Polytypic Two-Dimensional FeAs with High Anisotropy.

In the realm of two-dimensional (2D) crystal growth, the chemical composition often determines the thermodynamically favored crystallographic structures. This relationship poses a challenge in synthesizing novel 2D crystals without altering their chemical elements, resulting in the rarity of achieving specific crystallographic symmetries or lattice parameters. We present 2D polymorphic FeAs crystals that completely differ from bulk orthorhombic FeAs (Pnma), differing in the stacking sequence, i.e., polytypes. Preparing polytypic FeAs outlines a strategy for independently controlling each symmetry operator, which includes the mirror plane for 2Q-FeAs (I4/mmm) and the glide plane for 1Q-FeAs (P4/nmm). As such, compared to bulk FeAs, polytypic 2D FeAs shows highly anisotropic properties such as electrical conductivity, Young's modulus, and friction coefficient. This work represents a concept of expanding 2D crystal libraries with a given chemical composition but various crystal symmetries.

Effect of Residual Oxygen Concentration on the Lattice Parameters of Aluminum Nitride Powder Prepared via Carbothermal Reduction Nitridation Reaction.

Residual oxygen in wurtzite-type aluminum nitride (AlN) crystal, which significantly affects phonon transport and crystal growth, is crucial to thermal conductivity and the crystal quality of AlN ceramics. In this study, the effect of residual oxygen on the lattice of AlN was examined for as-synthesized and sintered samples. By controlling reaction time in the carbothermal reduction nitridation (CRN) procedure, AlN powder was successfully synthesized, and the amount of residual oxygen was systematically controlled. The evolution of lattice parameters of AlN with respect to oxygen conc. was carefully investigated via X-ray diffraction analysis. With increasing amounts of residual oxygen in the as-synthesized AlN, lattice expansion in the ab plane was induced without a significant change in the c-axis lattice parameter. The lattice expansion in the ab plane owing to the residual oxygen was also confirmed with high-resolution transmission electron microscopy, in contrast to the invariant lattice parameter of the sintered AlN phase. Micro-strain values from XRD peak broadening confirm that stress, induced by residual oxygen, expands the AlN lattice. In this work, the lattice expansion of AlN with increasing residual oxygen was elucidated via X-ray diffraction and HR-TEM, which is useful to estimate and control the lattice oxygen in AlN ceramics.

Direct Evidence on Effect of Oxygen Dissolution on Thermal and Electrical Conductivity of AlN Ceramics Using Al Solid-State NMR Analysis.

Aluminum nitride, with its high thermal conductivity and insulating properties, is a promising candidate as a thermal dissipation material in optoelectronics and high-power logic devices. In this work, we have shown that the thermal conductivity and electrical resistivity of AlN ceramics are primarily governed by ionic defects created by oxygen dissolved in AlN grains, which are directly probed using 27Al NMR spectroscopy. We find that a 4-coordinated AlN3O defect (ON) in the AlN lattice is changed to intermediate AlNO3, and further to 6-coordinated AlO6 with decreasing oxygen concentration. As the aluminum vacancy (VAl) defect, which is detrimental to thermal conductivity, is removed, the overall thermal conductivity is improved from 120 to 160 W/mK because of the relatively minor effect of the AlO6 defect on thermal conductivity. With the same total oxygen content, as the AlN3O defect concentration decreases, thermal conductivity increases. The electrical resistivity of our AlN ceramics also increases with the removal of oxygen because the major ionic carrier is VAl. Our results show that to enhance the thermal conductivity and electrical resistivity of AlN ceramics, the dissolved oxygen in AlN grains should be removed first. This understanding of the local structure of Al-related defects enables us to design new thermal dissipation materials.

Bulk Metamaterials Exhibiting Chemically Tunable Hyperbolic Responses.

