Study On Bionic Polymer Coating And CFD Simulation Of Membrane Oxygenator

The membrane oxy-enator is an essential medical device for cardiovascular surgery,lung transplantation waiting,and treatment of acute respiratory diseases.Due to the influence of the biocompatibility of hollow fiber membrane materials,the arrangement of tube bundles and the volume of the container,problems such as protein adsorption,platelet adhesion,and blood deposition occur during the use of a membrane oxy-enator.In addition,as the hollow fiber membrane of a membrane oxygenator is opaque,it is difficult to directly observe the blood perfusion kinetics through experiments.To improve the blood compatibility of the membrane oxygenator and quickly predict and optimize the performance of the oxygenator,this paper performed detailed research on the aspect of bionic polymer coating via computational fluid dynamics(CFD)simulations.Regarding the bionic polymer coating,a phosphorylcholine polymer coating with suitable anticoagulant blood ability and stability was developed to improve the blood compatibility of the membrane oxygenator.First,poly(MPC-co-LMA)(PML)was prepared by radical polymerization from 2-methyl-acryloxyethyl phosphocholine(MPC)and dodecyl methacrylate(LMA)as raw materials.The PML polymer coating is formed by coating the polymer solution on the surface of the polymethylpentene hollow fiber membrane(PMP-HFM).ATR-FTIR,XPS and SEM confirmed that the PML polymer was successfully coated onto the surface of PMP-HFM.A swelling degree study shows that the PML polymer film has good hydrophilic properties,and swelling kinetic analysis reveals that the PML polymer film exhibits excessive swelling during the swelling process.Platelet adhesion and whole-blood contact results indicate that the PML polymer coating on the surface of PMP-HFM can notably reduce platelet adhesion and thrombosis residue on the surface of the material.Solvent resistance test results show that the hydrophobic interaction between the PML coating and PMP-HFM is not sufficient to resist the dissolution of the ethanol or SDS solution,and the coating shedding phenomenon is observed.Second,poly(MPC-co-LMA-co-TSMA)(PMLT)coatings were prepared from MPC,LMA and TSMA.The cross-linking monomer TSMA was introduced to maintain the excellent blood compatibility of the phosphorylcholine polymer coating and to improve the adhesion between the coating and PMP-HFM substrate.The TSMA unit in the polymer forms a network structure through hydrolysis and cross-linking such that the PMLT coating is tightly wrapped across the substrate surface.The swelling degree study reveals that the PMLT polymer film also attains suitable hydrophilic properties.The cross-linked PMLT polymer coating exhibits an excellent solvent resistance and can resist the dissolution of the ethanol or SDS solution without the coating detaching.The PMLT polymer coating substantially reduces platelet adhesion on the surface of PMP-HFM and decreases the risk of blood clotting.Third,a poly(MPC-co-BMA-co-TSMA)(PMBT)coating was prepared from MPC,butyl methacrylate(BMA)and TSMA.The short-chain hydrophobic BMA unit was introduced to maintain the stability of the polymer coating and improve the hydrophilic compatibility of the phosphonylcholine polymer coating to blood.The swelling degree study indicated that at an MPC content lower than 45%,the EWC value of the PMBT polymer film was considerably higher than that of the PMLT polymer film,and the hydrophilicity of PMBT was higher than that of PMLT.After the PMBT coating was treated with an ethanol or SDS solution,the static contact angle of the surface almost remained unchanged,and the coating could be stably attached to the surface of PMP-HFM.Platelet adhesion and whole-blood contact test results showed that the PMBT polymer coating substantially improved the blood compatibility of the PMP-HFM surface.In terms of the CFD simulations,through the numerical simulation of the blood flow of the membrane oxygenator,internal flow field analysis of the oxygenator,blood damage analysis and biocompatibility research were conducted to provide theoretical guidance for the performance optimization of the oxygenator.First,with the separation membrane oxygenator for adults as the research object,the velocity distribution,pressure distribution and turbulence intensity distribution of the fluid in the oxygenator at different flow rates were studied.It was found that the isotropic porous medium model could accurately simulate the internal blood flow of the separated membrane oxygenator at a low flow rate(Q<3.00 L/min).The velocity vector diagram revealed that a large vortex occurred in the area of the outlet pipe of the oxygenator,which produced the phenomenon of blood recirculation and flow,and a high shear stress was observed,thus exacerbating the risk of red blood cell destruction,which is not conducive to the long-term use of separation membrane oxygenators.The pressure distribution cloud diagram showed that the pressure distribution inside the oxygenator was inclined and gradually reduced,and most of the pressure loss occurred in the hollow fiber membrane bundle,of which 53.3%was observed in the oxygenation chamber and 42.6%occurred in the variable greenhouse.The inlet and outlet positions of the membrane oxygenator are the hi-ghincidence areas of blood damage.The standard membrane hemolysis value(NIH)of the separation membrane oxygenator increased with increasing fluid flow,and the maximum was approximately 0.0835 g/100 L.Its biocompatibility satisfies the requirements of human use.Second,the flow inside the integrated membrane oxygenator for infants with a more complex fluid flow structure was numerically simulated.The results showed that at low flow(Q<2.00 L/min),the isotropic porous medium model could also accurately simulate the blood flow inside the integrated membrane oxygenator.In contrast to the separate membrane oxygenator,the internal fluid pressure of the integrated membrane oxygenator revealed a concentric and uniform downward trend.The pressure loss was mainly located in the oxy-enation chamber,and the the pressure loss in the oxygenation chamber was 5.53 times that in the variable greenhouse.At the same flow rate,the average residence time of red blood cells in the integrated membrane oxygenator was considerably shorter than that in the separated membrane oxygenator,and the risk of blood damage was lower.The NIH value of the integrated membrane oxygenator increased with the flow rate,but the maximum value was only 0.0032 g/100 L.