Hierarchical Microarchitectures Research Articles

Microstructural, Fluid Dynamic, and Mechanical Characterization of Zinc Oxide and Magnesium Chloride-Modified Hydrogel Scaffolds.

Scaffolds for the filling and regeneration of osteochondral defects are a current challenge in the biomaterials field, and solutions with greater functionality are still being sought. The novel approach of this work was to obtain scaffolds with biologically active additives possessing microstructural, permeability, and mechanical properties, mimicking the complexity of natural cartilage. Four types of scaffolds with a gelatin/alginate matrix modified with hydroxyapatite were obtained, and the relationship between the modifiers and substrate properties was evaluated. They differed in the type of second modifier used, which was hydrated MgCl2 in two proportions, ZnO, and nanohydroxyapatite. The samples were obtained by freeze-drying by using two-stage freezing. Based on microstructural observations combined with X-ray microanalysis, the microstructure of the samples and the elemental content were assessed. Permeability and mechanical tests were also performed. The scaffolds exhibited a network of interconnected pores and complex microarchitecture, with lower porosity at the surface (15 ± 7 to 29 ± 6%) and higher porosity at the center (67 ± 8 to 75 ± 8%). The additives had varying effects on the pore sizes and permeabilities of the samples. ZnO yielded the most permeable scaffolds (5.92 × 10-11 m2), whereas nanohydroxyapatite yielded the scaffold with the lowest permeability (1.18 × 10-11 m2), values within the range reported for trabecular bone. The magnesium content had no statistically significant effect on the permeability. The best mechanical parameters were obtained for ZnO samples and those containing hydrated MgCl2. The scaffold's properties meet the criteria for filling osteochondral defects. The developed scaffolds follow a biomimetic approach in terms of hierarchical microarchitecture and mechanical parameters as well as chemical composition. The obtained composite materials have the potential as biomimetic scaffolds for the regeneration of osteochondral defects.

Rational Electrochemical Design of Cuprous Oxide Hierarchical Microarchitectures and Their Derivatives for SERS Sensing Applications.

Rational morphology control of inorganic microarchitectures is important in diverse fields, requiring precise regulation of nucleation and growth processes. While wet chemical methods have achieved success regarding the shape-controlled synthesis of micro/nanostructures, accurately controlling the growth behavior in real time remains challenging. Comparatively, the electrodeposition technique can immediately control the growth behavior by tuning the overpotential, whereas it is rarely used to design complex microarchitectures. Here, the electrochemical design of complex Cu2O microarchitectures step-by-step by precisely controlling the growth behavior is demonstrated. The growth modes can be switched between the thermodynamic and kinetic modes by varying the overpotential. Cl- ions preferably adhered to {100} facets to modulate growth rates of these facets is proved. The discovered growth modes to prepare Cu2O microarchitectures composed of multiple building units inaccessible with existing methods are employed. Polyvinyl alcohol (PVA) additives can guarantee all pre-electrodeposits simultaneously evolve into uniform microarchitectures, instead of forming undesired microstructures on bare electrode surfaces in following electrodeposition processes is discovered. The designed Cu2O microarchitectures can be converted into noble metal microstructures with shapes unchanged, which can be used as surface-enhanced Raman scattering substrates. An electrochemical avenue toward rational design of complex inorganic microarchitectures is opened up.

Electrohydrodynamic printing of submicron-microscale hybrid scaffolds with improved cellular adhesion and proliferation behaviors

Electrohydrodynamic (EHD) printing has been considered as a mature strategy to mimic the hierarchical microarchitectures in native extracellular matrix (ECM). Most of the EHD-printed scaffolds possess single-dimensional fibrous structures, which cannot mimic the multi-dimensional architectures for enhanced cellular behaviors. Here we developed a two-nozzle EHD printing system to fabricate hybrid scaffolds involving submicron and microscale features. The polyethylene oxide- polycaprolactone (PEO-PCL) submicron fibers were fabricated via solution-based EHD printing with a width of 527 ± 56 nm. The PCL microscale fibers were fabricated via melt-based EHD printing with a width of 11.2 ± 2.3 μm. The hybrid scaffolds were fabricated by printing the submicron and microscale fibers in a layer-by-layer manner. The microscale scaffolds were utilized as a control group. Rat myocardial cells (H9C2 cells) were cultured on the two kinds of scaffolds for the culturing period of 1, 3 and 5 d. Biological results indicated that H9C2 cells showed enhanced adhesion and proliferation behaviors on the hybrid scaffold than those on the pure microscale scaffold. This work offers a facile and scalable strategy to fabricate multiscale synthetic scaffolds, which might be further explored to regulate cellular behaviors in the fields of tissue regeneration and biomedical engineering.

