Valve Prototype Research Articles

Modeling and Validation of Moving Coil Actuated Valve for Digital Displacement Machines

This paper concerns a novel moving coil actuator integrated with a high-performance seat valve for use in digital displacement machines (DDM), which is an emerging fluid power technology that sets strict actuator requirements in order to get a high energy conversion efficiency. Hence, the mechanical switching time must be in the millisecond range and the actuator power consumption must be in range of few tens of watts. The objectives are twofold: First, establish a proof-of-concept for the integrated actuator/valve that relies on several principles and mechanisms new or uncommon in fluid power applications. Second, formulate and validate a transient numerical model describing the actuator/valve. A coupled simulation model is established to predict the switching performance in which transient electromagnetic finite-element-analysis with dynamic remeshing is coupled to a set of ordinary differential equations describing the motion dynamics. In this way, the movement induced hydromechanical fluid forces caused by rapid acceleration of the valve plunger is coupled with the electromagnetic dynamics. The proposed model is compared rigorously against measurements obtained from a series of experiments based on a fully operational valve prototype. Comparisons of, e.g., transient flux density, current, and plunger position, show that the model describes both the actuator and the valve motion very well. Finally, results are presented when testing the prototype valve in fully operational DDM to establish proof-of-concept for the proposed valve concept. The actuator/valve is shown to be capable of rapid switching in less than 4 ms, while only consuming approximately 45 W corresponding to 0.7% of the machine output power.

Hemodynamic influence of design parameters of novel venous valve prostheses

Abstract Venous ulcers of the lower limbs are one clinical manifestation of chronic venous insufficiency. Currently, there is no venous valve prosthesis available. This study presents novel venous valve prostheses made of threedimensional electrospun fibrous nonwoven leaflets. The aim of this study was to prove the feasibility of the manufacturing process as well as to investigate design features of the venous valve prostheses from a hemodynamic point of view. An adapted pulse duplicator system (ViVitrolabs, Victoria, BC, CA) was used for characterization of the hydrodynamic performance. For eight different venous valve prototypes flow rate, effective orifice area and regurgitation fraction was investigated in vitro. In particular, tricusp valve designs showed an up to 40% higher effective orifice area as well as 15% higher maximum flowrate compared to bicusp valve designs. However, the regurgitation fraction of the bicusp valve designs is up to 86% lower compared to tricusp valve. Additionally, the hemodynamic performance of the tricuspid valves showed a high sensitivity regarding the leaflet length. Bicuspid valves are less sensitive to changes of design parameters, more sufficient and therefore highly reliable.

Durability Tests of Ball Valve Prototype with Flowmeter Operation

The results of the investigation of the prototypical ball valve are presented in this article. The innovation of the tested valve is a ball with a built-in measuring orifice. The valve has been subjected to durability tests. Leakage under three temperatures: ambient, -30°C and +100°C was analyzed. Sealing elements of the valve were tested for roughness and deviation of shape before and after the cycles of operation. Ball valve operation means cycles of open/close. It was planned to perform 1000 cycles at each temperature condition accordingly. Tests of the valve were performed under gas pressure equal to 10 MPa. The research was carried out under the Operational Program “Intelligent Development” (POIR 01.01.01-00-0013 / 15 “Development of devices for measurement of media flow on industrial trunk-lines”.

Theoretical and Experimental Research on a Three-Way Water Hydraulic Pressure Reducing Valve

A three-way water hydraulic pressure reducing valve (PRV) was developed in this paper for a test equipment in laboratory for adapting complex conditions. The designed PRV has a damping chamber with an orifice located at the spring chamber. Two types of throttles and orifice diameter were investigated through dynamic simulation and optimization, and their dimensions were determined and applied to the manufactured valve prototype. The static and dynamic performances of the valve were tested by experiments. At the preset pressure of 5.0 MPa, the outlet pressure variations for the pressure-reducing port and the relief port, are 0.73 MPa and 1.44 MPa, respectively, while the flow variation is up to 18.0 l/min. The experimental rising times and settling times of the PRV under the inlet pressure step for preset pressures of 5.0 MPa are 33.7 ms and 120.2 ms, respectively, and the overshoot is 3.76%. The test results at each preset pressure agree well with the simulation which verifies that the simulation model can be used to predict the dynamic performance of the PRV. The experimental results for the valve under flow step input conclude that it can work stably at small flow state. The research indicates that making the spring chamber a damping chamber by using an orifice is a feasible way to increase the pressure stability and the dynamic performance of the PRV. However, the damping effect of this structure is insufficient at high working pressure.

