Macroporous Architecture Research Articles

Flexible Hybrid Membranes with Ni(OH)2 Nanoplatelets Vertically Grown on Electrospun Carbon Nanofibers for High-Performance Supercapacitors.

The practical applications of transition metal oxides and hydroxides for supercapacitors are restricted by their intrinsic poor conductivity, large volumetric expansion, and rapid capacitance fading upon cycling, which can be solved by optimizing these materials to nanostructures and confining them within conductive carbonaceous frameworks. In this work, flexible hybrid membranes with ultrathin Ni(OH)2 nanoplatelets vertically and uniformly anchored on the electrospun carbon nanofibers (CNF) have been facilely prepared as electrode materials for supercapacitors. The Ni(OH)2/CNF hybrid membranes with three-dimensional macroporous architectures as well as hierarchical nanostructures can provide open and continuous channels for rapid diffusion of electrolyte to access the electrochemically active Ni(OH)2 nanoplatelets. Moreover, the carbon nanofiber can act both as a conductive core to provide efficient transport of electrons for fast Faradaic redox reactions of the Ni(OH)2 sheath, and as a buffering matrix to mitigate the local volumetric expansion/contraction upon long-term cycling. As a consequence, the optimized Ni(OH)2/CNF hybrid membrane exhibits a high specific capacitance of 2523 F g(-1) (based on the mass of Ni(OH)2, that is 701 F g(-1) based on the total mass) at a scan rate of 5 mV s(-1). The Ni(OH)2/CNF hybrid membranes with high mechanical flexibility, superior electrical conductivity, and remarkably improved electrochemical capacitance are condsidered as promising flexible electrode materials for high-performance supercapacitors.

Emulsion templated scaffolds with tunable mechanical properties for bone tissue engineering

Polymerised High Internal Phase Emulsions (PolyHIPEs) are manufactured via emulsion templating and exhibit a highly interconnected microporosity. These materials are commonly used as thin membranes for 3D cell culture. This study uses emulsion templating in combination with microstereolithography to fabricate PolyHIPE scaffolds with a tightly controlled and reproducible architecture. This combination of methods produces hierarchical structures, where the microstructural properties can be independently controlled from the scaffold macrostructure. PolyHIPEs were fabricated with varying ratios of two acrylate monomers (2-ethylhexyl acrylate (EHA) and isobornyl acrylate (IBOA)) and varying nominal porosity to tune mechanical properties. Young’s modulus, ultimate tensile stress (UTS) and elongation at failure were determined for twenty EHA/IBOA compositions. Moduli ranged from 63.01±9.13 to 0.36±0.04MPa, UTS from 2.03±0.33 to 0.11±0.01MPa and failure strain from 21.86±2.87% to 2.60±0.61%. Selected compositions were fabricated into macro-porous woodpile structures, plasma treated with air or acrylic acid and seeded with human embryonic stem-cell derived mesenchymal progenitor cells (hES-MPs). Confocal and two-photon microscopy confirmed cell proliferation and penetration into the micro- and macro-porous architecture. The scaffolds supported osteogenic differentiation of mesenchymal cells and interestingly, the stiffest IBOA-based scaffolds that were plasma treated with acrylic acid promoted osteogenesis more strongly than the other scaffolds.

Relationship between micro-porosity, water permeability and mechanical behavior in scaffolds for cartilage engineering

In tissue engineering the design and optimization of biodegradable polymeric scaffolds with a 3D-structure is an important field. The porous scaffold provide the cells with an adequate biomechanical environment that allows mechanotransduction signals for cell differentiation and the scaffolds also protect the cells from initial compressive loading. The scaffold have interconnected macro-pores that host the cells and newly formed tissue, while the pore walls should be micro-porous to transport nutrients and waste products. Polycaprolactone (PCL) scaffolds with a double micro- and macro-pore architecture have been proposed for cartilage regeneration. This work explores the influence of the micro-porosity of the pore walls on water permeability and scaffold compliance. A Poly(Vinyl Alcohol) with tailored mechanical properties has been used to simulate the growing cartilage tissue inside the scaffold pores. Unconfined and confined compression tests were performed to characterize both the water permeability and the mechanical response of scaffolds with varying size of micro-porosity while volume fraction of the macro-pores remains constant. The stress relaxation tests show that the stress response of the scaffold/hydrogel construct is a synergic effect determined by the performance of the both components. This is interesting since it suggests that the in vivo outcome of the scaffold is not only dependent upon the material architecture but also the growing tissue inside the scaffold׳s pores. On the other hand, confined compression results show that compliance of the scaffold is mainly controlled by the micro-porosity of the scaffold and less by hydrogel density in the scaffold pores. These conclusions bring together valuable information for customizing the optimal scaffold and to predict the in vivo mechanical behavior.

