Figure 1. Fluprophone intensity for concentrations ranging from 100 microgram/ml (a) to 1 nanogram/ml (f). Top row is control and the bottom is with a surface coated with Ag nanocubes of 50 nm edge length. MEF allows for detection limits to be lowered by a factor of 1000.
Venkat R. Bhethanabotla, Professor and Director of Materials Science & Engineering Program
Distribution of Ag nanocubes of the Surface of Metal-Enhanced Fluorescence Surface Acoustic Wave (MEF-SAW) Immunobiosensor
A new immunobiosensor principle has recently been conceived in the Bhethanabotla group 5, which utilizes the concept of metal-enhanced fluorescence, wherein a fluorophore next to a metallic nanostructure exhibits orders of magnitude (see Figure 1) increase in fluorescence intensity, thus impacting sensitivity. This metallic nanostructure has been optimized through FDTD calculations to be silver nanocubes dispersed on a surface at desired and specified density, and immobilized to stay put in place during sensor operation, which involves forces from a surface acoustic wave device to mix (improves incubation times) and remove non-specific binding proteins (improves sensitivity, and reduces false determinations). The REU student will be challenged to think about ways of achieving such a desired distribution of Ag nanoparticles on a sensor surface, with suggestions of possible processes to explore, such as nanolithography, spin coating, immobilization via molecular attachments, etc. Resources will be discussed and provided for an innovative distribution method to be pursued as a project, and results evaluated for scalability, reliability, impact on the sensor performance and economics.
Nathan Crane, Associate Professor of Mechanical Engineering
Additive manufacturing (AM) permits direct fabrication of complex systems directly from a digital model without the need for costly tooling. This capability enables fabrication of highly customized products and complex geometries that are not possible with traditional means. While there are many AM processes, each is available in a limited set of materials and often the properties of these materials deviate from traditional manufacturing methods. One alternative is to 3D print a mold that is then cast using traditional processes (Fig. 2). This approach achieves the quick delivery time and some of the geometric freedom of additive manufacturing. However, the constraints of removing the part from the mold limit the geometries that can be produced.
In this project, the REU student will investigate 3D printing of a water soluble mold that can be used for casting light metals and then all the residue can be dissolved away. By creating a complex cellular surface, the effective mechanical properties of a part can be tuned by several orders of magnitude. The student will develop parameters for spreading and printing the water soluble material using the binder jetting process. He/she will then measure the strength and pore structure obtained using different post-processing methods. The REU student will gain training in XRD, SEM, and mechanical testing processes. The resulting process will be demonstrated in the fabrication of porous metal components with locally tuned stiffness characteristics.
Figure 2. (top) Example of a complex cellular geometry that could not be cast without a 3D printed water-soluble mold. (Bottom) By varying lattice parameters, the effective modulus of elasticity can be varied by four orders of magnitude. FEA: finite element simulations.
Bob Frisina, Professor of Chemical & Biomedical Engineering
Neuroengineering of Sensory Systems
The Frisina group is developing an alternative wireless method, called plasmonic stimulation, for the stimulation of electrically excitable biological cells using a gold nanoelectrode (gold nanoparticle-coated micropipette) and a 532 nm green visible light. Because stimulation is localized and doesn’t spread like electrical stimulation, it has the potential to replace existing electrical stimulation based technologies such as in cardiac pacemakers, cochlear implants for the deaf and retinal implants. The Frisina group focuses on cochlear implants. Current efforts are aimed at stimulation of neonatal rat cardiomyocytes and SH-SY5Y neurons. Preliminary results indicate partial stimulation of the cells is possible (Fig. 3). Structuring of the nanoelectrode is the most critical part of the project whose performance depends upon many parameters like nanoparticle size and layer thickness, and size of the pipette. The REU student will be challenged to find the optimum parameters of the nanoelectrodes which can give action potentials (full stimulation of the cells). The project will involve synthesizing Au nanoparticles of different size and shape, coating techniques for fabricating the electrode, and understanding the effect of these variables quantitatively to achieve desired stimulation.
Figure 3. Experimental image of plasmonic stimulation of a SH-SY5Y neuron (left) and record (right) at holding potential of -63.0mV.
