Electronic and structural characteristics of Zr-incorporated Gd2O3 films on strained SiGe substrates.

Zr-incorporated Gd(2)O(3) films were grown on various substrates as a function of Zr content. The extent of interfacial reactions was found to be critically dependent on both the incorporated Zr content and the substrate type. Specifically, the silicide layer was suppressed and the Gd(2)O(3) phase was changed to ZrO(2) on a Si substrate with increasing Zr content. Crystalline Gd(2)Ge(2)O(7) was grown on a Ge substrate, as the result of interfacial reactions between Gd-oxide and the Ge substrate. However, interfacial reactions were not affected by the amount of Zr incorporated. On the SiGe/Si substrate, reactions between Gd-oxide and Si could be controlled effectively by the incorporation of Zr, while the extent of reactions with Ge was significantly enhanced as the Zr content increased. The formation of an interfacial layer between the film and the SiGe substrate resulted in a textured crystalline growth.

Effect of fiber structure on dialysate flow profile and hollow-fiber hemodialyzer reliability: CT perfusion study.

BACKGROUND: Uniform dialysate distributions in hollow-fiber hemodialyzers facilitate effective solute removal, and the fiber structure inside hemodialyzers plays a significant role in determining dialysate flow distribution and dialysis efficiency. The authors analyzed the effects of undulated fibers on dialysate flow profiles and hemodialyzer reliability using a perfusion CT technique. METHOD: Using a multi-detector row CT unit, perfusion studies were performed on two different types of hemodialyzers: (A) straight fiber configuration; (B) undulated fiber configuration (wavy-shaped fibers). Deconvolution theory was used for image processing to derive dialysate flows, dialysate volumes, and mean transit time distributions. Three-dimensional perfusion maps for the two types of hemodialyzers were reconstructed using high resolution images and these parameters were compared at hemodialyzer midsections. RESULTS: Dialysate maldistributions were observed in both types of hemodialyzer. However, dialysate flow distributions were more uniform in the undulated-fiber hemodialyzer, whereas more complex flow distributions developed in straight-fiber hemodialyzer. Reliability as determined using intraclass correlation coefficients was markedly higher for the hemodialyzer containing undulated fiber (0.968 vs. 0.496 for type A and type B, respectively). CONCLUSIONS: The undulated-fiber type was found to have more uniform, consistent dialysate flow profiles. It is believed that this type of hemodialyzer will be found helpful for measurement and prescription of the delivered hemodialysis dose due to its better consistency.

Three-dimensional dialysate flow analysis in a hollow-fiber dialyzer by perfusion computed tomography.

Perfusion computed tomography (PCT) is a means to rapidly and easily evaluate cerebral perfusion in patients presenting with acute stroke symptoms, which provides insights into capillary-level hemodynamics. In this study, we used PCT to analyze the 3-dimensional dialysate flow in a low-flux hemodialyzer equipped with a standard fiber bundle. The dynamic CT studies were performed with 64-channel multi-detector row CT (MDCT) at a dialysate flow rate of 500 ml/min and a 1.0 ml/sec injection rate of contrast agent. Central volume principle was used to calculate hydrodynamic parameters by deconvolution of time-density curves (TDCs). Functional maps of dialysate flow (DF), dialysate volume (DV), and mean transit time (MTT) could quantitatively describe the dialysate flow maldistribution, variations in fiber packing, and perfusion pressure distribution in a hemodialyzer, respectively. PCT by means of analysis was able to overcome the limitations of conventional imaging techniques for analyzing dialysate flow distributions in hollow-fiber dialyzers. Not only local hydrodynamic phenomena at microscopic level but also macroscopic flow behavior of dialysate were visualized quantitatively. Therefore, we concluded that PCT is a quantitative analysis method to provide better insights into hydrodynamics of hollow-fiber dialyzers and is expected to contribute to optimization of artificial kidneys.

Polymeric nanofiber web-based artificial renal microfluidic chip.

