| The protein binding capacity of traditional ion-exchange beads cannot meet the requirement for the purification of recombinant proteins compared with rapidly growth in the production.One of the keys to promote protein binding capacity of ion-exchange beads is to improve adsorption capacity.Based on above ideas,we fabricated a novel polymer-grafted ion-exchange bead via surface-initiated atom transfer radical polymerization(SI-ATRP)by grafting the monomer,methacryloxyethyltrimethyl ammonium chloride(DMC),to the poly(glycidyl methacrylate)(pGMA)matrix.The physicochemical properties and protein adsorption performance of the ion-exchange beads were investigated systematically.Firstly,polymer-grafted ion-exchange beads with different BIBB and DMC amount were synthesized,and the properties of the ion-exchange beads were systematically characterized.The results showed that the grafting of DMC significantly increased ionic capacity of ion-exchange beads and the size of the beads.The polymer layer would shrink in the dry condition,leading the size of the beads far less than their size in aqueous solution.The ionic capacity and the water content of the polymer-grafted ion-exchange beads not only were much higher than the non-grafted ion-exchange pGMA-NH2 but also increased with the added monomer amount.In this paper,the protein adsorption behavior on the polymer-grafted ion-exchange beads was investigated and the effects of chain density and length of the charged polymer as well as the salt concentration on the protein adsorption were systematically analyzed.The results showed that the adsorption capacity for γ-globulin on the polymer-grafted ion-exchange beads firstly increased with an increase of the polymer density and reached to a maximal value and then decreased with a further increase of the chain density due to the competition between the increases of protein adsorption sites and the steric exclusion effect.The maximal adsorption capacity for γ-globulin was obtained to be 808 mg/g wet beads,which is eight times higher than that of non-grafted pGMA-NH2 beads.The polymer-grafted ion-exchange beads exhibited higher salt sensitivity than non-grafted ion-exchange beads did.The adsorption capacity of polymer-grafted ion-exchange beads sharply reduced with a slight increase of the salt concentration.Finally,the preliminary study of the uptake kinetics for γ-globulin on the polymer-grafted ion-exchange beads showed that γ-globulin achieved rapidly adsorption equilibriums only within 10 min.However,the value of De/D0 fitted by the effective pore diffusion model is 0.24,much lower than the values in dextran-and PEI-grafted ion-exchange beads,demonstrated that the effective pore diffusion model was not proper to describe the kinetics of protein adsorption on polymer-grafted ion-exchange beads.The novel polymer-grafted ion-exchange beads prepared by SI-ATRP in this work possessed high adsorption capacity and rapid kinetics feature,and will be expected to the top of the listing for novel chromatographic materials in the purification of proteins. |
