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April 15th, 2010

Wooden bones

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It’s easy to not think very much about your bones. After all, they’re securely hidden away inside your body; not visible, except as hard lumps beneath your skin.

Funny thing, though: once you break one, it’s hard to think about anything else.

When first I wrote about bones, back in a 1993 instalment of this column, I told the story of my own broken-bone experience, for which I blame my big brother, Dwight (mainly because it was his fault).

I was seven years old and he was 12. We were both inside a big cardboard box that had held a refrigerator. For some reason, we’d decided it was fun to roll down the back steps inside this box. And it was fun, right up until Dwight’s friend from down the street jumped on top of the box. Inside, my brother was on top of my arm, which was up against the steps, and I was suddenly the startled owner of an L-shaped wrist.

My indignant initial reaction (I tried to say, “Now look what you’ve done,” but it came out more like “Glubbleulp!”) gave way to an intensely personal curiosity about bones. “Someday,” I vowed, “I will write science columns about them!”

This particular vow-fulfillment column was prompted by the report of a new procedure to turn blocks of wood, of all things, into artificial bones.

Developed by scientists at the Instituto di Scienza e Technologia dei Materiali Ceramici in Faenza, near Bologna, Italy, the wood-derived bone substitute promises to allow live bones to heal faster and more securely after a break than the metal and ceramic implants that are currently used.

It makes sense, because if you’ve ever seen a cross-section of a bone—there’s one at the Saskatchewan Science Centre, if you’d like to run down and have a look—you will have noticed that, far from being solid, it’s quite porous.

As I noted in that original column all those years ago, “We think of bones as hard, dead matter, like hair or fingernails, but they’re actually organs consisting of living cells embedded in a matrix of calcium phosphate and other calcium minerals, held together by collagen, the tough fibrous protein we also use to make ligaments, tendons and skin. Bone tissue constantly renews itself…dissolving old tissue and…depositing new tissue.”

That’s why broken bones can heal themselves. But when titanium is used as a bone implant, bone can’t interact with it. Instead, the titanium is simply encapsulated in fibrous tissue. Nor is it practical to introduce pores into the titanium: that weakens it to the point where it could break, inflicting more damage.

Wood, however, like bone, is porous. Bone tissue can interact with the new wood-based substitute bone, growing right into it, along with blood vessels, nerves and more.

Titanium and ceramic implants can also damage bone simply because they’re so much harder than it. Whereas natural bone flexes slightly (and that stress actually strengthens the bone), the harder, less flexible implants can apply so much stress to a particular area that the bone snaps.

So how do you go about turning wood into something approximating bone?

The process begins with a block of wood (rattan works best). It’s heated until nothing remains of it but pure carbon (i.e., charcoal). The charcoal is then sprayed with calcium, which creates calcium carbide, then heated further under intense pressure and treated with a phosphate solution. After about 10 days, the wood has become a bone-like material.

The cost? About $850 per block, which provides enough material, on average, for one bone implant. Virtually any size or shape can be created.

Dr. Anna Tampiere, leader of the research team, says the new material is strong enough to take the heavy loads bodies place on it, and durable enough that, unlike existing bone substitutes, it will never need replacing.

The bone substitute has been implanted into a flock of sheep. X-rays show that, indeed, the sheep’s bones have migrated into the wood substitute. With time, says Tampiere, “you don’t even see the join.”

Human tests are probably still about five years away, but so far there has been no sign of the sheep’s bodies rejecting the new material, raising hope that this new process could give us a natural, cheap and effective replacement for bones.

Bonus: these implants won’t set off metal detectors at airports.

Originally posted at Edward Willett. Link | Comments


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