Mechanical Rigidity Research Articles

Microscopic structural origin behind slowing down of colloidal phase separation approaching gelation.

The gelation of colloidal particles interacting through a short-range attraction is widely recognized as a consequence of the dynamic arrest of phase separation into colloid-rich and solvent-rich phases. However, the microscopic origin behind the slowing down and dynamic arrest of phase separation remains elusive. In order to access microscopic structural changes through the entire process of gelation in a continuous fashion, we used core-shell fluorescent colloidal particles, laser scanning confocal microscopy, and a unique experimental protocol that allows us to initiate phase separation instantaneously and gently. Combining these enables us to track the trajectories of individual particles seamlessly during the whole phase-separation process from the early stage to the late arresting stage. We reveal that the enhancement of local packing and the resulting formation of locally stable rigid structures slow down the phase-separation process and arrest it to form a gel with an average coordination number of z = 6-7. This result supports a mechanical perspective on the dynamic arrest of sticky-sphere systems based on the microstructure, replacing conventional explanations based on the macroscopic vitrification of the colloid-rich phase. Our findings illuminate the microscopic mechanisms behind the dynamic arrest of colloidal phase separation, the emergence of mechanical rigidity, and the stability of colloidal gels.

A Strong and Rigid Coordination Adaptable Network that Can Be Reprocessed and Recycled at Mild Conditions

A Strong and Rigid Coordination Adaptable Network that Can Be Reprocessed and Recycled at Mild Conditions

Structuration of biosorbents in the form of reinforced gelled and porous composites based on Opuntia ficus indica (cactus) extract and sodium alginate

The main objective of the proposed work was to optimize an adsorbent gel from biological material with the substitution of PVA by biopolymer extracted from cactus while maintaining the mechanical and sorption properties. The porous composite was based on cactus extract (CE) and sodium alginate (SA) and the mechanical properties and adsorption capacities of these beads were then compared with those modified using polyvinyl alcohol (PVA) and calcium carbonate (CC), respectively.Twenty formulations, based on CE, SA, PVA and CC, have made it possible to prepare, in accordance with an experimental design conducted in Mode 6, four major classes of beads. The three responses used to assess the evolution in bead performance were: the breaking point of the beads, bead rigidity based on a rheological study and the adsorption capacity of pentachlorophenol (PCP). The analysis of these responses showed that CE exerted a positive effect on both the mechanical strength (400–2200 Pa) and rigidity (5%–11%) of the beads, similar to that of PVA with the conservation of bead adsorption capacity (80–120 mg g−1of dry matter).The beads, based on CE and SA, revealed their regular shape with a porous structure and good chemical and physical stability. The FTIR spectral analysis suggested that the interactions between SA and CE take place via hydrogen interactions and/or covalent bonds between the hydroxyl and carboxyl groups.

Mechanical rigidity of bacterial membrane models: effects of lipids and peptides probed by MD

Antimicrobial peptides (AMPs) are membrane-targeting short sequence peptides that have potential for the development of new antibiotics. AMPs are generally cationic, and target negatively charged bacterial membranes, resulting in their disruption. The multiple peptide resistance factor (MprF) protein reduces AMP binding to bacterial membranes via the conversion of anionic phosphatidylglycerol (PG) lipids into either zwitterionic Alanyl-phosphatidylglycerol (Ala-PG) or cationic Lysyl-phosphatidylglycerol (Lys-PG) lipids, reducing the negative surface charge present on the membrane.

Morphological, barrier, thermal, and rheological properties of high-pressure treated co-extruded polylactide films and the suitability for food packaging

Commercial coextruded polylactide films have demonstrated high stiffness, gas and aroma barrier, but little is known about their microstructure and film morphology, in particular in a high-pressure (HP) environment. Therefore, the objective of this study is to examine the influence of the HP-treatment in the pressure range of 300–600 MPa for a residence time of 15 min, and thereafter, assessed changes in the morphological, thermal, rheological, optical, and barrier properties of two commercial co-extruded polylactide films with varying thickness (25-μm and 75-μm). The barrier properties of the films remained unchanged by the treatment except for the thin film (25-μm) that was treated at 600 MPa. The surface morphology and roughness of the thin films were affected by the HP-treatment while XRD analysis confirmed changes in the structure/crystallinity of PLA. The TGA curves demonstrated a variation in thermograms between the two films. HP-treated films exhibited predominating liquid-like property on the melt, and the thin films exhibited higher mechanical rigidity than the thick films. The results demonstrated that HP-treatment significantly affected microstructures of the film. More studies are required for the commercial success of these films by improving film properties and the interaction between the film and the food under high-pressure.

