CeO2-Supported TiO2-Pt Nanorod Composites as Efficient Catalysts for CO Oxidation.

Supported Pt-based catalysts have been identified as highly selective catalysts for CO oxidation, but their potential for applications has been hampered by the high cost and scarcity of Pt metals as well as aggregation problems at relatively high temperatures. In this work, nanorod structured (TiO2-Pt)/CeO2 catalysts with the addition of 0.3 at% Pt and different atomic ratios of Ti were prepared through a combined dealloying and calcination method. XRD, XPS, SEM, TEM, and STEM measurements were used to confirm the phase composition, surface morphology, and structure of synthesized samples. After calcination treatment, Pt nanoparticles were semi-inlayed on the surface of the CeO2 nanorod, and TiO2 was highly dispersed into the catalyst system, resulting in the formation of (TiO2-Pt)/CeO2 with high specific surface area and large pore volume. The unique structure can provide more reaction path and active sites for catalytic CO oxidation, thus contributing to the generation of catalysts with high catalytic activity. The outstanding catalytic performance is ascribed to the stable structure and proper TiO2 doping as well as the combined effect of Pt, TiO2, and CeO2. The research results are of importance for further development of high catalytic performance nanoporous catalytic materials.

Effect of Electrospinning Network Instead of Polymer Network on the Properties of PDLCs.

In this study, polymer-dispersed liquid crystal (PDLC) membranes were prepared by combining prepolymer, liquid crystal, and nanofiber mesh membranes under UV irradiation. EM, POM, and electro-optic curves were then used to examine the modified polymer network structure and the electro-optical properties of these samples. As a result, the PDLCs with a specific amount of reticular nanofiber films had considerably improved electro-optical characteristics and antiaging capabilities. The advancement of PDLC incorporated with reticulated nanofiber films, which exhibited a faster response time and superior electro-optical properties, would greatly enhance the technological application prospects of PDLC-based smart windows, displays, power storage, and flexible gadgets.

Fluorescent Dye-Doped Brightening Polymer-Stabilized Bistable Cholesteric Liquid Crystal Films.

Brightening polymer-stabilized bistable cholesteric liquid crystal (PSBCLC) films with doped fluorescent dyes were prepared using the polymerization-induced phase separation (PIPS) method. The transmittance performance behavior of these films in both states (focal conic and planar) and absorbance change in multiple dye concentrations were studied using a UV/VIS/NIR spectrophotometer. The change occurring in dye dispersion morphology with different concentrations was obtained by means of the polarizing optical microscope. The maximum fluorescence intensity of different dye-doped PSBCLC films was measured using a fluorescence spectrophotometer. Moreover, the contrast ratios and driving voltages of these films were calculated and recorded to demonstrate film performance. Finally, the optimal concentration of dye-doped PSBCLC films with a high contrast ratio and a relatively low drive voltage was found. This is expected to have great potential applications in cholesteric liquid crystal reflective displays.

Acridone-Based Host Materials for Green Phosphorescent and Thermally Activated Delayed Fluorescent OLEDs with Low-Efficiency Roll-Offs.

By linking the carbazole unit to the nitrogen atom of acridone through phenyl or pyridyl, two compounds, named 10-(4-(9H-carbazol-9-yl)phenyl)acridin-9(10H)-one (AC-Ph-Cz) and 10-(5-(9H-carbazol-9-yl)pyridin-2-yl)acridin-9(10H)-one (AC-Py-Cz) were designed and synthesized. These two materials, characterized with highly twisted and rigid structure, good thermal stability, and balanced carrier-transporting properties, were employed as host materials for green phosphorescent and thermally activated delayed fluorescent organic light-emitting diodes (OLEDs). The carbazole group, despite its small contribution to the highest occupied molecular orbitals (HOMOs) of these two materials, plays an essential role as an intramolecular host in energy delivering and improving the hole transporting ability of these two hosts. The incorporation of the electron-deficient pyridyl group as a linking group slightly improves the electron transporting capability of AC-Py-Cz. The green phosphorescent OLED (PhOLED) based on AC-Py-Cz exhibited excellent device performance with a turn-on voltage of 2.5 V, a maximum power efficiency and an external quantum efficiency (ηext ) of 89.8 lm W-1 and 25.2 %, respectively, benefitting from the better charge-balancing ability of AC-Py-Cz host due to the presence of the pyridyl bridge. More importantly, all the devices based on these two hosts showed low efficiency roll-off at high brightness due to the suppressed non-radiative transition in the emitting layer. In particular, the AC-Py-Cz-hosted green PhOLED exhibited an efficiency roll-off of 1.6 % from the maximum next at a high brightness of 1000 cd m-2 and a roll-off of 15.9 % at an extremely high brightness of 10000 cd m-2 . This study manifests that acridone-based host materials have great potential in fabricating OLEDs with low efficiency roll-off.

