Multicellular Tubes Research Articles

Bending performance of the AuxOcta multi-cellular beam structure

Auxetic cellular tubes are potential candidates for several engineering applications requiring resistance to bending due to the enormous demand for lightweight and high mechanical performance. Interestingly, we found that the preferential buckling mode can change the direction of deformation in the beam cross-section by applying negative Poisson's ratio cells in the lateral direction and is an effective modifying region. The bending response and energy absorption of multi-cellular tube with auxetic cells (Aux) and novel design tubes with auxetic and octagonal cells (AuxOcta) have been investigated with numerical and experimental systematically. These unique auxetic structures are produced by direct metal laser sintering (DMLS) with 316L stainless steel. The bending results show that the Aux tube indicates gradual local deformation in the loading region, while the cells of the AuxOcta tube beam are homogeneously deformed in the loading region. Moreover, AuxOcta structure is optimized to improve load-carrying and energy-absorbing capacities. This optimized AuxOcta structure (AuxOcta-G) offers superior bending performance from the test results. Compared to the Aux structure, the improvement in the specific load carrying (SLC) capacity of the AuxOcta-G structure above is 15% for 5 mm displacement, while the improvement in the specific energy absorption (SEA) approximately reaches 16%. The Finite Element Method (FEM) results showed that AuxOcta and AuxOcta-G structures offer a preferred behavior with a wide displacement range. This study provides a baseline for future investigation of hybrid beam design with a negative Poisson cross-section.

Initial stiffness of connection joining I-beam to concrete-filled multicellular steel tube wall

Concrete-filled multicellular steel tube (CF-MCST) wall is widely used in China in recent years. In the companion paper, the moment capacity of the connection joining an I-beam to a CF-MCST wall was studied. Realizing that the insight into the connection's stiffness would greatly benefit performing a fine structural analysis, this paper aims to propose a theoretical approach for approximating the rotational stiffness of the connection. Finite Element (FE) model is first established for analysis, which is validated by using the experimental results extracted from previous studies. In order to attain the stiffness resulting from the endplate and the wall individually, an additional companion FE model is employed, where the endplate's deformation is negligible by using an extreme great value for the Young's modulus of the endplate and the connection's rotation is therefore mainly attributed to the wall's local deformation near the connection. For the stiffness accounting for the deformation of the endplate, the stiffness accounting for the local deformation of the wall, and the connection's stiffness, parametric study is then performed via the validated FE models whose geometrical parameters falling into the range conventionally taken in the engineering. Based on the FE analysis results, the abstracted mechanical model is proposed, resulting in semi-empirical formulas where partial parameters are identified by the means of regression analysis. It is found that enlarging the geometrical parameters would improve the connection's stiffness. Among the parameters, the beam height has the most significant effects on the connection's stiffness. Accordingly, increasing the beam height first is suggested for the aim of enhancing the connection's stiffness. The comparison of the results obtained via the FE analyses and that obtained via the proposed theoretical approach shows a good agreement, and the error is <10% regarding the connection's stiffness.

Study on the crashworthiness of star-shaped multicellular tubes

Based on the conventional star-shaped tube, a star-shaped multicellular tube was proposed and designed; finite element modeling was carried out using Abaqus/Explicit software, and the accuracy of the finite element model was verified under axial impact, the crashworthiness study shows that the star-shaped multicellular tube is significantly improved compared to the conventional star-shaped tube for the same wall thickness and same mass conditions. Namely, for the same wall thickness conditions, the energy absorption of the star-shaped quadrangular multicellular tube (SSMT-4-140°) is 1.77 times that of the star-shaped quadrangular tube (SST-4-140°), and the crush force efficiency is 1.24 times that of SST-4-140°; at the same mass, the energy absorption of SSMT-4-140° is 1.17 times that of SST-4-140°, and the crush force efficiency is 1.14 times that of SST-4-140°. Subsequently, the parametric study of the number of corners N, angle between two adjacent corners θ°, and wall thickness on the star-shaped multicellular tube was systematically carried out. The results of this paper can provide valuable information toward the innovative design of multicell tube structures.

Energy absorption characteristics analysis of multicellular columns based on the origami centripetal folding method

In order to improve the crashworthiness of traditional Thin-Walled Struct, a new method for designing multicellular tubes is presented in this paper. In this work, multicellular columns based on origami centripetal folding method (MCOCFM) are proposed. The cross section of MCOCFM is designed in the way of origami. The mechanical properties of MCOCFM under uniaxial compression are analyzed by numerical simulation. Studies have shown that increased levels and wall thickness facilitate energy absorption. In addition, the theoretical prediction of MCF is in good agreement with the simulation results. Compared with some existing structures, MCOCFM has better crashworthiness.

