Grid-type Structure Research Articles

Biomedical porous scaffold fabrication using additive manufacturing technique: Porosity, surface roughness and process parameters optimization

Titanium is a most common and best biocompatible material. The demand and application of Ti alloy is increasing rapidly in orthopedics for clinical operations. The porous structures have been designed for bone tissue engineering or orthopedic applications due to its moderate Young's modulus, excellent compressive strength, biocompatibility and sufficient space for cell accommodation. The porous scaffolds with individual complex internal and external shape can be manufactured by additive manufacturing (AM) processes especially selective laser melting (SLM), both of these have great importance for repairing of large sectional bone defects. This advantage makes the SLM process one of the most competitive AM processes used in the biomedical fields. Seven different Ti–6Al–4V porous scaffolds (Diamond, Grid, Cross, Vinties, Tesseract, Star and Octet) of 15 mm cube with 65% porosity were designed using Rhino 6 software and fabricated through SLM using Ti–6Al–4V powders. This work mainly focused on porous scaffolds design and manufacturing by AM particularly SLM, can able to produce scaffolds of nanoscale grains because of its higher heating rate and lower holding time. But this process generally results insufficient compaction where desired function is not achieved. The scaffolds manufactured by SLM have relatively high accuracy of pore structure and low mechanical strength. Grid type structure exhibits lower surface roughness value and better manufacturing ability where error percentage of porosity is lower than the other scaffolds.The process parameters employed in the study like laser power, scanning speed, hatch distancing and layer thickness are the most significant factors that influence the defect behaviour and morphology of the SLM-fabricated samples. Porosity percentage and surface roughness of the scaffold palys a vital role on its desired functions. While the porosity percentage are also effected by input process parameters resulting the variation on effective elastic modulus. The increase in scanning speed leads to elevation of the cooling rate, which results in a finer microstructure. On the other hand, with lower scanning speeds, coarse microstructure is observed.

Improved Performance of an Electronic Waste Based Cost-Effective Microwave Absorber Using Cavitation

The requisition of cost-effective practical microwave absorbing material (MAM) to deplete electromagnetic (EM) waves has garnered much interest in current times. Aimed at reinforcing the electronic waste (e-waste) management and in the exploration of broadband absorber structure, a compositional variation of the hazardous printed circuit board and zinc-carbon battery cell (Zn-C) is investigated using a facile top-down fabrication technique. The dielectric analysis of samples is carried out in the range of 8.2–12.4 GHz (i.e., X-band) using a waveguide-based microwave measurement technique. A 1.7-mm-thick single-layer absorber achieves a minimum reflection coefficient (RC) of − 24.9 dB at 10.8 GHz with a 2.7 GHz bandwidth (BW) below − 10 dB threshold. Furthermore, the enhancement in absorption BW is accomplished by adding an array of periodic air cavities (grid-type structure) which results in an increase of BW below − 10 dB threshold. Moreover, the integration of planar structure with a grid-type structure imparts more prominent results and acquires 4.0 GHz BW below − 10 dB threshold with 1.7-mm coating thickness. In addition, the influence of the oblique angle of incidence is also investigated for optimized structures. The reliability of the obtained results has been verified by the finite-integration technique via the 3D modeling and EM analysis in computer simulation technology. The inclusion of air gap in the absorbers standardize the EM properties of the composite and result in impedance matching at a higher frequency. The results obtained demonstrate the practicability of the suggested structure and proved to be cutting-edge technology for researchers. It reveals that the e-waste composites have enormous potential in the development of lightweight, broadband, and cost-effective MAM for stealth applications.

Strategy for enhancing mechanical properties and bone regeneration of 3D polycaprolactone kagome scaffold: Nano hydroxyapatite composite and its exposure

Although attempts to improve tissue-engineering scaffolds have been made using composite materials (synthetic polymers, bioceramics, etc.), research on bone tissue engineering has been limited to improving mechanical properties because of the intrinsic drawbacks of the grid-type structures conventionally used as scaffolds. To overcome this limitation, this study proposes a polycaprolactone/nano-hydroxyapatite scaffold with a kagome structure formed via material-extrusion process. The kagome structure is reported to be a mechanically superior open-pore structure. The mechanical properties and in vitro cell activities of 3D scaffolds have been studied with respect to the nano-hydroxyapatite (nHA) content in the scaffold. The compressive modulus of the PCL/nHA scaffold with kagome structure was found to be significantly improved. In addition, nHA particles on the surface of the scaffold were exposed through alkaline erosion, improving bone-regenerating ability. The alkaline erosion did not affect the structural characteristics of the scaffold, including pore size, porosity, hydroxyapatite content, and compressive modulus. Additionally, we observed that the exposure of PCL/nHA particles promoted bone-regeneration activity through enhanced osteoconduction of the scaffold.

