Three-dimensional Macroporous Structures Research Articles

Calcium crosslinked macroporous bacterial cellulose scaffolds with enhanced in situ mineralization and osteoinductivity for cranial bone regeneration

The inherent biological inertness and lack of three-dimensional (3D) macroporous structures greatly hinder the use of pristine bacterial cellulose (BC) as a tissue engineering scaffold for bone regeneration. To address this issue, we developed a simple and effective strategy to fabricate a BC-based scaffold with excellent bioactivity and macroporous structure by crosslinking short-cut BC nanofibers using Ca2+. The Ca2+ crosslinked macroporous BC scaffold (MPBC@Ca) presents better structural stability due to the enhanced cellulose hydration. Importantly, the Ca2+ on the surface of BC nanofibers can serve as an active nucleation site to accelerate the deposition of hydroxyapatite (HAp), which is beneficial for the construction of biomimetic bone tissue extracellular matrix (ECM) microenvironment. The HAp-deposited MPBC@Ca scaffolds (HAp-MPBC@Ca) with biomimetic ECM microenvironment have excellent cytocompatibility and enhanced osteogenic differentiation of stem cells in vitro. Furthermore, the results of in vivo tests revealed that the HAp-MPBC@Ca scaffold has favorable osteoinductivity and accelerates cranial bone tissue regeneration. This study proposes a novel strategy to improve the bioactivity of BC and presents the great potential of biomimetic ECM microenvironment BC-based scaffold for repairing large cranial bone defects.

Production and mechanical characterization of Titanium Carbide ISOL target disks fabricated by direct ink writing

Titanium carbide boasts a large variety of high-temperature applications from aerospace to electronics and is also employed as Isotope Separation On-Line target for the production of Radioactive Ion Beams, which are employed in numerous research and technological fields, ranging from nuclear physics to medical applications. High working temperature, open and tailored porosity and resistance to thermal stresses are fundamental characteristics for this kind of targets. In this work, an extrusion-based additive manufacturing technique (Direct Ink Writing) was used for the fabrication of complex three-dimensional macro-porous structures in the shape of disks with dimensions compatible for their use as targets. An ink containing a suspension of TiC powders with solid loading of 47.5 vol% was prepared and its rheological properties were investigated. Afterwards, single filaments with an average diameter of 0.36 mm were produced and characterized with four-point bending tests to determine the bulk material tensile strength and Young's modulus. TiC targets were then manufactured and their mechanical properties were characterized with the Ball on Three Balls approach, a biaxial flexural test suitable for disk-shaped samples. For both flexural tests, a Finite Element model was developed representatively reproducing the experimental results. The calculated tensile strength values for both filaments and disks were analyzed with Weibull's statistical approach to provide reference stress limit, corresponding to a survival probability of 99.9%.

Evaporation-Induced Self-Assembly of Metal Oxide Inverse Opals: From Synthesis to Applications.

