Graft And Modification Of Poly(methyl Methacrylate)magnetic Microspheres And The Protein Immobilization

Magnetic polymer microspheres due to magnetic response,small particle size,large specific surface,good dispersion and biological compatibility,etc.,thus showing great potential in medicine,biology,physics and other fields.In this paper,the preparation,grafting,modification and application of poly?methyl methacrylate??PMMA?magnetic microspheres were studied.The main contents of this paper are listed as below.Firstly,Fe₃O₄ magnetic nanoparticles with superparamagnetism were prepared by coprecipitation method.PMMA magnetic microspheres were prepared by polymerization of methylmethacrylate?MMA?and characterized by scanning electron microscopy,it was found these microspheres to have good dispersion and sphericity.Then,the microspheres were esterified under alkaline conditions and the carboxyl functionalized PMMA magnetic microspheres were successfully obtained.The carboxyl content of the microspheres was 1.01mmol/g by chemical titration.Secondly,the carboxyl groups on the surface of the microspheres were activated to form activated esters,and then?PEI 600,PEI 1800,PEI 70000?were grafted onto the surface of the microspheres as spacer arms to prepare three kinds of PEI grafted magnetic microspheres?PEI 600-PMMA,PEI 1800-PMMA,PEI 70000-PMMA?.After that,the Cibacron Blue F3GA?CB?molecule was modified onto the spacer arm chain of the microspheres to prepare three kinds of CB-functionalized PMMA magnetic microspheres?CB-PEI 600-PMMA,CB-PEI 1800-PMMA,CB-PEI 70000-PMMA?.The results showed that PEI and CB have been successfully modified onto the surface of magnetic microspheres by infrared scanner.In addition,PEI grafted magnetic microspheres contained a large amount of charge,and the amino contents of PEI 600-PMMA,PEI 1800-PMMA and PEI 70000-PMMA were 0.28,0.41,0.60 mmol/g microspheres,respectively.Thirdly,the protein adsorption capacity of PEI grafted magnetic microspheres and CB functionalized magnetic microspheres was investigated by using bovine serum albumin?BSA?as the model protein.The results showed that,the adsorption capacity of PEI grafted magnetic microspheres and CB functionalized magnetic microspheres was significantly higher than that of unmodified PMMA magnetic microspheres.The experiment was further studied the effect of the temperature,BSA initial concentration,pH value and ionic strength.The results showed that the maximum adsorption capacity of CB-PEI 70000-PMMA magnetic microspheres was103.6 mg/g at pH 4.7.In addition,the adsorption properties of BSA were evaluated by the thermodynamic adsorption.The results showed that at experimental temperature,standard enthalpy?H>0,standard entropy?S>0,standard Gibbs free energy?G<0,which indicated the adsorption of BSA by microspheres was a spontaneous and endothermic process.Fourthly,BSA was immobilized by cross-linking encapsulation method using PEI1800-PMMA and CB-PEI 1800-PMMA magnetic microspheres as carrier.In addition,the influencing factors of BSA immobilized by cross-linking encapsulation were also investigated.The results showed that,compared with the physical adsorption method,the immobilization of BSA by the cross-linked encapsulation method can significantly improve the binding force between the carrier and the BSA,and increase the stability of the BSA fixation.At 35°C,the concentration of glutaraldehyde 0.07%and crosslinking time 1 h,BSA loading on PEI1800-PMMA and CB-PEI 1800-PMMA microspheres respectively reached 61.4 mg/g and80.9 mg/g.