| Poly(4-methyl-1-pentene)(PMP)has significant gas permeation properties because of its ultrahigh free volume polymer chain,thus it is widely applied in oxygen enrichment.Moreover,PMP shows outstanding mechanical and chemical resistance advantages over most polyolefins,wihich makes it promising in membrane oxygenator application.Diversified PMP microporous membrane fabrication methods have been developed,among which thermally induced phase separation(TIPS)method enjoys better operation flexibility,lower defect ratio,stronger mechanical strength,higher porosity,and more controllable pore size than conventional melt extrusion-dry stretch method.However,there are few reports about the fabrication of PMP hollow fiber membranes(HFMs)via TIPS,except for several in patent literatures.Therefore,this study attempted to investigate the fabrication technique of PMP HFMs via TIPS,and explore the surface modification method to improve the hemocompatibility of PMP HFMs.The structure-function relationship about the PMP microporous HFMs fabrication process optimization and the HFMs gas permeation rate was systematic evaluated via theoretical analysis,computational simulation and experimental verification.Moreover,PMP HFM surface modification was designed in two ways:surface plasma-induced chemical grafting including heparin and MPC,and surface physical roughing including superhydrophobic iPP coating and surface CF4 plasma etching.The surface modification methods was assessed based on the criterion in biomedical membrane oxygenator.Hemocompatibility experiment and in vitro oxygenation experiment was applied.Hopefully,an effective PMP HFM fabrication technique and surface hemocompatibility modification method could be raised in potential membrane oxygenator application.1.Optimization of PMP HFM fabrication technique via TIPS methodIn this section,the influence of some crucial parameters including diluent,PMP concentration,and so on in PMP HFM fabrication,was thoroughly discussed.Three potential diluent was explored from Hansen solubility parameter database,including dioctyl phthalate(DOP),dibutyl phthalate(DBP),and diphenyl ether(DPE).Thermal dynamic mechanism during TIPS process was established by PMP-diluent interaction prediction according to the Hansen solubility,and PMP-diluent phase diagram summary from experimental PMP-diluent thermal analysis.The fabrication technique optimization was based on two criteria:PMP HFM should guarantee enough gas permeation rate compared with commercial PMP oxygenator membranes and PMP HFM spinnability in laboratory should be stable.The results showed that single diluent like DOP,binary diluent selection like DOP and DBP showed good potential in PMP HFM fabrication with high gas permeation and effective open porosity.Based on the optimized diluent selection,when PMP concentration was 30 to 35%,the PMP HFM had potential application in oxygenator membranes.2.Dissipative particle dynamics study of PMP-diluent TIPS processIn the section,dissipative particle dynamics simulation was performed to construct the mesophase membrane morphologies of PMP during TIPS.The effects of some crucial parameters including diluent,PMP concentration,and PMP molecular weight were compared.The PMP morphologies and their diffusivities relationship were established from mesoscale molecular dynamics calculation.The results showed that better interconnectivity was produced when good diluent was selected.PMP concentration lead to different solidification morphologies,among which low PMP presented spherical scattered structure and high PMP concentration lead to worse pore interconnectivity.Lower PMP molecular weight helped to form porous structure with good interconnectivity,indicating small diffusion resistance.Compared with the structural and gas permeation results from experimental measurement,it was proved that DPD strategy in this investigation was an effective path for PMP HFMs fabrication optimization and gas permeation performance prediction of PMP HFMs.3.Surface hemocompatibility modification of PMP HFMsIn the section,low temperature plasma technique and surface coating were applied for PMP surface modification.Four kinds of hemocompatibility modification methods were designed,including plasma-induced surface monosort hydroxyl group modification,heparin grafting,phosphorylcholine MPC grafting,and surface superhydrophobic layer construction.Based on the fact that oxygen plasma surface treatment could introduce complicated functional group onto the surface,we designed NaBH4 reduction method to transfer them to monosort hydroxyl group.The plasma-induced modification,NaBH4 reduction method,heparin grafting,and phosphorylcholine MPC grafting,were characterized by ATR-FTIR,XPS.Surface superhydrophobic layer construction modification process was observed by SEM.The results showed that the surface chemical modification were successful,and superhydrophobic layer construction via both iPP coating and CF4 plasma etching was successful.4.Investigation of the application of modified PMP HFMs in membrane oxygenatorIn the section,the potential application of modified PMP HFMs in membrane oxygenator was investigated in two aspects:surface hemocompatibility to ensure excellent anticoagulation properties and in vitro oxygenation ability to characterize enough gas exchange in clinical oxygenation application.Surface hemocompatibility evaluation was applied in protein adsorption,platelet adhension,and coagulation time measurement.In vitro oxygenation ability was mainly compared by gas exchange rate during oxygenation and the plasma leakage time tests.The results showed that all modified PMP HFMs had excellent surface hemocompatibility,presented by low protein adsorption and platelet adhesion.Coagulation time results showed that heparin and MPC grafting had the best anticoagulating potential.In vitro gas exchange rate showed that hydrophilic modification and superhydrophobic iPP coating lead to decreased gas exchange rate and CF4 etching promoted gas exchange. |
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