Grid-type transparent conductive thin films of carbon nanotubes as capacitive touch sensors

Transparent conductive films are used in a wide variety of devices. While solar cell top electrodes as well as tablet and mobile phone screens require high optical transparency and low sheet resistance (>80% and <10 Ω/□) to maximize power efficiency; other, less demanding applications, such as those in capacitive touch panels and antistatic coatings, in which only small currents are involved, can be managed with coatings of moderate conductivity. In this paper, we show that area-selective argon plasma treated polyethylene terephthalate surfaces are suitable for localized deposition of carbon nanotubes from their aqueous dispersions by a simple dip coating and subsequent drying processes. The as-deposited carbon nanotubes form entangled networks in microscopic patterns over the plasma-treated surface areas with sheet resistance of <1 kΩ/□ and optical transparency of ~75%. Based on this process, we demonstrate grid-type transparent conductive thin films of carbon nanotubes as capacitive touch sensors. Since each process step is robust, easy to up and downscale, and may be implemented even in roll-to-roll and sheet-to-sheet fabrication, the demonstrated technology is promising to produce grid-type structures even at an industrial scale in the future.

2 × 2] Molecular Grids of Ni(II) and Zn(II) with Redox-Active 1,4-Pyrazine-Bis(thiosemicarbazone) Ligands

Tetranuclear complexes [M4(LR)4] with M = Ni(II) or Zn(II), with a [2 × 2] grid-type structure, were assembled in good yields and purity from the easily accessible but unprecedented pyrazine-bridged bis(thiosemicarbazone) protoligands (ligand precursors) H2LR (1,4-pyrazine-2,5-bis(R-carbaldehyde-thiosemicarbazone); R = Me, Et, iPr, or Ph). The complexes were characterised in solution by NMR, MS, IR, and UV-Vis absorption spectroscopy and (spectro)electrochemical methods. HR-MS spectra unequivocally reveal that the tetranuclear species are very stable in solution and any measurements represent these species. Only at higher temperatures (fragmentation in solution: MS and in the solid: TG-DTA) or upon the addition of protons (acidic UV-Vis titrations) can the tetrameric entities be decomposed. Single crystal XRD measurement remained preliminary. Rapid loss of co-crystallised solvent molecules within the [2 × 2] grid-type structures resulted in crystals of very poor quality, but the results were qualitatively in line with spectroscopy, electrochemistry, and quantum chemical (DFT) calculations. IR and NMR spectroscopy point clearly to a thiolate coordination of dianionic (deprotonated) ligands. The electrochemistry reveals four electronically coupled and reversible one-electron reductions centred largely at the pyrazine bridges. EPR and UV-Vis spectroelectrochemical measurements in combination with DFT calculation support the assignment.

Patterning of silver nanowire for grid formation by using ultrasonic assisted clean chemical etching for the application of high transparent electrode

We propose a novel, fast, clean, and dimensionally very accurate ultrasonic assisted technique for silver nanowire (AgNW) etching by using Ni etchant for the purpose of fabricating a grid type structure under static and ultrasonic conditions. A photoactive material pattern on an AgNW network was prepared by using a photolithography process, followed by chemical etching of unwanted AgNWs under static and ultrasonic conditions. The ultrasonic assisted etching process facilitates complete etching of the AgNW pattern (initial condition was 22.4 Ω resistance with 94% light transmittance) within 20–25 s, with almost 35.4% dimensional accuracy relative to the longer static etching condition (7.5 min). A combined process was followed for accurate dimensions because the initial short static etching process weakened the unwanted nanowire structure, while the secondary ultrasonic chemical etching process helps to remove all the AgNW residue from pattern area with faster etching.

A stable open-shell redox active ditopic ligand.

Herein we describe the synthesis, structure and electronic properties of an unusual redox-active ditopic ligand with a stable open-shell configuration. This stable phenoxyl radical features intense and very low energy electronic transitions in the near infrared (NIR) part of the spectrum and is structurally set up to strongly spin couple coordinated transition metal ions in [2 × 2] grid-type structures.

The continuing transformation of Acta Crystallographica Section E and the launch of IUCrData.

The continuing transformation of Acta Crystallographica Section E and the launch of IUCrData.

