A pit viper; (inset) an infrared image of prey. Image: Darbaniyan et al./Matter.
A pit viper; (inset) an infrared image of prey. Image: Darbaniyan et al./Matter.

Converting heat into electricity is a property thought to be reserved for stiff materials like crystals. But inspired by the infrared (IR) vision of snakes, a team of US researchers has now developed a mathematical model that reveals how to convert soft, organic structures into so-called 'pyroelectric' materials. This study, reported in a paper in Matter, proves that soft and flexible matter can be transformed into a pyroelectric material, and potentially solves a long-held mystery surrounding the mechanism of IR vision in snakes.

Materials that convert heat into an electric impulse are termed 'pyroelectric', and this property is typically only found in hard, inflexible substances. The mystery is how IR sensing snakes can achieve this heat-to-electricity conversion despite having a naturally soft anatomy.

"People thought we could explain the IR sensing of snakes if there was a hard, pyroelectric material in their pit organ, but nobody ever found one," says Pradeep Sharma, professor of mechanical engineering at the University of Houston. "So, we wondered whether just as we are trying to make these soft materials pyroelectric, maybe nature is doing the same thing."

Pit vipers and other snakes, like the aliens in the Predator series, are well-known for their heat sensing. In fact, the IR vision of pit vipers is so sensitive that "if an animal appears in pitch black darkness, even for a half a second 40cm away, the pit viper will be able to detect it," Sharma says.

This ability is achieved with a structure called a pit organ – a hollow chamber close to the snake's nostrils containing a thin, flexible membrane. "The pit organ plays an important role in processing heat into a signal they can detect," says Sharma. "However, the missing part of the equation was how the neuron cells within the pit organ membrane convert a heat signature into electricity to create that signal."

Using the physiology of the pit organ membrane as inspiration, Sharma and his team were able to construct a mathematical model to explain how this conversion from heat to electricity could be possible in a soft organic material.

"Our solution is deceptively simple," says Sharma. "Apart from more advanced design elements, to make a pyroelectric soft material all you need is to embed static, stable charges into the material and ensure they don't leak out. Then you must make sure the material is soft enough that it's capable of large deformation in shape and size and has a sensitivity to temperature. If you do that, they will act pyroelectric, and that's what we've been able prove in our model. And we believe that's what exactly nature is using because this process is simple and robust."

Lab experiments using soft materials have already begun to authenticate the model, though further research is needed to confirm whether this proposed mechanism is taking place in the neuron cells of the snake's pit organ membrane. Earlier work had implicated protein channels located within the membrane's neuron cells as playing an important role; however, the relation of those channels to the proposed mechanism in the paper is currently unknown.

"Using this model, I can confidently create an artificial soft material with pyroelectric properties – of that there is no doubt. And we are fairly confident that we have uncovered at least part of the solution of how these snakes are able to see in the dark," says Sharma. "Now that we've developed the model, other scientists can come forward and start doing the experiments to confirm or deny whether our theory about snake IR sensing is correct."

Next, Sharma wishes to continue his research into soft matter, exploring how to manipulate soft materials to generate electricity solely from a magnetic field. With enough research, Sharma hopes to inspire the development of pyro-, piezo- and magnetoelectric soft materials, expanding the possibilities of how we generate electricity.

This story is adapted from material from Cell Press, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.