title: Contact-free monitoring of vessel graft stiffness - proof of concept as a tool for vascular tissue engineering.
abstract: Tissue-engineered vessel grafts have to mimic the biomechanical properties of native blood vessels. Manufacturing processes often condition grafts to adapt them to the target flow conditions. Graft stiffness is influenced by material properties and dimensions and determines graft compliance. This proof-of-concept study evaluated a contact-free method to monitor biomechanical properties without compromising sterility. Forced vibration response analysis was performed on human umbilical vein (HUV) segments mounted in a buffer-filled tubing system. A linear motor and a dynamic signal analyser were used to excite the fluid by white noise (0-200 Hz). Vein responses were read out by laser triangulation and analysed by fast Fourier transformation. Modal analysis was performed by monitoring multiple positions of the vessel surface. As an inverse model of graft stiffening during conditioning, HUV were digested proteolytically, and the course of natural frequencies (NFs) was monitored over 120 min. Human umbilical vein showed up to five modes with NFs in the range of 5-100 Hz. The first natural frequencies of HUV did not alter over time while incubated in buffer (p = 0.555), whereas both collagenase (-35%, p = 0.0061) and elastase (-45%, p < 0.001) treatments caused significant decreases of NF within 120 min. Decellularized HUV showed similar results, indicating that changes of the extracellular matrix were responsible for the observed shift in NF. Performing vibration response analysis on vessel grafts is feasible without compromising sterility or integrity of the samples. This technique allows direct measurement of stiffness as an important biomechanical property, obviating the need to monitor surrogate parameters. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: Department of Cardiothoracic and Vascular Surgery, University of Ulm Medical Centre, Ulm, Germany.|Department of Cardiothoracic Surgery, University of Regensburg Medical Centre, Regensburg, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Hoenicka
authors.affiliation: Ostbayerische Technische Hochschule (OTH) Regensburg, FB Maschinenbau, Regensburg, Germany.
authors.forename: Marcel
authors.initials: M
authors.lastname: Kaspar
authors.affiliation: Department of Cardiothoracic Surgery, University of Regensburg Medical Centre, Regensburg, Germany.
authors.forename: Christof
authors.initials: C
authors.lastname: Schmid
authors.affiliation: Department of Cardiothoracic and Vascular Surgery, University of Ulm Medical Centre, Ulm, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Liebold
authors.affiliation: Ostbayerische Technische Hochschule (OTH) Regensburg, FB Maschinenbau, Regensburg, Germany.
authors.forename: Siegfried
authors.initials: S
authors.lastname: Schrammel
mesh_terms: D001696:Biomechanical Phenomena; D001807:Blood Vessel Prosthesis; D006801:Humans; D010196:Pancreatic Elastase / Q000494:pharmacology; D059748:Proteolysis / Q000187:drug effects; D013997:Time Factors; D023822:Tissue Engineering / Q000379:methods*; D014471:Umbilical Veins / Q000187:drug effects / Q000502:physiology; D014732:Vibration
chemical_list: D010196:Pancreatic Elastase
keywords: biomechanics; extracellular matrix; human umbilical vein; proteolysis; small calibre graft; vascular tissue engineering