Frontiers of Materials Science (v.11, #2)

Stem cell homing-based tissue engineering using bioactive materials by Yinxian Yu; Binbin Sun; Chengqing Yi; Xiumei Mo (93-105).
Tissue engineering focuses on repairing tissue and restoring tissue functions by employing three elements: scaffolds, cells and biochemical signals. In tissue engineering, bioactive material scaffolds have been used to cure tissue and organ defects with stem cell-based therapies being one of the best documented approaches. In the review, different biomaterials which are used in several methods to fabricate tissue engineering scaffolds were explained and show good properties (biocompatibility, biodegradability, and mechanical properties etc.) for cell migration and infiltration. Stem cell homing is a recruitment process for inducing the migration of the systemically transplanted cells, or host cells, to defect sites. The mechanisms and modes of stem cell homing-based tissue engineering can be divided into two types depending on the source of the stem cells: endogenous and exogenous. Exogenous stem cell-based bioactive scaffolds have the challenge of long-term culturing in vitro and for endogenous stem cells the biochemical signal homing recruitment mechanism is not clear yet. Although the stem cell homing-based bioactive scaffolds are attractive candidates for tissue defect therapies, based on in vitro studies and animal tests, there is still a long way before clinical application.
Keywords: stem cell homing; cell migration; cell proliferation; tissue engineering; scaffold; biochemical signals

Si-doping bone composite based on protein template-mediated assembly for enhancing bone regeneration by Qin Yang; Yingying Du; Yifan Wang; Zhiying Wang; Jun Ma; Jianglin Wang; Shengmin Zhang (106-119).
Bio-inspired hybrid materials that contain organic and inorganic networks interpenetration at the molecular level have been a particular focus of interest on designing novel nanoscale composites. Here we firstly synthesized a series of hybrid bone composites, silicon-hydroxyapatites/silk fibroin/collagen, based on a specific molecular assembled strategy. Results of material characterization confirmed that silicate had been successfully doped into nano-hydroxyapatite lattice. In vitro evaluation at the cellular level clearly showed that these Si-doped composites were capable of promoting the adhesion and proliferation of rat mesenchymal stem cells (rMSCs), extremely enhancing osteoblastic differentiation of rMSCs compared with silicon-free composite. More interestingly, we found there was a critical point of silicon content in the composition on regulating multiple cell behaviors. In vivo animal evaluation further demonstrated that Si-doped composites enabled to significantly improve the repair of cranial bone defect. Consequently, our current work not only suggests fabricating a potential bone repair materials by integrating element-doping and molecular assembled strategy in one system, but also paves a new way for constructing multi-functional composite materials in the future.
Keywords: silicate-doped; molecular assembly; biomimetic bone; bone regeneration; osteoblastic differentiation

In this study, a facile alcoholysis method was developed to synthesize BiOCl x Br1−x nanoplates at room temperature and atmospheric pressure. In this route, strong acid or alkaline environment was absolutely avoided to realize the high exposure of {001} crystal facets. The regular changes in XRD peaks and cell parameters as a function of the Br content strongly declared that the obtained BiOCl x Br1−x products belonged to a group of solid solutions. The 2D nanosheets with in-plane wrinkles were clearly observed in TEM images. Interestingly, as the Br content increased, band gaps of BiOCl x Br1−x solid solutions gradually decreased. The photocatalytic degradation of RhB under simulated sunlight irradiation indicated that BiOCl0.5Br0.5 had the best photocatalytic activity. From the viewpoint of crystal chemistry, the photocatalytic activity of BiOCl x Br1−x solid solutions was closely related with the exposure amount of {001} facets, interlayer spacing of (001) plane and energy-level position of valence band.
Keywords: BiOCl x Br1−x solid solutions; {001} facets exposure; internal electric field; interlayer spacing; energy-level position