In Vitro Hydrodynamic Assessment of a New Transcatheter Heart Valve Concept (the TRISKELE)

This study presents the in vitro hydrodynamic assessment of the TRISKELE, a new system suitable for transcatheter aortic valve implantation (TAVI), aiming to mitigate the procedural challenges experienced with current technologies. The TRISKELE valve comprises three polymeric leaflet and an adaptive sealing cuff, supported by a novel fully retrievable self-expanding nitinol wire frame. Valve prototypes were manufactured in three sizes of 23, 26, and 29 mm by automated dip-coating of a biostable polymer, and tested in a hydrodynamic bench setup in mock aortic roots of 21, 23, 25, and 27 mm annulus, and compared to two reference valves suitable for equivalent implantation ranges: Edwards SAPIEN XT and Medtronic CoreValve. The TRISKELE valves demonstrated a global hydrodynamic performance comparable or superior to the controls with significant reduction in paravalvular leakage. The TRISKELE valve exhibits enhanced anchoring and improved sealing. The valve is currently under preclinical investigation.

A new transcatheter heart valve concept (the TRISKELE): feasibility in an acute preclinical model

The aim of this study was to introduce and demonstrate the feasibility in an acute preclinical model of a new transcatheter heart valve concept with a self-expanding wire frame, polymeric leaflets and a sealing component. The TRISKELE valve was developed based on a previously validated polymeric leaflet design, an adaptive sealing cuff and a novel nitinol wire frame which reduces stress on the leaflets and radial pressure on the surrounding tissue. A valve prototype of 26 mm nominal diameter was manufactured by automated dip coating of a biostable polymer. The prototype was implanted via brachiocephalic approach in orthotopic position in an acute ovine model through a highly controllable multistage deployment process. The atraumatic retrievability of the valve after full expansion was verified in situ before final release in the optimal position. Observation indicated secure valve anchoring, adequate leaflet motion, and no interference of coronary flow or mitral valve function. The TRISKELE valve system has the potential to mitigate complications related to imprecise valve positioning, and may offer a safer and more economical TAVI solution to a broad range of patients. The valve is currently under preclinical investigation for its long-term function and durability.

Modeling and experimental verification of the flow characteristics of an active controlled microfluidic valve with annular boundary

The principle and structural configuration of an active controlled microfluidic valve with annular boundary driven by a circular piezoelectric unimorph actuator is presented in this article. Its active controlled flowrate is modeled using the classical laminated plate theory and the extended Bernoulli equation in fluid mechanics. According to the established mathematical model, we simulate and analyze the influence of the voltage applied to the circular piezoelectric unimorph actuator and the structural parameters on the flow characteristics. The prototypes of the active controlled microfluidic valves with annular boundaries of three different combinations of the inner and outer radii are fabricated and tested. The experimental results show that the active controlled microfluidic valves with annular boundaries possess the on/off switching capability and the continuous control capability of the fluid with simple structure and easy fabrication processing; the maximum flowrate of the active controlled microfluidic valve with the annular boundary with the inner and outer radii of 1.5 and 3.5 mm, respectively, is 0.14 mL/s when the differential pressure of the inlet and outlet of the active controlled microfluidic valve is 1000 Pa and the voltage applied to circular piezoelectric unimorph actuator is 100 V; and the established flowrate model can accurately predict the controlled flowrate of the active controlled microfluidic valves with the maximum relative error of 6.7%.