Two CdII/CoII‐Imidazolate Coordination Polymers: Syntheses, Crystal Structures, Stabilities, and Luminescent/Magnetic Properties

AbstractCadmium(II) based 2D coordination polymer [Cd(L1)2(DMF)2] (1) (L1 = 4,5‐dicyano‐2‐methylimidazolate, DMF = N,N′‐dimethylformamide) and 2D cobalt(II)‐imidazolate framework [Co(L3)4] (2) (L3 = 4,5‐diamide‐2‐ethoxyimidazolate) were synthesized under solvothermal reaction conditions. The materials were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X‐ray diffraction measurement (PXRD) and single‐crystal X‐ray diffraction. Compound 1 has hexacoordinate CdII ions and forms a zigzag chain‐like coordination polymer structure, whereas compound 2 exhibits a 2D square grid type structure. The thermal stability analysis reveals that 2 showed an exceptional thermal stability up to 360 °C. Also, 2 maintained its fully crystalline integrity in boiling water as confirmed by PXRD. The solid state luminescent property of 1 was not observed at room temperature. Compound 2 showed an independent high spin central CoII atom.

Research Communications - over 100 papers and counting!

Research Communications - over 100 papers and counting!

Synthesis and Structural Characterization of 1D and 2D Coordination Polymers based on Flexible 1, 3‐Adamantanediacetic Acid and Exo‐bidentate Organic Linkers

AbstractFive mixed‐linkers based coordination polymers, namely {M(1, 3‐Hadc)(bpy)(H2O)2}n [M = NiII (1), CoII (2)], {Zn(1, 3‐adc)(bpy)0.5}n (3), {Cd(1, 3‐Hadc)2(bpy)}n (4), and {Cu(1, 3‐Hadc)2(bpp)}n (5) [1, 3‐H2adc = 1, 3‐adamantanediacetic acid, bpy = 4, 4′‐bipyridine, bpp = 1, 3‐bis(4‐pyridyl)propane] were synthesized by solvent diffusion reactions. Their structures were determined by single‐crystal X‐ray diffraction analyses. Compounds 1 and 2 are isostructural and they have 1D linear coordination polymer structure that are further interdigitated via hydrogen bonding resulting in 2D extended networks. The dehydrated 1 shows type‐I profile for H2O vapor suggesting hydrophilic nature of the framework. In compound 3, a paddle‐wheel type secondary building unit (SBU) directs the overall structure to form a 2D square grid type structure. The 2D sheets further stack along the c axis in a AB fashion and leaves no void space. Compound 4 has a hexacoordinate CdII and forms a zigzag coordination polymer chain‐like structure and these chains form a 2D structure by hydrogen bonding interactions. Compound 5 contains a longer linker bpp compared to bpy and forms a 2D structure similar to that of 4. These results demonstrate that by changing the metal ions coordination mode versatile structures with different dimensionalities and network topologies can be realized in a same mixed linkers system.

Ag(I) and Cu(I) [2 × 2] Chiral Grids Containing Pyrimidine Ligands with Camphor Moieties. Arene Encapsulation

The C2 symmetric chiral ligand 4,6-bis[(4S,7R)-7,8,8′-trimethyl-4,5,6,7-tetrahydro-4,7-methaneindazol-2-yl]pyrimidine (bpzCampm) was synthesized and reacted with Cu(I) and Ag(I) salts to give four chiral [2 × 2] grid-type structures: [M4(bpzCampm)4]X4, M = Cu(I), Ag(I); X = BF4−, PF6−. The structures of the two BF4− derivatives were determined by X-ray diffraction. The grids contain facing ligands that are not parallel and, in contrast to the situation found in previous examples, the anions are not hosted within the cavities but toluene molecules are. In the case of the copper derivative, π-stacking interactions are established between the pyrimidine rings and these toluene molecules and others situated in the intercationic regions, giving rise to the formation of π-stacked columns with alternating pyrimidine and toluene molecules. Due to the chirality of bpzCampm, chiral cavities are generated in the crystalline structure. From NMR studies, it was concluded that the copper grids are maintained in solutio...

Surface topology of GaSe oxidized crystals

Changes in the surface topology of GaSe crystals caused by their oxidization are investigated by the atomic force microscopy method. The nucleation of a new phase of Ga 2O 3 intrinsic oxide takes place due to the formation of close arrays of nanoneedles precisely oriented normally to the GaSe surface. The temperature and duration of the oxidization process influences on form, sizes, and transformation of nanoneedles. Their sizes change insignificantly in the temperature range 400 to 600 ∘C and for an oxidation time of 1 to 4 h. The average dimension of the nanoneedles’ bases is in the range 50–60 nm and their height increases from 0.5 to 3.5 nm with increasing temperature. The increase of the oxidation temperature also leads to clusterization of nanoneedles in the form of a grid-type structure. The cells of such structure have arbitrary forms and their sizes considerably exceed those of nanoneedles.