A transient cell-shielding method for viable MSC delivery within hydrophobic scaffolds polymerized in situ

Cell-based therapies have emerged as promising approaches for regenerative medicine. Hydrophobic poly(ester urethane)s offer the advantages of robust mechanical properties, cell attachment without the use of peptides, and controlled degradation by oxidative and hydrolytic mechanisms. However, the application of injectable hydrophobic polymers to cell delivery is limited by the challenges of protecting cells from reaction products and creating a macroporous architecture post-cure. We designed injectable carriers for cell delivery derived from reactive, hydrophobic polyisocyanate and polyester triol precursors. To overcome cell death caused by reaction products from in situ polymerization, we encapsulated bone marrow-derived stem cells (BMSCs) in fastdegrading, oxidized alginate beads prior to mixing with the hydrophobic precursors. Cells survived the polymerization at >70% viability, and rapid dissolution of oxidized alginate beads after the scaffold cured created interconnected macropores that facilitated cellular adhesion to the scaffold in vitro. Applying this injectable system to deliver BMSCs to rat excisional skin wounds showed that the scaffolds supported survival of transplanted cells and infiltration of host cells, which improved new tissue formation compared to both implanted, pre-formed scaffolds seeded with cells and acellular controls. Our design is the first to enable injectable delivery of settable, hydrophobic scaffolds where cell encapsulation provides a mechanism for both temporary cytoprotection during polymerization and rapid formation of macropores post-polymerization. This simple approach provides potential advantages for cell delivery relative to hydrogel technologies, which have weaker mechanical properties and require incorporation of peptides to achieve cell adhesion and degradability.

Meso/macroporous nitrogen-doped carbon architectures with iron carbide encapsulated in graphitic layers as an efficient and robust catalyst for the oxygen reduction reaction in both acidic and alkaline solutions.

Meso-/macroporous nitrogen-doped carbon architectures with iron carbide encapsulated in graphitic layers are fabricated by a facile approach. This efficient and robust material exhibits superior catalytic performance toward the oxygen reduction reaction in both acidic and alkaline solutions and is the most promising alternative to a Pt catalyst for use in electrochemical energy devices.

Mussel-inspired biopolymer modified 3D graphene foam for enzyme immobilization and high performance biosensor

A simple and versatile method is described to construct high performance three-dimensional (3D) graphene-based enzyme biosensor. Monolithic and macroporous 3D graphene foam grown by chemical vapor deposition (CVD) was used as a freestanding electrode for co-immobilization of horseradish peroxidase (HRP) and a commonly used redox mediator, methylene blue (MB). Carbon nanotubes (CNTs) were employed as carriers of MB molecules to immobilize them on 3D graphene surface through strong π-π stacking force. Mussel-inspired biopolymer polydopamine (PDA) was formed by in-situ polymerization and served as a green linker, which could covalently graft HRP on the surface of 3D graphene/MB-CNTs electrode. In addition, PDA layer could also effectively prevent the leakage of inner electron mediators. Owing to the 3D macroporous architecture, exceptional properties of graphene and surface-bound mediators, the biosensor demonstrated outstanding performance for reagentless detection of H2O2 in terms of wide linear range (0.2μM to 1.1mM), high sensitivity (227.8μAmM−1cm−2), low detection limit (58.0nM), and fast response (reaching 95% of the steady current within 3s). The biosensor exhibited high reproducibility and stability.

Influence of shrub encroachment on CT-measured soil macropore characteristics in the Inner Mongolia grassland of northern China

The Inner Mongolia grassland of northern China is extensively affected by shrub encroachment. However, the influence of shrub encroachment on soil architecture is not well understood. The objective of this study was to quantify the architecture of soils beneath the shrub canopy and in the adjacent interspace grass area following the establishment of a shrub Caragana microphylla Lam. Study treatments were three transition states of C. microphylla that represent 1.32%, 12.96%, and 40.12% shrub densities and the grass patch as the control. A total of eighteen soil cores (0–50cm deep) were taken at the three sites with 3 replicates. At each site, three cores were from the shrub canopy and three from the grass patch, and cores were scanned with a GE HISPEED FX/I Medical Scanner. Numbers of macropores, macroporosity and macropore equivalent diameter within the 50cm soil profile were interpreted from X-ray computed tomography to analyze soil architecture. The results indicated that shrub encroachment significantly influenced soil macropores. Soils under shrub canopy had greater macroporosity, and developed deeper and longer macropores than those in the interspace grass. X-ray CT showed that macroporosity was 1.4–3.4 times greater in soil under C. microphylla L. than interspace grass. The intensity of shrub encroachment also had noticeable influences on soil macropore characteristics. Soil macroporosity decreased as shrub encroachment increased. In the grass patch, macropores were distributed mainly in the 0–200mm soil layer, while in the shrub patch, they were found throughout the 0–400mm soil layer. The large number of macropores found in soil under the shrub canopy can be attributed to greater root development and subsequent root decay. We speculate that a continual increase of anthropogenic disturbance would further lower the macroporosity of grasses, leading to an increase of surface flow and the decrease of infiltration, and macropore architecture could cause transport of water to the deeper soil layers in the shrub patches than in the grass patches.

