Immobilized biologically active entities having a high degree of biological activity

A medical device comprising:

• a substrate material;
• a polymeric covering material attached to at least a portion of a surface of said substrate material, a first plurality of biologically active entities having heparin cofactor II binding activity and a second plurality of biologically active entities having anti-thrombin III binding activity covalently attached to at least a portion of said polymeric covering material;
• and
• a biologically compatible composition combined with said polymeric covering material,
• wherein said biologically active entities have a heparin cofactor II binding activity of at least 5 picomoles heparin cofactor II per square centimeter (pmol/cm2) and at least 5 picomoles anti-thrombin III per square centimeter.