Polymeric Valve Research Articles

Novel "biomechanical" polymeric valve prostheses with special design for aortic and mitral position: a future option for pediatric patients?

In children, systemic heart valve replacement with bioprostheses is associated with accelerated valve degeneration, and mechanical prostheses require permanent anticoagulation. Novel "biomechanical" polymeric valve prostheses ("bio" = flexible, "mechanical" = synthetic), solely made of polycarbonate urethane (PCU), were tested in vitro and in a growing animal (calf) model with the aim of improved durability without permanent anticoagulation. The trileaflet aortic prosthesis has diminished pressure loss and reduced stress and strain peaks. The asymmetric bileaflet mitral valve mimics natural nonaxial inflow. The valves underwent long-term in vitro testing and in vivo testing in growing calves for 20 weeks [mitral (7), aortic (7)] with comparison to different commercial bioprostheses [mitral (7), aortic (2)]. In vitro durability of PCU valves was proved up to 20 years. Survival of PCU valves versus bioprostheses was 7 versus 2 mitral and 5 versus 0 aortic valves, respectively. Two animals with PCU aortic valves died of pannus overgrowth causing left ventricular outflow tract obstruction. Degeneration and calcification were mild (mitral) and moderate (aortic) in PCU valves but were severe in biological valves. There was no increased thrombogenicity of the PCU valves compared to bioprostheses. The novel polymeric valve prostheses revealed superior durability compared to current bioprostheses in growing animal model without permanent anticoagulation and thus, may be a future option for pediatric patients.

Fluid Dynamic Assessment of Three Polymeric Heart Valves Using Particle Image Velocimetry

Polymeric heart valves have the potential to reduce thrombogenic complications associated with current mechanical valves and overcome fatigue-related problems experienced by bioprosthetic valves. In this paper we characterize the in vitro velocity and Reynolds Shear Stress (RSS) fields inside and downstream of three different prototype trileaflet polymeric heart valves. The fluid dynamic differences are then correlated with variations in valve design parameters. The three valves differ in leaflet thickness, ranging from 80 to 120 mum, and commisural design, either closed, opened, or semi-opened. The valves were subjected to aortic flow conditions and the velocity measured using three-dimensional stereo Particle Image Velocimetry. The peak forward flow phase in the three valves was characterized by a strong central orifice jet of approximately 2 m/s with a flat profile along the trailing edge of the leaflets. Leakage jets, with principle RSS magnitudes exceeding 4,500 dyn/cm(2), were observed in all valves with larger leaflet thicknesses and also corresponded to larger leakage volumes. Additional leakage jets were observed at the commissural region of valves with the open and the semi-open commissural designs. The results of the present study indicate that commissural design and leaflet thickness influence valve fluid dynamics and thus the thrombogenic potential of trileaflet polymeric valves.

AN EXPERIMENTAL FLUID DYNAMIC STUDY OF A POLYMERIC TRILEAFLET HEART VALVE USING LDV

While mechanical heart valves (MHVs) remain the most widely implanted valves, polymeric valves have inherent advantages. These include both their larger effective orifice area and their lower leaflet closing velocities which minimize their cavitation, hemolysis, and platelet activation relative to MHVs. Currently, most polymeric valves are used as part of left ventricular assist devices and total artificial hearts. There is interest to use these valves as replacement valves, and characterizing their fluid dynamics will help achieve this goal. An in vitro laser Doppler velocimetry study was conducted on a 25 mm polymeric trileaflet heart valve (Abiomed Inc), in the aortic position. The valve is mounted in an acrylic conduit with aortic sinuses that allows for optical access upstream and downstream of the valve. A sodium/iodide/glycerin fluid that matches the kinematic viscosity of blood and the index of refraction of the model was used as a blood analog. Flow was driven using a ventricular assist device at a heart rate of 90 bpm, a flow rate of 4.5 l/min, and an aortic pressure of 130/90 mmHg. Mean velocity data was collected in four planes: one diameter upstream, one diameter downstream of the commissural plane, within the sinuses, and at the tip of the commissures. High velocity jets and high Reynolds stresses were measured near the orifice at the leaflet tips and between the leaflets. Recirculation occurs in the aortic sinuses, reducing the potential for thrombus formation.

