Development of an ultracompact integrated heart-lung assist device

Emergency Life Support System aiming preprimed oxygenator

Development have been achieved of a new blood pump for next generation Percutaneous Cardio-Pulmonary Support (PCPS) system and a novel surface coating method for silicone membrane hollow fiber by physical adsorption using a copolymer composed of a 2-Methacryloyloxyethyl phosphorylcholine (MPC) unit and a hydrophobic unit. The new blood pump, named the Troidal Convolution Pump (TCP), is based on the principle of a cascade pump and perfused 5 L/min and 350 mmHg at 2450 rpm. The novel copolymer composed of 30% MPC unit and 3-(methacryloyloxy) propyltris (trimethylsiloxy) silane (MPTSSi) unit (PMMSi30) was the most suitable molecular design on a silicone surface. The PMMSi30 coated surface adsorbed 7.2 % as much protein a non-coated surface adsorbed.

Thirty-day in-vivo performance of a wearable artificial pump-lung for ambulatory respiratory support

BACKGROUND

The purpose of this study was to evaluate the long-term in-vivo hemodynamics, gas transfer, and biocompatibility of an integrated artificial pump-lung (APL) developed for ambulatory respiratory support.

METHODS

The study was conducted in an ovine model by surgically placing the APL between the right atrium and pulmonary artery. Nine sheep were implanted. Heparin was infused as an anticoagulant. The device flow, gas transfer, and plasma free hemoglobin were measured daily. Hematologic data, platelet activation, and blood biochemistry were assessed twice a week. After 30 days, the sheep were euthanized for postmortem examination. The explanted devices were examined for gross thrombosis.

RESULTS

Five sheep survived for 29 to 31 days and were electively terminated. Four sheep died or were terminated early owing to mechanical failure of intravenous lines or device. The APL devices in the 5 long-term animals were capable of delivering an oxygen transfer rate of 148±18 mL/min at a flow rate of 2.99±0.46 L/min with blood oxygen saturation of 96.7%±1.3%. The device flow and oxygen transfer were stable over 30 days. The animals had normal end-organ functions except for surgery-related transient alteration in kidney function, liver function, and cell and tissue injury. There was no hemolysis. The device flow path and membrane surface were free of gross thrombus.

CONCLUSIONS

The APL exhibited the capability of providing respiratory support with excellent biocompatibility, long-term reliability, and the potential for bridging to lung transplant.

A novel wearable pump-lung device: in vitro and acute in vivo study

BACKGROUND

To provide long-term ambulatory cardiopulmonary and respiratory support for adult patients, a novel wearable artificial pump-lung device has been developed. The design features and in vitro and acute in vivo performance of this device are reported.

METHODS

This device features a uniquely designed hollow-fiber membrane bundle integrated with a magnetically levitated impeller that together form one ultracompact pump-lung device, which can be placed like current paracorporeal ventricular assist devices to allow ambulatory support. The device is 117 mm in length and 89 mm in diameter and has a priming volume of 115 ml. In vitro hydrodynamic, gas transfer and biocompatibility experiments were carried out in mock flow-loops using ovine blood. Acute in vivo characterization was conducted in an ovine model by surgically implanting the device between right atrium and pulmonary artery.

RESULTS

The in vitro results show that the device with a membrane surface area of 0.8 m(2) was capable of pumping blood from 1 to 4 liters/min against a wide range of pressures and transferring oxygen at a rate of up to 180 ml/min at a blood flow of 3.5 liters/min. Standard hemolysis tests demonstrated low hemolysis at the targeted operating condition. The acute in vivo results also confirmed that the device can provide sufficient oxygen transfer with excellent biocompatibility.

CONCLUSIONS

Based on in vitro and acute in vivo study findings, this highly integrated wearable pump-lung device can provide efficient respiratory support with good biocompatibility and it is ready for long-term evaluation.