Energy absorption comparison of conventional and dual gradient hierarchical multicellular tubes under axial impact

Energy absorption comparison of conventional and dual gradient hierarchical multicellular tubes under axial impact

Crushing analysis of hierarchical multicellular tubes with gradient character along axial and radial directions under oblique loads

To overcome the disadvantage of high initial peak crush force (IPCF) in hierarchical and gradient structures, the hierarchical multicellular tubes (HMTs) with gradient character along axial and radial directions are proposed based on the bidirectional structural characters of bamboo stem. Crashworthiness performances of HMTs under oblique loads are systematically studied by using numerical simulation. Results show that compared with the square tube with the same mass, HMTs have higher energy absorption capability under different impact angles. The maximum increases of specific energy absorption (SEA) and crush force efficiency (CFE) reach up to 67.02% and 806%, respectively. Whereas, the maximum decrease of IPCF reaches up to 79.92%. Effects of structural parameters, including hierarchical level, wall thickness and internode space, on the crashworthiness performances of HMTs are also fully investigated.

Energy absorption characteristics and crashworthiness of rhombic hierarchical gradient multicellular hexagonal tubes

In order to further improve the crashworthiness, this paper introduces hierarchies and gradients into thin-walled structures, and designs a new type of rhombic hierarchical gradient multicellular hexagonal tube (RHGMHT), which has the characteristics of hierarchies and gradients in structure. Experimental analysis showed that the mean crashing force (MCF) of 2nd order RHGMHT is greatly improved, and its crushing force efficiency (CFE) is increased by 104.91% compared with 0th order hexagonal tube (HT). The finite element model validated by the experiment is simulated to analyze its deformation mechanism and crashworthiness. Compared with other structures at the same mass, RHGMHT has higher specific energy absorption (SEA) and no increase in initial peak force (IPF). The parametric analysis shows that the SEA of 2nd order RHGMHT is 57.89% higher than that of the 0th order HT. In addition, increasing the mass of the structure can further improve the plateau force, but the IPF also increases with the mass. By comparing the thickness ratios of different rib plates, the analysis shows that different rib plate thicknesses significantly affect the deformation mode and thus the crashworthiness of the structure. Finally, according to the simplified super folded element (SSFE) theory, the MCF theoretical prediction model is established. The results show that the MCF predicted by theory is in good agreement with the MCF obtained by numerical simulation. The hierarchical gradient design proposed in this paper provides a certain guiding significance for the design of new energy absorbers.

Investigation of mechanical behavior of multi-cellular tubes with intermediate walls under lateral quasi-static loading

Investigation of mechanical behavior of multi-cellular tubes with intermediate walls under lateral quasi-static loading

Regulators of the secretory pathway have distinct inputs into single-celled branching morphogenesis and seamless tube formation in the Drosophila trachea

Biological tubes serve as conduits through which gas, nutrients and other important fluids are delivered to tissues. Most biological tubes consist of multiple cells connected by epithelial junctions. Unlike these multicellular tubes, seamless tubes are unicellular and lack junctions. Seamless tubes are present in various organ systems, including the vertebrate vasculature, C.elegans excretory system, and Drosophila tracheal system. The Drosophila tracheal system is a network of air-filled tubes that delivers oxygen to all tissues. Specialized cells within the tracheal system, called terminal cells, branch extensively and form seamless tubes. Terminal tracheal tubes are polarized; the lumenal membrane has apical identity whereas the outer membrane exhibits basal characteristics. Although various aspects of membrane trafficking have been implicated in terminal cell morphogenesis, the precise secretory pathway requirements for basal and apical membrane growth have yet to be elucidated. In the present study, we demonstrate that anterograde trafficking, retrograde trafficking and Golgi-to-plasma membrane vesicle fusion are each required for the complex branched architecture of the terminal cell, but their inputs during seamless lumen formation are more varied. The COPII subunit, Sec31, and ER exit site protein, Sec16, are critical for subcellular tube architecture, whereas the SNARE proteins Syntaxin 5, Syntaxin 1 and Syntaxin 18 are more generally required for seamless tube growth and maintenance. These data suggest that distinct components of the secretory pathway have differential contributions to basal and apical membrane growth and maintenance during terminal cell morphogenesis.

