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  • 1
    ISSN: 1524-475X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The purpose of this study was determine quantitative differences in collagen fiber orientation in a wound healing model in the presence of transforming growth factor-β2 and anti-transforming growth factor-β2,3 antibody. Full-thickness wounds were made in the paravertebral area of two young pigs. Wounds were treated once, topically, with either transforming growth factor-β2 or anti-transforming growth factor-β2 antibody, or with methylcellulose gel. Control wounds were left untreated. Tissue biopsies were obtained from each wound on days 7, 14 and 46 post wounding. Tissue sections were stained with hematoxylin and eosin, and collagen fiber preferred orientation was quantified using small angle light scattering. Our results indicated that wounds treated with transforming growth factor-β2 and anti-transforming growth factor-β2,3 antibody had a significantly higher degree of orientation of collagen fibers than normal unwounded skin on days 7, 14 and 46 (p 〈 0.001). Transforming growth factor-β2– treated wounds had a higher degree of orientation of collagen fibers than control wounds on days 7 and 14 (p 〈 0.001), and control wounds displayed a higher degree of orientation than wounds treated with anti-transforming growth factor-β2,3 and normal unwounded skin at all time points (p 〈 0.001). These results suggest that differences in the dermal collagen degree of orientation correlate with scarring, and show that small angle light scattering can be used quantitatively to assess differences in the collagen fiber architecture of dermal wounds.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Biomedical Engineering 5 (2003), S. 251-284 
    ISSN: 1523-9829
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Technology , Medicine
    Notes: For native and engineered biological tissues, there exist many physiological, surgical, and medical device applications where multiaxial material characterization and modeling is required. Because biological tissues and many biocompatible elastomers are incompressible, planar biaxial testing allows for a two-dimensional (2-D) stress-state that can be used to fully characterize their three-dimensional (3-D) mechanical properties. Biological tissues exhibit complex mechanical behaviors not easily accounted for in classic elastomeric constitutive models. Accounting for these behaviors by careful experimental evaluation and formulation of constitutive models continues to be a challenging area in biomechanical modeling and simulation. The focus of this review is to describe the application of multiaxial testing techniques to soft tissues and their relation to modern biomechanical constitutive theories.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Biomedical Engineering 5 (2003), S. 251-284 
    ISSN: 1523-9829
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Technology , Medicine
    Notes: Abstract For native and engineered biological tissues, there exist many physiological, surgical, and medical device applications where multiaxial material characterization and modeling is required. Because biological tissues and many biocompatible elastomers are incompressible, planar biaxial testing allows for a two-dimensional (2-D) stress-state that can be used to fully characterize their three-dimensional (3-D) mechanical properties. Biological tissues exhibit complex mechanical behaviors not easily accounted for in classic elastomeric constitutive models. Accounting for these behaviors by careful experimental evaluation and formulation of constitutive models continues to be a challenging area in biomechanical modeling and simulation. The focus of this review is to describe the application of multiaxial testing techniques to soft tissues and their relation to modern biomechanical constitutive theories.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of food science 53 (1988), S. 0 
    ISSN: 1750-3841
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An indepth biomechanical study was performed to characterize more fully the viscoelastic behavior of post-rigor bovine muscle, using samples oriented parallel and perpendicular to the muscle fiber direction. Two enzymes were used to degrade the intramuscular connective tissue (IMCT) to evaluate its mechanical contribution. An unusual stress-strain curve was found in the parallel oriented samples, with enzymolysis affecting the curve at strains larger than 8%. Reductions in stresses in both orientations due to enzymolysis were 50% with extensibility unchanged. Stress relaxation tests indicated that regardless of orientation or treatment the relative stress-relaxation was unchanged. IMCT contributed substantially to the mechanical response only at large deformations.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 198-199 (Jan. 2001), p. 255-260 
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Computational mechanics 26 (2000), S. 243-249 
    ISSN: 1432-0924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Chemically treated, biologically derived soft collagenous tissues are used extensively in medical devices. To enable prosthesis design through computational methods, physically realistic constitutive models are required. In the present study, a structural approach was utilized that incorporated experimentally measured angular distribution of collagen fibers. Using biaxial mechanical data from our previous study (Annals of Biomedical Engineering, vol. 26(5), pp. 892–902, 1998), the effective fiber and matrix stress–strain responses were predicted. The agreement with the experimental data supported the assumption that the mechanical effects of chemical treatment are equivalent to the addition of an isotropic elastic matrix. An important utility of this model is its ability to separate the effects of chemical treatment on the fibers and matrix. Applications of this approach include utilization in the design of novel chemical treatments that produce specific mechanical responses, the study of fatigue damage, and finite element implementation for tissue engineering scaffold design.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-9686