Optical Properties of New Third-Order Nonlinear Materials Modified by Click Chemistry.

A high-yielding click reaction was used to synthesize a series of highly conjugated, symmetrical, as well as asymmetrical compounds with a benzene core. Cyclic voltammetry and ultraviolet/visible absorption spectroscopy were carried out, and proved that the side groups of the benzene derivatives played an important role in the energy gaps, and affected the third-order non-linear optical response. The maximum absorption wavelength of the series of benzene derivatives showed an obvious red-shift. Moreover, the addition of resilient electron-withdrawing groups significantly narrowed the energy levels as compared with precursors. The third-order nonlinear properties of this benzene derivative were tested by the Z-scan technique. The expected properties of this series of molecules were obtained, and it was found that the series of molecules undergoes a transition from reverse saturable absorption to saturable absorption, which has certain reference significance for a nonlinear optical field.

Electro-Optical Characteristics of Polymer Dispersed Liquid Crystal Doped with MgO Nanoparticles.

In this paper, inorganic oxide MgO nanoparticles-doped polymer dispersed liquid crystal (PDLC) films were made from a mixture of the prepolymer, SLC1717 liquid crystal, and MgO nanoparticles by the polymerization induced phase separation (PIPS) process. To observe the effect of MgO concentration, PDLC was dispersed with 0.2, 0.4, 0.6, and 0.8 wt.% MgO. Electro-optical properties of the films have been investigated using LCD parameter meter and Scanning Electron Microscope (SEM) at room temperature. It is established that MgO nanoparticles affect the microstructure of PDLC films significantly because of the formed agglomerates of MgO nanoparticles. Results show an improvement in the electro-optical properties and a decrease in the driving voltage for doped systems with MgO nanoparticles. When the doping amount of MgO is 0.8 wt.%, the threshold voltage (Vth) is reduced to about 7.5 V. Therefore, MgO-doped PDLC is expected to become an excellent choice in the field of energy-saving.

Photoelectric and Self-Assembly Properties of Tetrasubstituted Pyrene Discotic Derivatives.

To investigate the self-assembly behavior of π-conjugated ethynyl-pyrene discotic derivatives, a series of ethynyl-pyrene discotic materials were designed and synthesized by Sonogashira coupling reaction. The π-conjugated structures were characterized by 1H-NMR, IR spectroscopy, and elemental analysis. The optical properties of the discotic materials were examined by UV/Vis spectra and fluorescence emission spectra. The band gap of each compound was calculated by cyclic voltammetry with UV/Vis spectroscopy. Interestingly, the substituted groups in the four symmetrical positions did affect the self-assembly properties of as-resulted nano/micro structures. Under the same conditions, compounds 4a-4d could be self-assembled into different morphologies such as micro-tubes (for 4a), micro-wires (for 4b and 4c), and micro-grain crystals (for 4d). All of the results indicated that the discotic materials have the potential for optoelectronic applications.

Dealloying Synthesis of Bimetallic (Au-Pd)/CeO2 Catalysts for CO Oxidation.