Stress effect on the resonance properties of single-crystal diamond cantilever resonators for microscopy applications

Micro-cantilever beams have been widely used for surface sensing applications as well as atomic force microscope. However, surface stress appears in cantilever beams due to a variety of factors such as the absorption of molecules, temperature variations, materials imperfectness, and the fabrication process. Single-crystal diamond (SCD) has been regarded as an ideal material for cantilever sensors through the surface effect due to the outstanding mechanical rigidity and chemical inertness. In this paper, the authors report on the SCD cantilever beams fabricated by a smart-cut method with high quality factors up to 14 000 and stress characterization by surface geometry curvature observation and Raman microscopy. Although both surface geometry profile and Raman shift show the existence of surface stress in the SCD cantilever beams, the resonance properties are little influenced and maintain excellent rigidity and high quality. Therefore, the SCD-on-SCD resonator provides a promising platform for high-reliability microscopy applications.

Explicit Analytical Solution for Random Close Packing in d=2 and d=3.

We present an analytical derivation of the volume fractions for random close packing (RCP) in both d=3 and d=2, based on the same methodology. Using suitably modified nearest neighbor statistics for hard spheres, we obtain ϕ_{RCP}=0.658 96 in d=3 and ϕ_{RCP}=0.886 48 in d=2. These values are well within the interval of values reported in the literature using different methods (experiments and numerical simulations) and protocols. This statistical derivation suggests some considerations related to the nature of RCP: (i)RCP corresponds to the onset of mechanical rigidity where the finite shear modulus emerges, (ii)the onset of mechanical rigidity marks the maximally random jammed state and dictates ϕ_{RCP} via the coordination number z, (iii)disordered packings with ϕ>ϕ_{RCP} are possible at the expense of creating some order, and z=12 at the fcc limit acts as a boundary condition.

High resolution imaging of viruses: Scanning probe microscopy and related techniques.

Scanning probe microscopy is a group of measurements that provides 3D visualization of viruses in different environmental conditions including liquids and air. Besides 3D topography it is possible to measure the properties like mechanical rigidity and stability, adhesion, tendency to crystallization, surface charge, etc. Choosing the right substrate and scanning parameters makes it much easier to obtain reliable data. Rational interpretation of experimental results should take into account possible artifacts, proper filtering and data presentation using specially designed software packages. Animal and human virus characterization is in the focus of many intensive studies because of their potential harm to higher organisms. The article focuses on high-resolution visualization of plant viruses. Tobacco mosaic virus, potato viruses X and B and others are not dangerous for the human being and are widely used in different applications such as vaccine preparation, construction of building units in nanotechnology and material science applications, nanoparticle production and delivery, and even metrology. The methods of virus's deposition, visualization, and consequent image processing and interpretation are described in details. Specific examples of viruses imaging are illustrated using the FemtoScan Online software, which has typical and all the necessary built-in functions for constructing three-dimensional images, their processing and analysis. Despite visible progress in visualizing the viruses using probe microscopy, many unresolved problems still remain. At present time the probe microscopy data on viruses is not systemized. There is no descriptive atlas of the images and morphology as revealed by this type of high resolution microscopy. It is worth emphasizing that new virus investigation methods will appear due to the progress of science.

Experimental Verification of Multipactor Suppression in Microstripline Using High Porosity Surfaces

We report computational and experimental research results confirming that surfaces with porosity exceeding a certain threshold will fully suppress multipactor in parallel-plate microstripline structures, while negligibly perturbing the RF transmission properties. Our research also identified a practical arrangement of nonuniform pores that provided the required high-porosity for multipactor suppression, but with enhanced mechanical rigidity. This alternative layout facilitates the fabrication process using commercially-available manufacturing methods. Porous, multipactor-resistant surfaces can be used in a wide range of high-power components including high-power microwave sources, antennas, filters, and transmission lines (TLs).

