The Body Plastic

BionicsTechnologies to recreate limbs and organs are taking medical bionics to a new level, as Drew Turney discovers.

The Wake Forest Institute for Regenerative Medicine in North Carolina is using 3-D printing to develop artificial kidneys, finger bones and ears.

SEARCH FOR ‘BIONICS’ on the web and you’ll find a huge array of electronic devices that attach to injured, diseased or otherwise damaged bodies.

Exoskeleton legs that look like robotic sci- fi warriors give paraplegics the power to walk. A procedure that re-routes muscles from a severed arm into chest muscles can give an amputee control over an artificial arm simply by thinking about it.

Soon, doctors and scientists hope not to have to rely on machinery at all – made-to-order replacement parts created from our own cells are tantalisingly within reach.

At medical bionics’ frontier, what’s changed dramatically in the last decade are the materials. “Particularly the electrode materials that create that interface between the bionic device and the living cells or tissue,” says Gordon Wallace, from the University of Wollongong’s Intelligent Polymer Research Institute, south of Sydney.

The aim of medical bionics has always been to find or fabricate inert materials that don’t rust or decay, and that the body doesn’t reject, but which still conduct electricity. Because of their non-corrosive natures, platinum and titanium are still popular.

But Wallace, among others, is looking beyond metal. He’s working with organic polymers, nanoscale carbons that work much more like parts of the body than metal pins and rods, and which increase the fidelity of information flow.

Instead of needing a computer or motor to translate muscle pressure into movement, materials based on or behaving like biological systems work at much smaller scales to transfer the information from a brain signal or muscle pressure to a bionic part more efficiently.

The advantages of such materials are that we can manufacture them with more precision, and they can be built so that the material itself can promote cell or biological growth.

New printing techniques are refining this process. Layer by layer, 3-D printers (essentially desktop fabrication plants) can build models from the ground up and with great precision. So far, this technology has mostly been used to create toy cars and dinosaurs out of plastic polymers, but there are success stories in medicine.

In June 2011, a team of doctors in Belgium used 3-D printing to create a new lower jawbone for an 83-year-old patient with a bone infection. Precise measurements of her unique musculature were taken using X-rays, and a one-off titanium device was created to exact specifications for surgeons to implant.

THEORETICALLY, ANY ORGAN or tissue could be created from scratch from a sample taken from a patient. The tissue can then be cultured so the cells do what they do best – divide and replicate. Computers can model the cellular structure of a skin graft, liver or heart, for instance, and the printer can produce it out one layer at a time using living cells taken from the patient.

“The preferred way to print 3-D tissues when you want to integrate cells is to take a sample, such as a stem cell, let it grow and reproduce to form a culture and then apply that to the model to print out the part,” Wallace says. “We’re also looking at a biopolymer to implant that interacts with the cells in the body to create the conduit for repair.”

Given this, what’s to stop us printing out anything we need, including bones, hair or teeth? According to Wallace, very little. “The materials development and hardware are coming together,” he says. “It’s at a very exciting stage. It’s not the possibilities that are limiting, it’s getting the right people thinking and talking to target the correct applications.”

In 2006, doctors at North Carolina’s Wake Forest Institute for Regenerative Medicine implanted patients with new bladders created using this cell layering process, but the process took 6–8 weeks of culture growth in a lab. Traditionally, a 3-D printer combines cells with other biomaterials to form organ and tissue prototypes.

a biodegradable structure or ‘scaffold’ model is produced from a network of polymer chains. The relevant precursor cells are sourced from the patient and applied to the scaffold. Over a given period, depending on the complexity of the organ, the cells cluster, fuse, grow and form around the structure. The scaffold slowly dissolves and you’re left with a completely manufactured human part.

Once the cells from a patient are collected, cultured and grown, 3-D printing can reduce this process from several weeks to just hours, because in many cases, there’s no need for the polymer chain scaffold. The printer simply lays the cells taken from the patient down in the correct shape on the fly.

In early 2009, a machine developed jointly by a Organovo, a company in San Diego that specialises in regenerative medicine, and Invetech, an engineering and automation firm in Melbourne, Australia, was unveiled, which the companies declare will one day print organs on demand to individual specifications. Organovo’s CEO, Keith Murphy, says the device will start with simple tissues like skin, muscle and short stretches of blood vessels for research only. But within five years, he expects the device to create blood vessels for grafts and bypass surgery.

FOR NOW, PROSTHETICS still have a major role to play in medical bionics. Here, also, there have been advances. For one thing, the computers that drive electronics are much smaller, faster and more powerful. That means a bionic part, such as an artificial hand, can be driven with more dexterity because the calculations made to move joints and motors are done faster and in more detail.

One of the major challenges in bionics, just like in robotics, is energy consumption. The common paradox of an electromechanical device is that the energy source required to drive it makes it heavier, so it needs more power. As you add more energy-generation capacity it becomes heavier again, and so on in an ever-increasing upward spiral.

As well, a prosthesis manipulated by the human body can’t exceed the body’s normal energy budget. For instance, if an existing upper arm muscle has to lift a bionic lower arm, the prosthesis shouldn’t weigh any more than its biological forebear did.

