Flexible Leaflet Polymeric Heart Valves - Cardiovascular and Cardiac Therapeutic Devices - page 101

Fig. 2 a Tri- and b bileaflet polycarbonate urethane valves for the aortic and mitral positions
respectively, produced by ADIAM life sciences, Erkelenz, Germany. A schematic of the robotic
droplet deposition technique used in the manufacture of these valves is shown in c (a, b with
permission: [ 2 ]; c courtesy of Josef Jansen, personal communication)
Fig. 3 a Ellipto-hyperbolic Estane heart valve dip-coated on a PEEK frame and b Elast-Eon
valves with closed and open commissures (with permission: [ 2 ] and [ 71 ])
Lycra (a PEUU Du Pont), to later versions made from the more advanced Elast-
Eon TM 3 (polysiloxane soft segment based polyurethanes (PSU) and polyurethane
ureas (PSUU) with 40 % MDI based hard segment, Elastomedic/Aortech) [ 59 - 66 ].
Durability of more than 300 mc (12 Hz) achieved with ellipto-hyperbolic Estane
valves [ 60 ] could be improved to over 450 million, with some valves achieving
800 mc (equivalent to 20 years), when changing to the diamine extended PEUU
[ 59 , 61 , 64 ]. Leaflet thicknesses of 60-200 lm did not influence durability in PEU
valves, but were directly related to durability of PEUU valves, with an optimum at
150 lm[ 59 ].
In vitro dynamic testing (in a fatigue tester) showed some calcification (similar
levels for PEU and PEUU) of leaflets associated with tears at the free edge or
commissures, degradation sites and sometimes with silicone present as additive or
lubricant (in the materials or due to frame injection moulding) [ 60 , 61 ]. Static
in vitro and in vivo calcification assessment highlighted the effect of low molec-
ular mass components in the polymers, as methanol and chloroform extracts and
extracted polymers showed differential degrees of calcification. The low molecular
mass extractables were generally shown to be accelerating factors in the calcifi-
cation process [ 60 , 61 ]. Hydrodynamic function tests in a simulated mitral position
of a pulse duplicator demonstrated that the PU valves had similar mean pressure