Macropores Formation Research Articles

Fatty Acid Binding Protein 5 Mediates Cell Death by Psychosine Exposure through Mitochondrial Macropores Formation in Oligodendrocytes.

Oligodendrocytes, the myelinating cells in the central nervous system (CNS), are critical for producing myelin throughout the CNS. The loss of oligodendrocytes is associated with multiple neurodegenerative disorders mediated by psychosine. However, the involvement of psychosine in the critical biochemical pathogenetic mechanism of the loss of oligodendrocytes and myelin in krabbe disease (KD) remains unclear. Here, we addressed how oligodendrocytes are induced by psychosine treatment in both KG-1C human oligodendroglial cells and mouse oligodendrocyte precursor cells. We found that fatty acid binding protein 5 (FABP5) expressed in oligodendrocytes accelerates mitochondria-induced glial death by inducing mitochondrial macropore formation through voltage-dependent anion channels (VDAC-1) and BAX. These two proteins mediate mitochondrial outer membrane permeabilization, thereby leading to the release of mitochondrial DNA and cytochrome C into the cytosol, and the activation of apoptotic caspases. Furthermore, we confirmed that the inhibition of FABP5 functions by shRNA and FABP5-specific ligands blocking mitochondrial macropore formation, thereby rescuing psychosine-induced oligodendrocyte death. Taken together, we identified FABP5 as a critical factor in mitochondrial injury associated with psychosine-induced apoptosis in oligodendrocytes.

Controllable Fabrication and Mechanism of Macropores Formation on p-Type Silicon

Macropores were prepared by electrochemical etching on p-type silicon. The effects of resistivity, etching time and HF concentration on the porosities and morphologies of macropores were investigated. It was found that the porosity of p-type macropores increased exponentially at the beginning with the increase of etching time under any other etching parameters. In addition, we discovered that HF concentration had significant effect on the surface and cross-section morphologies of macropores. The dependence of the macropore formation mechanism was discussed, and the hydrogen escape mechanism as well as current-burst-model (CBM) was employed to interpret the underlying mechanism and the morphology control during macropore formation.

Protective dissolution: generating secondary pores in zeolite by mechanochemical reaction.

Introduction of meso-/macropores into the intrinsic microporous framework of zeolites has raised substantial interest in catalytic reactions with bulky reactants. Herein, we report the formation of secondary meso-/macropores in Silicalite-1 zeolite by a solvent-free mechanochemical grinding process. The strategy allows the preservation of high crystallinity and microporosity of the pristine zeolite, and the generation of mesopores at room temperature and marcopores at higher temperatures. The roles of the tetrapropylammonium bromide (TPABr) and ammonium fluoride (NH4F) have been proposed and demonstrated. A protective layer is formed by TPA+ ions bonded with the surficial defects to shield the outer surface from the direct attack by F−. Instead, F− diffuses into the micropore system in a local aqueous environment within zeolite formed by the mechanochemical reaction. As a result, freely diffused F− selectively dissolves zones with structural defects to form secondary pores inside the zeolite. Moreover, this strategy proves highly effective in encapsulation of nanoparticles (Pt, Co) in the meso-/macropores of Silicalite-1 zeolite, forming a yolk–shell composite catalyst for potential applications.

