Mechanische Eigenschaften von Human- und Schweineperikard

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.In der Vergangenheit hat es umfangreiche Forschungsarbeiten über die mechanischen Eigenschaften von Rinderperikard gegeben, welches als biologisches Material für künstliche Herzklappen eingesetzt wird. Durch das Auftreten der Krankheit BSE in britischem Vieh wird heute jedoch nach alternativen Materialien gesucht. Humanes autogenes Perikard verspricht, keine Immunreaktionen auszulösen, die auch bei fixierten Fremdgeweben für eine allmähliche Kalzifizierung und damit Versprödung verantwortlich gemacht werden. Schweineperikard ist aufgrund seiner unbegrenzten Verfügbarkeit interessant. Eingehende Untersuchungen wurden vor allem mit verschiedenem tierischen Perikard durchgeführt. Die Testmethoden teilen sich in zwei Hauptgruppen mit uniaxialen bzw. biaxialen mechanischen Belastungen. Uniaxiale Zugversuche liefern grundlegende einfach reproduzierbare Daten, wohingegen biaxiale Belastungen als physiologischer angesehen werden, jedoch meist eine Reihe weiterer Parameter erfordern und einen komplexen Versuchsaufbau haben

Uniaxial tension test of human-skin invivo

The application of uniaxial tension in vivo is a common test method for investigating mechanical properties of the skin. This paper reports an investigation of the strain distributions on the skin surface produced by such a test method. The strains were shown to be non-homogeneous with major concentrations being present near the area of load application. At all sites within the test area, axial, lateral and shear strains were present but their magnitude depended both on their position within the test site and the overall extension. The axial and lateral strains were largest and most uniformly distributed within the area bounded by th loading tabs. The shear strains, however, were smallest in the are bounded by the tabs. The distribution of the three strains became similar if they were referred to the principal axes. The area of skin within the strained area became larger as the overall deformation increased because additional skin was recruited from the sites lateral to the strained area. The general form of the load/strain relations and lateral contractions were site- and extension-dependent, but were similar to those found in vitro

Effect of low-level laser treatment of tissue-engineered skin substitutes: contraction of collagen lattices

Fibroblast-populated collagen lattices (FPCL) are widely used in tissue-engineered artificial skin substitutes, but their main drawback is that interaction of fibroblasts and matrix causes contraction of the lattice, reducing it to about 20% of its original area. The effect of low-level laser treatment (LLLT) on the behavior of 3T3 fibroblasts seeded in collagen lattices containing 20% chondroitin-6-sulphate was investigated to determine whether LLLT could control the contraction of FPCL. A He-Ne laser was used at 632.8 nm to deliver a 5-mW continuous wave with fluences from 1 to 4 J/cm(2). Laser treatment at 3 J/cm(2) increased contraction of collagen lattices in the absence of cells but decreased contraction of cell seeded lattices over a 7-day period. The effect was energy dependent and was not observed at 1, 2, or 4 J/cm(2). There was no alteration in fibroblast viability, morphology, or mitochondrial membrane potential after any laser treatments, but the distribution of actin fibers within the cells and collagen fibers in the matrices was disturbed at 3 J/cm(2). These effects contribute to the decrease in contraction observed. LLLT may offer a means to control contraction of FPCL used as artificial skin substitutes

A theoretical investigation of ultrasonic transducer design for measurement of skin

Despite significant advances in ultrasonic instrumentation, accurate and repeatable measurements of skin structure and dimensions remain problematic. Skin structure is complicated and structural boundaries are non-planar and may be diffuse, inhibiting the application of inversion methods for skin thickness measurement. Coupling a transducer to the skin surface with water or aqueous gel can produce significant artefacts in thickness measurement, which may be prevented by using a rubber dry contact. This work describes a theoretical investigation of these problems, using the PZFlex finite element code as a virtual prototyping tool. Simulations show that non-planar and diffuse boundaries have significant effect on the output backscattered signals; and using of low loss rubber dry contact is possible but further work is required to determine the properties and optimum shape of the rubber interface

Contractile behaviour of 3T3 mouse fibroblasts in artificial skin substitutes: effect of different cell-seeding methods

With the rapid development of tissue engineering and gene therapy, collagen-based biomaterials are frequently used as cell transplant devices; an example is bio-artificial skin substitutes [1-3]. In this study, we determined the effects of two different cell-seeding methods, monolayer and suspension seeding, on the rate of contraction of free-floating collagen and collagenglycosaminoglycan (GAG) gel matrices in vitro. 3T3 mouse fibroblasts were cultured in/on the matrices for up to 7 days

A study of inversion layer transducers

Much recent interest has been expressed regarding inversion layer piezoelectric transducers. These are multi-layered devices, incorporating a reversal in piezoelectric polarisation in the stack thickness, creating the potential for extended bandwidth and enhanced even harmonic sensitivity in thickness drive structures. The transducer properties are determined in turn by the relative dimensions of the polarised zones, in addition to the mechanical load conditions at the transducer boundaries. This work presents an evaluation of different inversion layer configurations and piezoelectric materials, using the FE code PZFLEX as a virtual prototyping tool. The influence on non-uniform piezoelectric boundaries in lithium niobate transducers is addressed. The potential for multiple piezoelectric zones is also investigated, through modelling of three and more inversion layers through the transducer thickness. The influence of backing and matching on the transducer bandwidth and sensitivity is also considered. Experimental data is provided for lithium niobate plates and piezoelectric composite transducers, with the latter geared towards the enhanced detection of second harmonic backscatter in contrast agent imaging

Face bow and articulator for planning orthognathic surgery: 2 articulator

Patients who require orthognathic surgery may have asymmetry of the position of the temporomandibular joints relative to the maxilla, which is impossible to reproduce on the current semiadjustable articulators used for surgical planning. We describe a highly-adjustable spirit level orthognathic face bow that allows records to be made of patients with asymmetrical maxillae. The orthognathic articulator also allows the position of the condylar components of the articulator to be adjusted in three dimensions. The use of the new face bow and articulator made it possible to mount the dental casts of asymmetrical faces to reproduce their clinical appearance. The devices were evaluated by comparing the measurements of anatomical variables obtained from cephalometric radiographs with equivalent values obtained from the orthognathic articulator and casts mounted on the articulator. Although the measurements showed significant intersubject variability, the angle between the horizontal and maxillary occlusal plane, occlusal cant angle, and intercondylar widths, were not significantly different

Low level laser therapy on artificial skin substitutes : no significant effect on the proliferation rate of 3T3 mouse fibroblast cells

Summary of paper describing how low level laser therapy on artificial skin substitutes cause no significant effect on the proliferation rate of 3T3 mouse fibroblast cells