Sie Chin Tjong

Recent development in liquid-phase processing of single-walled carbon nanotubes (SWNTs) has revealed rod-coating as a promising approach for large-scale production of SWNT-based transparent conductors. Of great importance in the ink formulation is the stabilizer having excellent dispersion stability, environmental friendly and tunable rheology in the liquid state, and also can be readily removed to enhance electrical conductivity and mechanical stability. Herein we demonstrate the promise of graphene oxide (GO) as a synergistic stabilizer for SWNTs in water. SWNTs dispersed in GO is formulated into inks with homogeneous nanotube distribution, good wetting and rheological properties, and compatible with industrial rod coating practice. Microwave treatment of rod-coated films can reduce GOs and enhance electro-optical performance. The resultant films offer a sheet resistance of ~80 Ω/sq at 86% transparency, along with good mechanical flexibility. Doping the films with nitric acid can further decrease the sheet resistance to ~25 Ω/sq. Comparing with the films fabricated from typical surfactant-based SWNT inks, our films offer superior adhesion as assessed by the Scotch tape test. This study provides new insight into the selection of suitable stabilizers for functional SWNT inks with strong potential for printed electronics.

Antibacterial nanomaterials have attracted great interest in recent years, especially with an increase in antibiotic resistance of microbial organisms. However, deleterious properties such as aggregation, toxicity of nanoparticles, and low stability limit their practical application. In this respect, we have developed novel PLA-based fibrous mats with GO-Ag hybrid nanofillers through electrospinning for minimizing bacterial attachment and growth for biomedical applications. Polylactic acid (PLA) exhibits low tensile modulus and strength as well as no bactericidal ability. To enhance its tensile and bactericidal performances, 1 wt % graphene oxide (GO), and 1–7 wt % silver nanoparticle (AgNP) are incorporated into the PLA matrix. For comparison, electrospun PLA-1 wt % GO and PLA-AgNP nanocomposites have also been prepared. The morphological, mechanical and thermal properties as well as bactericidal activities of electrospun PLA-based nanocomposite fibrous mats have been investigated. Tensile tests show that the addition of 1 wt % GO or 1–7 wt % AgNPs to PLA leads to a drastic increase in its elastic modulus. Further enhancements in tensile modulus and strength of PLA can be obtained by adding GO-AgNP nanohybrids. The thermal stability of PLA is greatly improved by adding GO-AgNP nanohybrids. Agar disk diffusion test results indicate that the PLA-1 wt %GO nanocomposite has no inhibition zones against Esherichia coli (E. coli) and Staphylococcus aureus (S. aureus). However, GO nanofillers with lateral width of micrometer range act as effective anchoring sites for AgNPs. Thus, PLA-1 wt %GO-(1–7) wt % Ag hybrid fibrous mats exhibit excellent antibacterial effect against E. coli, while the PLA-1 wt %GO-Ag mats with higher AgNP loadings show bacterial inhibition toward S. aureus. The bactericidal effects of PLA-1 wt %GO-(1–7)%Ag hybrids are studied and analyzed using live/dead fluorescent imaging assay, quantitative antibacterial efficacy test, SEM examination and residual oxygen species measurement. Our work highlights the development of electrospun nanocomposite mats as promising antibacterial materials for biomedical applications and systematically depicts the bactericidal mechanism of PLA-GO-Ag nanocomposites.

Polyetheretherketone (PEEK) hybrid composites reinforced with inorganic nanohydroxyapatite (nHA) and multiwalled carbon nanotube (MWNT) were prepared by melt-compounding and injection molding processes. The additions of nHA and MWNT to PEEK were aimed to increase its elastic modulus, tensile strength, and biocompatibility, rendering the hybrids suitable for load-bearing implant applications. The structural behavior, mechanical property, wettability, osteoblastic cell adhesion, proliferation, differentiation, and mineralization of the PEEK/nHA-MWNT hybrids were studied. X-ray diffraction and SEM observation showed that both nHA and MWNT fillers are incorporated into the polymer matrix of PEEK-based hybrids. Tensile tests indicated that the elastic modulus of PEEK can be increased from 3.87 to 7.13 GPa by adding 15 vol % nHA and 1.88 vol % MWNT fillers. The tensile strength and elongation at break of the PEEK/(15% nHA)-(1.88% MWNT) hybrid were 64.48 MPa and 1.74%, respectively. Thus the tensile properties of this hybrid were superior to those of human cortical bones. Water contact angle measurements revealed that the PEEK/(15% nHA)-(1.88% MWNT) hybrid is hydrophilic due to the presence of nHA. Accordingly, hydrophilic PEEK/(15% nHA)-(1.88% MWNT) hybrid promoted the adhesion, proliferation, differentiation, and mineralization of murine MC3T3-E1 osteoblasts on its surface effectively on the basis of cell culture, fluorescence microscopy, MTT assay, WST-1 assay, alkaline phosphatase activity, and Alizarin red staining tests. Thus the PEEK/(15% nHA)-(1.88% MWNT) hybrid has the potential to be used for fabricating load-bearing bone implants.

We report that silver-decorated reduced graphene oxide (Ag–rGO) hybrid sheets are excellent building blocks for transparent conductive films (TCFs). Unlike rGO films that exhibit large sheet resistances, Ag–rGO films are much more conductive. By tuning the silver content, Ag–rGO film can achieve a sheet resistance as low as 56 Ω sq⁻¹ at ∼80% transparency, which is at least two orders of magnitude lower than that of rGO films. A significant increase in conductivity can be qualitatively explained by heavy electron doping of individual rGO sheets and “percolation” doping of the entire rGO film by silver nanoparticles (AgNPs). Analysis of the electro-optical performance indicates that the hybrid film is even far superior to single-walled carbon nanotube networks. In addition to their highly conductive nature, Ag–rGO hybrid films are flexible and environmentally stable, making them attractive for flexible device applications under severe conditions. Further optimization in the synthesis and fabrication schemes may lead to better TCFs with performances comparable to indium-doped tin oxide.

Graphene oxide (GO) and a nanohydroxyapatite rod (nHA) of good biocompatibility were incorporated into polylactic acid (PLA) through electrospinning to form nanocomposite fiber scaffolds for bone tissue engineering applications. The preparation, morphological, mechanical and thermal properties, as well as biocompatibility of electrospun PLA scaffolds reinforced with GO and/or nHA were investigated. Electron microscopic examination and image analysis showed that GO and nHA nanofillers refine the diameter of electrospun PLA fibers. Differential scanning calorimetric tests showed that nHA facilitates the crystallization process of PLA, thereby acting as a nucleating site for the PLA molecules. Tensile test results indicated that the tensile strength and elastic modulus of the electrospun PLA mat can be increased by adding 15 wt % nHA. The hybrid nanocomposite scaffold with 15 wt % nHA and 1 wt % GO fillers exhibited higher tensile strength amongst the specimens investigated. Furthermore, nHA and GO nanofillers enhanced the water uptake of PLA. Cell cultivation, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and alkaline phosphatase tests demonstrated that all of the nanocomposite scaffolds exhibit higher biocompatibility than the pure PLA mat, particularly for the scaffold with 15 wt % nHA and 1 wt % GO. Therefore, the novel electrospun PLA nanocomposite scaffold with 15 wt % nHA and 1 wt % GO possessing a high tensile strength and modulus, as well as excellent cell proliferation is a potential biomaterial for bone tissue engineering applications.