In this paper, we present a new method for the creation of a smaller dialyzer and do so by incorporating polymeric nanofiber web, which is known to have good filtration efficiency for broad particle sizes, into a poly (dimethylsiloxane)-based microplatform. We have developed a process that makes possible the efficient production of polyethersulfone and polyurethane nanofiber web and that, itself, incorporates an electrospinning method. We have combined the nanofiber web with the PDMS-based microfluidic platform to create a chip-based portable hemodialysis system. With the dialyzing chip, we evaluated the filtration capability of molecules in broad ranges of sizes and compared the filtration capability of nanofiber membranes with that of PES and polyvinylidene fluoride porous membranes (sheet type): we discovered that the nanofiber membranes have better filtration performance than the other membranes. Blood cells were not mechanically affected during their filtration and their transportation through the chip. In conclusion, we have demonstrated the feasibility of chip-based hemodialysis, and we expect that our method suggested in this paper will be applied to the development of small light-weight dialyzers for the realization of portable hemodialysis systems.

A numerical study on the effect of side hole number and arrangement in venous cannulae.

Insertion of cannulae into vessels may apply non-physiological load and stress on blood cells, such that adenosine diphosphate may increase and result in hemolysis. Authors used the computational method to simulate the blood flow inside of the cannula. We limited the research to within the drainage cannulae. Nine different cannulae categorized by the number of side holes of 4, 12, and 20, and also categorized by the array type as staggered array, in-line array, and alternative in-line array were studied and compared to the cannulae with no side holes by using computational fluid dynamics. We evaluated the flow rate, the wall shear stress, and the shear rate, and compared them with one another to estimate the effect of the side holes. The flow rate is not proportional to the number of the side holes. However, larger number of side holes can reduce the mean shear rate.

Development of a new pulsatile extracorporeal life support device incorporating a dual pulsatile blood pump.

A new pulsatile extracorporeal life support device (ECLS) has been developed, designed to sustain pulsatile blood flow during emergency cardiopulmonary resuscitations and cardiopulmonary operations. This device features two identical pulsatile pumps that operate alternately and can therefore provide blood inflow in a more uniform manner than similar systems featuring a single-pump configuration. In order to confirm the presumed benefits of this newly-developed dual pulsatile pump configuration, we have conducted a series of in vitro experiments designed to compare the properties of the new system with a single pump system, specifically with regard to pump delivery rate and active filling efficiency. Our results reveal that the dual pump configuration can, indeed, deliver a higher flow than can the single-pump system, and exhibits an active filling efficiency superior to that of the single-pump configuration. We performed a series of animal experiments to measure the pulsatility of the dual-pump configuration in terms of equivalent energy pressure (EEP). In order to measure EEP, we measured femoral arterial pressure and pump outflow. The results of our animal experiments revealed that the newly-developed pulstile ECLS exhibits sufficient pulsatility in terms of the EEP considerations.

Design of a subcutaneous vascular access device using Ni-Ti SMA clamps for hemodialysis.

A subcutaneous vascular access device which utilizes an Ni-Ti shape memory alloy (Ni-Ti SMA) spring, has been developed as a new method for subcutaneous vascular access in the treatment of hemodialysis patients. Until now, the connection between the SVAD and needle cannot be externally monitored, and the clamp must be opened and closed with a percutaneous needle by a nephrologist. The SMA-SVAD accomplishes the opening and closing of its clamp using two Ni-Ti SMA springs, and a transcutaneous energy transmission system (TET) transmits energy to the Ni-Ti SMA springs without the need for percutaneous wires. Two SMA springs open and close the clamp of the SMA-SVAD, without affecting any of the other parts of the system. Wasted thermal energy is reduced to minimal values via electrical regional heating methods. The state of the SMA-SVAD can be monitored according to the amount of power consumed by the external energy transmitter. In in-vitro experiments, when the clamp was opened and the pressure difference in the hemodialysis machine was set to 50 mmHg, water flow through SMA-SVAD reached 500 ml/min. The maximal surface temperatures of the SVAD and catheter were successfully maintained at proper levels (approximately 38-39 degrees C), approximately 2-3 degrees higher than the temperature of the surrounding tissues. The time elapsed from the initiation of energy transmission until the opening of the SMA clamp was 5 seconds.

