Microcomputed tomography scans showing (A) the thorny and tubular layers of the jackfruit with the mesocarp layer in between and (B) a cross-section of the tubular layer. Lazarus et al., Acta Biomaterialia 166 (2023) 430-446.
During impact, cracks propagate between the thorns (A). Significant fiber bridging occurs as cracks propagate (B). cracks prefer to propagate between thorns even under slower loading conditions (C). Reproduced from: Lazarus et al., Acta Biomaterialia 166 (2023) 430-446.
Impact tests on 3D printed samples showing those without thorns crack all the way through whereas those with thorns crack laterally and spread damage across the surface of the material. Lazarus et al., Acta Biomaterialia 166 (2023) 430-446.Researchers have designed impact-resistant materials inspired by the largest edible fruit on Earth, the jackfruit. Ripe fruit can reach up to 50 kg in weight and unripe fruit can survive falls of over 25 m. To withstand high-energy impacts, the fruit has evolved a unique layered structure comprising a thorny exterior and porous inner layer of tubular structures. Now, for the first time, the jackfruit’s remarkable nature has been systematically analyzed [Lazarus et al., Acta Biomaterialia 166 (2023) 430-446, https://doi.org/j.actbio.2023.04.040 ].
“In the past few decades, researchers have turned to nature for blueprints in designing materials with improved properties,” explains first author, Benjamin S. Lazarus. “Biological materials have managed to achieve remarkable mechanical properties that rival the best synthetic counterparts… by forming clever and intricate designs on each length scale, from the macro to the micro and nanoscale.”
But while most attention has focused on the animal world, relatively little has been paid to plants and, especially, the protective exterior of fruits and nuts. Now, the team from the University of California San Diego, Massachusetts Institute of Technology, Universidad Nacional Autónoma de México, University Center SENAI CIMATEC, and the Military Institute of Engineering-IME in Brazil has used tomography, electron and optical microscopy, and mechanical testing to reveal the fruit’s secrets.
“Our goal was to [understand] what makes the jackfruit so impact resistant and [if] the features can be transferred to engineered materials for protective gear, automotive, aerospace or industrial applications,” says Lazarus.
The combination of techniques allowed the researchers to determine the mechanical properties, visualize fracture behavior, and understand how the structure and composition of each layer contributes to the overall impact resistance.
During impact, the tubules in the inner layer deform first, followed by the thorny outer layer, which plays a particularly important role. Consisting of fiber bundles running from the base to tip embedded in a matrix of softer cells, like a fiber-reinforced composite, the thorns withstand large deformations before failing. Their wavy, wrinkled surface densifies during compression and conical shape, which initially collapses at the top while becoming progressively more resistant during axial deformation. Finally, the thorns’ bases are irregular hexagons, deflecting cracks and providing tortuous paths for propagation.
“The layers work together to provide a progressive, graceful failure mechanism, [which] is beneficial because… only one region gives way at a time [instead of] a single catastrophic failure,” points out Lazarus.
3D-printed models mimicking these structural features show markedly better performance and, since they are relatively easy to achieve, hold great promise for engineered materials.