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Spare parts

A bionic eye, a new heart grown in the lab, spinal implants that will help quadriplegics walk again... Will we soon be able to replace any body part at will?

Things have certainly come a long way since Australian scientists first developed the bionic ear 30 years ago.

That first relatively crude cochlear implant has morphed into what one of its creators calls "the world's most sophisticated medical bionics device" — with researchers now working on versions that will allow users to enjoy music and distinguish individual voices in a crowd.

Scientists are now looking at ways of using the experience gained from the cochlear implant to create a range of other spare parts for the human body.

It's an endeavour that puts some unlikely experts together in the same room, from doctors and neuroscientists, to experts in wireless technology, to those developing new types of plastic for replacement parts.

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The bionic eye

If a bionic ear can help the profoundly deaf hear, why not a bionic eye to help the blind see? The drive to develop an Australian bionic eye, one of the ideas to come out of the Australia 2020 Summit last year, recently received $50 million in Federal Government funding.

Researchers are now working on a device that comprises a very small video camera mounted on a pair of eyeglasses. Wireless technology connects the camera to the retinal ganglion cells (a type of neuron located in the retina of the eye), which then sends the visual information to the brain for processing.

"The principle is similar to the bionic ear, but there are a lot more technical challenges," says Professor Rob Shepherd, a member of the team that developed the first cochlear implant and the director of the Bionic Ear Institute, which is collaborating on research into the bionic eye.

While the bionic ear can deliver a useful amount of auditory information with only 22 electrodes, the more complex nature of vision means a useful replacement eye would need at least 100, perhaps even 1000 electrodes.

Bionic eyes are expected to be most useful for people with retinitis pigmentosa, a genetic disease which typically causes vision loss during the teenage years or early 20s, and for older people with vision loss from age-related macular degeneration. Children born blind might also benefit down the track.

While the signals the bionic eye sends will probably be pretty crude compared to normal vision, Shepherd says, the adaptability of the human brain — in particular, its 'plasticity' or ability to learn by forming new connections between neurons — should mean that people with vision loss will eventually be able to interpret the new types of signals.

Australian researchers have already developed a 100-electrode prototype that could be tested in humans within three years, Shepherd says. A world first 1000-electrode model is currently under development here and could be ready for clinical trials in about five years.

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Regenerating hearts

Axolotls and salamanders can do it, so why can't humans? Growing a new limb, or new heart tissue is an automatic response to injury in many reptiles and fish, says Professor Peter Currie, deputy director of the Australian Regenerative Medicine Institute at Monash University.

Apart from bionics, the main strand of research in the drive to create new human body parts is in the field of tissue regeneration. Unlike bionics, which uses engineering to replace damaged body parts, tissue regeneration aims to harness our body's intrinsic capacity to regenerate itself.

"The key will be understanding how the animals that can regenerate do it," Currie says. "Fish are the champion regenerators: if you cut off their fin it will regrow. If you cut their heart, it will regrow."

With cardiovascular disease the leading cause of death in Australia, scientists are trying to find a way of stimulating the human heart to replace or repair muscle tissue.

Unfortunately for humans, once our heart sustains damage — for example, the cell death that occurs during a heart attack — it is damaged for good, a situation which can mean a poor outcome for survivors, including heart failure and death.

Human hearts do have an intrinsic capacity to regenerate, at least in theory, Currie says. They contain cells that multiply in the laboratory when extracted, behaving very much like stem cells — those embryonic or adult cells that have the capacity to develop into any cell in the body.

The challenge for scientists is to find a way of stimulating these cells to start regenerating while they are still in our bodies.

Research groups in the USA and UK are working on a protein called thymosin beta 4, essential for the development of the embryonic heart. It encourages the growth of new heart cells, particularly those related to blood vessels, and improves the function of the heart following damage — in mice at least.

The protein is currently being tested in the first phase of human clinical trials in healthy volunteers and, if safe, will be tested in people with heart damage.

Researchers around the globe are now on the hunt for a molecule that would stimulate regrowth of, not just blood vessels, but heart muscle, Currie says — a breakthrough that would bring dramatic improvements for patients.

Growing an entire human heart in a Petri dish is still a long way off, he says. Although we are beginning to understand how to use stem cells to grow bone, muscle or nerve, we don't yet know how to make a complex system like a heart that incorporates many different types of cells.

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Let them walk again

Swifter results may come from research that combines the normally separate fields of tissue regeneration and bionics.

The emerging field of bionic regeneration is developing polymer implants that can be used to stimulate cell regeneration in people with spinal cord injuries, or other neural or muscle damage that the human body cannot repair on its own.

A team at the Intelligent Polymer Research Institute at the University of Wollongong is working on a bionic polymer implant that could allow paraplegics to walk again. This implant delivers electrical stimulation to the damaged spinal cord, encouraging it to grow and repair itself, while also providing a bio-friendly scaffold for the new cells to attach to.

Polymers are the material of choice for such bionic devices because they are more easily tolerated by the body than metals, but can still be used to conduct an electrical signal. The implants could also contain proteins and other molecules that would help promote nerve growth.

The Holy Grail, says team leader Professor Gordon Wallace, is a device that biodegrades when its job is done, using the energy produced by its own dissolution to power the electrical signals.

Wallace hopes to begin testing the spinal implant in animals within two years, with human trials to follow if successful.

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An expanding catalogue

Fixing a faulty heart, ears, eyes and legs are just the beginning. Faced with an aging population, scientists around the world are working on dramatically expanding the catalogue of available spare parts for the human body, from growing replacement arteries within our own bodies, to developing a robotic arm that can be controlled directly by neural impulses from the brain.

Bionic eye researcher Shepherd believes the country that produced the first bionic ear is uniquely placed to make a contribution to that effort.

"I am very passionate about this subject," he says. "I think there's a real opportunity in Australia to be world leaders in this area."

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