Design And Study On A Novel Hollow-fiber Membrane Artificial Lung

Artificial lung, also called as oxygenator, which is to provide cardiopulmonary bypass during open-heart surgery, performs a function of exchanging O₂ and removing CO₂ from blood. It also serves as a bridge to lung transplant and a needed appliance for treatment patients with acute respiratory failure. Due to O₂ and CO₂ permeating through one-channel, the extracorporeal membrane oxygenators used in clinical and commercial application at present have still some disadvantages, such as lower gas exchange capability, more inadequate blood transport efficiency; shorter service time. In addition, membrane parts of oxygenators used in clinical application in China almost rely on importation. Therefore, the paper will design and study a novel two-channel hollow-fiber membrane oxygenator with different permeation channels for O₂ and CO₂.To improve permeability for O₂, biocompatibility and anticoagulation of hollow fibers coated liquid crystal/silicone rubber membrane, five kinds of olefine acid cholesteryl ester derivatives (such as acrylic acid cholesterol ester, vinylacetic acid cholesterol ester, pentenoic acid cholesterol ester, hexenoic acid cholesterol ester and 11-alkenoic acid cholesterol ester) were synthesized respectively by 2n acylation method and a super esterification method. Their chemical structures and liquid crystal behaviors were characterized by using FTIR, DSC and polarized microscopy with a hot stage. The research results showed that the super acylation catalyst method could improve obviously yield and purity, low toxicity and simplify operation process. Apart from crylic acid cholesterol ester, the other cholesterol esters showed cholesteryl liquid crystal behavior. Liquid crystal/silicone rubber crosslinked membranes were prepared firstly by using silicone rubber, silicone oil containing hydrogen and cholesterol ester liquid crystal as matrix materials. Some influential factors (such as difference pressure, testing temperature, substituent group, vulcanizing time, liquid crystal content, mechanics property) on permeability and permselectivity for the crosslinked membranes were studied. The results showed that the crosslinked membranes had better membrane-forming, permeability and permselectivity, especially better permeability for oxygen than normal modified silicon rubber membranes. For example, at pressure difference of 0.1 MPa and testing temperature of 40℃, the permeability coefficient and separation factor of the crosslinked membrane were up to 789 Barrer and 3.40, respectively. So, the crosslinked membrane can be used as coating membrane material of hollow fiber for membrane artificial lung.An ionomer membrane containing cobalt was prepared by sulfonated reaction, neutralization reaction and complex reaction. We discovered a peculiar behavior of gas permeation that CO₂ could permeate spontaneously through the membrane from the downstream side toward the upstream side of N₂ gas or air. The CO₂ reverse permeation behavior is a novel gas permeation behavior and has not been reported so far. The permeability and CO₂ reverse permeation behavior of the ionomer membrane were investigated. The results showed the ionomer membrane had better permeability for CO₂ and relatively poorer permeability for O₂. For example, at 25℃and the pressure difference of 0.1 MPa, the permeability coefficients for CO₂ and O₂ were 170 Barrer and 28 Barrer, respectively. Based on these properties, the ionomer membrane can be used as coating membrane material for a novel membrane artificial lung, which can exclude CO₂ from blood by a shell material.The biocompatibility of the crosslinked membrane and the ionomer membrane were studied by measurement of the haemolysis ratio, the dynamic blood clotting test and the platelet adhesion test. By contrast, the heparinized crosslinked membrane and ionomer membrane were prepared by an ionic linkage method. The results showed that these membranes exhibited better biocompatibility to satisfy the needs of membrane materials of membrane artificial lung.A self-assembled dip-coating technology using double-components was designed firstly to improve currently industrialized dip-coating technology using one-component for hollow fiber. The dip-coating conditions of the double-components technology were optimized: the concentration of liquid crystal/silicone rubber solution was 5.0%; the vulcanizing time was 10 minutes; curing temperature was under 60℃.According to the double-components dip-coating technology, the liquid crystal/silicone rubber crosslinked membranes with facilitated transportation for O₂ were coated on the surface of hollow fiber. And the ionomer membranes with better permeability for CO₂ and relatively poorer permeability for O₂ were coated on the wall of gradient ceramic. By using the gradient ceramic as an out-housing material and the hollow fiber membrane as a matrix material, a novel two-channel hollow-fiber membrane oxygenator with different permeation channels for O₂ and CO₂ was designed firstly. The membrane oxygenator has not been reported in the world. In contrast, a one-channel hollow-fiber membrane oxygenator with one permeation channel for O₂ and CO₂ was assembled. The properties of the one-channel membrane oxygenator in vitro were measured by using normal saline and deionized water as a substitute for blood. The results showed the one-channel membrane oxygenator had better oxygenation performance which was close to that of commercial membrane oxygenator in the world. For example, when the flow rate of normal saline was 450 ml/min, O₂ transfer rate and pressure drop were 48.3 ml/(min·m²) and 21.6 mmHg, respectively.By comparison of the one-channel membrane oxygenator, the two-channel hollow-fiber membrane oxygenator had higher O₂ transfer rate, lower pressure drop and longer service time. These suggested that the liquid crystal/silicone rubber crosslinked membrane and the ionomer membrane were benefit to improve oxygenation performance of membrane artificial lung. Therefore, it is speculated that the two-channel hollow-fiber membrane oxygenator will posses better research prospect and greater value in application.