Author + information
- Paul De Sciscio1,
- Michele De Sciscio2,
- Jacob Brubert1,
- Marta Serrani1,
- Joanna Stasiak1 and
- Geoff Moggridge1
Few polymeric valves have advanced beyond preclinical investigation despite different polymers, geometries and manufacturing techniques being adopted. Recently, styrenic block copolymers (BCPs) consisting of alternating blocks of glassy and rubbery polymer have been proposed. In order to optimize a transcatheter valve fabricated from BCPs, we sought to quantify the effect of design change on hydrodynamic function.
Transcatheter aortic valves (23mm) were fabricated from 3 BCPs: poly(styrene-block-isobutylene-block-styrene); SIBS, poly (styrene-block-isoprene-block-styrene); SIS and poly(styrene-block-ethylene-propylene-block-styrene); SEPS. A polyurethane (Elast-Eon) was used for comparison. Five design parameters were evaluated (stent attachment, free-edge geometry, leaflet thickness, modulus and molecular orientation) across 4 pulsatile flow rates (3.9 -7.1 L/min), with hydrodynamic function reported as effective orifice area (cm2), mean pressure gradient (mmHg), total regurgitant fraction (%) and energy loss (mJ).
Figure 1 presents the relationship between thickness and hydrodynamic function for each polymer at a simulated cardiac output of 5.0L/min. Controlling for modulus, leaflet thickness was inversely correlated with EOA (B1=-2.223, p<0.001) and total regurgitant fraction (B1=-24.415, <0.001), and positively correlated with mean pressure gradient (B1=30.796, <0.001). Adopting the ISO-5840 minimum performance requirements, the estimated maximum leaflet thickness using SIS, SIBS, SEPS and Elast-Eon was 0.38 mm, 0.30 mm, 0.36 mm, 0.35 mm, respectively. Pairwise comparison revealed a significant difference between a plano-concave and plano-convex profile for EOA (+13.37%, p<0.001), transvalvular pressure (-18.15%, p<0.001) and total regurgitation (-14.33% ± 0.46, p<0.001). Domain orientation parallel to the leaflet base demonstrated a significant improvement in EOA at low flow rates (+4.21% and +6.00% at 3.9L/min and 5.0 L/min, respectively). Conversely, perpendicular orientation demonstrated a significant reduction in total regurgitation and closed valve energy loss. At low flow rates, including 5L/min, material selection did not effect hydrodynamic function for a given thickness. Likewise, no difference was observed with a change in leaflet-stent attachment.
Adopting the ISO-defined minimum performance requirements, maximum leaflet thickness was experimentally determined for a series of BCPs. Further study evaluating long-term in vitro fatigue is required to validate both the utility of targeting the minimum hydrodynamic requirements and the durability of a BCP-based transcatheter valve.
STRUCTURAL: Valvular Disease: Aortic