Sep 2011, Volume 5 Issue 3

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    Yiyang LIN, Chuanbin MAO

    Supramolecular self-assembly has proven to be a reliable approach towards versatile nanomaterials based on multiple weak intermolecular forces. In this review, the development of bio-inspired supramolecular self-assembly into soft materials and their applications are summarized. Molecular systems used in bio-inspired “bottom-up self-assembly” involve small organic molecules, peptides or proteins, nucleic acids, and viruses. Self-assembled soft nanomaterials have been exploited in various applications such as inorganic nanomaterial synthesis, drug or gene delivery, tissue engineering, and so on.

    Shun-Feng WANG, Xiao-Hong WANG, Lu GAN, Matthias WIENS, Heinz C. SCHR?DER, Werner E. G. MüLLER

    In the last 15 years biomineralization, in particular biosilicification (i.e., the formation of biogenic silica, SiO2), has become an exciting source of inspiration for the development of novel bionic approaches, following “Nature as model”. Among the silica forming organisms there are the sponges that have the unique property to catalyze their silica skeletons by a specific enzyme termed silicatein. In the present review we summarize the present state of knowledge on silicatein-mediated “biosilica” formation in marine sponges, the involvement of further molecules in silica metabolism and their potential application in biomedicine. Recent advancements in the production of bone replacement material and in the potential use as a component in the treatment of osteoporosis are highlighted.

    Ling-Hao HE, Lu YAO, Rui XUE, Jing SUN, Rui SONG

    Solvent played an important role in the formation of calcium phosphate phase of the chitosan/calcium phosphate composites. In this investigation, ethanol-acetic acid mixtures were employed as solvents, and various calcium phosphate phases, such as brushite, amorphous calcium phosphate, and hydroxyapatite, were introduced into the chitosan/calcium phosphate composites by using in-situ preparation process. The results showed that the structures of composite were influenced remarkably by the morphology and the distribution of calcium phosphate phase. In addition, the bioactivity of composites was governed mainly by the characters of calcium phosphate phases in composites, since calcium phosphate phases could induce the growth of hydroxyapatite coating on the surfaces of composites. On the surface of chitosan/brushite composite, the formed hydroxyapatite coating consisted of oriented plate crystallites, which self-assembled into spherical-like crystals. When other calcium phosphate phase was introduced into composites, the polymorphs of hydroxyapatite layer would change greatly. The oriented plate crystallites became bigger, and meanwhile, the self-assembled aggregates became less and smaller. In addition, with the shift of the prior nucleating point, the growth orientation of plate crystallites was transformed.

    Ying SHI, Song WANG, Xiu-Mei WANG, Qiang CAI, Fu-Zhai CUI, Heng-De LI

    A new type of collagen mimetic peptide, (PKG)n(POG)2n(DOG)n, with charged-domain ends had been designed and successfully prepared in this work, which self-assembled into collagen-like triple helices homotrimers. The collagen-like homotrimers underwent higher level of self-assembly via static electrical interaction between positive and negative domains. Transmission electron microscope (TEM) examinations showed three typical morphologies of homotrimer assembly, which were defined as film, bicontinuous and fibril morphology in this paper. The film was formed in the initial stage and gradually transformed to bicontinuous or fibril morphology to improve stability of the assemblies or decrease surface energy. Furthermore, mechanism of assembly process was proposed based on TEM observations and theoretical analyses of packing equation.

    Zhi HUANG, Yan CHEN, Qing-Ling FENG, Wei ZHAO, Bo YU, Jing TIAN, Song-Jian LI, Bo-Miao LIN

    For reconstruction of irregular bone defects, injectable biomaterials are more appropriate than the preformed biomaterials. We herein develop a biomimetic in situ-forming composite consisting of chitosan (CS) and mineralized collagen fibrils (nHAC), which has a complex hierarchical structure similar to natural bone. The CS/nHAC composites with or without mesenchymal stem cells (MSCs) are injected into cancellous bone defects at the distal end of rabbit femurs. Defects are assessed by radiographic, histological diagnosis and Raman microscopy until 12 weeks. The results show that MSCs improve the biocompatibility of CS/nHAC composites and enhance new bone formation in vivo at 12 weeks. It can be concluded that the injectable CS/nHAC composites combined with MSCs may be a novel method for reconstruction of irregular bone defects.

    Akimasa KOJI, Javed IQBAL, Rong-Hai YU, Zheng-Jun ZHANG

    Cobalt and cobalt oxide nanocrystals were synthesized on Si substrates from aqueous cobalt nitrate [Co(NO3)2·6H2O] powder via chemical vapor deposition method. Scanning electron microscope, field emission scanning electron microscope, and transmission electron microscope observations show different morphologies, such as continuous films, nano-bars, nano-dices, and nano-strings, depending on the synthesis temperature. The crystal structure characterization was conducted using X-ray diffraction methods. Furthermore, the properties of the samples were characterized using Raman spectroscopic analysis and vibrating sample magnetometer. The morpholo- gy change was discussed in terms of synthesis environments and chemical interactions between cobalt, oxygen, and silicon.

    Xiang MAO, Zheng-Ping LI, Zhi-Yong TANG

    Direct mixture of Au3+ with glutathione (GSH), which act as both reduction agents and stabilizers, in aqueous solution gave rise to production of gold nanoparticles (Au NPs) with uniform sizes of around 21 nm. The GSH stabilizer Au NPs in solution show immediate aggregation after addition of 1 mol/L NaCl aqueous solution containing Pb2+ ions. The Pb2+-induced aggregation in Au NP solution is monitored by both colorimetric response and UV-vis spectroscopy. A rather broad linear range (from 0.1 to 30 μmol/L) and low detection limit (0.1 μmol/L) are explored for Au NP sensors used for detection of Pb2+ ions. Furthermore, the response of GSH-stabilized Au NPs toward Pb2+ ions is specific compared with other possible interferants (Hg2+, Mg2+, Zn2+, Ni2+, Cu2+, Co2+, Ca2+, Mn2+, Cd2+, and Ba2+).

    Jin WANG, Pei-Jing WANG, Peng GAO, Lan JIANG, Shuo LI, Zeng-Guo FENG

    Combining with XRD analysis, Fourier transform infrared (FTIR) spectroscopy is employed to discern the self-assembled structures of β-cyclodextrins (β-CDs) threaded onto the polymer backbone in the polyrotaxanes (PRs) by means of the relative changes of absorption intensity of the characteristic peaks of β-CDs at 1153 and 1025 cm-1. For quantitative analysis, six parameters are proposed to describe the relative absorption intensity variations of these peaks associated with a channel-type crystal structure or a dispersed structure of β-CDs entrapped. Among them, absorbance ratio (AR), relative absorbance difference (RAD) and transmittance difference (TD) values are suitable. When the AR, RAD and TD data get below 1.04, 4.8 and 1.27, respectively, the PRs obtained would possess a dispersed structure. If these values go beyond 1.32, 34.5 and 9.47, respectively, they would hold a channel-type crystal structure. This finding provides a useful judgment to distinguish the self-assembled structures of β-CDs residing along the polymer backbone in the PRs.