Smart valve: Polymer actuator to moisture soil control

The adequate use of water for irrigation in agriculture is a widespread concern. In this study, we developed an autonomous smart system consisting of a new hydrogel into a valve, which regulates the flow of water according to soil moisture. The main objective was to find an alternative to avoid waste of water. Yet, hydrogel development and study of the quantitative relationship between its properties and soil moisture were also important to achieve this aim. The hydrogel was synthesized from tris[(hydroxymethyl) methyl]acrylamide (NAT) copolymerized with methyl methacrylate (MMA) and crosslinked with N,N′-methylene bis(acrylamide) (BIS). The use of cellulose (2% w/v) avoids hydrogel breakage during swelling-deswelling. The relation between swelling ratio, force of expansion and moisture was evaluated for the novel hydrogel. It was found that as soil moisture increases, the gel swells, while expansion force diminishes. These properties showed linear relationship in the range studied. The three-dimensional network formed by flexible chains has the attribute of exerting a great force when it expands (≅15N for a hydrogel disc of 1cm2). When the material was put in contact with the ground, it swelled and deswelled without breaking. The hydrogel within the valve was able to open and close the passage of water. The valve prototype was tested during four months with a plant. During this period, only three liters of irrigation water were used monthly, instead of about half a liter daily. Hence, an autonomous actuator capable of controlling soil moisture was developed based on a new hydrogel.

The Experimental Study on the Influence Factors in Adhesive Dispensing Dot Diameter of Impact Jetting Valve

To obtain much higher accurate jetting dispensing, an investigation on a jetting valve with ball needle and conical nozzle is done in this paper. The theoretical model on the relationship among needle, nozzle, and adhesive during the impact process is established first. The experiments are done on a jetting valve prototype, and the results show that there are two factors that influence the ball needle impact speed: the spring compression and the impact stroke. The spring compression has little influence on the dispensing dot diameter from jetting, while the impact stroke greatly influences the dispensing dot diameter. Within a certain range, the dispensing dot diameter increases with stroke until the impact stroke reaches a certain value, then the dispensing dot diameter remains stable. Besides, when the nozzle structure stays the same, increasing the ball diameter of the needle will also increase the dispensing dot. The experimental result matches the theoretical model well. After the needle structure and impact parameter optimization on the prototype, the dispensing diameter can achieve Φ0.22 mm, while the jetting viscosity is 1200 cps, the nozzle diameter Φ0.06 mm, impact needle diameter Φ1.5 mm, and stroke 0.06 mm. Therefore, the investigation, in this paper, can be used as the design basis for a high-accuracy jetting valve.

Fluid dynamic characterization of a polymeric heart valve prototype (Poli-Valve) tested under continuous and pulsatile flow conditions.

Only mechanical and biological heart valve prostheses are currently commercially available. The former show longer durability but require anticoagulant therapy; the latter display better fluid dynamic behavior but do not have adequate durability. New Polymeric Heart Valves (PHVs) could potentially combine the hemodynamic properties of biological valves with the durability of mechanical valves. This work presents a hydrodynamic evaluation of 2 groups of newly developed supra-annular, trileaflet prosthetic heart valves made from styrenic block copolymers (SBC): Poli-Valves. 2 types of Poli-Valves made of SBC and differing in polystyrene fraction content were tested under continuous and pulsatile flow conditions as prescribed by ISO 5840 Standard. A pulse duplicator designed ad hoc allowed the valve prototypes to be tested at different flow rates and frequencies. Pressure and flow were recorded; pressure drops, effective orifice area (EOA), and regurgitant volume were computed to assess the behavior of the valve. Both types of Poli-Valves met the minimum requirements in terms of regurgitation and EOA as specified by the ISO 5840 Standard. Results were compared with 5 mechanical heart valves (MHVs) and 5 tissue heart valves (THVs), currently available on the market. Based on these results, PHVs based on styrenic block copolymers, as are Poli-Valves, can be considered a promising alternative for heart valve replacement in the near future.

