The Role Of Zeta Potential In The Manufacture Of Healthcare Materials

By Matthew Cantelo, Lucideon

In the manufacture of healthcare products and medical materials, especially ceramic materials like zirconia (used as an implant material) and hydroxyapatite (synthetic bone replacement material), there is often a stage in the manufacturing process involving a powder suspension. The behaviour of this powder suspension will correlate strongly to (a) how well it is processed and so (b) final yields and product performance. Surface chemistry dominates the particle-particle interactions in suspension, with different materials having different surface charges. These interactions in turn dictate suspension rheology. Zeta potential is used to investigate and monitor the surface interactions in powder suspensions, and can also be used to optimise the processing method. In a previous white paper, the in-depth theory of zeta potential was presented and discussed, whereas this white paper will discuss its applications for the manufacture of some healthcare materials and how Lucideon has assisted some of these manufacturers.

Zeta Potential – The Theory
All inorganic materials form a surface charge when dispersed in a liquid, usually water in industrial processes. The material will either form a positive or negative surface charge in the liquid, and this charge will attract counter-ions from the liquid. This forms a double layer of tightly bound counter-ions close to the surface of the particle, and a more diffuse layer containing both positive and negative ions that offset the surface charge on the particle.

Zeta potential is defined as the energy required to shear a particle and its associated double layer away from the bulk solution. It is measured in millivolts (mV) and can be positive or negative. A large zeta potential (± 50 mV) is indicative of a stable system, where the particles are well dispersed and there is minimal flocculation. A low zeta potential (± 10 mV) indicates an unstable system, where there is lots of flocculation occurring and the particles are not properly dispersed. A value of ±25 mV is considered to be the minimum for a stable system.