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Hiebl B.,Center for Biomaterial Development | Hiebl B.,Helmholtz Center Geesthacht | Jung F.,Center for Biomaterial Development | Jung F.,Helmholtz Center Geesthacht | And 7 more authors.
Clinical Hemorheology and Microcirculation | Year: 2010

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°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 ≤ 120 mmHg) the variation of the lateral arch module diameter was only marginal, whereas at 300 mmHg pressure the peripheral modules followed vein dilation up to a diameter of 5.0 to 5.5 mm. The cuff also maintained the pre-shaped round profile in the central and peripheral modules during the pressure increase and the consecutive cuff expansion. The study showed that the first nitinol based vein cuff for external valvuloplasty was processed well enough by electropolishing and sterilization to allow culturing of L929 fibroblast-like cells on the cuff surface as a test of general biocompatibility. The cuff also proved to limit dilation of varicose veins at physiological and pathological blood pressures in vitro. Further tests with primary cells from the venous wall will follow to test the specific biocompatibility before tests in vivo can be envisaged. © 2010 - IOS Press and the authors. All rights reserved.

Wagermaier W.,Center for Biomaterial Development | Zander T.,Center for Biomaterial Development | Hofmann D.,Center for Biomaterial Development | Kratz K.,Center for Biomaterial Development | And 4 more authors.
Macromolecular Rapid Communications | Year: 2010

The dual- and triple-shape effects of multiphase polymer networks that contain two crystallizable chain segments have been assessed in situ by combining X-ray measurements with thermomechanical investigations. The studied polymer, named CLEG, is a multiphase polymer network of crystallizable poly(ε-caprolactone) (PCL) with grafted polyethylene glycol) (PEG) side chains. Wideangle (WAXS) and small-angle X-ray scattering (SAXS) measurements were combined with temperature-controlled in situ tensile testing experiments. This integrated approach enables systematic investigation and interpretation of relevant structural features during the programming procedures and the thermally-induced recovery process. Main results concern the combined effect of PCL and PEG crystals on shape fixation, the specific role of low-melting PCL crystallites in the fixation of the low temperature temporary shape, and the different orientation behavior of PCL and PEG crystals during certain stages of the programming procedure. These results demonstrate that crystal orientation effects are dominant for the PCL crystals. The effects of the low temperature PCL crystals could only be investigated when synchrotron radiation was applied. These findings indicate the great potential of in situ X-ray investigations for the creation of design-relevant knowledge about the microscopic foundations of dual- and triple-shape effects in appropriate polymer systems. (Figure Presented) © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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