Present status and future perspectives on the development of bioartificial kidneys for the treatment of acute and chronic renal failure patients

A bioartificial renal tubule device (BTD) consisting of a hollow-fiber module and human proximal tubular epithelial cells has been completed technically by Humes and colleagues and a few other groups. Humes and colleagues developed BTD, treated acute kidney injury patients with multiorgan failure by continuous hemofiltration (CHF) in conjunction with BTD, and reported a significantly higher survival rate than that by CHF with BTD without cells in the Food and Drug Administration phase IIa trial. However, BTD has never been approved by the US Government, as the CHF+BTD treatment did not show a significant difference from the control group in the phase IIb trial. Human proximal tubular epithelial cells were confirmed to be overgrown on artificial membrane, which resulted in the inhibition of active transports and the metabolism of essential substances. Function of the BTD could be maintained in a U0126-contained medium, even if the BTD had to have been waited by a new acute kidney injury patient for several weeks. For wearable kidneys, heparin-covalently bound membrane or methacryloyloxyethyl phosphorylcholine (MPC) polymer-coated membranes are candidates for antithrombogenic hemofilters, while endothelial progenitor cells from a cord blood, CD133(+) cells-attached hemofilter in which the permeability of the cells was enhanced by the enlarged diameter of fenestrae by treating with cytochalasin B are another candidate. The MPC blend membrane containing 1% of the MPC polymer in polysulfone was developed as a BTD module. MPC was 7 times larger at the sponge layer than at the skin layer of the membrane, resulting in hemocompatibility at the sponge layer and cytocompatibility at the skin layer.

Functional and biocompatibility performances of an integrated Maglev pump-oxygenator

To provide respiratory support for patients with lung failure, a novel compact integrated pump-oxygenator is being developed. The functional and biocompatibility performances of this device are presented. The pump-oxygenator is designed by combining a magnetically levitated pump/rotor with a uniquely configured hollow fiber membrane bundle to create an assembly free, ultracompact, all-in-one system. The hemodynamics, gas transfer and biocompatibility performances of this novel device were investigated both in vitro in a circulatory flow loop and in vivo in an ovine animal model. The in vitro results showed that the device was able to pump blood flow from 2 to 8 L/min against a wide range of pressures and to deliver an oxygen transfer rate more than 300 mL/min at a blood flow of 6 L/min. Blood damage tests demonstrated low hemolysis (normalized index of hemolysis [NIH] approximately 0.04) at a flow rate of 5 L/min against a 100-mm Hg afterload. The data from five animal experiments (4 h to 7 days) demonstrated that the device could bring the venous blood to near fully oxygen-saturated condition (98.6% +/- 1.3%). The highest oxygen transfer rate reached 386 mL/min. The gas transfer performance was stable over the study duration for three 7-day animals. There was no indication of blood damage. The plasma free hemoglobin and platelet count were within the normal ranges. No gross thrombus is found on the explanted pump components and fiber surfaces. Both in vitro and in vivo results demonstrated that the newly developed pump-oxygenator can achieve sufficient blood flow and oxygen transfer with excellent biocompatibility.

Development of a reflected optical fiber system for measuring oxygen saturation in an integrated artificial heart-lung system

The purpose of this study was to develop a blood oxygen saturation (OS) monitoring system for use with an integrated artificial heart-lung system (IAHLS). The OS monitoring system consists of two paired optical fiber probes (OFPs) and a measurement system. To investigate the effect of the OFP configuration and incident light wavelength on the relationship between OS and the reflectance ratio for wavelengths of 810 and 645 nm, we performed theoretical analyses of the relationship between OS and R810/R645 using a diffusion equation. The prototype OFP located on the blood outlet port of our IAHLS housing was evaluated using an in vitro test. An OS range of 65-100% was adjusted to supply oxygen and nitrogen gas to the IAHLS. The blood flow rate was maintained at 3 L/min by the rotational speed of an impeller in the IAHLS. The OS-corrected blood from the IAHLS was measured using a commercial gas analyzer. The correlation coefficients (r(2)) between the theoretical ratio of R810/R645 and OS, and between measured OS and the reflectance ratio of R810/R645 were 0.97 and 0.78, respectively. In conclusion, we confirmed that the development of this oximetry system is applicable for IAHLS.

