Xinyu Shen

Preparation and characterization of homogeneous chitosan–polylactic acid/hydroxyapatite nanocomposite for bone tissue engineering and evaluation of its mechanical properties

Homogeneous nanocomposites composed of hydroxyapatite and chitosan in the presence of polylactic acid were synthesized by a novel in situ precipitation method. The morphological and compositional properties of composites were investigated. Hydroxyapatite nanoparticles in a special rod-like shape with a diameter of about 50nm and a length of about 300nm were distributed homogeneously within the chitosan-polylactic acid matrix. The interaction between the organic matrix and the inorganic crystallite and the formation mechanism of the rod-like nanoparticles were also studied. The results suggested that the formation of the special rod-like nanoparticles could be controlled by a multiple-order template effect. High-resolution images showed that the rod-like inorganic particles were composed of randomly orientated subparticles about 10nm in diameter. The mechanical properties of the composites were evaluated by measuring their compressive strength and elastic modulus. The data indicated that the addition of polylactic acid can make homogeneous composites scaffold resist significantly higher stress. The elastic modulus of the composites was also improved by the addition of polylactic acid, which can make them more beneficial for surgical applications.

Surface Functionalization of Titanium with Chitosan/Gelatin via Electrophoretic Deposition: Characterization and Cell Behavior

The electrophoretic deposition (EPD) is a versatile and cost-effective technique for fabricating advanced coatings. In this study, chitosan/gelatin (CS/G) coatings were prepared on titanium substrates via EPD. The prepared coatings were characterized using fluorescence microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and shear bond strength testing. It was found that CS/G coatings had a similar macroporous structure. The gelatin content in the CS/G coatings gradually increased with the increase of the gelatin in the blend solutions. The shear bond strength of the CS/G coatings also increased with the increasing gelatin content. In vitro biological tests demonstrated that human MG63 osteoblast-like cells achieved better affinity on the coatings with higher gelatin content. Therefore, it was concluded that EPD was an effective and efficient technique to prepare CS/G coatings on the titanium surface and that CS/G coatings with higher gelatin content were promising candidates for further loading of functional agents.

Investigation of the effects of 30% hydrogen peroxide on human tooth enamel by Raman scattering and laser-induced fluorescence.

The safety of tooth bleaching, which is based upon hydrogen peroxide (HP) as the active agent, has been questioned. Our aim was to investigate the effects of 30% HP on human tooth enamel. The specimens were divided randomly into three groups and treated with distilled water, HCl, and HP, respectively. Raman scattering and laser-induced fluorescence of enamel were determined before and after treatment. Microhardness testing and scanning electron microscopy were also used. The results of Raman scattering showed that the Raman relative intensity of enamel changed significantly after HP and HCl treatment. These findings were consistent with the results of microhardness testing and morphological observations. In addition, a small band at 876 cm(-1) due to O-O stretching of HP became pronounced during HP treatment, which provided direct evidence that HP has the ability to penetrate enamel. Meanwhile, the results of laser-induced fluorescence revealed that HP caused the greatest fluorescence reduction. This suggested that the organic matter in enamel might be greatly affected by HP, which was also supported by the results of microhardness. It can be concluded, therefore, that the 30% HP may have adverse effects on the mineral and the organic matter of human tooth enamel.

Preparation and evaluation of collagen-silk fibroin/hydroxyapatite nanocomposites for bone tissue engineering.

A new in situ precipitation technique was developed to synthesize collagen-silk fibroin/hydroxyapatite nanocomposites. The componential properties and morphological of nanocomposites were investigated. It was revealed that the inorganic phase in the nanocomposite was carbonate-substituted hydroxyapatite with low crystallinity. Morphology studies showed that hydroxyapatite particles with size ranging from 30 to 100 nm were distributed uniformly in the polymer matrix. According to the TEM micrographs, inorganic particles were composed of more fine sub-particles whose diameters were between 2 and 5 nm in size without regular crystallographic orientation. The mechanical properties of the composites were evaluated by measuring their elastic modulus. The data indicated that the elastic modulus of nanocomposites was improved by the addition of silk fibroin. Finally, the cell biocompatibility of the composites was tested in vitro, which showed that they have good biocompatibility. These results suggest that the collagen-silk fibroin/hydroxyapatite nanocomposites are promising biomaterials for bone tissue engineering.

Incorporation of homogeneous Co3O4 into a nitrogen-doped carbon aerogel via a facile in situ synthesis method: implications for high performance asymmetric supercapacitors

A novel high-performance electrode material, nitrogen-doped carbon aerogel/cobalt oxide (NCA/Co3O4) material, was prepared by a facile, one step and in situ coating method, followed by a freeze-drying process. The effects of different amounts of Co3O4 on the structural properties, specific surface areas, elemental compositions and electrochemical performance of the composite electrodes were investigated. Consequently, the electrode with 75% mass content of Co3O4 exhibited excellent electrochemical performance, in particular, a high specific capacitance of 616 F g−1 at a current density of 1 A g−1, excellent rate capability (445 F g−1 at 20 A g−1) and outstanding cycle performance. In addition, the asymmetric supercapacitor assembled with NCA/Co3O4-3 and NCA electrodes could be cycled in a high voltage range of 1.5 V and deliver a maximum energy density of 33.43 W h kg−1 at a power density of 375 W kg−1. The enhanced electrochemical performance is attributed to the complementary contributions of the 3D interconnected porous structure and the efficient pseudocapacitance of the uniformly dispersed Co3O4 nanoparticles. The preparation method offers a new fabrication strategy to in situ fabricate carbon-supported metal oxide electrodes for high-performance energy storage applications.

