Frontiers of Materials Science (v.7, #2)

Marine CaCO3 skeletons have tailored architectures created by nature, which give them structural support and other functions. For example, seashells have dense lamellar structures, while coral, cuttlebone and sea urchin spines have interconnected porous structures. In our experiments, seashells, coral and cuttlebone were hydrothermally converted to hydroxyapatite (HAP), and sea urchin spines were converted to Mg-substituted tricalcium phosphate, while maintaining their original structures. Partially converted shell samples have mechanical strength, which is close to that of compact human bone. After implantation of converted shell and spine samples in rat femoral defects for 6 weeks, there was newly formed bone growth up to and around the implants. Some new bone was found to migrate through the pores of converted spine samples and grow inward. These results show good bioactivity and osteoconductivity of the implants, indicating the converted shell and spine samples can be used as bone defect fillers. The interconnected porous HAP scaffolds from converted coral or cuttlebone that have pore size larger than 100 ?m likely support infiltration of bone cells and vessels, and finally encourage new bone ingrowth.
Keywords: seashell; sea urchin spine; coral; cuttlebone; hydrothermal conversion; hydroxyapatite (HAP); β-tricalcium phosphate (β-TCP)

Hyperthermia has long been considered as an adjuvant therapy for treating various diseases. Cancer treatment exploiting hyperthermia shows great clinical potential for a wide range of tumors. Importantly, the efficacy of hyperthermal therapy has recently been enhanced by the development of functional nanomaterials. The unique physicochemical properties of nanomaterials afford the specific localization of hyperthermia to primary tumors and early-stage cancers. In particular, due to their high rate of light-to-heat conversion and their capacity to be activated by tissue-penetrating electromagnetic radiation, near-infrared (NIR) light-absorbing plasmonic nanomaterials have attracted considerable attention as candidates for noninvasive photothermal therapy. The purpose of this article is to provide a overview on the current development in multifunctional nanomaterials capable of combined hyperthermia-chemotherapy delivery.
Keywords: combination therapy; multifunctional nanoparticle; drug delivery; hyperthermia; photothermal therapy

Silk fibroin (SF) is a kind of natural polymers with a great potential in biomedical application. Due to its good biocompatibility, biodegradability and minimal inflammatory reaction, SF is an excellent candidate for generating tissue engineering scaffolds. Electrospinning is a simple and effective method to fabricate nanofibers, which has several amazing characteristics such as very large surface area to volume ratio, flexibility in surface functionalities, and superior mechanical performance. The electrospun nanofibers from SF and its blends have been used for varied tissue engineering. This paper will give a brief review about the structure, properties and applications of SF and blend nanofibers via electrospinning.
Keywords: electrospinning; nanofiber; silk fibroin (SF); biodegradable polymer

Irradiation effects on nanocrystalline materials by Yong-Qin Chang; Qiang Guo; Jing Zhang; Lin Chen; Yi Long; Fa-Rong Wan (143-155).
In recent years, nanocrystalline materials with grain size below 100 nm have attracted much interest due to their excellent chemical, physical, and optical properties. This review focuses on the irradiation effects of nanocrystalline materials. It has been generally believed that nanocrystalline materials have a great potential to increase irradiation resistance in the future reactor because of a large fraction of grain boundaries or interfaces that could absorb and annihilate mobile defects which produced during irradiation. Some calculation results and experiment results revealed that nanocrystalline materials can enhance irradiation resistance, while some reports showed that nanocrystalline materials exhibit worse irradiation resistance, or even amorphous at a lower irradiation dose compared with their bulk materials. During the irradiation process, the grain growth dominated by irradiation dose, thermal effect or defects was also disputed. Irradiation is also an important tool to tailor the grain size, phase structure and physical properties of the materials.
Keywords: nanocrystalline material; irradiation; resistance; grain growth

Microstructural characterization of polycrystalline materials by synchrotron X-rays by Leyun Wang; Meimei Li; Jonathan Almer; Thomas Bieler; Rozaliya Barabash (156-169).
Third generation synchrotron X-rays provide an unprecedented opportunity for microstructural characterization of many engineering materials as well as natural materials. This article demonstrates the usage of three techniques for the study of structural materials: differential-aperture X-ray microscopy (DAXM), three-dimensional X-ray diffraction (3DXRD), and simultaneous wide angle/small angle X-ray scattering (WAXS/SAXS). DAXM is able to measure the 3D grain structure in polycrystalline materials with high spatial and angular resolution. In a deformed material, streaked diffraction peaks can be used to analyze local dislocation content in individual grains. Compared to DAXM, 3DXRD is able to map grains in bulk materials more quickly at the expense of spatial resolution. It is very useful for studying evolving microstructures when the materials are under deformation. WAXS/SAXS is suitable for studying materials with inhomogeneous structure, such as precipitate strengthened alloys. Structural information revealed by WAXS and SAXS can be combined for a deeper insight into material behavior. Future development and applications of these three techniques will also be discussed.
Keywords: differential-aperture X-ray microscopy (DAXM); three-dimensional X-ray diffraction (3DXRD); wide angle/small angle X-ray scattering (WAXS/SAXS)

