REU Site Program in Functional Materials CU-Boulder

RESEARCH PROJECTS
The research projects offered to the student participants span the field of advanced materials research. The following brief descriptions of representative research projects provide a glimpse into the type of opportunities available to the participants.

Bioinspired hydrogels for cartilage tissue engineering (Prof. Anseth) Upon injury, cartilage has a limited ability to repair itself due to its avascular and aneural nature. Therefore, numerous efforts have investigated ways to regenerate new living cartilage tissue by developing biodegradable, biocompatible scaffolds to facilitate chondrocyte attachment and provide an environment that promotes cell proliferation and extracellular matrix formation. This project aims to synthesize biologically inspired chemistries to create multifunctional macromers that can be photopolymerized to form hydrogels and simultaneously encapsulate cells. The importance of the scaffold chemistry, mechanics, and degradation rate on the evolving cartilaginous tissue formation will be investigated.

Novel Thiol and Vinyl Monomers for Advanced Thiol-Ene Polymer Applications (Prof. Bowman) Thiol-ene photopolymerizations offer a unique advantage to high temperature coating, adhesive, and dental material applications due fast polymerization kinetics, lack of oxygen inhibition, high degradation temperatures, and a reduction in polymerization shrinkage and shrinkage-induced stress. However, application of thiol-ene resins is limited by the chemistry of thiol and vinyl monomers commercially available. Currently, few multifunctional thiol or vinyl monomers with rigid backbones are available commercially. This project will primarily focus on developing novel multifunctional thiol and vinyl monomers using isocyanate-alcohol additions and carboxylic acid – alcohol condensations. The aim of this project is to synthesize monomers that while mechanically rigid, are readily photopolymerized at room or body temperature without the use of additional solvents.

Photopolymerization for signal amplification in the detection of molecular recognition (Prof. Bowman) Molecular recognition events such as the hybridization of a nucleic acid to a probe oligonucleotide or the binding of an antigen to an antibody can be used in the identification of pathogens and disease states. Since nucleic acids or antigens of interest may be present in low levels in patient samples, it is necessary to employ a method of either target or signal amplification. We are investigating photopolymerization as a chemical analog to conventional biological amplification techniques. Briefly, we have synthesized molecules that couple the binding of multiple photoinitiators to a recognition event of interest. In the presence of monomers and light, these initiators can be used to grow a polymer that is visible by eye in cases where a recognition event has taken place. We have identified one organic monomer formulation that polymerizes within twenty minutes. We would like to identify others that are faster and also safer to work with; this goal will be the focus of an REU summer project.

Chondrocytes Encapsulated in Hydrogels for Cartilage Tissue Engineering (Prof. Bryant) Tissue engineering utilizes healthy cells distributed three-dimensionally within a biodegradable polymeric matrix known as a scaffold. We are particularly interested in designing scaffolds based on poly(ethylene glycol) (PEG) hydrogels for cartilage tissue engineering. Chondrocytes (the cells responsible for producing cartilage) sense mechanical loading through changes that occur in their tissue environment and respond by alterations in their cell signaling pathways and gene expression, which ultimately affect overall tissue composition. This process is known as mechanotransduction. We hypothesize that the PEG hydrogel exerts a strain on the encapsulated cells thus inducing their mechanotransduction pathways – a potentially powerful tool for fabricating scaffolds that when combined with additional external mechanical cues (such as an applied dynamic load) may promote functional tissue growth. This project will investigate the influence of hydrogel structure on the mechanotransduction pathways of chondrocytes.

Wet Particle Collisions (Prof. Davis) Particulate systems are prevalent in nature and in industries such as pharmaceutical, ceramics, cosmetics, food, plastics, fertilizers, detergents, filtration, and building material for earth based systems. Low-gravity applications include solids processing, mining of lunar and Martian soil, powdered food and drink, fluidized beds and filtration. The reduced role of gravity must be understood to improve current unit operations. The proposed project will target systems of particulates coated with thin layers of viscous liquids in environments that mimic microgravity conditions. A student on this project will perform various experiments and use photo imagery to capture the trajectories of collisions between wet particles. From the experimental images coefficients of restitution and critical impact velocities can be calculated. This goal of these experiments is to gain a better understanding of the physical mechanisms governing wet particulate flows in a low-gravity environment.