A study on reducing eddy current loss of sleeve and improving torque density using ferrofluid of a surface permanent magnet synchronous motor

It has advantages such as high power density and miniaturisation when the motor operates at high speed. However, as a side effect, the loss density is much higher than that of a constant speed motor. In addition, a retaining sleeve is inserted in the high-speed motors to prevent the rotor from scattering. This insertion deteriorates the performance due to the increase of airgap, and eddy current loss occurs in the sleeve. In order to improve these shortcomings, the sleeve is redesigned in this paper. A groove was dug into the retaining sleeve and ferrofluid was injected. Ferrofluid refers to water or oil mixed with ultra-fine powder. Since the permeability of ferrofluid is greater than that of airgap, it is possible to have high output and high efficiency. Since the material of the sleeve is non-permeable, the performance is reduced with the same effect as increasing the airgap. However, if a ferrofluid is inserted by digging a groove in the retaining sleeve, the magnetic flux from the magnet flows into the stator through the ferrofluid, which has the same effect as reducing the airgap. Therefore, the torque density increases. Also, the eddy current loss is reduced through the retained sleeve groove. Moreover, a sleeve skew structure was used to further reduce the eddy current loss. In this paper, the mechanical rigidity at the rated speed was also taken into consideration. As a result, eddy current loss was reduced and torque density was improved. This is verified through the final finite element analysis.

Electromechanics of lipid-modulated gating of potassium channels

Experimental studies reveal that the anionic lipid phosphatidic acid (POPA), non-phospholipid cholesterol, and cationic lipid DOTAP inhibit the gating of voltage-sensitive potassium (Kv) channels. Here, we develop a continuum electromechanical model to investigate the interaction of these lipids with the ion channel. Our model suggests that: (i) POPA lipids may restrict the vertical motion of the voltage-sensor domain through direct electrostatic interactions; (ii) cholesterol may oppose the radial motion of the pore domain of the channel by increasing the mechanical rigidity of the membrane; and (iii) DOTAP can reduce the effect of electrostatic forces by regulating the dielectric constant at the channel–lipid interface. The electromechanical model predictions for the three lipid types match well with the experimental observations and provide mechanistic insights into lipid-dependent gating of Kv channels.

Formulation of zwitter-ionic terpolymeric hydrogels and their comprehensive rheological investigation

With the rapid enhancement in pharmaceutics, cosmetics, medical applications, and water contamination, the demand of hydrogels with varying properties is increasing day by day. Hydrogels with keen properties like pH sensitive, thermosensitive, biocompatibility, visco-elasticity, mechanical rigidity, and resistive to exterior stress are of great interest. In order to attain such properties for above mentioned applications, a zwitter ionic hydrogel was synthesized having flexible nature, pH sensitive and is tested using rheometer. Rheological properties are elucidated using frequency sweep and flow curve analysis. The fluidity index lower than unity indicates the non-Newtonian shear thinning behavior. The lower value of shear thinning makes it a feasible candidate to be used in paints and cosmetics industries like nail polish, lotions etc. Values for consistency index increased with rising temperature and increasing amount of AMPS. The increase in consistency coefficient and yield stress with increasing temperature from 25 to 35 ̊C indicates the strengthing of hydrogels which will facilitates jellification of drug delivery system on skin. Modified Bingham model was found the best fit to our rheological data. The thermodynamic data obtained revealed higher activation energy for ZHG-02 with greater concentration of AMPS than ZHG-01 with lower amount of AMPS.

New crosslinked membranes based on cardo-poly(etherketone) and poly(ethylene imine) for the vanadium redox flow battery

• Low-cost membranes for VFRBs are synthesized by crosslinking PEI with PEKC. • x %PEI-PEKC membranes exhibt low AR and low VO 2+ permeability simultenously. • The 50%PEI-PEKC membrane displays superior VRFB efficiencies and cycling stability. Developing polymer membranes with low cost, high ionic conduction and low vanadium ion permeability simultaneously for the vanadium redox flow battery (VRFB) is a huge challenge to macromolecule design and engineering. Herein, a series of high-performance and low-cost macromolecule cross-linked membranes for VRFB are synthesized from cardo-poly(etherketone) (PEKC) and poly(ethylene imine) (PEI) through a straightforward lactamization reaction between the primary amines in PEI and lactones in PEKC. Owing to the acid-base interaction between amino groups of PEI and sulfonic acid (SA), crosslinked x %PEI-PEKC membranes exhibit excellent SA adsorption capability and low area resistance. Meanwhile, the formed macromolecule multi-crosslinked networks significantly improve the membrane-forming property of PEI and endow membranes with superior mechanical rigidity and low vanadium ion permeability simultaneously. Consequently, the 50%PEI-PEKC membrane exhibit a nearly 90 times higher ion selectivity of 24.71 × 10 5 S min cm −3 than Nafion 115. The assembled VRFB with 50%PEI-PEKC displays higher battery efficiencies than Nafion 115 at 60–160 mA cm −2 , which also possesses superior cycling stability at 100 mA cm −2 .