It’s also becoming clearer that, instead of coming up with better external gadgetry to power bionics, often the body itself might be the best enterprise partner. Wallace talks about futuristic-sounding programs like biofuel cells that generate energy from blood glucose and biodegradable batteries based on organic conductors.

THE AIM OF MEDICAL bionics is to match the complexity of biological systems so that prosthetics can do everything the body does. Suppose you lose your hand in an accident – the muscles that move your fingers are in your lower arm, so there are still some nerves and muscles to work with. In theory, then, an interface between your lower arm and a bionic hand could interpret commands sent from your brain and pass the information into the bionic device. But it needs to work both ways – touch and other sensation signals will need to flow from the bionic hand back to the brain.

“Several research groups are trying to stimulate the touch centres of the brain directly with microelectrode arrays,” says Gerald Loeb, biomedical engineer at the University of Southern California, Los Angeles, and one of the scientists behind a unique technology called Bio-Tac. “It’ll take years to figure out how to encode the subtle sensations we rely on.”

Since those sensations are subtle, it’s going to take a powerful system to replicate it, he adds. “Because a lot of what we do with tactile sensing is subconscious, like adjusting your grip to keep something from slipping from your grasp, that part will be easiest to replace by algorithms that control the prosthetic directly.”

What’s more, being able to interpret commands from or stimulate the brain by artificial means works both ways, because as a tool it’s quite easily reprogrammed. The Brain That Changes Itself, a 2007 bestseller by Canadian psychiatrist Norman Doidge, is full of examples of people changing their neural framework through experimentation, practice or therapy. “The brain’s very plastic and has some adaptability to relearn how to do things in some of these applications,” Wallace agrees.

An exciting example of how the body can be better than electronics to drive prosthetics is a Rehabilitation Institute of Chicago project.

The Institute developed a process called re-innervation, which takes muscle- contracting signals from the brain and amplifies them so that the controls of a prosthetic arm can translate them into action. Four major nerves that travel down the arm were rerouted to grow into muscles in the chests of amputee patients. So when the brain issued the command to close a fist, a muscle in the chest instead of the (absent) hand or arm made it happen, driving the prosthetic arm to close its fist.

But the researchers got a surprise. Incredibly, stimulating the nerves gave the patient the illusion of sensation in their lost limb. It opens up the possibility of building sensors in the prosthetic that can report back to the nerves of the chest and give the brain the illusion of feedback from a biological hand – anything from temperature to the pressure and texture of real sensation. It could give prosthetic users long dreamed-of speed and dexterity.

THE OTHER IMPORTANT aspect of bionics isn’t just that the brain drives them, but also that they report back to the brain effectively, giving the user the feedback needed to operate at ‘biological’ speed. Think of the array of movements and controls involved when you walk up stairs or catch a ball in flight. There’s a huge amount of data transmitted between your brain and muscles, almost all of it unconscious.

Mechanising that information to drive a prosthetic system of only mechanical components can be a huge undertaking. That much speed relies on the high sensitivity of biological feedback, from the skin, the body’s balance systems and from muscles.

Bio-Tac, created by Gerald Loeb and his team, is a robotic hand that can identify 117 materials by touch. It works because the fingers have ‘fingerprints’, patterns on the surface that report vibrations from different surfaces to a sensor. It works the same way as your own fingerprints, which vibrate at different rates according to what material you’re touching.

“Your fingertips and lips have the most specialised tactile sensors in the body by far,” says Loeb. “When you go to the clothing store, the first thing you do after seeing something you like is stroke it to determine the ‘feel’ of the cloth.”

We’re still a long way from replicating the fine detail or sheer volume of sensory and control data zooming around the 80 billion neurones and 70km of nerves we each carry. The brain still generates the requisite signals to drive your body whether you’ve lost an arm or your eyesight’s degrading, but “accessing and deciphering them is a monumental task”, says Gregg Suaning, a biomedical engineer at the University of New South Wales in Sydney.

Bionics’ first tentative steps into the area have resulted in a system called BrainGate. At Rhode Island’s Brown University in the U.S., researchers in brain–computer interfaces, restorative neurotechnology and assistive robot technology from BrainGate’s brain– computer interface enables people who have lost the use of their arms to control a cursor with the power of thought.

This tiny neural interface can detect and record brain signals, allowing a direct connection with a computer. Is it so hard to conceive, if these techniques were put together, of a human head attached to a completely bionic body?

It’s tempting to imagine where a few more decades of self-powered robotics, interface technology and fine motor control will lead us. Is it so hard to conceive, if these techniques were put together, of a human head attached to a completely bionic body? Exoskeleton devices that enable paraplegics to walk upright already exist, thanks to motors and actuators for movement and gyroscopes and accelerometers for balance and orientation – just like the ones in your smart phone.

The seamless melding of different disciplines will take bionics to a world beyond mere metal and wires. Wallace can see a future many in bionic medicine considered science fiction only five years ago. “I think there’s a general feeling that we’re going to make very significant progress within a decade,” he says.