July 22nd, 2013 | guest informant
Wild about Wolverine — Attaching Adamantium Claws To An X-Man’s Skeleton
Wolverine. One of the most powerful, engaging, and controversial characters in the Marvel Universe. Or in any comics universe, really. He’s got some amazing characteristics, powers and abilities. Chief among those are Wolverine’s amazing adamantium claws. They are unbreakable and sharp as a Samurai’s katana. They were grafted to Wolverine’s skeleton, we are told. But how do they stay in there?
See, I started reading about Wolverine in the mid 1970s, shortly after his debut in The Incredible Hulk. It was around the same time that I became captivated by another technical marvel – The Six Million Dollar Man. Steve Austin didn’t have swords grafted to his arms, but he did have some fancy technology implanted and imbedded inside his body. Again, how did that bionic arm stay on and the bionic stuff in the arm (and elsewhere) stay connected to his skeleton?
Of course all these implants did all kinds of cool stuff. Stuff like cutting and blocking and lifting. And I was (and am) impressed by that for sure. But the nascent scientist in me was amazed at what held it all in. Why didn’t Wolverine’s claws come right off the bones in his forearms when he tried to cut through something? And, for those anatomy aficionados in the crowd, why don’t the claws flip over when his radius move as he turns his wrist? While I can’t provide an answer to the last question, science continues to provide some clues to the former.
Once again it’s tissue engineering and materials science to the rescue. I’m fascinated by these related branches of biomedical engineering. Seriously. If I wasn’t already committed to this whole neuroscience brain-and-behaviour gig I’d be all over biomedical engineering. And some recent discoveries in this field related to bone implants have significant implications for how we might really attach adamantium to bone. After we discover adamantium, of course. (This is your cue, metallurgical engineers. In the words of Stan Lee–Excelsior!)
So, while they weren’t busy discovering adamantium, researchers at M.I.T. (and friends) were busy discovering how to improve the fidelity, stability, and viability of making attachments to bone. And, in one of those amazingly fitting juxtapositions that science and life produce, it involves a process very much akin to and relevant for costumed superheroes–superglue.
It gets even better, though. That’s because they were trying to improve the strength of bone connection to implanted devices especially those made from titanium. The coolest element this side of adamantium and vibranium. Titanium is commonly used in the manufacture of joint replacements, most notably the hip. Titanium also gets extra cool kudos by virtue of being a real element.
What this team discovered was that they could stimulate better growth between bone and titanium by using a special superglue adhesive in rats. This adhesive consisted of multilayers of ceramics and nanolayers of polymers mixed up with protein. This super-slurry mix included signaling molecules that bone would normally detect as bone. Since bone likes to grow back to itself, the basic concept was to trick the body into thinking the titanium implant was bone (or at least bone-like).
This was accomplished by making many, many, ultra-thin layers that then worked like superglue to help get bone cells to grow together. This worked much better than conventional bone cement that has a more brittle and less stable outcome. It’s kind of like really good double-sided tape. Except it’s biological tape that grows both ways and has bone growth proteins (for those keeping score it’s osteoinductive bone morphogenetic protein–2, or BMP-2 for short) that help stimulate this growth.
I love this study. Like much of the best science it’s simple and elegant. Lead author Nisarg Shah and colleagues made all kinds of advanced measures (like regulatory hormone release and stem cell differentiation) on how well implants adhered to bone using this new procedure. But some of the measures were also very simple and included how much force was required to pull the implants out when different adhesives were used. The bottom line is that this new approach seems to be a great improvement on the old bone cement model. This is a very real world concern for joint replacements such as hip and knee in humans.
This study using a rodent model is a fantastic proof of principle that dramatic improvements in the fidelity and stability of implanted devices in humans is on the horizon. Human trials are planned next and will the next test of this approach. We really are on the road that will take us to more stable implants of many devices.
We’re currently shooting from the hip, but can claws really be that far away?
© E. Paul Zehr (2013)
E. Paul Zehr is a frequent guest poster here on extraordinary medical matters. This is his info page. His most recent book is INVENTING IRON MAN: THE POSSIBILITY OF A HUMAN MACHINE.