hydroxyapatite and calcium sulphate in NaCl water

[li bri]

Hello, I'm trying to design a small analysis of a synthetic bone mass substitute. Its according to product descriptions made of 40% hydroxyapatite and 60% calcium sulphate of which the Calcium Sulphate is meant to slowly wash out in order for new bone to grow in. The synthetic bone also has some added iohexol for radio opacity.

1 mL of hardened mass will be placed in 5 mL isotonic NaCl. The idea is to analyse how much Calcium concentration rises over time in order to determine how fast the Ca Sulphate fase is washed out.

Will hydroxyapatite or Calcium make bonds with Cloride? How much can I expect the Calcium concentration to change in 37 celcius? Will the pH rise?

I know the description is a bit lacking. I'm just looking for some pointers or advice.

 

Thanks in advance!

[John Cuthber]

Just to simplify things, lets imagine you just have some gypsum i.e. hydrated calcium sulphate (without the hydroxyapatite ) and you put it in water.

Some will dissolve. If I remember rightly the solubility is about 0.1%w/w. That's small, but fairly easy to measure.

So, initially the calcium concentration will be near zero (depending on how pure your water is), and it will rise to some constant value which represents a saturated solution.

The speed at which it will do that depends on lots of things.

Finely powdered gypsum will reach saturation faster than coarse material.

The gypsum will also dissolve faster if the solution is stirred.

 

Then there's the question of what difference the salt makes. The simple answer is probably not much difference. The gypsum is likely to dissolve a little better in salt water than in pure water.

But in the body, things are slightly different,

The material which dissolves will be carried away and will probably be excreted via the kidneys.

So, what you might want to  think of is a set-up where the saline is replaced regularly or, even better, where it flows continuously past the material.

Not such an easy experiment, but much more representative of the real situation in the body.

 

[li bri]

Hello John, thank you for your reply! The study is actually designed to mimic the biological system. Some water will be removed in regular intervals and replaced. I'm quite sure that the hydroxyapatite is more or less insoluble both in vitro and in vivo, even though it might lose its structural integrity and turn into a paste (has been seen in vivo). I just need to make sure that the calcium sulphate wont make any precipitation that might damage the measuring equipment.

Also any thoughts on iohexol and salt water?

Cheers