Polymer actuator valves toward controlled drug delivery application

A novel controlled drug delivery system in which drug release is achieved by electrochemically actuating an array of polymeric valves on a set of drug reservoirs has been developed. The valves are bilayer structures, made in shape of a flap hinged on one side to a valve seat, consisting of thin films of evaporated gold and electrochemically deposited polypyrrole (PPy). Drugs (dry or wet) were pre-stored in an array of these reservoirs and their release is accomplished by bending the bilayer flaps away from the substrate with a small applied bias. In vitro color dye release experiment has been conducted. Seventy-five percent less energy consumption was achieved with this bilayer polymer valve design to open a same size reservoir compared to metal-corrosion based valves. Complex release patterns such as multiple drug pulsatile release and continuous linear release have been successfully implemented through flexible control of valve actuation sequence. These valves can be actuated under closed-loop-control of sensors responding to a specific biological or environmental stimulus, leading to potential applications in advanced responsive drug delivery systems.

Flow‐induced Platelet Activation in a St. Jude Mechanical Heart Valve, a Trileaflet Polymeric Heart Valve, and a St. Jude Tissue Valve

Polymer heart valves have been under investigation since the 1960s, but their success has been hampered by an overall lack of durability mainly due to calcification of the leaflets and a relatively high rate of thromboembolic complications. A new polymer (Quatromer) trileaflet design was tested for its thrombogenic potential and was compared to that of existing prosthetic heart valves routinely implanted in patients: a St. Jude Medical bileaflet mechanical heart valve (MHV) and a St. Jude porcine bioprosthetic tissue valve. The valves were mounted in a left ventricular assist device and the procoagulant activity of the platelets was measured using a platelet activation state (PAS) assay. The PAS measurements indicated that the platelet activation level induced by the polymeric valve was very similar to that induced by the St. Jude Medical MHV and the St. Jude tissue valve. No significant difference was observed between the three valves, indicating that they have a comparable thrombogenic potential.

A Comparison of Flow Field Structures of Two Tri-Leaflet Polymeric Heart Valves

Polymeric heart valves have the potential to reduce thrombogenic complications associated with current mechanical valves and overcome fatigue-related problems experienced by bioprosthetic valves. In this in vitro study, the velocity fields inside and downstream of two different prototype tri-lealfet polymeric heart valves were studied. Experiments were conducted on two 23 mm prototype polymeric valves, provided by AorTech Europe, having open or closed commissure designs and leaflet thickness of 120 and 80 microm, respectively. A two-dimensional LDV system was used to measure the velocity fields in the vicinity of the two valves under simulated physiological conditions. Both commissural design and leaflet thickness were found to affect the flow characteristics. In particular, very high levels of Reynolds shear stress of 13,000 dynes/cm2 were found in the leakage flow of the open commisure design. Maximum leakage velocities in the open and closed designs were 3.6 m/s and 0.5 m/s respectively; the peak forward flow velocities were 2.0 m/s and 2.6 m/s, respectively. In both valve designs, shear stress levels exceeding 4,000 dyne/cm2 were observed at the trailing edge of the leaflets and in the leakage and central orifice jets during peak systole. Additionally, regions of low velocity flow conducive to thrombus formation were observed in diastole. The flow structures measured in these experiments are consistent with the location of thrombus formation observed in preliminary animal experiments.

New Flexible Polymeric Heart Valve Prostheses for the Mitral and Aortic Positions