Cationic surface-modified regenerated nanocellulose hydrogel for efficient Cr(VI) remediation

Because nanocellulose has a large specific surface area and abundant hydroxyl functional groups due to its unique nanomorphology, interest increases as an eco-friendly water treatment material. However, the distinctive properties of nanocellulose, which exists in a dispersion state, strongly hamper its usage in practical water treatment processes. Additionally, nanocellulose shows low performance in removing anionic pollutants because of its anionic characteristics. In an effort to address this challenge, regenerated cellulose (RC) hydrogel was fabricated through cellulose's dissolution and regeneration process using an eco-friendly aqueous solvent system. Subsequently, a crosslinking process was carried out to introduce the cationic functional groups to the RC surface PEI coating (P/RC). As a result, the PEI surface cationization process improved the mechanical rigidity of RC and showed an excellent Cr(VI) removal capacity of 578 mg/g. In addition, the prepared P/RC maintained more than 90% removal efficiency even after seven reuses.

High temperature co-firing of 3D-printed Al[sbnd]ZnO/Al2O3 multi-material two-phase flow sensor

Sensors are crucial in the understanding of machines working under high temperatures and high-pressure conditions. Current devices utilize polymeric materials as electrical insulators which pose a challenge in the device's lifespan. Ceramics, on the other hand, is robust and able to withstand high temperature and pressure. For such applications, a co-fired ceramic device which can provide both electrical conductivity and insulation is beneficial and acts as a superior candidate for sensor devices. In this paper, we propose a novel fabrication technique of complex multi-ceramics structures via 3D printing. This fabrication methodology increases both the geometrical complexity and the device's shape precision. Structural ceramics (alumina) was employed as the electrical insulator whilst providing mechanical rigidity while a functional ceramic (alumina-doped zinc oxide) was employed as the electrically conductive material. The addition of sintering additives, tailoring the printing pastes' solid loadings and heat treatment profile resolves multi-materials printing challenges such as shrinkage disparity and densification matching. Through high-temperature co-firing of ceramics (HTCC) technology, dense high quality functional multi-ceramics structures are achieved. The proposed fabrication methodology paves the way for multi-ceramics sensors to be utilized in high temperature and pressure systems in the near future.

Pressure-Biased Nanopores for Excluded Volume Metrology, Lipid Biomechanics, and Cell-Adhesion Rupturing.

Nanopore sensing has been widely used in applications ranging from DNA sequencing to disease diagnosis. To improve these capabilities, pressure-biased nanopores have been explored in the past to-primarily-increase the residence time of the analyte inside the pore. Here, we studied the effect of pressure on the ability to accurately quantify the excluded volume which depends on the current drop magnitude produced by a single entity. Using the calibration standard, the inverse current drop (1/ΔI) decreases linearly with increasing pressure, while the dwell drop reduces exponentially. We therefore had to derive a pressure-corrected excluded volume equation to accurately assess the volume of translocating species under applied pressure. Moreover, a method to probe deformation in nanoliposomes and a single cell is developed as a result. We show that the soft nanoliposomes and even cells deform significantly under applied pressure which can be probed in terms of the shape factor which was introduced in the excluded volume equation. The proposed work has practical applications in mechanobiology, namely, assessing the stiffness and mechanical rigidity of liposomal drug carriers. Pressure-biased pores also enabled multiple observations of cell-cell aggregates as well as their subsequent rupture, potentially allowing for the study of microbial symbioses or pathogen recognition by the human immune system.

Structure and Mechanical Stabilities of the Three-Way Junction Motifs in Prohead RNA.

