FSI-based approach for heart valve prosthesis optimization: a polymeric prototype case-study. F., P., F., S., T., C., G., M., J., S., D., B., & A., R. Volume Prague, Czech Republic, July 5-8, 2015.
abstract   bibtex   

Introduction: Mechanical and bio-prosthetic heart valves provide life-saving solutions, but critical comorbidities (e.g. thrombogenic failures, premature degradation) still occur. These major issues suggested the concept of next-generation devices, such as polymeric heart valves (PHV) [Bezuidenhout, 2014]. Preliminary in-vitro tests showed promising results, but a complete methodology that provides an overview of their performances still lacks. At this aim, we developed a full fluid-structure interaction (FSI) method that mimics the operative conditions of an experimental testing set-up so as to deeply investigate the fluid dynamic, kinematic and thrombogenic performances of the x-SIBS Polynova polymeric prototype valve [Claiborne, 2013], aiming at its optimization.

Materials and methods: The geometry of the FSI model was derived from technical drawings of the Polynova valve and the ViVitro Pulse Duplicator (ViVitro Labs Inc., Victoria, BC, Canada). Numerical simulations were performed with the explicit solver LS-DYNA (LSTC, Livermore CA, USA). Ventricular (Pv) and aortic (Pao) pressure waveforms were extracted from experimental testing [Claiborne, 2013] and used as boundary conditions at the Inlet and Outlet reservoirs of the fluid domain. As regards the thrombogenicity analysis of the device, numerical particles (i.e. ideal human platelets) were injected in ventricular position and an in-house post-processing tool was used to calculate their stress-time (τ(t)) histories and to condense them into a thrombogenic “footprint”. Commissural hot-spots and central-jet trajectories were selected and programmed into a hemodynamic shearing device. The mechanically-induced platelet activation state (PAS) was quantified by means of an innovative experimental protocol [Bluestein, 2013].

Results: As a first step, characterizing parameters (i.e., Qpeak, Vmax, ΔPmean, EOA) were compared between the numerical solution and experimental data to assess the reliability of the proposed FSI method (Table 1). At the peak systolic phase, the blood flow was characterized by a centred and regular profile, related to a symmetric open position of the leaflets (Figure 1). Commissural trajectories exhibited higher level of PAS than central-jet ones, respectively, 5% and 2% with respect to the maximum possible platelet activation.

FSIExperimental
Qpeak (ml/s)447.71454
Vmax3.373.42
ΔPmean (mmHg)18.6020.91
EOA (cm^2)1.541.47

Table 1: Verification of the numerical model

image

Figure 1: Overall characterization of the Polynova polymeric prototype valve

Discussion: The experimental verification of the FSI model showed reliable results and the thrombogenic analysis identified critical geometrical hot-spots - commissural zones - which mostly activates platelets and may represent the key-feature that governs the thrombogenic impact of trileaflet prosthesis. We confidently suggest that our analysis can provide a step-forward into the optimization process of valvular prosthesis.

References:

Bezuidenhout et al., Biomat. 36:6-25, 2015

Claiborne et al., J Biomech Eng, 135(2), 2013

Bluestein et al., J Biomech, 46(2):338-44

@proceedings{n20,
  cpaper				   = {1},
  Title                    = {{FSI-based approach for heart valve prosthesis optimization: a polymeric prototype case-study}},
  Author                   = {Piatti F. and Sturla F. and Claiborne T. and Marom G. and Sheriff J. and Bluestein D. and Redaelli A.},
  Booktitle				   = {The 21st Congress of the European Society of Biomechanics (ESB2015)},
  address 				   = {Prague, Czech Republic}, 
  month					   = {July 5-8}, 
  Year                     = {2015}, 

  Abstract				   = {
														<p>Introduction: Mechanical and bio-prosthetic heart valves provide life-saving solutions, but critical comorbidities (e.g. thrombogenic failures, premature degradation) still occur. These major issues suggested the concept of next-generation devices, such as polymeric heart valves (PHV) [Bezuidenhout, 2014]. Preliminary in-vitro tests showed promising results, but a complete methodology that provides an overview of their performances still lacks. At this aim, we developed a full fluid-structure interaction (FSI) method that mimics the operative conditions of an experimental testing set-up so as to deeply investigate the fluid dynamic, kinematic and thrombogenic performances of the x-SIBS Polynova polymeric prototype valve [Claiborne, 2013], aiming at its optimization.</p>
														<p>Materials and methods: The geometry of the FSI model was derived from technical drawings of the Polynova valve and the ViVitro Pulse Duplicator (ViVitro Labs Inc., Victoria, BC, Canada). Numerical simulations were performed with the explicit solver LS-DYNA (LSTC, Livermore CA, USA). Ventricular (Pv) and aortic (Pao) pressure waveforms were extracted from experimental testing [Claiborne, 2013] and used as boundary conditions at the Inlet and Outlet reservoirs of the fluid domain. As regards the thrombogenicity analysis of the device, numerical particles (i.e. ideal human platelets) were injected in ventricular position and an in-house post-processing tool was used to calculate their stress-time (τ(t)) histories and to condense them into a thrombogenic “footprint”. Commissural hot-spots and central-jet trajectories were selected and programmed into a hemodynamic shearing device. The mechanically-induced platelet activation state (PAS) was quantified by means of an innovative experimental protocol [Bluestein, 2013].</p>
														<p>Results: As a first step, characterizing parameters (i.e., Qpeak, Vmax, ΔPmean, EOA) were compared between the numerical solution and experimental data to assess the reliability of the proposed FSI method (Table 1). At the peak systolic phase, the blood flow was characterized by a centred and regular profile, related to a symmetric open position of the leaflets (Figure 1). Commissural trajectories exhibited higher level of PAS than central-jet ones, respectively, 5% and 2% with respect to the maximum possible platelet activation.</p>
														<table><tbody><tr><td></td><td>FSI</td><td>Experimental</td></tr><tr><td>Qpeak (ml/s)</td><td>447.71</td><td>454</td></tr><tr><td>Vmax</td><td>3.37</td><td>3.42</td></tr><tr><td>ΔPmean (mmHg)</td><td>18.60</td><td>20.91</td></tr><tr><td>EOA (cm^2)</td><td>1.54</td><td>1.47</td></tr></tbody></table>
														<p>Table 1: Verification of the numerical model</p>
														
														<img alt="image" src="pages/Piatti-ESB2015.jpg"  class="img-responsive">
														
														<p>Figure 1: Overall characterization of the Polynova polymeric prototype valve</p>
														
														<p>Discussion: The experimental verification of the FSI model showed reliable results and the thrombogenic analysis identified critical geometrical hot-spots - commissural zones - which mostly activates platelets and may represent the key-feature that governs the thrombogenic impact of trileaflet prosthesis. We confidently suggest that our analysis can provide a step-forward into the optimization process of valvular prosthesis.</p>
														<p>References:</p>
														<p>Bezuidenhout et al., Biomat. 36:6-25, 2015</p>
														<p>Claiborne et al., J Biomech Eng, 135(2), 2013</p>
														<p>Bluestein et al., J Biomech, 46(2):338-44</p>
							}		
}

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