Frontiers of Materials Science (v.9, #4)

The development of metal hydrides using as concentrating solar thermal storage materials by Xuanhui Qu; Yang Li; Ping Li; Qi Wan; Fuqiang Zhai (317-331).
Metal hydrides high temperature thermal heat storage technique has great promising future prospects in solar power generation, industrial waste heat utilization and peak load regulating of power system. This article introduces basic principle of metal hydrides for thermal storage, and summarizes developments in advanced metal hydrides high-temperature thermal storage materials, numerical simulation and thermodynamic calculation in thermal storage systems, and metal hydrides thermal storage prototypes. Finally, the future metal hydrides high temperature thermal heat storage technique is been looked ahead.
Keywords: metal hydride; concentrating solar power; heat storage

Recent progress in injectable bone repair materials research by Zonggang Chen; Xiuli Zhang; Lingzhi Kang; Fei Xu; Zhaoling Wang; Fu-Zhai Cui; Zhongwu Guo (332-345).
Minimally invasive injectable self-setting materials are useful for bone repairs and for bone tissue regeneration in situ. Due to the potential advantages of these materials, such as causing minimal tissue injury, nearly no influence on blood supply, easy operation and negligible postoperative pain, they have shown great promises and successes in clinical applications. It has been proposed that an ideal injectable bone repair material should have features similar to that of natural bones, in terms of both the microstructure and the composition, so that it not only provides adequate stimulus to facilitate cell adhesion, proliferation and differentiation but also offers a satisfactory biological environment for new bone to grow at the implantation site. This article reviews the properties and applications of injectable bone repair materials, including those that are based on natural and synthetic polymers, calcium phosphate, calcium phosphate/polymer composites and calcium sulfate, to orthopedics and bone tissue repairs, as well as the progress made in biomimetic fabrication of injectable bone repair materials.
Keywords: bone repair material; polymer; calcium phosphate; calcium sulfate; biomimetic

Biomaterials for reconstruction of cranial defects by Tao Song; Zhi-Ye Qiu; Fu-Zhai Cui (346-354).
Reconstruction of cranial defect is commonly performed in neurosurgical operations. Many materials have been employed for repairing cranial defects. In this paper, materials used for cranioplasty, including autografts, allografts, and synthetic biomaterials are comprehensively reviewed. This paper also gives future perspective of the materials and development trend of manufacturing process for cranioplasty implants.
Keywords: cranioplasty; autograft; allograft; metallic material; bioceramics; mineralized collagen

Corrosion resistance of Zn–Al layered double hydroxide/poly(lactic acid) composite coating on magnesium alloy AZ31 by Rong-Chang Zeng; Xiao-Ting Li; Zhen-Guo Liu; Fen Zhang; Shuo-Qi Li; Hong-Zhi Cui (355-365).
A Zn–Al layered double hydroxide (ZnAl-LDH) coating consisted of uniform hexagonal nano-plates was firstly synthesized by co-precipitation and hydrothermal treatment on the AZ31 alloy, and then a poly(lactic acid) (PLA) coating was sealed on the top layer of the ZnAl-LDH coating using vacuum freeze-drying. The characteristics of the ZnAl-LDH/PLA composite coatings were investigated by means of XRD, SEM, FTIR and EDS. The corrosion resistance of the coatings was assessed by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results showed that the ZnAl-LDH coating contained a compact inner layer and a porous outer layer, and the PLA coating with a strong adhesion to the porous outer layer can prolong the service life of the ZnAl-LDH coating. The excellent corrosion resistance of this composite coating can be attributable to its barrier function, ion-exchange and self-healing ability.
Keywords: magnesium; corrosion; layered double hydroxide (LDH); poly(lactic acid) (PLA); ion-exchange; self-healing

