New artificial skin can feel real pain


(CNN)Pain may not be desirable, but it's essential for survival. An effective and sophisticated defense mechanism, pain is our body's way of telling us that something's wrong and that we should take immediate action to avoid injury.

Skin -- the body's largest organ -- is constantly monitoring for pain. It can trigger pain-avoiding actions automatically through reflexes, for example when we touch something dangerously hot.
Now, researchers at RMIT University in Melbourne, Australia, have created an artificial skin that mimics this mechanism and reacts to pain stimuli.
Made of silicone rubber, it has the texture of real skin and is also "very similar to skin in its mechanical properties," says Madhu Bhaskaran, an engineering professor at RMIT University and the project's lead researcher. 
It could lead to groundbreaking innovations in prosthetics and robotics.
The skin is made of silicone rubber, which is also used in some types of contact lenses.

Fast response

Just like real skin, the artificial version is designed to react when pressure, heat or cold surpass a pain threshold. Its outer layers sandwich electronic circuits studded with sensors, which respond to stimuli.
"The fascinating thing about our body is that it works by sending electrical signals into a central nervous system," says Bhaskaran. Electronic circuits work in a similar way, and are just as fast, she explains.
When we touch something burning hot, pain receptors in our skin send an electrical signal through our nerves to the brain. The brain sends its own electrical signal to initiate a response -- for example a withdrawal reflex to move the affected limb away from the heat.
In much the same way, when one of the sensors in the artificial skin detects a pain stimulus, it sends an electrical signal to the brain-mimicking parts of the structure, Bhaskaran says. This can be programmed to trigger a movement.
"The key here is thresholds," says Bhaskaran. She explains that although we sense stimuli constantly, we only react when the stimulus exceeds a threshold, "like touching something very hot." The brain and the skin compare stimuli and identify which are dangerous, she says. When creating the artificial skin, the scientists set those thresholds for the brain-mimicking electronics.
The result is artificial skin that can differentiate between the gentle touch of a pin or a painful stab.
Just like real skin, the artificial one is also stretchable.

Smart prosthetics

The artificial skin could help to create smart prosthetics covered with a functional skin that reacts to pain like human limbs, allowing the wearer to know if they're touching something that could cause damage.
"We've come a long way with prosthetics, but the focus has been heavily on the motor actions that the prosthetic limb can perform," says Bhaskaran. Because conventional artificial limbs don't have skin, they don't sense external dangers. "Having a skin-like layer would make it much more lifelike," she says.
Steve Collins, an expert in prostheses and exoskeletons at Stanford University in the US, who is not involved with the project, agrees: "When a person loses a portion of their limb to amputation, they lose not only bone and muscle but also somatosensory organs," he says, referring to organs that provide sensations like heat or pressure. While structure and movement have received a lot of attention in prosthesis design, sensing may be the key to obtaining human-like performance with artificial limbs, he says.