Ms. Sacks et Db. Smith, EFFECTS OF ACCELERATED TESTING ON PORCINE BIOPROSTHETIC HEART-VALVE FIBER ARCHITECTURE, Biomaterials, 19(11-12), 1998, pp. 1027-1036
We undertook the following study to quantitatively assess the changes
in porcine bioprosthetic heart valve (PBHV) fiber architecture to incr
easing levels of fatigue damage using an in vitro accelerated test mod
el. PBHVs were subjected to 0-500 million test cycles at 16 Hz, and sm
all-angle light scattering (SALS) was used to quantify the gross fiber
structure of the cusps. The degree of gross fiber alignment remained
essentially constant from 0 to 500 million cycles over the entire cusp
. Increasing fiber orientation randomness, indicative of local damage,
was observed only in the vicinity of the nodulus of Arantii after 50
million cycles. The SALS data from the damaged regions suggested shear
ing between fiber layers, which may be part of the failure process and
accelerates valve failure. Histological analysis revealed a relativel
y intact gross fiber structure with the collagen fiber crimp remaining
, although delamination and de-registration of the crimp was also obse
rved. Accelerated tested PBHVs also demonstrated a pronounced 'sagging
', which began at the earliest cycle number tested (1.4 million cycles
) and whose rate decreased logarithmically with cycle number. Results
of this study suggest that PBHV cusps can alter their shape without an
y visually apparent material yielding or fiber failure under continual
cyclic loading. Further, while most of the 4 mmHg pressure fixed PBHV
's gross fiber architecture remains unchanged after 500 million cycles
of accelerated testing, localized accumulated fiber damage can occur
on a sub-visual structural level as early as 50 million cycles. (C) 19
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