Why are nuts hard to crack? This question is answered in reports in Science (AAAS) News, 10 August 2021, Royal Society Open Science 11 August 2021, doi: 10.1098/rsos.210399 and Advanced Materials 20 October 2020, 10.1002/adma.202004519.
Over the last few years Notburga Gierlinger, a biophysicist at University of Natural Resources and Life Sciences, Vienna, and colleagues have been studying some of the world’s toughest nuts, including pistachio, walnut, pecan, hazelnut, and macadamia to find out what makes them so resistant to cracking. The researchers have studied the biomechanics of their shells and examined their microscopic structures, and how the shell components are combined to give them strength and resilience.
At the microscopic level walnuts and pistachios shells were the hardest to break due to tight coils of fibres in their cell wall along with the cells having a complex interlocking structure. Each cell has lobes and indentations that fit together like a three-dimensional puzzle. This gives the cells a huge surface area for gripping surrounding cells. The researchers found it was impossible to pry the cells apart. Cracks in the shells went through the cells, like breaking the puzzle pieces of a 3D puzzle, rather than separating them.
Pistachio shells had the most interlocking lobes, and were the hardest to crack. Pistachios normally open along a naturally formed suture line, but anyone who has tried to crack unopened pistachios will know how hard they are to break into despite their thin shells.
Overall, nuts gained their strength from combinations of components including cells with hard dense cell walls, thick tough fibrous tissue, and in the overall size and shape of the nut. The research team wrote: “On the macroscopic scale, strengthening occurs via an increased shell thickness, spherical shape, small size, and a lack of extended sutures”.
Editorial Comment: Macadamias score highly in three out of four of the properties listed by the researchers. They are spherical with small sutures, and have thick, fibre reinforced shells, which makes them extremely strong in terms of how much compression force is required to break open a whole nut. A normal nutcracker is not enough – just ask any Australian who has tried to crack them by bashing them with a hammer or squeezing them in an old-fashioned carpenter’s G-clamp. This is quite an art, as the nuts are smooth, round and hard to hold. Also, a macadamia kernel is soft, so if you use too much force you end up with a smashed kernel with hard sharp shards of shell embedded in it. (Both editors of this newsletter know this from experience.) Fortunately, for macadamia nut lovers, more efficient industrial methods have been developed for cracking them without smashing the kernels, but it took clever creative design to do this.
Note that it is not just substance these nutshells are made of, but the organisation of the materials that resulted in their toughness. Industrial designers and engineers know this well, and are working on creating strong materials inspired by strong materials found in living things. These biomimetic materials involve similar mixes of intricate geometry and clever combinations of materials with different but complementary properties. Usually this design process involves computer modelling and experimental trials, all of which involve knowledge of geometry and properties of materials, before getting it right.
Therefore, when you crack your favourite nuts give thanks to the Creator who made the original shells using materials He created according to His pre-created laws of physics and chemistry that He built into the world.
Creation Research News 20 October 2021
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