Current prosthetic heart valves necessitate permanent anticoagulation or have limited durability and impaired hemodynamic performance compared with natural valves. We report in vivo and in vitro results with new polymeric valve prostheses that have a special design for the mitral and aortic positions. The aims are improved durability and elimination of the need for permanent anticoagulation. The mitral and aortic prostheses (Adiam Life Science, Erkelenz, Germany) are made entirely of polycarbonate urethane (PCU). The bileaflet asymmetric mitral valve mimics natural, nonaxial inflow, which creates a left ventricular vortex, saving energy for systolic ejection of blood. The trileaflet aortic prosthesis has diminished pressure loss and reduced stress and strain peaks at the commissures. The valves were subjected to long-term in vitro testing and in vivo testing in a growing calf model (20 weeks; 7 mitral and 7 aortic valves) with comparison with 2 commercial bioprostheses (7 mitral, 2 aortic). Two-dimensional echocardiography was performed after implantation and prior to sacrifice with autopsy and valve examination. In vitro durability of the PCU valves was proved up to 20 years. In vivo durability and hemodynamics were superior to those of all bioprostheses. Survival of PCU valves versus bioprostheses was 7 versus 2 mitral valves and 5 versus 0 aortic valves, respectively. Two animals with PCU aortic valves died of pannus overgrowth that caused severe left ventricular outflow tract obstruction without changes in the valves. Degeneration and calcification were mild (mitral) and moderate (aortic) in PCU valves but were severe in biological valves. There was no increased thrombogenicity of the PCU valves compared with bioprostheses. The new flexible polymeric aortic and mitral valve prostheses were superior to current bioprostheses in animal testing.

Polymer micro piezo valve with a small dead volume

A polymer valve with a small dead volume in the range of 6 nl and a response time faster than 1 ms is presented. The valve structure is simple and therefore easy to fabricate by injection molding or hot embossing. A layer of silicone rubber applied by a stamping technique not only promotes the sealing of the valve but also defines the gluing area during assembly. The fabrication is based on the AMANDA-process, which allows low-cost batch production of polymer micro devices.

EXPERIMENTAL STUDY OF THE HYDRODYNAMIC PERFORMANCE OF THE SNU POLYMER VALVE

The SNU (Seoul National University) polymer valve is a mono-leaflet polymer valve for artificial heart. In this work, the hydrodynamic performance of the SNU polymer valve was evaluated in the view of geometric parameters. The geometrical parameters were selected as three folds, 1) whether the leaflet floats, 2) the thickness of the leaflet (0.2mm, 0.3mm) and 3) with/without a purge hole. Total eight types of valves were fabricated to have each different combination of the three parameters. The total waveform of the pressures and the volume flow rate were measured and recorded in a mock circulation system and the hydrodynamic performance parameters, 1) the pressure loss coefficient, 2) the closing volume, and 3) the leakage volume, were calculated from the waveform data. The correlation between the geometric parameters and the hydro-dynamic performance parameters was assessed by statistical methods. The valves with floating type 0.3 mm thick leaflet showed to have lower pressure loss coefficient than the non-floating type equivalents, but similar tendency was not seen in the valves with 0.2mm thick leaflet. All floating leaflet valves had larger closing volume than non-floating equivalents. In low flow condition, the thickness of leaflet did not show any effect on the closing volume. However, the valves with thick leaflet showed larger closing volume in the case of high flow. The purge hole induced more leakage volume in all cases, but it did not affect the pressure loss coefficient and the closing volume.

High Performance P(VDF-TrFE-CFE) Terpolymer for BioMEMs and Microfluidic Devices

ABSTRACTBioMEMs and microfluidic devices have gained a lot of attention in recent years due to their emerging applications in biochemical analysis, medical diagnosis, chemical analysis and synthesis, drug discovery and drug delivery, biosensing and biomimetic systems. The materials requirements for bioMEMs are biocompatible, chemically modifiable, easy to fabricate, economic, compliable and smart. Among various materials, the electroactive polymeric materials can best meet these requirements. Recently, we developed a group of poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) based terpolymers which have very high strain level and high energy density. The longitudinal and transverse strain of these materials can reach about –7% and 4.5%, and the elastic energy density is around 1.1 J/cm3, which are very attractive for the development of polymeric pump, valve and other microfluidic components for all polymer-based bioMEMs and microfluidic integrated system. This paper reports on the recent efforts on the optimization of the terpolymer performance and development of microfluidic components using the electroactive terpolymers for bioMEMs.

The improved Jellyfish Valve: durability enhancement with sufficient blood compatibility.

