Mechanical Rigidity Research Articles

Utilizing Frémy's Salt to Increase the Mechanical Rigidity of Supramolecular Peptide-Based Gel Networks.

Peptide-based supramolecular gels are an important class of biomaterials that can be used for biomedical applications ranging from drug delivery to tissue engineering. Methodology that allows one to readily modulate the mechanical properties of these gels will allow yet even a broader range of applications. Frémy's salt is an inorganic salt and long-lived free radical that is known to oxidize phenols. Herein, we show that Frémy's salt can be used to dramatically increase the mechanical rigidity of hydrogels formed by tyrosine-containing self-assembling β-hairpin peptides. When Frémy's salt is added to pre-formed gels, it converts tyrosine residues to o-quinones that can subsequently react with amines present within the lysine side chains of the assembled peptide. This results in the installation of chemical crosslinks that reinforce the gel matrix. We characterized the unoxidized and oxidized gel systems using UV-Vis, transmission electron microscopy and rheological measurements and show that Frémy's salt increases the gel rigidity by nearly one order of magnitude, while retaining the gel's shear-thin/recovery behavior. Thus, Frémy's salt represents an on-demand method to modulate the mechanical rigidity of peptide-based self-assembled gels.

Enhancing the flame retardancy of lyocell fabric finished with an efficient, halogen-free flame retardant.

A novel flame retardant (PNPG) containing phosphorus and nitrogen was synthesized through the reaction of neopentyl glycol, phosphoric acid and urea, and was then used for preparation of flame retardant lyocell fabric through a dip-dry-cure finishing process. The structure of the PNPG was confirmed by proton nuclear magnetic resonance spectroscopy (1H-NMR) and Fourier transform infrared spectroscopy (FT-IR). The flame retardancy and thermal stability of the treated fabric were evaluated by a cone calorimetry test and thermogravimetric analysis (TG), which showed that the char residue of the treated fabric at 800 °C was as high as 39.7% under a nitrogen atmosphere. At the same time, the peak heat release rate (PHRR) and total heat release (THR) were significantly reduced by 92.9% and 81.2%, respectively. Obviously, the presence of flame retardant can effectively improve the thermal stability and flame retardancy of lyocell fabrics. In addition, thermogravimetric analysis combined with Fourier transform infrared spectroscopy (TG-IR), scanning electron microscopy (SEM), and Raman spectroscopy indicated that the flame retardant mechanism was consistent with the condensed phase and gas phase mechanism. The limiting oxygen index (LOI) of the treated samples could reach 39.3%, moreover, even after 20 laundering cycles (LCs), the LOI values of the samples finished at 28.3% with 120 g L−1 flame retardant remaining, which confirmed the durability and high flame retardancy of the treated samples. In addition, the mechanical properties, whiteness, rigidity and flexibility of the fabrics treated with PNPG were insignificantly reduced within a more acceptable range than the original samples. In summary, the flame retardant described herein has excellent flame retardant properties and char-forming ability, and it is suitable for the preparation of flame retardant lyocell fibers.

Алгоритм формирования внутренней структуры изделия с учетом напряженно-деформированного состояния на примере трехточечного изгиба

An algorithm is proposed for optimizing the internal structure of a sample obtained by 3D printing, while maintaining the mechanical strength and rigidity. The basis is the pre-calculated stress-strain state of the sample in an elastic isotropic setting. Numerical simulation results are obtained showing the performance of the optimized design using the example of the three-point bending problem. Comparison of the results of numerical modeling, optimized and monolithic samples, in elastic isotropic formulation is presented

Mechanical rigidity of a shape-memory metal-organic framework increases by crystal downsizing.

Soft porous nanocrystals with a pronounced shape-memory effect exhibit two- to three-fold increase in elastic modulus compared to the microcrystalline counterpart as determined by atomic force microscopy nanoindentation. The increase in rigidity is consistent with the known shape-memory effect displayed by the framework solid at the nanoscale. Crystal downsizing can offer new avenues for tailoring the mechanical properties of metal-organic frameworks.