Construction of Au/g-C3N4/ZnIn2S4 plasma photocatalyst heterojunction composite with 3D hierarchical microarchitecture for visible-light-driven hydrogen production

In this paper, a novel Au/g-C3N4/ZnIn2S4 plasma photocatalyst heterojunction composite with 3D hierarchical microarchitecture has been successfully constructed by integrating Au/g-C3N4 plasmonic photocatalyst composite with 3D ZnIn2S4 nanosheet through a simple hydrothermal process. The Au nanoparticles were firstly anchored on the surface of pristine g-C3N4 material to get Au/g-C3N4 plasmonic photocatalyst. Ascribing to the surface plasmon resonance of Au nanoparticles, the obtained Au/g-C3N4 plasmonic photocatalyst shows a significant improved photocatalytic activity toward hydrogen production from water with visible light response comparing with pristine g-C3N4. Further combining Au/g-C3N4 plasmonic photocatalyst with 3D ZnIn2S4 nanosheet to construct a heterojunction composite. Owing to the synergistic effect of the surface plasmon resonance of Au nanoparticles in Au/g-C3N4 and the heterojunction structure in the interface of Au/g-C3N4 and ZnIn2S4, the prepared Au/g-C3N4/ZnIn2S4 plasma photocatalyst heterojunction composite shows an excellent photocatalytic activity toward hydrogen production from water with visible light response, which is around 7.0 and 6.3 times higher than that of the pristine C3N4 and Znln2S4 nanosheet, respectively. The present work might provide some insights for exploring other efficient heterojunction photocatalysts with excellent properties.

Cortical‐Folding‐Inspired Multifunctional Reduced Graphene Oxide Microarchitecture Arrays on Curved Substrates

AbstractAlthough controlled wrinkling is demonstrated to be a powerful tool for micro/nanofabrication, large‐area fabrication of microarchitecture arrays on curved substrates by surface wrinkling still remains challenging. Inspired by the cortical folding, a facile method for transforming graphene oxide (GO) patterns into multiscale microarchitecture arrays on curved substrates is developed. Mass production of hierarchical GO papillae arrays can be realized by homogeneous compression of patterned GO/rubber bilayers. The reduced GO (rGO) papillae arrays show superhydrophobicity with tunable adhesion to water, enabling good performance in microdroplet manipulation. Besides, the papillae are capable of regulating the formation of microcracks in the rGO films upon stretching. Similar to the mechanical sensing system of spiders, a crack‐based strain sensor with high gauge factor (≈81), good linearity (0–15%), and fast responding speed (<40 ms) is demonstrated. In addition, the strain sensor is capable of detecting and recognizing multiple deformation modes including stretching, poking, and touching. This work reveals novel cortical folding morphology and provides a simple fabrication method for multifunctional hierarchical microarchitectures on curved substrates, which may find applications in biomimetic microstructures, smart wetting surfaces, and wearable electronics.

