Directional Transport of a Liquid Drop between Parallel-Nonparallel Combinative Plates.

Liquids confined between two parallel plates can perform the function of transmission, support, or lubrication in many practical applications, due to which to maintain liquids stable within their working area is very important. However, instabilities may lead to the formation of leaking drops outside the bulk liquid, thus it is necessary to transport the detached drops back without overstepping the working area and causing destructive leakage to the system. In this study, we report a novel and facile method to solve this problem by introducing the wedgelike geometry into the parallel gap to form a parallel-nonparallel combinative construction. Transport performances of this structure were investigated. The criterion for self-propelled motion was established, which seemed more difficult to meet than that in the nonparallel gap. Then, we performed a more detailed investigation into the drop dynamics under squeezing and relaxing modes because the drops can surely return in hydrophilic combinative gaps, whereas uncertainties arose in gaps with a weak hydrophobic character. Therefore, through exploration of the transition mechanism of the drop motion state, a crucial factor named turning point was discovered and supposed to be directly related to the final state of the drops. On the basis of the theoretical model of turning point, the criterion to identify whether a liquid drop returns to the parallel part under squeezing and relaxing modes was achieved. These criteria can provide guidance on parameter selection and structural optimization for the combinative gap, so that the destructive leakage in practical productions can be avoided.

Effects on the pulmonary hemodynamics and gas exchange with a speed modulated right ventricular assist rotary blood pump: a numerical study.

Rotary blood pumps (RBPs) are the newest generation of ventricular assist devices. Although their continuous flow characteristics have been accepted widely, more and more research has focused on the pulsatile modulation of RBPs in an attempt to provide better perfusion. In this study, we investigated the effects of an axial RBP serving as the right ventricular assist device on pulmonary hemodynamics and gas exchange using a numerical method with a complete cardiovascular model along with airway mechanics and a gas exchange model. The RBP runs in both constant speed and synchronized pulsatile modes using speed modulation. Hemodynamics and airway O2 and CO2 partial pressures were obtained under normal physiological conditions, and right ventricle failure conditions with or without RBP. Our results showed that the pulsatile mode of the RBP could support right ventricular assist to restore most hemodynamics. Using speed modulation, both pulmonary arterial pressure and flow pulsatility were increased, while there was only very little effect on alveolar O2 and CO2 partial pressures. This study could provide basic insight into the influence of pulmonary hemodynamics and gas exchange with speed modulated right ventricular assist RBPs, which is concerned when designing their pulsatile control methods.

Primary side control of load voltage for transcutaneous energy transmission.

Transcutaneous energy transmission (TET) is considered as a good way to wirelessly power the implanted devices in human bodies. The load voltage provided from the TET to the implanted device should be kept stable to ensure the device working well, which however, is easily affected by the required power variation for different body movements and coil-couple malposition accompanying skin peristalsis. Commonly, the load voltage applied onto the device should be measured and feedback for power is regulated by implanting sensing and communication units into the body, which causes additional energy cost, increased size and weight of the implanted device. This paper takes the TET for artificial heart as an example to propose a novel primary side control method of the load voltage for TET, which does not require any additional implanted components. In the method, sensing coils are used to measure the malposition between the transmitter coil (TC) and receiver coil, and the magnitude of the TC current outside the human body. The measurement results are used to estimate the load voltage inside the body through calculation, whose value provide a base to develop a PI control system to regulate the input power of TET for the load voltage stability. The proposed method is experimentally validated on an actual TET for artificial heart by varying its load in a wide range under serious coil-couple malposition. With applying the primary side control, the variation of the load voltage is reduced to only 25 % of that without the control.

A transcutaneous energy transmission system for artificial heart adapting to changing impedance.

This article presents a coil-coupling-based transcutaneous energy transmission system (TETS) for wirelessly powering an implanted artificial heart. Keeping high efficiency is especially important for TETS, which is usually difficult due to transmission impedance changes in practice, which are commonly caused by power requirement variation for different body movements and coil-couple malposition accompanying skin peristalsis. The TETS introduced in this article is designed based on a class-E power amplifier (E-PA), of which efficiency is over 95% when its load is kept in a certain range. A resonance matching and impedance compressing functions coupled network based on parallel-series capacitors is proposed in the design, to enhance the energy transmission efficiency and capacity of the coil-couple through resonating, and meanwhile compress the changing range of the transmission impedance to meet the load requirements of the E-PA and thus keep the high efficiency of TETS. An analytical model of the designed TETS is built to analyze the effect of the network and also provide bases for following parameters determination. Then, according algorithms are provided to determine the optimal parameters required in the TETS for good performance both in resonance matching and impedance compressing. The design is tested by a series of experiments, which validate that the TETS can transmit a wide range of power with a total efficiency of at least 70% and commonly beyond 80%, even when the coil-couple is seriously malpositioned. The design methodology proposed in this article can be applied to any existing TETS based on E-PA to improve their performance in actual applications.

