Cell wall composition determines handedness reversal in helicoidal cellulose architectures of Pollia condensata fruits

Chiral asymmetry is important in a wide variety of disciplines and occurs across length scales. While several natural chiral biomolecules exist only with single handedness, they can produce complex hierarchical structures with opposite chiralities. Understanding how the handedness is transferred from molecular to the macroscopic scales is far from trivial. An intriguing example is the transfer of the handedness of helicoidal organizations of cellulose microfibrils in plant cell walls. These cellulose helicoids produce structural colors if their dimension is comparable to the wavelength of visible light. All previously reported examples of a helicoidal structure in plants are left-handed except, remarkably, in the Pollia condensata fruit; both left- and right-handed helicoidal cell walls are found in neighboring cells of the same tissue. By simultaneously studying optical and mechanical responses of cells with different handednesses, we propose that the chirality of helicoids results from differences in cell wall composition. In detail, here we showed statistical substantiation of three different observations: 1) light reflected from right-handed cells is red shifted compared to light reflected from left-handed cells, 2) right-handed cells occur more rarely than left-handed ones, and 3) right-handed cells are located mainly in regions corresponding to interlocular divisions. Finally, 4) right-handed cells have an average lower elastic modulus compared to left-handed cells of the same color. Our findings, combined with mechanical simulation, suggest that the different chiralities of helicoids in the cell wall may result from different chemical composition, which strengthens previous hypotheses that hemicellulose might mediate the rotations of cellulose microfibrils.

The Effectiveness of Basalt Fiber in Lightweight Expanded Clay to Improve the Strength of Concrete Helicoidal Staircase

Staircase is a very important structural element found in mostly buildings of more than a floor. The properties of materials and designs used in constructing this structural element are very important. This study addresses the development of ultra-lightweight concrete. How ultra-lightweight concrete can effectively work in helicoidal structure. The flexural strength of this staircase was analysed on a finite element software SCAD. The designed lightweight aggregates concrete is targeted to be used in staircase of a structure having the shape of helicoid. In the concrete, chopped basalt fiber portion was added to each concrete mixture specimen reinforced as reinforcement. The basalt fiber percentages used are 0, 0.45, 0.9, 1.2 and 1.6. The developed lightweight expanded clay basalt fiber concrete showed significant increase in the flexural strength. The loads applied on this helicoidal concrete staircase in SCAD were derived from the laboratory experiments conducted on the concrete specimens on the 28 days curing period. This combination of values exceeds, to the researchers' knowledge, the performance of all other lightweight building materials. Furthermore, the developed lightweight concrete possesses excellent durability properties.

Research on the Impact Resistance of the Periodic Helicoidal Multilayer Bionic Structure Based on Osteon Microstructure

Background: As a typical biological material, bone have excellent mechanical properties and plays an important role in supporting the animal body and protecting organs, osteon is an important part of bone. It is found that the osteon is composed of thin and thick lamellae which are periodic and approximately concentric, every 5 lamellae is a cycle, the periodic helix angle of mineralized collagen fibers in two adjacent sub-lamellae is 30°. Four biomimetic composite models with different fiber helix angles were established and fabricated according to the microstructure of mineralized collagen fibers in osteon. Based on the impact analysis of four kinds of bionic composite models, the effects of the fiber periodic helicoidal structure on the impact resistance and energy dissipation of multi-layer bionic composite were investigated. Results: The analysis results show that the fiber helix angle affects the impact damage resistance and energy dissipation of multi-layer fiber reinforced composites. Among the four kinds of multi-layer composite models, the composite model with helix angle of 30° has better comprehensive ability to resist impact damage. The test results show that the impact damage area of the specimen with 30° helix angle is smallest among the four types of bionic specimens, which is consistent with the results of finite element impact analysis. Furthermore, in the case of no impact damage, the smaller the fiber helix angle is, the more uniform the stress distribution is and more energy is dissipated in the impact process. Conclusions: The periodic helicoidal structure of mineralized collagen fibers in osteon are the result of natural selection of biological evolution. This structure can effectively improve the ability of cortical bone to resist external impact. The research results can provide useful guidance for the design and manufacture of high-performance and strong impact resistant biomimetic composites.

Construction of exact minimal parking garages: nonlinear helical motifs in optimally packed lamellar structures

Minimal surfaces arise as energy minimizers for fluid membranes and are thus found in a variety of biological systems. The tight lamellar structures of the endoplasmic reticulum and plant thylakoids are comprised of such minimal surfaces in which right- and left-handed helical motifs are embedded in stoichiometry suggesting global pitch balance. So far, the analytical treatment of helical motifs in minimal surfaces was limited to the small-slope approximation where motifs are represented by the graph of harmonic functions. However, in most biologically and physically relevant regimes the inter-motif separation is comparable with its pitch, and thus this approximation fails. Here, we present a recipe for constructing exact minimal surfaces with an arbitrary distribution of helical motifs, showing that any harmonic graph can be deformed into a minimal surface by exploiting lateral displacements only. We analyse in detail pairs of motifs of the similar and of opposite handedness and also an infinite chain of identical motifs with similar or alternating handedness. Last, we study the second variation of the area functional for collections of helical motifs with asymptotic helicoidal structure and show that in this subclass of minimal surfaces stability requires that the collection of motifs is pitch balanced.

