Research On Preparation And Application Of Functional PVDF Membranes For Adsorption

Poly(vinylidene fluoride) membranes have been developed for a variety of fields, such as chemical and environmental engineering, food, medicine and biochemistry, due to their thermostability, chemical resistance and good mechanical property. Compared with the other materials, PVDF has the further advantage of being capable for use in protein blotting because of its high protein-binding capacity and biocompatibility. It is considered to be a very promising biomaterial in the field of biomedical analysis.In this study, functional PVDF membranes for adsorption were prepared by vapor induced phase separation and immersion precipitation. The effects of various membrane formation parameters on their morphologies and property were investigated. Then, the applications were expanded after surface modified of these membranes. The adsorption dynamics simulation of Bovine Serum Albumin (BSA) onα-type andβ-type PVDF crystal surface were further studied.Mainly research of the thesis is focuses on the following aspects.(1) Preparation of symmetric network PVDF membranes for protein adsorption via vapor induced phase separationPVDF membranes for protein adsorption were prepared by vapor induced phase separation from PVDF/N,N-dimethyl acetamide (DMAC)/ water system. The effects of evaporation atmosphere, temperature and humidity during the preparation of the membranes on their morphologies were investigated by SEM. With low temperature and high humidity, polymer crystallization mechanism dominated the membrane formation process, and the casting solution formed membranes with symmetric morphologies in the vapor phase containing 0.79% DMAC. The effect of additives on the membrane structure and performance was also investigated. The results of adsorption experiment showed that the binding capacity of Bovine Serum Albumin (BSA) increased with the appearance of circular network morphology and the decrease of mean pore size of the membrane. With the addition of LiCl to the casting solution, the obtained membrane can adsorb BSA up to 160μg/cm2.(2) Preparation of symmetric network PVDF membranes for protein adsorption via immersion precipitationSymmetric network PVDF membranes without dense skin layer were prepared by immersion precipitation in a water/TEP/PVDF system to improve protein adsorption. In order to investigate the effects of different membrane morphologies and PVDF crystal types on protein-binding capacity, different dope, baths and preparation condition were used to modify the membrane structure and performance. By comparing the effect of TEP content in the bath on membrane morphology, it was found that the TEP in the bath hindered the phase-separation kinetics. As a result, the casting dope slowly entered the phase-separation boundaries, leading to the so-called delayed-type demixing. The porosity of PVDF membranes increased along with the increase of TEP content in the bath. For a slow crystallization process(higher TEP bath content and lower temperature of bath), crystallization was expected to take place at a lower rate such that PVDF chains had enough time to arrange themselves intoβ-type. Theβ-type PVDF crystal was polar because of it all-trans arrangement. It tended to adsorb BSA through hydrogen bonding or electrostatic force between the weak-negative F and the weak-positive H atoms. And the protein remained bound with more points of attachment. Thus, the interaction of electrostatic force between a-type and BSA is smaller than that withβ-type. M34 improved the adsorption of protein up to 194μg/cm2.(3) The application of functional adsorption PVDF membranesPVDF merbranes prepared in this work were used for Western-blot, Colloidal gold enhanced immunochromatography assay and Dot-blot. It was found that the asymmetric PVDF membrane can not be used in Western-blot due to its asymmetric structure with a skin layer and weak protein binding capacity. Proteins on the sodium dodecyl sulfate polyacrylamide gel electrophoresis gels were successfully electro-blotted onto M34. Compared with commercial PVDF membranes, it was feasible for the PVDF membranes M34 prepared in this work be used for Western-blot; Hydrophilic surface modification of membrane M34 was performed by 1%STP treatment. Then used in colloidal gold enhanced immunochromatography assay, which had a good chromatographic property (T line< 50s, C line< 200s) and strong color development(T line:G6-G9, C line:G7-G9); The PVDF/NC blend membrane M90 was successfully used in Dot-blotting as the solid membrane. The brown dot can be seen on the membrane when the positive sample was used. Compared with commercial NC membranes, the effect of color development was stronger.(4) PVDF-Ser affinity membraneWe firstly used L-serine (Ser) as ligands separately, PVDF hollow-fiber membrane as the bare membrane,1,6-hexanediamine as the spacer arm to make new types of affinity membrane for endotoxin removal from human plasma. For human plasma sample, the clearance efficiency of lab-made PVDF-Ser affinity membrane module could reach 48.3% at lml/min velocity. The endotoxin adsorption capability was 0.027EU/cm2 with little effect on other biochemical indicators, the loss of total protein (including the various types of enzyme) was 14.9% and the recovery rate of albumin is 92.4%; Then, amplified lab-made PVDF-Ser affinity membrane modules were used in animal experiments. The results showed that PVDF-Ser affinity membrane has good blood compatibility and the amplified module could effectively remove endotoxin from domestic pig, it could reduce concentrations of tumor necrosis factor(TNF-a) and interleukin(IL-6), thereby the inflammatory reaction was inhabited.(5) The adsorption dynamics simulation of BSA onα-type andβ-type PVDF crystal surfaceThe adsorption dynamics of BSA on a-type andβ-type PVDF crystal surface were studied in detail. It was showed that electrostatic and VDW interaction between β-type PVDF crystal and BSA was 200KJ/mol stronger than a-type PVDF crystal. There are four types of residues (ASP 85, SER 465, GLU 490, TYR 492) which participated in the adsorption of BSA onto theβ-type PVDF crystal, but they were not participated onto the a-type. The combine of more residues participated in adsorption and larger interaction energy betweenβ-type PVDF crystal and BSA made the protein binding capacity ofβ-type PVDF crystal was larger than a-type.