Studying live animals is never easy, as the animal usually has to cooperate to some extent. For many animals, biologists have therefore resorted to attaching tracking devices to their ears, paws or skin, allowing them to keep an eye on the animals using radio transmission, acoustic devices or even cellular and satellite tags. But what do you do with animals that are small, fragile and live in environments not suitable for electronics? In other words, what do you do when working with small fish? Well, researchers from the New Mexico State University have found a solution with custom 3D printed fish backpacks – which actually enable them to study tissue regeneration in the fish.
To be sure, fish could previously already be equipped with tags and clips that can track movement, but many biologists are interested in far more complex data, such as electric activity on a cellular level. And that is where these ‘fish backpacks’ come in, which have been pioneered by professor of biology Graciela Unguez, professor of engineering Wei Tang and a team of undergraduate students. The concept was already presented at the international conference of the IEEE Engineering in Medicine and Biology Society in Italy this summer, and was the result of a two-year research collaboration that also included local systems engineering company Visgence.
Through this collaboration, these special fish backpacks were actually 3D printed to fit as snugly around fish bodies as possible without damaging the skin. “We are calling it a backpack because that’s what it is,” said Unguez. “It is attached to the fish like a backpack and the fish will be carrying equipment.” They are obviously 3D printed in non-conducting materials, and actually feature various small holsters that enable the fish to carry gear around for various applications.
While the concept of a fish backpack is simply very cool, the real breakthrough is in the fact that this brings electrical manipulation to underwater research – where it was previously impossible due to environmental limitations and equipment corrosion. The system itself contains a remote control, a stimulator circuit, a strong battery (lasts for more than 100 days), and provides valuable assistance in neuroscience research. “The stimulation pattern is a simple square pulse waveform,” said Tang, who led the design process for the system’s sensor and stimulator circuits. “We can control the amplitude and the repetition rate of these pulses.”
The first fish to actually be wearing this special gear are the lab’s long-tailed knife fish, and the packs are helping the biologists to study their nervous systems and their relation to regeneration through changing stimuli. “What I’m studying is looking to understand what role the nervous system has on regeneration if we’re removing inputs to the nervous system. Does it come back, what size, or what does it heal?” said Unguez. “So as they’re free swimming, we provide different stimuli. We want to know what impacts the inputs have on regeneration. To us, we cut our finger and it doesn’t come back, but we want to know how they do it and then one day maybe apply it to those animals that cannot.”
The long-tailed knife fish (also known as yellow-stripe fish) can be found south of the equator in South America and Africa, and are especially knowns for their ‘electric organ’. This generates an electrical field around the body, and it is believed that it helps the fish regenerate lost cells, tissue and even organs – just like how lizards can regrow tails. The electric organ’s cells actually develop from the fish’s skeletal muscle. Without any exterior manipulation, it allows for tissue restoration when a portion of the fish’s tail is removed or injured. Thanks to the 3D printed backpack, Unguez can effectively modify the electrical activity through the backpack’s stimulator circuit, and collect electrical pattern data from these regenerative experiments.
Of course electricity is present in every creature, and relies on very complex brain circuitry. But even that can be manipulated, and this study could yield clues as to how that can be achieved. “We can then start studying how the different types of stimulation that we deliver can affect the fish’s ability not only to regenerate its tail, but also to change the properties of skeletal muscle and electric organ tissues,” Unguez said. “An ideal, dream question is: Is it possible for us to convert some of our muscles into an electric organ, or a completely different cell type that we don’t have? I think the answer is yes – it’s just a matter of those electrical activity patterns basically giving the cells different signals, telling it what to make, what not to make, what shape to take on, etc.”
But the potential of these 3D printed backpacks goes even further than their current setup. They could be used to track multiple fish simultaneously, or they could be linked to wireless sensors to study the electric discharge of entire schools of fish. “To have the capacity to remotely record and gather data from fish 24/7, that’d be great,” said Unguez. “We hope that a lot of people in our scientific community can see this as an opportunity for underwater research.” Besides tissue generation, electric circuits use for navigation, mate selection, communication, finding prey and self-defense could also be studied in the future.
What’s more, Unguez already said that the same principles could be applied to creatures living out in the wild for a variety of other research purposes. “I have my specific interests, but I think that having this available, anything that you may want to put on fish, you can. It just becomes an issue of what you want to put on, but that hasn’t even been available (in the past),” said Unguez.“Such as does it change its pliability or flex? Then we would do tests in seawater. So we would test different things and then put it out there and people will be creative in using it how they want.” More will be revealed in a forthcoming paper that covers the 3D printing process and results on how the packs changed over long-term use.