I use this blog as a soap box to preach (ahem... to talk :-) about subjects that interest me.

Saturday, July 31, 2010

Technology that gets under your skin

For the Merriam-Webster dictionary, Bionics is “a science concerned with the application of data about the functioning of biological systems to the solution of engineering problems”(1). Similarly, Wikipedia defines Bionics as “the application of biological methods and systems found in nature to the study and design of engineering systems and modern technology”(2). Bionics has many applications, but what interests me is that it helps develop devices that support, enhance, or even completely replace functions of the human body. And to do their job, such devices must become part of the people who carry them. They represent the first steps of man-machine integration.

Pirate and adventure films have made us all familiar with examples of Bionics in the form of wooden legs and metal hooks replacing amputated hands. But prostheses have come a long way since those primitive devices. Modern artificial limbs, and in particular artificial hands, are very complex objects full of electronic circuitry. Sensors attached to the nervous system or the muscles of the amputee allow him to control the movements of a bionic limb. After a period of training, the movements of the artificial limb feel very similar to those of the natural limb before the amputation.

When you attempt to make a movement, the part of the brain in charge of movement control sends to the appropriate muscles electrical signals. These signals travel via nerves and cause on the skin surface weak but detectable voltage levels. Modern bionic limbs measure the voltages present on the skin to estimate strength and destination of the nerve signals. They then use that information to control mechanical actuators that emulate the muscles. This makes possible for an amputee to perform most of the operations he was able to do with his natural limb.

The bones and tendons of mechanical limbs are made of steel and aluminium, and their muscles consist of electric actuators. This makes them potentially much stronger than their natural counterparts. It is therefore not surprising that some bioengineering companies have looked at ways of using the same technologies to strengthen able men. Perhaps the greatest advances in this area have taken place in Japan, which is a leader in the design and manufacturing of industrial robots.

 Figure 1: HAL 5(3)

Figure 1 shows HAL 5, a robot suit(4) specifically designed to increase physical capabilities. It weighs approximately 23 kg and if it is not already in full production when you read this post, it should happen soon. I have read that it could be yours to use for some fifteen thousand dollars plus a yearly maintenance fee.

Military organisations in most developed countries, and in particular the American Defense Advanced Research Projects Agency (DARPA), are very interested in this type of research. Already in the year 2000, the U.S. Army Natick Soldier Systems Center (NSSC) developed the Future Warrior Concept (see Figure 2), which included the following central subsystems tailored to each individual:

  • The Information Central, located in the headgear and providing maps, 180° display, very high speed broadband communication link, sensors covering 360°, and head protection.
  • The Survivability Central, consisting of the following three layers of combat uniform: a protective outer layer made of electro-spun nanofibres, a power layer to augment the physical strength of the wearer, and the life critical inner layer. The life critical layer, directly in contact with the body of the wearer, is intended to have a monitoring function of vital signs, hydration state, stress level by means of mouth sensors, thermal state, sleep status, and workload capacity. Additionally, it includes a network of narrow tubing providing heating or cooling as needed. The life critical layer can also be used to administer nutrients, drugs, and other chemicals in response to injuries or other abnormal conditions.
  • The Duration Central, consisting of a micro turbine generator. Each plug-in fuel cartridge can supply the necessary power for up to six days.

In future, soldiers on the battlefield will be nodes of a tactical network. They will be able to exploit the latest sensing and communication technologies to gain full awareness of their environment. A robotic suit will provide a protective exoskeleton while at the same time augmenting their physical capabilities. Robert Heinlein described something very similar in his novel Starship Troopers, published for the first time in 1959, but they will become reality in just a few years, well before humanity will reach the stars.

 Figure 2: The Future Warrior Concept(5)

Robotic suits are exciting stuff, but other applications of bionics have proven themselves extremely useful for a wider part of humanity to overcome impairments. One example is the cochlear implant, often called bionic ear. Over the past forty years, more than one hundred thousand people worldwide have gained or regained their sense of hearing thanks to this device. It consists of two parts, one surgically implanted on the side of the head, and one external. The two parts communicate through skin and muscle via radio waves.

As you can see from Figure 3, the implanted part consists of a thin electrode that coils inside the snailshell-like cochlea and a thicker part housing the radio antenna and electronic circuitry. The external part consists of a headpiece with the antenna (visible in Figure 3), a microphone, and a sound processor.