Approaching ideal energy absorption through the multicellular structure with gradient material distribution

Energy absorption of traditional tubular energy absorbers is restricted by the low structure efficiency, which makes the mean crushing force of the structure usually much lower than its yield strength. The combination of a multicellular design and a gradient-thickness strategy significantly improves the energy-absorption ability of thin-walled energy absorbers while reducing weight. Gradient-thickness multicellular tubes (GTMT) were studied in this paper to demonstrate this advantage. Mechanical performances of GTMT with two material-distribution principles, sample gradient thickness (SGT) and modified gradient thickness (MGT), were investigated experimentally and numerically, primarily in terms of folding behaviors, energy-absorption ability, and load-carrying capacity undulation. Wire-cut electrical discharge machining technology was used to create a series of aluminum alloy specimens that were then compressed under quasistatic loading conditions.Following that, finite element method was used to run detailed numerical simulations. The effect of geometric configuration was determined after conducting parametric studies with different cell density and thickness gradient coefficients. The results showed that, compared to a traditional multicellular tube, a gradient-thickness one with MGT material distribution can improve structural efficiency with a stable loading history. Increases in cell density and thickness gradient coefficient have positive effects on energy-absorption ability; however, excessively high parameter values will lead to global bending deformation and weaken the mean crushing force. Therefore, reasonable parameter matching is vital. The result shows that when the cell density reached 9 × 9 and the thickness gradient coefficient reached 1.4, the mean crushing force was 98.16% of the full-plastic strength of the matrix, and there was no irregular deformation, indicating that ideal energy absorption is almost achieved. These achievements pave a way for achieving ideal energy absorption.

Crashworthiness optimization of a multicellular thin-walled tube with triangular cells

This article optimizes a multicellular thin-walled tube with N-equilateral triangles (MTTN), which was inspired from the microstructure of the cross-section of bamboo. The crashworthiness of MTTN under axial impact was analyzed, and the sensitivity analysis was conducted for the geometric parameters of MTT24, which exhibited the best crashing performance among MTTNs with N ≤ 30. It was found that the order in radial direction has a weak influence on the crashworthiness of MTT24, while the cell-wall thickness and the inner-tube diameter could significantly affect the crashworthiness of MTT24. Then, a multi-objective optimization was carried out for the MTT24 to further improve its crushing performance. The wall thickness and inner diameter of the thin-walled tube were selected as design variables, while the minimum peak crushing force (PCF) and the maximum specific energy absorption (SEA) were set as objectives. The obtained Pareto front enables the thin-walled tube to achieve the best possible crush resistance under the conditions of maximum SEA and minimum PCF. With a constraint of PCF ≤ 200 kN, the SEA and MCF of MTT24 were improved by 11.40% and 68.20%, respectively, compared with the benchmark.

Study on the moment capacity of a connection joining an I-beam to concrete-filled multicellular steel tube walls

Recently, concrete-filled multicellular steel tube (CF-MCST) walls are being widely used in China. This paper presents a theoretical and numerical study on the moment capacity of a beam-to-wall connection in which an endplate and two side-plates grip the wall-end by welding, and then the beam is connected to the endplate by the welded flanges and the bolted web. Finite element (FE) analysis is conducted, and its accuracy is validated by comparing the analysis results with experimental results in literature. A parametric study of the connection is conducted to gain insight into the mechanical behavior of the connection. Yield line analysis is used to derive equations predicting the moment capacity. Comparison between the analyses shows good agreement between the predicted capacities and the FE analysis results. The error rate was less than 10%. The minimum required thickness of the endplate is derived for developing the full moment strength of the beam. A minimum endplate total length (1.42b + hb) is obtained and verified to ensure the full strength development of the beam when the endplate thickness is the minimum value. Finally, design recommendations are proposed.

Improving Blast Performance of Reinforced Concrete Panels Using Sacrificial Cladding with Hybrid-Multi Cell Tubes

