When D≫D0,  asymptotes to the scaling law σts∝D−1/2 predicted by LEFM (26⇓–28). We model the spicule as a tight, coaxial assembly of annular, cylindrical beams (30) with a single solid beam at its center. In the constant-area, constant-thickness, and aggregate load capacity plots ρ0=0.0. Once we have an accurate model, we could use the equations to design spicule-like, layered beams that are much stronger than today’s state-of-the-art structures. These silica cylinders decrease in thickness from the spicule’s core to the periphery (22⇓–24) and, inspired by their internal geometric regularity, the goal of this study was to explore additional mechanical benefits of the spicule’s laminated architecture.
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The black crosses correspond to ρn=ρ^n, the optimal-strength radii sequence, for ρ0=0.0, 0.4, and 0.5. We quantitatively compare the measured radii sequences with the optimal-strength radii sequence and also with several alternate radii sequences (Discussion, Comparison of Measured and Optimal Radii Sequences). 1 A and B). Unlike a soft, squishy kitchen sponge, the marine sponge that I study, Euplectella aspergillum, is stiff and strong. The most famous glass sponge is a species of Euplectella, known as the “Venus flower basket,” which builds its skeleton in a way that entraps a certain species of crustacean inside for life.
Specifically, we explored the possibility that the structural feature of decreasing silica cylinder thickness is an adaptation for increasing the strength of spicules under a wide range of external loading regimes. (Image Credit: Espinosa et al., Nature Communications 2, 173 2011). As can be noted from Table 1 and Fig. A Increase font size. Structure of Leucosolenia 3. However, whether the spicule’s architecture is a simple outcome of its growth process or is specifically optimized for multifunctionality, it clearly offers the sponge skeleton an exceptional mechanical advantage. Although the distal region of each spicule that is located beneath the sediment surface is subjected to a diverse set of mechanical loads, from the shape and position of the surface barbs, we infer that the spicules are primarily loaded at the barbs by a system of forces that act in the proximo-distal direction (Fig. 1C). For example, the shell protects the clam from predators.
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The interfaces between the bricks in this wall prevent cracks from growing in a straight path through the shell. We do not capture any email address.
We take ρ0 to be nonnegative and less than unity.
(C) A scanning electron microscope (SEM) image of the distal end of an anchor spicule, showing the spicule’s terminal crown-like structure and its recurved barbs. S2). In SI Text, section S6 we show that the silica cylinder thicknesses are smaller than an estimate of the cylinders’ critical length scale. This difference suggests that there is something missing in our model, and that we need to go back and revise these equations. However, we believe that this last assumption is justified for the following reason. The animals eventually grow too large to escape the sponge, so they are forced to "stay put" for the rest of their lives. The structural principles obtained from this study thus provide potential design insights for the fabrication of high-strength beams for load-bearing applications through the modification of their internal architecture, rather than their external geometry. See SI Text, section S7 for details. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1415502112/-/DCSupplemental. The results corresponding to the τnn that produced the smallest d value are also shown in Table 1. Each spicule is covered with recurved barbs and has an internal architecture consisting of a solid core of silica surrounded by an assembly of coaxial silica cylinders, each of which is separated by a thin organic layer. An alternate mechanics model based on the idea of controlling flaws has been put forward to explain the trend of decreasing thicknesses in the spicule’s internal structure (32). For ρn to be well defined it is necessary that n>1. In fact, T depends on all of the constants x=(ϱ0,…,ϱn,ε0) and the radii sequence ρn, because M depends on ϱj and ρn, andT=MGa,where G is a positive constant. In our model, we quantify the spicule’s ability to function as an effective structural element by its load capacity, which we define as the largest tensile force that the spicule can transmit from its surface barbs to the skeleton without failing. This evolutionary process can produce extremely efficient mechanical designs that often look nothing like those used in the engineered world. The origin is chosen to be the centroid of Ω and x1, x2 are the Cartesian coordinates in the e^1, e^2 directions, respectively (Fig. For example, I am studying sponges that live at the bottom of the ocean to learn new ways to make stronger beams – the structures that hold up everything from our homes to the frames of our cars and the bridges we drive over. Clam shells are tough because this mineral is not randomly packed together, but rather is arranged in a pattern that looks like a microscopic brick wall. It has an amazingly complex skeleton that consists of an intricate assembly of fibers, known as spicules, no larger than a human hair. This article is a PNAS Direct Submission. The intricate skeleton of Euplectella aspergillum (left), and the Eiffel Tower (right). We use  for modeling σ33 because it is the simplest form that allows a tension and a bending moment to be transmitted across Ω. For reference, we also computed d with ρ^n replaced by radii sequences for which the cylinders’ cross-sectional areas and thicknesses are, respectively, constant.