The nanorod-structured (Au-Pd)/CeO2 catalysts with different Au/Pd ratios were prepared from Al-Ce-Au-Pd precursor alloys through combined dealloying and calcination treatment. XRD, SEM, TEM, XPS, Raman spectroscopy, and N2 adsorption-desorption measurements were applied to test the structure and physicochemical properties of samples. Catalytic evaluation results imply that the (Pd0.15-Au0.15)/CeO2 catalyst calcined at 500 °C possesses optimal catalytic activity for CO oxidation when compared with other catalysts with different Au/Pd ratios or (Pd0.15-Au0.15)/CeO2 calcined at other temperatures, whose 50% and 99% reaction temperature can be reached as low as 50 and 85 °C, respectively. This superior catalytic property is attributed to their robust nanorod structure and the introduction of noble bimetal Pd and Au, which can construct a nanoscale interface to access fast electron motion, thus enhancing catalytic efficiency.

The regulating effect of trace elements Si, Zn and Sr on mineralization of gelatin-hydroxyapatite electrospun fiber.

Biomineralization approaches have been increasingly adopted to synthesizing advanced materials with superior properties. Nevertheless, the potential influence of inorganic trace elements on the mineralization process of collagen has been rarely reported, despite of the significant progress achieved on exploiting the critical roles of organic polymers in regulating the collagen mineralization. To this aim, the potential roles of Si, Zn and Sr in regulating the mineralization of gelatin-hydroxyapatite (HA) composite fibers have been examined in this study. The results indicated that the incorporation of trace elements not only promoted the biomineralization of gelatin, but also led to drastic change in the mineralization behavior. In particular, the gelatin-SiHA sample showed uniform mineralization predominantly inside the fibers, with nucleation and growth directions along the c-axis of the gelatin fibers. On the contrary, the gelatin-HA sample showed nucleation outside the fibers and spherical mineral crystals on top of fibers, typical structure for heterogeneous nucleation. As the mineralization process proceeded, the gelatin-ZnHA and gelatin-SrHA samples evolved into having similar structure as the gelatin-SiHA sample, despite of showing totally different mineralization behaviors at early time. Overall, the incorporation of trace elements seemed to lower the nucleation barriers, led to a more homogeneous mineralization mode within the fiber region and formation of mineralized structures closer to those in natural bone. Moreover, mineralized samples with trace elements demonstrated improved adhesion and cytoskeleton organization of osteoblastic cells. Such finding would provide important insight for understanding the mineralization process and the optimal design of advanced biological materials.

Epigallocatechin gallate mediated sandwich-like coating for mimicking endothelium with sustained therapeutic nitric oxide generation and heparin release.

In-stent restenosis after stenting is generally characterized by an inflammatory response, excessive proliferation of smooth muscle cells, and delayed healing of the endothelium layer. In this study, inspired by catechol/gallol surface chemistry, a sandwich-like layer-by-layer (LBL) coating was developed using chitosan and heparin as polyelectrolytes, along with the embedding of an epigallocatechin gallate/copper (EGCG/Cu) complex. The embedding of EGCG stabilized the coating by various intermolecular interactions in the LBL coating (e.g., π-π stacking, weak intermolecular crosslinking, and enriched hydrogen bonding) and supported the sustained release of the cargo heparin over 90 days. This design enabled a biomimetic endothelium function in terms of the sustained release of heparin and continuous in situ generation of nitric oxide, driven by the catalytic decomposition of endogenous S-nitrostothiols by copper ions. The result showed enhanced durability of anticoagulation and suppressed inflammatory response. Moreover, the "sandwich-like" coating supported the growth of endothelial cells and up-regulated the protein expression of vascular endothelial growth factor, while effectively suppressing the proliferation and migration of smooth muscle cells (SMCs) via the up-regulation of cyclic guanosine monophosphate. Ex vivo and in vivo experiments demonstrated the effectiveness of the sandwich-like coating in preventing thrombosis formation, suppressing the growth of SMCs, reducing the infiltration and activation of inflammatory cells, and ultimately achieving rapid in situ endothelialization. Hence, the EGCG-assisted sandwich-like coating might be used as a robust and versatile surface modification strategy for implantable cardiovascular devices.