Babu Joseph, Professor of Chemical and Biomedical Engineering
Synthesis and Characterization of Composite Catalysts for Cascade Reactions
A new materials strategy to improve catalytic performance in complex reaction networks has been the focus of recent efforts in the Joseph group. The strategy consists of coating conventional catalysts with microporous zeolite materials on which a second catalyst layer can be applied. Conceptually, for production of higher hydrocarbons in the range of typical fuel cuts from methane and water, the strategy is shown in Fig. 4. The specific reaction network was selected because single-step conversion of natural gas to fuels and chemicals is a difficult challenge and would have huge societal impact. Recently, the successful coating of a zeolite on a reforming catalyst has been achieved for the improved conversion of methane with minimal higher hydrocarbon conversion. The REU student will be challenged to design and synthesize zeolite coatings onto core catalysts to control and determine the coating thickness in a processing methodology that is controllable, tunable, and scalable. Resources and guidance will be provided for this strategy to be viable as a project and materials developed will also be evaluated for their catalytic performance and impact on the intensified process economics and footprint.
Figure 4. Layered catalyst for intensified energy conversion processes.
John N. Kuhn, Associate Professor of Chemical & Biomedical Engineering
Towards Prototyping and Manufacturing of 2-D Materials for Photocatalytic Applications
Photocatalytic pollutant degradation and fuel production from CO2 and H2O are current focal points of the Kuhn group. 10-13 The main challenge for photocatalytic conversion is that electron-hole pairs generated from a majority of the absorbed photons do not initiate the reaction, but rather re-combine. As a result, the quantum yields are very low. To lower the recombination rates and thus increase the desired conversion, the application of materials without large volumes where the charge carriers can recombine is proposed. 2D materials are crystalline materials in which repetition occurs in 2 dimensions (2D) rather than 3. The REU student will be tasked to evaluate the various synthesis routes, such as colloidal and chemical vapor deposition, of candidate 2D chalcogenide materials for photocatalytic applications. Resources will be discussed and provided for an innovative processing methodology to be pursued, and results evaluated for scalability, reliability, impact on the charge carrier recombination rates and photocatalytic performance, and economics.
Shengquin Ma, Associate Professor of Chemistry
Construction of metal-organic frameworks for chemical fixation of CO2
Development of viable carbon dioxide capture and sequestration (CCS) technologies to reduce greenhouse emissions is imperative given the global warming issue. An attractive means of effective sequestration is chemical conversion of captured CO2 into value-added chemicals, which requires exploration of effective catalysts. The goal of the REU project is to synthesize catalytically active porous MOF materials and evaluate their performances in chemical fixation of CO2 (see Fig. 5). The student will learn how to synthesize MOFs using hydro/solvothermal methods. Upon successful growth of MOF crystals, the student will be taught how to utilize single crystal x-ray diffraction and powder x-ray diffraction to characterize the structure of prepared MOF crystals. In addition, the REU student will be trained to use a gas sorption apparatus to measure the porosities and surface areas, and he use of a thermal gravimetric instrument to assess. After characterization of the prepared porous MOF materials, the student will work with graduate students to perform catalytic reactions of chemical fixation of CO2 to evaluate performance of the MOF catalysts. Innovative thinking in designing suitable MOF structures for this appliction is the expected learning outcome in this project.
Figure 5. Chemical fixation of CO2 using a MOF-based catalyst.
Sylvia Thomas, Associate Professor of Electrical Engineering
Functional Membrane Materials for Energy, Water, and Bio Devices
The Thomas group researches in the area of advanced materials for applications in alternative energy sources, sustainable environments, and bio-applications. The group uses electrospinning growth processing, material characterization, and membrane fabrication of inorganic and organic materials. The focus of this project is to examine the electrospinning processing of nanofiber thin films consisting of cobalt doped antimony tin oxide to be used as a coating layer in a solar cell structure. The REU student will fabricate thin films using the electrospinning system with an emphasis on developing protocols for their manufacture. The thin film membranes will be characterized and then tested in a solar cell with a CoO doped ATO membrane layer versus a non-coated cell.
Ryan Toomey, Professor of Chemical and Biomedical Engineering
Tissue Engineering via Smart Material Approaches
Tissue engineering promises significant quality of life enhancement for those in need of a transplant while reducing health care costs. The Toomey group envisions organ regeneration as “Living Legos” that can be assembled to overcome the obstacles with scaffold-based regeneration. Efforts are to combine such technologies with non-destructive quick-release to assemble complex 3D tissues from well-defined microtissues. An additive tissue fabrication process has been developed based on unique polymeric surface that offers the chemical and topological cues (such as light or temperature) for construction of an organized cellular monolayer of a well-defined shape, referred to as SSSPs (Fig. 6). This REU project would focus on scaffoldless printing of complex tissues with intact subunit organization with the ultimate goal to engineer viable tissues (e.g. skeletal or cardiac muscle, skin) with integrated support structures such as vasculature and innervation. The student would design and synthesize polymer stamps, with a focus on streamlining the procedure to enable manufacturing. The student would also study application of the materials by measuring fibroblasts adhesion and release as a function of strain induced by the shape-shift.