Figure 3: The cochlear implant(6)

Normally, hearing cells stimulate the auditory nerve in response to mechanical stimuli from the inner ear. When these cells are unable to perform their function, the result is one form of complete deafness. The bionic ear resolves the problem by capturing sounds with the microphone, converting them to the appropriate electrical signals with the sound processor, and directly stimulating the auditory nerve with its thin electrode.

Hip and in general joint replacements are other applications of bionics that have become commonplace. Although they require more invasive surgery than bionic ears, such operations are conceptually simpler, and a well established industry has developed around them. The same is true for artificial heart valves. But the replacement of a whole heart with an artificial one is another matter.

Over the past decades, heart transplants have almost become routine. More than two thirds of the patients live longer than five years after the operation, and some conduct a normal life for decades. But all around the world the number of people in desperate need of heart replacement significantly exceeds the number of donors. Moreover, transplant recipients are forced to take anti-rejection medication for the rest of their lives. As immune rejection is caused by differences between the genetic make-ups of donor and recipient, an artificial heart causes milder reactions.

With the current level of technology and medical care, an artificial heart can extend the life of the recipient by longer than one year. Although this is not enough to make artificial hearts suitable as permanent replacements, it is often sufficient to keep the patients alive until a donated heart becomes available. One of the most successful artificial hearts to date is the Jarvis-7 heart, implanted in hundreds of patients since 1982(7).

In any case, while natural organs continuously regenerate and repair themselves and can therefore last for decades, the mechanical components of their artificial counterparts are subject to wear and fail after maximum a few years of operation. The biotechnologists need to overcome this obstacle if artificial hearts are to become truly permanent.

There are many other prostheses in different stages of development. For example, retinal implants aim at restoring eyesight by converting light to electrical impulses and then directly stimulating the optical nerves. This follows the successful strategy adopted for the bionic ear and has had some limited success.

All the examples I have presented so far consist of self-contained electromechanical devices to replace or complement the functioning of limbs and organs. But several researchers are concentrating their efforts in a different direction. They use active electronic circuits to stimulate or suppress individual functions of our organs.

The most widely known example of this category of applications is the heart pacemaker.
The human heart, like the heart of all mammals, consists of two pairs of chambers. The pair on the right side pumps blood to the lungs where it can absorb oxygen. The pair on the left side pumps blood through the whole body so that it can deliver its oxygen to where it is needed. Each pair consists of two chambers connected via a unidirectional valve, similar to the valves found in bicycle pumps. When the first chambers of the pairs (each called atrium, a Latin word that means courtyard) simultaneously contract, the blood they contain is pushed through the valves to the corresponding second chambers (each called ventricle, from a Latin word that means small belly). A tenth of a second later, a second contraction squeezes the ventricles and pushes the blood out of the heart.

This pumping cycle, our heart beat, repeats on average eighty times a minute. Each cycle starts when a group of nerve cells located in the right atrium (called sinus node) cause the heart to contract by stimulating it with electrical impulses. When the sinus node doesn’t work properly or when the electrical impulses it generates fail to reach their destination, it becomes necessary to stimulate the heart with an artificial pacemaker.

Modern pacemakers can control all four chambers of the heart. They can also sense changes in the movement and respiration of the carrier and adjust the pulse rate accordingly. Furthermore, they only operate when they detect that the heart needs pacing, thereby extending their operational life to ten or more years.

The great new frontier in implants is in direct brain stimulation. As scientists gain a better understanding of how the brain works, new techniques become available to control the effects of brain damage and brain diseases. Deep brain stimulation is making possible for people with Tourrette syndrome and Parkinson’s disease to conduct an almost normal life. The epileptic crisis suppressor works along similar lines but operates on different parts of the brain. How long before you will be able to buy a device to stimulate the pleasure centres of your brain?

(1) http://www.merriam-webster.com/dictionary/bionics
(2) http://en.wikipedia.org/wiki/Bionics
(3) http://www.cyberdyne.jp/english/robotsuithal/img/img_robotsuithal.jpg
HAL™ is a trade mark of Cyberdine Inc., and stands for Hybrid Assistive Limb.
(4) ROBOT SUIT® and CYBERDYNE® are registered trademarks of Cyberdine Inc.
(5) Obtained from http://www.natick.army.mil/soldier/media/fact/individual/FW.htm
(6) Public domain image provided by the National Institutes of Health (U.S.A.) and downlodable from http://en.wikipedia.org/wiki/Image:Cochlear_implant.jpg
(7) http://www.jarvikheart.com/basic.asp?id=69

No comments:

Post a Comment