The Jellyfish Valve is one of the most promising polymer valves for artificial hearts. The present problems to be solved are 1) how to prevent a membrane fracture and 2) how to eliminate a calcification, because both of these problems were observed in experiments with goats after 312 days and 414 days of pumping. Finite element analysis demonstrated that mechanical tensile strain induced in the membrane at valve closure was clearly consistent with the fracture location as well as calcification area in in vivo experiments. Based on this finding, a new valve seat with an additional concentric ring 14 mm in diameter and 0.5 mm in width was finally developed. The maximum strain was dramatically reduced to 52% by the design improvement. Moreover, accelerated fatigue tests demonstrated that the improved valve was 10 times more durable as compared with the original valve, which was equivalent to an in vivo duration of 8.3 years. In animal experiments, including 31 days and 46 days use in a total artificial heart (TAH), no thrombus was found despite the lack of anticoagulant or antiplatelet therapies. These results indicate that the improved Jellyfish Valve might be one of the most durable polymer valves, able to perform in artificial hearts for a long period of time.

Application of the moving-actuator type pump as a ventricular assist device: in vitro and in vivo studies.

A moving actuator type pump has been developed as a multifunctional Korean artificial heart (AnyHeart). The pump consists of a moving actuator as an energy converter, right and left sacs, polymer (or mechanical) valves, and a rigid polyurethane housing. The actuator containing a brushless DC motor moves back and forth on an epicyclical gear train to produce a pendular motion, which compresses both sacs alternately. Of its versatile functions of ventricular assist device and total artificial heart use, we have evaluated the system performance as a single or biventricular assist device through in vitro and in vivo experiments. Pump performance and anatomical feasibility were tested using various animals of different sizes. In the case of single ventricular assist device (VAD) use, one of the sacs remained empty and a mini-compliance chamber was attached to either an outflow or inflow port of the unused sac. The in vitro and in vivo studies show acceptable performance and pump behavior. Further extensive study is required to proceed to human application.

DNA amplification and hybridization assays in integrated plastic monolithic devices.

PCR amplification, DNA hybridization, and a hybridization wash have been integrated in a disposable monolithic DNA device, containing all of the necessary fluidic channels and reservoirs. These integrated devices were fabricated in polycarbonate plastic material by CO2 laser machining and were assembled using a combination of thermal bonding and adhesive tape bonding. Pluronics polymer phase change valves were implemented in the devices to fulfill the valving requirements. Pluronics polymer material is PCR compatible, and 30% Pluronics polymer valves provide enough holding pressure to ensure a successful PCR amplification. By reducing the temperature locally, to approximately 5 degrees C, Pluronics valves were liquefied and easily opened. A hybridization channel was made functional by oligonucleotide deposition, using Motorola proprietary surface attachment chemistry. Reagent transport on the device was provided by syringe pumps, which were docked onto the device. Peltier thermal electrical devices powered the heating and cooling functionality of the device. Asymmetrical PCR amplification and subsequent hybridization detection of both Escherichia coli K-12 MG1655 and Enterococcus faecalis DNAE genes have been successfully demonstrated in these disposable monolithic devices.

Implications for the establishment of accelerated fatigue test protocols for prosthetic heart valves.

The goal of this research is to establish a reliable methodology for accelerated fatigue tests of prosthetic heart valves. A polymer valve was the subject, and the influence of various drive parameters on durability was investigated in three different machines. Valve lifetime was notably shortened by increasing the cyclic rate or stroke even though the maximum pressure difference at valve closure was maintained at 120 mm Hg. These results demonstrate that adjustment of the maximum transvalvular pressure is not sufficient to ensure tests are conducted under the same conditions and indicate that measurement of the dynamic load would be more efficacious. Moreover, the locations of tears sustained in the accelerated tests differed from those encountered in an animal experiment although in both cases the locations were entirely consistent with the areas of strain concentration revealed by finite element analysis. These findings should be discussed during a revision of ISO 5840.

ANYHEART

Purpose: An implantable pulsatile BVAD with small volume and light weight and with the versatility of ventless LVAD without a separate compliance chamber was developed. Methods: This electro-mechanical BVAD comprises actuator including energy converter and reduction gear train, blood sacs, the polymer valves and implantable controller. To monitor the status of the AnyHeart from everywhere and at any time, portable PDA monitor and web-based remote monitoring system were developed. Results: The main body of AnyHeart (ver. AH-350) is 106mm(L), 87mm (W), and 67mm(H). The weight and maximum cardiac output is 780g and 7L/min, respectively. The AnyHeart could be used as ventless LVAD. The number ot animal experiments and the longest survival records were 5 cases, 28 days for LVAD, and 18 cases, 17 days for BVAD respectively, The PDA local monitor replaced bulky PC monitor. The web-based remote system had functions such as data recording and posting through the internet. All of these systems were tested in animal experiments. Through 12th-24th July 2001, there was the first clinical implantation of the AnyHeart.

