Race for the Surface: Surface Zeta Potential Analysis of Implants

In biomedical applications, solid materials need to becharacterized in terms of their functional groups at theoutermost surface. Mainly four properties influencethe biocompatibility:

• Charge in aqueous environment (surfacecharge)
• Hydrophilicity (wettability)
• Roughness
• Chemical composition

The interface between the biomaterial’s surface andthe surrounding physiological fluid determines thecompatibility with its environment. However, theseinterfacial properties are difficult to characterize andare commonly derived from separate analyses of solidsurface and liquid phase. A method that allowsbiomaterial analysis under real life conditions issurface zeta potential analysis by means of streamingpotential or current measurement.

For investigating the streaming potential or streamingcurrent, the surface gets contact with an electrolytesolution, which is typically a diluted salt solution (e.g.1 mmol/l KCl). Due to acidic or basic interactionscharges are formed, which lead to a dissociation ofacidic surface groups and a protonation of basicgroups on the surface. Negative surface charge leadsto a negative zeta potential, and positive surfacecharge leads to a positive zeta potential. However, thezeta potential is a parameter that cannot be measureddirectly, but an electrokinetic effect needs to be usedwhich is called the streaming potential.