Bogdan C. Donose

Effects of surface charge and hydrophobicity on anodic biofilm formation, community composition, and current generation in bioelectrochemical systems.

The focus of this study was to investigate the effects of surface charge and surface hydrophobicity on anodic biofilm formation, biofilm community composition, and current generation in bioelectrochemical systems (BESs). Glassy carbon surfaces were modified with -OH, -CH3, -SO3(-), or -N(+)(CH3)3 functional groups by electrochemical reduction of aryl diazonium salts and then used as anodes with poised potential of -0.2 V (vs Ag/AgCl). The average startup times and final current densities for the -N(+)(CH3)3, -OH, -SO3(-), and -CH3, electrodes were (23 d, 0.204 mA/cm(2)), (25.4 d, 0.149 mA/cm(2)), (25.9 d, 0.114 mA/cm(2)), and (37.2 d, 0.048 mA/cm(2)), respectively. Biofilms on different surfaces were analyzed by nonturnover cyclic voltammetry (CV), fluorescence in situ hybridization (FISH), and 16S rRNA gene amplicon pyrosequencing. The results demonstrated that 1) differences in the maximum current output between surface modifications was correlated with biomass quantity, and 2) all biofilms were dominated by Geobacter populations, but the composition of -CH3-associated biofilms differed from those formed on surfaces with different chemical modification. This study shows that anode surface charge and hydrophobicity influences biofilm development and can lead to significant differences in BESs performance. Positively charged and hydrophilic surfaces were more selective to electroactive microbes (e.g. Geobacter) and more conducive for electroactive biofilm formation.

A novel carbon nanotube modified scaffold as an efficient biocathode material for improved microbial electrosynthesis

We report on a novel biocompatible, highly conductive three-dimensional cathode manufactured by direct growth of flexible multiwalled carbon nanotubes on reticulated vitreous carbon (NanoWeb-RVC) for the improvement of microbial bioelectrosynthesis (MES). NanoWeb-RVC allows for an enhanced bacterial attachment and biofilm development within its hierarchical porous structure. 1.7 and 2.6 fold higher current density and acetate bioproduction rate normalized to total surface area were reached on NanoWeb-RVC versus a carbon plate control for the microbial reduction of carbon dioxide by mixed cultures. This is the first study showing better intrinsic efficiency as biocathode material of a three-dimensional electrode versus a flat electrode: this comparison has been made considering the total surface area of the porous electrode, and not just the projected surface area. Therefore, the improved performance is attributed to the nanostructure of the electrode and not to an increase in surface area. Unmodified reticulated vitreous carbon electrodes lacking the nanostructure were found unsuitable for MES, with no biofilm development and no acetate production detected. The high surface area to volume ratio of the macroporous RVC maximizes the available biofilm area while ensuring effective mass transfer to and from the biofilm. The nanostructure enhances the bacteria-electrode interaction and microbial extracellular electron transfer. When normalized to projected surface area, current densities and acetate production rates of 3.7 mA cm−2 and 1.3 mM cm−2 d−1, respectively, were reached, making the NanoWeb-RVC an extremely efficient material from an engineering perspective as well. These values are the highest reported for any MES system to date.

Self-assembling polystyrene-block-poly(ethylene oxide) copolymer surface coatings: Resistance to protein and cell adhesion

In this paper we report a method for biomaterial surface modification that utilizes the self-assembly of block copolymers of poly(styrene-block-ethylene oxide) (PS-PEO) to generate micro-phase separated surfaces with varying density PEO domains. These PS-PEO self-assembled surfaces showed a significant reduction in protein adsorption compared to control polystyrene surfaces. The adhesion of NIH-3T3 fibroblast cells was shown to be significantly affected by the surface coverage of PEO nano-domains formed by copolymer self-assembly. These nano-domains, when presented at high number density (almost 1000 domains per square micron), were shown to completely prevent cellular attachment, even though small amounts of protein were able to bind to the surface.