Retracted] Graphene: A Multifunctional Nanomaterial with Versatile Applications

Graphene is a 2D material of high quality obtained from a single atom with unique electronic properties. Graphene has the potential to improve the efficiency, versatility, and durability of a wide range of materials and their applications, but its commercial exploitation will require further study. Due to its flatness and semiconductivity in addition to its high surface area, high mechanical rigidity, high thermal stability, superior thermal conductivity, and electrical conductivity, good biocompatibility, and easy functionalization, graphene is the best candidate for multifunctional applications which opened up new possibilities for potential devices and systems. Every type of graphene material is found to exhibit different and unique tunable properties. Graphene is the best candidate in making nanocomposite‐based electrochemical sensors. Graphene is among the best electronic materials, but synthesizing a single sheet of graphene has received less attention. The objective of this chapter is to bring awareness to readers on the synthesis, properties, and applications of graphene. The limitations of the current knowledge base and prospective research directions related to graphene materials have also been illustrated.

Process parameter optimization in underwater Friction Stir welding of dissimilar aluminium alloy butt joints by design of experiment

Friction Stir Welding (FSW) is a nontraditional joining method that is used for the attachment of similar and divergent substances, which are comparatively difficult to be welded by fusion techniques. They are extensively used for joining metals in different applications. Also, this welding is more energy-competent and eco-responsive when contrasted with traditional fusion methods. The FSW has various degrees of prevalence when compared with conventional fusion. Generally, the mechanical properties of heat-treatable alloys are reduced due to thermal cycles and the roughening of the reinforcing expeditions in the FSW, resulting in joint softening. The Underwater Friction Stir Welding (UWFSW) is a preferred methodology to prevail over these problems. This procedure is appropriate for the heat treatable materials which are responsive to thermal activities throughout the fusion cycle. In this work, the UWFSW was carried for welding dissimilar alloys AA7075 and AA6082 with dimensions of 150 × 100 × 6 mm. The Hot work steel H13 was used as a tool material. Also, the influence of the fusion characteristics, including tool rotational speed, tool traverse speed, and tool tilt angle on the micro-arrangement and tensile characteristics of the UWFSW joints of AA7075 and AA6082 alloy, were investigated using Taguchi’s method. The S/N fraction scrutiny revealed that the optimum mechanical rigidity was attained at a tool rotational speed of 1200 rpm, tool fusion speed of 40 mm/min, and tool tilt angle of 1°. In accordance with the ANOVA method, the maximum input of parameters were analyzed for the objective functions, including the UTS (MPa), % of elongation, and micro hardness in the different zones (NZ, TMAZ, HAZ).

An injectable PEG hydrogel controlling neurotrophin-3 release by affinity peptides

Neurotrophin-3 growth factor can improve cochlear neuron survival, and localized delivery of this protein to the round window membrane in the middle ear may be able to reverse sensorineural hearing loss. Thus, the goal of this work was to develop an injectable hydrogel delivery system that can allow localized release of neurotrophin-3 in a controlled and sustained manner. We identified a PEG hydrogel formulation that uses thiol-vinyl sulfone Michael addition for crosslinking. This injectable formulation provides elastic hydrogels with higher mechanical rigidity, better bio-adhesion and longer residence time than Poloxamer hydrogels currently being investigated clinically for hearing loss. In vivo, PEG hydrogels induce local immune responses comparable to biocompatible Poloxamer hydrogels, yet they released payloads at a ~5-fold slower rate in the subcutaneous area. Based on this injectable hydrogel formulation, we designed an affinity-based protein release system by modifying PEG hydrogels with affinity peptides specific to neurotrophin-3 proteins. We verified the sustained release of neurotrophin-3 from peptide-conjugated PEG hydrogels resulting from the reversible interaction between peptides and proteins. The rate of affinity-controlled release depends on the polymer concentrations, the affinity of peptides and the peptide-to-protein ratios. Collectively, we developed an injectable hydrogel formulation for localized delivery of neurotrophin-3, which provides affinity-controlled release and longer delivery time compared to Poloxamer hydrogels.