Present status and perspective of the development of a bioartificial kidney for chronic renal failure patients

A bioartificial tubule device was applied for the treatment of 10 acute renal failure and multiple organ failure patients by Humes et al. A bioartificial kidney for chronic renal failure patients, however, has never been applied. In order to develop a bioartificial kidney for preventing and treating long-term complications of maintenance dialysis patients, we have to overcome difficulties such as antithrombogenic issue of hemofilters and development of long functioning tubule devices in the context of economical and easy treatment. Continuous hemofilters should modify with an antithrombogenic material on the inner surfaces of membranes to get more hemocompatible characteristics. We are developing an antithrombogenic continuous hemofilter coating with methacryloyloxyethyl phosphorylcholine polymer which will mimic phospholipid layers of human cell membrane on the inner surface of a hemofilter. The transportability of H2O, Na+, and glucose of bioartificial tubule devices using polysulfone hollow fiber modules and porcine proximal tubular epithelial cells LLC-PK1 were evaluated using two kinds of circuits of different medium inside and outside of the cell-attached hollow fiber membrane. Transport of H2O, Na+, and glucose were significantly increased when 2.5 g/dL of albumin was added, and plateaued on the eight day and then decreased thereafter until the 13th day. Transfection of a specific gene into human tubular epithelial cells might be required to keep contact inhibition in order to maintain a confluent monolayer for longer duration.

Development of an implantable oxygenator with cross-flow pump

Thrombogenicity, a problem with long-term artificial lungs, is caused by blood-biomaterial interactions and is made worse by nonuniform flow, which also causes decreased gas exchange. To overcome these obstacles, we changed the inlet and added a uniform flow pump to our previous oxygenator design. Conventional membrane oxygenators have a (1/2)-inch port for the inlet of blood. These port structures make it difficult for the blood to flow uniformly in the oxygenator. In addition, the complex blood flow patterns that occur in the oxygenator, including turbulence and stagnation, lead to thrombogenicity. A cross-flow pump (CFP) can result in uniform blood flow to the inlet side of an oxygenator. In this study, we evaluated the usefulness of an integrated oxygenator with a fiber bundle porosity of 0.6 and a membrane surface area of 1.3 m2. The inlet part of the oxygenator is improved and better fits the outlet of the CFP. Each of the three models of the improved oxygenator has a different inlet taper angle. The computational fluid dynamics analysis showed that, compared with the original design, uniform flow of the integrated oxygenator improved by 88.8% at the hollow fiber membrane. With the integrated oxygenator, O2 transfer increased by an average of 20.8%, and CO2 transfer increased by an average of 35.5%. The results of our experiments suggest that the CFP, which produces a wide, uniform flow to the oxygenator, is effective in attaining high gas exchange performance.

Research into the development of a wearable bioartificial kidney with a continuous hemofilter and a bioartificial tubule device using tubular epithelial cells

Current hemodialysis treatment is insufficient because of intermittent treatment and loss of tubular function. In order to overcome the loss of tubular function, a bioartificial kidney has been developed consisting of continuous hemofiltration (CHF) with 10 L/day of filtrate and a bioartificial tubule device using proximal tubular epithelial cells and hollow fiber membranes. Ten L/day of CHF enabled plasma levels of urea, creatinine, uric acid and, beta2-microglobulin in eight renal failure patients to be maintained at remarkably low levels. The concept was tested with 6 L (4 mL/min) of 10 L/day (7 mL/min) filtrate regenerated by a bioartificial tubule device and 4 L/day (3 mL/min) replaced by food and drinks. Lewis lung cancer-porcine kidney 1 (LLC-PK1) cells with a cell density of 107 cells/mL were seeded inside polysulfone hollow fiber modules four times at 1 h intervals while rotating the module 90 degrees each time, and were cultured for 48 h to form confluent monolayers. The leak rates of urea and creatinine across LLC-PK1 cell-attached polysulfone membrane modules (membrane areas: 56 cm2 and 4000 cm2) were investigated. Via conversion from 56 m2 to 1 m2 hollow fiber modules with LLC-PK1 cells for 24 h, the transport rates of H2O, glucose and Na+ were, respectively, 40, 65 and 35% of the target transported amounts from 6 L/day of filtrate. The rates are expected to approach 100% when 4-5 g/dL of albumin is added to the basal portion of the medium since the results were obtained without the addition of albumin for colloidal osmotic pressure.

