Hemodynamic Performance and Thrombogenic Properties of a Superhydrophobic Bileaflet Mechanical Heart Valve

Thirty-year outcomes of low-intensity anticoagulation for mechanical aortic valve

The long-term safety, efficacy, and outcomes of low-intensity anticoagulation for mechanical heart valves remain unclear. This study aimed to evaluate the long-term outcomes of low-intensity anticoagulation therapy after aortic valve replacement (AVR) with a mechanical prosthesis. This retrospective cohort study consulted medical records and conducted a questionnaire to investigate 519 patients who underwent single AVR with the St. Jude Medical bileaflet valve and were in sinus rhythm. All patients were followed up with an international normalized ratio (INR) target of 1.6-2.5, and their INR values were checked throughout the follow-up period. The survival rate, incidence of major adverse cardiac and cerebrovascular events (MACCE), and risk factors for cardiac death and MACCE were investigated. The total follow-up was 9793 patient-years, and the follow-up periods were 19.9 (standard deviation [SD]: 7.9) years. The mean INR was 2.03 (SD: 0.54). Survival rates from cardiac death were 93.6% in 20 years and 85.2% in 30 years. Advanced age ≥ 70 years was the only significant risk factor for cardiac death and MACCE, and the INR < 2.0 was not significant risk factor for MACCE including thromboembolism or bleeding events. Low-intensity anticoagulation with an INR of 1.6-2.5 for patients with sinus rhythm after AVR with a bileaflet mechanical valve is safe and effective, even over 30 years.

New insights and novel perspectives in bileaflet mechanical heart valve prostheses thromboresistance

BACKGROUND

Although well-known for their thromboresistance, bileaflet mechanical heart valves (BMHV) require lifelong anti-thrombotic therapy. This must be associated with a certain level of thrombogenicity. Since both thromboresistance and thrombogenicity are explained by the blood-artificial surface or liquid-solid interactions, the aim of the present study was to explore BMHV thromboresistance from new perspectives. The wettability of BMHV pyrolytic carbon (PyC) occluders was investigated in under-liquid conditions. The submerged BMHV wettability clarifies the mechanisms involved in the thromboresistance.

METHODS

The PyC occluders of a SJM Regent™ BMHV were previously laser irradiated, to create a surface hierarchical nano-texture, featuring three nano-configurations. Additionally, four PyC occluders of standard BMHV (Carbomedics, SJM Regent™, Bicarbon™, On-X®), were investigated. All occluders were evaluated in under-liquid configuration, with silicon oil used as the working droplet, while water, simulating blood, was used as the surrounding liquid. The under-liquid droplet-substrate wetting interactions were analyzed using contact angle goniometry.

RESULTS

All the standard occluders showed very low contact angle, reflecting a pronounced affinity for non-polar molecules. No receding of the contact line could be observed for the untreated occluders. The smallest static contact angle of around 61° could be observed for On-X® valve (the only valve made of full PyC). The laser-treated occluders strongly repelled oil in underwater conditions. A drastic change in their wetting behaviour was observed depending on the surrounding fluid, displaying a hydrophobic behaviour in the presence of air (as the surrounding medium), and showing instead a hydrophilic nature, when surrounded by water.

CONCLUSIONS

BMHV "fear" water and blood. The intrinsic affinity of BMHV for nonpolar fluids can be translated into a tendency to repel polar fluids, such as water and blood. The blood-artificial surface interaction in BMHV is minimized. The contact between blood and BMHV surface is drastically reduced by polar-nonpolar Van der Waals forces. The "hydro/bloodphobia" of BMHV is intrinsically related to their chemical composition and their surface energy, thus their material: PyC indeed. Pertaining to thromboresistance, the surface roughness does not play a significant role. Instead, the thromboresistance of BMHV lies in molecular interactions. BMHV wettability can be tuned by altering the surface interface, by means of nanotechnology.

