Understanding the extracellular electron transfer mechanisms of electroactive bacteria could help determine their potential in microbial fuel cells (MFCs) and their microbial syntrophy with redox-active minerals in natural environments. However, the mechanisms of extracellular electron transfer to electrodes by sulfate-reducing bacteria (SRB) remain underexplored. Here, we utilized double-chamber MFCs with carbon cloth electrodes to investigate the extracellular electron transfer mechanisms of Desulfovibrio vulgaris Hildenborough (DvH), a model SRB, under varying lactate and sulfate concentrations using different DvH mutants. Our MFC setup indicated that DvH can harvest electrons from lactate at the anode and transfer them to cathode, where DvH could further utilize these electrons. Patterns in current production compared with variations of electron donor/acceptor ratios in the anode and cathode suggested that attachment of DvH to the electrode and biofilm density were critical for effective electricity generation. Electron microscopy analysis of DvH biofilms indicated DvH utilized filaments that resemble pili to attach to electrodes and facilitate extracellular electron transfer from cell to cell and to the electrode. Proteomics profiling indicated that DvH adapted to electroactive respiration by presenting more pili- and flagellar-related proteins. The mutant with a deletion of the major pilus-producing gene yielded less voltage and far less attachment to both anodic and catholic electrodes, suggesting the importance of pili in extracellular electron transfer. The mutant with a deficiency in biofilm formation, however, did not eliminate current production indicating the existence of indirect extracellular electron transfer. Untargeted metabolomics profiling showed flavin-based metabolites, potential electron shuttles.IMPORTANCEWe explored the application of Desulfovibrio vulgaris Hildenborough in microbial fuel cells (MFCs) and investigated its potential extracellular electron transfer (EET) mechanism. We also conducted untargeted proteomics and metabolomics profiling, offering insights into how DvH adapts metabolically to different electron donors and acceptors. An understanding of the EET mechanism and metabolic flexibility of DvH holds promise for future uses including bioremediation or enhancing efficacy in MFCs for wastewater treatment applications.

The engineering of biomaterial interfaces is an area of ongoing study, with relevance in furthering the understanding of basic cell behavior as well as promoting desired outcomes for clinical applications. Here, we report a facile drop cast method to fabricate nanobiocomposite films atop medical grade Titanium (Ti) composed of both organic (chitosan, Cs) and inorganic (Laponite™, Lap) components, with scanning electron and atomic force microscopy indicating uniform and reproducible film composition. We further demonstrate controlled cell behavior of two clinically relevant primary cell types – human mesenchymal stromal cells (hMSCs) and osteoblasts – seeded atop the films. For both cell types, Cs incorporation decreased cell area and increased Form Factor (corresponding to a more rounded morphology) in a dose-dependent manner, with subsequent Lap incorporation “recovering” larger areas and more spread morphologies back toward those observed on Ti alone. Collectively, these results indicate the potential of the drop cast fabrication as a platform technique with which to predict the in vivo regenerative performance of interfacial biomaterials.

Many commercial applications of carbon nanotubes (CNTs) have not yet been realized owing to their limited water processability that leads to poor electrical performance. We report the syntheses of oxidized single-walled carbon nanotubes (SWCNTs) with improved percolating network connectivity and conductivity in thin films processed from aqueous colloids mixed with dispersing agents including LAPONITE® nanoparticles and surfactants. The influences of clay loading and acid functionalization on surface morphology and the self-assembly of interconnected networks in SWCNT films were studied. Conductive atomic force microscopy (c-AFM) analyses indicated that the most favorable nanonetwork for charge conduction was achieved at a low loading of LAPONITE® nanoparticles. In addition, hydrazine reduction treatments after acid functionalization led to augmented electrical conductivities in the CNT films regardless of the extent of clay loading. These studies provide important insight on tuning the heterointerfaces that control CNT self-assembly and polydispersity and may prove insightful to realize percolating networks for green energy applications.

