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1. The Dragonfly Wing Project

   Zheng, Hao ; Akbarzadeh, Masoud ( January 2022 , Architectural design)

   del Campo, Matias ; Leach, Neil (Ed.)

   Nature has always been the master of design skills to which humans only aspire to, but new approaches bring that aspiration closer to our reach than ever before. Through 4.5 billion years of iterations, nature has shown us its extraordinary craftsmanship, breeding a variety of species whose body structures have gradually evolved to adapt to natural phenomena and make full use of their unique characteristics. The dragonfly wing, among body structure is an extreme example of efficient use of materials and minimal weight while remaining strong enough to withstand the tremendous forces of flight. It has long been the object of scientific research examining its structural advantages to applying their principles to fabricated designs.1 We can imitate its form and create duplicates, but thoroughly understanding the dragonfly wing’s mechanism, behavior and design logic is no trivial task. 

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2. Lightweight Structures and the Geometric Equilibrium in Dragonfly Wings

   Zheng, Hao ; Hablicsek, Marton ; Akbarzadeh, Masoud ( October 2021 , International Association of Shell and Spatial Structures)

   This research investigates the use of graphic statics in analyzing the structural geometry of a natural phenomenon to understand their performance and their relevant design parameters. Nature has always been inspiring for designers, engineers, and scientists. Structural systems in nature are constantly evolving to optimize themselves with their boundary conditions and the applied loads. Such phenomena follow certain design rules that are quite challenging for humans to formulate or even comprehend. A dragonfly wing is an instance of a high-performance, lightweight structure that has intrigued many researchers to investigate its geometry and its performance as one of the most light-weight structures designed by nature [1]. There are extensive geometrical and analytical studies on the pattern of the wing, but the driving design logic is not clear. The geometry of the internal members of the dragonfly wings mainly consists of convex cells which may, in turn, represent a compression-only network on a 2D plane. However, this phenomenon has never been geometrically analyzed from this perspective to confirm this hypothesis. In this research, we use the methods of 2D graphic statics to construct the force diagram from the given structural geometry of the wing. We use algebraic and geometric graphic statics to unfold the topological and geometric properties of the form and force diagrams such as the degrees of indeterminacies of the network [2]. We then reconstruct the compression-only network of the wing for more than 300 cases for the same boundary conditions and the edge lengths of the independent edges of the network. Comparing the magnitude of the internal forces of the reconstructed network with the actual structure of the wing using the edge length of the force diagram will shed light on the performance of the structure. Multiple analytical studies will be provided to compare the results in both synthetic and natural networks and drive solid conclusions. The success in predicting the internal force flow in the natural structural pattern using graphic statics will expand the use of these powerful methods in reproducing the exact geometry of the natural structural system for use in many engineering and scientific problems. It will also ultimately help us understand the design parameters and boundary conditions for which nature produces its masterpieces. 

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3. Multivalent Interactions Drive the Toxoplasma AC9:AC10:ERK7 Complex To Concentrate ERK7 in the Apical Cap

   https://doi.org/10.1128/mbio.02864-21  

   Back, Peter S. ; O’Shaughnessy, William J. ; Moon, Andy S. ; Dewangan, Pravin S. ; Reese, Michael L. ; Bradley, Peter J. ( February 2022 , mBio)

   Boyle, Jon P. (Ed.)

   ABSTRACT The Toxoplasma inner membrane complex (IMC) is a specialized organelle that is crucial for the parasite to establish an intracellular lifestyle and ultimately cause disease. The IMC is composed of both membrane and cytoskeletal components, further delineated into the apical cap, body, and basal subcompartments. The apical cap cytoskeleton was recently demonstrated to govern the stability of the apical complex, which controls parasite motility, invasion, and egress. While this role was determined by individually assessing the apical cap proteins AC9, AC10, and the mitogen-activated protein kinase ERK7, how the three proteins collaborate to stabilize the apical complex is unknown. In this study, we use a combination of deletion analyses and yeast two-hybrid experiments to establish that these proteins form an essential complex in the apical cap. We show that AC10 is a foundational component of the AC9:AC10:ERK7 complex and demonstrate that the interactions among them are critical to maintaining the apical complex. Importantly, we identify multiple independent regions of pairwise interaction between each of the three proteins, suggesting that the AC9:AC10:ERK7 complex is organized by multivalent interactions. Together, these data support a model in which multiple interacting domains enable the oligomerization of the AC9:AC10:ERK7 complex and its assembly into the cytoskeletal IMC, which serves as a structural scaffold that concentrates ERK7 kinase activity in the apical cap. IMPORTANCE The phylum Apicomplexa consists of obligate, intracellular parasites, including the causative agents of toxoplasmosis, malaria, and cryptosporidiosis. Hallmarks of these parasites are the IMC and the apical complex, both of which are unique structures that are conserved throughout the phylum and required for parasite survival. The apical cap portion of the IMC has previously been shown to stabilize the apical complex. Here, we expand on those studies to determine the precise protein-protein interactions of the apical cap complex that confer this essential function. We describe the multivalent nature of these interactions and show that the resulting protein oligomers likely tether ERK7 in the apical cap. This study represents the first description of the architecture of the apical cap at a molecular level, expanding our understanding of the unique cell biology that drives Toxoplasma infections. 

