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Study Reveals New Geometric Shape Used By Nature to Pack Cells Efficiently.

a) Scheme representing planar columnar/cubic monolayer epithelia. Cells are simplified as prisms. b) Scheme illustrating a fold in a columnar/cubic monolayer epithelium. Cells adopt the called “bottle 23 shape” that would be simplified as frusta. c) Mathematical model for an epithelial tube. d) Modelling clay figures illustrating two scutoids participating in a transition and two schemes for scutoids solids. Scutoids are characterized by having at least a vertex in a different plane to the two bases and present curved surfaces. e) A dorsal view of a Protaetia speciose beetle of the Cetoniidae family. The white lines highlight the resemblance of its scutum scutellum and wings with the shape of the scutoids. Illustration from Dr. X with permission. f) Three-dimensional reconstruction of the cells forming a tube. The four-cell motif (green, yellow, blue and red cells) shows an apico-basal cell intercalation. g) Detail of the apico-basal transition showing how the blue and yellow cells contact in.

As an embryo develops tissues bend into complex three-dimensional shapes that lead to organs. Epithelial cells are the building blocks of this process forming for example the outer layer of skin. They also line the blood vessels and organs of all animals.

These cells pack together tightly. To accommodate the curving that occurs during embryonic development it has been assumed that epithelial cells adopt either columnar or bottle-like shapes.

However a group of scientists dug deeper into this phenomenon and discovered a new geometric shape in the process.

They uncovered that during tissue bending epithelial cells adopt a previously undescribed shape that enables the cells to minimize energy use and maximize packing stability.

Y and colleagues first made the discovery through computational modeling that utilized Voronoi diagramming (In mathematics, a Voronoi diagram is a partitioning of a plane into regions based on distance to points in a specific subset of the plane. That set of points (called seeds, sites, or generators) is specified beforehand, and for each seed there is a corresponding region consisting of all points closer to that seed than to any other. These regions are called Voronoi cells. The Voronoi diagram of a set of points is dual to its Delaunay triangulation) a tool used in a number of fields to understand geometrical organization.

“During the modeling process the results we saw were weird” says Y. “Our model predicted that as the curvature of the tissue increases columns and bottle-shapes were not the only shapes that cells may developed. To our surprise the additional shape didn’t even have a name in math ! One does not normally have the opportunity to name a new shape”.

The group has named the new shape the “scutoid” for its resemblance to the scutellum–the posterior part of an insect thorax or midsection.

To verify the model’s predictions the group investigated the three-dimensional packing of different tissues in different animals. The experimental data confirmed that epithelial cells adopted shapes and three-dimensional packing motifs similar to the ones predicted by the computational model.

Using biophysical approaches the team argues that the scutoids stabilize the three-dimensional packing and make it energetically efficient. As Y puts it: “We have unlocked nature’s solution to achieving efficient epithelial bending”.

Their findings could pave the way to understanding the three-dimensional organization of epithelial organs and lead to advancements in tissue engineering.

“In addition to this fundamental aspect of morphogenesis” they write “the ability to engineer tissues and organs in the future critically relies on the ability to understand and then control the 3D organization of cells”.

Adds Y: “For example if you are looking to grow artificial organs this discovery could help you build a scaffold to encourage this kind of cell packing accurately mimicking nature’s way to efficiently develop tissues”.

Scientists Create ‘Impossible’ Materials in Simple Way.

Crystal structures of iron-nitrogen compounds. Orange and blue balls show the positions of Fe and N atoms respectively. a Fe3N2 at 50 ? GPa. The structure is built of quadrilateral face-capped trigonal prisms NFe7 which are interconnected by sharing trigonal faces and edges. b FeN at 50 ? GPa with NiAs structure type. c FeN2 at 58 ? GPa; Shown are the FeN6 octahedra which are connected into infinite chains through common edges and aligned along the c-axis. These chains are interconnected through common vertices. Additional linkage between FeN6 octahedra is provided via N-N bonds. d FeN4 at 135 ? GPa. In the structure of FeN4 each Fe atom is a member of two non-planar five-member Fe[N4] metallacycles which are almost parallel to the (1-10) lattice plane. Nitrogen atoms form infinite zigzag chains running along the c-direction.

Scientists from Georgian Technical University and colleagues from the International Black Sea University and Sulkhan Saba Orbeliani University have created nitrides, a material previously considered impossible to obtain. More amazing they have shown that the material can be obtained using a very simple method of direct synthesis.

Nitrides are actively used in superhard coatings and electronics. Usually the nitrogen content in these materials is low and it is therefore difficult to get the nitrogen levels to exceed the levels of transition metals (as the nitrogen bonds are too high energy).

Compounds rhenium and iron which the researchers chose for the experiments embody this problem particularly well. As such the researchers decided to change the synthesis from ordinary conditions on Earth to a condition of ultra-high pressure.

«This method is one of the most promising ways to create new high quality materials and it opens up fantastic opportunities. There are well-known examples like artificial diamonds and cubic boron nitride (CBN) which existed in a natural form. However the idea to consciously create materials that are impossible [to make] in nature is our know-how» commented X.

According to X the experiments produced results almost immediately. Nitrogen together with a transition metal is placed into a diamond anvil cell and a simple direct synthesis is carried out under high pressure.

Rhenium nitride has a characteristic of low compressibility so it potentially has very high mechanical characteristics and the characteristic of superhardness – which is important for example in improving the quality of cutting tools» X added.

X believes the research group will later clarify whether the materials are superconductors or magnets and whether they are suitable for spintronics.

Their backward chaining requires more experimental facilities for further analysis. Those facilities are already underway however and are likely to bear fruit within the next year.

If the research team proves the material’s assumed superhardness then within 5 years we will be able to see the «impossible» materials being used in commercial fields.