(Invited) Template Free Method for Macroporous SnO2 Thin Film Sensors

Transition metal oxides are attractive candidates for gas sensing thanks to their interesting semiconductive properties [1,2]. In particular, tin oxide (SnO2) is the most utilized n-type metal oxide semiconductor, as it typically provides high sensitivity to a large variety of gas analytes. In this study, we are using the versatility of solution-based approaches to prepare MOS materials at the nanoscale and to control critical film morphology parameters for gas sensing such as crystallinity, grain size, film thickness, as well as surface area (through porosity) – the focus of this paper. In the literature, methods of preparing porous SnO2 have been reported many times. However, they are either i) simple but yield SnO2 with small, hard to access pores (sol-gel), potentially non-contiguous films (nanoparticles packing), or ii) they are more complex and in turn more costly (use of porogen, electrochemical processes etc.). Here, we report on a simple, template-free, one-step process that, if deposited in the right conditions, inherently yields highly porous films with large pores (Fig. 1b). The morphology of the macropores was unanticipated with the pores being self-organized, and completely open to the surface. An important parameter to obtain these pores is to deposit the solution at an optimal aging time, as illustrated in Figure 1. Additionally, other factors such as solution concentration and pH, or the nature of the solvent can also impact the macropores formation. The role played by these factors will be discussed, and hypotheses on the macropores formation mechanism will be proposed. The presence of these macropores led to a two-fold increase in sensitivity in our gas sensing measurements (Fig. 1e, 1f) [3]. Altogether, these results suggest that solution-based processes are very powerful to prepare highly sensitive metal oxide gas sensors. The unique morphologies achieved could be highly advantageous in the context of an electronic nose. References K. Lionti et.al., TechConnect Briefs 2017, Chap. 7, p.219A. Fasoli et.al., IEEE International Symposium on Olfaction and Electronic Nose 2017, p.978K. Lionti et al., 2017, US10020199B1. Figure 1

Nano gold coated hierarchically porous zinc titanium oxide sol–gel based thin film: fabrication and photoelectrochemical activity

In this work, for the first time homogeneously distributed near periodic macroporous (HDPM) with nested mesoporous (hierarchically porous) semicrystalline zinc titanium oxide (ZTO) thin film on pure silica glass and fluorine doped tin oxide coated glass substrates was deposited by sol–gel dip coating technique from an optimized precursor solution of zinc nitrate hexahydrate and titanium isopropoxide with acetylacetone in low boiling solvents. The HDPM film formation was carried out by simple breath figure method where the pore formation occurred from the generated water droplets via molecular condensation onto the as-deposited cold solution film surface owing to solvent evaporation. Zinc to titanium ratio in precursor solution, room relative humidity and other critical parameters were tailored towards optimization of the periodic macropores formation. Gold nanoparticles (NPs) were further deposited onto the ZTO thin films by solution technique. Crystallinity, surface morphology and microstructure of the thin films were critically analyzed by X-ray diffraction, atomic force, scanning, and transmission electron microscopic studies. The photoelectrochemical (PEC) performance of the films was examined under visible light irradiation. A significant improvement in PEC activity was observed in nano Au coated hierarchically porous thin film. This facile fabrication process could be applied in different mixed metal oxide thin films for improving the PEC activity of the materials.

Facile synthesis of soft-templated carbon monoliths with hierarchical porosity for fast adsorption from liquid media

An easy synthesis of carbon monoliths with hierarchical porosities is presented here combining phenolic sol-gel and soft-templating methods (use of amphiphilic surfactant Pluronic F127 as mesopores template). By varying the synthesis conditions, purely microporous or micro-mesoporous or micro-meso-macroporous carbon materials were obtained. While micropores and mesopores arise during the carbonisation, macropores formation occurs during the gelling step through a controlled macroscopic phase separation process. The same pyrolytic temperature was used to ensure comparable surface chemistry (proved by FTIR and TGA-MS measurements for the templated samples), textural properties were investigated by a group of techniques: TEM, CO2 and N2 sorption, Hg porosimetry and SAXS. The benefit of the different porosities was evidenced on blocs of 1–2.5 mm diameter by studying adsorption kinetic of phenol and methylene blue aqueous solutions. Due to comparable surface chemistry of the templated samples, only their difference of porosity was considered as a decisive factor for the kinetics of adsorption. The relative role of each porosity was evidenced and quantified. It was found that mesopores are crucial for a fast transport of adsorptive into the adsorption sites (micropores/smaller mesopores) while the additional presence of macropores further accelerates the rate of sorption for both adsorptives.

Hierarchical sol–gel derived porous titania/carbon nanotube films prepared by controlled phase separation

Titania/carbon nanotube (CNT) composite films containing hierarchical interconnected porous structure have the advantages of high surface area of mesoporous structure and micro-channels of titania as well as high conductivity and charge separation properties of CNTs. In this research, the composites were prepared with controlled phase separation of titania sol. The main parameters to control the phase separation and macroporous morphology of the films including water content, stabilizer content, polyethylene glycol content, sol concentration, and deposition speed were investigated. X-ray diffraction and Raman spectroscopy confirmed the presence of CNTs together with anatase titania phase. Transmission electron microscopy showed that a very thin layer of titania was formed on CNT surface which improved interface of TiO2/CNT. It was found that macropores grew either with increasing water or polyethylene glycol content. However, stabilizer content and deposition speed had an inverse effect on macropores formation. Furthermore, sol concentration caused binodal decomposition and hence widened the pore size distribution. Although CNTs were ineffective in macropores formation, they strongly affected the transparency and charge separation of the composite films.