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4. FROM NEOS TO TNOS: HOW REGOLITH IS SHAPING THE SMALL WORLDS OF OUR SOLAR SYSTEM

   Brisset, J. ( June 2023 , Asteroids, Comets, Meteors Conference 2023)

   Introduction: With the capture of the first high- resolution, in-situ images of Near-Earth Objects (NEOs) a couple of decades ago [1–4], the ubiquity of regolith and the granular nature of small objects in the Solar System became apparent. Benefiting from an increased access to high computing power, new numerical studies emerged, modeling granular structures forming and evolving as small bodies in the Solar System [5–7]. Now adding laboratory studies on granular material strength for asteroid and other small body applications [8,9], we are steadily progressing in our understanding of how regolith is shaping the interiors and surfaces of these worlds. In addition, our ever-more powerful observation capabilities are uncovering interesting dust-related phenomena in the outer skirts of our Solar System, in the form of activity at large heliocentric distances and rings [10–12]. We find that our recent progress in understanding the behavior of granular material in small body environments also has applications to the more distant worlds of Centaurs and Trans-Neptunian Objects (TNOs). Internal Strength: We currently deduce internal friction of rubble piles from the observation of large numbers of small asteroids and their rotation rates, combined with the associated numerical simulations [13,14]. In the laboratory, we study internal friction of simulant materials using shear strength measurements [8]. Combining observations, modeling, and laboratory work, the picture emerges of rubble pile interiors being composed of coarse grains in the mm to cm range. The irregular shapes of the grains lead to mechanical interlocking, thus generating the internal friction required to match observations of the asteroid population [8,9]. We find that the presence of a fine fraction in the confined interior of a rubble pile actually leads weaker internal strength [9]. Surface Strength: Deducing surface regolith strength for NEOs is usually performed via average slope measurements [15–17] or, most notably, observing the outcome of an impact of known energy [18]. In the laboratory, we measure the angle of repose of simulant material via pouring tests, as well as its bulk cohesion using shear strength measurements [8]. In some cases, this allows us to infer grain size ranges for various regions of the surface and subsurface of pictured NEOs, beyond the resolution of their in-situ images. Surface Activity: The Rosetta mission revealed that a number of activity events on comet 67P/Churyumov–Gerasimenko were linked to active surface geology, most notably avalanches and cliff collapses [19]. In addition, the role of regolith strength in asteroid disruption patterns has been inferred from numerical simulations of rotating rubble piles [20]. By studying strength differences in simulant samples, it becomes apparent that a difference in cohesion between a surface and its subsurface layer can lead to activity events with surface mass shedding, without the presence of volatiles sublimating as a driver [8]. We show that such differences in surface strength can be brought upon by a depletion in fine grains or a change in composition (e.g. depletion in water ice) and could account for regular activity patterns on small bodies, independently of their distance to the Sun. This is of particular interest to the study of Centaur activity and a potential mechanism for feeding ring systems. 

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5. Effect of variations in manufacturing and material properties on the self-folding behaviors of hydrogel and elastomer bilayer structures

   https://doi.org/10.1039/D2SM01104B  

   Zhao, Jiayu ; Kazemi, Hesaneh ; Kim, H. Alicia ; Bae, Jinhye ( November 2022 , Soft Matter)

   The stimuli-responsive self-folding structure is ubiquitous in nature, for instance, the mimosa folds its leaves in response to external touch or heat, and the Venus flytrap snaps shut to trap the insect inside. Thus, modeling self-folding structures has been of great interest to predict the final configuration and understand the folding mechanism. Here, we apply a simple yet effective method to predict the folding angle of the temperature-responsive nanocomposite hydrogel/elastomer bilayer structure manufactured by 3D printing, which facilitates the study of the effect of the inevitable variations in manufacturing and material properties on folding angles by comparing the simulation results with the experimentally measured folding angles. The defining feature of our method is to use thermal expansion to model the temperature-responsive nanocomposite hydrogel rather than the nonlinear field theory of diffusion model that was previously applied. The resulted difference between the simulation and experimentally measured folding angle ( i.e. , error) is around 5%. We anticipate that our method could provide insight into the design, control, and prediction of 3D printing of stimuli-responsive shape morphing ( i.e. , 4D printing) that have potential applications in soft actuators, robots, and biomedical devices. 

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