T-PLS NEW PULSATILE BLOOD PUMP TECHNOLOGY FROM CARDIAC ARREST TO HEART RECOVERY

The conventioal non-pulsatile blood pump of the roller-type or the centrifugal pump are used for present ECMO application. We have developed the Twin Pulse Life Support (T- PLS) and performed animal experiments. As T- PLS is a portable device with small size, it can he used, sequencially, from the emergency care to the surgical operation and the patients recovery. The T- PLS system consists of two blood sac and oxygenator. The polypropylene hollow fiber membrane oxygenator (Univoxtm- IC, Baxter) was used. The polyurethane polymer valves are used at the inlet and outlet sides of the tubular blood sacs. Non- pulsatile ECMO system as centrifugal pump may generate negative pressure as high 2s − 200 to − 700 mmHg in the drainage circuit which may cause cavitation, and the pump output are independent upon the afterload However, T- PLS flow's pre-load dependency and after-load-independent pump output can make the system to he automatically controlled In animal experiments, the degree of the blood damages was lower than the other conventional pumps. These animal and in-vitro experimental results show that the pulsatile flow can be safely produced for physiological blood flows in the brain, heart, and the lung.

Microactuators toward microvalves for responsive controlled drug delivery

A responsive controlled drug release system in which the delivery of drugs is achieved by actuating miniature metal or polymeric valves has been introduced. These valves might be actuated under the control of a sensor responding to a specific biological stimulus. This approach offers better reproducibility and easier control than drug release achieved by passive diffusion out of a polymer host matrix. The metal valve systems, which are irreversible, consist of thin suspended non-porous layers that can be electrochemically dissolved or disintegrated by water electrolysis. The reversible polymeric valve systems, also called ‘artificial muscle’, are prepared from a blend of redox polymer and hydrogel that swells and shrinks either by applying a suitable bias or through a specific chemical reaction. In one of the several possible configurations for the artificial muscle valves such as the sphincter configuration, the blend is electropolymerized within an array of holes, which open and close corresponding to the shrinking and swelling of the polymer actuator. The swelling and shrinking property of the blends is characterized by video monitoring and by in situ conductivity measurements. Significantly larger magnitude of swelling and shrinking were observed for the blend than the redox polymer itself. The blend also appeared smoother and more voluminous. The largest actuation was obtained for the blend consisting of polyaniline and poly(2-hydroxyethylmethacrylate)-poly( N-vinylpyrrolidinone). The results demonstrate that it is possible to apply artificial muscle for the fabrication of microactuator valves for responsive controlled drug delivery.

Biomechanical Analysis of an Accelerated Fatigue Test Method for Polymer Valves.

Biomechanical Analysis of an Accelerated Fatigue Test Method for Polymer Valves.

Trials on an Extension of the ISO Standard of Accelerated Fatigue Test for Prosthetic Heart Valves: Application for Polymer Valves

Trials on an Extension of the ISO Standard of Accelerated Fatigue Test for Prosthetic Heart Valves: Application for Polymer Valves

The computational approach applied to the design and structural verification of a trileaflet polymeric heart valve

This study represents an application of the computational methods to the design and structural verification of a cardiac trileaflet polymeric valve. Numerical methods are commonly used for mechanic, fluid dynamic and thermal preliminary testing of engineering devices. In this paper commercial codes have been used to design and analyse a device which operates in contact with a biologic environment. Several simplifications are necessary to fulfill this aim due to the actual characteristics of the material, loads and boundary conditions. Six 3-D valve models have been developed and their mechanic behavior compared. The results allow an evaluation of the method that has been adopted and of the simplifications imposed. The method can be used to solve biomedical engineering problems though it requires an accurate description of the geometric and operating characteristics of both the device and its environment together with a critical evaluation of the results.