Hemodynamic and thrombogenic analysis of a trileaflet polymeric valve using a fluid–structure interaction approach

Surgical valve replacement in patients with severe calcific aortic valve disease using either bioprosthetic or mechanical heart valves is still limited by structural valve deterioration for the former and thrombosis risk mandating anticoagulant therapy for the latter. Prosthetic polymeric heart valves have the potential to overcome the inherent material and design limitations of these valves, but their development is still ongoing. The aim of this study was to characterize the hemodynamics and thrombogenic potential of the Polynova polymeric trileaflet valve prototype using a fluid–structure interaction (FSI) approach. The FSI model replicated experimental conditions of the valve as tested in a left heart simulator. Hemodynamic parameters (transvalvular pressure gradient, flow rate, maximum velocity, and effective orifice area) were compared to assess the validity of the FSI model. The thrombogenic footprint of the polymeric valve was evaluated using a Lagrangian approach to calculate the stress accumulation (SA) values along multiple platelet trajectories and their statistical distribution. In the commissural regions, platelets were exposed to the highest SA values because of highest stress levels combined with local reverse flow patterns and vortices. Stress-loading waveforms from representative trajectories in regions of interest were emulated in our hemodynamic shearing device (HSD). Platelet activity was measured using our platelet activation state (PAS) assay and the results confirmed the higher thrombogenic potential of the commissural hotspots. In conclusion, the proposed method provides an in depth analysis of the hemodynamic and thrombogenic performance of the polymer valve prototype and identifies locations for further design optimization.

Fiber heart valve prosthesis: Early in vitro fatigue results.

Transcatheter aortic valve replacement has become today a largely considered alternative technique to surgical valve replacement in patients with high risk for open chest surgery. Biological valve tissue used in the transcatheter devices has shown success over 5 years now, but the procedure remains expensive. Moreover, different studies point out potential degradations that the tissue can undergo when folded to lower diameter and released in calcified environment with irregular geometry, which may jeopardize the durability of the device. The use of synthetic materials, like textile in particular, to replace biological valve leaflets would help reducing the procedure costs, and limit the degradations when the valve is crimped. Textile polyester material has been extensively used in the vascular surgery and is characterized by outstanding folding and strength properties combined with proven biocompatibility. However, the friction effects that occur between filaments and between yarns within a fabric under flexure loading could be critical for the resistance of the material on the long term. The purpose of this study was to assess the early fatigue performances of textile valve prototypes under accelerated cyclic loading up to 200 Mio cycles. Durability tests show that the fibrous material undergoes rearrangements between fibrous elements within the textile construction and the mechanical properties are modified on the long term. But testing is not complete with 200 Mio cycles. The material should be tested up to a higher number of cycles in future work to test the effective long-term durability. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 986-992, 2016.

Mechanical degradation of biological heart valve tissue induced by low diameter crimping: An early assessment

Transcatheter aortic valve implantation (TAVI) has become today an increasingly attractive procedure to relieve patients from aortic valve disease. However, the procedure requires crimping biological tissue within a metallic stent for low diameter catheter insertion purpose. This step induces specific stress in the leaflets especially when the crimping diameter is small. One concern about crimping is the potential degradations undergone by the biological tissue, which may limit the durability of the valve once implanted. The purpose of the present work is to study the effect of low diameter crimping on the mechanical performances of pericardium valve prototypes. The prototypes were compressed to a diameter of 1mm within braided stents for 20min. SEM observations performed on crimped material show that crimped leaflets undergo degradations characterized by apparent surface defects. Moreover mechanical extension tests were performed on pericardium strips before and after crimping. The strips (15mm long, 5mm wide) were taken from both crimped and native leaflets considering 2 different valve diameters, 19 and 21mm. In order to prevent the premature drying of the pericardium tissue during the procedure, the biological tissue was kept in contact with a formaldehyde solution. Results show that the ultimate strength value decreases nearly by up to 50%. The modifications observed in the material may jeopardize the long term durability of the device. However, further tests are necessary with a larger amount of samples to confirm these early results.