Superhydrophobic Biological Fluid-Repellent Surfaces: Mechanisms and Applications

Superhydrophobic biological fluid-repellent surfaces (SBFRSs) have attracted great attention in the treatment of blood and urine-related diseases because of their unique wettability and compatibility, which creates a new path for the development of medical apparatus and instruments, and are expected to create advances in various fields. Here, this review provides an up-to-date summary of research progress on the repellent mechanism and application of SBFRSs. The underlying physical and chemical principles for designing superhydrophobic surfaces are first introduced. Then, the dialectical influences of solid-liquid interactions between superhydrophobic surfaces and biological fluids on the wettability and compatibility are emphatically expounded. Subsequently, attention is drawn to the recent applications of SBFRSs in biomedical fields, such as surgical medical apparatus, implant materials, extracorporeal circulation devices, and biological fluid detection. Finally, the outlook and challenges in terms of employing SBFRSs are also discussed. This review is expected to provide a comprehensive guidance for the preparation of SBFRSs with compatibility and long-term superhydrophobic stability that is closely related to clinical applications.

Bio-inspired hemocompatible surface modifications for biomedical applications

When blood first encounters the artificial surface of a medical device, a complex series of biochemical reactions is triggered, potentially resulting in clinical complications such as embolism/occlusion, inflammation, or device failure. Preventing thrombus formation on the surface of blood-contacting devices is crucial for maintaining device functionality and patient safety. As the number of patients reliant on blood-contacting devices continues to grow, minimizing the risk associated with these devices is vital towards lowering healthcare-associated morbidity and mortality. The current standard clinical practice primarily requires the systemic administration of anticoagulants such as heparin, which can result in serious complications such as post-operative bleeding and heparin-induced thrombocytopenia (HIT). Due to these complications, the administration of antithrombotic agents remains one of the leading causes of clinical drug-related deaths. To reduce the side effects spurred by systemic anticoagulation, researchers have been inspired by the hemocompatibility exhibited by natural phenomena, and thus have begun developing medical-grade surfaces which aim to exhibit total hemocompatibility via biomimicry. This review paper aims to address different bio-inspired surface modifications that increase hemocompatibility, discuss the limitations of each method, and explore the future direction for hemocompatible surface research.

Controlling the Flow Separation in Heart Valves Using Vortex Generators

A comprehensive computational study is performed to investigate the effectiveness of vortex generators (VGs) applied to mechanical bi-leaflet heart valves. Co-rotating and counter-rotating VG configurations are compared to a control valve without VGs. Detailed flow fields are obtained and used to elucidate the underlying flow physics. It was found that VGs reduce flow separation over the leaflets and hence reduce the Reynolds shear stress (RSS) in the vicinity regions of heart valve. The co-rotating VG configuration demonstrates a better performance compared with the counter-rotating configuration in terms of the RSS, turbulent kinetic energy production and velocity distributions, especially in the peripheral jet flows. The fraction of blood damage in the co-rotating configuration shows a 4.7% reduction in comparison to the control case, while a 3.7% increase is observed in the counter-rotating configuration. The passive flow control technique of applying co-rotating VG illustrates a great potential to help mitigate the hemodynamic factors leading to potential blood damage risk.

Computational Methods for Fluid-Structure Interaction Simulation of Heart Valves in Patient-Specific Left Heart Anatomies

Given the complexity of human left heart anatomy and valvular structures, the fluid–structure interaction (FSI) simulation of native and prosthetic valves poses a significant challenge for numerical methods. In this review, recent numerical advancements for both fluid and structural solvers for heart valves in patient-specific left hearts are systematically considered, emphasizing the numerical treatments of blood flow and valve surfaces, which are the most critical aspects for accurate simulations. Numerical methods for hemodynamics are considered under both the continuum and discrete (particle) approaches. The numerical treatments for the structural dynamics of aortic/mitral valves and FSI coupling methods between the solid Ωs and fluid domain Ωf are also reviewed. Future work toward more advanced patient-specific simulations is also discussed, including the fusion of high-fidelity simulation within vivo measurements and physics-based digital twining based on data analytics and machine learning techniques.

