In this video, University of Waikato’s Dr Michael Mucalo outlines the main processing steps taken in the conversion of cancellous cow bone into a mineral shell of hydroxyapatite. Small, shaped pieces of this can be used as a bone substitute in certain types of bone replacement operations. He also explains how this type of hydroxyapatite can be plasma-sprayed onto implants to improve their biocompatibility.
Laurens van Lieshout
DR MICHAEL MUCALO
Basically, you take the material from what we call the femur bone of the cow, known as the condyle, it’s the big huge bone which supports the beast, and then you chop it out, and you go for the spongy bone, the cancellous bone in the middle, and you chop that with a bandsaw. And when you do that, basically you are left with a lot of blood and guts, and you need to boil that out, and that is done at about 100 degrees Celsius with water in a pressure cooker. You do it over about 6–12 hours, and then we take it out, we dry it out, and then it is placed in a muffler furnace. This is a furnace which you can heat up to 1,000 degrees Celsius, and that evaporates or burns off all the organic stuff in the bone. And what you are left with is a mineral shell of hydroxyapatite, the calcium phosphate in the bone.
We take that material, we can make shapes out if it, chop it into cubes or cylinders, and then we can use it as is and wash it afterwards to remove any byproducts, and we do further treatments with it. You can take this bone and grind it up and basically make a powder, and then you can pass it through a spraying apparatus. It consists of a plasma torch – which is very high-temperature sort of plasma which is like another state of matter – and you pass the particles through this very-high temperature torch, they partially melt, and they are sort of flung against a surface that you want to coat. They form splats, they build up, you make a nice rough surface of this hydroxyapatite, and that is called a plasma coating, and that is how you treat implants to improve their biocompatibility – so how well they get integrated by the body.
It is quite rough material. When you look at it under a very high-magnification microscope, an electron microscope, it looks pretty tortuous and pretty rough and porous, but that is good for the body because it helps tissues and cells to sort of invade it, colonise the material.