A novel Ag/AgCl/chitosan composite photocatalyst was successfully prepared by a simple one-step method. During this progress, environmentally benign chitosan not only served as reductant to reduce Ag+ to Ag0 species, but also acted as supporter for Ag/AgCl nanoparticles. XRD, SEM, EDX, UV-vis DRS and XPS were employed to characterize the as-prepared simples. SEM images of Ag/AgCl/chitosan composites revealed that Ag/AgCl nanoparticles were successfully loaded onto chitosan without obvious aggregation. All Ag/AgCl/chitosan composites exhibited efficient photocatalytic activity for the degradation of rhodamine B (RhB) under visible-light irradiation. The result of photocatalytic degradation experiment indicated that 20% of the mass ratio of AgCl to chitosan was the optimum, and after 40 min photocatalytic reaction, the degradation rate reached about 96%.
Keywords: Ag/AgCl; surface plasmon resonance; one-step; chitosan; photocatalysis

Novel twin-Christmas tree-like PbWO4 microcrystals have been prepared via a convenient aqueous solution route at room temperature under the assistance of β-cyclodextrin (β-CD). The product was characterized by XRD, EDX, SEM, TEM, UV-vis and PL and BET techniques. It was found that β-CD plays an important role in the forming of twin-Christmas tree-like PbWO4 microcrystals. A five-step growth mechanism was proposed to explain the formation of such twin-Christmas tree-like structures. The photocatalytic performance of PbWO4 microcrystals was evaluated by measuring the decomposition rate of methylene blue (MB) and malachite green (MG) solution under the UV irradiation, and the photocatalytic results indicated that as-prepared PbWO4 microcrystals exhibit good and versatile photocatalytic activity as well as excellent recyclability.
Keywords: PbWO4 ; twin-Christmas tree-like; growth mechanism; UV irradiation; photocatalyst

A cubic Prussian blue (PB) with the hollow interior was successfully synthesized by direct dissociation followed by a controlled self-etching process. The etching process also made hollow Prussian blue (HPB) a porous structure. SEM, TEM and XRD were employed to confirm the structure and morphology of the prepared materials. Then HPB and chitosan (CS) were deposited on a glassy carbon electrode (GCE), used to determine H2O2. The amperometric performance of HPB/CS/GCE was investigated. It was found that the special structure of HPB exhibits enhanced performance in the H2O2 sensing.
Keywords: Prussian blue; hollow structure; hydrogen peroxide; sensor; non-enzyme; electrocatalyst

Facile synthesis and electrochemical properties of layered Li[Ni1/3Mn1/3Co1/3]O2 as cathode materials for lithium-ion batteries by Yingfang Zhu; Jingwei You; Haifu Huang; Guangxu Li; Wenzheng Zhou; Jin Guo (155-161).
A layered oxide Li[Ni1/3Mn1/3Co1/3]O2 was synthesized by an oxalate co-precipitation method. The morphology, structural and composition of the as-papered samples synthesized at different calcination temperatures were investigated. The results indicate that calcination temperature of the sample at 850°C can improve the integrity of structural significantly. The effect of calcination temperature varying from 750°C to 950°C on the electrochemical performance of Li[Ni1/3Mn1/3Co1/3]O2, cathode material of lithiumion batteries, has been investigated. The results show that Li[Ni1/3Mn1/3Co1/3]O2 calcined at 850°C possesses a higher capacity retention and better rate capability than other samples. The reversible capacity is up to 178.6 mA∙h∙g-1, and the discharge capacity still remains 176.3 mA∙h∙g-1 after 30 cycles. Moreover, our strategy provides a simple and highly versatile route in fabricating cathode materials for lithium-ion batteries.
Keywords: Li[Mn1/3Ni1/3Co1/3]O2 ; cathode material; oxalate co-precipitation; lithiumion battery

Electrochemically stable nanostructured nickel titanate (NiTiO3) was prepared by sol-gel method and the structural and electrochemical properties were studied in the presence of H2SO4+CH3OH electrolyte. XRD and Raman studies confirmed the single phase of NiTiO3 with the rhombohedral structure. Thermal stability was studied by TGA. Microstructure analysis by SEM confirmed the uniformly distributed spherical shaped NiTiO3 particles, and TEM studies showed the spherical shaped particles with an average size of 90 nm. The UV-Vis analysis shows the absorption spectrum of NiTiO3, while the FTIR spectrum showed the vibrations related to Ni-O and Ti-O stretching. Electrochemical tests were carried out by cyclic voltammetry (CV) and polarization studies. The CV measurements were made at room temperature as well as at 60°C: at room temperature, the NiTiO3 did not show any activity towards methanol oxidation whereas there observed an activity at the potential of 0.69 V at the operating temperature of 60°C. The ilmenite structured NiTiO3 has oxygen vacancies, most probably on the surface, which could have also contributed to the methanol oxidation. Thus the nanostructured NiTiO3 is proposed to be an active support material for metal electrocatalysts.
Keywords: electrocatalyst; methanol oxidation; electrochemical; nanomaterials; NiTiO3

