Mary B. Chan-Park

3D Graphene–Cobalt Oxide Electrode for High-Performance Supercapacitor and Enzymeless Glucose Detection

Using a simple hydrothermal procedure, cobalt oxide (Co(3)O(4)) nanowires were in situ synthesized on three-dimensional (3D) graphene foam grown by chemical vapor deposition. The structure and morphology of the resulting 3D graphene/Co(3)O(4) composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The 3D graphene/Co(3)O(4) composite was used as the monolithic free-standing electrode for supercapacitor application and for enzymeless electrochemical detection of glucose. We demonstrate that it is capable of delivering high specific capacitance of ∼1100 F g(-1) at a current density of 10 A g(-1) with excellent cycling stability, and it can detect glucose with a ultrahigh sensitivity of 3.39 mA mM(-1) cm(-2) and a remarkable lower detection limit of <25 nM (S/N = 8.5).

Single-crystalline NiCo2O4 nanoneedle arrays grown on conductive substrates as binder-free electrodes for high-performance supercapacitors

In this work, we have successfully grown single-crystalline nanoneedle arrays of NiCo2O4 on conductive substrates such as Ni foam and Ti foil through a simple solution method together with a post-annealing treatment. Remarkably, the NiCo2O4–Ni foam binder-free electrode exhibits greatly improved electrochemical performance with very high capacitance and excellent cycling stability.

Macroporous and Monolithic Anode Based on Polyaniline Hybridized Three-Dimensional Graphene for High-Performance Microbial Fuel Cells

Microbial fuel cell (MFC) is of great interest as a promising green energy source to harvest electricity from various organic matters. However, low bacterial loading capacity and low extracellular electron transfer efficiency between the bacteria and the anode often limit the practical applications of MFC. In this work, a macroporous and monolithic MFC anode based on polyaniline hybridized three-dimensional (3D) graphene is demonstrated. It outperforms the planar carbon electrode because of its abilities to three-dimensionally interface with bacterial biofilm, facilitate electron transfer, and provide multiplexed and highly conductive pathways. This study adds a new dimension to the MFC anode design as well as to the emerging graphene applications.

Superhydrophobic and superoleophilic hybrid foam of graphene and carbon nanotube for selective removal of oils or organic solvents from the surface of water

A monolithic 3D hybrid of graphene and carbon nanotube was synthesized by two-step chemical vapor deposition. Owing to its superhydrophobic and superoleophilic properties, it can selectively remove oils and organic solvents from water with high absorption capacity and good recyclability.

Hydrogel based on interpenetrating polymer networks of dextran and gelatin for vascular tissue engineering

Hydrogel networks are highly desirable as three-dimensional (3-D) tissue engineering scaffolds for cell encapsulation due to the high water content and ability to mimick the native extracellular matrix. However, their application is limited by their nanometer-scale mesh size, which restricts the spreading and proliferation of encapsulated cells, and their poor mechanical properties. This study seeks to address both limitations through application of a novel cell-encapsulating hydrogel family based on the interpenetrating polymer network (IPN) of gelatin and dextran bifunctionalized with methacrylate (MA) and aldehyde (AD) (Dex-MA-AD). The chemical structure of the synthesized Dex-MA-AD was verified by (1)H-NMR and the degrees of substitution of MA and AD were found to be 14 and 13.9+/-1.3 respectively. The water contents in all these hydrogels were approximately 80%. Addition of 40 mg/ml to 60 mg/ml gelatin to neat Dex-MA-AD increased the compressive modulus from 15.4+/-3.0 kPa to around 51.9+/-0.1 kPa (about 3.4-fold). Further, our IPN hydrogels have higher dynamic storage moduli (i.e. on the order of 10(4)Pa) than polyethylene glycol-based hydrogels (around 10(2)-10(3)Pa) commonly used for smooth muscle cells (SMCs) encapsulation. Our dextran-based IPN hydrogels not only supported endothelial cells (ECs) adhesion and spreading on the surface, but also allowed encapsulated SMCs to proliferate and spread in the bulk interior of the hydrogel. These IPN hydrogels appear promising as 3-D scaffolds for vascular tissue engineering.

Synthesis of graphene–carbon nanotube hybrid foam and its use as a novel three-dimensional electrode for electrochemical sensing

Three-dimensional (3D) graphene–carbon nanotube (CNT) hybrids are synthesized by two-step chemical vapor deposition (CVD) under atmospheric pressure. As revealed by scanning electron microscopy (SEM), the hybrid is a monolithic graphene foam with conformal coverage of a dense CNT mesh. We further demonstrate that the obtained graphene–CNT hybrid foams can be used as novel 3D electrochemical electrodes for sensing applications. Specifically, the 3D graphene–CNT electrodes exhibit a high sensitivity (∼470.7 mA M−1 cm−2) and low detection limit (∼20 nM with S/N ≈ 9.2) for dopamine detection. Modified with horseradish peroxidase and Nafion, the 3D hybrid electrodes are also used to detect H2O2 with a high sensitivity (137.9 mA M−1 cm−2), low detection limit (∼1 μM with S/N ≈ 17.4), and wide linear detection range (10 μM–1 mM).