Extraordinary properties of traditional hyperbolic metamaterials, not found in nature, arise from their man-made subwavelength structures causing unique light-matter interactions. However, their preparation requiring nanofabrication processes is highly challenging and merely provides nanoscale two-dimensional structures. Stabilizing their bulk forms via scalable procedures has been a sought-goal for broad applications of this technology. Herein, we report a new strategy of designing and realizing bulk metamaterials with finely tunable hyperbolic responses. We develop a facile two-step process: (1) self-assembly to obtain heterostructured nanohybrids of building blocks and (2) consolidation to convert nanohybrid powders to dense bulk pellets. Our samples have centimeter-scale dimensions typically, readily further scalable. Importantly, the thickness of building blocks and their relative concentration in bulk materials serve as a delicate means of controlling hyperbolic responses. The resulting new bulk heterostructured material system consists of the alternating h-BN and graphite/graphene nanolayers and exhibits significant modulation in both type-I and type-II hyperbolic resonance modes. It is the first example of real bulk hyperbolic metamaterials, consequently displaying the capability of tuning their responses along both in-plane and out-of-plane directions of the materials for the first time. It also distinctly interacts with unpolarized and polarized transverse magnetic and electronic beams to give unique hyperbolic responses. Our achievement can be a new platform to create various bulk metamaterials without complicated nanofabrication techniques. Our facile synthesis method using common laboratory techniques can open doors to broad-range researchers for active interdisciplinary studies for this otherwise hardly accessible technology.

Fabrication and evaluation of 3D printed BCP scaffolds reinforced with ZrO2 for bone tissue applications.

Fused deposition modeling (FDM) is a promising 3D printing and manufacturing step to create well interconnected porous scaffold designs from the computer-aided design (CAD) models for the next generation of bone scaffolds. The purpose of this study was to fabricate and evaluate a new biphasic calcium phosphate (BCP) scaffold reinforced with zirconia (ZrO2 ) by a FDM system for bone tissue engineering. The 3D slurry foams with blending agents were successfully fabricated by a FDM system. Blending materials were then removed after the sintering process at high temperature to obtain a targeted BCP/ZrO2 scaffold with the desired pore characteristics, porosity, and dimension. Morphology of the sintered scaffold was investigated with SEM/EDS mapping. A cell proliferation test was carried out and evaluated with osteosarcoma MG-63 cells. Mechanical testing and cell proliferation evaluation demonstrated that 90% BCP and 10% ZrO2 scaffold had a significant effect on the mechanical properties maintaining a structure compared that of only 100% BCP with no ZrO2 . Additionally, differentiation studies of human mesenchymal stem cells (hMSCs) on BCP/ZrO2 scaffolds in static and dynamic culture conditions showed increased expression of bone morphogenic protein-2 (BMP-2) when cultured on BCP/ZrO2 scaffolds under dynamic conditions compared to on BCP control scaffolds. The manufacturing of BCP/ZrO2 scaffolds through this innovative technique of a FDM may provide applications for various types of tissue regeneration, including bone and cartilage.

Fe-Doping Effect on Thermoelectric Properties of p-Type Bi0.48Sb1.52Te3.

The substitutional doping approach has been shown to be an effective strategy to improve ZT of Bi2Te3-based thermoelectric raw materials. We herein report the Fe-doping effects on electronic and thermal transport properties of polycrystalline bulks of p-type Bi0.48Sb1.52Te3. After a small amount of Fe-doping on Bi/Sb-sites, the power factor could be enhanced due to the optimization of carrier concentration. Additionally, lattice thermal conductivity was reduced by the intensified point-defect phonon scattering originating from the mass difference between the host atoms (Bi/Sb) and dopants (Fe). An enhanced ZT of 1.09 at 300 K was obtained in 1.0 at% Fe-doped Bi0.48Sb1.52Te3 by these synergetic effects.

Structurally nanocrystalline-electrically single crystalline ZnO-reduced graphene oxide composites.

ZnO, a wide bandgap semiconductor, has attracted much attention due to its multifunctionality, such as transparent conducting oxide, light-emitting diode, photocatalyst, and so on. To improve its performances in the versatile applications, numerous hybrid strategies of ZnO with graphene have been attempted, and various synergistic effects have been achieved in the ZnO-graphene hybrid nanostructures. Here we report extraordinary charge transport behavior in Al-doped ZnO (AZO)-reduced graphene oxide (RGO) nanocomposites. Although the most challenging issue in semiconductor nanocomposites is their low mobilities, the AZO-RGO nanocomposites exhibit single crystal-like Hall mobility despite the large quantity of nanograin boundaries, which hinder the electron transport by the scattering with trapped charges. Because of the significantly weakened grain boundary barrier and the proper band alignment between the AZO and RGO, freely conducting electrons across the nanograin boundaries can be realized in the nanocomposites. This discovery of the structurally nanocrystalline-electrically single crystalline composite demonstrates a new route for enhancing the electrical properties in nanocomposites based on the hybrid strategy.

