Surface Glycosylation Of Polypropylene Microporous Membrane

Carbohydrates are ubiquitous in living entities and play a major role in many biological processes, such as blood coagulation, immune response, fertilization, cell growth, embryogenesis and cellular signal transfer, which are essential for the survival of living entities. Carbohydrates have been found on the surface of nearly every cell in the form of polysaccharides, glycoproteins, glycolipids or/and other glycoconjugates. The carbohydrates on the external cell membrane, known as the glycocalyx, play essential roles in many biological functions which can be classified into two opposite aspects. The one is contributing to steric repulsion that prevents undesirable non-specific adhesion of other proteins and cells. The other is serving as sites for the docking of other cells, biomolecules and pathogens in a more or less specific recognition process. In this thesis, a series of protocols were established to achieve glycosylated polypropylene microporous membrane (PPMM) surface for the mimic of glycocalyx layer on cell membrane. The glycosylated layer on the polypropylene membrane surface was expected to mimic both the anti-nonspecific adsorption and specific recognition properties of the glycocalyx on the cell surface.Two glycomonomers, 2-gluconamidoethyl methacrylate (GAMA) and α-allyl glucoside (AG), bearing linear and cyclic glucose residues respectively were synthesized. Glycosylation of the PPMM surface was carried out by the UV-induced graft polymerizations of these two glycomonomers. The graft polymerization processes could be controlled by monomer concentration, UV-irradiation time and photoinitiator concentration. Grafting density (GD) increased with the monomer concentration, however, the increase slowed down in high concentration cases. UV-irradiation time affected GD obviously at forepart until 25 min after which the GD showed no more increase. GD increased with photoinitiator concentration first and declined at higher concentration cases. Chemical and morphological changes of the membrane surface were confirmed by attenuated total reflectance Fouriertransform infrared spectroscopy (FT-IR/ATR) and X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Water contact angle on the glycosylated PPMM surface decreased with the increase of GD, which indicated an enhanced hydrophilicity for the modified membrane. The surface tethered glycopolymer with linear saccharide residues was more effective in the enhancement of hydrophilicity than the cyclic one.Two novel approaches for the surface glycosylation of PPMM were developed including UV-induced graft polymerizations of functional monomers and subsequent immobilization of saccharide residues by the reactions between amino groups and sugar lactones. 2-Aminoethyl methacrylate hydrochloride (AEMA) was grafted to the PPMM surface and the amino group was reacted with D-gluconolactone. Acrylamide (AAm) was also used as functional monomer and grafted to the PPMM surface. The amide groups were then transferred to amino groups by Hofmann rearrangement reaction. The resulted primary amine groups reacted with D-gluconolactone for the immobilization of saccharide residues. The AAm showed much higher GD and sugar immobilization amount than those of AEMA. The amino group reaction ratio was maintained around 80% with the increase of PAEMA GD. However, in the AAm cases, the amino group reaction ratio decreased significantly with PAAm GD. Chemical and morphological changes of the membrane surface before and after each step were confirmed by FT-IR/ATR, XPS and scanning electron microscopy (SEM). The surface wettability was investigated by time-dependent water contact angle measurement.Surface-initiated atom transfer radical polymerization (ATRP) was employed to achieve controlled glycosylation of PPMM. Comb-like and linear glycopolymers of GAMA were tethered to the PPMM surface by different initiator structures. For the construction of comb-like glycopolymer tethered PPMM, 2-hydroxylmethyl methacrylate was first grafted to the PPMM surface by UV-induced graft polymerization. Reaction between hydroxyl groups and 2-bromopropionyl bromide gave the immobilization of ATRP initiator. Surface initiated ATRP of GAMA was thencarried out. For the generation of linear glycopolymer by ATRP, the PPMM surface was brominated by UV irradiation in bromine solution. The bromine bonded to the PPMM surface was then serves as initiator for the surface initiated ATRP of GAMA. Adding water to the solvent system increased the polymerization rate significantly and, however, suffered the loss of controllability. CuBr₂ served as an effective deactivator with which the polymerization process could be well controlled. The chemical and morphological changes of the modified membrane surfaces were characterized by FT-IR/ATR, XPS and atomic force microscopy(AFM).The anti-nonspecific adsorption properties of PGAMA glycosylated PPMM were evaluated by static bovine serum albumin (BSA) adsorption, dynamic permeation fluxes of pure water and BSA solution and static platelet adhesion. Adsorbed BSA and platelet decreased and, on the contrary, BSA flux increased remarkably with the increase of the GAMA GD. All these results gave evidences that glycosylation with GAMA evidently improve the anti-nonspecific adsorption properties of the PPMM surface. Surface tethered glycopolymer with comb-like chain structure showed much better anti-nonspecific adsorption property than that of the linear one. On the other hand, the specific recognition properties of PAG glycosylated PPMM were estimated by Concanavalin A (Con A) recognition. The AG glycosylated PPMM surface showed significant glycoside cluster effect to Con A, a glucose specific lectin, but none binding activity to peanut agglutinin (PNA), a galactose specific lectin. The recognition between the glycosylated membrane surface and Con A could be inhibited by glucose and mannose which are two saccharides specificly binding to Con A. On the other hand, galactose showed no inhibition effect to the recognition which indicated the specificity of the interaction between the glycosylated membrane surface and Con A.