Wireless patient monitoring system for a moving-actuator type artificial heart.

In this study, we developed a wireless monitoring system for outpatients equipped with a moving-actuator type pulsatile bi-ventricular assist device, AnyHeart. The developed monitoring system consists of two parts; a Bluetooth-based short-distance self-monitoring system that can monitor and control the operating status of a VAD using a Bluetooth-embedded personal digital assistant or a personal computer within a distance of 10 meters, and a cellular network-based remote monitoring system that can continuously monitor and control the operating status of AnyHeart at any location. Results of in vitro experiments demonstrate the developed system's ability to monitor the operational status of an implanted AnyHeart.

Self-management protocol for a moving-actuator type artificial heart.

In this paper, we describe the development of a self-management protocol for a controller of a moving-actuator type artificial heart, AnyHeart. The developed protocol analyzes motor current signals and detects abnormal pumping statuses. If preset abnormal pumping statuses are detected by an implemented algorithm, a controller triggers an emergency management procedure and transmits an alarm message to predetermined medical and engineering staffs via a cellular phone network to notify them of an abnormal pumping status occurrence and its likely cause. Results of in vitro performance experiments showed that the developed protocol can detect simulated abnormalities in motor current, manage the operating status of the blood pump during an emergency, and transmit an alarm message as desired.

Development of counterpulsation algorithm for a moving-actuator type pulsatile LVAD.

A pulsatile left ventricular assist device (LVAD) was used to support the aortic blood pumping function of an injured left ventricle, and as a result helped its recovery. It is important to observe a left ventricle's pumping status and to adjust the operating status of a LVAD to reduce the left ventricle's pumping load and thus to enhance its recovery. To observe the left ventricle's pumping status, an electrocardiogram (ECG) signal is generally used because it is a result of the natural heart's blood pumping function. In this paper, we describe the development of an ECG based counterpulsation control algorithm that prevents simultaneous aortic blood co-pumping by a left ventricle and a moving-actuator type pulsatile LVAD and as a result, reduces the natural heart's pumping load. In addition, to verify the algorithm's applicability for LVAD control we designed three ECG based automatic pump control algorithms that use a developed counterpulsation control algorithm. These algorithms control the operating status of a LVAD automatically and, at the same time, maintain a counterpulsing status. The results of in vitro experiments show that the counterpulsing effect between a left ventricle and a LVAD was successfully produced and that the newly designed automatic pump control algorithms met their own control purposes with a counterpulsing effect.

Home care artificial heart monitoring system via internet.

The availability of a remote management system, which provides both physiological-related information about the patient and device-related information about the implanted device, would be helpful during in vivo experiments or clinical trials involving artificial heart implantation. In order to be able to monitor the course of the in vivo experiment continuously regardless of the patient's location, an internet-based remote monitoring system was developed, which can monitor physiological-related information such as pressure (AoP, LAP, RAP, PAP) and flow data, as well as device-related information such as current, direction and pump operating conditions. The home care artificial heart monitoring system which we developed consists of four main components, which are the transcutaneous information transmission system (TITS), local monitoring station (LMS), data server station (DSS), and client monitoring station (CMS). The device-related information and physiological-related information can be transmitted in real time from a patient in a remote non-clinical environment to the specialist situated in a clinic depending on the current capabilities and availability of the internet. The local monitoring station situated at the remote site is composed of a data acquisition and preprocessing unit connected to a computer via its RS-232 port, and which communicate using a Java-based client-server architecture. The remote monitoring system so developed was used during an in vivo experiment of the artificial heart implantation for 2 months and performed successfully according to design specifications.

Robust motor speed control under time varying loads in moving actuator type artificial heart (AnyHeart).

