Biomedical Engineering Reference
In-Depth Information
4.2 Manufacture and Characterization of Fabrics and Grafts
4.2.1 Manufacture of Fabric Socks
Fabric socks were manufactured using braiding and knitting processes, respec-
tively, (Secant Medical LLC, Perkasie, PA, USA) according to the required
specification including longitudinal and circumferential force-displacement char-
acteristics, inner diameter, fabric wall thickness, fiber thickness, pore size and
surface coverage. The force-displacement characteristics of the manufactured
prototypes were determined experimentally. In an iterative process, the compari-
son of the experimental data with the numerically predicted requirements was
utilized to select the most promising prototype candidates and to guide the man-
ufacturing of subsequent fabric generations.
4.2.2 Mechanical Characterization of Fabric Socks
Longitudinal and circumferential tensile test were conducted using an Instron 5544
universal testing machine (Instron Corp., Norwood, MA, USA) in phosphate-
buffered saline solution at 37
C) to determine the force-displacement relationships
in the two principal directions of the fabric socks. For circumferential tests,
samples (length: 36.0 mm) were placed over two pins whereas for longitudinal
tensile tests, samples (length: 48.0 mm) were clamped flat at both ends using
custom-made fabric clamps. The cross-head speed was 200 mm/min [
16
,
17
] for
all tests. The samples were tested to a maximum strain of 50 % and 100 % for
circumferential and longitudinal tests, respectively. All tests were conducted in
accordance with relevant standards [
16
,
17
] as indicated in
Sect. 4.1.2
.
4.2.3 Manufacture of Graft Samples
Non-reinforced graft samples comprised a 50 mm porous graft sections (manu-
factured as described in
Sect. 3
) and two 20 mm e-PTFE graft anastomoses (inner
diameter: 4 mm, wall thickness: 30 lm; Atrium, Hudson, NH). The e-PTFE
sections anastomosed to the porous graft by repeated application and drying of a
polyurethane solution (5 % PUR by mass in Chloroform) while the segments were
constrained on a central mandrel. The e-PTFE graft ends ensured a) that graft
samples were not damaged due to attachment in the test fixture and b) consistent
longitudinal strains during testing. For reinforced grafts, fabric socks were applied
over the porous scaffolds ensuring uniformity. At one of the anastomotic regions of
the porous graft, the fabric was anastomosed to the structure by additional
application of a polyurethane solution (10 % PUR by mass in Chloroform). A
higher concentrated polyurethane solution was used to reduce the absorption into
the porous structure. Once this anastomotic region was cured, the fabric sock was
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