially shiftable in the effective direction on the inside, is fixedly connected to the radially outer clamping jaw sustainer by means of at least one connection strut and the piston of which, acting radially outwardly, engages the radially inner clamping jaw sustainer.