Multimaterial bioprinting approaches and their implementations for vascular and vascularized tissues

Multimaterial bioprinting is a promising technology integrating multimaterial setups into bioprinting platforms for the fabrication of multicellular, heterogeneous and functional tissue constructs. By simultaneously or sequentially dispensing different categories of materials including cell-laden hydrogels or extracellular matrix components, sacrificial materials and scaffolding polymers with hierarchical microarchitecture, multimaterial bioprinting has achieved several milestones for the native tissue biomimicry. Particularly, reconstruction of multiscale, hierarchically branched vascular networks within engineered tissues has been residing as a grand challenge for the fabrication of tissues with long term viability and functionality, which hampers the transition of engineered constructs from research to clinic. To date, various multimaterial bioprinting approaches have been proposed to address the need for fabrication of vascular or vascularized tissues. In this review, a comprehensive overview is given to demonstrate the potential of multimaterial bioprinting technology for the biofabrication of vascular and vascularized tissues. In this regard, different multimaterial bioprinting approaches developed so far are described thoroughly, following the introduction of bioprinting modalities employed in tissue engineering and organization of vascular tissues. Subsequently, multimaterial bioprinting of vascular and vascularized tissues are presented with the main emphasis on the developed fabrication strategies and applied techniques. Comparative evaluation of the multimaterial bioprinting approaches and future perspectives are also delivered to reader.

Conformal Self-Assembly of Nanospheres for Light-Enhanced Airtightness Monitoring and Room-Temperature Gas Sensing.

The fabrication of conformal nanostructures on microarchitectures is of great significance for diverse applications. Here a facile and universal method was developed for conformal self-assembly of nanospheres on various substrates including convex bumps and concave holes. Hydrophobic microarchitectures could be transferred into superhydrophilic ones using plasma treatment due to the formation of numerous hydroxyl groups. Because of superhydrophilicity, the nanosphere suspension spread on the microarchitectures quickly and conformal self-assembly of nanospheres can be realized. Besides, the feature size of the conformal nanospheres on the substrates could be further regulated by plasma treatment. After transferring two-dimensional tungsten disulfide sheets onto the conformal nanospheres, the periodic nanosphere array was demonstrated to be able to enhance the light harvesting of WS2. Based on this, a light-enhanced room-temperature gas sensor with a fast recovery speed (<35 s) and low detecting limit (500 ppb) was achieved. Moreover, the WS2-covered nanospheres on the microarchitectures were very sensitive to the changes in air pressure due to the formation of suspended sheets on the convex bumps and concave holes. A sensitive photoelectronic pressure sensor that was capable of detecting the airtightness of vacuum devices was developed using the WS2-decorated hierarchical architectures. This work provides a simple method for the fabrication of conformal nanospheres on arbitrary substrates, which is promising for three-dimensional microfabrication of multifunctional hierarchical microarchitectures for diverse applications, such as biomimetic compound eyes, smart wetting surfaces and photonic crystals.

Biomorphic triangulations: constructing an additional formation pathway to achieve hierarchical self-evolution in biomorphs

Materials self-evolve to possess complex hierarchical micro-architectures.

Construction of 3D hierarchical microarchitectures of Z-scheme UiO-66-(COOH)2/ZnIn2S4 hybrid decorated with non-noble MoS2 cocatalyst: A highly efficient photocatalyst for hydrogen evolution and Cr(VI) reduction

To solve the problem of energy shortage and environmental pollution, the construction of properly designed photocatalysts is a promising method. Here, UiO-66-(COOH)2/ZnIn2S4 Z-scheme photocatalyst decorated with MoS2 nanosheets was designed and constructed as a novel 3D hierarchical structure via hydrothermal methods. In this particular 3D hierarchical structure, the UiO-66-(COOH)2 nanoparticles are decorated in the interweaving petal nanosheets of ZnIn2S4 microspheres, while the co-catalyst of MoS2 is folded at the edge of these interweaving petals. The excellent heterojunctions with highly exposed catalytic active sites are correspondingly built, and the close interfacial interaction between UiO-66-(COOH)2, MoS2 and ZnIn2S4 create a stage for fast transfer of photogenerated electrons, which are both effective for the photocatalytic reaction process. Also, the Z-scheme charge-transfer process improves the oxidizability and reducibility between UiO-66-(COOH)2 and ZnIn2S4. As a result, the optimized UiO-66-(COOH)2/MoS2/ZnIn2S4 photocatalyst exhibits excellent photocatalytic hydrogen production (18.794 mmol h−1 g−1) and reduction of Cr(VI) (0.06850 min−1) under simulated solar light irradiation, which are 15.3 and 6.7 times higher than that of bare ZnIn2S4, respectively, and also the prominent stability and excellent recyclability are obtained. This study provides new insights into the research on the Z-scheme system containing MOF components for growing energy and environmental demands.

