Re: What chemical to use to re-calcify a chicken bone?

Dear Susan,

Very interesting question, but one with no easy answer, I'm afraid. In 
forming a mineralized bone, cells called "osteoblasts" secrete a very 
particular, complex mixture of proteins called "osteoid" that is mainly 
(90%) collagen (a fiber-forming protein), but includes growth factors and 
many other kinds of molecules, most of whose functions are not well 
understood at this time. The osteoid gets laid down in layers about the 
thickness of one cell, and then mineral crystallizes in it from the 
surrounding fluids to make bone. The layers get built up over time as bones 
grow. You have obviously succeeded in extracting the mineral from the bone 
(scientists who work with bones call this "demineralization"). You probably 
used either vinegar or the chemical EDTA to do that, leaving you with a 
rubbery, flexible bone without the stiffness of the mineral crystals. 
That's a great way to understand which properties of bones come from which 
components - flexibility and toughness from the protein and hardness and 
stiffness from the mineral.

The mineral part of bone is called "hydroxyapatite," and it's made of 
calcium, phosphorus, oxygen, and hydrogen. The chemical formula for 
hydroxyapatite is written this way: [3Ca3(PO4)2]·(OH)2. Exactly how the 
crystals form is a very active area of scientific research, one that could 
have importance for being able to treat certain diseases like rickets, 
where the mineral doesn't get deposited due a deficiency of vitamin D, 
which is important in the process. Unfortunately, we don't have the answer 
yet as to how to do it directly, just indirectly, like by giving vitamin D 
and letting the body work its magic. 

In a way, trying to get the mineral back in is a little like trying to 
un-cook an egg!. Bone forms in the very precisely controlled, complex 
environment of the body. Once you chemically dissolve the crystals - at the 
same time causing some chemical changes to the osteoid -  about all you 
could hope for might be to try to get some calcium phosphate to crystallize 
on the outer surface. You might try to do this by dissolving as much 
calcium phosphate as you can in water (that is, make what's called a 
"saturated solution" that even has a little undissolved material sitting in 
the bottom of a jar), and then let your demineralized bone sit in it for a 
a few days. Ideally, you might use 3 bones. Keep one in its natural state 
for comparison, keep one in the demineralized state, and then you can 
compare the three of them. Calcium phosphate is available in many school 
chemistry labs or from chemical supply houses, and it comes in quite a few 
different chemical forms, some more acidic and some more basic when they 
dissolve in water. Since we know that acid can remove the mineral, you 
should probably try the "dibasic" form, which it will say on the label. 
Give it a try. You may end up concluding that trying to do in a jar what 
the body does by itself can be pretty difficult, but in science, you need 
to try the experiment. Good luck!!

Paul Odgren, Ph.D.
Dept. of Cell Biology
University of Massachusetts Medical School
Worcester