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1. Glial peroxisome dysfunction induces axonal swelling and neuroinflammation in Drosophila

   https://doi.org/10.1093/g3journal/jkae243  

   Sodders, Maggie; Das, Anurag; Bai, Hua (October 2024, G3: Genes, Genomes, Genetics)

   Tennessen, J (Ed.)

   Abstract Glial cells are known to influence neuronal functions through glia–neuron communication. The present study aims to elucidate the mechanism behind peroxisome-mediated glia–neuron communication using Drosophila neuromuscular junction (NMJ) as a model system. We observe a high abundance of peroxisomes in the abdominal NMJ of adult Drosophila. Interestingly, glia-specific knockdown of peroxisome import receptor protein, Pex5, significantly increases axonal area and volume and leads to axon swelling. The enlarged axonal structure is likely deleterious, as the flies with glia-specific knockdown of Pex5 exhibit age-dependent locomotion defects. In addition, impaired peroxisomal ether lipid biosynthesis in glial cells also induces axon swelling. Consistent with our previous work, defective peroxisomal import function upregulates pro-inflammatory cytokine upd3 in glial cells, while glia-specific overexpression of upd3 induces axonal swelling. Furthermore, motor neuron-specific activation of the JAK-STAT pathway through hop overexpression results in axon swelling. Our findings demonstrated that impairment of glial peroxisomes alters axonal morphology, neuroinflammation, and motor neuron function. 

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2. Delayed buckling of spherical shells due to viscoelastic knockdown of the critical load

   https://doi.org/10.1098/rspa.2021.0253  

   Stein-Montalvo, Lucia; Holmes, Douglas P.; Coupier, Gwennou (September 2021, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences)

   We performed dynamic pressure buckling experiments on defect-seeded spherical shells made of a common silicone elastomer. Unlike in quasi-static experiments, shells buckled at ostensibly subcritical pressures, i.e. below the experimentally determined critical load at which buckling occurs elastically, often following a significant delay period from the time of load application. While emphasizing the close connections to elastic shell buckling, we rely on viscoelasticity to explain our observations. In particular, we demonstrate that the lower critical load may be determined from the material properties, which is rationalized by a simple analogy to elastic spherical shell buckling. We then introduce a model centred on empirical quantities to show that viscoelastic creep deformation lowers the critical load in the same predictable, quantifiable way that a growing defect would in an elastic shell. This allows us to capture how both the deflection at instability and the time delay depend on the applied pressure, material properties and defect geometry. These quantities are straightforward to measure in experiments. Thus, our work not only provides intuition for viscoelastic behaviour from an elastic shell buckling perspective but also offers an accessible pathway to introduce tunable, time-controlled actuation to existing mechanical actuators, e.g. pneumatic grippers. 

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3. Food LEGO: Building hollow cage and sheet superstructures from starch

   https://doi.org/10.1126/sciadv.adi7069  

   Kierulf, Arkaye; Mosleh, Imann; Li, Jieying; Li, Peilong; Zarei, Amin; Khazdooz, Leila; Smoot, James; Abbaspourrad, Alireza (February 2024, Science Advances)

   The idea of building large structures from small building blocks has had a long history in the human imagination, from the beautifully intricate shells assembled from silica by unicellular algae to the Egyptian pyramids built from stone. Carrying this idea into the food industry has important implications. Here, we introduce a Pickering emulsion platform for building superstructures like hollow cages and sheets using starch granules as building blocks. In food, these superstructures occupy up to six times more space than their constituent parts, thereby delivering a viscosity greater by an order of magnitude than unstructured starch. To achieve this higher viscosity, they use an alternative superstructure mechanism as opposed to the classic swelling mechanism of individual particles. These super-thickeners may reduce calories, cut production costs, and stretch the global food supply, demonstrating how we can design the future by playing with our food. 

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4. Topological solitons, cholesteric fingers and singular defect lines in Janus liquid crystal shells

   https://doi.org/10.1039/C9SM02033K  

   Durey, Guillaume; Sohn, Hayley R.; Ackerman, Paul J.; Brasselet, Etienne; Smalyukh, Ivan I.; Lopez-Leon, Teresa (March 2020, Soft Matter)

   Topological solitons are non-singular but topologically nontrivial structures in fields, which have fundamental significance across various areas of physics, similar to singular defects. Production and observation of singular and solitonic topological structures remain a complex undertaking in most branches of science – but in soft matter physics, they can be realized within the director field of a liquid crystal. Additionally, it has been shown that confining liquid crystals to spherical shells using microfluidics resulted in a versatile experimental platform for the dynamical study of topological transformations between director configurations. In this work, we demonstrate the triggered formation of topological solitons, cholesteric fingers, singular defect lines and related structures in liquid crystal shells. We show that to accommodate these objects, shells must possess a Janus nature, featuring both twisted and untwisted domains. We report the formation of linear and axisymmetric objects, which we identify as cholesteric fingers and skyrmions or elementary torons, respectively. We then take advantage of the sensitivity of shells to numerous external stimuli to induce dynamical transitions between various types of structures, allowing for a richer phenomenology than traditional liquid crystal cells with solid flat walls. Using gradually more refined experimental techniques, we induce the targeted transformation of cholesteric twist walls and fingers into skyrmions and elementary torons. We capture the different stages of these director transformations using numerical simulations. Finally, we uncover an experimental mechanism to nucleate arrays of axisymmetric structures on shells, thereby creating a system of potential interest for tackling crystallography studies on curved spaces. 

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5. Buckling of geometrically confined shells

   https://doi.org/10.1039/c8sm02035c  

   Stein-Montalvo, Lucia; Costa, Paul; Pezzulla, Matteo; Holmes, Douglas P. (February 2019, Soft Matter)

   We study the periodic buckling patterns that emerge when elastic shells are subjected to geometric confinement. Residual swelling provides access to range of shapes (saddles, rolled sheets, cylinders, and spherical sections) which vary in their extrinsic and intrinsic curvatures. Our experimental and numerical data show that when these moderately thick structures are radially confined, a single geometric parameter – the ratio of the total shell radius to the amount of unconstrained material – predicts the number of lobes formed. We present a model that interprets this scaling as the competition between radial and circumferential bending. Next, we show that reducing the transverse confinement of saddles causes the lobe number to decrease with a similar scaling analysis. Hence, one geometric parameter captures the wave number through a wide range of radial and transverse confinement, connecting the shell shape to the shape of the boundary that confines it. We expect these results to be relevant for an expanse of shell shapes, and thus applicable to the design of shape-shifting materials and the swelling and growth of soft structures. 

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