Modulating cationicity of chitosan hydrogel to prevent hypertrophic scar formation during wound healing.

It is of great clinical significance to design wound dressing materials with combined excellent wound healing properties and superior capability to suppress hypertrophic scar formation. This study aimed to examine if and how the cationicity of chitosan would affect the hypertrophic scar-related outcomes, through preparing carboxymethyl chitosan hydrogels with different genipin concentrations (2.5%, 5%, 10% and 15%, respectively). An optimum window of chitosan cationicity (5% in our case) demonstrated potential to mitigate hypertrophic scar in wound healing by suppressing the expression of a-smooth muscle actin (a-SMA) and promoting secretion of type I matrix metalloproteinases (MMP-1). In vivo, the CMCS-5% hydrogel again showed smaller, thinner and smoother wound appearance. Moreover, the CMCS-5% sample with additional incorporation of 2% (V/V) Aloe vera gel exhibited further improved performance in scar inhibition. Overall, such findings might have important implications in chitosan-based wound dressing design for high-quality wound repair and effective scar inhibition.

Green Tea Polyphenol Induced Mg2+-rich Multilayer Conversion Coating: Toward Enhanced Corrosion Resistance and Promoted in Situ Endothelialization of AZ31 for Potential Cardiovascular Applications.

As a promising biodegradable metallic material, magnesium (Mg) and its alloys have attracted special attention in the recent decade. However, challenges still remain due to its high corrosion rate and insufficient biocompatibility after implantation. In this work, we prepare a simple and versatile green tea phenol-metal induced multilayer conversion coating (Mg2+ incorporated epigallocatechin gallate (EGCG) coating) on magnesium alloys' (AZ31) substrate by layer-by-layer (LBL) method. The surface morphology results revealed that, with the incorporation of Mg2+, the as-formed EGCG/Mg coating was rich in phenol-Mg complex and presented more homogeneous and dense morphology, with far less cracks than the pure EGCG coating. The in vitro degradation rate and corrosion resistance were studied by electrochemical corrosion tests and monitoring of the changed pH value and hydrogen evolution, respectively, which revealed that the corrosion rate was effectively decreased compared to that of bare AZ31 after it was protected by EGCG/Mg coating. In vitro and ex vivo thrombogenicity test demonstrated the EGCG/Mg coatings presented an impressive improvement in decreasing the adhesion and activation of platelets and erythrocytes, in activated partial thromboplastin time (APTT), and in antithrombogenicity compared to those of bare AZ31. Owing to the mild degradation rate, in combination with the biological function of EGCG, enhanced endothelial cells' (ECs') adhesion and proliferation, suppressed smooth muscle cells' (SMCs') adhesion/proliferation, and inhibited cytokine release were observed on EGCG/Mg coated AZ31 alloy. Besides, the in vivo subcutaneous embedding experiment suggested that the EGCG/Mg coating performed more mild tissue response due to the improved corrosion resistance to the surrounding microenvironment. Moreover, for in vivo abdominal aorta assay, the EGCG/Mg coated AZ31 wire presented better corrosion resistance and enhanced re-endothelialization compared to bare AZ31 wire. These results suggested the potential of using green tea polyphenol induced Mg2+-rich multilayer conversion coating for enhanced corrosion protection and desired biocompatibility of biodegradable cardiovascular implants.

Effect of zinc substitution in hydroxyapatite coating on osteoblast and osteoclast differentiation under osteoblast/osteoclast co-culture.