Hydroxylation of Phenol on Iron-Containing Mesoporous Silica with Hierarchical Macroporous Architecture

Abstract Iron-containing mesoporous silica with hierarchical macroporous architecture (Fe-MMS) was prepared by applying a solvent evaporation method. In the hydroxylation of phenol with H2O2, the advantageous structure of Fe-MMS realized the higher selectivity for formation of dihydroxybenzene (catechol and hydroquinone) as compared to Fe-containing mesoporous silica (Fe-MS).

Enhanced photocatalytic properties of TiO2-loaded porous silica with hierarchical macroporous and mesoporous architectures in water purification

Porous silica with hierarchical macroporous and mesoporous architectures can serve as an advanced material in the design of composite photocatalysts with TiO2 for water purification.

Macroporous materials by self-assembly of linear oligo(phenylsilsesquioxanes).

Materials with macroporous architecture were prepared in a template-free system using linear oligo(phenyl- silsesquioxanes) (Ph-LPSQ), obtained in a two-step, one-pot, acid/base sol-gel method. The spontaneous self-assembly of silsesquioxane chains is governed by !-! interactions between side substituents and facilitated by the backbone rigidity of the polymer. The porous structure of the material can be changed on adjusting the processing conditions (concentration of Ph-LPSQ solution, the ratio solvent/nonsolvent and rate of stirring during precipitation). Ph-LPSQ oligomers can be also used for modification of silica particles and preparation of interesting macro-mesoporous materials of narrow pore size. Morphology and properties of the polymer and self-assembled particles were characterized by nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopies, wide angle X-ray scattering (WAXS), scanning electron microscopy SEM, mercury intrusion porosimetry, fluorescence spectroscopy and dynamic light scattering.

Zeolite with oriented arrays of macrochannels from zeolitic building block disassembly

Zeolite materials with oriented macroporous and/or mesoporous structures hold promise not only for advanced catalysis and separation but also advanced applications such as medicines, photonics, photoelectronics, and other emerging nanotechnologies. Here we present a simple route for the generation of the oriented macropores in zeolite crystals through the direct disassembly of zeolitic building blocks formed during the crystal growth process by NaOH. The formation of the oriented macropores was predetermined by the generation of Na+ and OH− ions in zeolite crystals. NaOH amount in the initial gel was controlled at a high level to induce these ions into zeolite crystals by promoting the aggregate growth. The active Na+ and OH− ions released from the coalescence of the aggregates could dissolve the less stable crystalline domains or crack the T–O–T bonds along the crystal lattice planes resulting in the disassembly of the zeolitic building block and the formation of the oriented macropores. The zeolite product exhibits a monolithic morphology composed of mordenite (MOR) crystals with c-axis-aligned macrochannels. The monolith and oriented macroporous architecture with its good hydrothermal stability could make it as an interesting material platform for fundamental studies of the structure–properties correlation and the special applications.

Amphiphilic carbonaceous material-based hierarchical porous carbon aerogels for supercapacitors

Novel hierarchical porous carbon aerogels (PCAs) derived from amphiphilic carbonaceous material (ACM) have been mass-prepared via a facile solvent exchange induced self-assembly process and subsequent carbonization and KOH activation. The resulting products are stacked up by highly interconnected carbon nanoparticles with a certain amount of micropores and mesopores, which aggregate to build a three-dimensional macroporous architecture. The hierarchical porous structure facilitates fast ion transportation inside the electrode simultaneously preserving efficient ion surface electrochemical reactions. Capacitive and rate performances were evaluated by fabricating symmetric capacitors with both aqueous and organic electrolytes. The PCA-0.5 and PCA-1.0 electrodes exhibit superior specific capacitances of 261.2 and 227.9 F g−1 at a current density of 0.05 A g−1 in 6 M KOH electrolyte, and still remain 145.5 and 175.4 F g−1 as the current density increases to 100 A g−1, respectively. Remarkably, the PCA-0.5 and PCA-1.0 electrodes show stable cycle durability with a slight capacitance loss of 8.2 and 11.2 % after 5000 cycles at 1 A g−1, respectively. Furthermore, in organic electrolyte system, the PCA-1.0 electrode manifests an outstanding capacitance of 155.4 F g−1 at a current density of 0.05 A g−1. The encouraging results demonstrate that PCAs are a sort of promising and competitive supercapacitors electrode materials.