MEMBRANE FINITE ELEMENT FOR MODELING HEART WALL

Modeling of heart wall deformation remains a challenge due to complex structure of tissue, which contains different group of cells and connective tissue. Muscle cells are dominant where, besides stresses coming from tissue deformation, active stresses are generated representing the load which produces heart motion and function. These cells form a helicoidal structure within so- called wall sheets and are considered as tissue fibers. Usual approach in the finite element (FE) discretization is to use 3D isoparametric elements. The dominant stresses lie in the sheet planes, while normal stresses in the wall normal directions are of the order smaller. Taking this stress state into account, we explore a possibility to model heart wall by membrane finite elements, hence considering the wall as a thick membrane (shell without bending effects). The membrane element is composite, containing layers over the thickness and variation of the direction of fibers. The formulated element is applied to a simplified left ventricle geometry to demonstrate a possibility to simulate heart mechanics by models which are much smaller and simpler for use than 3D conventional models.

Optical anticounterfeiting photonic bilayer film based on handedness of solid-state helicoidal structure

Anticounterfeiting photonic bilayer DH-CLCsolid films were fabricated by sandwiching two CLCsolid films having different handedness. The encrypted information is only disclosed under right-handed circular polarized light.

Evidence of a cellulosic layer in Pandoravirus tegument and the mystery of the genetic support of its biosynthesis

Pandoraviruses are giant viruses of amoebae with 1 μm-long virions. They have an ovoid morphology and are surrounded by a tegument-like structure lacking any capsid protein nor any gene encoding a capsid protein. In this work, we studied the ultrastructure of the tegument surrounding Pandoravirus massiliensis virions and noticed that this tegument is composed of a peripheral sugar layer, an electron-dense membrane, and a thick electron-dense layer consisting in several tubules arranged in a helicoidal structure resembling that of cellulose. Pandoravirus massiliensis particles were stained by Calcofluor white, a fluorescent dye of cellulose, and the enzymatic treatment of particles by cellulase showed the degradation of the viral tegument. We first hypothesized that the cellulose tegument could be synthesized by enzymes encoded by Pandoravirus. Bioinformatic analyses revealed in Pandoravirus massiliensis, a candidate gene encoding a putative cellulose synthase, with a homology with the BcsA domain, one of the catalytic subunits of the bacterial cellulose synthase, but with a low level of homology. This gene was transcribed during the replicative cycle of Pandoravirus massiliensis, but several arguments run counter to this hypothesis. Indeed, even if this gene is present in other Pandoraviruses, the one of the strain studied is the only one to have this BcsA domain and no other enzymes involved in the synthesis of cellulose could be detected, although we cannot rule out that such genes could have been undetected among the large proportion of Orfans of Pandoraviruses. As an alternative, we investigated whether Pandoravirus could divert the cellulose synthesis machinery of the amoeba to its own account. Indeed, contrary to what is observed in the case of infections with other giant viruses such as mimivirus, it appears that the transcription of the amoeba, at least for the cellulose synthase gene, continues throughout the growth phase of envelopes of Pandoravirus. Finally, we believe that this scenario is more plausible. If confirmed, it could be a unique mechanism in the virosphere.

DNA Nanotechnologies for the Design of Bio-Inspired Soft Nanocomposites With Reversible Rigidity

Structures and mechanisms in soft robotics are primarily based on chemically versatile species such as hydrogels, polymers, or elastomers, thus offering great potential for the design of adaptive core properties. In particular, tunable rigidity is highly desirable to enable control of soft grippers or for advanced robot locomotion. However, most of the strategies explored so far rely on mechanisms, such as phase transitions or shape memory effects, that require heavy external hardware or have a limited range of tunable rigidity. In this work, we propose a novel strategy inspired by the sea cucumber dermis mechanism. High aspect ratio carbon nanotubes (CNTs) are reversibly interconnected by DNA oligonucleotides within a polyacrylamide (PAAm) hydrogel. The combination of the excellent mechanical properties of CNTs and the reversible hybridization of DNA strands into a stable double-helicoidal structure allowed the reversible tunability of mechanical properties over one order of magnitude (from ∼100 Pa to ∼1 kPa) within minutes by increasing the temperature beyond the melting temperature of DNA strands (∼50 °C). First, the functionalization strategy of CNTs with DNA strands is described and characterized. The aggregation of CNTs driven by the DNA hybridization is then demonstrated. The mechanical properties of hydrogels functionalized with CNTs are finally analyzed using rheology measurements.

Liquid-Crystalline Dispersions of Double-Stranded DNA

In this review, we compare the circular dichroism (CD) spectra of liquid-crystalline dispersion (LCD) particles formed in PEG-containing aqueous-salt solutions with the purpose of determining the packing of ds DNA molecules in these particles. Depending on the osmotic pressure of the solution, the phase exclusion of ds DNA molecules at room temperature results in the formation of LCD particles with the cholesteric or the hexagonal packing of molecules. The heating of dispersion particles with the hexagonal packing of the ds DNA molecules results in a new phase transition, accompanied by an appearance of a new optically active phase of ds DNA molecules. Our results are rationalized by way of a concept of orientationally ordered “quasinematic” layers formed by ds DNA molecules, with a parallel alignment in the hexagonal structure. These layers can adopt a twisted configuration with a temperature increase; and as a result of this process, a new, helicoidal structure of dispersion particle is formed (termed as the “re-entrant” cholesteric phase). To prove the cholesteric pattern of ds DNA molecules in this phase, the “liquid-like” state of the dispersion particles was transformed into its “rigid” counterpart.