Electrical properties of glucose-sensitive hydrogels: swelling and conductivity relationships

A Review of the Mechanism, Properties, and Applications of Hydrogels Prepared by Enzymatic Cross-linking

Hydrogels, as biological materials, are widely used in food, tissue engineering, and biomedical applications. Nevertheless, many issues remain in the preparation of hydrogels by physical and chemical methods, such as low bioaffinity, weak mechanical properties, and unstable structures, which also limit their applications in other fields. However, the enzymatic cross-linking method has the advantages of high catalytic efficiency, mild reaction conditions, and the presence of nontoxic substances. In this review, we evaluated the chemical, physical, and biological methods of preparing hydrogels and introduced three common cross-linking enzymes and their principles for preparing hydrogels. This review introduced the applications and properties of hydrogels prepared by the enzymatic method and also provided some suggestions regarding the current situation and future development of hydrogels prepared by enzymatic cross-linking.

Covalent Immobilization of Glucose Oxidase onto New Modified Acrylonitrile Copolymer/Silica Gel Hybrid Supports

New polymer/silica gel hybrid supports were prepared by coating high surface area of silica gel with modified acrylonitrile copolymer. The concentrations of the modifying agent (NaOH) and the modified polymer were varied. GOD was covalently immobilized on these hybrid supports and the relative activity and the amount of bound protein were determined. The highest relative activity and sufficient amount of bound protein of the immobilized GOD were achieved in 10% NaOH and 2% solution of modified acrylonitrile copolymer. The influence of glutaraldehyde concentration and the storage time on enzyme efficiency were examined. Glutaraldehyde concentration of 0.5% is optimal for the immobilized GOD. It was shown that the covalently bound enzyme (using 0.5% glutaraldehyde) had higher relative activity than the activity of the adsorbed enzyme. Covalently immobilized GOD with 0.5% glutaraldehyde was more stable for four months in comparison with the one immobilized on pure silica gel, hybrid support with 10% glutaraldehyde and the free enzyme. The effect of the pore size on the enzyme efficiency was studied on four types of silica gel with different pore size. Silica with large pores (CPC-Silica carrier, 375 A) presented higher relative activity than those with smaller pore size (Silica gel with 4, 40 and 100 A). The amount of bound protein was also reduced with decreasing the pore size. The effect of particle size was studied and it was found out that the smaller the particle size was, the greater the activity and the amount of immobilized enzyme were. The obtained results proved that these new polymer/silica gel hybrid supports were suitable for GOD immobilization.