Flow assessment as a function of pump timing of tubular pulsatile pump for use as a ventricular assist device in a left heart simulator

INTRODUCTION

Although mechanical circulatory support saved many lives during the last decade, clinical observations have shown that the continuous flow pumps are associated with a much higher incidence of gastrointestinal bleeding and kidney problems, among others, compared with the earlier generation pulsatile pumps. However, the presence of several moving mechanical components made pulsatile pumps less durable, bulky, and prone to malfunction, ultimately leading to bias in favor of continuous flow designs.

OBJECTIVE

The aim of the current work is to create a prototype tubular pulsatile pump and to test the timing of the pump in a left heart simulator.

METHODS

A left heart simulator to mimic pumping from a failing heart was created. This was used to experimentally test the output of a prototype ventricular assist device relative to a failing heart in the form of flow and pressure. The effect of pulsation timing was quantified.

RESULTS

A failing heart was simulated with an average flow rate of 1.1 L/min and a systolic pressure of 47 mmHg. With the pump, the flow rate increases to 4.8 L/min and a systolic pressure of 110mmHg, in a copulsation mode, while activating for 300-400 ms. If the activation time is reduced, or increased, the pump becomes less effective. Load on the heart is reduced when the pump operates in a counterpulsation mode.

CONCLUSION

A pulsatile pump, like the one proposed, provides adequate output for mechanical circulatory support, while minimizing the number of moving parts that could otherwise lead to tribological wear.

Calcific Aortic Stenosis-A Review on Acquired Mechanisms of the Disease and Treatments

Calcific aortic stenosis is a progressive disease that has become more prevalent in recent decades. Despite advances in research to uncover underlying biomechanisms, and development of new generations of prosthetic valves and replacement techniques, management of calcific aortic stenosis still comes with unresolved complications. In this review, we highlight underlying molecular mechanisms of acquired aortic stenosis calcification in relation to hemodynamics, complications related to the disease, diagnostic methods, and evolving treatment practices for calcific aortic stenosis.

Surface modification strategies to improve titanium hemocompatibility: a comprehensive review

Titanium and its alloys are widely used in different biomaterial applications due to their remarkable mechanical properties and bio-inertness. However, titanium-based materials still face some challenges, with an emphasis on hemocompatibility. Blood-contacting devices such as stents, heart valves, and circulatory devices are prone to thrombus formation, restenosis, and inflammation due to inappropriate blood-implant surface interactions. After implantation, when blood encounters these implant surfaces, a series of reactions takes place, such as protein adsorption, platelet adhesion and activation, and white blood cell complex formation as a defense mechanism. Currently, patients are prescribed anticoagulant drugs to prevent blood clotting, but these drugs can weaken their immune system and cause profound bleeding during injury. Extensive research has been done to modify the surface properties of titanium to enhance its hemocompatibility. Results have shown that the modification of surface morphology, roughness, and chemistry has been effective in reducing thrombus formation. The main focus of this review is to analyze and understand the different modification techniques on titanium-based surfaces to enhance hemocompatibility and, consequently, recognize the unresolved challenges and propose scopes for future research.

Laser texturing of a St. Jude Medical mechanical heart valve prosthesis: the proof of concept

OBJECTIVES

The liquid-solid interactions have attracted broad interest since solid surfaces can either repel or attract fluids, configuring a wide spectrum of wetting states (from superhydrophilicity to superhydrophobicity). Since the blood-artificial surface interaction of bileaflet mechanical heart valves essentially represents a liquid-solid interaction, we analysed the thrombogenicity of mechanical heart valve prostheses from innovative perspectives. The aim of the present study was to modify the surface wettability of standard St. Jude Medical Regent™ occluders.

METHODS

Four pyrolytic carbon occluders were irradiated by means of ultra-short pulse laser, to create 4 different nanotextures (A-D), the essential prerequisite to achieve superhydrophobicity. The static surface wettability of the occluders was qualified by the contact angle (θ) of 2 µl of purified water, using the sessile drop technique. The angle formed between the liquid-solid and the liquid-vapour interface was the contact angle and was obtained by analysing the droplet images captured by a camera. The morphology of the occluders was characterized and analysed by a scanning electron microscope at different magnifications.

