Newswise \u2014 Nature has invented countless types of pointy appendages, and scientists have long sought to explain what makes these structures so effective at puncturing other things. A new study models the key physical characteristics of puncturing tools to reflect their diversity in nature, finding that the shape of a biological tool is driven in part by tradeoffs between its puncture efficiency and its ability to resist bending or buckling.<\/p>\n
The findings are described in the journal Science Advances.<\/p>\n
\u201cThere\u2019s a vast diversity of puncture tools in nature, like fangs and stingers and spines and thorns,\u201d said Philip Anderson, a professor of evolution, ecology and behavior<\/a> who led the new research. \u201cIt\u2019s ubiquitous across the entire tree of life, including plants, animals, fungi, bacteria, and viruses.\u201d<\/p>\n Anderson has spent more than two decades studying how the laws of physics and biomechanics influence evolutionary processes, focusing primarily on the predatory or defensive structures that plants and animals use to damage, impale, grasp, impede or inject defensive compounds into other organisms.<\/p>\n For the new study, he and his colleagues looked at tools across plant and animal kingdoms to try to identify common physical attributes.<\/p>\n \u201cScientists are interested in finding underlying physical laws that all this diversity has to adhere to,\u201d Anderson said. Studies often focus on a single species at a time, examining things like the shape of its tool, the speed at which it is deployed and the efficiency with which it punctures a given material. The findings are sometimes reported as if they reflect universal physical laws.<\/p>\n \u201cBut when it comes to biology, I think we need to embrace the diversity of it,\u201d Anderson said. \u201cIf there was a universal law, then I would expect all puncture tools to look more similar to each other, but they don\u2019t. There\u2019s great variety in how these puncture tools work.\u201d<\/p>\n To better understand the principles driving such diversity, Anderson and his colleagues digitally modeled the primary characteristics of puncture tools in nature.<\/p>\n \u201cWe took two very basic measurements, one of which is its taper,\u201d he said. \u201cIf you look at a puncture tool from the side, is it a big broad triangle, like a shark\u2019s tooth? Or is it a thin, elongated triangle, like a fang? And then we also looked at its cross-section. Is it more round, like an elephant\u2019s tusk? Or is it flattened, like a stingray barb?\u201d<\/p>\n Years of studies of the puncture performance of differently shaped tools have shown that while pointed objects that are rounder in cross-section may do a good job of initiating a fracture, flatter tools are likely to penetrate a material more deeply because they do not have to displace as much of the target material, Anderson said.<\/p>\n \u201cThe flatter it is, the easier time it should have inserting itself, because it has to push the material apart less,\u201d he said. \u201cYou\u2019re making a very thin wound versus a wide, circular one.\u201d<\/p>\n But flatness comes with other concerns, he said. Flatter materials may be more susceptible to bending or buckling, which could be detrimental to the organism. So, the researchers also calculated each tool\u2019s ability to resist buckling.<\/p>\n In simulations, the team compared the puncture performance of 25 cone shapes that varied in both taper and cross-sectional shape \u2014 equivalent to the variation seen across the more than 140 biological puncture tools they measured. For each of the 25 cone models, they calculated \u201chow much energy it takes for a tool to create a fracture and insert itself\u201d to a specific depth, Anderson said.<\/p>\n The long list of species that guided the dimensions of the cones reflects the diversity of tools found in vertebrates, invertebrates and plants.<\/p>\n The analysis revealed that some cones performed better than others across both puncture efficiency and buckling resistance.<\/p>\n \u201cWe could see a combined performance, where maybe you\u2019ve got a tool that\u2019s decently resistant to buckling and also does a good job of puncturing. But if you tried to make it better at resisting buckling, you would lose puncture performance, and vice versa,\u201d Anderson said. \u201cSo, you\u2019re almost looking for a middle ground where both of these types of performance are being as optimized as they can be.\u201d<\/p>\n The cones with the highest performance on both measures include those whose taper and roundness were most like a scorpion\u2019s stinger, a king cobra\u2019s fangs, a rose prickle, a shark tooth, the talons of a red-tailed hawk, the mandibles of an army ant and the love dart of at least one land snail, Anderson said.<\/p>\n Just as interesting, he said, was a look at cone types that punctured efficiently but were more susceptible to buckling. This includes cones shaped more like cactus spines, which are more disposable, say, than something like a carnivore\u2019s canines \u201cso it doesn\u2019t matter if they break.\u201d<\/p>\n Tools like a carnivore\u2019s canines appear to be more optimized to resist buckling, but puncture less efficiently. This may reflect their function, Anderson said. Perhaps for some species it is more important to be able to grasp their prey with their teeth than to pierce the flesh of their targets and risk breaking their teeth.<\/p>\n \u201cA mammal doesn\u2019t want to break its tooth because it only gets two: the baby tooth and the adult tooth,\u201d he said. \u201cSo, evolutionarily, it\u2019s more important. You get better survivorship if you prevent that tool from breaking.\u201d<\/p>\n Similarly, fish spines may do more to protect the animals from being eaten than to pierce the flesh of potential prey.<\/p>\n \u201cIt may not be that the fish need to be puncturing other animals,\u201d Anderson said. \u201cMaybe they\u2019re just making themselves too big to swallow.\u201d<\/p>\n Anderson said the findings should be useful to the field of bioinspiration, where new tools are designed to reproduce the form and functionality of something found in nature.<\/p>\n \u201cRather than looking at just one organism at a time and saying, \u2018We\u2019re going to mimic that,\u2019 I think we\u2019re finding that it would be more useful to look at overall trends, to see what a range of biological puncture tools are doing, and draw inspiration from that,\u201d he said.<\/p>\n Anderson also is an affiliate of the Beckman Institute for Advanced Science and Technology<\/a> at the U of I.<\/p>\n The National Science Foundation supported this research.<\/p>\n