Synthesis of a robust control system for two-mass electric drive by H∞-theory

The practice of designing and operating control systems for industrial facilities has shown that systems synthesized according to the criteria of modular and symmetric optima, as well as by quadratic quality criteria, are sensitive to changes in the parameters of the controlled object, incoming characteristics, disturbing influences, the structure and parameters of the object model changing, which used in control loops. Such systems can lose optimality as well as productivity, if information about the object and operating environment is known with some probability or uncertainty. For an industrial electric drive, changes in load torque, moment of inertia of rotating parts, supply voltage and environmental characteristics (temperature, vibration) are especially significant. These changes affect both the mechanical characteristics rigidity and the transients’ quality.
 Robust control systems provide a required quality of work when changing the characteristics of impacts and instability of the control object parameters in a wide range. In the presence of uncertainties, a robust controller provides robust stability and quality for all admissible uncertainties.
 The synthesis of robust control systems with an H∞-speed controller of a two-mass electric drive by methods of H∞-theory is presented in order to prove the possibility of using algorithms for a given stabilization and speed control, as well as providing the necessary degree of sensitivity to parametric and coordinate disturbances acting on the control object. Application of the method of robust controllers’ synthesis taking into account the requirements for the quality of a controlled coordinate transient processes in the control system. The analysis of the operation of a synthesized robust system with an H∞-speed controller using digital modeling on mathematical models in the MATLAB / Simulink environment is carried out. The possibility of the speed independent control, the steady-state error and the nature of the transient processes of the controlled coordinate in the synthesized electric drive control system is shown.

Mechanical Flexibility of DNA: A Quintessential Tool for DNA Nanotechnology.

The mechanical properties of DNA have enabled it to be a structural and sensory element in many nanotechnology applications. While specific base-pairing interactions and secondary structure formation have been the most widely utilized mechanism in designing DNA nanodevices and biosensors, the intrinsic mechanical rigidity and flexibility are often overlooked. In this article, we will discuss the biochemical and biophysical origin of double-stranded DNA rigidity and how environmental and intrinsic factors such as salt, temperature, sequence, and small molecules influence it. We will then take a critical look at three areas of applications of DNA bending rigidity. First, we will discuss how DNA’s bending rigidity has been utilized to create molecular springs that regulate the activities of biomolecules and cellular processes. Second, we will discuss how the nanomechanical response induced by DNA rigidity has been used to create conformational changes as sensors for molecular force, pH, metal ions, small molecules, and protein interactions. Lastly, we will discuss how DNA’s rigidity enabled its application in creating DNA-based nanostructures from DNA origami to nanomachines.

(Invited) Organic Single-Ion Conductors for All-Solid-State Lithium Metal Batteries

The all-solid-state lithium metal batteries (ASSLMBs) have recently garnered considerable attention as a next-generation energy storage system beyond current state-of-the-art lithium-ion batteries (LIBs). A key component enabling the ASSLMBs is solid-state electrolytes. Previous studies on solid-state electrolytes have mostly focused on inorganic-based ionic conductors (e.g., sulfides and oxides).[1] Despite their notable progresses in ionic conductivity, the inorganic solid electrolytes have still suffered from grain boundary resistance, poor contact/interfacial instability with electrodes, and mechanical rigidity, thus posing formidable challenges for their practical use. As an alternative to the inorganic solid electrolytes, an interest in organic single-ion conductors has newly emerged owing to their facile processability, physical flexibility, intimate contact with electrodes, versatile chemistry, and high cation transport capability.[2] In sharp contrast to conventional dual-ion polymeric conductors (e.g., a mixture of polymer matrix and lithium salts), the organic single-ion conductors do not contain freely movable anions that could often cause unwanted side reactions with electrodes and charge polarization, thereby providing improvements in electrode-electrolyte stability and electrochemical sustainability of cells.Here, this talk presents a new class of organic single-ion conductors (OSICs) as a facile material strategy that can outperform conventional inorganic conductors. Two different design concepts[3] were proposed for the OSICs with a focus on immobilizing anions: (i) covalently tethering anions to covalent organic framework (COF) and (ii) electrostatically trapping anions by polymer–ceramic hybrid electrolytes. These OSICs allowed the cation transference numbers to reach unity (t +>0.9), contributing to reversible stripping/plating of Li electrodes along with alleviating a concern on dendritic growth. Moreover, the structural and physicochemical uniqueness of the OSICs (in specific, directionally ordered porous structure of the COF and conformability/interfacial stability and electrophoresis-driven ion rectifying effect of the hybrid electrolytes) enabled their successful application in ASSLMBs. We envision that the OSICs described herein hold promise as an effective and versatile material platform to move ASSLMBs closer to commercialization.