Zinc is an essential trace element required for bone remodelling process, but its role in such process remains to be elucidated. In particular, inconsistent results have been reported on the effect of Zn on osteoclastic responses, and supplement of receptor activator of nuclear factor kappa-B ligand (RANKL) factors has been commonly adopted. Co-culture is a suitable approach to elucidating the role of Zn in bone remodelling process, by better imitating the cellular environment as the presence of osteoblasts plays critical role in modulating osteoclastic functions. In this study, zinc-substituted HA coatings have been deposited using a liquid precursor plasma spraying process at two different concentrations (1, 2 wt.%). The effect of zinc substitution on osteoblastic and osteoclastic differentiation has been studied in vitro. In particular, a cultivation regime was designed to first induce osteoblastic differentiation of rat bone marrow stromal cells (BMSCs) for 14 days, and then induce osteoclastic differentiation of osteoclast-like precursor RAW 264.7 cells through the aid of the osteoblasts formed for additional 14 days, in the absence of the external addition of RANKL. The results showed that Zn substitution moderately promoted the BMSC differentiation into the osteoblasts and reduced the osteoclastic activity in early time (1 day co-culture). However, promotion of the osteoclastic activity were observed at later stages, as indicated by the significantly enhanced expressions of trap5b and IL-1 (8- and 15-day co-culture) and moderate stimulation of the nucleus integration and formation of the multinucleated cells (14-day co-culture). Such stimulating effect of the osteoclastic activity was absent under mono-culture of RAW 264.7 cell, with simple RANKL supplementation. The results suggest that both the zinc and the presence of MSC/osteoblast play profound and highly interacted roles on osteoclast differentiation and activity, which is critical in modulating the bone remodelling process.

Modulation of osteogenic and haemostatic activities by tuning cationicity of genipin-crosslinked chitosan hydrogels.

Chitosan as a natural cationic polysaccharide has drawn wide interests as surface modification materials in orthopedic applications, with the potential to achieve combined osteogenic, antimicrobial and haemostatic functions. The cationicity of chitosan has been reported to play an important role in modifying the osteoblastic cell responses and the antibacterial activities, while its effect on the haemostatic properties has been rarely studied. To this aim, we prepared carboxymethyl chitosan hydrogels with different cationicity through crosslinking with different concentrations of genipin (1%, 2.5%, 5% and 10%). The genipin concentration strongly influenced both mesenchymal stem cell (MSC) responses and blood coagulation activity for chitosan-hydroxyapatite samples. Increasing genipin concentration overall enhanced the osteogenic and haemostatic potentials, and an optimum window of chitosan cationicity (5% genipin in our case) led to both the best MSC response and coagulant activities. In particular, the cationicity had demonstrated a profound modulation effect on the haemostatic activities of chitosan samples, through influencing three different aspects of the coagulation processes, including intrinsic coagulation pathway, aggregation and activation of platelet, and activation of erythrocyte. Tuning the crosslinking degree thus provides a simple and effective approach to achieving combined osteogenic and haemostatic functions, which has great potential in surface modification of surgical implants.

Directing the osteoblastic and chondrocytic differentiations of mesenchymal stem cells: matrix vs. induction media.

While both induction culture media and matrix have been reported to regulate the stem cell fate, little is known about which factor plays a more decisive role in directing the MSC differentiation lineage as well as the underlying mechanisms. To this aim, we seeded MSCs on HA-collagen and HA-synthetic hydrogel matrixes, which had demonstrated highly different potentials toward osteoblastic and chondrocytic differentiation lineages, respectively, and cultured them with osteogenic, chondrogenic and normal culture media, respectively. A systematic comparison has been carried out on the effects of induction media and matrix on MSC adhesion, cytoskeleton organization, proliferation, and in particular differentiation into the osteoblastic and chondrocytic lineages. The results demonstrated that the matrix selection had a much more profound effect on directing the differentiation lineage than the induction media did. The strong modulation effect on the transcription activities might be the critical factor contributing to the above observations in our study, where canonical Wnt-ß-Catenin signal pathway was directly involved in the matrix-driven osteoblastic differentiation. Such findings not only provide a critical insight on natural cellular events leading to the osteoblastic and chondrocytic differentiations, but also have important implications in biomaterial design for tissue engineering applications.

Electrospun PCL/Gelatin composite fibrous scaffolds: mechanical properties and cellular responses.

