Prosthetic legs (etc) are usually detachable objects that end in a cup or ball socket that connects to the opposing cup or ball socket on the body itself. This means that the prosthetic limb is not fully secured to the body.
In 2004, a two-year research project ended, which developed a prosthetic attachment method which embeded a titanium socket directly into whatever natural bone remained in the patients limb. This allowed a much more solid connection, which reduced chafing and heat.
This kind of prosthetic is good for end-point bones, but for bones that are intended to be inside your body, potentially rubbing or pressing against tissues, you need something that is completely embeddable and shaped for your individual body.
If you’re lucky enough to own a working 3D printer, you’ll know how amazing they are. You imagine it, you can print it.
In 2004, a 3D-printed skull was created for a woman who had a chronic bone-thickening disorder that was literally squashing her brain.
Bones are probably the easiest human implantable structures to 3D print, as they are basically just solid structures. Organs and tissues are more difficult.
While bones also usually help to create red blood cells through the marrow contained in the center, if you are just replacing one bone, you should be okay – there is enough marrow in the bones of the entire body that losing a little of it is not going to make much difference.
There are printing materials that can be used to emulate bone so that the body can meld with it easier, such as CT-Bone, which you can print with adjustable porosity so that neighbouring cells can get a good grip on it.
Everyone is shaped different. Some people will have long bones, thick, thin, short, twisted. You can’t create off-the-shelf bone replacements. Every one of them is designed for a specific person. And if that person is young, then it will need to be replaced in a few years as well as the rest of the body grows but the implant doesn’t.
In order to get the shape right, you must scan the existing bone that you intend to replace. Of course, that’s a little tricky, as it’s inside the body and you won’t be able to take it out of the body until after the printing itself is completed, so you need to use a medical scanner.
CT scanning is usually used for scanning bones, and MRI is usually used for scanning tissue. However, CT scans use X-rays, which can be dangerous.
from scan to 3D print. image from http://www.think3d.in
A recent development in scanning is “black bone MRI“, which produces a high contrast image where bone is black (hence the name), and tissue is a much lighter uncontrasted colour. Basically, it makes the bones stand out much more, making it easier for automated processes to use the images to recreate 3D models.