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Materials Science in Additive Manufacturing Flexural behavior of bio-inspired sutures

The recent discovery of the suture structure in diabolical structures and understanding the mechanical responses
ironclad beetle (Phloeodes diabolicus) has attracted many and their governing mechanisms [37-39] . FDM printing is a
researchers to study its behavior under different test material extrusion technique where thermoplastic material
conditions . This beetle species acts dead to protect from is melted and extruded through a hot end to create the
[24]
predators since they are unable to fly. The flying beetles printing layers . Performing mechanical testing on 3D
[40]
have hardened forewings, which act as a protection layer printed bio-inspired structures is beneficial in developing
for underlying hindwings [25-28] . The elytra of the diabolical guidelines for future modifications and optimizations of
ironclad beetle perform remarkable crush resistance from the designs. While AM materials have different properties
predators in nature. The tough exoskeleton is a result of than natural materials, continuous structural design
fusion of two elytra by a suture joint, which runs along the optimizations and mechanical testing would help to
whole length of the abdomen. These interlocking sutures with understand the failures, deformations, and damages in
ellipsoidal geometry, known as blades, are tougher than the biological structures [41,42] .
triangular and hemispherical blades, which are commonly In this research work, diabolical ironclad beetle’s
found in other terrestrial beetles. Figure 1D-F shows the suture-inspired designs were printed using polylactic acid
diabolical ironclad beetle, a cross-section of the elytra (PLA), one of the most popular thermoplastic materials
and the suture connection between two elytra. The suture used in FDM printing due to their biodegradability and
joints in diabolical ironclad beetle help to resist bending ease of printing, good strength, and stiffness [43-46] . The
moments to protect vital internal organs. By incorporating flexural behavior was then analyzed using a three-point
interlocking suture interfaces into a biological system, the bending test, followed by digital image correlation (DIC)
energy dissipation of the structure is regulated [24,29-31] . and numerical simulation to provide more insight into the
Most biological structures contain complex hierarchical bending response of the suture structure. As mentioned
arrangements that are difficult to fabricate through before, since the suture joint helps resist bending moments
conventional manufacturing techniques [32,33] . Due to the in the beetle structure to protect internal organs, the
design freedom, quality of the product and process control research is focused on understanding the flexural
ability, 3D printing has the potential to develop lightweight properties of this bio-inspired suture structure. This suture
complex structures [34-36] . Among various AM techniques, interlocking mechanism would be greatly beneficial in
fused deposition modeling (FDM) – a trademark of connecting dissimilar materials without any external
Stratasys or fused filament fabrication – a commonly joining techniques and connecting small parts could
used term by open hardware community/RepRap is a develop large modular parts through interlocking without
convenient printing method for developing bio-inspired limiting to the small print volume in many 3D printers.
A B C

D E F

Figure 1. (A) Skull of a domestic shorthair cat , (B) cranial suture in white-tailed deer , (C) alligator internasal suture , (D) Phloeodes diabolicus,
[22]
[23]
[21]
(E) cross-section of the elytra, (F) suture that connects two elytra (with copyright permission from the journal) [24]
Volume 1 Issue 2 (2022) 2 https://doi.org/10.18063/msam.v1i2.9