Peptide-Functionalized Nanostructured Microarchitectures Enable Rapid Mechanotransductive Differentiation.

Microenvironmental factors play critical roles in regulating stem cell fate, providing a rationale to engineer biomimetic microenvironments that facilitate rapid and effective stem cell differentiation. Three-dimensional (3D) hierarchical microarchitectures have been developed to enable rapid neural differentiation of multipotent human mesenchymal stromal cells (HMSCs) via mechanotransduction. However, low cell viability during long-term culture and poor cell recovery efficiency from the architectures were also observed. Such problems hinder further applications of the architectures in stem cell differentiation. Here, we present improved 3D nanostructured microarchitectures functionalized with cell-adhesion-promoting arginylglycylaspartic acid (RGD) peptides. These RGD-functionalized architectures significantly upregulated long-term cell viability and facilitated effective recovery of differentiated cells from the architectures while maintaining high differentiation efficiency. Efficient recovery of highly viable differentiated cells enabled the downstream analysis of morphology and protein expression to be performed. Remarkably, even after the removal of the mechanical stimulus provided by the 3D microarchitectures, the recovered HMSCs showed a neuron-like elongated morphology for 10 days and consistently expressed microtubule-associated protein 2, a mature neural marker. RGD-functionalized nanostructured microarchitectures hold great potential to guide effective differentiation of highly viable stem cells.

Hierarchically structured microgels of SPIONs, nanofibers, and alginate for copper ion removal

Microgels have been developed for various practical applications such as heavy metal removal. However, their internal structures are difficult to control for a specific application. This study, for the first time, confirms that a hierarchical structure improves the ability of microgels in heavy metal ion removal. Superparamagnetic iron oxide nanoparticles (SPIONs) were incorporated into polylactic acid nanofibers which were then incorporated into alginate microgels, both of which have metal removal capability. A combination of electrospinning and spraying was used to prepare the microgels. The fibers outside the microgels were selectively dissolved out in a subsequent step. The fiber density inside the microgels could be controlled by the electrospinning time. This SPION-loaded nanofiber-entrapped alginate microgel showed outstanding Cu2+ ion adsorption compared to ones without SPIONs or nanofibers. This hierarchical microarchitecture of microgel could find various applications in the fields of future environmental applications.

Electrohydrodynamic 3D printing of layer-specifically oriented, multiscale conductive scaffolds for cardiac tissue engineering.

Mimicking the hierarchical microarchitecture of native myocardium in vitro plays an important role in cardiac tissue engineering. Here we present a novel strategy to produce multiscale conductive scaffolds with layer-specific fiber orientations for cardiac regeneration by combining solution-based and melt-based electrohydrodynamic (EHD) printing techniques. Polycaprolactone (PCL) microfibers were printed by melt-based EHD printing and the fiber orientation was flexibly controlled in a layer-by-layer manner according to user-specific design. The as-printed microfibrous scaffolds can provide the seeded cells necessary contact cues to guide layer-specific cellular alignments. Sub-microscale conductive fibers were simultaneously incorporated inside the well-organized PCL scaffolds by solution-based EHD printing, which significantly improved the conductivity as well as the cellular adhesion and proliferation capacity. The multiscale conductive scaffolds can further direct the multiple-layer alignments of primary cardiomyocytes and facilitate cardiomyocyte-specific gene expressions, which exhibited enhanced synchronous beating behavior compared with pure microfibrous scaffolds. It is envisioned that the proposed hybrid EHD printing technique might provide a promising strategy to fabricate multifunctional micro/nanofibrous scaffolds with biomimetic architectures, electrical conductivity and even biosensing properties for the regeneration of electroactive tissues.