Figure 6. Shape-shifting surface protrusions (SSSPs) with (a) low aspect ratio (e.g. 0.5) undergo lateral swelling upon stimulus, while (b) high aspect ratio (e.g. 2) results in buckled geometries, as seen in 3D reconstructions from confocal images. (c) Schematic diagram of tissue module contact printing: cells growing on stamp protrusions are contacted to a target surface or tissue to allow apical adhesion, a stimulus triggers large strains that induce basal release from the stamp, and the intact tissue modules are transferred. (d) Stripes of aligned fibroblasts that have been transferred from thermoresponsive SSSPs to a fibronectin coated surface via strain induced by a 5°C reduction.
Jing Wang, Associate Professor of Electrical Engineering
Scalable Hydrothermal Synthesis and Additive Manufacturing of Polymer-Piezoelectric Nanocomposites for Acoustic Sensors and Transducers
The Wang group works mainly in the areas of functional nanomaterials and micro-machined transducers or microsystems. In the field of functional nanomaterials, his group has explored new techniques for controllable and scalable manufacturing of nanostructured materials by hydrothermal synthesis, atomic layer deposition (ALD), solvent blending, etc. (Fig. 7). Examples include first-reported growth of densely-packed, free-standing ZnO nanowires on the sidewall of high aspect ratio trenches or patterned ALD seed layers, nano-manufacturing of diodes with bandgap-engineered multi-layer tunnel junctions, synthesis and molding of ceramic-elastomer composites with high permittivity and low loss over a wide range of microwave frequencies. Meanwhile, piezoelectric thin-film transducers have been studied for sensing, acoustic wave detection and signal processing, which has led to micro-fabricated resonant mass sensors with a sub-attogram (10-18g) resolution. Hence, it is highly desirable to consolidate the efforts in the areas of piezoelectric nanomaterials and transducer devices while reducing the design cycle by exploiting reproducible and scalable additive manufacturing processes. The REU student will be trained to optimize the hydrothermal synthesis of anisotropic nanowires or nanoparticles and preparation of polymer-piezoelectric nanocomposites with tailored properties. The student will work closely with graduate students to gain experience with design and additive manufacturing of piezoelectric transducers for resonant sensing, energy harvesting or acoustic emission detection prototypes. The additive manufactured polymer-piezoelectric composite transducers are anticipated to provide the best compromise between piezoelectric coefficient, elastic properties and coupling efficiency, while enabling novel 3D designs.
Figure 7. Conceptual illustration of the hydrothermal growth of free-standing, densely packed ZnO nanowires on trench sidewall or patterned ALD seed layers and the measured frequency response of a piezoelectrically-transduced resonant sensor.
Thomas Weller, Professor and Chair Electrical Engineering
Laser Annealing of Ferroelectric Thin Films for Functional Digitally-Manufactured Microwave Devices
The Weller group is investigating solutions for highly integrated front-end radiofrequency electronics for next generation machine-to-machine communications (Internet of Things, or IoT) that will operate in high multi-path and high-clutter environments. A technique being studied is direct integration of reconfigurable antenna systems onto integrated circuit modules using direct digital manufacturing. An example is a new tri-polar antenna design (Fig. 8, top) which has proven to be robust to high-multipath environments. This antenna system will be fabricated using a digital printing technique that combines fused deposition modeling of thermoplastic materials with micro-dispensing of conductive pastes (Fig. 8, bottom). In order to enable real-time reconfigurability, the antennas will be coupled with tunable matching circuits that utilize ferroelectric thin film materials. An important goal is to develop a process that is compatible with digital manufacturing and has temperatures well below the damage threshold of semiconductor devices. The approach is to employ in-situ laser annealing of the ferroelectric thin films. The REU student will be trained to perform SEM and XRD characterization of the laser-annealed ferroelectric films, as well as RF characterization to measure the electrical properties. The student will also work with graduate students to learn laser-processing techniques and gain experience with fused deposition modeling and micro-dispensing.
Figure 8. Package-mounted tri-polar antenna system (top); printer with micro-dispensing head for pastes, FDM head for plastics and a 10 W picosecond laser.