Adsorption characteristics of various proteins to a titanium surface

Adsorption characteristics of 18 proteins, with different sizes and isoelectric points, to a titanium oxide surface were studied. The adsorption isotherms were categorized based on protein type and pH: type 1, irreversible adsorption; type 2, Langmuir-type reversible adsorption; and type 3, reversible and irreversible adsorption. Most of the proteins tested were irreversibly adsorbed in the pH range of 3–8, whereas most adsorbed reversibly at pH 8.5–9.4. Protamine, with a pI value of 12, adsorbed reversibly in the pH range of 3–9. pH values that gave maximal sums of irreversibly and reversibly adsorbed proteins were in the pH range of 3–8 and tended to increase slightly with the pI value of the corresponding protein. pH values that gave maximal quantities of irreversibly adsorbed protein ranged between 4–6 and were nearly independent of pI.