The utilization of sacrificial layers to strengthen civilian structures against terrorist attacks is of great interest to engineering experts in structural retrofitting. The sacrificial cladding structures are designed to be attached to the façade of structures to absorb the impact of the explosion through the facing plate and the core layer progressive plastic deformation. Therefore, blast load striking the non-sacrificial structure could be attenuated. The idea of this study is to construct a sacrificial cladding structure from multicellular hybrid tubes to protect the prominent bearing members of civil engineering structures from blast hazard. The hybrid multi-cell tubes utilized in this study were out of staking composite layers (CFRP) around thin-walled tubes; single, double, and quadruple (AL) thin-walled tubes formed a hybrid single cell tube (H-SCT), a hybrid double cell tube (H-DCT), and a hybrid quadruple cell tube (H-QCT). An unprotected reinforced concrete (RC) panel under the impact of close-range free air blast detonation was selected to highlight the effectiveness of fortifying structural elements with sacrificial cladding layers. To investigate the proposed problem, Eulerian–Lagrangian coupled analyses were conducted using the explicit finite element program (Autodyn/ANSYS). The numerical models’ accuracy was validated with available blast testing data reported in the literature. Numerical simulations showed a decent agreement with the field blast test. The proposed cladding structures with different core topologies were applied to the unprotected RC slabs as an effective technique for blast loading mitigation. Mid-span deflection and damage patterns of the RC panels were used to evaluate the blast behavior of the structures. Cladding structure achieved a desired protection for the RC panel as the mid-span deflection decreased by 62%, 78%, and 87% for H-SCT, H-DCT, and H-QCT cores, respectively, compared to the unprotected panels. Additionally, the influence of the skin plate thickness on the behavior of the cladding structure was investigated.

Fusion of airways during avian lung development constitutes a novel mechanism for the formation of continuous lumena in multicellular epithelia.

During development of the avian lung, the initially terminally branched epithelial tree later forms a continuous network of airways. This occurs via a large-scale epithelial fusion event, wherein airways that originate proximally collide with those that originate distally to form one continuous lumen. Here, we found that prior to fusion, the epithelium of the embryonic chicken lung undergoes a shape change to permit the initiation and extension of new branches which contain the cells that initiate contact. These changes in epithelial shape coincide with the differentiation of smooth muscle cells that wrap the airways. From these nascent epithelial branches, individual cells form cytoskeletal protrusions that extend toward and form a bridge with their target airway. Additional cells then join the fusion site, forming a bilayered epithelium. During this process, the basement membrane around the prefusion epithelium degrades and then reforms after fusion. The epithelial bilayer then undergoes apoptosis, clearing the path between the two lumens. The process of airway epithelial fusion in the developing chicken lung constitutes a novel mechanism for the generation of complex multicellular tubes and suggests a conserved role for smooth muscle in the shaping of airway epithelia.

Finite element investigations on the effect of stiffeners in polygonal tubes under axial impact

Multi-cell tubular structures are gaining much interest in the crashworthiness field, owing to their extensive applications in automotive vehicles as lightweight energy-absorbing structures in collision events. The current paper examines the numerical simulation of axial impact loading of thin-walled aluminium multi cellular polygonal tube of different configurations. Nonlinear impact simulations were performed on multi cellular polygonal tubes using finite element ABAQUS/CAE explicit code to examine the influence of stiffeners. From the overall results obtained, the crashworthiness performance of the proposed multi cellular tubes of various configurations were compared. Moreover, square section multi-cellular tubes were retained as most prominent for higher specific energy absorption. This type of structures was found to be effective one to improve the crashworthiness performance during impact events.

Lateral Crushing and Energy Absorption Behavior of Multicellular Tube Structures

Thin-walled metallic tubular elements are extensively employed as an impact energy attenuator in modern vehicles owing to light weight, easy fabrication and average cost. Besides, the novel multi-cell tubular structures have superior energy absorption characteristics related to a conventional simple cell tube. In this research article, the finite element simulation of thin-walled aluminium alloy extruded multicellular structure under lateral impact loading is investigated. Nonlinear impact simulations were performed on multicellular tubes of various configurations using finite element ABAQUS/CAE explicit code. From the outcomes attained, the energy absorption capability of various multicellular tube structures were compared and it shows that multicellular tubes have more remarkable than that of traditional simple cell tubes. Moreover, square shaped multicellular structure tube were retained as most prominent for higher energy absorption. This type of multicellular tubes was found to be effective one to improve the lateral crashworthiness performance.

Engineering small tubes with changes in diameter for the study of kidney cell organization.

Multicellular tubes are structures ubiquitously found during development and in adult organisms. Their topologies (diameter, direction or branching), together with their mechanical characteristics, play fundamental roles in organ function and in the emergence of pathologies. In tubes of micrometric range diameters, typically found in the vascular system, renal tubules or excretory ducts, cells are submitted to a strong curvature and confinement effects in addition to flow. Then, small tubes with change in diameter are submitted to a local gradient of shear stress and curvature, which may lead to complex mechanotransduction responses along tubes, and may be involved in the onset or propagation of cystic or obstructive pathologies. We describe here a simple method to build a microfluidic device that integrates cylindrical channels with changes in diameter that mimic in vivo tube geometries. This microfabrication approach is based on molding of etched tungsten wires, which can achieve on a flexible way any change in diameter in a polydimethylsiloxane (PDMS) microdevice. The interest of this biomimetic multitube system has been evidenced by reproducing renal tubules on chip. In particular, renal cell lines were successfully seeded and grown in PDMS circular tubes with a transition between 80 μm and 50 μm diameters. Thanks to this biomimetic platform, the effect of the tube curvature has been investigated especially regarding cell morphology and orientation. The effect of shear stress on confluent cells has also been assessed simultaneously in both parts of tubes. It is thus possible to study interconnected cell response to differential constraints which is of central importance when mimicking tubes present in the organism.