Preparation and enhancement of ionic conductivity in Al-added garnet-like Li6.8La3Zr1.8Bi0.2O12 lithium ionic electrolyte by Yu Xia; Liang Ma; Hui Lu; Xian-Ping Wang; Yun-Xia Gao; Wang Liu; Zong Zhuang; Li-Jun Guo; Qian-Feng Fang (366-372).
Garnet-like Li6.8La3Zr1.8Bi0.2O12 (LLZBO) + x mol.% Al2O3 (x = 0, 1.25, 2.50) lithium ionic electrolytes were prepared by conventional solid state reaction method under two different sintering temperatures of 1000°C and 1100°C. XPS, induced coupled plasma optical emission spectrometer (ICP-OES), XRD and AC impedance spectroscopy were applied to investigate the bismuth valance, lithium concentration, phase structure and lithium ionic conductivity, respectively. Electrical measurement demonstrated that ionic conductivity of Al-added LLZBO compounds could be obviously improved when the sample sintering temperature increased from 1000°C to 1100°C. The highest ionic conductivity 6.3×10-5 S/cm was obtained in the LLZBO-1.25%Al sample sintered at 1100°C, in consistent with the lowest activation energy 0.45 eV for the lithium ion migration. The mechanism related with good ionic conductivity in the Al-added LLZBO sample was attributed to the lattice distortion induced by the partial Al substitution at Zr sites, which is helpful to improve the migration ability of Li ions in lattice.
Keywords: garnet lithium electrolyte; cubic Li7La3Zr2O12 ; AC impedance; ionic conductivity; activation energy

Specific heat treatment of selective laser melted Ti–6Al–4V for biomedical applications by Qianli Huang; Xujie Liu; Xing Yang; Ranran Zhang; Zhijian Shen; Qingling Feng (373-381).
The ductility of as-fabricated Ti–6Al–4V falls far short of the requirements for biomedical titanium alloy implants and the heat treatment remains the only applicable option for improvement of their mechanical properties. In the present study, the decomposition of as-fabricated martensite was investigated to provide a general understanding on the kinetics of its phase transformation. The decomposition of asfabricated martensite was found to be slower than that of water-quenched martensite. It indicates that specific heat treatment strategy is needed to be explored for as-fabricated Ti–6Al–4V. Three strategies of heat treatment were proposed based on different phase transformation mechanisms and classified as subtransus treatment, supersolvus treatment and mixed treatment. These specific heat treatments were conducted on selective laser melted samples to investigate the evolutions of microstructure and mechanical properties. The subtransus treatment leaded to a basket-weave structure without changing the morphology of columnar prior β grains. The supersolvus treatment resulted in a lamellar structure and equiaxed β grains. The mixed treatment yielded a microstructure that combines both features of the subtransus treatment and supersolvus treatment. The subtransus treatment is found to be the best choice among these three strategies for as-fabricated Ti–6Al–4V to be used as biomedical implants.
Keywords: titanium alloy; selective laser melting (SLM); heat treatment; microstructure; mechanical property

Hierarchical charge distribution controls self-assembly process of silk in vitro by Yi Zhang; Cencen Zhang; Lijie Liu; David L. Kaplan; Hesun Zhu; Qiang Lu (382-391).
Silk materials with different nanostructures have been developed without the understanding of the inherent transformation mechanism. Here we attempt to reveal the conversion road of the various nanostructures and determine the critical regulating factors. The regulating conversion processes influenced by a hierarchical charge distribution were investigated, showing different transformations between molecules, nanoparticles and nanofibers. Various repulsion and compressive forces existed among silk fibroin molecules and aggregates due to the exterior and interior distribution of charge, which further controlled their aggregating and deaggregating behaviors and finally formed nanofibers with different sizes. Synergistic action derived from molecular mobility and concentrations could also tune the assembly process and final nanostructures. It is suggested that the complicated silk fibroin assembly processes comply a same rule based on charge distribution, offering a promising way to develop silk-based materials with designed nanostructures.
Keywords: silk; self-assembly; charge; nanostructure; nanofiber