RESULTS

The scanning electron microscope analysis of the textures revealed 2 different configurations of the pillars since A and B showed well-rounded shaped tops and C and D flat tops. The measured highest contact angles were comprised between 108.1° and 112.7°, reflecting an improved hydrophobicity of the occluders. All the textures exhibited, to different extents, an orientation (horizontal or vertical), which was strictly related to the observed anisotropy.

CONCLUSIONS

In this very early phase of our research, we were able to demonstrate that the intrinsic wettability of pyrolytic carbon occluders can be permanently modified, increasing the water repellency.

In Vivo Blood-Repellent Performance of a Controllable Facile-Generated Superhydrophobic Surface

Fabrication of a blood-repellent surface is essential for implantable or interventional medical devices to avoid thrombosis which can induce several serious complications. In this research, a novel micropatterned surface was fabricated via a facile and cost-effective method, and then, the in vitro and in vivo blood-repellent performances of the controllable superhydrophobic surface were systematically evaluated. First, a facile and cost-effective strategy was proposed to fabricate a controllable superhydrophobic surface on a medically pure titanium substrate using an ultraviolet laser process, ultrasonic acid treatment, and chemical modification. Second, the superhydrophobicity, durability, stability, and corrosion resistance of the superhydrophobic surface were confirmed with advanced testing techniques, which display a high contact angle, low adhesion to water and blood, and excellent resistant element precipitation. Third, the platelet-rich plasma and whole blood were applied to evaluate the hemocompatibility of the superhydrophobic surface by means of an in vitro experiment, and no blood cell activation or aggregation was observed on the superhydrophobic surface. Finally, hollow tubes with an inner superhydrophobic surface were implanted into the left carotid artery of rabbits for 2 weeks to verify the biocompatibility in vivo. The superhydrophobic surface could effectively eliminate blood cell adhesion and thrombosis. No obvious inflammation or inordinate proliferation was found by histological analysis. This research provides a facile and cost-effective strategy to prepare a blood-repellent surface, which may have promising applications in implanted biomedical devices.

Fabrication of a gradient hydrophobic surface with parallel ridges on pyrolytic carbon for artificial heart valves

Effective surface modification to endow pyrolytic carbon (PYC) with long-term anti-thrombotic performance is highly demanded. In this work, a gradient hydrophobic surface on PYC was prepared by creating parallel ridges via the combination of laser etching technology and surface fluorosilanization. Scanning electron microscopy (SEM) observation confirms that the gradient hydrophobic surface is composed of a bare PYC region and four regions of parallel ridges with varying distances. The gradient hydrophobic surface is stable in air, phosphate buffer solution (PBS), and flowing PBS. Additionally, the gradient hydrophobic surface on PYC shows spontaneous droplet motion and much lower flow resistance than bare PYC. Compared to bare PYC, the gradient hydrophobic surface on PYC exhibits better blood compatibility and anti-adhesion performance. The results presented in this paper confirm that creating a gradient hydrophobic surface is an effective way of achieving long-lasting anti-thrombosis property.

Blood repellent superhydrophobic surfaces constructed from nanoparticle-free and biocompatible materials

Durable and environment friendly superhydrophobic surfaces are needed for a set of important applications. Biomedical applications, in particular, impose stringent requirements on the biocompatibility of the materials used in the fabrication of superhydrophobic surfaces. In this study, we demonstrate the fabrication of mechanically durable superhydrophobic surfaces via an in-situ structuring strategy starting from natural carnauba wax and biocompatible polydimethylsiloxane (PDMS) materials. The transfer of the structure of the paper to a free-standing PDMS film provided the microscale structure. On top of this structured surface, the wax was spray-coated, initially resulting in a relatively homogeneous film with limited liquid repellence. The key in achieving superhydrophobicity was rubbing the surface for in-situ generation of a finely textured wax coating with a water contact angle of 169° and a sliding angle of 3°. The hierarchically structured surface exhibits mechanical robustness as demonstrated with water impact and linear abrasion tests. We finally demonstrate repellence of the surfaces against a range of blood products including platelet suspension, erythrocyte suspension, fresh plasma, and whole blood.