Anion−π Interactions as Controlling Elements in Self-Assembly Reactions of Ag(I) Complexes with π-Acidic Aromatic Rings

Reactions of 3,6-bis(2'-pyridyl)-1,2,4,5-tetrazine (bptz) and 3,6-bis(2'-pyridyl)-1,2-pyridazine (bppn) with the AgX salts (X = [PF6]-, [AsF6]-, [SbF6]-, and [BF4]-) afford complexes of different structural motifs depending on the pi-acidity of the ligand central ring and the outer-sphere anion. The bptz reactions lead to the polymeric [[Ag(bptz)][PF6]]infinity (1) and the dinuclear compounds [Ag2(bptz)2(CH3CN)2][PF6]2 (2) and [Ag2(bptz)2(CH3CN)2][AsF6]2 (3), as well as the propeller-type species [Ag2(bptz)3][AsF6]2 (4) and [Ag2(bptz)3][SbF6]2 (5a and 5b). Reactions of bppn with AgX produce the grid-type structures [Ag4(bppn)4][X]4 (6-9), regardless of the anion present. In 6-9, pi-pi stacking interactions are maximized, whereas multiple and shorter (therefore stronger) anion-pi interactions between the anions and the tetrazine rings are established in 1-5b. These differences reflect the more electron-rich character of the bppn pyridazine ring as compared to the bptz tetrazine ring. The evidence gleaned from the solid-state structures was corroborated by density functional theory calculations. In the electrostatic potential maps of the free ligands, a higher positive charge is present in the bptz as compared to the bppn central ring. Furthermore, the electrostatic potential maps of 3, 4, and 5b indicate an electron density transfer from the anions to the pi-acidic rings. Conversely, upon addition of the [AsF6]- ions to the cation of 7, there is negligible change in the electron density of the central pyridazine ring, which supports the presence of weaker anion-pi interactions in the bppn as compared to the bptz complexes. From the systems studied herein, it is concluded that anion-pi interactions play an important role in the outcome of self-assembly reactions.

Multiple expression of molecular information: enforced generation of different supramolecular inorganic architectures by processing of the same ligand information through specific coordination algorithms

The multisubunit ligand 2 combines two complexation substructures known to undergo, with specific metal ions, distinct self-assembly processes to form a double-helical and a grid-type structure, respectively. The binding information contained in this molecular strand may be expected to generate, in a strictly predetermined and univocal fashion, two different, well-defined output inorganic architectures depending on the set of metal ions, that is, on the coordination algorithm used. Indeed, as predicted, the self-assembly of 2 with eight CuII and four CuI yields the intertwined structure D1. It results from a crossover of the two assembly subprograms and has been fully characterized by crystal structure determination. On the other hand, when the instructions of strand 2 are read out with a set of eight CuI and four MII (M = Fe, Co, Ni, Cu) ions, the architectures C1-C4, resulting from a linear combination of the two subprograms, are obtained, as indicated by the available physico-chemical and spectral data. Redox interconversion of D1 and C4 has been achieved. These results indicate that the same molecular information may yield different output structures depending on how it is processed, that is, depending on the interactional (coordination) algorithm used to read it. They have wide implications for the design and implementation of programmed chemical systems, pointing towards multiprocessing capacity, in a one code/ several outputs scheme, of potential significance for molecular computation processes and possibly even with respect to information processing in biology.

Reliability considerations in the placement of control system components

This paper presents a methodology, along with applications to a grid type structure, for incorporating reliability considerations in the decision for actuator placement on large space structures. The method involves the minimization of a criterion that considers mission life and the reliability of the system components. It is assumed that the actuator gains are to be readjusted following failures, but their locations cannot be changed. The goal of the design is to suppress vibrations of the grid and the integral square of the grid modal amplitudes is used as a measure of performance of the control system. When reliability of the actuators is considered, a more pertinent measure is the expected value of the integral; that is, the sum of the squares of the modal amplitudes for each possible failure state considered, multiplied by the probability that the failure state will occur. For a given set of actuator locations, the optimal criterion may be graphed as a function of the ratio of the mean time to failure of the components and the design mission life or reservicing interval. The best location of the actuators is typically different for a short mission life than for a long one.

Control of persistance in EL panels

The performance of electroluminescent (EL) display panels which employ photoconductors (PC) as the control element is strongly dependent upon the design of the panel, the processing techniques and the materials used in construction. This discussion will be limited to variable persistence panels and the factors which control the shape of the brightness wave envelope. Through proper design and construction, square wave brightness output is possible. Data are presented on panels with (1) a simple layered structure, (2) a layered structure with an optical barrier between the EL and PC layers, (3) a grid type structure, and finally (4) a grid structure with a transparent ohmic conductor between the EL and PC elements.