Electrospinning of hybrid polymer has gained widespread interest by taking advantages of the biological property of the natural polymer and the mechanical property of the synthetic polymer. However, the effect of the blend ratio on the above two properties has been less reported despite the importance to balance these two properties in various tissue engineering applications. To this aim, we investigated the electrospun PCL/Gelatin composite fibrous scaffolds with different blend ratios of 4:1, 2:1, 1:1, 1:2, 1:4, respectively. The morphology of the electrospun samples was observed by SEM and the result showed that the fiber diameter distribution became more uniform with the increase of the gelatin content. The mechanical testing results indicated that the 2:1 PCL/Gelatin sample had both the highest tensile strength of 3.7 MPa and the highest elongation rate of about 90%. Surprisingly, the 2:1 PCL/Gelatin sample also showed the best mesenchymal stem cell responses in terms of attachment, spreading, and cytoskeleton organization. Such correlation might be partly due to the fact that the enhanced mechanical property, an integral part of the physical microenvironment, likely played an important role in regulating the cellular functions. Overall, our results indicated that the PCL/Gelatin sample with the blend ratio of 2:1 was a superior candidate for scaffolds for tissue engineering applications.

The essential role of inorganic substrate in the migration and osteoblastic differentiation of mesenchymal stem cells.

The physical environment, which is an integral part of the stem cell niche, is critical in regulating stem cell functions and differentiation into specific lineages. Previous studies have primarily focused on modulating the polymeric matrixes, including the extracellular matrix. Here, we report that the presence of the inorganic substrate (Ti and hydroxyapatite (HA)) in addition to the collagen overlayer plays an essential role in cytoskeletal organization, migration and differentiation of mesenchymal stem cells (MSCs). The osteogenic differentiation of MSCs was suppressed on pure collagen substrate alone, despite collagen greatly enhancing the MSC adhesion and proliferation. The results indicated a strong correlation between MSC motility and osteoblastic differentiation. In particular, the presence of the inorganic matrix promoted the activation of the canonical WNT-ß-Catenin pathway and stimulated transcription, leading to osteoblastic differentiation, which was likely due to the internal forces generated "dynamically" during cell migration. Compared to the Ti substrate, hydroxyapatite promoted the collagen self-assembly and the formation of the collagen fibrous network, which is critical for MSC motility and osteogenic differentiation. The HA-collagen matrix exhibited the most favourable stress fibre formation, the longest migration distance (2.8-fold higher than that of the pure collagen sample and 1.9-fold higher than that of Ti-collagen), and the best osteogenic differentiation activities. These findings might have important implications for our understanding of the fundamental MSC functions and the optimal design of bone regeneration materials.

Modulation of cationicity of chitosan for tuning mesenchymal stem cell adhesion, proliferation, and differentiation.

The aim of this study was to modulate the cationicity of chitosan to influence the mesenchymal stem cell (MSC) responses in terms of cell adhesion, proliferation, and differentiation. The authors prepared water-soluble carboxymethyl chitosan hydrogels using genipin as the crosslinking agent. The chitosan cationicity was modulated by varying the genipin content from 0.5 to 10 wt. %. The results indicated that the cationicity exerted a striking modulation effect on various MSC responses. The increase of the genipin content, i.e., decrease of the free amino group content (cationicity), overall promoted the MSC adhesion, cytoskeleton organization, proliferation, and differentiation into the osteogenic lineage. A surprising cell alignment effect was also observed on chitosan samples with high genipin concentrations (>2.5%). The chitosan sample with the highest genipin concentrations (10%) exhibited the best MSC proliferation and highest protein expression levels toward osteogenic lineages. The genipin content also showed a strong modulation effect on MSC condensation, and cell-cell and cell-matrix interactions, as suggested by the expressions of the sry related HMG box9 (Sox9), intercellular adhesion molecule 1, and N-Cadherin. Overall, the authors have demonstrated that modulation of cationicity (amino content) of chitosan is an effective and simple approach to tuning various MSC responses, including adhesion, proliferation, differentiation, as well as cell-cell interactions. Such findings might have important implications in biomaterial design for various biomedical applications.