Potential of Superhydrophobic Surface for Blood-Contacting Medical Devices

Medical devices are indispensable in the healthcare setting, ranging from diagnostic tools to therapeutic instruments, and even supporting equipment. However, these medical devices may be associated with life-threatening complications when exposed to blood. To date, medical device-related infections have been a major drawback causing high mortality. Device-induced hemolysis, albeit often neglected, results in negative impacts, including thrombotic events. Various strategies have been approached to overcome these issues, but the outcomes are yet to be considered as successful. Recently, superhydrophobic materials or coatings have been brought to attention in various fields. Superhydrophobic surfaces are proposed to be ideal blood-compatible biomaterials attributed to their beneficial characteristics. Reports have substantiated the blood repellence of a superhydrophobic surface, which helps to prevent damage on blood cells upon cell-surface interaction, thereby alleviating subsequent complications. The anti-biofouling effect of superhydrophobic surfaces is also desired in medical devices as it resists the adhesion of organic substances, such as blood cells and microorganisms. In this review, we will focus on the discussion about the potential contribution of superhydrophobic surfaces on enhancing the hemocompatibility of blood-contacting medical devices.

Laser Superficial Fusion of Gold Nanoparticles with PEEK Polymer for Cardiovascular Application

This paper analyses the possibility of obtaining surface-infused nano gold particles with the polyether ether ketone (PEEK) using picosecond laser treatment. To fuse particles into polymer, the raw surface of PEEK was sputtered with 99.99% Au and micromachined by an A-355 laser device for gold particle size reduction. Biomimetic pattern and parameters optimization were key properties of the design for biomedical application. The structures were investigated by employing surface topography in the presence of micron and sub-micron features. The energy of the laser beam stating the presence of polymer bond thermalisation with remelting due to high temperature was also taken into the account. The process was suited to avoid intensive surface modification that could compromise the mechanical properties of fragile cardiovascular devices. The initial material analysis was conducted by power–depth dependence using confocal microscopy. The evaluation of gold particle size reduction was performed with scanning electron microscopy (SEM), secondary electron (SE) and quadrant backscatter electron detector (QBSD) and energy dispersive spectroscopy (EDS) analysis. The visibility of the constituted coating was checked by a commercial grade X-ray that is commonly used in hospitals. Attempts to reduce deposited gold coating to the size of Au nanoparticles (Au NPs) and to fuse them into the groove using a laser beam have been successfully completed. The relationship between the laser power and the characteristics of the particles remaining in the laser irradiation area has been established. A significant increase in quantity was achieved using laser power with a minimum power of 15 mW. The obtained results allowed for the continuation of the pilot study for augmented research and material properties analysis.

Clinical mid-term outcomes of the Chinese-made CL-V bileaflet mechanical heart valve in Chinese patients

Background

The CL-V full-carbon bileaflet mechanical heart valve is a novel Chinese-made prosthetic valve. This study evaluated the mid-term outcomes of the CL-V bileaflet mechanical heart valve after implantation in Chinese patients.

Methods

This study retrospectively enrolled a total of 38 consecutive patients who underwent elective mechanical heart valve replacement (MHVR) with two different valve types from April 2004 and May 2010, including 18 patients with the CL-V bileaflet mechanical heart valve (44.4% male, mean age 47.4±6.2 years, mean body weight 64.7±11.9 kg) and 20 patients with the St. Jude mechanical heart valve (45.0% male, mean age 49.7±7.6 years, mean body weight 66.1±11.1 kg). All patients underwent follow-up clinical evaluations in the outpatient department at all-time points.

Results

No complications occurred during the mean 61.3 months follow-up time (range, 47–102 months). The cardiothoracic ratios (52.7%±4.5% vs. 50.1%±4.0%), left atrium diameter (46.5±7.6 vs. 44.8±9.3 mm), left ventricular diastolic diameter (47.6±4.9 vs. 48.2±8.5 mm) and left ventricular ejection fraction (65.4%±8.7% vs. 64.5%±8.0%) were not significantly different between the two groups (P>0.05). Transthoracic Doppler echocardiography showed that the hemodynamic indexes were not significantly different between the two groups at 1 year and 3 years (P>0.05). Furthermore, no significant differences were found between the two groups in hemocompatibility indexes at both 6 months and 3 years postoperatively (P>0.05).