Melt electrospinning of poly(ε-caprolactone) scaffolds: Phenomenological observations associated with collection and direct writing

Melt electrospinning and its additive manufacturing analogue, melt electrospinning writing (MEW), are two processes which can produce porous materials for applications where solvent toxicity and accumulation in solution electrospinning are problematic. This study explores the melt electrospinning of poly(ε-caprolactone) (PCL) scaffolds, specifically for applications in tissue engineering. The research described here aims to inform researchers interested in melt electrospinning about technical aspects of the process. This includes rapid fiber characterization using glass microscope slides, allowing influential processing parameters on fiber morphology to be assessed, as well as observed fiber collection phenomena on different collector substrates. The distribution and alignment of melt electrospun PCL fibers can be controlled to a certain degree using patterned collectors to create large numbers of scaffolds with shaped macroporous architectures. However, the buildup of residual charge in the collected fibers limits the achievable thickness of the porous template through such scaffolds. One challenge identified for MEW is the ability to control charge buildup so that fibers can be placed accurately in close proximity, and in many centimeter heights. The scale and size of scaffolds produced using MEW, however, indicate that this emerging process will fill a technological niche in biofabrication.

Improving surface and transport properties of macroporous hydrogels for bone regeneration.

Hydrogels have been frequently considered as suitable materials for hard tissue engineering as mineralized extracellular matrix analogue. However, major lacks in bone-substitution still concern the mimicking of native microenvironment for promoting cell differentiation into osteogenic way. Here, we propose the study of mineralized macroporous hydrogels (mMHs) made of poly(ethylenglycol)diacrylate fabricated by the combination of ultraviolet photopolymerization/salt leaching technique and treated by osteopromotive medium. We demonstrate that peculiar morphological and chemical features of mMH are crucial to create a reservoir system able to efficiently recruit environmental signals to cells. In particular, mass transport mechanisms are regulated by the coupling of a Knudsen-type diffusion within the void space of the pores with a standard diffusion mechanism through the pores walls. Meanwhile, the deposition of hydrophilic mineral phases onto the pore surface further affects transport mechanisms, in view of their capability to establish interactions with water molecules and to exert mechanical constrains on the swelling of the hydrogel network, thus promoting slower diffusion kinetics. These properties concur to influence in vitro human mesenchymal stem cells activities: macropore architecture of the hydrogel-like network positively affects cell recognition as compared to nonporous scaffolds, while osteopromotive treatment mainly allows to guide differentiation in osteogenic way as proved by staining of in vitro formed Ca-rich mineral deposits (i.e., alizarin red) and expression via reverse transcription-polymerase chain reaction of main bone markers. Hence, mMH is promising to develop three-dimensional scaffolds as experimental model to study in vitro cell events during bone regeneration.

Osseointegration of dental implants in 3D-printed synthetic onlay grafts customized according to bone metabolic activity in recipient site

Onlay grafts made of monolithic microporous monetite bioresorbable bioceramics have the capacity to conduct bone augmentation. However, there is heterogeneity in the graft behaviour in vivo that seems to correlate with the host anatomy. In this study, we sought to investigate the metabolic activity of the regenerated bone in monolithic monetite onlays by using positron emission tomography–computed tomography (PET-CT) in rats. This information was used to optimize the design of monetite onlays with different macroporous architecture that were then fabricated using a 3D-printing technique. In vivo, bone augmentation was attempted with these customized onlays in rabbits. PET-CT findings demonstrated that bone metabolism in the calvarial bone showed higher activity in the inferior and lateral areas of the onlays. Histological observations revealed higher bone volume (up to 47%), less heterogeneity and more implant osseointegration (up to 38%) in the augmented bone with the customized monetite onlays. Our results demonstrated for the first time that it is possible to achieve osseointegration of dental implants in bone augmented with 3D-printed synthetic onlays. It was also observed that designing the macropore geometry according to the bone metabolic activity was a key parameter in increasing the volume of bone augmented within monetite onlays.