    Keywords: Abdominal aortic aneurysm ; Curvature ; Tortuosity ; Three-dimensional reconstruction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Abdominal aortic aneurysm (AAA) is a local, progressive dilation of the distal aorta that risks rupture until treated. Using the law of Laplace, in vivo assessment of AAA surface geometry could identify regions of high wall tensions as well as provide critical dimensional and shape data for customized endoluminal stent grafts. In this study, six patients with AAA underwent spiral computed tomography imaging and the inner wall of each AAA was identified, digitized, and reconstructed. A biquadric surface patch technique was used to compute the local principal curvatures, which required no assumptions regarding axisymmetry or other shape characteristics of the AAA surface. The spatial distribution of AAA principal curvatures demonstrated substantial axial asymmetry, and included adjacent elliptical and hyperbolic regions. To determine how much the curvature spatial distributions were dependent on tortuosity versus bulging, the effects of AAA tortuosity were removed from the three-dimensional (3D) reconstructions by aligning the centroids of each digitized contour to the z axis. The spatial distribution of principal curvatures of the modified 3D reconstructions were found to be largely axisymmetric, suggesting that much of the surface geometric asymmetry is due to AAA bending. On average, AAA surface area increased by 56% and abdominal aortic length increased by 27% over those for the normal aorta. Our results indicate that AAA surface geometry is highly complex and cannot be simulated by simple axisymmetric models, and suggests an equally complex wall stress distribution. © 1999 Biomedical Engineering Society. PAC99: 8719Rr, 8759Fm, 8757Gg
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-9686
    Keywords: Surface fitting ; Curvature ; Finite elements ; Heart valves ; Abdominal aortic aneurysm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The surface geometry of anatomic structures can have a direct impact upon their mechanical behavior in health and disease. Thus, mechanical analysis requires the accurate quantification of three-dimensional in vivo surface geometry. We present a fully generalized surface fitting method for surface geometric analysis that uses finite element based hermite biquintic polynomial interpolation functions. The method generates a contiguous surface of C2 continuity, allowing computation of the finite strain and curvature tensors over the entire surface with respect to a single in-surface coordinate system. The Sobolev norm, which restricts element length and curvature, was utilized to stabilize the interpolating polynomial at boundaries and in regions of sparse data. A major advantage of the current method is its ability to fully quantify surface deformation from an unstructured grid of data points using a single interpolation scheme. The method was validated by computing both the principal curvature distributions for phantoms of known curvatures and the principal stretch and principal change of curvature distributions for a synthetic spherical patch warping into an ellipsoidal shape. To demonstrate the applicability to biomedical problems, the method was applied to quantify surface curvatures of an abdominal aortic aneurysm and the principal strains and change of curvatures of a deforming bioprosthetic heart valve leaflet. The method proved accurate for the computation of surface curvatures, as well as for strains and curvature change for a surface undergoing large deformations. © 2000 Biomedical Engineering Society. PAC00: 8719Rr, 8719Hh, 8768+z, 0260Ed, 0210Sp
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Annals of biomedical engineering 26 (1998), S. 892-902 
    ISSN: 1573-9686
    Keywords: Chemical fixation ; Constitutive modeling ; Bioprostheses ; Heart valves ; Small angle light scattering ; Mechanical properties ; Pericardium: mechanical properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract To facilitate bioprosthetic heart valve design, especially in the use of novel antimineralization chemical technologies, a thorough understanding of the multiaxial mechanical properties of chemically treated bovine pericardium (BP) is needed. In this study, we utilized a small angle light scattering based tissue pre-sorting procedure to select BP specimens with a high degree of structural uniformity. Both conventional glutaraldehyde (GL) and photo-oxidation (PO) chemical treatment groups were studied, with untreated tissue used as the control group. A second set of GL and PO groups was prepared by prestretching them along the preferred fiber direction during the chemical treatment. An extensive biaxial test protocol was used and the resulting stress-strain data fitted to an exponential strain energy function. The high structural uniformity resulted in both a consistent mechanical response and low variability in the material constants. For free fixed tissues, the strain energy per unit volume for GL treated BP was ∼ 2.8 times that of PO treated BP at an equibiaxial Green’s strain level of 0.16. Prestretched tissues exhibited a profound increase in both stiffness and the degree of anisotropy, with the GL treatment demonstrating a greater effect. Thus, structural control leads to an improved understanding of chemically treated BP mechanical properties. Judicious use of this knowledge can facilitate the design and enhanced long-term performance of bioprosthetic heart valves. © 1998 Biomedical Engineering Society. PAC98: 8790+y, 8745Bp, 8780+s
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of elasticity 61 (2000), S. 199-246 
    ISSN: 1573-2681
    Keywords: biaxial mechanical testing ; constitutive modeling of planar biomaterials ; homogeneity ; mechanical properties of collagenous tissues
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A fundamental goal in constitutive modeling is to predict the mechanical behavior of a material under a generalized loading state. To achieve this goal, rigorous experimentation involving all relevant deformations is necessary to obtain both the form and material constants of a strain-energy density function. For both natural biological tissues and tissue-derived soft biomaterials, there exist many physiological, surgical, and medical device applications where rigorous constitutive models are required. Since biological tissues are generally considered incompressible, planar biaxial testing allows for a two-dimensional stress-state that can be used to characterize fully their mechanical properties. Application of biaxial testing to biological tissues initially developed as an extension of the techniques developed for the investigation of rubber elasticity [43, 57]. However, whereas for rubber-like materials the continuum scale is that of large polymer molecules, it is at the fiber-level (∼1 μm) for soft biological tissues. This is underscored by the fact that the fibers that comprise biological tissues exhibit finite nonlinear stress-strain responses and undergo large strains and rotations, which together induce complex mechanical behaviors not easily accounted for in classic constitutive models. Accounting for these behaviors by careful experimental evaluation and formulation of a constitutive model continues to be a challenging area in biomechanics. The focus of this paper is to describe a history of the application of biaxial testing techniques to soft planar tissues, their relation to relevant modern biomechanical constitutive theories, and important future trends.
    Type of Medium: Electronic Resource
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