Three-dimensional deformation mode of multicellular epithelial tube under tension and compression tests

Three-dimensional deformation mode of multicellular epithelial tube under tension and compression tests

The C. elegans Intestine As a Model for Intercellular Lumen Morphogenesis and In Vivo Polarized Membrane Biogenesis at the Single-cell Level: Labeling by Antibody Staining, RNAi Loss-of-function Analysis and Imaging.

Multicellular tubes, fundamental units of all internal organs, are composed of polarized epithelial or endothelial cells, with apical membranes lining the lumen and basolateral membranes contacting each other and/or the extracellular matrix. How this distinctive membrane asymmetry is established and maintained during organ morphogenesis is still an unresolved question of cell biology. This protocol describes the C. elegans intestine as amodel for the analysis of polarized membrane biogenesis during tube morphogenesis, with emphasis on apical membrane and lumen biogenesis. The C. elegans twenty-cell single-layered intestinal epithelium is arranged into a simple bilaterally symmetrical tube, permitting analysis on a single-cell level. Membrane polarization occurs concomitantly with polarized cell division and migration during early embryogenesis, but de novo polarized membrane biogenesis continues throughout larval growth, when cells no longer proliferate and move. The latter setting allows one to separate subcellular changes that simultaneously mediate these different polarizing processes, difficult to distinguish in most polarity models. Apical-, basolateral membrane-, junctional-, cytoskeletal- and endomembrane components can be labeled and tracked throughout development by GFP fusion proteins, or assessed by in situ antibody staining. Together with the organism's genetic versatility, the C. elegans intestine thus provides a unique in vivo model for the visual, developmental, and molecular genetic analysis of polarized membrane and tube biogenesis. The specific methods (all standard) described here include how to: label intestinal subcellular components by antibody staining; analyze genes involved in polarized membrane biogenesis by loss-of-function studies adapted to the typically essential tubulogenesis genes; assess polarity defects during different developmental stages; interpret phenotypes by epifluorescence, differential interference contrast (DIC) and confocal microscopy; quantify visual defects. This protocol can be adapted to analyze any of the often highly conserved molecules involved in epithelial polarity, membrane biogenesis, tube and lumen morphogenesis.

CCM-3 Promotes C. elegans Germline Development by Regulating Vesicle Trafficking Cytokinesis and Polarity

Cerebral cavernous malformations (CCMs) are vascular defects of the CNS that arise from loss of integrity of the endothelial cells lining blood capillaries, causing leakage of blood into the brain [1]. This results in headaches, seizures, and/or hemorrhagic stroke, depending on the location of the lesion. CCM affects 0.5% of the population and follows anautosomal dominant inheritance pattern caused bymutations in one of the three genes: CCM1 (gene name KRIT1), CCM2 (also known as malcavernin orOSM), and CCM3 (gene name PDCD10) [2, 3], with the earliest onset and most severe prognosis occurring in CCM3 patients [4]. The three CCM genes encode structurally distinct scaffold proteins that function in multiple complexes [5-9]. Using the C.elegans germline as a model of multicellular tube development, we show here that CCM-3 is enriched at the luminal membrane of the germline and the contractile ring of dividing cells in the embryo. Loss of ccm-3 results in defective RAB-11-mediated endocytic recycling, which in turn is necessary for gonadal lumen (rachis) formation, completion of cytokinesis, and localization of cell-surface receptors. CCM-3-mediated localization of anillin and non-muscle myosin to the lateral surfaces of germ cells is required for proper cytoskeletal organization, subsequent oocyte growth, and localization of polarity proteins. Biochemical analysis reveals conservation of the STRIPAK complex and distinct roles for GCK-1 (germinal center kinase III family protein) and striatin/CASH-1 in controlling the localization and function of CCM-3. Taken together, our data establish CCM-3 as a novel regulator of rachis lumenization and polarity establishment during embryogenesis.