Inspiring though his story is, there are already available much more sophisticated, anatomically correct prosthetics, some even seamlessly controlled by the brain itself. Yet, for the longest time, prosthetics wasn't too attractive a sector: Amputees were usually old and poorer folks with uncontrolled diabetes or other vascular diseases. With just a million amputees in America, a tiny market by US standards, it was not worth investing to develop high-tech, lifelike bionic parts.

Then came the mounting number of injured soldiers serving in Iraq. Improved body armour, speedier evacuation of casualties and better emergency surgery resulted in more survivors - but also more amputees. These amputees were a different breed though: Young soldiers whose warrior ethos - never accept defeat - meant they demanded more than your grandfather's prosthetics.

The US Department of Defence (DOD) rightly felt obliged to do something, so it began pouring money into research. For instance, there is a US$48.5 million (S$66 million) project to build a thought-controlled upper limb system by next year that will look, feel and be at least as strong as the real thing.

Most motorised limbs currently available are strapped against a shoulder and controlled by sensors on an amputee's own arm that can read muscle contractions. Since 2005, doctors have been able to take nerves from the shoulder that used to go to the arm and transfer the nerves to chest muscles. Now a patient just needs to think about what he wants the arm to do, and electrical signals from the chest muscles will 'tell' the prosthetic limb to do just that.

If the patient thinks: 'Open hand', the relevant part of his chest muscles contracts and electrodes detecting these contractions inform the computerised arm to open the hand. Because the sensation nerves to the hand can also be re-routed to the chest, when the patient is touched on the hand, she can feel it.

Eventually she would be able to 'feel' what she is touching with the hand. The hand now comes with five individually powered fingers that have miniature hydraulics and can be moved independently of one another.

The moveable finger joints mean that the hand is nimble enough to do keyboard work, pick up styrofoam cups without crushing them and lift 20kg loads. In January, a Scottish firm came up with the I-Limb System that can do hundreds of push-ups, lift very heavy loads and whose wrists can rotate 360 degrees. A lethal weapon?

Still, while you can 'think' open and close the hand or rotate the wrist, you can't do all of the actions simultaneously. As a result, even picking up a jug to pour some milk remains a cumbersome multi-step process.

But look for a quantum leap from the DOD project. Go to www.ted.com/talks/view/id/82 for a video preview of the amazing progress already achieved in developing a solution for double shoulder disartics, or amputees who have lost both upper limbs.

By contrast, lower limb prostheses are harder to perfect. Though they don't perform the precise and fine functions that hands and fingers are made for, the lower limbs have to bear our body weight, so they require more power.

Traditional lower limb prostheses were quite heavy and uncomfortable because they required a waist belt to swing the legs with each step. The hips did all the work to draw the feet forward, so the back tended to get sore by day's end. Socks were stuffed between prosthesis and stump to cushion the impact but chafing still occurred.

These days, scanner technology enables silicon gel cushions to be customised for the stump. There is less perspiration and so less chafing too. Thus peg legs, with the best socket technology, could well suffice for some. Painlessness in use may be the most important consideration here.

But young amputees want to be able to return to an active lifestyle. So artificial intelligence is being added to a prosthetic knee system to enable it to adapt and learn from your gait to optimise control. By taking angle and force measurements over 1,000 times a second, the position-sensing, load-

measuring microprocessors enable the knee to detect, respond to and keep pace with changes in how fast you are walking, the load you are carrying and the terrain you are tackling.

The motor-powered, tendon- like springs propel you over irregular ground so your gait is smoother than it would be with conventional systems. The springs also do not buckle easily, so you are less likely to stumble.

Last July, the Massachusetts Institute of Technology developed the first motor-powered, computer-controlled prosthetic ankle- foot system which can relax or stiffen as the terrain demands. Heavier than the traditional prosthetic foot, it uses a motor instead of human power, so it requires less energy. The eventual aim is to replicate current success with upper limbs so that intelligent knee-ankle-foot systems can be controlled directly by the brain.

But the power source remains a problem. Batteries need to be large enough to last a long time before they need to be recharged but not so heavy you waste energy lugging them around in your 'legs'. Scientists are looking at piezoelectric materials that produce electricity on their own when they are mechanically deformed - pulled, stretched, compressed, etc. This may be one way to create self-powered prostheses.

An out-of-the-box solution could well be exoskeletons. Think of Ironman. The DOD is investing US$50 million to develop an exoskeleton suit that soldiers can wear that would mimic everything they do, just better. With it, they could run faster, carry heavier weapons and leap over higher barriers. View its prototype - the XOS - at engadget.com/2007/11/

25/sarcos-military-exoskeleton-becomes-a-frightening-reality/ and be blown away.

At the Barrier Free 2008 trade show in Osaka late in April, visitors tried on Honda's 'walking assist device'. Made using its own ASIMO robot technology, the wearable exoskeleton has sensors to sample hip angles and force continuously so that the wearer is always kept upright. Its many motors increase the stride, so the elderly wearer can walk around more confidently, even with heavy loads.

One day soon, growing old might not entail becoming physically challenged too.

andyho@sph.com.sg