Modification Of Polyacrylonitrile-based Membranes With Phospholipid Moieties

Polyacrylonitrile-based homopolymer and copolymers, which possess excellent membrane forming property and high mechanical and chemical stability, have been successfully used as membrane materials in the fields of water treatment, pervaporation and dialysis. However, the relatively poor hydrophilicity and biocompatibility for this type of membrane limit its further applications in bioengineering and biomedicine. In this paper, to endow this conventional membrane with improved hydrophilicity and hemocompatibility, a series of protocols were established to introduce phospholipid moieties onto the polyacrylonitrile-based membrane surface. The surface layer formed by the phospholipid moieties on the membrane surface can create a biocompatible interface for the enzyme immobilization. It is expected that this interface can improve the activity and stability of the immobilized enzyme. The relative experiment and results are summarized as follow:2-Methacryloyloxy-ethyl phosphorylcholine (MPC) as functional agent was incorporated into PAN by water-phase precipitation copolymerization with (NH₄)₂S₂O₈-NaHSO₃ as initiator. Effects of monomer concentration, AN/HEMA ratio, initiator concentration, reaction temperature and reaction time were explored. FT-IR and H-NMR were used to characterize the poly(acrylonitrile-co-2-methacryloyloxyethyl phosphorylcholine) (PANCMPC). It was found that the optimal conditions for the copolymerization of AN and MPC in water were obtained as follows: (1) total monomer concentration, 30g/100mL water; (2) initiator/monomer ratio (oxidant/monomer in fact), 1/500; (3) reaction temperature, 60°C; and (4) reaction time, 3h. Under the optimal condition, the molecular weight of PANCMPC varies from 10×10⁴ to 30×10⁴, and MPC content in the PANCMPC can be controlled through changing the reaction condition. The properties of PANCMPC membrane were studied by breaking strength, water contact angle, protein adsorption, platelets and macrophage adhesion measurements. It was found that the mechanical property, hydrophilicity and biocompatibility of polyacrylonitrile-based membranes could be improved by copolymerization of AN with MPC.Acrylonitrile-based copolymers containing phospholipid moieties were synthesized by a two-step process, which includes the copolymerization of acrylonitrile and2-hydroxyethyl methacrylate (HEMA) conducted in water and the reaction of the resultant poly(acrylonitrile-co-2-hydroxyethyl methacrylate)s (PANCHEMA) with 2-chloro-2-oxo-l,3,2-dioxaphospholane (COP) followed by the ring-opening reaction of COP with trimethylamine. It was found that the mole fraction of phospholipid moieties in the copolymer could be increased by increasing the content of HEMA in copolymer during the copolymerization of acrylonitrile with HEMA. The water contact angle, the amount of BSA adsorption, the platelets and macrophage adhesion on the PLCANCP membranes surface were obviously lower than those on the PAN and PANCHEMA membrane surface, which indicated that both the hydrophilicity and biocompatibility of the acrylonitrile-based copolymer membranes could be improved efficiently by this process.Based on the study of phase separation behavior, PANCHEMA asymmetric membranes were fabricated by phase inversion method and a facile approach for the surface modification of PANCHEMA membrane by introducing phospholipid moieties was developed, which involved the reaction of the PANCHEMA membrane with COP followed by the ring-opening reaction of COP with trimethylamine. The content of the phospholipid moieties on the membrane surface, which can be mainly modulated by the content of reactive hydroxyl groups in PANCHEMA, has a great influence on the performances of the studied membranes. With the increase of the phospholipid moieties content at the modified membrane surface, the hydrophilicity and biocompatibility on the basis of water contact angle, BSA adsorption, platelets and macrophage adhesion can be improved significantly without affecting any bulk properties. Moreover, this method can affords the advantages of avoiding the troublesome purification process and keeping the phospholipid moieties on the film surface.PANCMPCs with excellent biocompatibility were electrospun into nanofibrous membranes with a mean diameter of 90 ran as the supports for enzyme immobilization. Lipase from Candida rugosa was immobilized on these nanofibrous membranes by adsorption. The properties of the immobilized enzyme on these PANCMPC nanofibrous membranes were assayed and compared with those of enzyme on the PAN nanofibrous and casting membranes, respectively. It was found that, the observed lipase loading on these nanofibours membranes was up to 22.0 mg/g, which was over 10 times of that on the casting membrane. The activity retention of immobilized lipaseincreases from 56.4% to 76.8% with increasing phospholipid content from 0 to 9.6mol% in the copolymer membranes. The Km values were decreased for the immobilized Upases, while the Vmax value of the immobilized lipase on the PANCMPC was obviously higher than that on the PAN membrane.