Dec 2011, Volume 5 Issue 4
    

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  • REVIEW ARTICLE
    Junyi ZHU, Su-Huai WEI

    Overcoming the doping bottleneck in semiconductors, especially in wide band gap semiconductors, has been a challenge in semiconductor physics for many years. In this paper, we review some recent progresses in enhancing doping by surfactant and strain. We show that surfactant and strain are two effective approaches to enhance dopant solubility in epitaxial growth. The surfactant can introduce an energy level deep inside the band gap, making the host compound less stable, thus lower the formation energy of the intentional dopant. The strain enhanced doping is based on the observation that dopant induces volume change in the host. If the external strain is in the same direction as the dopant induced volume change, the formation energy of the dopant is reduced. This effect can be used to tune doping sites, thus doping type, in a host. A hybrid method to both include strain and surfactant is proposed, which can be a promising general method to further enhance doping.

  • REVIEW ARTICLE
    Roshan JAMES, Meng DENG, Cato T. LAURENCIN, Sangamesh G. KUMBAR

    This manuscript focuses on bone repair/regeneration using tissue engineering strategies, and highlights nanobiotechnology developments leading to novel nanocomposite systems. About 6.5 million fractures occur annually in USA, and about 550,000 of these individual cases required the application of a bone graft. Autogenous and allogenous bone have been most widely used for bone graft based therapies; however, there are significant problems such as donor shortage and risk of infection. Alternatives using synthetic and natural biomaterials have been developed, and some are commercially available for clinical applications requiring bone grafts. However, it remains a great challenge to design an ideal synthetic graft that very closely mimics the bone tissue structurally, and can modulate the desired function in osteoblast and progenitor cell populations. Nanobiomaterials, specifically nanocomposites composed of hydroxyapatite (HA) and/or collagen are extremely promising graft substitutes. The biocomposites can be fabricated to mimic the material composition of native bone tissue, and additionally, when using nano-HA (reduced grain size), one mimics the structural arrangement of native bone. A good understanding of bone biology and structure is critical to development of bone mimicking graft substitutes. HA and collagen exhibit excellent osteoconductive properties which can further modulate the regenerative/healing process following fracture injury. Combining with other polymeric biomaterials will reinforce the mechanical properties thus making the novel nano-HA based composites comparable to human bone. We report on recent studies using nanocomposites that have been fabricated as particles and nanofibers for regeneration of segmental bone defects. The research in nanocomposites, highlight a pivotal role in the future development of an ideal orthopaedic implant device, however further significant advancements are necessary to achieve clinical use.

  • RESEARCH ARTICLE
    Xi LIU, Ying WANG, Jin HE, Xiu-Mei WANG, Fu-Zhai CUI, Quan-Yuan XU

    Neuronal progenitor cells cultured on gold-coated glass surfaces modified by different chemical functional groups, including hydroxyl (-OH), carboxyl (-COOH), amino (-NH2), bromo (-Br), mercapto (-SH), -Phenyl and methyl (-CH3), were studied here to investigate the influence of surface chemistry on the cells’ adhesion, morphology, proliferation and functional gene expression. Focal adhesion staining indicated in the initial culture stage cells exhibited morphological changes in response to different chemical functional groups. Cells cultured on -NH2 grafted surface displayed focal adhesion plaque and flattened morphology and had the largest contact area. However, their counter parts on -CH3 grafted surface displayed no focal adhesion and rounded morphology and had the smallest contact area. After 6 days culture, the proliferation trend was as follows: -NH2>-SH>-COOH>-Phenyl>-Br>-OH>-CH3. To determine the neural functional properties of the cells affected by surface chemistry, the expression of glutamate decarboxylase (GAD67), nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) were characterized. An increase of GAD67 expression was observed on -NH2, -COOH and -SH grafted surfaces, while no increase in NGF and BDNF expression was observed on any chemical surfaces. These results highlight the importance of surface chemistry in the fate determination of neuronal progenitor cells, and suggest that surface chemistry must be considered in the design of biomaterials for neural tissue engineering.

  • RESEARCH ARTICLE
    Hui-Yun ZHOU, Dong-Ju ZHOU, Wei-Fen ZHANG, Ling-Juan JIANG, Jun-Bo LI, Xi-Guang CHEN

    In this work, chitosan/cellulose acetate microspheres (CCAM) were prepared by the method of W/O/W emulsion with no toxic reagents. The microspheres were spherical, free flowing, and non-aggregated, which had a narrow size distribution. More than 90% of the microspheres had the diameter ranging from 200 to 280 μm. The hemolytic analysis indicated that CCAM was safe and had no hemolytic effect. The implanted CCAM did not produce any significant changes in the hematology of Sprague-Dawley (SD) rats, such as white blood cell, red blood cell, platelet, and the volume of hemoglobin. In addition, the levels of serum alanine aminotransferase, blood urea nitrogen, and creatinine had no obvious changes in SD rats implanted with CCAM, surger thread, or normal SD rats without any implantation. Thus, the CCAM had good blood compatibility and had no hepatotoxicity or renal toxicity to SD rats. Furthermore, CCAM with or without the model drug had good tissue compatibility with respect to the inflammatory reaction in SD rats and showed no significant difference from that of SD rats implanted with surgery thread. CCAM shows promise as a long-acting delivery system, which had good biocompatibility and biodegradability.