A novel nanocomposite for bone tissue engineering based on chitosan–silk sericin/hydroxyapatite: biomimetic synthesis and its cytocompatibility

A simple and effective approach was developed to synthesize chitosan–silk sericin/hydroxyapatite nanocomposites by in situ precipitation and two methods of alkali diffusion were carried out in this study. The objective of this paper was to investigate the different properties of the nanocomposites. SEM showed that the rod-like hydroxyapatite particles with a diameter of 20–50 nm were distributed homogeneously within the chitosan–silk sericin matrix, and the formation mechanism was also investigated. The results of FTIR and XRD indicated that the inorganic phase in the nanocomposite was carbonate-substituted hydroxyapatite with low crystallinity. In terms of mechanical properties, chitosan–silk sericin/hydroxyapatite nanocomposites exhibited a higher elastic modulus and compressive strength than that of the chitosan/hydroxyapatite nanocomposites. In vitro cytocompatibility of the nanocomposite was evaluated by CCK-8 assay and SEM through MG63 osteoblast cells cultured on the samples, which demonstrated that they are non-toxic and support cell growth. These results suggest that the chitosan–silk sericin/hydroxyapatite nanocomposites are promising biomaterials for bone tissue engineering.

A detailed study of homogeneous agarose/hydroxyapatite nanocomposites for load-bearing bone tissue.

Agarose/hydroxyapatite (agar/HA) nanocomposites for load-bearing bone substitutes were successfully fabricated via a novel in situ precipitation method. Observation via SEM and TEM revealed that the spherical inorganic nanoparticles of approximately 50 nm were well dispersed in the organic matrix, and the crystallographic area combined closely with the amorphous area. The uniform dispersion of HA nanoparticles had prominent effect on improving the mechanical properties of the agar/HA nanocomposites (the highest elastic modulus: 1104.42 MPa; the highest compressive strength: 400.039 MPa), which proved to be potential load-bearing bone substitutes. The thermal stability of agarose and nanocomposites was also studied. The MG63 osteoblast-like cells on the composite disks displayed fusiform and polygonal morphology in the presence of HA, suggesting that the cell maturation was promoted. The results of cell proliferation and cell differentiation indicated that the cells cultured on the agar/HA composite disks significantly increased the alkaline phosphatase activity and calcium deposition. The structural role of agarose in the composite system was investigated to better understand the effect of biopolymer on structure and properties of the composites. The optimal properties were the result of a comprehensive synergy of the components.

Rational design of uniformly embedded metal oxide nanoparticles into nitrogen-doped carbon aerogel for high-performance asymmetric supercapacitors with a high operating voltage window

We report the design of a high-performance asymmetric supercapacitor (ASC) based on manganese monoxide/carbon aerogel (MnO/NCA) composites as the positive electrode and iron oxide/carbon aerogel (Fe2O3/NCA) composites as the negative electrode. The prepared MnO/NCA hybrid composites display a highly interconnected network structure with ultrathin MnO nanoparticles uniformly embedded into the 3D nitrogen-doped carbon matrix. Because of the synergistic effects of the highly conductive carbon aerogel and highly pseudocapacitive metal oxides, the hybrid MnO/NCA electrode exhibits highly effective surface area, greatly enhanced ion transportation, and excellent electrochemical performance, in comparison with other MnOx-based electrode materials. Matching it with the Fe2O3/NCA cathode, the novel ASC devices can achieve a high voltage window of 2.0 V, delivering a remarkable energy density of 48.67 W h kg−1 at a power density of 1000 W kg−1 and still retains 27.39 W h kg−1 at a high power density of 10 kW kg−1, consequently giving rise to stable cycling performance. These encouraging results will provide a fresh route for the design and fabrication of metal oxide@carbon aerogel materials for application in next-generation storage systems.

Bio-templated synthesis of hierarchically ordered macro-mesoporous anatase titanium dioxide flakes with high photocatalytic activity

Highly ordered macro-mesoporous anatase titanium dioxide (TiO2) flakes were synthesized by a sol–gel method in an acidic medium, using fresh natural rose (Rosa hybrida L.) petals and triblock copolymer P123 (EO20PO70EO20) as dual templates. The resulting flakes were characterized by Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption–desorption analysis. The results reveal that the bimodal porous material is in the anatase phase, and the three-dimensionally ordered macroporous walls are composed of highly ordered mesopores. The Brunauer–Emmett–Teller (BET) surface area and the average size of mesopores are 125.91 m2 g−1 and 4.79 nm, respectively. The photocatalytic activity of the porous TiO2 flakes was evaluated by photodegrading rhodamine B (RhB) under ultraviolet (UV) light. The obtained TiO2 flakes exhibited a slightly higher photocatalytic activity than commercial photocatalyst Degussa P25.

Biomineralization-inspired synthesis of chitosan/hydroxyapatite biocomposites based on a novel bilayer rate-controlling model

In order to prepare sophisticated biomaterials using a biomimetic approach, a deeper understanding of biomineralization is needed. Of particular importance is the control and regulation of the mineralization process. In this study, a novel bilayer rate-controlling model was designed to investigate the factors potentially influencing mineralization. In the absence of a rate-controlling layer, nano-scale hydroxyapatite (HA) crystallites exhibited a spherical morphology, whereas, in the presence of a rate-controlling layer, HA crystallites were homogeneously dispersed and spindle-like in structure. The mineralization rate had a significant effect on controlling the morphology of crystals. Furthermore, in vitro tests demonstrated that the reaction layer containing spindle-like HA crystallites possessed superior biological properties. These results suggest that a slow mineralization rate is required for controlling the morphology of inorganic crystallites, and consumption by the rate-controlling layer ensured that the ammonia concentration remained low. This study demonstrates that a biomimetic approach can be used to prepare novel biomaterials containing HA crystallites that have different morphologies and biological properties.