Wei-I Hung

Nanocasting Technique to Prepare Lotus-leaf-like Superhydrophobic Electroactive Polyimide as Advanced Anticorrosive Coatings

Nanocasting technique was used to obtain a biomimetic superhydrophobic electroactive polyimide (SEPI) surface structure from a natural Xanthosoma sagittifolium leaf. An electroactive polyimide (EPI) was first synthesized through thermal imidization. An impression of the superhydrophobic Xanthosoma sagittifolium leaf was then nanocasted onto the surface of the EPI so that the resulting EPI was superhydrophobic and would prevent corrosion. Polydimethylsiloxane (PDMS) was then used as a negative template to transfer the impression of the superhydrophobic surface of the biomimetic EPI onto a cold-rolled steel (CRS) electrode. The superhydrophobic electroactive material could be used as advanced coatings that protect metals against corrosion. The morphology of the surface of the as-synthesized SEPI coating was investigated using scanning electron microscopy (SEM). The surface showed numerous micromastoids, each decorated with many nanowrinkles. The water contact angle (CA) for the SEPI coating was 155°, which was significantly larger than that for the EPI coating (i.e., CA = 87°). The significant increase in the contact angle indicated that the biomimetic morphology effectively repelled water. Potentiodynamic and electrochemical impedance spectroscopic measurements indicated that the SEPI coating offered better protection against corrosion than the EPI coating did.

3D-bioprinting approach to fabricate superhydrophobic epoxy/organophilic clay as an advanced anticorrosive coating with the synergistic effect of superhydrophobicity and gas barrier properties†

Correction for ‘3D-bioprinting approach to fabricate superhydrophobic epoxy/organophilic clay as an advanced anticorrosive coating with the synergistic effect of superhydrophobicity and gas barrier properties’ by Chi-Hao Chang et al., J. Mater. Chem. A, 2013, 1, 13869–13877.

Biocompatibility Study of Gold Nanoparticles to Human Cells

Gold nanoparticle (GNP) is one of the most stable and popular nanoparticles, which receives considerable attention due to their applications in biomedical imaging and diagnostic tests. However, its cytotoxicity has not been fully investigated. Here we report the effects on biocompatibility of water-soluble GNPs with different sizes and concentrations to human bone marrow mesenchymal stem cells (hBMSCs) and human hepatoma carcinoma cells (HuH-7). Cytotoxicity was analyzed at different time points using MTT assay after coculturing with different concentrations of GNPs. Both cells incubated with 71.1 µg/mL 15- and 30-nm GNPs exhibited more than 80 % cell survival. However, cell viability decreased to less than 60% after incubated with 31.6 µg/mL 5-nm GNPs for 5 days. GNP 15 nm in size was chosen for the following experiments. According to Annexin V and propidium iodide (PI) analysis, the percentage of necrotic cells increased gradually with the concentration of GNPs increased. Approximately 1.5 fold increase in the level of reactive oxygen species (ROS) was found, suggesting that necrosis might be triggered by ROS production after GNPs were endocytosed by cells. Alkaline phosphatase activity and calcium deposition of hBMSCs during osteogenic differentiation were inhibited slightly by coculturing with GNPs. A similar observation was made in adipogenic hBMSCs, in which the accumulation of triacylglycerides was repressed by the addition of GNPs. In conclusion, despite 15- and 30-nm GNPs had little toxicity to hBMSCs and HuH-7 cells, they still had some influence on both osteogenic and adipogenic capabilities of hBMSCs.

Synthesis of electroactive mesoporous gold–organosilica nanocomposite materials via a sol–gel process with non-surfactant templates and the electroanalysis of ascorbic acid

Electroactive mesoporous organosilica nanocomposites (EMONs) and electroactive mesoporous gold-organosilica nanocomposites (EMGONs) were successfully prepared in this work and were applied in ascorbic acid (AA) sensing. EMONs were synthesized by using an aniline pentamer (AP) as an electroactive segment which controlled the redox ability and influenced the degree of sensitivity of the nanocomposites towards AA. EMGONs were successfully prepared by a one-pot synthesis in HAuCl4 aqueous solution with different concentrations. Gold nanoparticles (AuNPs) were selectively reduced on an AP segment in an EMON matrix, which acted as a reductant as well as providing a large surface area to absorb and react with chloroaurate anions (AuCl4 -). The gold particle size can be controlled by varying the concentration of HAuCl4 (aq.), and distributed AuNPs with controllable size were fabricated for the EMGONs. A sensor constructed from an EMGON-modified carbon-paste electrode (CPE) demonstrated 21-fold and 6.3-fold higher electrocatalytic activity towards the oxidation of AA compared to those constructed using a bare CPE and EMON-modified CPE, respectively. The high surface area of the EMGON-modified CPE exhibited a good electrochemical response towards AA at a low oxidative potential with good stability and sensitivity and a wide linear analytical detection range.