Selenium (Se) plays a specific role in human health, especially for its antitumor effect. Incorporation of selenium into biocompatible hydroxyapatite (HAP) may endow the materials with novel characteristics. In the current work, a series of seleniumdoped hydroxyapatite (Se-HAP) nanoparticles with different Se/P ratios were synthesized by a modified chemical precipitation. It was revealed that the powders with/without heattreatment were nano-sized needle-like HAP while the heat-treated samples have high crystallinity. The addition of selenium decreases the crystallinity of the synthesized apatite, and also takes a negative effect on the thermal stability of the as-prepared powders. The Se-HAP nanoparticles with Se/P molar ratio not more than 5% sintered at 900°C can achieve good crystallinity and thermal stability.
Keywords: selenium; hydroxyapatite; thermal stability; crystallinity

Evaluation on biocompatibility of biomedical polyurethanes with different hard segment contents by Dai-Wei Ma; Rong Zhu; Yi-Yu Wang; Zong-Rui Zhang; Xin-Yu Wang (397-404).
In this paper, polyurethane (PU) materials with different contents of hard segment (20%, 25%, 30%) were prepared based on hexamethylene diisocyanate and polycarbonate diols by solution polymerization. The obtained polycarbonate-urethane (PCU) elastomers were characterized by very good hydrophobic property and excellent resistance to hydrolysis. Hemolysis, recalification time and platelet-rich plasma adhesion were used to evaluate the blood compatibility of the materials. L929 cells cultured with leach liquor of these PU membranes were selected to perform the cytotoxicity experiments. The results indicate that the hemolysis rates of PU membranes are all less than 5%, which can meet the requirement of the national standards for biomaterials. However, compared with 20% and 30% groups, the recalification time of the sample containing 25% hard segment is longer, while the number of platelet adhesion is less. Additionally, cells cultured in the leach liquor of PU membranes with 25% hard segment proliferated relatively more thriving, meaning that this proportion of the material has the lowest cytotoxicity.
Keywords: polyurethane (PU); hydrolytic stability; blood compatibility; cytotoxicity

Chitosan-collagen/organomontmorillonite scaffold for bone tissue engineering by Xianshuo Cao; Jun Wang; Min Liu; Yong Chen; Yang Cao; Xiaolong Yu (405-412).
A novel composite scaffold based on chitosan-collagen/organomontmorillonite (CS-COL/OMMT) was prepared to improve swelling ratio, biodegradation ratio, biomineralization and mechanical properties for use in tissue engineering applications. In order to expend the basal spacing, montmorillonite (MMT) was modified with sodium dodecyl sulfate (SDS) and was characterized by XRD, TGA and FTIR. The results indicated that the anionic surfactants entered into interlayer of MMT and the basal spacing of MMT was expanded to 3.85 nm. The prepared composite scaffolds were characterized by FTIR, XRD and SEM. The swelling ratio, biodegradation ratio and mechanical properties of composite scaffolds were also studied. The results demonstrated that the scaffold decreased swelling ratio, degradation ratio and improved mechanical and biomineralization properties because of OMMT.
Keywords: chitosan (CS); collagen (COL); montmorillonite (MMT); sodium dodecyl sulfate (SDS)

Macrocellular vitreous carbon with the improved mechanical strength by Oleg Smorygo; Alexander Marukovich; Vitali Mikutski; Andika Pramono (413-417).
Vitreous carbons with regular macrocellular structure, open interconnected porosity, high specific strength and hydraulic permeability were synthesized by infiltration of the epoxy resin into the sacrificial template made from the carbamide granules. Polyvinylpyrrolidone (PVP) solution in ethanol was used as the template binder. When the resin setting and the template extraction had been performed, the resultant porous material was pyrolysed in the nitrogen flow. Depending on PVP concentration in the template binder, final vitreous carbons had the following properties: bulk density at 0.17-0.22 g/cm3; porosity at 85.7%-89.0%; window size at 447-735 µm; Darcian permeability coefficient at (0.64-9.5)×10-9m2; non-Darcian permeability coefficient at (0.53-3.36)×10-4 m. High specific strength of above 8×103 Pa/(kg·m-3) was attained.
Keywords: vitreous carbon; cellular material; porous material