The SUCCESS-LEADERS (Leading Educational and Academic Directions to Enhance Retention in STEM) project aims to develop, refine and implement practices that will advance understanding of the factors affecting retention and career pathways of low-income, at-risk populations. The production of academically talented, energetic STEM students with diverse backgrounds trained as leaders capable of propagating transformative mentoring skills will positively impact this nation’s workforce. We aim to produce innovative technological leaders who thrive in a diverse multidisciplinary community. Our institution has a longstanding history of success with NSF STEM education initiatives and has used program assessment to build upon these successes in establishing lasting institutional enterprises based on funded models. The small and supportive nature of a liberal arts college provides significant strength in encouraging at risk students to persist in STEM disciplines through strong mentoring in both curricular and research arenas. As a small liberal arts college offering engineering we are particularly suited to facilitate the development of future leaders of a diverse STEM workforce. This project further broadens our inclusive recruiting strategy by building relationships with small, rural under-resourced public high schools in order to attract and retain talented students to STEM fields. Students originating from rural areas face unique challenges persisting in STEM fields. We aim to address these challenges by providing dedicated mentors and enabling the development of a tight knit, supportive cohort of scholars across disciplines. We focus on professional development activities that build the skills necessary to participate in mentoring activities, both as a mentee and a mentor to others. Connecting scholars with potential mentors, 1) in their peer group; 2) in their discipline as academic advisors; 3) in courses as professors; 4) in research as project advisors; and 5) in the workforce as professional contacts, enables personal growth and professional advancement of both the mentor and mentee. To encourage the students to be proactive in making professional contacts, we stress attendance at seminars within their STEM disciplines. Students are offered an opportunity to participate in the IMPACT program that aims to connect students to STEM professionals in industry. Placing students in the role of mentor, as STEM ambassadors to their community high schools, fosters student leadership and builds capacity for the initiative going forward. The program includes placing STEM students together into general education courses like the “first-year preceptorial” and the “sophomore research seminar” themed with sufficient breadth in order to ask students both to embrace how their discipline can contribute to the emerging concerns within the theme, but also to encourage discourse among the students in different STEM disciplines. In addition to internal assessment conducted as part of the analysis for our current grant, data from a longitudinal retrospective analysis will be presented on the academic and professional pathways of prior NSF-DUE funded students. This will include prior cohorts totaling approximately 90 students who have matriculated over the last decade to compare their academic pathways during their undergraduate years and beyond against similar STEM-oriented students of the same class years in order to critically examine our efforts and identify the most impactful practices in achieving the project goals.

Polyaniline composites with graphene and graphene oxide have received broad interest for applications in charge separation and storage in electrical devices. Syntheses via in situ polymerization of aniline in colloidal dispersions of graphene oxide have afforded nanocomposites of polyaniline intercalated within graphene oxide nanosheets. The simultaneous inclusion of LAPONITE® nanoparticles has improved aqueous phase processability and thin film formation. Mechanical, morphological and conductivity studies including atomic force microscopy and scanning electron microscopy were employed to study the host-guest interactions and heterointerfaces that govern self-assembly. Adhesion and conductivity values within graphene oxide/polyaniline/LAPONITE® (GOPL) nanocomposites were tuned by varying the weight ratios of polyaniline : graphene oxide. These studies inform ongoing work to use GOPL nanomaterials for clean energy harvesting and storage applications.

Obstacles to the commercialization of carbon nanotubes (CNTs) in alternative energy and clean water applications include high production costs, aggregation problems, and poor water solubility. We report the use of Laponite nanoparticles to improve the aqueous phase fabrication of single-walled CNT (SWCNT) percolating networks. SWCNT/Laponite films were cast at varied Laponite and CNT ink concentrations to optimize polydispersity. Structural and morphological characterization identified isolated aggregates, coalesced aggregates, and interconnected networks. Conductive atomic force microscopy studies confirmed that the nanocomposite films maintained their electrical transport properties after heteromixing. Incorporating Laponite improved CNT aqueous dispersibility, prevented aggregation, and promoted continuous, homogenous film formation. (C) 2018 Elsevier B.V. All rights reserved.