Flexible Leaflet Polymeric Heart Valves - Cardiovascular and Cardiac Therapeutic Devices - page 103

Fig. 4 POSS-PCU heart valve design (a) and prototype (b) developed by UCL [ 46 ]. Schematic
representation (c) of the SSAV valve by the same group aimed at facilitating easy surgical
procedure with minimal tissue damage and improved hemodynamic performance [ 77 ] (with
permission from respective references given)
200 lm leaflet thickness) [ 73 ]. There was only a small difference in hemodynamic
properties, but dip casting proved far superior in terms of durability, with at least
160 mc achieved compared to 100 million or less for the thermoformed valves.
Finite element modelling of the alpharabola design showed reduction in principal
tensile stress to 60 % of that of spherical leaflet geometry [ 74 ].
Nanocomposite POSS-PCU materials recently developed by the group of Alex
Seifalian at University College London [ 75 ] showed improved mechanical prop-
erties over PCU controls and exhibited good surface properties and resistance to
platelet adhesion [ 46 ]. A prototype heart valve made from this material is shown in
Fig. 4 a, b. In vitro assessment of a semi-stented surgical aortic valve (SSAV), 100,
150 and 200 lm leaflet valves based on this technology was performed and
compared to control valves of similar size. The SSAV design (Fig. 4 c) was shown
to have improved performance over a conico-spherical design using finite element
modelling and pulse duplication tests [ 76 ] and had lower transvalvular pressure
drops, regurgitation and energy losses and a significantly increased calculated
EOA than that control bioprosthetic valves [ 77 ].
2.4 Other Polymer Valves
A number of alternate polymers had been evaluated for use in flexible leaflet
valves. During the late 1950s Roe et al. switched to silicone only after unsuc-
cessful trials with polyvinyl alcohol, polyethylene and plasticized polyvinyl
chloride (PVC, that lost flexibility after relatively short periods in the bloodstream
due to loss of plasticizer in the case of PVC) [ 26 ].
Poly(styrene-b-isobutylene-b-styrene) (SIBS; Quatromer TM , Innovia LLC),
either as is or with polypropylene reinforcement fibres, has been proposed as a
polymeric leaflet material due to its mechanical properties between that of silicone