Conclusions

The mid-term follow-up results of the CL-V bileaflet mechanical heart valve were similar to those of the St. Jude Medical heart valve, which showed stable hemodynamics and good blood compatibility. Chinese-made CL-V bileaflet mechanical heart valves can be a substitute for St. Jude Medical heart valves, and can be widely used in cardiac surgery.

Trial registration

Chinese Clinical Trial Registry ChiCTR2000034158.

Impact of superhydrophobicity on the fluid dynamics of a bileaflet mechanical heart valve

OBJECTIVE

The objective of this study is to evaluate the impact of superhydrophobic coating on the hemodynamics and turbulence characteristics of a bileaflet mechanical valve in the context of evaluating blood damage potential.

METHODS

Two 3D printed bileaflet mechanical valves were hemodynamically tested in a pulse duplicator under physiological pressure and flow conditions. The leaflets of one of the two valves were sprayed with a superhydrophobic coating. Particle Image Velocimetry was performed. Pressure gradients (PG), effective orifice areas (EOA), Reynolds shear stresses (RSS) and instantaneous viscous shear stresses (VSS) were calculated.

RESULTS

(a) Without SH coating, the PG was found to be 14.53 ± 0.7 mmHg and EOA 1.44 ± 0.06 cm2. With coating, the PG obtained was 15.21 ± 1.7 mmHg and EOA 1.39 ± 0.07 cm2; (b) during peak systole, the magnitude of RSS with SH coating (110Pa) exceeded that obtained without SH coating (40 Pa) with higher probabilities to develop higher RSS in the immediate wake of the leaflet; (c) The magnitudes range of instantaneous VSS obtained with SH coating were slightly larger than those obtained without SH coating (7.0 Pa versus 5.0 Pa).

CONCLUSION

With Reynolds Shear Stresses and instantaneous Viscous Shear Stresses being correlated with platelet damage, SH coating did not lead to their decrease. While SH coating is known to improve surface properties such as reduced platelet or clot adhesion, the relaxation of the slip condition does not necessarily improve overall hemodynamic performance for the bileaflet mechanical valve design.

Superhydrophobic Liquid-Solid Contact Triboelectric Nanogenerator as a Droplet Sensor for Biomedical Applications

Superhydrophobic surfaces repel water and other liquids such as tissue fluid, blood, urine, and pus, which can open up a new avenue for the development of biomedical devices and has led to promising advances across diverse fields, including plasma separator devices, blood-repellent sensors, vascular stents, and heart valves. Here, the fabrication of superhydrophobic liquid-solid contact triboelectric nanogenerators (TENGs) and their biomedical applications as droplet sensors are reported. Triboelectrification energy can be captured and released when droplets are colliding or slipping on the superhydrophobic layer. The developed superhydrophobic TENG possesses multiple advantages in terms of simple fabrication, bendability, self-cleaning, self-adhesiveness, high sensitivity, and repellency to not only water but also a variety of solutions, including blood with a contact angle of 158.6°. As a self-powered sensor, the developed prototypes of a drainage bottle droplet sensor and a smart intravenous injection monitor based on the superhydrophobic liquid-solid contact TENG can monitor the clinical drainage operation and intravenous infusion in real time, respectively. These prototypes suggest the potential merit of this superhydrophobic liquid-solid contact TENG in clinical application, paving the way for accurately monitoring clinical drainage operations and intravenous injection or blood transfusion in the future.