The Moving Actuator type artificial heart(AnyHeart) as well as many other artificial hearts uses a motor as its power source. For controllability of control parameters such as pump rate, pump output, blood pressure profile and flow form, the precise motor speed control is important. However, because the implantable device has limited carrying capacity of hardware components in size and number, applying diverse motor control methods are not possible. In addition, the existing PI (Proportional-Integral) motor controller does not show satisfactory performance. A new controller that is sufficiently robust for the changes of load and physical system parameters has been designed and tested. The robust speed controller is based on the sliding mode control method that is applicable to a system of which the ranges of uncertainty in physical parameters are known. In a mock circulation system test, the actual speed showed good tracking characteristics in respect to the reference speed. Fast follow-up characteristics were also observed under high afterload and speed conditions. The speed error, current and power consumption were reduced by about 40%. The proposed control technique overcomes the limitations of the PI controller, and makes important improvements in both performance and stability.

A preclinical cadaver fitting study of implantable biventricular assist device-- AnyHeart.

A multifunctional, Korean-made artificial heart (AnyHeart) was developed, and prior to its clinical application, a cadaver-fitting study was performed. The study proposed to determine the optimal cannulation approach, implantation technique and route of the cannula to minimize the organ compression of AnyHeart. The anatomical feasibility and a variety of surgical techniques were evaluated using ten preserved, human cadavers. Implanting AnyHeart with ease is possible using various approaches, including a median sternotomy, and a right or left lateral thoracotomy. The lateral thoracotomy approach is shown to be safe and reproducible, especially in patients who have already undergone an operation that used a median sternotomy. The results of this study will guide improvements in the designs of cannulae and AnyHeart for future clinical applications.

Recent progress of moving-actuator type mechanical circulatory support systems: AnyHeart and T-PLS.

The mechanical circulatory support system using moving-actuator mechanisms were developed by Seoul National University and Korea University. AnyHeart is a fully implanted pulsatile bi-ventricular assist device, and T-PLS is a pulsatile flow versatile extracorporeal life support system. Through lots of in-vitro and in-vivo experiments, the developed mechanical systems are faced to produce on commercial scale. This paper describes the recent progress of two mechanical circulatory support systems, AnyHeart and T-PLS.

Estimation of coupled assist flows in a moving-actuator bi-ventricular assist device using interventricular pressure.

An assist flow estimation scheme for a moving-actuator biventricular assist device (MA-BVAD) using interventricular pressure (IVP) has been developed. The scheme uses a waveform feature parameter of IVP, peak IVP time (PIT), for estimation of the filling volumes of both left and right blood sacs simultaneously. In a regression analysis on data from an in vivo test in an 85 Kg male calf for 20 days, the PIT was found to have high correlation with the blood sac filling volume (R=0.883: left filling volume, R=0.967: right filling volume). A conceptual equation hypothesizing this correlation between PIT and filling volume was established based on the observation and the unknown parameters were identified using least squares parameter optimization. The estimation equation identified proved highly accurate (R=0.916 for left flow, R=0.970 for right flow). The accuracy of the estimation scheme promises very good practical applicability.

AnyHeart: a single-piece heart-saving implantable artificial heart (BVAD)--monitoring and estimation.

AnyHeart is a single-piece, implantable biventricular assist device. This electromechanical BVAD has a moving-actuator mechanism. To monitor the status of AnyHeart from anywhere at any time, a portable personal digital assistant (PDA) monitor and web-based remote monitoring system were developed. The PDA local monitoring system has replaced bulky personal computer monitoring systems. The web-based remote monitoring system has several functions such as data collecting, storing, and posting through the internet. Basically, interventricular pressure (IVP) is a parameter indicating the filling level of the blood chambers of AnyHeart. The pump output can be estimated using IVP, which is acquired noninvasively from AnyHeart. With the proposed method, we can estimate the pump output with a small margin of error.

Applications of the pulsatile flow versatile ECLS: in vivo studies.