ConspectusInverse opals (IOs) are highly interconnected three-dimensional macroporous structures with applications in a variety of disciplines from optics to catalysis. For instance, when the pore size is on the scale of the wavelength of visible light, IOs exhibit structural color due to diffraction and interference of light rather than due to absorption by pigments, making these structures valuable as nonfading paints and colorants. When IO pores are in an ordered arrangement, the IO is a 3D photonic crystal, a structure with a plethora of interesting optical properties that can be used in a multitude of applications, from sensors to lasers. IOs also have interesting fluidic properties that arise from the re-entrant geometry of the pores, making them excellent candidates for colorimetric sensors based on fluid surface tension. Metal oxide IOs, in particular, can also be photo- and thermally catalytically active due to the catalytic activity of the background matrix material or of functional nanoparticles embedded within the structure.Evaporation-induced self-assembly of sacrificial particles has been developed as a scalable method for forming IOs. The pore size and shape, surface chemistry, matrix material, and the macroscopic shape of the IO, as well as the inclusion of functional components, can be designed through the choice of deposition conditions such as temperature and humidity, types and concentrations of components in the self-assembly mixture, and the postassembly processing. These parameters allow researchers to tune the optical, mechanical, and thermal transport properties of IOs for optimum functionality.In this Account, we focus on experimental and theoretical studies to understand the self-assembly process and properties of metal oxide IOs without (bare) and with (hybrid) plasmonic or catalytic metal nanoparticles incorporated. Several synthetic approaches are first presented, together with a discussion of the various forces involved in the assembly process. The visualization of the deposition front with time-lapse microscopy is then discussed together with analytical theory and numerical simulations to determine the conditions needed for the deposition of a continuous IO film. Subsequently, we present high-resolution scanning electron microscopy (SEM) of assembled colloids over large areas, which provides a detailed view of the evolution of the assembly process, showing that the organization of the colloids is initially dictated by the meniscus of the evaporating suspension on the substrate, but that gradually all grains rotate to occupy the thermodynamically most favorable orientation. High-resolution 3D transmission electron microscopy (TEM) is then presented together with analysis of the wetting of the templating colloids by the matrix precursor to provide a detailed picture of the embedding of metallic nanoparticles at the pore–matrix interface. Finally, the resulting properties and applications in optics, wetting, and catalysis are discussed, concluding with an outlook on the future of self-assembled metal-oxide-based IOs.

Synthesis, characterization and water-absorption behavior of tartaric acid-modified cellulose gel fromcorn stalk pith

The eco-benign water-absorbent gel was obtained by modification of tartaric acid (TA) onto parenchyma cellulose from corn stalk pith (CSP) in N, N-dimethylacetamide (DMAc)/LiCl system. The water affinity of the gel was aided with TA as both grafting agent and cross-linker via esterification. The degree of swelling was strongly influenced by TA amount, reaction temperature and duration, and the absorbency of TA-esterified product reached up to about 417 g H2O/g dry gel. The three-dimensional macro-porous structures of the bio-absorbent led to fast penetration and diffusion of water into gel. Studies of absorption behavior in deionized water showed that the initial water uptake followed the non-Fickian mechanism, the Schott second-order equation governed the swelling kinetics, and the later part of swelling was relaxation of polymer chains. FTIR and X-ray diffraction analyses confirmed successful modification of TA molecules onto cellulose chains through the formation of ester bonds and transition of crystalline forms from cellulose Ⅰ to cellulose Ⅱ. Moreover, thermogravimetric outcomes illustrated the thermal resistance of the TA-esterified gel with a loose structure was lower than SCP cellulose. This work designed a green water-absorbent that could be potentially utilized as favorable water retention material in agriculture and horticulture.

Synthesis of three-dimensional macro-porous networks of carbon nanotubes by chemical vapor deposition of methane on Co/Mo/Mg catalyst

Three-dimensional (3D) macro-porous structures composed by carbon nanotubes (CNTs) are synthesized by chemical vapor deposition (CVD) of methane at 1173K and atmospheric pressure on Co/Mo/Mg catalyst. 3D-structures are due to formation of interconnected CNT bundles. Strong metal/support interaction, breaking of the metal particles and large difference between surface- and bulk-diffusion are at base of the “double-base” growth mechanism, proposed to account for their formation. The variation of CH4 partial pressure (0.32–1.00atm) reflects on changes in the products’ morphology and carbon yield. These changes result to be determined by the competition between effects (release of H2 and spreading and diffusion of the carbon atoms over and into the catalyst) promoted by the CH4 dissociation. At lower CH4 partial pressure the rate of dissolution of the C atoms is faster than that of the Co/Mo dispersion and bundled CNTs prevailingly form; at higher CH4 partial pressure the situation inverts and unbundled component of the 3D-structures increases.

Three-dimensionalization of ultrathin nanosheets in a two-dimensional nano-reactor: macroporous CuO microstructures with enhanced cycling performance.

Three-dimensional (3D) macroporous CuO structures composed of ultrathin nanosheets were successfully synthesized by employing a liquid-liquid interface as a two-dimensional (2D) nano-reactor. The macroporous structure helped CuO to retain the exposed surface during reactions, thus significantly enhancing the long term cycling performance both in photocatalysis and lithium ion batteries.