Development of bioartificial kidneys

Bioartificial kidneys, which consist of continuous haemofiltration and bioartificial tubules using tubular epithelial cells, have been studied since 1987. The bioartificial tubules consist of hollow fibre modules and tubular epithelial cells grown on the hollow fibre membranes after coating with extracellular matrices. The kinds of tubular epithelial cells, extracellular matrices and artificial membranes therefore have been investigated and then the most appropriate cell and materials have been selected on the basis of the development of bioartificial kidneys. Successful seeding to form confluent monolayers on the surfaces of hollow fibers is not easy, but this method has already been established. Renal assist devices using human renal proximal tubular epithelial cells have been used in the treatment of acute renal failure patients with endotoxemia by Humes et al., and successful treatment of acute renal failure patients with these devices was reported in 2001 and 2002, in which the improved mortality rate of those patients was shown. A bioartificial kidney, in which cDNA of multidrug resistance protein-1 was transfected into tubular epithelial cells that were then grown on the outer surfaces of hollow fibers, was used in the experimental treatment of digoxin-intoxicated dogs. Rapidly reduced digoxin levels were noted in the plasma of the dogs after treatment. Bioartificial kidneys, however, have never been used in the long-term treatment of a maintenance dialysis patient, although patients need those kidneys. In order to establish long-term treatment with a bioartificial kidney, each haemofilter has to function for more than one week without systemic anticoagulation and a bioartificial tubule must function for 3-4 weeks.

Design Progress of the Ultracompact Integrated Heart Lung Assist Device-Part 1: Effect of Vaned Diffusers on Gas-Transfer Performances

The integrated heart lung assist device (IHLAD) has been developed to overcome the problems of currently available extracorporeal membrane oxygenation devices. The integrated structure of a centrifugal blood pump and cylindrical bundle of polyolefin hollow-fibers has allowed a remarkably compact size for the device. This study deals with the design change of the IHLAD that added to the vaned diffuser between the impeller of the centrifugal pump and the hollow-fiber bundle with a view to enhancing the gas-transfer performance. Ex vivo gas-transfer performance tests were carried out, as well as hydrodynamic characteristics and hemolysis test using fresh goat blood. The oxygen transfer rate was generally improved, and the carbon dioxide removal rate was slightly improved. Intolerable amount of hemolysis (index of hemolysis= 0.177) was caused by the IHLAD, which must be resolved by improving the design in the future.

Design Progress of the Ultracompact Integrated Heart Lung Assist Device-Part 2: Optimization of the Diffuser Vane Profile

The configuration of the vaned diffuser of the integrated heart lung assist device (IHLAD) has been revised to reduce mechanical blood trauma caused by the device. The flow visualization study of the flow near the diffuser vanes revealed the existence of a rotating stall which deteriorates the hydrodynamic performance of the device and augments the chance for blood cells to pass through the regions with intense shearing forces. Design changes of the diffuser included decrease in vane number from 7 to 5 and decrease in passage width from 3 mm to 2 mm. This design change was effective to suppress initiation of a rotating stall. Improvement of hydrodynamic performance and antihemolytic properties was confirmed with the newly designed configuration based on the flow visualization study.

Results of an artificial-lung survey to lung transplant program directors

BACKGROUND

Lung transplantation is the only treatment for patients with end-stage lung disease. However, the scarcity of donor organs illustrates the need for alternatives. Recent success in the use of ventricular assistance has stimulated research in technology designed as a bridge to lung transplantation. Some laboratories have demonstrated significant advances in the development of artificial lungs, and clinical applications are on the horizon. In preparation, we sought to gather information from the lung transplant community regarding issues related to testing and potential trials of artificial lungs.

METHODS

We constructed a survey and distributed it to lung transplant program directors recognized by the United Network for Organ Sharing. Topics included required animal studies, preferred designs, logistics of clinical trials, and patient diagnoses most appropriate for such a trial.

RESULTS

The 31 programs responding to the survey performed 72% of all lung transplants in the United States in 1999. Ninety-seven percent supported a Phase I trial using an artificial lung as a bridge to lung transplantation. Additionally, 58% specifically supported a trial in which organ allocation would be prioritized to enrolled patients. Idiopathic pulmonary fibrosis was the diagnosis thought most appropriate for inclusion in initial clinical trials.

CONCLUSIONS

Widespread support exists for the development and use of an artificial lung as a bridge to lung transplantation. Information from transplant centers regarding device design and application can influence laboratories developing artificial lungs, and such communication will be essential as this technology progresses from the bench-top to the bedside.