Equal Coded Digital Hydraulic Valve System – Improving Tracking Control with Pulse Frequency Modulation

Previous research on digital fluid power indicates down-scaling to be beneficial to the characteristics of digital valves. This theoretical aspect yields to use equal size on/off valves in digital hydraulic valve systems. A simple miniaturized on/off valve, having orifice diameter of 0.7mm, have been developed to study the feasibility of this approach. A manifold manufacturing technology also has been developed to facilitate a compact framework for the valve system containing dozens of the miniature valves. The first equal coded valve system prototype contains 16 miniature valve prototypes. A natural modulation method for an equal coded valve system is Pulse Number Modulation (PNM), where the output depends on the number of activated valves. With this modulation method, resolution of the output is equivalent to the number of the valves in the control edge. Limited resolution hampers the tracking control performance especially at low velocity where small steps in flow rate are required. The main purpose of this paper is to study the feasibility of Pulse Frequency Modulation (PFM) to improve the controllability of the equal coded valve system at the velocities below the minimum velocity of PNM control. Poor controllability at low velocities is one of the main challenges of the digital hydraulic valve systems. Characteristics of the PFM method are analysed and an experimental study is carried out to measure the improvement of the PFM method on the tracking control performance. The study indicates that the PFM method is an effective way to improve tracking control performance at low velocity.

Transcatheter fiber heart valve: Effect of crimping on material performances.

Transcatheter aortic valve implantation (TAVI) has become a popular alternative technique to surgical valve replacement. However, the biological valve tissue used in these devices appears to be fragile material in the long term particularly due being folded for low diameter catheter insertion purposes and when released in a calcified environment with irregular geometry. Textile polyester material is characterized by outstanding folding and strength properties combined with proven biocompatibility. It could therefore be considered as a replacement for biological valve leaflets in the TAVI procedure. The folding process associated with crimping, however, may degrade the filaments involved in the fibrous assembly and limit the durability of the device. The purpose of the present work is to study the effect of different crimping conditions on the mechanical performances of textile valve prototypes made from various fabric constructions. Results show that crimping generates some creases in the fabrics, which surface topography varies with fabric construction and crimping configuration. The mechanical properties of the crimped materials are globally slightly reduced. To determine how critical the modifications due to crimping are for prosthesis durability, more detailed long term in vitro and in vivo trials with crimped textile prototypes are needed in addition to this preliminary work.

Fiber heart valve prosthesis: Influence of the fabric construction parameters on the valve fatigue performances

Transcatheter aortic valve replacement (TAVR) has become today a largely considered alternative technique to surgical valve replacement in patients who are not operable or patients with high risk for open chest surgery. However, the biological valve tissue used in the devices implanted clinically appears to be fragile material when folded for low diameter catheter insertion purpose and released in calcified environment with irregular geometry. Textile polyester material is characterized by outstanding folding and strength properties combined with proven biocompatibility. It could thereof be considered to replace biological valve leaflets in the TAVR procedure. The textile construction parameters must however be tuned to obtain a material compatible with the valve requested durability. In that context, one issue to be addressed is the friction effect that occurs between filaments and between yarns within a fabric under flexure loading. This phenomenon could be critical for the resistance of the material on the long term. The purpose of the present work is to assess the fatigue performances of textile valve prototypes made from different fabric constructions (monofilament, multifilament, calendered mutifilament) under accelerated cyclic loading. The goal is to identify, which construction is the best suited to long term fatigue stress. Results show that calendered multifilament and monofilament fabric constructions undergo strong ruptures already from 40 Mio cycles, while non calendered multifilament appears more durable. The rupture patterns observed point out that durability is directly related to the flexure stiffness level of the fibrous elements in the construction.

Design and Research of a New Thermostatic Valve

This study designed a new type of intelligent thermostatic mixing valve which could keep the temperature and flux of the outlet water constant by the adaptive controller. It firstly established mathematical model of the valve about angle-flux and angle-temperature and then it applied the Fluent software to numerical simulation of the valve about flow field based on the two-equation turbulence model. Finally, it designed the intelligent controller hardware and developed the controlling software of the valve. With the controller and it finished experiments with the thermostatic valve prototype. The results of simulation and experiments prove that the correctness of the theoretical research and they can be used to improve designing of the thermostatic valve.