Cuticle darkening correlates with increased body copper content in Drosophila melanogaster

Insect epidermal cells secrete a cuticle that serves as an exoskeleton providing mechanical rigidity to each individual, but also insulation, camouflage or communication within their environment. Cuticle deposition and hardening (sclerotization) and pigment synthesis are parallel processes requiring tyrosinase activity, which depends on an unidentified copper-dependent enzyme component in Drosophila melanogaster. We determined the metallomes of fly strains selected for lighter or darker cuticles in a laboratory evolution experiment, asking whether any specific element changed in abundance in concert with pigment deposition. The results showed a correlation between total iron content and strength of pigmentation, which was further corroborated by ferritin iron quantification. To ask if the observed increase in iron body content along with increased pigment deposition could be generalizable, we crossed yellow and ebony alleles causing light and dark pigmentation, respectively, into similar genetic backgrounds and measured their metallomes. Iron remained unaffected in the various mutants providing no support for a causative link between pigmentation and iron content. In contrast, the combined analysis of both experiments suggested instead a correlation between pigment deposition and total copper body content, possibly due to increased demand for epidermal tyrosinase activity.

Bioinspired Suprahelical Frameworks as Scaffolds for Artificial Photosynthesis.

Framework materials have shown promising potential in various biological applications. However, the state-of-the-art components show low biocompatibility or mechanical instability, or cannot integrate both optics and electronics, thus severely limiting their extensive applications in biological systems. Herein, we demonstrate that amide-based bioorganic building blocks, including dipeptides and dipeptide nucleic acids, can self-assemble into hydrogen-bonded suprahelix architectures of controllable handedness, which then form suprahelical frameworks with diverse cavities. Especially, the cavities can be tuned to be hydrophilic or hydrophobic, and the shortest diagonal distance can be modulated from 0.5 to 1.8 nm, with the volume proportion in the unit cell changing from 5 to 60%. Furthermore, the hydrogen bonding networks result in high mechanical rigidity and semiconductively optoelectronic properties, which allow the utilization of the suprahelical frameworks as supramolecular scaffolds for artificial photosynthesis. Our findings reveal amide-based suprahelix architectures acting as bioinspired supramolecular frameworks, thus extending the constituents portfolio and increasing the feasibility of using framework materials for biological applications.

Compound Impedance Control of a Hydraulic Driven Parallel 3UPS/S Manipulator

The hydraulic parallel manipulator combines the high-power density of the hydraulic system and high rigidity of the parallel mechanism with excellent load-carrying capacity. However, the high-precision trajectory tracking control of the hydraulic parallel manipulator is challenged by the coupling dynamics of the parallel mechanism and the high nonlinearities of the hydraulic system. In this study, the trajectory control of a 3-DOF symmetric spherical parallel 3UPS/S manipulator is evaluated. Focusing on the highly coupling and nonlinear system dynamics, a compound impedance control method for a hydraulic driven parallel manipulator is proposed, which combines impedance control with the spatial motion characteristics of a parallel manipulator. The control strategy is divided into the inner and outer loops. The inner loop controls the impedance of the actuator in the joint space, and the outer loop controls the impedance of the entire platform in the task space to compensate the coupling of the actuators and improve the tracking accuracy of the moving platform. Compound impedance control does not require force or pressure sensors and is less dependent on modeling precision. The experimental results show that the compound impedance control effectively improves the tracking accuracy of the moving platform. This research proposes a compound impedance control strategy for a 3-DOF hydraulic parallel manipulator, which has high tracking precision with a simple and cheap system configuration.

