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Abstract

Introduction

Protocol

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Materials

References

Bioengineering

Protocol for Relative Hydrodynamic Assessment of Tri-leaflet Polymer Valves

Published: October 17th, 2013

DOI:

10.3791/50335

1Tissue Engineered Mechanics, Imaging and Materials Laboratory, Department of Biomedical Engineering, Florida International University, 2Department of Mechanical and Aerospace Engineering, University of Florida , 3College of Medicine, University of Florida , 4King Faisal Specialty Hospital and Research Center, Jeddah, Saudi Arabia

There has been renewed interest in developing polymer valves. Here, the objectives are to demonstrate the feasibility of modifying a commercial pulse duplicator to accommodate tri-leaflet geometries and to define a protocol to present polymer valve hydrodynamic data in comparison to native and prosthetic valve data collected under near-identical conditions.

Limitations of currently available prosthetic valves, xenografts, and homografts have prompted a recent resurgence of developments in the area of tri-leaflet polymer valve prostheses. However, identification of a protocol for initial assessment of polymer valve hydrodynamic functionality is paramount during the early stages of the design process. Traditional in vitro pulse duplicator systems are not configured to accommodate flexible tri-leaflet materials; in addition, assessment of polymer valve functionality needs to be made in a relative context to native and prosthetic heart valves under identical test conditions so that variability in measurements from different instruments can be avoided. Accordingly, we conducted hydrodynamic assessment of i) native (n = 4, mean diameter, D = 20 mm), ii) bi-leaflet mechanical (n= 2, D = 23 mm) and iii) polymer valves (n = 5, D = 22 mm) via the use of a commercially available pulse duplicator system (ViVitro Labs Inc, Victoria, BC) that was modified to accommodate tri-leaflet valve geometries. Tri-leaflet silicone valves developed at the University of Florida comprised the polymer valve group. A mixture in the ratio of 35:65 glycerin to water was used to mimic blood physical properties. Instantaneous flow rate was measured at the interface of the left ventricle and aortic units while pressure was recorded at the ventricular and aortic positions. Bi-leaflet and native valve data from the literature was used to validate flow and pressure readings. The following hydrodynamic metrics were reported: forward flow pressure drop, aortic root mean square forward flow rate, aortic closing, leakage and regurgitant volume, transaortic closing, leakage, and total energy losses. Representative results indicated that hydrodynamic metrics from the three valve groups could be successfully obtained by incorporating a custom-built assembly into a commercially available pulse duplicator system and subsequently, objectively compared to provide insights on functional aspects of polymer valve design.

Heart valve disease often results from degenerative valve calcification1, rheumatic fever2, endocarditis3,4 or congenital birth defects. When valve damage occurs, causing stenosis and/or regurgitation valve prolapse and cannot be surgically repaired, the native valve is usually replaced by a prosthetic valve. Currently available options include mechanical valves (cage-ball valves, tilting disk valves, etc.), homograft, and bioprosthetic valves (porcine and bovine valves). Mechanical valves are often recommended for younger patients based on their durability; however the patient is required to remain on anticoagulant therapy to....

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1. Preparation

  1. Design and fabricate an assembly to accommodate a tri-leaflet valve geometry. This will at minimum include a valve holder to suture-in the valve leaflets and a tube to house the valve holder and surrounding accessories to secure the assembly onto the pulse duplicator system. In our case, we utilized a commercially available pulse duplicator system available from ViVitro Labs Inc. (Victoria, BC). Valve holder design as well as pre and post assembly configurations are depicted in Fig.......

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Representative flow and pressure waveforms are shown in Figures 3, 4 and 5. The plots were averaged over the sample size of valves tested for each group, which was, n = 5, 4, and 2 valves for polymer, native porcine and bi-leaflet groups, respectively. The mean hydrodynamic metrics and the standard error of the mean for these sample sizes are presented in Table 1.

Figure 1

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In this study, we have demonstrated the utility of modifying a commercially available pulsatile duplicator unit to accommodate tri-leaflet valve geometries so that hydrodynamic testing of polymer and native porcine valves can be performed. Specifically in our case, the system modified was a ViVitro left heart and systemic simulator system (Figure 1a) controlled via the ViViTest data acquisition system (ViVitro Systems, Inc, Victoria, BC, Canada). However, the system is not unlike several in vitro

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A seed grant from the University of Florida - College of Medicine is gratefully acknowledged. Graduate studies (Manuel Salinas) were supported through a minority opportunities in biomedical research programs - research initiative for scientific enhancement (MBRS-RISE) fellowship: NIH/NIGMS R25 GM061347. Financial support from the Wallace H. Coulter Foundation through Florida International University's, Biomedical Engineering Department is also gratefully acknowledged. Finally, the authors thank the following students for their assistance during various stages of the experimental process: Kamau Pier, Malachi Suttle, Kendall Armstrong and Abraham Alfonso.

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Name Company Catalog Number Comments
Name of Reagent/Material Company Catalog Number Comments
Pump ViVitro Labs http://vivitrolabs.com/products/superpump/
Flow Meter and Probe Carolina Medical Model 501D http://www.carolinamedicalelectronics.com/documents/FM501.pdf
Pressure Transducer ViVitro Labs HCM018
ViVitro Pressure Measuring Assembly ViVitro Labs 6186
Valve holder WB Engineering Designed by Florida International University. Manufactured by WB Engineering
Pulse Duplicator ViVitro Labs PD2010 http://vivitrolabs.com/wp-content/uploads/Pulse-Duplicator-Accessories1.pdf
Pulse Duplicator Data Acquisition and Control System, including ViViTest Software ViVitro Labs PDA2010 http://vivitrolabs.com/products/software-daq
Porcine Hearts and Native Aortic Valves Mary's Ranch Inc
Bi-leaflet Mechanical Valves Saint Jude Medical http://www.sjm.com/
High Vacuum Grease Dow Corning Corporation http://www1.dowcorning.com/DataFiles/090007b281afed0e.pdf
Glycerin McMaster-Carr 3190K293 99% Natural 5 gal
Phosphate Buffered Saline (PBS) Fisher Scientific MT21031CV 100 ml/heart
Antimycotic/Antibiotic Solution Fisher Scientific SV3007901 1 ml in 100 ml of PBS/heart; 20 ml for ViVitro System
NaCl Sigma-Aldrich S3014-500G 9 g/L of deionized water
Deionized Water EMD Millipore Chemicals Millipore Deionized Purification System. 1.3 L for ViVitro System, 200 ml for heart valve dissection process

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