From the resulting images, we measured the sequence of silica cylinder radii by fitting circles to the cylinder boundaries starting with the spicule’s core (Fig. Then, through natural selection, organisms with better designs often outlive those with worse ones and hand off the blueprints of those designs to their offspring through genetic inheritance. Using a newly developed structural mechanics model for composite beams, we demonstrate that the unique internal geometry that maximizes a beam’s strength correlates well with the geometry observed in the native spicules. This prediction can be interpreted to mean that the cylinders will all fail at once. (ii) An individual cylinder fails when the normal component of the traction σ33 on its cross-section exceeds its bulk tensile strength. v) We found that the thicknesses corresponding to ρ^n decrease from the spicule’s core to its periphery. To thoroughly test our hypothesis, it is necessary to confirm some of our model’s key assumptions, such as (i) that the spicule fails according to the failure criterion outlined in Results, Spicule’s Load Capacity and (ii) just before failure, σ33 on Ω varies in an optimal fashion so that the spicule’s load capacity is as large as possible. The most famous glass sponge is a species of Euplectella, shown here in the northwestern Gulf of Mexico.
Because we treat each of the cylinders and the core as structural beams, the maximum principal stress at every point within the spicule is σ33.
If you cut one open, you’ll find that the spicule’s glass is arranged in concentric layers that look a lot like tree rings. These results demonstrate that the spicule’s internal structure is consistent with our model, supporting our hypothesis that the internal structure is an adaptation aimed at increasing the spicule’s load capacity. Researchers are using the glassy skeletons of marine sponges as inspiration for the next generation of stronger and taller buildings, longer bridges, and lighter spacecraft. Favorite Answer. By subscribing you become an AG Society member, helping us to raise funds for conservation and adventure projects.
3B). (B) A close-up of a group of anchor spicules. My research focuses on a specialized group of spicules that act like roots to anchor the sponge to the soft sediment of the ocean floor. Vincent JFV (1990) Stiff materials – fibrous composites. This type of stress discontinuity generally implies a slip or a tear in the material. The remarkable properties of biological structural materials can often be attributed to the composite arrangement of their constituents. (D) SEM image of an anchor spicule’s cross-section, taken at a smooth proximal region along the spicule’s length. (B) σ33 on Ω when the model transmits a tension equal to its peak load capacity ℒ^n, for different n. The stress component σ33 is computed using  for the optimal values of ϱj and ε0 given by [S17] and [S18], for G=1. A cross-section of an Euplectella aspergillum spicule showing the arrangement of microscopic concentric layers of glass inside it.. (Image Credit: James C. Weaver). Development.
Commonly called the âVenus flower basket,â this sponge builds its skeleton in a way that entraps a certain species of crustacean inside for life. Home Topics Science & Environment How sea sponges can influence modern architecture. Consequently, none of the conclusions drawn from the structural mechanics model are affected as a result of this assumption.] Similarly, it is also possible that the spicule’s internal architecture is connected to a different metric of the spicule’s mechanical efficiency, such as the failure curvature—the largest curvature the spicule can withstand without failing. Glass sponges in the class Hexactinellida are animals commonly found in the deep ocean. IMAGINE A FUTURE in which buildings tower miles over the streets below, tourists take day trips to the edge of our atmosphere, and multiple space stations can be spotted drifting across the night sky. 23.
However, modern developments have brought attention to the fact that if a structure’s characteristic dimension is smaller than a critical length scale, which is a characteristic of the structure’s material and geometry, then strength no longer depends on size (14, 29). The proof of this result is given in SI Text, section S4.2.
For example, the hard shells of clams and oysters are made up of aragonite, a brittle mineral that is the main ingredient in limestone. Through the detailed analysis of these complex skeletal materials, useful design lessons can be extracted that can be used to guide the synthesis of synthetic constructs with novel performance metrics (16⇓⇓⇓–20).