Can you rephrase you question?

Are you interested in measurements or theoretical aspect? 1.67 is ratio of stochiometric hydroxyapatite. Slight deviations may be due to variations in hydroxyapatite chemistry, greater difference may be result of presence of phosphates, i.e. defective or non mature bone formation.

Vladimir Dusevich : Thank you for the response. theoretically that the ratio of Ca / P molarity to bone generally varies depending on gender, age, health, etc. Why is the Ca / P ratio 1.67 ideal for use as a bone scaffold?

Amin Shavandi

Thank you for the response Professor Amin Shavandi

• Please respond to the professor

  Amin Shavandi

  I am currently preparing hydroxyapatite by hydrothermal method.
• my workflow:

• based on my workflow, according to the professor where the critical point usually occurs in the hydroxyapatite phase change

What do you mean writing “hydroxyapatite phase change”? Prior asking questions, you should learn the proper terminology. Regarding your workflow, the entire process can be speeded up by using faster rates of H3PO4 addition and omitting the aging process because everything that is important occurs during the hydrothermal treatment.

In literature Ca/P ratio variation in human bones is greatly exaggerated, thanks to a lot of papers with poorly performed analysis. In incompetent hands most methods tend to give significant systematic error.

Energy dispersive spectroscopy or MP-AES can be used to determine Ca/P ratio of bone

Bones have a low crystallinity HAp form Ca10−x(PO4)6−x(HPO4)x(OH)2−x. where x tend to decrease with the age leading to a mineral structure close to stoechiometric hydroxyapatite. in order to determine properly your Ca/P from a bone sample, the best method is to titrate Ca by (atomic absorption) and the mineral PO4 by colorimetric titration.

Thank you for all the responses Sergey V. Dorozhkin , Vladimir Dusevich , Vineet Kumar and Imane Demnati . this really helped me

I would like to add something to Imane´s answer...

Ca can be determined by chemical titration (the most used method determines Ca and Mg simultaneously and then you need another reaction to titrate just Mg in order to subtract its value and obtain Ca content). Or you can determine Ca2+ by Atomic Absorption Spectroscopy (usually flame instruments for the range of concentrations of Ca in hydroxyapatite). For phosphate, the colorimetric method is OK, or you can use potentiometry to measure negative ions.

As for the question: WHY do we use the ratio Ca/P of 1.67 (=10/6) as an "ideal" value for a bone graft material knowing that it is not a constant value is living bone?

In young bone, the hydroxyapatite is usually calcium deficient and that ratio is initially smaller (from 1.5). Other ionic substitutions also occur. With age, that ratio gets closer to the stoichiometric value of 1.67 and the crystals get more pure and crystalline.

My answer to this "WHY 1.67 ?" is that we need a reference value for the implanted materials so that the organism can recognise them as biocompatible and similar to the biological, naturally produced bone tissue.

Don´t worry so much with the accuracy of that value.

There are many more variables to consider in order to obtain a good scaffold for bone repair!

Gabriela Martins Thank you for the responses. it was really helped me

X-ray fluorescence can give you an idea of ​​the percentage of each atom in the raw material, which makes it easier to calculate the Ca / P ratio. this method remains approximate because the characterization is done on a surface.

Mufid Al Islam