  • RESEARCH ARTICLE
    Punuri Jayasekhar BABU, Pragya SHARMA, Mohan Chandra KALITA, Utpal BORA

    This report describes the use of ethnolic extract of Fagopyrum esculentum leaves for the synthesis of gold nanoparticles. UV-visible spectroscopy analysis indicated the successful formation of gold nanoparticles. The synthesized nanoparticles were characterized by transmission electron microscopy (TEM), high resolution TEM (HRTEM) and were found to be spherical, hexagonal and triangular in shape with an average size of 8.3 nm. The crystalline nature of the gold nanoparticles was confirmed from X-ray diffraction (XRD) and selected-area electron diffraction (SAED) patterns. Fourier transform infrared (FT-IR) and energy-dispersive X-ray analysis (EDX) suggested the presence of organic biomolecules on the surface of the gold nanoparticles. Cytotoxicity tests against human HeLa, MCF-7 and IMR-32 cancer cell lines revealed that the gold nanoparticles were non-toxic and thus have potential for use in various biomedical applications.

  • RESEARCH ARTICLE
    Jing SUN, Lu YAO, Qiao-Ling ZHAO, Jin HUANG, Rui SONG, Zhi MA, Ling-Hao HE, Wei HUANG, Yong-Mei HAO

    The crystallization modification of poly(vinylidene fluoride) (PVDF) was investigated for the blend films of PVDF and poly(methyl methacrylate) (PMMA). The mass crystallinity (χc) and further, the β-phase content (F(β)) of PVDF, were studied for the as-prepared blend films with different mass ratios. In addition, the variations of χc and F(β) were systematically probed once the PMMA component was removed from the related blend systems. DSC, FTIR and XRD measurements all indicated that 1) χc, F(β) and even the content of α-phase (F(α)) decreased with the addition of PMMA; 2) with the extraction of PMMA, both χc and F(β) increased while F(α) decreased. It is worth noting that the increase of χc and F(β) depended on the relative amount of extracted PMMA (EPMMA), i.e., the more PMMA was removed, the more χc and F(β) increased. These results reveal the hindrance effect from the PMMA constituent to the crystallization of PVDF, and consequently, this restriction would be released when the PMMA was extracted.

  • RESEARCH ARTICLE
    K. R. VISHNU MAHESH, H. N. NARASIMHA MURTHY, B. E. KUMARA SWAMY, S. C. SHARMA, R. SRIDHAR, Niranjan PATTAR, M. KRISHNA, B. S. SHERIGARA

    The dispersion of montmorillonite (MMT) in vinylester for preparing nanoclay/vinylester gel coat was reported. Two sets of MMT/vinylester specimens, namely Type 1 and Type 2, were prepared for comparative studies. Type 1 specimens were prepared using ultrasonication only, and Type 2 specimens were prepared using both ultrasonication and twin-screw extrusion. According to XRD and TEM results, Type 2 specimens showed lower levels of nanoclay agglomeration and higher levels of exfoliation. DSC results showed that the glass transition temperatures of Type 2 specimens are higher than those of Type 1 specimens. TGA results showed that the residual weight of 4 wt.% MMT/vinylester of Type 1 was 7.38%, while the corresponding value of Type 2 was 13.5%, indicating lower thermal degradation in the latter. MMT/vinylester/glass and MMT/vinylester/carbon specimens were fabricated and tested for mechanical and fire retardation behaviours. Type 2 based nanocomposite laminates showed greater values of ultimate tensile strength, flexural strength, interlaminar shear strength, impact strength, horizontal burning rate, and vertical burning rate than Type 1 based laminates. SEM images of tensile fractured surfaces revealed that Type 2 based laminates have no or less agglomeration of nanoclay than Type 1 based laminates.

  • COMMUNICATION
    Xiao-Long YU, Bin ZHANG, Xiu-Mei WANG, Ying WANG, Lin QIAO, Jin HE, Juan WANG, Shuang-Feng CHEN, In-Seop LEE, Fu-Zhai CUI

    Hepatoma cells (Hepg2s) as typical cancer cells cultured on hydroxyl (-OH) and methyl (-CH3) group surfaces were shown to exhibit different proliferation and morphological changes. Hepg2s cells on -OH surfaces grew much more rapidly than those on -CH3 surfaces. Hepg2s cells on -OH surfaces had the larger contact area and the more flattened morphology, while those on -CH3 surfaces exhibited the smaller contact area and the more rounded morphology. After 7 days of culture, the migration of Hepg2s cells into clusters on the -CH3 surfaces behaved significantly slower than that on the -OH surfaces. These chemically modified surfaces exhibited regulation of Hepg2s cells on proliferation, adhesion, and migration, providing a potential treatment of liver cancer.