Hollow Fiber Membrane Decorated with Ag/MWNTs: Toward Effective Water Disinfection and Biofouling Control

The currently applied disinfection methods during water treatment provide effective solutions to kill pathogens, but also generate harmful byproducts, which are required to be treated with additional efforts. In this work, an alternative and safer water disinfection system consisting of silver nanoparticle/multiwalled carbon nanotubes (Ag/MWNTs) coated on a polyacrylonitrile (PAN) hollow fiber membrane, Ag/MWNTs/PAN, has been developed. Silver nanoparticles of controlled sizes were coated on polyethylene glycol-grafted MWNTs. Ag/MWNTs were then covalently coated on the external surface of a chemically modified PAN hollow fiber membrane to act as a disinfection barrier. A continuous filtration test using E. coli containing feedwater was conducted for the pristine PAN and Ag/MWNTs/PAN composite membranes. The Ag/MWNT coating significantly enhanced the antimicrobial activities and antifouling properties of the membrane against E. coli. Under the continuous filtration mode using E. coli feedwater, the relative flux drop over Ag/MWNTs/PAN was 6%, which was significantly lower than that over the pristine PAN (55%) at 20 h of filtration. The presence of the Ag/MWNT disinfection layer effectively inhibited the growth of bacteria in the filtration module and prevented the formation of biofilm on the surface of the membrane. Such distinctive antimicrobial properties of the composite membrane is attributed to the proper dispersion of silver nanoparticles on the external surface of the membrane, leading to direct contact with bacterium cells.

Biomimetic control of vascular smooth muscle cell morphology and phenotype for functional tissue-engineered small-diameter blood vessels

Small-diameter blood vessel substitutes are urgently needed for patients requiring replacements of their coronary and below-the-knee vessels and for better arteriovenous dialysis shunts. Circulatory diseases, especially those arising from atherosclerosis, are the predominant cause of mortality and morbidity in the developed world. Current therapies include the use of autologous vessels or synthetic materials as vessel replacements. The limited availability of healthy vessels for use as bypass grafts and the failure of purely synthetic materials in small-diameter sites necessitate the development of a biological substitute. Tissue engineering is such an approach and has achieved promising results, but reconstruction of a functional vascular tunica media, with circumferentially oriented contractile smooth muscle cells (SMCs) and extracellular matrix, appropriate mechanical properties, and vasoactivity has yet to be demonstrated. This review focuses on strategies to effect the switch of SMC phenotype from synthetic to contractile, which is regarded as crucial for the engineering of a functional vascular media. The synthetic SMC phenotype is desired initially for cell proliferation and tissue remodeling, but the contractile phenotype is then necessary for sufficient vasoactivity and inhibition of neointima formation. The factors governing the switch to a more contractile phenotype with in vitro culture are reviewed.

A photopolymerized antimicrobial hydrogel coating derived from epsilon-poly-L-lysine.

Hydrogels made from epsilon-poly-l-lysine-graft-methacrylamide (EPL-MA) have been found to have impressive wide spectrum antimicrobial activity against both bacteria (specifically Escherichia coli, Pseudomonas aeruginosa, Serratia marcescens and Staphylococcus aureus) and fungi (specifically Candida albicans and Fusarium solani). The EPL-MA hydrogel also possesses in vitro biocompatibility and EPL-MA solution is relatively non-hemolytic: the concentration needed for onset of human red blood cell (hRBC) hemolysis is 12,500 μg/mL so that the selectivity for the pathogenic microorganisms over hRBCs is 230-1560. Further, EPL-MA hydrogel can be conveniently ultraviolet-immobilized onto plasma-treated plastic surfaces to form thin highly adherent antimicrobial hydrogel coatings for medical devices and implants.

Cationic peptidopolysaccharides show excellent broad-spectrum antimicrobial activities and high selectivity.

The ongoing emergence of drug resistance in pathogens calls for continuing development of novel antimicrobial molecules. [ 1–3 ] Cationic antimicrobial peptides (AMPs) and their synthetic analogues, which target the pathogen cytoplasmic membrane, demonstrate a promising approach to lower the probability of development of pathogen resistance. [ 4 , 5 ] The microbial cytoplasmic membrane is surrounded by cell wall, a barrier which must be penetrated by all effective antimicrobial molecules. [ 6 , 7 ] However, the structural affi nity of antimicrobial molecules with the microbial cell wall has generally not been considered in previous designs of cationic antimicrobial polymers. Peptidoglycan is a common component of the bacteria cell wall, a feature absent from animal cells, so that peptidoglycanmimicry may be exploited to achieve high antimicrobial activity with low hemolytic activity. [ 8 ] Here, we report a new class of antimicrobial polymers based on cationic peptidopoly saccharides that mimic the peptidoglycan structure and that show excellent antimicrobial activity and high selectivity. The optimum tested peptidopolysaccharide, specifi cally a copoly mer of chitosan and polylysine (CSg -K 16 ), is effective against clinically signifi cant Gram-negative and Gram-positive bacteria and fungi with low minimum inhibitory concentrations (5–20 μ g mL − 1 , or 0.2–0.9 μ M), high selectivity ( > 5000–10 000) and low toxicity to mammalian cells. Our preliminary results of low/non secretion of tumor necrosis factorα by cultured macro phages when challenged with CSg -K 16 also suggests that the compound stimulates little or no infl ammatory response. The cationic charge of our peptidopolysaccharides causes them to target the anionic microbial cell envelope, and their structural affi nity with microbial cell wall constituents promotes their penetration of the cell wall to reach the cytoplasmic membrane, where the peptidopolysaccharide acts as an effective membrane disruptor. The combination of these features results in excellent antimicrobial activity and selectivity. This class of antimicrobial