Multifunctional 3D Micro-Nanostructures Fabricated through Temporally Shaped Femtosecond Laser Processing for Preventing Thrombosis and Bacterial Infection

Blood-contacting medical devices that directly inhibit thrombosis and bacterial infection without using dangerous anticoagulant and antibacterial drugs can save countless lives but have proved extremely challenging. Here, a useful methodology is proposed that employs temporally shaped femtosecond laser ablation combined with fluorination to fabricate multifunctional three-dimensional (3D) micro-nanostructures with excellent hemocompatibility, zero cytotoxicity, outstanding biocompatibility, bacterial infection prevention, and long-term effectiveness on NiTi alloys. These multifunctional 3D micro-nanostructures present 0.1% hemolysis ratio and almost no platelet adhesion and activation, repel blood to inhibit blood coagulation in vitro, maintain 100% cell viability, and have exceptional stability over 6 months. Moreover, the multifunctional 3D micro-nanostructures simultaneously suppress bacterial colonization to form biofilm and kill 100% colonized Pseudomonas aeruginosa (P. aeruginosa) and 95.6% colonized Staphylococcus aureus (S. aureus) after 24 h of incubation, and bacterial residues can be easily removed. The fabrication method in this work has the advantages of simple processing, high efficiency, high quality, and high repeatability, and the new multifunctional 3D micro-nanostructures can effectively prevent thrombosis and bacterial infection, which can be widely applied to various clinical needs such as biomedical devices and implants.

Transient Study of Flow and Cavitation Inside a Bileaflet Mechanical Heart Valve

A mechanical heart valve (MHV) is an effective device to cure heart disease, which has the advantage of long life and high reliability. Due to the hemodynamic characteristics of blood, mechanical heart valves can lead to potential complications such as hemolysis, which have damage to the blood elements and thrombosis. In this paper, flowing features of the blood in the valve are analyzed and the cavitation mechanism in bileaflet mechanical heart valve (BMHV) is studied. Results show that the water hammer effect and the high-speed leakage flow effect are the primary causes of the cavitation in the valve. Compared with the high-speed leakage flow effect, the water hammer has a greater effect on the cavitation strength. The valve goes through four kinds of working condition within one heart beating period, including, fully opening stage, closing stage and fully closing stage. These four stages, respectively, make up 8.5%, 16.1%, 4.7% and 70.7% of the total period. The cavitation occurs on the fully closing stage. When the valve is in closing stage, the high pressure downstream of the valve lasts for about 20 ms and the high-speed leakage flow lasts for about 200 ms. This study systematically analyzes the causes of cavitation emerged in the process of periodic motion, which proposes the method for characterizing the intensity of the cavitation, and can be referred to for the cavitation suppression of the BHMV and similar valves.

Experimental analysis of pulsatile flow characteristics in prosthetic aortic valve models with stenosis

Bioprosthetic valves are widely used for aortic valve replacements for patients with severe aortic diseases. However, tissue-engineered leaflets normally deteriorate over time due to calcification, leading to life-threatening conditions that would require re-operation. The hemodynamics induced by a prosthetic stenosis is complicated and not fully understood. This in vitro experimental study focuses on the fluid dynamics of two aortic valve models with different prosthetic stenosis conditions. An in vitro cardiovascular flow simulator was utilized to provide the pulsatile physiological flow conditions. Phase-locked particle image velocimetry (PIV) and high-frequency pressure sensors were employed to measure the flow fields and pressure waveforms. Pressure data were evaluated for the two models representing moderate and severe stenosis conditions, respectively. The severe prosthetic stenosis induced a prolonged ejection period and increased acceleration time ratio. PIV results suggest the severe prosthetic stenosis resulted in a two-fold increase in peak jet velocity and a three-fold increase in peak turbulence kinetic energy compared to the moderate stenosis case. The severe stenosis also caused rapid expansion of the jet downstream of the valve orifice and increased eccentricity of the jet flow. The maximum Reynolds shear stress in the severe stenosis case was found similar to the bileaflet mechanical valve reported by previous literature, which was below the risk threshold of blood cell damage but could potentially increase the risks of platelet activation and aggregation.