Morphologically tuned 3D/1D rutile TiO2 hierarchical hybrid microarchitectures engineered by one-step surfactant free hydrothermal method

Present investigation reports on the surfactant free hydrothermal synthesize of the morphologically tuned hierarchical hybrid rutile titanium oxide (TiO2) microarchitectures showing three dimensional microflower structures and cook pine tree like structures on the one dimensional nanorods formed over TiO2 seed layer coated glass substrates by tuning growth temperature. TiO2 seed layer of ∼100nm thick was coated on the glass substrates employing sol–gel spin coating method and then rutile TiO2 microarchitectures were synthesized on the TiO2 seed layer by one-step surfactant free hydrothermal method. Deposited samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, UV–vis spectroscopy and photoluminescence spectroscopy techniques. Influence of the growth temperature on the crystallinity, morphology and optical properties along with the growth mechanism to achieve hierarchical microarchitectures was investigated. Present work revealed that the structural, morphological and optical properties of the TiO2 hierarchical microarchitectures strongly depend on the growth temperature. Further we proposed a model for the cause to effect possible morphological changes of rutile TiO2 microarchitectures as a function of growth temperatures on the TiO2 seeded glass substrates.

Surfactant-free hydrothermal synthesis of CePO4 microbundles assembled by aligned nanorods

In this research, CePO4 microbundles composed of aligned nanorods have been successfully synthesized through a facile surfactant-free hydrothermal route. The whole synthetic process was rather simple and green. And different synthetic parameters including the aging time and acidic strength were investigated such to understand the formation of the novel hierarchical microarchitectures. It was found that the hydrothermal time, as well as the acidic strength of the precursor media played a key role in mediating the assembly of one-dimensional micrcobundles from initially formed nanorods. Based on a series of experimental observations, a ‘precipitation-growth’ mechanism is proposed to describe the growth of the unique microstructures.

Facile fabrication of flower like self-assembled mesoporous hierarchical microarchitectures of In(OH)3 and In2O3: In(OH)3 micro flowers with electron beam sensitive thin petals

A template and capping-reagent free facile fabrication method for mesoporous hierarchical microarchitectures of flower-like In(OH)3 particles under benign hydrothermal conditions is reported. Calcination of In(OH)3 to In2O3 with the retention of morphology is also described. Both In(OH)3 and In2O3 microstructures were analyzed with SEM, EDX, TEM and powder X-ray diffraction. The crystal sizes for In(OH)3 and In2O3 were calculated using the Scherrer equation. In In(OH)3 the thin flakes at the periphery of micro flowers were electron beam sensitive. The mechanism of self-assembly process was analyzed as well.

MoS2-graphene/ZnIn2S4 hierarchical microarchitectures with an electron transport bridge between light-harvesting semiconductor and cocatalyst: A highly efficient photocatalyst for solar hydrogen generation

Exploiting photocatalysts with characteristics of cost effectiveness, environmental friendliness, visible light response, high reactivity and good durability is a great challenge for solar H2 generation. Here, we synthesis of MoS2-graphene composite as a highly-efficient cocatalyst to enhance the photocatalytic activity of ZnIn2S4 under visible light irradiation. Through the optimizing of each composition proportion, the hierarchical MoS2-graphene/ZnIn2S4 photocatalyst shows the highest H2 evolution rate of 4169μmolh−1g−1 under visible light irradiation in presence of Na2S and Na2SO3 as sacrificial reagents when the content of MoS2-graphene is 1.2wt% and the weight ratio of MoS2 to graphene is 10:1, which is almost 22.8 times higher than that of pure ZnIn2S4. More importantly, the ternary MoS2-graphene/ZnIn2S4 composite exhibits much higher photocatalytic activity than Pt-loaded ZnIn2S4 photocatalyst, suggesting that the MoS2-graphene composite can act as a more efficient cocatalyst than the commonly used Pt metal. The superior catalytic activity of MoS2-graphene cocatalyst can be assigned to the positive synergistic effect between MoS2 and graphene, which act as a hydrogen evolution reaction catalyst and an electron transport bridge, respectively. The effective charge transfer from ZnIn2S4 to MoS2 through graphene is demonstrated by the significant enhancement of photocurrent responses in MoS2-graphene/ZnIn2S4 composite photoelectrodes.

