M.Sc Thesis

M.Sc StudentGrabstain Violet
SubjectAdsorption of Proteins on Temperature-Sensitive Hydrogel
DepartmentDepartment of Chemical Engineering
Supervisor PROF. Havazelet Bianco-Peled


The physical properties of stimuli - responsive polymers, often termed  "smart materials", are sensitive to environmental variables such as variables such as solvent composition, temperature, pH or electric field. A well-known instance of a "smart material" is the temperature sensitive polymer poly(N-isopropylacrylamide) (PNIPA). PNIPA is soluble in water below the “volume phase transition temperature” Tc of ca. 32oC, but the chains collapse and precipitate above it. A hydrophilic - hydrophobic transition also appears in cross-linked PNIPA hydrogels. PNIPA microgels may offer several advantages over PNIPA-modified surfaces when used as sorbents in temperature-sensitive chromatography. Yet, a full exploitation of these advantages requires a better understanding of the mechanisms controlling the separation process. As a model system, we have studied the binding of three proteins (Bovine serum albumin (BSA), Ovalbumin and Lysozyme) to PNIPA microgels both below (25oC) and above (37oC) the volume phase transition temperature of the gel Tc. The analysis of the binding isotherms has shown that although an average gel particle contained a larger amount of protein below the phase transition temperature, the concentration of the protein within the particle was higher above this temperature. A comparison between the three studied proteins have shown that below Tc the binding increases with a decrease in the molecular weight. These findings were attributed to changes in the binding loci due to temperature swings around Tc: while a sorption mechanism is dominant below this temperature, surface-adsorption was more important above it. On the other hand, no significant difference in the bound protein amounts was observed above the phase transition temperature.