prosthetic limbs can do wonders to restore lost function in some amputees, but one thing they can not do is to restore a precise sense of touch. Now, researchers report that one day in the not too distant, arms and legs may have an artificial sense of touch closely resembling the real thing. Using a two-layer thin flexible plastic, scientists have created new electronic sensors that send signals to the brain tissue of mice that mimic nerve messages of touch sensors in human skin.
Several research teams have long worked on the restoration of touch to people with prostheses. 2 years ago, for example, a group at Case Western Reserve University in Cleveland, Ohio, reported giving people with prosthetic hands a sense of touch by the wiring of the pressure sensors on the hands of the peripheral nerves in their arms.
However, although progress has restored a rudimentary sense of touch, sensors and signals are very different from those sent by mechanoreceptors, natural touch sensors into the skin. For starters, natural mechanoreceptors placed on what amounts to a digital signal. When they feel the pressure, they shoot a stream of nerve impulses; the higher the pressure, the higher the pulse frequency. But past tactile sensors have been analog devices, where more pressure produces a stronger electrical signal, instead of a more common current pulse. The electrical signals must then be sent to another processing chip which converts the force signal to a digital pulse stream that is only then sent to the peripheral nerves or the brain tissue.
Inspired by natural mechanoreceptors, researchers led by Zhenan Bao, a chemical engineer at Stanford University in Palo Alto, California, set to make sensors that churn out digital signals directly. The Bao group began by refining sensors that they first made 5 years ago. In this earlier work, the group designed tiny rubber pillars containing conductive carbon nanotubes of electricity, which were placed on a pair of electrodes together. When no pressure is applied, the rubber, which is an insulator prevents current from flowing between the two electrodes. But when touched, pressure crushes the pillars, pushing drivers nanotubes together to make a continuous electrical path and allowing current to flow. When the pressure is removed, the rubber pillars bounce back to their original shape.
In their current work, Bao and his colleagues turned their pillars inverted pyramids and refined their size so they were sensitive to a range of pressures from a light touch to a handful of steady hand. They also changed the configuration of the electrodes and adds another layer of flexible electronic devices, called ring oscillators, which convert the electrical signals coming out of touch sensitive pyramids to a stream of digital electrical impulses. The result is that, just like the natural signals mechanoreceptors-when more pressure is applied, oscillators prove pulses at a higher frequency.
Bao But the group does not stop there. The Stanford team also wanted to see if brain tissue could receive those signals. This usually done by inserting metal electrodes in the somatosensory cortex called animal and watch their response. But metal electrodes can quickly damage the natural brain tissue, making it impossible to study the transfer of signals over extended periods. So for their study, Bao's team decided to send electronic impulses from touch sensors to a diode that emits light, which turns them into a train of pulses of blue light. The Bao team and in partnership with Stanford colleagues, led by Karl Deisseroth, the genetically mouse somatosensory cortex tissue engineer to absorb blue light and fire in response. They sacrificed some of designed mice and isolated a slice of somatosensory cortex sensitive to light, which remained viable for several hours. Finally, they tested their tactile sensors and monitored if the mouse brain tissue received signals and fired in response. In today Science , they report that the neural tissue of the brain faithfully shooting modes from the touch sensor. This raises the hope that these sensors can possibly help restore a natural sense of touch to amputees, Bao said.
"It's great to see research in this direction, and this document is particularly impressive," said John Rogers, a chemist and expert in flexible electronics at the University of Illinois, Urbana-Champaign. Rogers and Bao notes however that give amputees a natural sense like touch has some way to go. Doctors, for example, will not be able to conceive of human brain tissue to receive light signals. This means that researchers will have to find other ways to transmit electrical signals of a prosthesis in the brain in a way that is safe and stable for long periods of time. Bao said she hopes to use the flexible organic electronics for this task as . well Finally, as these search son are woven together, it is likely to give people with dentures a whole new feel for their environment
(credit video. Bao research Group )
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