Mechanoelectrochemical synthesis and properties of porous nano-Ti–6Al–4V alloy with hydroxyapatite layer for biomedical applications

Formation of porous morphology in nanocrystalline mechanically alloyed and electrochemically etched Ti–6Al–4V biomedical alloy was investigated. The alloy was electrochemically etched in a mixture of H 3PO 4 and HF. The electrochemical etching results in broad range from micro(nano)-macropores formation in the surface layer, with diameter in the range of 3 nm–60 µm. On the etched surface hydroxyapatite was electrochemically deposited by using 0.042 M Ca(NO 3) 2 + 0.025 (NH 4) 2HPO 4 + 0.1M HCl electrolyte. In this way bioactive surface was prepared. The pores in the surface acts as anchors for the hydroxyapatite, which grows inside them. Due to the porous morphology, the etched as well as HA deposited surface is promising for hard tissue implant applications. The nanocrystalline alloy has a nanohardness and Young modulus in the range of 993–1275 HV and 137–162 GPa, respectively.

Electrochemical trench etching of silicon triggered via mechanical nanocontacts

We report a method to produce microstructures on silicon wafers using a microscratching technique followed by a subsequent electrochemical trench etching in hydrofluoric-based electrolyte. Micro-scratches are used to trigger macropore formation. We show that mask-less dissolved trenches with aspect ratios up to 1:7 are formed at the scratched regions on (0 0 1)Si surface. The micro-scratches orientate the macropores formation by aligning them in the scratching direction. We propose that dislocations formed during scratching are firstly dissolved leading to the formation of V-shape grooves. The V-shape geometries obtained by this way are used to initiate the macropores nucleation; i.e. due to the geometry, an avalanche current occurs at the grooves base and thus induces local dissolutions of the substrate. High rate local dissolutions are achieved by back-side illumination of the Si wafer.

Triblock copolymer and poly(ethylene glycol) as templates for monolithic silica material with bimodal pore structure

To synthesize monolithic silica materials with bimodal pore structures, a new dual-templating system of triblock copolymer and poly(ethylene glycol) was proposed and a subcritical water oxidation method was introduced to remove the organic templates. In this new system, triblock copolymer Pluronic P123 and poly(ethylene glycol) (PEG) mainly served as the templates for mesopores and macropores, respectively. The influence of PEG molecular weight, PEG concentration and TEOS concentration on the bimodal pore structure was investigated. The macro–mesoporous structure of synthesized monolithic silica materials with tetraethoxysilane (TEOS) as the silica source has been confirmed by a nitrogen adsorption–desorption measurement and SEM observations. The monolithic silica materials with macro–mesoporous structure were synthesized successfully using the new template system. The macropores size ranged from 0.6 μm to 4 μm and the silica skeleton size was from 0.5 μm to 1.5 μm. The mesopore size was decided by the composition of P123/PEG. PEG could enlarge the mesopore size from 3–4 nm (only P123 applied) to 8–10 nm. Using PEG with different molecular weights as template, two different macropore morphologies were observed and two possible mechanisms of macropores formation were hypothesized, named as the micelles mechanism and the network mechanism, respectively.

Gelatin manipulation of latent macropores formation in brushite cement.

Macroporous brushite cement was prepared from a mixture of beta-tricalcium phosphate (beta-TCP) and monocalcium phosphate monohydrate (MCPM) using gelatin powder as a latent templates. In a setting reaction coexisting with gelatin, closed packed, open-pore structure with 100-200 microm macropores are obtained after immersion of the set cement into PBS buffer (pH 7.4) at 37 degrees C for 1-4 weeks. The macroporous brushite cement has compressive strength of 15 MPa originally, which reducing to 5.5 MPa with macropore formation gradually in comparison to that of cancellous bone (5-10 MPa).