The viscoelastic, hyperelastic and scale dependent behaviour of freshly excised individual skin layers

Micro-devices using mechanical means to target skin for improved drug and vaccine delivery have great promise for improved clinical healthcare. Fully realizing this promise requires a greater understanding of key micro-biomechanical properties for each of the different skin layers - that are both the mechanical barriers and biological targets of these devices. Here, we performed atomic force microscopy indentation on a micro-nano scale to quantify separately, in fresh mouse skin, the viscous and elastic behaviour of the stratum corneum, viable epidermis and dermis. By accessing each layer directly, we examined the response to nanoindentation at sub-cellular and bulk-cellular scale. We found that the dermis showed greatest mechanical stiffness (elastic moduli of 7.33-13.48 MPa for 6.62 μm and 1.90 μm diameter spherical probes respectively). In comparison, the stratum corneum and viable epidermis were weaker at 0.75-1.62 MPa and 0.49-1.51 MPa respectively (again with the lower values resulting from indentations with the large probe 6.62 μm). The living cell layer of the epidermis (viable epidermis) showed greatest viscoelasticity - almost fully relaxing from shallow indentation - whilst the other layers reached a plateau after relaxing by around 40%. With small scale (sub-micron) AFM indentation, we directly determined the effects of different layer constituents - in particular, the dermis showed that some indents contacted collagen fibrils and others contacted ground substance/cellular areas. This work has far reaching implications for the design of micro-devices using mechanical means to deliver drugs or vaccines into the skin; providing key characterized mechanical property values for each constituent of the target delivery material.

Flame oxidation of stainless steel felt enhances anodic biofilm formation and current output in bioelectrochemical systems

Stainless steel (SS) can be an attractive material to create large electrodes for microbial bioelectrochemical systems (BESs), due to its low cost and high conductivity. However, poor biocompatibility limits its successful application today. Here we report a simple and effective method to make SS electrodes biocompatible by means of flame oxidation. Physicochemical characterization of electrode surface indicated that iron oxide nanoparticles (IONPs) were generated in situ on an SS felt surface by flame oxidation. IONPs-coating dramatically enhanced the biocompatibility of SS felt and consequently resulted in a robust electroactive biofilm formation at its surface in BESs. The maximum current densities reached at IONPs-coated SS felt electrodes were 16.5 times and 4.8 times higher than the untreated SS felts and carbon felts, respectively. Furthermore, the maximum current density achieved with the IONPs-coated SS felt (1.92 mA/cm(2), 27.42 mA/cm(3)) is one of the highest current densities reported thus far. These results demonstrate for the first time that flame oxidized SS felts could be a good alternative to carbon-based electrodes for achieving high current densities in BESs. Most importantly, high conductivity, excellent mechanical strength, strong chemical stability, large specific surface area, and comparatively low cost of flame oxidized SS felts offer exciting opportunities for scaling-up of the anodes for BESs.

Effect of alcohol-water exchange and surface scanning on nanobubbles and the attraction between hydrophobic surfaces

Atomic force microscopy (AFM) was used to examine how different alcohols affect the hydrophobic attraction between a hydrophobic silica colloidal probe and a hydrophobic silica wafer. The experiments were performed in water and in water after rinsing alcohol (methanol, ethanol, or 1-propanol) throughout the AFM system. In all three cases the range of the attractive force increased after alcohol-water exchange, with 1-propanol showing the largest increase in range followed by ethanol and methanol. Additionally, experiments were performed before and after scanning the flat substrate with the colloidal probe. The range of the attractive force substantially increased with increasing scanning area. The attraction was explained by nanobubble bridging with a capillary force model with constant bridge volume proposed. The bridge volume (constant during each of the force curve measurements), contact angle and rupture distance were also determined for different scan sizes. The correlation between the rupture distance and bridge volume agreed with the available prediction.