Numerical estimation of hemolysis from the point of view of signal and system.

The power-law based models for predicting shear-induced hemolysis are widely used in the optimization design of blood-contacting devices. However, this category of models has fallen short of accuracy when compared with the results of the in vitro experiments. The aim of this study is to develop an alternative model from the point of view of signal and system. Under the action of constant shear stress, the released hemoglobin was regarded as the output of system, and the system function that characterized the resistance to hemolysis was derived from the power-law equation. Two state variables were introduced to adequately capture the history of the system. The proposed model takes into account another known empirical formula, the threshold equation, by setting a nonzero initial condition of the blood. By comparing the estimated results with the published experimental data, it showed that the accuracy of the proposed model was notably improved. Furthermore, the analysis in frequency domain indicated that the damage contribution of the time-varying shear stress decreased with the increase of frequency. As the frequency domain analysis is important in many fields, it may play a role in the estimation of hemolysis in the future.

Flocculating characteristic of activated sludge flocs: interaction between Al(3+)) and extracellular polymeric substances.

Aluminum flocculant can enhance the flocculating performance of activated sludge. However, the binding mechanism of aluminum ion (Al(3+)) and extracellular polymeric substances (EPS) in activated sludge is unclear due to the complexity of EPS. In this work, three-dimensional excitation emission matrix fluorescence spectroscopy (3DEEM), fluorescence quenching titration and Fourier transform infrared spectroscopy (FT-IR) were used to explore the binding behavior and mechanism between Al(3+) and EPS. The results showed that two fluorescence peaks of tyrosine- and tryptophan-like substances were identified in the loosely bound-extracellular polymeric substances (LB-EPS), and three peaks of tyrosine-, tryptophan- and humic-like substances were identified in the tightly bound-extracellular polymeric substances (TB-EPS). It was found that these fluorescence peaks could be quenched with Al(3+) at the dosage of 3.0 mg/L, which demonstrated that strong interactions took place between the EPS and Al(3+). The conditional stability constants for Al(3+) and EPS were determined by the Stern-Volmer equation. As to the binding mechanism, the -OH, N-H, C=O, C-N groups and the sulfur- and phosphorus-containing groups showed complexation action, although the groups in the LB-EPS and TB-EPS showed different behavior. The TB-EPS have stronger binding ability to Al(3+) than the LB-EPS, and TB-EPS play an important role in the interaction with Al(3+).

Numerical hemolysis performance evaluation of a rotary blood pump under different speed modulation profiles.

Introduction: Speed modulation methods have been studied and even used clinically to create extra pulsation in the blood circulatory system with the assistance of a continuous flow rotary blood pump. However, fast speed variations may also increase the hemolysis potential inside the pump. Methods: This study investigates the hemolysis performance of a ventricular assist rotary blood pump under sinusoidal, square, and triangular wave speed modulation profiles using the computational fluid dynamics (CFD) method. The CFD boundary pressure conditions of the blood pump were obtained by combining simulations with the pump's mathematical model and a complete cardiovascular lumped parameter model. The hemolysis performance of the blood pump was quantified by the hemolysis index (HI) calculated from a Eulerian scalar transport equation. Results: The HI results were obtained and compared with a constant speed condition when the blood pump was run under three speed profiles. The speed modulations were revealed to slightly affect the pump hemolysis, and the hemolysis differences between the different speed modulation profiles were insignificant. Discussion: This study suggests that speed modulations could be a feasible way to improve the flow pulsatility of rotary blood pumps while not increasing the hemolysis performance.

A novel design of spiral groove bearing in a hydrodynamically levitated centrifugal rotary blood pump.

