In vitro evaluation of a nitinol based vein cuff for external valvuloplasty

This study shows first in vitro tests of a nitinol based vein cuff developed for external valvuloplasty. In contrary to currently existing vein cuffs the tested model enables minimal invasive implantation and also maintains its round pre-shaped profile at body temperature (37 degrees C). The examination of the cuff surface structure by scanning electron microscopy, profilometry and X-ray photoelectron spectroscopy after sterilization with ethylene oxide and before cyto-compatibility testing revealed a nearly smooth surface (mean square roughness Rq 66 +/- 33 nm) which was primarily composed of nickel, oxygen, titanium, carbon and silicon where nickel was the least fraction (Ni: 0.7%, Ti: 1.7%, Si: 15.8%, O: 29.5%, C: 52.3%) of the surface elements. Si and C are supposed to be contaminations caused by a final cuff polishing with silicon carbide at the end of the manufacturing process. To evaluate cyto-compatibility initial cell adherence and cell activity were assessed. The results showed good initial cell adherence of L929 fibroblast-like cells on the cuff surface already after 24 h. The results also revealed no inhibitory effects on the activity of these cells (MTS test) later on. The test setup developed to analyse functionality in a dynamic mode was shown to be suited at blood pressures up to 300 mmHg. The cuff successfully limited dilation of varicose veins (Vena saphena magna) at physiological blood pressures (< 120 mmHg) and also in cases of hypertonia (300 mmHg) to the diameter determined by the cuff (4.0 mm) over thecomplete testing period. This indicates that the clasp based cuff closure mechanism is suited to close the cuff under variable physiological and pathological blood pressure conditions. The cuff structure only allowed minimal adaptation on the inhomogenously dilating vein profile in the both peripheral cuff modules. Both peripheral modules followed the vessel dilation in correlation to the applied pressure. At pressures within the physiological range