Oil spill cleanup from sea water by carbon nanotube sponges by Ke Zhu; Yuan-Yuan Shang; Peng-Zhan Sun; Zhen Li; Xin-Ming Li; Jin-Quan Wei; Kun-Lin Wang; De-Hai Wu; An-Yuan Cao; Hong-Wei Zhu (170-176).
Oil spills in the sea have caused many serious environmental problems worldwide. In this study, carbon nanotube (CNT) sponges were used to cleanup oil slicks on sea waters. This method was compared with two traditional representative sorbents, including polypropylene fiber fabric and woolen felt. The CNT sponges had a larger oil sorption capacity than the other two sorbents. The maximum oil sorption capacity (Q m) of the CNT sponge was 92.30 g/g, which was 12 to 13.5 times larger than the Q m of the other two sorbents (the Q m of the polypropylene fiber fabric and woolen felt were 7.45 and 6.74 g/g, respectively). In addition, unlike the other two sorbents, the CNT sponge was superhydrophobic and did not adsorb any water during oil spill cleanup. CNT sponges are potentially very useful for cleaning up oil spills from sea water.
Keywords: carbon nanotube (CNT); sponge; oil spill; sorption capacity; sea water

Effect of silk sericin on morphology and structure of calcium carbonate crystal by Rui-Bo Zhao; Hua-Feng Han; Shao Ding; Ze-Hao Li; Xiang-Dong Kong (177-183).
In this paper, silk sericin was employed to regulate the mineralization of calcium carbonate (CaCO3). CaCO3 composite particles were prepared by the precipitation reaction of sodium carbonate with calcium chloride solution in the presence of silk sericin. The as-prepared samples were collected at different reaction time to study the crystallization process of CaCO3 by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and X-ray diffraction (XRD). The results showed that silk sericin significantly affected the morphology and crystallographic polymorph of CaCO3. With increasing the reaction time, the crystal phase of CaCO3 transferred from calcite dominated to vaterite dominated mixtures, while the morphology of CaCO3 changed from disk-like calcite crystal to spherical vaterite crystal. These studies showed the potential of silk sericin used as a template molecule to control the growth of inorganic crystal.
Keywords: silk sericin; calcium carbonate (CaCO3); calcite; vaterite; biomineralization

The thermal shock behavior of ZrB2-SiC ceramics was studied with water, air and methyl silicone oil as quenching media, respectively. The temperature of all coolants was room temperature (25°C) and the residual strength of the ceramics after quenching was tested. The strength of the ceramics after water quenching had an obvious drop when the temperature difference, ΔT, was about 275°C, while the residual strength of the specimens quenched by air and silicone oil only varied a little and even increased slightly when the temperature difference was higher than 800°C. The different thermal conductive coefficient of the coolants and surface heat transfer coefficient resulted in the differences in the thermal shock behavior. The formation of oxidation layer was beneficial for improving the residual strength of the ceramics after quenching.
Keywords: ultra-high temperature ceramic (UHTC); zirconium diboride (ZrB2); silicon carbide (SiC); thermal shock resistance; mechanical property

Strength and fatigue properties of three-step sintered dense nanocrystal hydroxyapatite bioceramics by Wen-Guang Guo; Zhi-Ye Qiu; Han Cui; Chang-Ming Wang; Xiao-Jun Zhang; In-Seop Lee; Yu-Qi Dong; Fu-Zhai Cui (190-195).
Dense hydroxyapatite (HA) ceramic is a promising material for hard tissue repair due to its unique physical properties and biologic properties. However, the brittleness and low compressive strength of traditional HA ceramics limited their applications, because previous sintering methods produced HA ceramics with crystal sizes greater than nanometer range. In this study, nano-sized HA powder was employed to fabricate dense nanocrystal HA ceramic by high pressure molding, and followed by a three-step sintering process. The phase composition, microstructure, crystal dimension and crystal shape of the sintered ceramic were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Mechanical properties of the HA ceramic were tested, and cytocompatibility was evaluated. The phase of the sintered ceramic was pure HA, and the crystal size was about 200 nm. The compressive strength and elastic modulus of the HA ceramic were comparable to human cortical bone, especially the good fatigue strength overcame brittleness of traditional sintered HA ceramics. Cell attachment experiment also demonstrated that the ceramics had a good cytocompatibility.
Keywords: nanocrystal hydroxyapatite ceramic; three-step sintering; mechanical property; fatigue strength; cytocompatibility

Nanocrystalline Zn1 − x Cu x O (x = 0, 0.02, 0.04, 0.06, 0.08) samples were synthesized by a novel auto-combustion method using glycine as the fuel material. The structural, optical and magnetic properties of the samples were characterized using XRD, SEM, photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies. The XRD spectra of samples reveal the hexagonal wurtzite structures of ZnO. As the copper content increases, a diffraction peak at 2θ = 39° corresponding to secondary phase of CuO ([111] crystalline face) appears when x ⩽ 6 mol.%. PL spectra of the samples show a strong ultraviolet (UV) emission and defect related visible emissions. Cu-doping in ZnO can effectively adjust the energy level in ZnO, which leads to red shift in the emission peak position in UV region. The EPR spectra of Cu-doped ZnO nanoparticles show a distinct and broad signal at room temperature, suggesting that it may be attributed to the exchange interactions within Cu2+ ions.
Keywords: Cu-doped ZnO; auto-combustion; luminescence; electron paramagnetic resonance (EPR)