Fe-MOFs as signal probes coupling with DNA tetrahedral nanostructures for construction of ratiometric electrochemical aptasensor

A ratiometric electrochemical aptasensor is proposed for the detection of thrombin. In the sensor, the iron metal-organic frameworks (Fe MOFs)-labeled aptamer as signal tags was used as signal probe (SP), and the electrolyte solution [Fe(CN)6]3-/4- was utilized as an inner reference probe (IR). In the presence of thrombin, the signal of Fe-MOFs can be detected. Meanwhile, the signal of [Fe(CN)6]3-/4-IR almost remains stable. Accordingly, thrombin concentration can be monitored with the ratio response of IFe-MOFs-SP/I[Fe(CN)6]3-/4--IR. The proposed ratiometric biosensor owns a strong ability to eliminate the disturbance that arises from different DNA loading densities, environmental impact and instrumental efficiency. DNA nanotetrahedron (NTH) with three-dimensional (3D) scaffold can effectively eliminate nonspecific adsorption of DNA and protein. The accessibility of target molecules and loading amounts of signal substances could be increased because of the enhanced mechanical rigidity of well-designed 3D NTH. Thus, detection reproducibility and sensitivity can be further improved. Moreover, the biosensor only requires conjugation with one electroactive substance. The modification procedure can be greatly simplified. The biosensor owns high sensitivity with the detection limit of 59.6 fM. We expect that it will emerge as a generalized ratiometric sensor that may be useful for detecting target analytes.

Collagen-Inspired Helical Peptide Coassembly Forms a Rigid Hydrogel with Twisted Polyproline II Architecture.

Collagen, the most abundant protein in mammals, possesses notable cohesion and elasticity properties and efficiently induces tissue regeneration. The Gly-Pro-Hyp canonical tripeptide repeating unit of the collagen superhelix has been well-characterized. However, to date, the shortest tripeptide repeat demonstrated to attain a helical conformation contained 3–10 peptide repeats. Here, taking a minimalistic approach, we studied a single repeating unit of collagen in its protected form, Fmoc-Gly-Pro-Hyp. The peptide formed single crystals displaying left-handed polyproline II superhelical packing, as in the native collagen single strand. The crystalline assemblies also display head-to-tail H-bond interactions and an “aromatic zipper” arrangement at the molecular interface. The coassembly of this tripeptide, with Fmoc-Phe-Phe, a well-studied dipeptide hydrogelator, produced twisted helical fibrils with a polyproline II conformation and improved hydrogel mechanical rigidity. The design of these peptides illustrates the possibility to assemble superhelical nanostructures from minimal collagen-inspired peptides with their potential use as functional motifs to introduce a polyproline II conformation into hybrid hydrogel assemblies.

Encapsulation of ginger oil in alginate-based shell materials

Hydrogels consisting of a blend of sodium alginate and κ-carrageenan aqueous solutions were prepared using Ca2+ as the gelling agent in a shell material formulation for encapsulation of food-grade ginger oil. A preliminary study on the rheological and textural behavior of two hydrogels prepared from (1) alginate water solution and (2) alginate blended with κ-carrageenan in water showed that the latter produced gels with higher values of elastic and viscous moduli and gel strength, related to added mechanical rigidity. In the encapsulation of ginger oil, 4 formulations of shell material were prepared from 1% w/w alginate solution and from the blend of 1% w/w alginate solution with 1.5% w/w κ-carrageenan (at 80:20 v/v ratio) with and without incubation in a 0.1 w/w chitosan solution as a final coating in a two-stage capsule hardening procedure. The ability of the formulated shell materials to protect the encapsulated ginger oil from oxidative degradation was measured using both primary and secondary oxidation products using peroxide value, p-anisidine value, and thiobarbituric acid reactive substances. Encapsulated ginger oil gave lower values of the oxidation products compared to unencapsulated. Moreover, the ginger oil extracted from capsules with alginate and κ-carrageenan, along with chitosan as the final coating, showed the lowest content of oxidation products throughout the storage period, suggesting a better protection of ginger oil.

