Thursday, September 24, 2009

SMORGASBORG #7: Endoskeletons part B

What do Sam Worthington, Peter Weller, and Will Smith have in common? They're all dreamy, and they all play characters in movies who have devices implanted into their bodies. In their films the only issues they seem to have with their artificial parts are emotional ones, but putting a foreign object into a human body without adverse physical effects is actually pretty hard to do.

Note the chiseled endoskeletal cheekbones.

Marcus (Worthington) in Terminator Salvation, is apparently the lone humanoid organism to have survived Skynet's experimentation to build a cyborg with a metallic endoskeleton. Why would this be so hard? (Other than the fact that a machine dominated society using humans as lab rats wouldn't really care that much if there were a lot of casualties.) Living tissue and many types of metals have problems getting along together.

Metals for making cyborgs, or hip or knee replacements, have to be corrosion resistant and biocompatible. If you have an allergy to nickel, you sure don't want a nickel implant, or a nickel belt buckle, or a phone with nickel in it.

Metals shed ions. In order for the body to tolerate the metal well, it can't leach too much into the surrounding tissue. Although your body uses some metals for metabolism (copper, iron, magnesium, etc.), too much can cause toxicity. You don't want that metal plate in your head shedding too much of anything near your brain(1).

So you can imagine that corrosion resistant types of metals, plastics, or ceramics, would be a good idea. Using incompatible metals could interfere with normal tissue growth near the implant(2). Blood acidity and ph balance can have a corrosive effect on metals. If metals shed into the bloodstream, your whole body may have a (systemic) reaction. Organs that filter blood, like the liver and kidneys may accumulate unhealthy amounts of metal ions, which is bad. And don't forget cancer! You have to be careful that whatever you're implanting isn't carcinogenic 20 years after you've implanted it.

Cobalt-chromium alloys, stainless steel, and titanium have been reported to have minimal tissue reactions in rabbits, dogs, and people. If Terminator Salvation was going to be really accurate, we should have seen some rabbit cyborgs hopping around killing humans.

Although there are always many things to consider, many people enjoy their artificial joints (made of plastics and metals) or eye lenses (plastics), or boobs (silicone) and never have any problems. 300,000 women per year receiving breast implants can't be all wrong, can they(3)?

Once you find biocompatible materials to implant in the body, you also want them to last. Fatigue resistance is important. You don't want parts to break or bend like a lug nut on an airplane wing.

If we're talking about hip replacements, "... chrome is favoured if tensile and fatigue strength are required, titanium is favoured if load sharing with adjacent bone (uncemented prostheses) is required (titanium has a similar modulus to cortical bone)(4)." So it really depends on what you're going to do with that hip and whether you glue the prosthetic, or just jam it in there really tight.

Bo Jackson, cute enough to be a cyborg, and a super-human athlete.

The metal and the bone it's embedded in, making up the structure of an artificial joint, are able to withstand normal physical stresses. Professional athletes with joint replacements often end up with complications because they put super-human stress on their bodies. The metal may bend, the bone holding it may break, or the prosthetic starts to work its way lose. For this reason, RoboCop with his combination of exoskeleton and implanted sensory parts, Spooner and his entirely prosthetic limb, and Marcus with a full body endoskeleton are the creme de la creme of the Hollywood Cyborgs.

1. Which is why they use titanium or niobium in the skull.
2. This can lead to chronic inflammation and scarring in the area.
3. Women with breast implants do not qualify as cyborgs.
4. Page 394 from Imaging of the Hip and Bony Pelvis: techniques and applications, by Arthur Mark Davies, Karl J.Hohnson, Richard Wihehouse. Read it on Google books, otherwise it costs over $200!

Friday, September 4, 2009

SMORGASBORG #6: Endoskeletons part A

Before we get started on the cyborg thing, I'd like to introduce a new term I coined last week due to a wicked cold (or maybe it was H1N1...). What is this term? Boughing. Cough so hard you try to barf, and there you have it. It's practical and combines two signs(1) of illness into one convenient word.

RoboCop isn't smiling because he's sensitive about his teeth

Might RoboCop bough? Certainly. He has a digestive system(2), such as it is, and a respiratory system. Just because he is mostly metal exoskeleton doesn't mean he can't catch a cold.

Might the Terminator bough? No. He has no respiratory system that involves lungs, and no digestive system providing an esophagus for vomit. Come to think of it, he doesn't eat food, and therefore has no vomit. Come to think of it, we don't know that he even has a functional transversus abdominis(3), the muscle that does most of the work during forced exhalation, like coughing.

Transversus abdominis is the deepest (and most petulant)
of the muscles at the waist.

Exo- means "without" or "external" while endo- means "within" or "internal." Marcus (Terminator Salvation) and the Terminator (from the great state of California) are excellent examples of cyborgs with endoskeletons.

A variety of Terminator endoskeletons

It seems that the Borg don't necessarily have to have endoskeletons per se(4). Some of them appear mostly organic with a new eye and exoskeletal structures. The Queen, however, has an endoskeletal cranium and vertebral column mounted in a machine structure with other fleshy parts. She's hard to figure out.

The remains of the Borg Queen

The implantation of fabricated devices into the cyborg is what interests me about the whole endoskeleton thing. Even Pearl from Cyborg(5) has this type of physiological intimacy with technology. This is really where the metal hits the meat.

For decades, people have been walking (and running and dancing) around with all sorts of artificial devices imbedded in their bodies. The list runs from simple screws to hold broken bones together, to artificial joints, to cochlear implants, to artificial corneas... and don't forget the occasional misplaced hemostat!

Why would some people say he was a cyborg? Because he has a cochlear implant.

Scissors in a patient, from an interesting blog called The Sterile Eye

As long as surgeons have been implanting devices (accidentally and on purpose) they have also been taking copious notes about the substances those devices are made of. It turns out that finding the right material to do the job is harder than you'd think.

Next time we look a different physiological reactions to implants.

1. Remember, signs are objective, observable, data like coughing or vomiting. Symptoms are subjective, like a sore throat or nausea.
2. It just occurred to me. RoboCop/Murphy has teeth but eats the equivalent of babyfood. If he doesn't chew and exercise his teeth, they will get soft and weak. Do they give him dentures in RoboCop 2?
3. The transversus abdominis, along with two other muscles at the waist, the external and internal obliques, are commonly known as bacon in our porcine friends. Hey... it's a theme! H1N1 is swine flu, and now I've mentioned bacon!)
4. If anyone proficient in Borg lore wishes to comment and educate me, please do!
5. What a bad movie that was.