Cylindrical Membrane Pores with Well-Defined Grafted Linear and Comblike Glycopolymer Layers for Lectin Binding

Glycopolymers with well-defined linear or comblike structure were grafted to poly(ethylene terephthalate) (PET) track-etched membrane surface by surface-initiated atom transfer radical polymerization (ATRP). Bromoalkyl initiator was directly immobilized onto PET membrane surface, and the ATRP of 2-lactobionamidoethyl methacrylate (LAMA) was then carried out to yield the grafted linear glycopolymer. Comblike poly(LAMA) was constructed on PET membrane by a two-step sequence. First, ATRP of 2-hydroxyethyl methacrylate (HEMA) was initiated from the PET surface, and alkyl bromide was then immobilized to poly(HEMA) chains The initiator-immobilized poly(HEMA) served as a surface tethered macroinitiator for the ATRP of poly(LAMA) and resulted in comblike polyLAMA branches. The ATRP conditions for both LAMA and HEMA were optimized, and the thus-established grafting was well controlled. The dry layer thickness (DLT) of grafted polymers was deduced from results of capillary flow porometer measurements. Effective hydrodynamic layer thickness was estimated from pure water permeability. Data revealed that the grafted linear poly(LAMA) and poly(HEMA) had relatively low chain density and exhibited a collapsed coil conformation in dry state. After grafting of poly(LAMA) chains to poly(HEMA) this collapse was significantly hindered by the steric influence of poly(LAMA) branches on the poly(HEMA) main chains, and more than 3 times increase in DLT could be observed. Nonspecific protein binding, studied with bovine serum albumin, was very low for membranes with grafted linear poly(LAMA) while no adsorbed protein could be detected for the comblike poly(LAMA) architecture. Both membranes were then used for binding of peanut agglutinin, a lectin specifically binding to galactose. Under conditions where protein could only diffuse into the membrane pores, comblike poly(LAMA) showed only slight enhancement of binding capacity in comparison with the linear poly(LAMA). However, with convective flow through the membranes, binding capacity of the comblike poly(LAMA) layer was significantly increased and a capacity up to 23.6 mg/cm(3) was achieved. Specific lectin binding with high capacities, corresponding to 3-dimensional protein stacking in the grafted layers, could be confirmed.