Concentric Tube Robots for Minimally Invasive Surgery: Current Applications and Future Opportunities

Minimally Invasive Surgery (MIS) evolved as an alternative to open surgical approaches, and resulted in reduced surgical trauma and faster recovery. However, the confined workspace, loss of depth perception, compromised hand-eye coordination, as well as extended learning curves precluded the surgeons from adapting this approach in all cases. Unlike rigid robots that are characterized with mechanical rigidity and limited degrees-of-freedom (DOFs), continuum robots were developed mainly for interventional medicine. A special class of continuum robots are Concentric Tube Robots (CTRs), that have diameters comparable to those of catheters and steerable needles. Since their introduction, huge effort has been dedicated to the kinematic modelling and real-time control. Due to their intrinsic actuation capability, miniaturization potential and controllable mechanical properties, they have been adopted for different surgical applications. Experimental tests based on phantom and cadaveric studies were performed to prove their feasibility. This review encompasses the generic design, modelling and control methods of CTRs. It also addresses, in detail, their different surgical applications. Finally, related main research limitations and future opportunities are briefly discussed.

Physicomechanical Properties of Epoxy Composites Based on Low-Viscosity Phosphazene-Containing Epoxy-Resorcinol Resins

The physicomechanical and rheological characteristics of epoxyphosphazene-modified binders based on an epoxy-resorcinol resin and isophorone diamine and diaminodiphenyl sulfone hardeners are investigated. It is shown that the introduction of epoxyphosphazene into the epoxy resin helps to maintain the technological characteristics of the binder at an acceptable level and to attain a 40% increase in the mechanical strength and rigidity of cured compositions possessing high heat resistance.

Mechanical Properties of GFR & Graphite Epoxy Polymer Composites

Composite materials have the great potential and widely used as building material in numerous applications. Polymer composite material obtains the necessary properties in a controlled significant degree by the selection of strands and lattice. The properties of the materials have been selected by choosing the correct proportion of matrix and reinforcements. To build the quality of the material by expanding the fiber substance of the material. In this current examination, the mechanical properties of the glass fiber and graphite is strengthened with epoxy polymer composite were considered. Here the open embellishment method was received for the manufacture of the polymer composite The mechanical properties, for example, rigidity, compression quality, sway quality and water ingestion test was resolved according to the ASTM norms. The mechanical properties were improved as the filaments support content expanded in the grid material.

Modification of poly(ethylene 2,5-furandicarboxylate) with aliphatic polycarbonate diols: 1. Randomnized copolymers with significantly improved ductility and high CO2 barrier performance

Poly(ethylene 2,5-furandicarboxylate) (PEF) is a very promising biobased polymer possessing very high mechanical strength, rigidity and gas barrier performance. But its poor ductility and toughness may limit its applications. In this study, PEF-based copolymers with high intrinsic viscosity were successfully synthesized via melt polycondensation of dimethyl 2,5-furandicarboxylate (DMFD) and ethylene glycol in the presence of a copolycarbonate diol (PPeHC diol) as produced from 1,5-pentylene diol (PeDO), 1,6-hexylene diol (HDO) and dimethyl carbonate, and characterized with 1H NMR, 13C NMR, DSC, TGA, tensile, impact and gas barrier testing. The products were “randomnized” as a result of ester-carbonate exchange reaction occurring along melt polycondensation, and therefore became amorphous copolymers possessing composition-dependent physico-mechanical properties which can be tunable from rigid-to-ductile thermoplastics to thermoplastic elastomers. Particularily, the copolymers with φPPeHC of 25 wt% and 30 wt% are thermoplastics possessing greatly improved ductility (elongation at break up to 194%) and CO2 barrier performance higher than poly(ethylene terephthalate) (PET; BIFCO2 3.6–2.8), and retaining high tensile modulus (2.2–1.9 GPa) and yielding strength (69–58 MPa) comparable to the bottle-grade PET. In comparison, the copolymer with φPPeHC of 40 wt% behaves as a high performance thermoplastic elastomer with excellent gas barrier performance as well as high tensile strength (23 MPa).