A High-Rate V2 O5 Hollow Microclew Cathode for an All-Vanadium-Based Lithium-Ion Full Cell.

V2O5 hollow microclews (V2O5-HMs) have been fabricated through a facile solvothermal method with subsequent calcination. The synthesized V2O5-HMs exhibit a 3D hierarchical structure constructed by intertangled nanowires, which could realize superior ion transport, good structural stability, and significantly improved tap density. When used as the cathodes for lithium-ion batteries (LIBs), the V2O5-HMs deliver a high capacity (145.3 mAh g(-1)) and a superior rate capability (94.8 mAh g(-1) at 65 C). When coupled with a lithiated Li3VO4 anode, the all-vanadium-based lithium-ion full cell exhibits remarkable cycling stability with a capacity retention of 71.7% over 1500 cycles at 6.7 C. The excellent electrochemical performance demonstrates that the V2O5-HM is a promising candidate for LIBs. The insight obtained from this work also provides a novel strategy for assembling 1D materials into hierarchical microarchitectures with anti-pulverization ability, excellent electrochemical kinetics, and enhanced tap density.

THE DIFFERENTIAL CONSTITUTIVE EQUATION AND MODEL OF ABALONE NACRE BY NANOINDENTER

Nacre has a complex hierarchical microarchitecture that spans over multiple length scales from nanoscale to macroscale. Its structures are optimized leading to extraordinary mechanical performance and energy absorption. Nacre's special characteristics of the self-assembly method have attracted the interest of material scientists to develop laminated composite materials, molecular scale self-assembly and biomineralization. Nanoindentation testing can determine a material's anisotropic properties through a single indentation. In the present study, nanoindentation stress–strain curves were used to characterize the complete mechanical behavior of nacre of abalone shell. A differential constitutive equation was developed with time-dependent spring constants k and viscosities η. Furthermore, to describe the complex viscoelastic behavior of abalone nacre, a descriptive representation of the linear viscoelasticity law for the multilayer matrix was formulated. A qualitative model for the relationship between nacre structure and mechanical properties of nacre may help develop bionic composite materials for micro-aircraft, bionic tribology, bionic medical apparatus and bionic organs (tissue engineering).

A Model of Sheath of Bovine Horn Coupled Nano-Mechanical Properties and Microstructures

With the long-term evolution, the bovine horn as the primary protective and offensive weapon has superior mechanical properties. The bovine horn consists of two parts, the keratinous horn sheath and the bony core. The keratinous is natural composite material with a highly toughness and can bear impact and repeated loads during fighting. It has a complex hierarchical microarchitecture. To establish the qualitative model for finding the possible relationship between structure and mechanical properties of bovine horn, in this paper, the model was established that based on the parameters provided by microstructure imaging and nanoindentation testing from transverse and longitudinal directions. Which would provide information useful for the developing bionic composite materials for micro-aircraft, bionic tribology, bionic medical apparatus and bionic organs (tissue engineering).

Are all osteocytes equal? Multiscale modelling of cortical bone to characterise the mechanical stimulation of osteocytes

Bone continuously adapts its internal structure to accommodate the functional demands of its mechanical environment. This process is orchestrated by a network of mechanosensitive osteocytes that respond to external mechanical signals and recruit osteoblasts and osteoclasts to alter bone mass to meet loading demands. Because of the irregular hierarchical microarchitecture of bone tissue, the precise mechanical stimuli experienced by osteocytes located in different regions of the tissue is not well-understood. The objective of this study is to characterise the local stimulus experienced by osteocytes distributed throughout the tissue structure. Our models predict that an inhomogeneous microstructural strain field contributes to osteocytes receiving vastly different stimuli at the cellular level, depending on their location within the microstructure. In particular, osteocytes located directly adjacent to micropores experienced strain amplifications in their processes of up to nine times the applied global strain. Furthermore, it was found that the principal orientation of lamellar regions was found to contribute significantly to the magnitude of the stimulus being received at the cellular level. These findings indicate that osteocytes are not equal in terms of the mechanical stimulus being received, and we propose that only a subset of osteocytes may be sufficiently stimulated to function as mechanoreceptors.