Synthesis and electroactive properties of poly(amidoamine) dendrimers with an aniline pentamer shell

Poly(amidoamine) (PAMAM) dendrimers with different generations (G = 2, 3 and 4) were synthesized, peripherally modified with aniline pentamers and studied for their redox and dopable behavior under different pH conditions. It was found that the electron transition of the πB–πQ band red-shifted and the size of PAMAM G2 decreased in an alkaline medium. The chemical oxidation process and the color change of these modified dendritic macromolecules were measured by cyclic voltammetry (CV) and electrochromism. All of the dendrimers showed three redox peaks in the CV. The current density of the voltammograms increased with increasing the number of aniline pentamer segments at the periphery. A drastic color change was observed when a linear potential sweep was applied. The thermal properties of the electroactive dendrimers were evaluated by differential scanning calorimetry and thermogravimetric analysis.

CYTOTOXICITY AND DIFFERENTIATION EFFECTS OF GOLD NANOPARTICLES TO HUMAN BONE MARROW MESENCHYMAL STEM CELLS

Gold nanoparticles (GNPs) are widely used in chemical sensing, drug delivery, biomedical imaging, and photothermal therapy due to their strong and size-tunable surface plasmon resonance, fluorescence, and easy-surface functionalization. In this study, we investigated the effects of water-dispersed GNPs on the cytotoxicity and differentiation of human bone marrow mesenchymal stem cells (hBMSCs) and the associated death pathway. The results showed that the viability of hBMSCs was dependent upon the size of GNPs. Further, GNPs at the smallest size exhibited the highest cytotoxicity after treatment for 5 days and also substantially suppressed the number of colony-forming unit-fibroblast (CFU-F) of hBMSCs after continuous exposure for 21 days. Although large and medium sizes of GNPs had minor cytotoxicity to the cells, the sizes of CFU-F formed in the groups treated with GNPs at medium and large sizes were smaller compared to the control group. Further study of the cell death pathway using GNPs at medium size found that GNPs triggered hBMSCs necrosis, possibly by oxidative stress after GNPs were endocytosed. In addition, GNPs exerted the inhibitory effects on induced osteogenesis and adipogenesis of hBMSCs. Alkaline phosphatase (ALP) activity and calcium mineralization during osteogenic induction as well as the accumulation of triacylglycerides in adipogenic hBMSCs were repressed significantly by coculturing with GNPs at medium size. Our results suggest that the application of GNPs as long-term tracers for the activities of mesenchymal stem cells (MSCs) should be carefully evaluated.

Self-Assembly Behavior of Amphiphilic Poly(amidoamine) Dendrimers with a Shell of Aniline Pentamer

A series of amphiphilic poly(amidoamine) dendrimers (PAMAM, G2-G5) composed of a hydrophilic core and a hydrophobic shell of aniline pentamer (AP) were synthesized and characterized. The modified dendrimers self-assembled to vesicular aggregates in water with the critical aggregation concentration (CAC) decreased in the order of G2 > G3 > G4 > G5. It was found that the modified dendrimers self-organized into spherical aggregates with a bilayer vesicular structures and that the dendrimers in higher generation have more order structure, which may be attributed to the crystallization induced by the compacted effect of AP segments. In addition, larger spherical vesicles were observed under acidic and alkaline conditions, as compared with sizes of aggregates in neutral medium. At low pH, the tertiary amine groups of PAMAM-AP were transformed to ammonium salts; the polarons were formed from AP units by doping with strong acids, thereby leading to the stability of vesicular aggregates being better than that in double distilled water. Nevertheless, in high pH environment, the deprotonation of PAMAM-AP caused the enhancement of π-π interactions, resulting in generation of twins or multilayered vesicles.

