A reader who would like to remain anonymous asks:
As a disabled person whose body is basically falling apart (details too gross to go into), I've been wondering for a long time when I can get my cyborg transformation underway. What's the status of materials that are compatible with being implanted in the body?
First of all, Anonymous, my best wishes. I hope that the next advance coming 'round the bend is a comfort to you. There are two fundamental approaches to organ-level repair: the biological approach, which includes transplants and tissue engineered organs, or what we'll call the cybernetic approach, which creates replacements out of artificial materials capable of appropriately interacting with the body. Keeping this in mind, let's take a look at the cutting edge of human-machine interfaces.
The use of the term "cybernetic" hints at where the difficulty lies - traditionally, cybernetics is the study of the interactions within complex systems with an emphasis on feedback and control. The body is a terrifically complex system, which can be maddening to meddle with - surprisingly forgiving in some respects, infuriatingly recalcitrant in others.
Full disclosure - I'm a cyborg. I wear corrective lenses and shoes that modify my feet appropriately for an urban environment. It's not exactly Robocop, true, but according to the loosest definition, most of us already have a complicated relationship with technology blurring the line between "me" and "stuff." It's not a relationship that's going to get simpler. The relatively simple implants and prosthetics of today will soon give way to devices that interface more completely and naturally with the body. We have a number of biocompatible materials available to us already, from titanium to various polymers. They aren't perfect by any means, but the body can be surprisingly accommodating.
Sometimes you can avoid implantation altogether with an exoskeletal assist. A weakened body can recover some of its strength via an exoskeleton that senses an intended motion of the wearer and reinforces it.
For organs no longer present, there are robotic limbs that obey commands given by the mind. The bionic limb below senses commands from the wearer and (with a lot of practice) obeys. Obviously the connection between nerve and the robot limb is unusual, but the brain is pretty good at making unfamiliar signals familiar with use.
Even entire arms can be replaced, by rerouting the motor nerves that control the arm to the chest where they can be read by the robotic arm's shoulder mount.
Having a cybernetic limb sounds great until you consider how much you depend upon your sense of touch. Walking with a leg that's asleep is no mean feat, and have you ever tried to eat a meal fresh from the dentist before the novocane wears off? Sure, your shiny robot hand is sturdy, but the wineglass you want to pick up with it isn't - and just because the hand won't be damaged by that hot stove doesn't mean the flesh attached to your extremely conductive prosthesis won't be. The first thing they did after fitting Luke Skywalker with a replacement was test to see that he could feel with it.
When the sensory nerves connecting the brain to the missing limb are also rerouted to the chest, a touch on the patient's chest can feel like someone's brushing against fingers that are no longer there, or stretching skin that no longer exists. While the recovered sensations are currently somewhat random, further research into the phenomena along with a robot arm including sensors that feed back to the sensory nerves in the chest could give us cybernetic replacements capable of being tickled.
Astounding as these interfaces are, the devices themselves are still wearable - that is to say, removable. We won't neglect the truly implantable devices. For example, Matt Nagel, though quadriplegic, can use the 96 electrodes implanted into his motor cortex to move a cursor on a computer screen or command a robot arm by thought alone.
The senses have not been neglected, either. Though the resolution of existing bionic eye implants is as of yet only in the tens of pixels, these devices allow the wearers enough vision to dramatically improve their quality of life. No word yet on whether they'll come in mirrorshades.
Finally, there is the cochlear implant, used regularly by over 100,000 people worldwide to directly stimulate the auditory nerves of the deaf or extremely hard of hearing. These have been around since the late '70s, but only recently has the technology become advanced and popular enough to encourage users to hack their own implants.
You'll know that the human-machine interface has truly arrived when the first thing you do post-implantation is replace the standard firmware with an open-source alternative.
Terry Johnson is a biology researcher at UC Berkeley and io9's resident biogeek. If you have a question you'd like Terry to answer, email him at: email@example.com.