The core structure of phi29 prohead RNA (pRNA) is composed of three major helices organized into three-way junction pRNA (3WJ-pRNA) and has stout structural rigidity along the coaxial helices. Prohead RNAs of the other Bacillus subtilis bacteriophages such as GA1 and SF5 share similar secondary structure and function with phi29; whether these pRNAs have similar mechanical rigidity remains to be elucidated. In this study, we constructed the tertiary structures of GA1 and SF5 3WJ-pRNAs by comparative modeling. Both GA1 and SF5 3WJ-pRNAs adopt a similar structure, in which three helices are organized as the three-way junction and two of the three helices are stacked coaxially. Moreover, detailed structural features of GA1 and SF5 3WJ-pRNAs are also similar to those of phi29 3WJ-pRNA: all of the bases of the coaxial helices are paired, and all of the adenines in the junction region are paired, which eliminates the interference of A-minor tertiary interactions. Hence, the coaxial helices tightly join to each other, and the major groove between them is very narrow. Two Mg2+ ions can thus fit into this major groove and form double Mg clamps. A steered molecular dynamics simulation was used to study the mechanical properties of these 3WJ-pRNAs. Both GA1 and SF5 3WJ-pRNAs show strong resistance to applied force in the direction of their coaxial helices. Such mechanical stability can be attributed to the Mg clamps.

Experimental and Numerical Simulation of Neuro Fuzzy Based Cartesian Robot for Soft Material Cutting

Present technology used for soft material cutting robot are laser, water-jet, ultrasonic, plasma and oxy-gas cutting. The scope for designing and fabrication of soft material cutting robots are increasing due to its cost effectiveness and quality of cutting. Cartesian robots are mainly used in assembly and manufacturing applications. They also have a high degree of mechanical rigidity, accuracy, and repeatability. A previous work of more elementary kind was used as a skeleton model to start this work The purpose of the work is the maintenance and implementation of a 4 Degree of freedom robot and also to provide intelligence to the robot using Fuzzy logic and Neuro-Fuzzy for soft material cutting. The kinematic modeling of robot manipulator is done using Denavit-Hartenberg (D-H) parameterization method and Euler-Lagrange method is used for dynamic analysis to determine actuator torque for each joint. The image is acquired with the help of the digital camera which is fixed in a suitable position so that it can scan the entire workspace. Prewitt edge detection algorithm was used for image processing and analysis. The signal for the cutting is interfaced through the Arduino Uno r3 controller.

Changes in Cell Morphology and Actin Organization in Embryonic Stem Cells Cultured under Different Conditions.

The cellular cytoskeleton provides the cell with a mechanical rigidity that allows mechanical interaction between cells and the extracellular environment. The actin structure plays a key role in mechanical events such as motility or the establishment of cell polarity. From the earliest stages of development, as represented by the ex vivo expansion of naïve embryonic stem cells (ESCs), the critical mechanical role of the actin structure is becoming recognized as a vital cue for correct segregation and lineage control of cells and as a regulatory structure that controls several transcription factors. Naïve ESCs have a characteristic morphology, and the ultrastructure that underlies this condition remains to be further investigated. Here, we investigate the 3D actin cytoskeleton of naïve mouse ESCs using super-resolution optical reconstruction microscopy (STORM). We investigate the morphological, cytoskeletal, and mechanical changes in cells cultured in 2i or Serum/LIF media reflecting, respectively, a homogeneous preimplantation cell state and a state that is closer to embarking on differentiation. STORM imaging showed that the peripheral actin structure undergoes a dramatic change between the two culturing conditions. We also detected micro-rheological differences in the cell periphery between the cells cultured in these two media correlating well with the observed nano-architecture of the ESCs in the two different culture conditions. These results pave the way for linking physical properties and cytoskeletal architecture to cell morphology during early development.

Bioinspired soft microrobots actuated by magnetic field

In contrast to traditional large-scale robots, which require complicated mechanical joints and material rigidity, microrobots made of soft materials have exhibited amazing features and great potential for extensive applications, such as minimally invasive surgery. However, microrobots are faced with energy supply and control issues due to the miniaturization. Magnetic field actuation emerges as an appropriate approach to tackle with these issues. This review summarizes the latest progress of biomimetic soft microrobots actuated by magnetic field. Starting with an overview of the soft material and magnetic material adopted in the magnetic field actuated soft microrobots, the various fabrication methods and design structures of soft microrobots are summarized. Subsequently, practical and potential applications, such as targeted therapy, surgical operation, and the transportation of microscopic objects, in the fields of biomedicine and environmental remediation are presented. In the end, some current challenges, and the future development trends of magnetic soft microrobots are briefly discussed. This review is expected to offer a helpful guidance for the new researchers of biomimetic soft microrobots actuated by magnetic field.