Rights: University of Waikato. All Rights Reserved. Published 5 October 2012 Download

Carefully controlling the pH of the hydrogel and soaking it in solutions containing calcium and carbonate ions can initiate the mineralisation process. Professor Kate McGrath, of the MacDiarmid Institute, describes this lab procedure. It is now possible to manipulate when crystallisation occurs, how much occurs and what shape the crystals will take up.


We make the chitosan hydrogel and then we introduce the calcium ions and the carbonate ions. And we do that in a way so that they don’t spontaneously start to form calcium carbonate.

So for calcium carbonate, in acidic conditions, the calcium ions and the carbonate ions don’t associate well with each other, but as you start to move to neutral pH or basic pH, then they start to precipitate. So as long as you keep your hydrogel system acidic first and then allow the pH to increase to neutral or basic, you can control when you actually get mineralisation to occur and where you get mineralisation to occur.

You can manipulate how much mineralisation occurs by changing the concentration of calcium ions and carbonate ions that you utilise. We can also add other components to replicate the proteins that are in the native system, so we use a synthetic polymer, polyacrylic acid.

So all of these things together allow us to manipulate when, how, in what shape, how much crystallisation actually occurs. 

Dr Natasha Munro