Analyzing the Function of Cartilage Replacements: A Laboratory Activity to Teach High School Students Chemical and Tissue Engineering Concepts

A cartilage tissue engineering laboratory activity was developed as part of the Exciting Discoveries for Girls in Engineering (EDGE) Summer Camp sponsored by the Women In Engineering Program (WIEP) at Purdue University. Our goal was to increase awareness of chemical engineering and tissue engineering in female high school students through a laboratory activity that incorporated a number of National Research Council learning objectives for science and engineering. This manuscript describes the context of the activity, detailed instructions to perform the activity, and a summary of the feedback. As a result of the activity, participants knew more about the chemical engineering profession and were able to form stronger and more educated opinions about their career interests

Reaction Mechanism for Oxygen Evolution on RuO2, IrO2, and RuO2@IrO2 Core-Shell Nanocatalysts

Iridium dioxide, IrO2, is second to the most active RuO2 catalyst for the oxygen evolution reaction (OER) in acid, and is used in proton exchange membrane water electrolyzers due to its high durability. To improve the activity of IrO2-based catalysts, we prepared RuO2@IrO2 core-shell nanocatalysts using carbon-supported Ru as the template. At 1.48 V, the OER specific activity of RuO2@IrO2 is threefold that of IrO2. While the activity volcano plots over wide range of materials have been reported, zooming into the top region to clarify the rate limiting steps of most active catalysts is important for further activity enhancement. Here, we verified theory-proposed sequential water dissociation pathway in which the O–O bond forms on a single metal site, not via coupling of two adsorbed intermediates, by fitting measured polarization curves using a kinetic equation with the free energies of adsorption and activation as the parameters. Consistent with theoretical calculations, we show that the OER activities of IrO2 and RuO2@IrO2 are limited by the formation of O adsorbed phase, while the OOH formation on the adsorbed O limits the reaction rate on RuO2

A Self-Sufficient Nitrate Groundwater Remediation System: Geobacter Sulfurreducens Microbial Fuel Cell Fed by Hydrogen from a Water Electrolyzer

Nitrate contamination of groundwater is a major problem, especially in farming areas where nitrogen-based fertilizers are used. Geobacter sulfurreducens electrodes were electrochemically evaluated for their ability to reduce nitrate with implications for groundwater remediation. G. sulfurreducens were optimized for nitrate reduction by modifying growth media during subculture. The Geobacter were then cast on Toray carbon paper electrodes and immobilized with pectin. Cyclic voltammetry demonstrated that the electrodes bioelectrocatalytically reduce nitrate with an onset potential of −0.25 V vs. SCE. Amperometry was used to evaluate nitrate concentrations between 0.5 and 270 mM. The limit of detection is 8 mM with a linear range of 20 mM to 160 mM. Evaluation by a Michaelis Menten kinetic model yields a KM of 110 ± 10 mM. The Geobacter sulfurreducens electrodes were incorporated into a nitrate reducing microbial fuel cell which was fed nitrate contaminated water by a peristaltic pump and hydrogen from a proton exchange membrane (PEM)-based water electrolysis cell and yielded a remediation rate of 6 mg/cm2/day

Pathways to Ultra-Low Platinum Group Metal Catalyst Loading in Proton Exchange Membrane Electrolyzers

Hydrogen is one of the world\u27s most important chemicals, with global production of about 50 billion kg/year. Currently, hydrogen is mainly produced from fossil fuels such as natural gas and coal, producing CO2. Water electrolysis is a promising technology for fossil-free, CO2-free hydrogen production. Proton exchange membrane (PEM)-based water electrolysis also eliminates the need for caustic electrolyte, and has been proven at megawatt scale. However, a major cost driver is the electrode, specifically the cost of electrocatalysts used to improve the reaction efficiency, which are applied at high loadings (\u3e3 mg/cm2 total platinum group metal (PGM) content). Core-shell catalysts have shown improved activity for hydrogen production, enabling reduced catalyst loadings, while reactive spray deposition techniques (RSDT) have been demonstrated to enable manufacture of catalyst layers more uniformly and with higher repeatability than existing techniques. Core-shell catalysts have also been fabricated with RSDT for fuel cell electrodes with good performance. Manufacturing and materials need to go hand in hand in order to successfully fabricate electrodes with ultra-low catalyst loadings (\u3c0.5 mg/cm2 total PGM content) without significant variation in performance. This paper describes the potential for these two technologies to work together to enable low cost PEM electrolysis systems

Improving Student Preparedness for Entering the Workforce: A Hands-On Experience in Project Management for a Graduate-Level Protein Engineering Class

A hands-on polypeptide engineering experience that focuses on project management was developed and incorporated in a graduate-level course. The goal was to have doctoral students in chemical engineering learn about project planning tools, and experience what it might be like to plan and execute a project in industry or business. The motivation behind this goal was to help students best-utilize their technical skills in the private sector, where 42% of doctoral recipients in science and engineering work