Synthesis of Poly-l-glutamic Acid Grafted Silica Nanoparticles and Their Assembly into Macroporous Structures

Polypeptide-coated silica nanoparticles represent an interesting class of organic-inorganic hybrids since the ordered secondary structure of the polypeptide grafts imparts functional properties to these nanoparticles. The synthesis of a poly-l-glutamic acid (PLGA) silica nanoparticle hybrid by employing N-carboxyanhydride (NCA) polymerization to synthesize the polypeptide chains and Cu catalyzed azide alkyne cycloaddition reaction to graft these chains onto the silica surface is reported. This methodology enables the synthesis of well-defined polypeptide chains that are attached onto the silica surface at high surface densities. The PLGA-silica conjugate particles are well dispersed in water, and have been thoroughly characterized using multinuclear ((13)C, (29)Si) solid state NMR, thermogravimetric analysis, Fourier transform infrared, dynamic light scattering, and transmission electron microscopy. The pH-dependent reversible aggregation of the PLGA-silica particles, driven by the change in PLGA structure, has also been studied. Preliminary results on the use of aqueous dispersions of silica-PLGA for the preparation of three-dimensional macroporous structures with oriented pores by ice templating methodology are also demonstrated. These macroporous materials, comprising a biocompatible polymer shell covalently attached to rigid inorganic cores, adopts an interesting lamellar structure with fishbone-type architecture.

Macroporous oxide structures with short-range order and bright structural coloration: a replication from parrot feather barbs

Three-dimensional (3-D) macroporous structures with a short-range order of pore arrangements are of both scientific significance and consequent technological impact. Inspired by parrot feather barbs that display a bright blue structural color, artificial 3-D macroporous SiO2 and TiO2 structures were successfully fabricated by using the barbs as templates. Structural and optical characterization show that the fabricated structures are 3-D bi-continuous macroporous structures with short-range order and display bright structural colors.

Effect of heating rate on the fabrication of tunable ordered macroporous structures mediated by colloidal crystal template

Two- and three-dimensional macroporous structures have attracted much attention over the past decade because of their outstanding properties. In general, two separate procedures are needed for fabricating respective two-dimensional (2D) and three-dimensional (3D) macroporous structures. In this study, one process capable of structure-tuning is reported, which can be used for the preparation of (2D) and (3D) macroporous structures via the employment of different heating rates for calcination during the colloidal crystal template-mediated process. After infiltrating the colloidal crystal template with SiO 2 and ZnO nanoparticles, a calcinations step was employed to remove the polymer template. A faster heating rate will destroy the 3D macroporous structure, leading to only a residual monolayer of pore array on the substrate. However, a slower rate will improve the mechanical strength of the 3D macroporous framework resulting from the sintering effects of ceramic nanoparticles for a longer heating time. Then, a high-quality three-dimension macroporous structure can be fabricated. So the key point of the structure-tuning process is attributed to the morphological changes and enhanced mechanical strength of ceramic framework during calcinations. In summary, this process is a simple procedure for tuning macroporous structure mediated by colloidal crystal template.

P-type macroporous silicon having three-dimensional structure.

Macroporous silicon with three-dimensional structure was fabricated using organic-based electrolyte, dimethylformamide (DMF), in the p-type silicon. The obtained three-dimensional macroporous structures grew wholly along the <100> orientation of the p-type silicon wafer.

Two- and three-dimensional photonic crystals made of macroporous silicon and liquid crystals

Variations of the refractive index can be utilized in order to shift the stop band in periodic structures, such as photonic crystals. We report on investigations about three-dimensional macroporous silicon structures that are filled with a liquid crystal. Fourier transform infrared measurements indicate that a shift of the photonic band edge can be induced by changing the temperature. The director field in macropores within the silicon structure is investigated by H-NMR2 spectroscopy and compared to director field simulations. The latter method indicates a preferred parallel orientation of the director in the nematic state. Based on this finding, we analyze the optical properties.