Particle and Fluid Transport In Surface-Modified Microfluidic Channels (Profs. Davis/Anseth) Microfluidic devices are used to perform various types of biological analyses, from DNA analysis to cell sorting, quickly, cheaply, and portably. Particles and fluid travel differently in microchannels than on the macro scale (e.g. turbulence, often used for mixing, is absent), and understanding these differences is vital to optimization of microfluidic devices. Physico-chemical modifications of the channel surface (such as chemical functionality or surface charge) can affect the observed flows. A student on this project will use video microscopy and particle tracking techniques to investigate and quantify the motion of polymer particles and various cell lines in microfluidic channels with different types of surface modifications. This research will lead to a better understanding of how interactions between particles/cells and channel surfaces can influence their motion in microfluidic channels.

Adsorption of Liquid Mixtures in Zeolite Crystals (Profs. Falconer/Noble) Zeolites are crystalline structures with uniform, molecular-sized pores, and we use them as building blocks to prepare zeolite membranes that exhibit high selectivity for separations. To understand the behavior of zeolite membranes and to improve their separation ability, the processes that control permeation rates (adsorption and diffusion) must be understood. This project will measure adsorption of organic mixtures in zeolite crystals so mathematical models of pervaporation can be used to predict separation. We recently developed a gravimetric and volumetric method with GC analysis to measure adsorption of liquid mixtures in zeolite crystals. This project will measure adsorption of several organic mixtures (xylenes, alkanes/alkenes) on two types of zeolites. Comparisons will be made to vapor-liquid equilibrium calculated from the HYSIS simulator, and adsorption isotherms will be modeled as Langmuir adsorption with two adsorption sites.

High Flux Zeolite Membranes for Pervaporation (Profs. Falconer/Noble) Zeolite membranes consist of continuous layers of intergrown zeolite crystals prepared on porous supports. Typical membranes are 20-100 µm thick. These membranes have significant advantages over polymer membranes because they are stable to high temperatures and in the presence of reactive chemicals. Their pores are of molecular dimensions and uniform in size. We propose to use newly-developed procedures to prepare thin membranes using seeding of nanocrystals and masking of the porous supports. The thinner membranes are expected to have much higher fluxes than current membranes. These membranes will be used in pervaporation to determine their ability to separate organics from aqueous solution as a function of temperature and concentration. The separation selectivity will be correlated with the fugacity of the organic in the feed to develop predictive ability.

Nanocoatings on Particles Using Atomic Layer Deposition (Prof. George) The surface chemistry of fine particles can be controlled independently of bulk properties if nanometer scale films can be deposited on the particles. Nanocoatings on particles are important to change the chemical properties, to define a particular functionality and to add protection and stability. Sub-micron sized nanoparticles are particularly difficult to coat because of their tendency to form aggregates. However, such coatings can be achieved using atomic layer deposition (ALD) where self-limiting sequential surface chemistry is carried out. An ALD fluidized bed reactor is available for the nano coating of fine particles. The particles can be characterized by transmission electron microscopy and x-ray photoelectron spectroscopy. Applications exist in numerous businesses including electronics, medical, advanced materials, and defense, among others
We have pioneered new atomic layer deposition (ALD) methods that have shown great potential in allowing very conformal coatings to be deposited on particles. ALD is based on sequential, self-limiting surface chemical reactions. These sequential reactions are performed with gas phase precursors that are able to coat particles very uniformly provided that the particles are agitated during deposition. This agitation is provided with a new rotary drum reactor that rotates in vacuum and its porous stainless steel walls allow the gas phase reactants and products to diffuse in and out while the rotary drum is rotating to agitate the particles. We are currently working on the ALD of various metal and oxide nanocoatings on different inorganic and organic particles.
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Liquid-crystal read-outs for detection of molecular recognition events (Prof. Gill/Schwartz) The detection of molecular recognition events, such as DNA hybridization or antibody/antigen binding, is at the heart of molecular diagnostics and continues to enable the genomic and proteomic revolutions. Detection typically involves biomolecular “probes” with a radioactive or fluorescent “label". The elimination of these labels would not only decrease the cost of detection, but also permit new applications that require real-time detection. It was recently shown that the anchoring of liquid crystal molecules is modified by the adsorption of amphiphilic molecules at the water/liquid crystal interface; such changes are easily visualized using polarized light. This effect will be exploited to detect specific molecular recognition by using synthetic peptide-amphiphiles, which contain a sequence of amino acid residues that is recognized as a receptor by certain proteins.