Catalysts for Nitrogen Reduction to Ammonia

The production of synthetic ammonia remains dependent on the energy- and capital-intensive Haber-Bosch process. Extensive research in molecular catalysis has demonstrated ammonia production from dinitrogen, albeit at low production rates. Mechanistic understanding of dinitrogen reduction to ammonia continues to be delineated through study of molecular catalyst structure, as well as through understanding the naturally occurring nitrogenase enzyme. The transition to Haber-Bosch alternatives through robust, heterogeneous catalyst surfaces remains an unsolved research challenge. Catalysts for electrochemical reduction of dinitrogen to ammonia are a specific focus of research, due to the potential to compete with the Haber-Bosch process and reduce associated carbon dioxide emissions. However, limited progress has been made to date, as most electrocatalyst surfaces lack specificity towards nitrogen fixation. In this Review, we discuss the progress of the field in developing a mechanistic understanding of nitrogenase-promoted and molecular catalyst-promoted ammonia synthesis and provide a review of the state of the art and scientific needs for heterogeneous electrocatalysts

Engineered Interaction Between Short Elastin-Like Peptides and Perfluorinated Sulfonic-Acid Ionomer

Control of ionomer thin films on metal surfaces is important for a range of electrodes used in electrochemical applications. Engineered peptides have emerged as powerful tools in electrode assembly because binding sites and peptide structures can be modulated by changing the amino acid sequence. However, no studies have been conducted showing peptides can be engineered to interact with ionomers and metals simultaneously. In this study, we design a single-repeat elastin-like peptide to bind to gold using a cysteine residue, and bind to a perfluorinated sulfonic-acid ionomer called Nafion® using a lysine guest residue. Quartz crystal microbalance with dissipation monitoring and atomic force microscopy are used to show that an elastin-like peptide monolayer attached to gold facilitates the formation of a thin, phase-separated ionomer layer. Dynamic light scattering confirms that the interaction between the peptide with the lysine residue and the ionomer also happens in solution, and circular dichroism shows that the peptides maintain their secondary structures in the presence of ionomer. These results demonstrate that elastin-like peptides are promising tools for ionomer control in electrode engineering

Interactions of Polyproline II Helix Peptides with Iron(III) Oxide

Interactions of a peptide with polyproline II helical secondary structure with maghemite (iron(III) oxide, Fe2O3) surfaces were characterized using a variety of surface techniques. A quartz crystal microbalance with dissipation was used to measure the hydrated mass and thickness (92 ± 29 ng/cm2 and 0.89 ± 0.27 nm, respectively) of a layer which formed after a sensor coated with Fe2O3 was exposed to the peptide in aqueous solution. The analysis revealed that the peptide formed a stable thin layer on the sensor. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy of the monolayer were employed to study the relationship between the metal and the peptide. Finally, Fe2O3 nanoparticles were incubated with the peptide, and analysis of the settling and particle size revealed that the presence of the peptide reduced the occurrence of large aggregates in solution

Scalable Production of Peptides for Enhanced Struvite Formation via Expression on the Surface of Genetically Engineered Microbes

A promising method for recycling phosphate from wastewater is through precipitation of struvite (MgNH4PO4·6H2O), a slow-release fertilizer. Peptides have been shown to increase the yield of struvite formation, but producing peptides via solid phase synthesis is cost prohibitive. This work investigates the effects of peptide-expressing bacteria on struvite precipitation to provide a sustainable and cost-efficient means to enhance struvite precipitation. A peptide known for increased struvite yield was expressed on a membrane protein in Escherichia coli(E. coli), and then 5 mL precipitation reactions were performed in 50 mL culture tubes for at least 15 min. The yield of struvite crystals was examined, with the presence of peptide-expressing E. coli inducing significantly higher yields than nonpeptide-expressing E. coli when normalized to the amount of bacteria. The precipitate was identified as struvite through Fourier transform infrared spectroscopy and energy dispersive spectroscopy, while the morphology and size of the crystals were analyzed through optical microscopy and scanning electron microscopy. Crystals were found to have a larger area when precipitated with the peptide-expressing bacteria. Additionally, bacteria–struvite samples were thermogravimetrically analyzed to quantify their purity and determine their thermal decomposition behavior. Overall, this study presents the benefits of a novel, microbe-driven method of struvite precipitation, offering a means for scalable implementation

Clickable Polymer Scaffolds Enable Ce Recovery with Peptide Ligands

Rare earth elements (REEs) are a vital part of many technologies with particular importance to the renewable energy sector and there is a pressing need for environmentally friendly and sustainable processes to recover and recycle them from waste streams. Functionalized polymer scaffolds are a promising means to recover REEs due to the ability to engineer both transport properties of the porous material and specificity for target ions. In this work, REE adsorbing polymer scaffolds were synthesized by first introducing poly(glycidyl methacrylate) (GMA) brushes onto porous polyvinylidene fluoride (PVDF) surface through activator generated electron transfer atom transfer radical polymerization (AGET ATRP). Azide moieties were then introduced through a ring opening reaction of GMA. Subsequently, REE-binding peptides were conjugated to the polymer surface through copper catalyzed azide alkyne cycloaddition (CuAAC) click chemistry. The presence of GMA, azide, and peptide was confirmed through Fourier transform infrared spectroscopy. Polymer scaffolds functionalized with the REE-binding peptide bound cerium, while polymer scaffolds functionalized with a scrambled control peptide bound significantly less cerium. Importantly, this study shows that the REE binding peptide retains its functionality when bound to a polymer surface. The conjugation strategy employed in this work can be used to introduce peptides onto other polymeric surfaces and tailor surface specificity for a wide variety of ions and small molecules