In situ gelation of PEG-PLGA-PEG hydrogels containing high loading of hydroxyapatite: in vitro and in vivo characteristics

Thermosensitive hydrogels are renowned carriers that are used to deliver a variety of drugs with the aim of combating diseases. In this study, the injectability of thermosensitive hydrogels comprised of poly(ethylene glycol)-poly(lactic acid-co-glycolic acid)-poly(ethylene glycol) (PEG-PLGA-PEG, PELGE) and hydroxyapatite (HA) were examined for their ability to deliver bone morphological protein 2 (BMP-2). The physicochemical characteristics of PELGE, HA, and PELGE/HA hydrogel composites were investigated by (1)H NMR, GPC, FTIR, XRD, SEM, and TEM. The rheological properties, injectability, in vitro degradation, and in vivo biocompatibility were investigated. The hydrogel with a weight ratio of 4:6 of polymer to HA was found to be resistant to auto-catalyzed degradation of acidic monomers (LA, GA) for a period of 70 days owing to the presence of alkaline HA. Injectability was quantitatively determined by the ejected weight of the hydrogel composite at room temperature and was a close match to the weight amount predetermined by the syringe pump. The results not only revealed that the PELGE/HA hydrogel composite presented a minor tissue response in the subcutis of ICR mice at eight weeks, but they also indicated an acceptable tolerance of the hydrogel composite in animals. Thus, PELGE/HA hydrogel composite is expected to be a promising injectable orthopedic substitute because of its desirable thermosensitivity and injectability.

Advanced Anticorrosive Coatings Prepared from Polymer-Clay Nanocomposite Materials

Corrosion control is an important subject of increasing interest to the modern metallic finishing industry. Surface modification of metallic substrates by organic or polymeric coatings is an essential approach for enhancing surface properties such as wear, oxidation, and corrosion. Various conventional techniques are utilized to depositing the desired materials onto the metallic substrate to achieve surface modifications with better protection for the substrate. Organic or polymeric coatings on metallic substrates provide an effective barrier between the metal and its environment and/or inhibit corrosion through the presence of chemicals. Chromium-containing compounds (CC) have generally been used as effective anticorrosive coatings in the past decades. However, due to the environmental and health concerns, CCs may need to be replaced by alternative materials that would not pose biological and ecological hazards. Thus, research has focused on the development of novel polymeric coating materials that contain effective anticorrosive agents. During the early stage of corrosion protection engineering, various neat organic or polymeric coatings were developed. These coatings generally function as a physical barrier against aggressive species such as O2 and H+ that cause decomposition. Examples of representative polymers are include epoxy resins [MacQueen & Granata, 1996; Dang et al., 2002], polyurethanes [Moijca et al., 2001], and polyesters [Malshe & Sangaj, 2006; Deflorian et al., 1996]. Moreover, conjugated polymers such as polyaniline [Wessling & Posdorfer, 1999; Tan & Blackwood, 2003], polypyrrole [Iroh & Su, 2000, Krstajic et al., 1997], and polythiophene [Kousik et al., 2001], have also been employed as advanced anticorrosive coatings due to their redox catalytic properties, forming metal oxide passivation layers on metallic substrates. Conversely, not all neat polymeric coatings are permanently impenetrable because small defects in the coatings can lead to gateways that allow corrosive species to attack the metallic substrate; thus, localized corrosion can occur. As a second line of defense against corrosion, various nanoscale inorganic additives have been incorporated into various polymer matrices to generate a series of organic–inorganic hybrid anticorrosive coatings. Recently, montmorrillonite (MMT)–layered silicate (clay) has attracted intensive research interest for the preparation of polymer–clay nanocomposites (PCNs) because its lamellar elements display high in–plane strength, stiffness, and high aspect ratios. Typically, the chemical structures of MMT consist of two fused silica tetrahedral sheets that sandwich an

Preparation and thermal properties of UV-curable polyacrylate–gold nanocomposite foams

In this study, we prepare UV-curable polyacrylate–gold nanocomposites (PGNs) for the first time and analyze their thermal properties. The microemulsion architectures of these PGNs contain gold nanoparticles (GNPs) whose surface is modified with carboxyl groups; furthermore, 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) monomers are first chemisorbed onto the surface of the GNPs and then photopolymerized to form a shell. The effects of the dispersion characteristics of GNPs in a PGN matrix were analyzed by transmission electron microscopy (TEM). PGN foams (FPGNs) can be obtained by subjecting the as-prepared bulk PGN materials to physical batch foaming processes, where nitrogen is used as a blowing agent. The cellular structures of the prepared FPGNs were investigated by scanning electron microscopy (SEM). FPGNs containing 15 nm GNPs (herein, denoted by FPGN-15) were found to exhibit a smaller cell size and a higher cell density than FPGNs containing 25 nm GNPs (herein, denoted by FPGN-25). FPGN materials exhibit an apparent increase in thermal stability (including decomposition temperature (Td)) as well as a decrease in the thermal transport properties (including thermal conductivity (k) and thermal diffusivity (α)) as compared to their corresponding bulk PGN materials. Moreover, results of the measurements of the compression modulus showed that the mechanical strength of FPGN-15 and FPGN-25 increased by 72% and 57%, respectively, as compared to that of neat polyacrylate foam.