Unoxidized graphene/alumina nanocomposite: fracture- and wear-resistance effects of graphene on alumina matrix.

It is of critical importance to improve toughness, strength, and wear-resistance together for the development of advanced structural materials. Herein, we report on the synthesis of unoxidized graphene/alumina composite materials having enhanced toughness, strength, and wear-resistance by a low-cost and environmentally benign pressure-less-sintering process. The wear resistance of the composites was increased by one order of magnitude even under high normal load condition (25 N) as a result of a tribological effect of graphene along with enhanced fracture toughness (KIC) and flexural strength (σf) of the composites by ~75% (5.60 MPa·m(1/2)) and ~25% (430 MPa), respectively, compared with those of pure Al2O3. Furthermore, we found that only a small fraction of ultra-thin graphene (0.25-0.5 vol%, platelet thickness of 2-5 nm) was enough to reinforce the composite. In contrast to unoxidized graphene, graphene oxide (G-O) and reduced graphene oxide (rG-O) showed little or less enhancement of fracture toughness due to the degraded mechanical strength of rG-O and the structural defects of the G-O composites.

Highly transparent and conducting graphene-embedded ZnO films with enhanced photoluminescence fabricated by aerosol synthesis.

Graphene/inorganic hybrid structures have attracted increasing attention in research aimed at producing advanced optoelectronic devices and sensors. Herein, we report on aerosol synthesis of new graphene-embedded zinc oxide (ZnO) films with higher optical transparency (>80% at visible wavelengths), improved electrical conductivity (>2 orders of magnitude, ∼ 20 kΩ/□), and enhanced photoluminescence (∼ 3 times), as compared to bare ZnO film. The ZnO/graphene composite films, in which reduced graphene oxide nanoplatelets (∼ 4 nm thick) are embedded in nanograined ZnO (∼ 50 nm in grain size), were fabricated from colloidal suspensions of graphene oxide with an aqueous zinc precursor. These new luminescent ZnO/graphene composites, with high optical transparency and improved electrical conductivity, are promising materials for use in optoelectronic devices.

Fabrication of blended polycaprolactone/poly(lactic-co-glycolic acid)/ß-tricalcium phosphate thin membrane using solid freeform fabrication technology for guided bone regeneration.

This study developed a bioabsorbable-guided bone regeneration membrane made of blended polycaprolactone (PCL), poly(lactic-co-glycolic acid) (PLGA), and beta-tricalcium phosphate (ß-TCP) using solid freeform fabrication (SFF) technology. The chemical and physical properties of the membrane were evaluated using field emission scanning electron microscopy, energy dispersive spectroscopy, and a tensile test. In vitro cell activity assays revealed that the adhesion, proliferation, and osteogenic differentiation of seeded adipose-derived stem cells (ADSCs) were significantly promoted by the PCL/PLGA/ß-TCP membranes compared with PCL/PLGA membranes. When the PCL/PLGA and PCL/PLGA/ß-TCP membranes were implanted on rabbit calvaria bone defects without ADSCs, microcomputed tomography and histological analyses confirmed that the SFF-based PCL/PLGA/ß-TCP membranes greatly increased bone formation without the need for bone substitute materials. Moreover, tight integration, which helps to prevent exposure of the membrane, between both membranes and the soft tissues was clearly observed histologically. The SFF-based PCL/PLGA and PCL/PLGA/ß-TCP membranes retained their mechanical stability for up to 8 weeks without significant collapse. Furthermore, PCL/PLGA/ß-TCP underwent adequate degradation without a significant immune response at 8 weeks.

Effect of pore architecture and stacking direction on mechanical properties of solid freeform fabrication-based scaffold for bone tissue engineering.