Macroporous flower-like graphene-nanosheet clusters used for electrochemical determination of dopamine

Well-defined flower-like graphene-nanosheet clusters (f-RGO) have been facilely and cost-effectively fabricated by electrochemical method on the surface of a glassy carbon electrode (GCE). The obtained f-RGO was directly used for the detection of dopamine (DA) via cyclic voltammetry (CV) and differential pulse voltammetry (DPV) technique. The structure of f-RGO was confirmed by scanning electron microscopy (SEM). It is observed that the f-RGO exhibits typical flower-like interconnected macroporous architecture, which contributes much to the high performance toward DA detection as compared with that of the layer-stacking RGO. For f-RGO, DPV measurement gives a wide liner range from 5μM to 70μM and 100μM to 600μM, respectively, and a good detection limit of 3μM (S/N=3) for the determination of DA. Moreover, the determination of DA with f-RGO is highly selective and reproducible, with a relative standard deviation of 3.0%.

Dry-gel synthesis of hierarchical TS-1 zeolite by using P123 and polyurethane foam as template

Hierarchical TS-1 zeolites have been prepared via a rapid dry-gel conversion (DGC) technique from carbon–titanosilicate composite. The carbon–titanosilicate composite was fabricated by dipping the silicon source, titanium source and P123 tri-block copolymer into polyurethane (PU) foam, and then carbonized in situ. The carbon–titanosilicate composite was transformed into TS-1 zeolites by DGC method with the aid of zeolite seeding gel. The dual carbon templates with different size obtained from carbonation of P123 and PU were used to direct mesostructure and macroporous architectures respectively. The resulting samples were characterized by X-ray diffraction, IR spectroscopy, SEM and N2 adsorption to evaluate the textural properties. The hierarchical zeolites exhibits large pore volumes (0.3–0.8cm3g−1), hierarchical pore sizes (2–50nm), and high external surface areas (158–211m2g−1). Epoxidation of 1-hexene and cyclohexene were used as probe reaction to survey the catalytic capacity of the resulted zeolites and this hierarchical zeolite showed well catalytic capacities to epoxidation of cyclohexene.

Rapid one-step synthesis and electrochemical performance of NiO/Ni with tunable macroporous architectures

Rapid and economical fabrications of macroporous materials are of general interest in various fields of energy storage, energy conversion, catalysis and gas sensors. In this paper, macroporous NiO/Ni powders were achieved in a flash by the direct decomposition of a metal complex, which is template-free, surfactant-free and highly effective. The metal complex was achieved by simply mixing nickel acetate, nickel nitrate, hydrazine hydrate and glycine in water. The pore size, porosity and even morphology of the porous network (three- or two-dimensional architectures) can be conveniently tuned by adjusting the composition of the complex. It is found that, the amounts of hydrazine hydrate and glycine in the reactants affected the morphology of the porous network; whilst that of nickel acetate determined the macropores. The electrochemical performance of the achieved macroporous NiO/Ni as anodes in Li-ion batteries was comparatively investigated. The 3D macroporous NiO/Ni powders exhibited better electrochemical performances than that of 2D macroporous NiO/Ni and 3D compact NiO/Ni because of its better electrical conductivity and unique porous architecture. The presence of Ni and the continuous network of 3D structures improved the electrical conductivity of electrode materials. In addition, the macroporous architectures not only favored the ingress of electrolytes but also compensated the large volume change of the active materials during the cycling.

ChemInform Abstract: Three Dimensional Macroporous Architectures and Aerogels Built of Carbon Nanotubes and/or Graphene: Synthesis and Applications

AbstractReview: 211 refs.

Reinforcing bioceramic scaffolds with in situ synthesized ε‐polycaprolactone coatings

In situ ring-opening polymerization of ε-caprolactone (ε-CL) was performed to coat β-tricalcium phosphate (β-TCP) scaffolds fabricated by robocasting in order to enhance their mechanical performance while preserving the predesigned macropore architecture. Concentrated colloidal inks prepared from β-TCP commercial powders were used to fabricate porous structures consisting of a three-dimensional mesh of interpenetrating rods. Then, ε-CL was in situ polymerized within the ceramic structure using a lipase as catalyst and toluene as solvent, to obtain a highly homogeneous coating and full impregnation of in-rod microporosity. The strength and toughness of scaffolds coated by ε-polycaprolactone (ε-PCL) were significantly increased (twofold and fivefold increase, respectively) over those of the bare structures. Enhancement of both properties is associated to the healing of preexisting microdefects in the bioceramic rods. These enhancements are compared to results from previous work on fully impregnated structures. The implications of the results for the optimization of the mechanical and biological performance of scaffolds for bone tissue engineering applications are discussed.