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  • 1
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 39 (1998), S. 215-221 
    ISSN: 0021-9304
    Keywords: bovine pericardium ; collagen fibers ; light scattering ; bioprostheses ; heart valves ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: In Part I of this work we used small-angle light scattering (SALS) to quantify the fiber architecture of 20 bovine pericardial sacs, along with corresponding tissue-thickness measurements, to determine optimal material selection sites. In order to determine the anatomic consistency of these sites, the fiber architecture and thickness data from all 20 sacs were averaged together using a cartographic analysis method that took advantage of the geometry of the prolate spheroid mold used to process the sacs. Optimal selection sites were determined based on a local criteria where all fiber preferred directions within a 2.54-cm circular area were within ±10°. The largest contiguous area (LCA) for the entire BP sac was 20.54 cm,2 located in the vicinity of the left ventricle of the heart. The LCA tissue thicknesses were also relatively uniform, further supporting the use of these areas. However, even within these optimal areas there was a ±20° standard deviation in local fiber preferred directions, resulting in at best a 40° spread in local preferred directions. The observed structural variability may be due to regionally heterogeneous physiologic loadings induced by the ligamentous attachments. These attachments may alter the regional fiber preferred orientation to support local mechanical loadings. Overall, given the inherent structural variability of the BP sac, we conclude that use of anatomic location alone will not consistently guarantee the selection of tissue specimens with a highly homogeneous and predictable fibrous structure. It is thus suggested that a direct fiber measurement presorting method be employed when selecting BP specimens for bioprosthetic applications where tissue structural homogeneity and uniformity is critical. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 215-221, 1998.
    Additional Material: 9 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 39 (1998), S. 207-214 
    ISSN: 0021-9304
    Keywords: bovine pericardium ; heart valves ; bioprostheses ; light scattering ; collagen fibers ; tissue thickness ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Use of bovine pericardium as an engineered biomaterial in the fabrication of bioprosthetic heart valves is limited, in part, by substantial intra- and intersac variations in its fibrous structure. To quantitatively assess this variability, we determined the fiber architecture of 20 whole BP sacs. Each sac was mounted on a prolate spheroidal mold, cleared and preserved in 100% glycerol, then sectioned into four equisized quadrants. This preparation method allowed for accurate intersac comparisons and minimized tissue distortions. The fiber architecture was evaluated by small-angle light scattering (SALS) using a 2.54-mm rectilinear grid resulting in ∼1200 SALS measurements per quadrant, along with tissue thickness measured at 55 locations per quadrant. The fiber architecture was described in terms of fiber preferred directions, degree of orientation, and asymmetry of the fiber angular distribution. The BP sac fiber architecture demonstrated substantial intra- and intersac variability, with local fiber preferred directions changing by as much as 90° within ∼5 mm. Overall, most sacs revealed potential selection areas in the apex region characterized by a high degree of orientation, high uniformity in fiber preferred directions, and uniform tissue thickness. However, the size, location, and fiber orientation of these potential selection areas varied sufficiently from sac-to-sac to question whether anatomic location alone is sufficient for consistent localization of regions of high structural uniformity suitable for improved BHV design. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 207-214, 1998.
    Additional Material: 8 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 41 (1998), S. 131-141 
    ISSN: 0021-9304
    Keywords: aortic valve ; collagen fibers ; light scattering ; bioprostheses ; pressure ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: We undertook this study to establish a more quantitative understanding of the microstructural response of the aortic valve cusp to pressure loading. Fresh porcine aortic valves were fixed at transvalvular pressures ranging from 0 mmHg to 90 mmHg, and small-angle light scattering (SALS) was used to quantify the gross fiber structure of the valve cusps. At all pressures the fiber-preferred directions coursed along the circumferential direction. Increasing transvalvular pressure induced the greatest changes in fiber alignment between 0 and 1 mmHg, with no detectable change past 4 mmHg. When the fibrosa and ventricularis layers of the cusps were re-scanned separately, the fibrosa layer revealed a higher degree of orientation while the ventricularis was more randomly oriented. The degree of fiber orientation for both layers became more similar once the transvalvular pressure exceeded 4 mmHg, and the layers were almost indistinguishable by 60 mmHg. It is possible that, in addition to retracting the aortic cusp during systole, the ventricularis mechanically may contribute to the diastolic cuspal stiffness at high transvalvular pressures, which may help to prevent over distention of the cusp. Our results suggest a complex, highly heterogeneous structural response to transvalvular pressure on a fiber level that will have to be duplicated in future bioprosthetic heart valve designs. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 131-141, 1998.
    Additional Material: 8 Ill.
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