Fabrication of a three-dimensional (3D) scaffold with increased mechanical strength may be an essential requirement for more advanced bone tissue engineering scaffolds. Various material- and chemical-based approaches have been explored to enhance the mechanical properties of engineered bone tissue scaffolds. In this study, the effects of pore architecture and stacking direction on the mechanical and cell proliferation properties of a scaffold were investigated. The 3D scaffold was prepared using solid freeform fabrication technology with a multihead deposition system. Various types of scaffolds with different pore architectures (lattice, stagger, and triangle types) and stacking directions (horizontal and vertical directions) were fabricated with a blend of polycaprolactone and poly lactic-co-glycolic acid. In compression tests, the triangle-type scaffold was the strongest among the experimental groups. Stacking direction affected the mechanical properties of scaffolds. An in vitro cell counting kit-8 assay showed no significant differences in optical density depending on the different pore architectures and stacking directions. In conclusion, mechanical properties of scaffolds can be enhanced by controlling pore architecture and stacking direction.

The economic disease burden of measles in Japan and a benefit cost analysis of vaccination, a retrospective study.

BACKGROUND: During 1999-2003, Japan experienced a series of measles epidemics, and in Action Plans to Control Measles and the Future Problems, it was proposed that infants be immunized soon after their one-year birthday.In this study, we attempted to estimate the nationwide economic disease burden of measles based on clinical data and the economic effectiveness of this proposal using the benefit cost ratio. METHODS: Our survey target was measles patients treated at Chiba-Nishi general hospital from January 1999 to September 2001. Two hundred ninety-one cases were extracted from the database. The survey team composed of 3 pediatricians and 1 physician from Chiba-Nishi general hospital examined patient files and obtained additional information by telephone interview.We analyzed data based on a static model, which assumed that the number of measles patients would be zero after 100% coverage of single-antigen measles vaccine.Costs were defined as the direct cost for measles treatment, vaccination and transportation and the indirect cost of workdays lost due to the nursing of patients, hospital visits for vaccination or nursing due to adverse reactions. Benefits were defined as savings on direct and indirect costs. Based on these definitions, we estimated the nationwide costs of treatment and vaccination. RESULTS: Using our static model, the nationwide total cost for measles treatment was estimated to be US$ 404 million, while the vaccination cost was US$165 million. The benefit cost ratio of the base case was 2.48 and ranged from 2.21 to 4.97 with sensitivity analysis. CONCLUSIONS: Although the model has some limitations, we conclude that the policy of immunizing infants soon after their one-year birthday is economically effective.

Development of a hybrid scaffold with synthetic biomaterials and hydrogel using solid freeform fabrication technology.

Natural biomaterials such as hyaluronic acid, gelatin and collagen provide excellent environments for tissue regeneration. Furthermore, gel-state natural biomaterials are advantageous for encapsulating cells and growth factors. In cell printing technology, hydrogel which contains cells was printed directly to form three-dimensional (3D) structures for tissue or organ regeneration using various types of printers. However, maintaining the 3D shape of the printed structure, which is made only of the hydrogel, is very difficult due to its weak mechanical properties. In this study, we developed a hybrid scaffold consisting of synthetic biomaterials and natural hydrogel using a multi-head deposition system, which is useful in solid freeform fabrication technology. The hydrogel was intentionally infused into the space between the lines of a synthetic biomaterial-based scaffold. The cellular efficacy of the hybrid scaffold was validated using rat primary hepatocytes and a mouse pre-osteoblast MC3T3-E1 cell line. In addition, the collagen hydrogel, which encapsulates cells, was dispensed and the viability of the cells observed. We demonstrated superior effects of the hybrid scaffold on cell adhesion and proliferation and showed the high viability of dispensed cells.

Surface modification with fibrin/hyaluronic acid hydrogel on solid-free form-based scaffolds followed by BMP-2 loading to enhance bone regeneration.