INTRODUCTION: T-PLS (Twin-Pulse Life Support) is the first commercial pulsatile ECLS (Extra Corporeal Life Support) device (1). The dual sac structure of T-PLS can effectively reduce high membrane oxygenator inlet pressure and hemolysis. To verify both the use of T-PLS for ECLS and the advantages of T-PLS, we tested various models. METHOD AND RESULTS: In the partial CPB (cardio pulmonary bypass) model (swine), T-PLS (N = 6), and Biopump (N = 2), a single pulsatile pump (N = 2), were compared. In the case of single pulsatile flow, during pump systole, pressure increased to 700 - 800 mmHg at the inlet port of the membrane oxygenator. fHb, a hemolysis measurement value, was about 80 mg/dL at 3 hours. On the contrary, because of T-PLS's dual sac system, the pressure of T-PLS had a maximum value of about 250 mmHg and fHb was similar to that of the commercial centrifugal pumps. In the total CPB model (bovine, N = 6), the heart was stopped via cardioplegia (Kcl). T-PLS flow was maintained at 3.0-4.5 L/min. T-PLS functioned like a natural heart, having a pulse pressure of 26-43 mmHg and a pulse rate of 40-60 bpm (beats per minute). In the emergency case model (canine, N = 6), T-PLS was started 10 minutes after cardiac arrest from electronic shock. In spite of cardiac arrest for a period of 40 minutes, the heart was recovered after defibrillation. In the ARDS (Acute Respiratory Distress Syndrome) model (canine, N = 6), minimal ventilator parameters were set: tidal volume 130 ml, respiration rate = bpm, FiO2 = 10%. Three hours after starting T-PLS, PO2 of the carotid artery blood (after 2 hours: 195 +/- 89.4; after 3 hours: 258 +/- 99.3 mmHg) was above half the value of the femoral artery but was within normal range. CONCLUSION: It is suggested that a portable pulsatile ECLS like T-PLS may be used as a CPB device and as an alternative CPR (cardiopulmonary resuscitation) device in the case of cardiac arrest. Due to the pulsatile flow, oxygenated blood is delivered to the patient without overloading the ARDS patients heart.

In vivo evaluation of lumbrokinase, a fibrinolytic enzyme extracted from Lumbricus rubellus, in a prosthetic vascular graft.

BACKGROUND: Lumbrokinase (LK) is a fibrinolytic enzyme purified from the earthworm Lumbricus rubellus. To investigate the fibrinolytic and antithrombotic effects of lumbrokinase, a series of animal experiments were performed. METHODS: The Dacron graft (3 mm in diameter, 3 cm in length) were treated with LK via two different methods, simple dipping and covalent bonding METHODS: Covalent bonding was performed by UV reaction to polyacrylic acid. The grafts were interposed into the inferior vena cava of the rabbits and harvested for 5 hours, 1, 2 and 4 weeks after the implantation. RESULTS: The LK non-treated graft (n=4) were totally occluded with thrombus 5 hours after the implantation. Both types of LK treated graft (n=8) were patent 1 week after the implantation. The grafts treated with the simple dipping method (n=4) were occluded with thrombus 2 weeks after the implantation. The grafts treated with covalent bonding (n=4) were patent 4 weeks after the implantation. Ultrastructural analysis of the luminal surface of the patent grafts by scanning electron microscopy revealed the thin plasma protein layer to be about 5 micro in thickness with platelet adhesions. CONCLUSIONS: Lumbrokinase has potential antithrombotic effects in a small diameter vascular prosthesis. The covalent bonding method proved to be more effective than the simple dipping method.

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.

Comparative analysis of texture characteristics of malignant and benign tumors in breast ultrasonograms.

We evaluated various texture features and region of interest (ROI) types of breast ultrasonograms in order to determine the best-performing combinations for differentiating between benign and malignant solid breast nodules. A total of 21 breast ultrasonograms (12 benign, nine malignant) containing solid breast nodules were evaluated. Eight ROI types were defined around the nodules. The texture feature of each ROI was measured and the ratios of texture features were calculated for each pair of ROIs. This procedure was repeated for five different feature types, thus yielding texture feature ratios for 140 different combinations of ROIs and texture features. We evaluated the performance of the texture feature ratio in differentiating between benign and malignant nodules using t test analysis. Evaluating the top ranked texture and ROI combinations, we found edge density and mutual information were the best two texture features, and that the ROI types of outside lesion and lesion margin had good performance.