Good washout is very important in spiral groove bearing (SGB) designs when applied to blood pumps due to the micrometer scales of lubrication films and groove depths. To improve washout, flow rate or leakage through SGBs should be as large as possible. However, this special goal violates conventional SGB designs in which no leakage is desired as the leakage would decrease load-carrying capacity significantly. So, a design concept is formed fulfilling the two goals of high load-carrying capacity and large flow rate: let groove width decrease along flow path and the mating surface of the rotor rotate with a direction facilitating the flow through the grooves. Under this concept, a novel SGB is designed, contrary to conventional ones, with groove width decreasing with increasing spiral radius. This SGB is mounted on the motionless upper plate of our designed centrifugal blood pump, with the mating surface of rotor rotating with a direction facilitating the outward flow. To assess SGB designs, a characteristic plane is originally presented relating to pressure-normalized load-carrying capacity and flow rate. Comparisons between various kinds of SGB designs are made, and computational fluid dynamics (CFD) results are plotted in this characteristic plane from which load/flow performances can be directly read out. CFD and comparison results show that the new designs have superior load/flow characteristics. However, the impact of SGB designs upon hemolysis/thrombus formation is still to be verified according to the concept presented.

Effects of membrane reference state on shape memory of a red blood cell.

By using a three-dimensional continuum model, we simulate the shape memory of a red blood cell after the remove of external forces. The purpose of this study is to illustrate the effect of membrane reference state on cell behavior during the recovery process. The reference state of an elastic element is the geometry with zero stress. Since the cell membrane is composed of cytoskeleton and lipid bilayer, both the reference states of cytoskeleton (RSC) and lipid bilayer (RSL) are considered. Results show that a non-spherical RSC can result in shape memory. The energy barrier due to non-spherical RSC is determined by the ratio of the equator length to the meridian length of the RSC. Thus different RSCs can have similar energy barrier and leading to identical recovery response. A series of simulations of more intermediate RSCs show that the recovery time scale is inversely proportional to the energy barrier. Comparing to spherical RSL, a spheroid RSL contributes to the energy barrier and recovery time. Furthermore, we observe a folding recovery due to the biconcave RSL which is different from the tank treading recovery. These results may motivate novel numerical and experimental studies to determine the exact RSC and RSL.

Flexible Tactile Sensor Array Based on Aligned MWNTs-PU Composited Sub-Microfibers.

This present paper describes a novel method to fabricate tactile sensor arrays by producing aligned multi-walled carbon nanotubes (MWNTs)-polyurethane (PU) composite sub-microfiber (SMF) arrays with the electrospinning technique. The proposed sensor was designed to be used as the artificial skin for a tactile sensation system. Although thin fibers in micro- and nanoscale have many good mechanical characteristics and could enhance the alignment of MWNTs inside, the high impedance as a consequence of a small section handicaps its application. In this paper, unidirectional composite SMFs were fabricated orthogonally to the parallel electrodes through a low-cost method to serve as sensitive elements (SEs), and the impedances of SEs were measured to investigate the changes with deformation caused by applied force. The particular piezoresistive mechanism of MWNTs disturbed in SMF was analyzed. The static and dynamic test results of the fabricated tactile sensor were also presented to validate the performance of the proposed design.

Numerical simulations of wall contact angle effects on droplet size during step emulsification.

Terrace-based microfluidic devices are currently used to prepare highly monodisperse micro-droplets. Droplets are generated due to the spontaneous pressure drop induced by the Laplace pressure, and so the flow rate of a dispersed phase has little effect on droplet size. As a result, control over the droplet is limited once a step emulsification device has been fabricated. In this work, a terrace model was established to study the effect of the wall contact angle on droplet size based on computational fluid dynamics simulations. The results for contact angles from 140° to 180° show that a lower contact angle induces wall-wetting, increasing the droplet size. The Laplace pressure equations for droplet generation were determined based on combining pressure change curves with theoretical analyses, to provide a theoretical basis for controlling and handling droplets generated through step emulsification.

Detecting Malposition of Coil Couple for Transcutaneous Energy Transmission.