Bone tissue engineering often requires a well-defined scaffold that is highly porous. The multi-head deposition system (MHDS), a form of solid freeform fabrication, has raised great interest as a method for fabricating scaffolds, since it yields a highly porous inter-connective structure without the use of cytotoxic solvents, and permits the diffusion of nutrients and oxygen. However, this method is not suitable for introducing proteins, as it includes a heating process. Hydrogels incorporated with protein coating of the scaffold surface could overcome this MHDS limitation. In the present study, the surface of a scaffold fabricated using MHDS was coated with a mixture of fibrin and hyaluronic acid (HA) and used as a vehicle for delivery of both bone morphogenetic protein-2 (BMP-2) and adipose-derived stromal cells (ASCs). Fibrin/HA coating of the scaffold significantly enhanced initial cell attachment. Furthermore, the in vitro release of BMP-2 from fibrin/HA-coated scaffolds was sustained for 3 days and it stimulated the alkaline phosphatase activity of ASCs seeded on the scaffold for 10 days more actively and continuously than did the soluble BMP-2 that was added to the culture media, not the scaffold itself. Importantly, the transplantation of undifferentiated ASCs inoculated on BMP-2-loaded, fibrin/HA-coated scaffolds resulted in more improved bone formation and mineralization than did the transplantation of undifferentiated ASCs seeded on uncoated scaffolds or on fibrin/HA-coated scaffolds without BMP-2, but containing BMP-2 in the cell suspension medium. These results show that BMP-2-loaded, fibrin/HA-coated scaffolds fabricated using MHDS may be useful in stimulating bone regeneration from undifferentiated ASCs in vivo.

Evaluating cell proliferation based on internal pore size and 3D scaffold architecture fabricated using solid freeform fabrication technology.

The scaffold, as a medical component to regenerate tissues or organs in humans, plays an important role in tissue engineering. Recently, solid freeform fabrication (SFF) technology using computer-assisted methods was applied to address the problems of conventional fabrication methods in which the internal/outer architectures cannot be controlled. In this report, we propose suitable scaffolds for bone tissue regeneration considering the internal pore size and scaffold architecture. Poly(propylene fumarate) was used as the biodegradable photopolymer, and scaffolds were fabricated using microstereolithography (MSTL). We observed the relationship between the internal pores and architecture, and the proliferation of pre-osteoblast cells. To demonstrate the superiority of MSTL, we fabricated conventional and SFF scaffolds, and measured the cell proliferation rates for each. The results showed that cell proliferation on the MSTL scaffold was clearly superior and indicated that MSTL would be a good replacement for current conventional methods.

Effect of thermal degradation of SFF-based PLGA scaffolds fabricated using a multi-head deposition system followed by change of cell growth rate.

Solid free-form fabrication (SFF) technology is used to fabricate scaffolds with controllable characteristics including well-defined pore size and porosity. The multi-head deposition system (MHDS), one form of SFF technology, may be more advantageous than others for fabricating scaffolds because a MHDS does not require the use of a cytotoxic solvent. This method, however, may induce the thermal degradation of raw materials and a subsequent decrease in the material's molecular weight, whereby hydrolytic degradation, resulting in acidic by-products, might be accelerated. This study investigated whether fabrication of poly(lactic-co-glycolic acid) (PLGA) scaffolds using a MHDS with various residence times in the heating step induces thermal degradation and affects the proliferation of cells seeded on the scaffold in vitro. To answer this question, we fabricated porous three-dimensional PLGA scaffolds using residence times of 1, 3, 5 and 7 days for groups 1 through 4, respectively. Degradation behavior of the scaffolds was observed for 7 weeks in phosphate-buffered saline solution (pH 7.4) at 37 degrees C. The molecular weight, glass transition temperature and mechanical properties were compared for PLGA scaffolds fabricated with each of the four residence times at 120 degrees C. The proliferation rate of MC3T3-E1 cells grown on each group of scaffolds was compared to investigate the effect of acidic by-products on the growth of seeded cells in vitro. The heat process applied in fabrication of SFF-based PLGA scaffolds induced considerable thermal degradation followed by a decrease in molecular weight and mechanical compressive strength of the scaffolds in groups 3 and 4, which had more than 3 days residence time. Moreover, the cell proliferation rate was significantly higher for group 1 than for groups 3 and 4.

Solid free-form fabrication-based PCL/HA scaffolds fabricated with a multi-head deposition system for bone tissue engineering.

