AVS 50th International Symposium
    Biomaterial Interfaces Monday Sessions
       Session BI-MoM

Paper BI-MoM9
Activity of the Model Enzyme Urease Adsorbed on Different Colloidal Oxide Particles

Monday, November 3, 2003, 11:00 am, Room 307

Session: Protein-Surface Interactions
Presenter: K. Rezwan, ETH Zurich, Switzerland
Authors: K. Rezwan, ETH Zurich, Switzerland
J. Voros, ETH Zurich, Switzerland
M. Textor, ETH Zurich, Switzerland
L.J. Gauckler, ETH Zurich, Switzerland
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Whilst metal oxides are directly used for applications where their extreme hardness is necessary (e.g. femoral head replacement), most metallic biomaterials are themselves covered by a protective, stable oxide film such as titanium oxide on titanium. In these cases proteins only interact with the oxide film and not with the underlying metal. Closer investigations of the protein - oxide interface are therefore vital to the biomaterials field as it strives to make the transition from merely bio-inert to fully bioactive implant materials. It is assumed, that not only the amount of adsorbed protein but also its conformation is important for cell proliferation. A change of protein structure would hamper the cell receptors (situated within the cell membrane) to recognize the specific protein function. As a consequence, the cell would not adhere and proliferate on the preliminary adsorbed protein layer and not accept the adsorbed proteins as body own proteins but rather see them as intruders. This fatal mistake, made by the cell, is assumed to be one of the reasons which promotes local inflammation and tissue mutations. Assessing the conformational changes of a protein after adsorption is a delicate matter and can be measured by using for instance circular dichroism. In the case of enzymes, one can also measure the activity of the enzyme before and after adsorption. We used the model enzyme urease for our studies where the catalysis of urea was monitored by measuring the electrical conductivity as a function of time. The aim of this study was to compare the activity (and hence the conformational state) of urease after adsorption onto different colloidal oxide particles. We found that urease adsorbed onto TiO2 showed the highest activity and urease on Al2O3 the lowest. The measurements showed also an adsorption time dependency, which indicated further conformational changes after adsorption.