Aluminum and copper matrix nanocomposites reinforced by graphene nanoplatelets (GNPs) were successfully fabricated by a wet mixing method followed by conventional powder metallurgy. The uniform dispersion of GNPs within the metal matrices showed that the wet mixing method has a great potential to be used as a mixing technique. However, by increasing the GNPs content, GNPs agglomeration was more visible. DSC and XRD of Al/GNPs nanocomposites showed that no new phase formed below the melting point of Al. Microstructural observations in both nanocomposites reveal the evident grain refinement effect as a consequence of GNPs addition. The interfacial bonding evaluation shows a poor interfacial bonding between GNPs and Al, while the interfacial bonding between Cu and GNPs is strong enough to improve the properties of the Cu/GNPs nanocomposites. In both composites, the coefficient of thermal expansion decreases as a function of GNPs while, their hardness is improved by increasing the GNPs content as well as their elastic modulus.
Keywords: nanocomposite; aluminum; copper; graphene; microstructure; thermal expansion

Electronic structure and bonding interactions in Ba1−x Sr x Zr0.1Ti0.9O3 ceramics by Jegannathan Mangaiyarkkarasi; Subramanian Sasikumar; Olai Vasu Saravanan; Ramachandran Saravanan (182-189).
An investigation on the precise electronic structure and bonding interactions has been carried out on Ba1−x Sr x Zr0.1Ti0.9O3 (short for BSZT, x = 0, 0.05, 0.07 and 0.14) ceramic systems prepared via high-temperature solid state reaction technique. The influence of Sr doping on the BSZT structure has been examined by characterizing the prepared samples using PXRD, UV-visible spectrophotometry, SEM and EDS. Powder profile refinement of X-ray data confirms that all the synthesized samples have been crystallized in cubic perovskite structure with single phase. Charge density distribution of the BSZT systems has been completely analyzed by the maximum entropy method (MEM). Co-substitution of Sr at the Ba site and Zr at the Ti site into the BaTiO3 structure presents the ionic nature between Ba and O ions and the covalent nature between Ti and O ions, revealed from MEM calculations. Optical band gap values have been evaluated from UV-visible absorption spectra. Particles with irregular shapes and well defined grain boundaries are clearly visualized from SEM images. The phase purity of the prepared samples is further confirmed by EDS qualitative spectral analysis.
Keywords: barium titanate; X-ray diffraction; Rietveld refinement; maximum entropy method; bonding

Microstructure and mechanical properties of tungsten composite reinforced by fibre network by Linhui Zhang; Yan Jiang; Qianfeng Fang; Zhuoming Xie; Shu Miao; Longfei Zeng; Tao Zhang; Xianping Wang; Changsong Liu (190-196).
In this paper the tungsten-fibre-net-reinforced tungsten composites were produced by spark plasma sintering (SPS) using fine W powders and commercial tungsten fibres. The relative density of the samples is above 95%. It was found that the recrystallization area in the fibres became bigger with increasing sintering temperature and pressure. The tungsten grains of fibres kept stable when sintered at 1350°C/16 kN while grown up when sintered at 1800°C/16 kN. The composite sintered at 1350°C/16 kN have a Vickers-hardness of ~610 HV, about 2 times that of the 1800°C/16 kN sintered one. Tensile tests imply that the temperature at which the composites (1350°C/16 kN) begin to exhibit plastic deformation is about 200°C-250°C, which is 400°C lower than that of SPSed pure W. The tensile fracture surfaces show that the increasing fracture ductility comes from pull-out, interface debonding and fracture of fibres.
Keywords: tungsten-fibre-net; spark plasma sintering; recrystallization; tensile test