In this study, we fabricated polycaprolactone/hydroxyapatite (PCL/HA) scaffolds with a multi-head deposition system, a solid free-form fabrication technology that was developed in our previous study. The bone regeneration potential of the scaffolds was compared with that of PCL scaffolds fabricated with the same system. The fabricated scaffolds had a pore size of 400 mum and a porosity of 66.7%. The PCL/HA scaffolds had higher mechanical strength and modulus than the PCL scaffolds. To compare the osteogenic potential, the two types of scaffolds were seeded with rat osteoblasts and cultured in vitro or implanted subcutaneously into athymic mice. The cells cultured on PCL/HA scaffolds expressed higher levels of osteopontin and osteonectin, both of which are osteogenic proteins. The PCL/HA scaffolds resulted in larger bone area and calcium deposition in the implants compared to the PCL scaffolds.

Evaluation of solid free-form fabrication-based scaffolds seeded with osteoblasts and human umbilical vein endothelial cells for use in vivo osteogenesis.

We investigated the feasibility of using solid free-form fabrication (SFF)-based scaffolds seeded with osteoblasts, derived from human adipose-derived stem cells, and human umbilical vein endothelial cells (HUVECs) to enhance osteogenesis. To accomplish this goal, SFF-based polycaprolactone/poly-lactic-co-glycolic acid/tricalcium phosphate scaffolds were fabricated using a multihead deposition system, which is one SFF technique. The blended polycaprolactone/poly-lactic-co-glycolic acid/TCP scaffolds were seeded with human osteoblasts and HUVECs and implanted into calvaria defects in rats. At 8 and 12 weeks after implantation, microcomputed tomography, real-time polymerase chain reaction, and histological assays (hematoxylin and eosin staining and Alizarin red staining) were conducted to determine the effects of SFF-based scaffolds on osteogenic potential. In vivo experiments indicated that the osteoblast-only and osteoblast-HUVEC group produced bone formation. Additionally, scaffolds in the osteoblast-HUVEC group had the largest area of new bone tissue. Therefore, we demonstrated through microcomputed tomography and histological assays that scaffolds seeded with both human osteoblasts and HUVECs were superior to other groups for effective bone formation.

Solid Free-form Fabrication Technology and Its Application to Bone Tissue Engineering.

The development of scaffolds for use in cell-based therapies to repair damaged bone tissue has become a critical component in the field of bone tissue engineering. However, design of scaffolds using conventional fabrication techniques has limited further advancement, due to a lack of the required precision and reproducibility. To overcome these constraints, bone tissue engineers have focused on solid free-form fabrication (SFF) techniques to generate porous, fully interconnected scaffolds for bone tissue engineering applications. This paper reviews the potential application of SFF fabrication technologies for bone tissue engineering with respect to scaffold fabrication. In the near future, bone scaffolds made using SFF apparatus should become effective therapies for bone defects.

Guided bone regeneration by poly(lactic-co-glycolic acid) grafted hyaluronic acid bi-layer films for periodontal barrier applications.

A novel protocol for the synthesis of biocompatible and degradation controlled poly(lactic-co-glycolic acid) grafted hyaluronic acid (HA-PLGA) was successfully developed for periodontal barrier applications. HA was chemically modified with adipic acid dihydrazide (ADH) in the mixed solvent of water and ethanol, which resulted in a high degree of HA modification up to 85 mol.%. The stability of HA-ADH to enzymatic degradation by hyaluronidase increased with ADH content in HA-ADH. When the ADH content in HA-ADH was higher than 80 mol.%, HA-ADH became soluble in dimethyl sulfoxide and could be grafted to the activated PLGA with N,N'-dicyclohexyl carbodiimide and N-hydroxysuccinimide. The resulting HA-PLGA was used for the preparation of biphasic periodontal barrier membranes in chloroform. According to in vitro hydrolytic degradation tests in phosphate buffered saline, HA-PLGA/PLGA blend film with a weight ratio of 1/2 degraded relatively slowly compared to PLGA film and HA coated PLGA film. Four different samples of a control, OSSIX(TM) membrane, PLGA film, and HA-PLGA/PLGA film were assessed as periodontal barrier membranes for the calvarial critical size bone defects in SD rats. Histological and histomorphometric analyses revealed that HA-PLGA/PLGA film resulted in the most effective bone regeneration compared to other samples with a regenerated bone area of 63.1% covering the bone defect area.