Theoretical and Experimental Research on a Pressure-Reducing Valve for a Water Hydraulic Vane Pump

In order to control the high PV value between the vanes and the cam ring in a water hydraulic vane pump, a pressure-reducing valve with a constant pressure ratio was developed in this study. The pressure and leakage characteristics of the valve were theoretically analyzed by simulation and the experiments were also conducted based on the valve prototype. The theoretical analysis agrees well with the experimental results. Further, these results reveal that the pressure ratio of the valve decreases to the design value with the increasing working pressure. Additionally, the leakage of the valve rises simultaneously with the increasing working pressure and can be reduced significantly by decreasing the clearance between the valve body and the spool. The presented research not only proves the successful development of the pressure-reducing valve but also lays a foundation for the investigation of a high-pressure water hydraulic vane pump.

Dielectric Elastomer Jet Valve for Magnetic Resonance Imaging-Compatible Robotics

This paper presents the design and experimental characterization of a binary jet valve, specifically developed to control an all-polymer needle manipulator during intramagnetic resonance imaging (MRI) prostate interventions (biopsies and brachytherapies). The key feature of the MRI-compatible valve is its compact dual-stage configuration. The first stage is composed of a low-friction jet nozzle, driven by a small rotary dielectric elastomer actuator (DEA). The second stage provides sufficient air flow and stability for the binary robotic application through an independent air supply, activated by a bistable spool. A hyperelastic stress-strain model is used to optimize the geometrical dimensions of the DEA jet assembly. Fully functional valve prototypes, made with 3M's VHB 4905 films, are monitored with a high-speed camera in order to quantify the system's shifting dynamics. The impact of nozzle clearance, dielectric elastomer film viscoelasticity, mechanical friction, and actuator torque generation on overall dynamic behavior of two different valve setups is discussed. Results show an overall shifting time of 200–300 ms when the friction of the nozzle and DEA actuation stretches are minimized. Low shifting time combined with compactness, simplicity, and low cost suggest that the low friction DEA-driven jet valves have great potential for switching a large number of pneumatic circuits in an MRI environment as well as in traditional pneumatic applications.

In Vitro Evaluation of a Novel Hemodynamically Optimized Trileaflet Polymeric Prosthetic Heart Valve

Calcific aortic valve disease is the most common and life threatening form of valvular heart disease, characterized by stenosis and regurgitation, which is currently treated at the symptomatic end-stages via open-heart surgical replacement of the diseased valve with, typically, either a xenograft tissue valve or a pyrolytic carbon mechanical heart valve. These options offer the clinician a choice between structural valve deterioration and chronic anticoagulant therapy, respectively, effectively replacing one disease with another. Polymeric prosthetic heart valves (PHV) offer the promise of reducing or eliminating these complications, and they may be better suited for the new transcatheter aortic valve replacement (TAVR) procedure, which currently utilizes tissue valves. New evidence indicates that the latter may incur damage during implantation. Polymer PHVs may also be incorporated into pulsatile circulatory support devices such as total artificial heart and ventricular assist devices that currently employ mechanical PHVs. Development of polymer PHVs, however, has been slow due to the lack of sufficiently durable and biocompatible polymers. We have designed a new trileaflet polymer PHV for surgical implantation employing a novel polymer-xSIBS-that offers superior bio-stability and durability. The design of this polymer PHV was optimized for reduced stresses, improved hemodynamic performance, and reduced thrombogenicity using our device thrombogenicity emulation (DTE) methodology, the results of which have been published separately. Here we present our new design, prototype fabrication methods, hydrodynamics performance testing, and platelet activation measurements performed in the optimized valve prototype and compare it to the performance of a gold standard tissue valve. The hydrodynamic performance of the two valves was comparable in all measures, with a certain advantage to our valve during regurgitation. There was no significant difference between the platelet activation rates of our polymer valve and the tissue valve, indicating that similar to the latter, its recipients may not require anticoagulation. This work proves the feasibility of our optimized polymer PHV design and brings polymeric valves closer to clinical viability.