Hemocompatibility of Super-Repellent surfaces: Current and Future

Virtually all blood-contacting medical implants and devices initiate immunological events in the form of thrombosis and inflammation. Typically, patients receiving such implants are also given large doses of anticoagulants, which pose a high risk and a high cost to the patient. Thus, the design and development of surfaces with improved hemocompatibility and reduced dependence on anticoagulation treatments is paramount for the success of blood-contacting medical implants and devices. In the past decade, the hemocompatibility of super-repellent surfaces (i.e., surfaces that are extremely repellent to liquids) has been extensively investigated because such surfaces greatly reduce the blood-material contact area, which in turn reduces the area available for protein adsorption and blood cell or platelet adhesion, thereby offering the potential for improved hemocompatibility. In this review, we critically examine the progress made in characterizing the hemocompatibility of super-repellent surfaces, identify the unresolved challenges and highlight the opportunities for future research on developing medical implants and devices with super-repellent surfaces.

Adverse Hemodynamic Conditions Associated with Mechanical Heart Valve Leaflet Immobility

Artificial heart valves may dysfunction, leading to thrombus and/or pannus formations. Computational fluid dynamics is a promising tool for improved understanding of heart valve hemodynamics that quantify detailed flow velocities and turbulent stresses to complement Doppler measurements. This combined information can assist in choosing optimal prosthesis for individual patients, aiding in the development of improved valve designs, and illuminating subtle changes to help guide more timely early intervention of valve dysfunction. In this computational study, flow characteristics around a bileaflet mechanical heart valve were investigated. The study focused on the hemodynamic effects of leaflet immobility, specifically, where one leaflet does not fully open. Results showed that leaflet immobility increased the principal turbulent stresses (up to 400%), and increased forces and moments on both leaflets (up to 600% and 4000%, respectively). These unfavorable conditions elevate the risk of blood cell damage and platelet activation, which are known to cascade to more severe leaflet dysfunction. Leaflet immobility appeared to cause maximal velocity within the lateral orifices. This points to the possible importance of measuring maximal velocity at the lateral orifices by Doppler ultrasound (in addition to the central orifice, which is current practice) to determine accurate pressure gradients as markers of valve dysfunction.

Superhydrophobic Blood-Repellent Surfaces

Superhydrophobic surfaces repel water and, in some cases, other liquids as well. The repellency is caused by topographical features at the nano-/microscale and low surface energy. Blood is a challenging liquid to repel due to its high propensity for activation of intrinsic hemostatic mechanisms, induction of coagulation, and platelet activation upon contact with foreign surfaces. Imbalanced activation of coagulation drives thrombogenesis or formation of blood clots that can occlude the blood flow either on-site or further downstream as emboli, exposing tissues to ischemia and infarction. Blood-repellent superhydrophobic surfaces aim toward reducing the thrombogenicity of surfaces of blood-contacting devices and implants. Several mechanisms that lead to blood repellency are proposed, focusing mainly on platelet antiadhesion. Structured surfaces can: (i) reduce the effective area exposed to platelets, (ii) reduce the adhesion area available to individual platelets, (iii) cause hydrodynamic effects that reduce platelet adhesion, and (iv) reduce or alter protein adsorption in a way that is not conducive to thrombus formation. These mechanisms benefit from the superhydrophobic Cassie state, in which a thin layer of air is trapped between the solid surface and the liquid. The connections between water- and blood repellency are discussed and several recent examples of blood-repellent superhydrophobic surfaces are highlighted.

Coalescence-Induced Self-Propulsion of Droplets on Superomniphobic Surfaces

We utilized superomniphobic surfaces to systematically investigate the different regimes of coalescence-induced self-propulsion of liquid droplets with a wide range of droplet radii, viscosities, and surface tensions. Our results indicate that the nondimensional jumping velocity V_j^* is nearly constant (V_j^* ≈ 0.2) in the inertial-capillary regime and decreases in the visco-capillary regime as the Ohnesorge number Oh increases, in agreement with prior work. Within the visco-capillary regime, decreasing the droplet radius R₀ results in a more rapid decrease in the nondimensional jumping velocity V_j^* compared to increasing the viscosity μ. This is because decreasing the droplet radius R₀ increases the inertial-capillary velocity V_ic in addition to increasing the Ohnesorge number Oh.