The role of iron in sulfide induced corrosion of sewer concrete

The sulfide-induced corrosion of concrete sewer is a widespread and expensive problem for water utilities worldwide. Fundamental knowledge of the initiation and propagation of sewer corrosion, especially the interactions between chemical reactions and physical structure changes, is still largely unknown. Advanced mineral analytical techniques were applied to identify the distribution of corrosion products and the micro-cracking that developed along the corrosion boundary. It was found that sewer concrete corrosion caused by reactions with sulfuric acid progressed uniformly in the cement of concrete. In contrast to conventional knowledge, iron rust rather than gypsum and ettringite was likely the factor responsible for cracking ahead of the corrosion front. The analysis also allowed quantitative determination of the major corrosion products, i.e., gypsum and ettringite, with the latter found closer to the corrosion front. The conceptual model based on these findings clearly demonstrated the complex interactions among different chemical reactions, diffusion, and micro-structure changes.

Autotrophic hydrogen-producing biofilm growth sustained by a cathode as the sole electron and energy source

It is still unclear whether autotrophic microbial biocathode biofilms are able to self-regenerate under purely cathodic conditions without any external electron or organic carbon sources. Here we report on the successful development and long-term operation of an autotrophic biocathode whereby an electroactive biofilm was able to grow and sustain itself with CO2 as a sole carbon source and using the cathode as electron source, with H2 as sole product. From a small inoculum of 15 mg COD (in 250 mL), containing 30.3% Archaea, the bioelectrochemical system operating at -0.5 V vs. SHE enabled an estimated biofilm growth of 300 mg as COD over a period of 276 days. A dramatic change in the microbial population was observed during this period with Archaea disappearing completely (<0.1% of population). The predominant phyla enriched were Proteobacteria (57.3%), Firmicutes (12.4%), Bacteroidetes (11.6%) and Actinobacteria (1.1%). Up to 9.2 L H2 m(-2) day(-1) (1.88 A m(-2)) was achieved when the cathode potential was decreased to -0.75 V vs. SHE. This study demonstrates that purely autotrophic biofilm growth coupled to proton reduction to hydrogen alone can be sustained with a cathode as the sole electron source, while avoiding the development of H2-consuming microorganisms such as methanogens and acetogens.

Purification and conformational analysis of a key exopolysaccharide component of mixed culture aerobic sludge granules.

The application of aerobic sludge granules in wastewater treatment could increase the intensity of wastewater treatment processes because of their greater density and size relative to conventional sludge flocs. It has been suggested that granules are distinguished from flocs by gel forming exopolysaccharides. In this study, evidence is presented linking a specific exopolysaccharide component with granule extracellular polymeric substance (EPS) gelation. Granular EPS comprised three components: high-molecular-weight (MW) exopolysaccharide, medium-MW proteins and glycosides, and low-MW proteins and glycosides. The high-MW fraction was separated by fractional precipitation and preparatory-scale gel permeation chromatography (GPC). The MW profile of this fraction appears to be exclusively attributable to high-MW polysaccharide. The exopolysaccharide exists as a gel at normal wastewater treatment operating pH (i.e., 6.0-8.5), whereas the low/medium-MW material does not. Conformational analysis by atomic force microscopy (AFM) of the dried material showed that the polysaccharide forms pearl-necklace-like, intramolecularly condensed structures when dissolved in Milli-Q water and partially relaxed helical aggregates when in alkali solution. Consequently, the gel-forming property of EPS in the aerobic sludge granules tested is probably associated with high-MW polysaccharide components.

The examination of graphene oxide for rechargeable lithium storage as a novel cathode material

A sustainable cathode is critical to developing green lithium storage devices. Conducting polymers, radical polymers and carbonyl-based polymers are the three most important types of polymer-based sustainable cathode materials. Here we report that graphene oxide enriched with epoxide, without being reduced, is a promising sustainable carbonaceous cathode material for rechargeable lithium storage. Graphene oxide containing a large quantity of epoxide can have a high capacity of 360.4 mA h g−1 at 50 mA g−1, which significantly surpasses those of many polymer cathodes and conventional lithium-transition metal oxide cathodes. The good stability of this epoxide-based cathode was demonstrated. Density functional theory calculations indicate that the lithiation of epoxide is energetically favorable (−1.21 eV) and the original epoxide structure can be restored after delithiation with a small barrier (0.23 eV).