Transcutaneous energy transmission technology based on coil coupling is widely required for various wireless powering implanted devices in human body. However, the coupling performance is commonly affected by malposition between coils in practice. It is difficult for users to know the actual position of the implanted receiver coil (RC) and how to realign the transmitter coil (TC) outside the body. This article proposes a detecting method of coil-coupling malposition based on a sensing board with coil array fitted on the TC. In this article, the sensing system and the data processing algorithm separating the sensing coil (SC) signals induced by TC and RC currents, respectively, are introduced. Then, an analytical model formulating the induction effect between the RC and SCs is given. Inverse computation algorithms of the malposition based on the processed sensing data and the induction effect model are presented at last. The proposed method is validated by experiments simulating malposition both in distance and concentricity on an actual coil couple. The results show that the sensing system can provide accurate parameterized guide for users to adjust the installation of the TC for good energy transmission performance.

Pulse-pressure-enhancing controller for better physiologic perfusion of rotary blood pumps based on speed modulation.

Sufficient pulsation is important for physiologic perfusion if adequate flow is to be guaranteed. A fuzzy control method for rotary blood pumps using active speed modulation is proposed in this article. It maintains the mean aortic pressure to provide sufficient perfusion while it simultaneously enhances the pulse pressure. The controller uses the indices extracted from the aortic pressure as feedback to determine the amplitude and offset of the rectangular speed modulation waveform, which is synchronous with the cardiac cycle. An additional algorithm is included to prevent regurgitation. The controller is tested both in a baroreflex-cardiovascular model and in a preliminary in vitro experiment. Simulation results demonstrate that the controller is able to increase the pulse pressure to approximately 20 mm Hg and at the same time maintains the mean pressure at 100 mm Hg, when heart failure occurs. It is also quite robust under various physiologic disturbances. Experimental results show that the speed modulation can be implemented in real pumps and that the controller is feasible in practice.

[Analysis of the fractal structure of activated sludge flocs].

The small-angle light scattering (SALS) experiment was executed to calculate the fractal region, and the data of particle size distribution was fitted by Gamma equation. Besides, the atomic force microscope (AFM) and confocal laser scanning microscopy (CLSM) were used to observe the morphology of the microstructure of the sludge flocs under different scales. The results showed that the sluge floc was constituted by a series of clusters with different sizes. The surface of the floc was unsmooth with various "holes" and "gaps" and there were a range of pore structures within the sludge floc. For sludge flocs at large scales, a variety of pore texture coexisted, forming a transport channel for the nutrients and water in the sludge. The results also showed that the fractal structure was present in sludge flocs in the size range of 0.5-50 microm and the particle size distribution was fitted to the Gamma equation distribution model, indicating that the sludge floc formation process is a process dominated by Cluster-Cluster flocculation.

Collapse of an antibubble.

In contrast to a soap bubble, an antibubble is a liquid globule surrounded by a thin film of air. The collapse behavior of an antibubble is studied using a high-speed video camera. It is found that the retraction velocity of the thin air film of antibubbles depends on the thickness of the air film, e, the surface tension coefficient σ, etc., and varies linearly with (σ/ρe)(1/2), according to theoretical analysis and experimental observations. During the collapse of the antibubble, many tiny bubbles can be formed at the rim of the air film due to the Rayleigh instability. In most cases, a larger bubble will emerge finally, which holds most of the volume of the air film.

A fast building and effective hydraulic pediatric mock circulatory system for the evaluation of a left ventricular assist device.

A mock circulatory system (MCS) has been proven a useful tool in the development of a ventricular assist device. Nowadays a MCS aimed at the evaluation of pediatric blood pumps, which require many different considerations compared with that of adults, has become an urgent need. This article presents the details on how the dynamic process of the left ventricle, which is described in terms of the pressure-volume loop (P-V loop), and the properties of the circulation such as compliance and resistance are simulated by hydraulic elements. A simple control method is introduced to reproduce the physiological afterload and preload sensitivities of the mock ventricle for the first time. Hemodynamic performance of the system is obtained by medical sensors to validate the similarity of the device to the native cardiovascular system. The actual sensitivities of the mock ventricle are obtained intuitively from the changes of the P-V loops. The aortic input impedance of the MCS is also obtained and compared with the data from previous medical reports. At last a pediatric left ventricular assist device (LVAD) prototype is introduced for testing to further verify the effectiveness of the MCS. The experimental results indicate that this pediatric MCS is capable of reproducing basic hemodynamic characteristics of a child in both normal and pathological conditions and it is sufficient for testing a pediatric LVAD. Besides, most components constituting the main hydraulic part of this MCS are inexpensive off-the-shelf products, making the MCS easy and fast to build.