Characterization of Polymerizable Nanoporous Lyotropic Liquid Crystal Membranes (Prof. Gin) Reverse Osmosis (RO) is used as a cost-effective technique for desalination and production of pure water for drinking and industrial applications. RO also plays an important role in military operations for on-site generation of pure water. Current commercial membranes suffer from low fluxes on account of their ‘non porous’ structure and are susceptible to severe degradation due to chlorine in the treated water, and fouling due to organic contaminants. Our novel lyotropic liquid crystal (LLC) membranes have ordered pores ca. 1-2 nm diameter and the membranes are resistant to chlorine degradation but suffer from lower flux and ionic rejection due to misaligned liquid crystal (LC) layers. This project involves study of the effect of solvent and the water concentration in the monomer solution on the permeate flux and ionic rejection of the final LLC membrane.

Mixing and Segregation in an Elutriating Fluidized Bed (Prof. Hrenya) Fluidized beds play a key role in the production of new materials, by facilitating a high level of mixing between solid and fluid reagents. In some applications, like in catalytic cracking, the material is allowed to exit the top of the reactor together with the flow (it is allowed to 'elutriate'). Elutriation can also be an undesirable side effect and yet, little fundamental understanding of this process is had presently. A student involved in this project will run experiments to determine the extent to which the two species of particles mix or segregate during operation, both by non-invasive optical methods and by applying soil-mechanics techniques to the sampling of a suddenly-stopped fluidized bed. From these measurements and from interaction with the two industrial partners with whom we colaborate on this project, the student will then contribute toward the refinement of numerical models that better predict the mix state of the reactor and the effects of this on elutriation rates.

Microparticle mediated delivery of IL10 for the treatment of chronic pain (Prof. Mahoney) Interleukin-10, an anti-inflammatory cytokine has achieved considerable interest as a therapeutic molecule for the treatment of pathological pain states in the spinal cord. Despite the promise of IL10 as a therapeutic molecule, the protein is rapidly degraded and high doses must injected multiple times in order to achieve a therapeutic effect. To be effective and safely used in humans, a chronic, localized method of delivery that can be administered to a patient in a single intervention is preferred. The focus of this work is to develop a polymer-based delivery technology that can be directly injected into the spinal CSF to provide sustained release of therapeutically active levels of IL10 for at least 90 days. A REU student working on this project will begin by preparing biodegradable microparticles that release Interleukin-10 protein or plasmid DNA. The student will also be responsible for characterizing and measuring the rate of IL-10 release from microparticles. Finally, the student will perform histological and biochemical assays on tissue samples derived from animals treated with delivery systems..

Gas Sensing Mechanism of Metal-Insulator-Semiconductor Devices (Prof. Medlin) As the importance of increasing energy efficiency and reducing emissions has grown, so too has the need for low-cost solid state chemical sensors for environmental and process monitoring. Metal-insulator-semiconductor (MIS) devices are a promising class of sensors that are highly responsive to hydrogen-containing gases. A typical MIS sensor structure consists of a catalytic metal gate deposited on a thin tunneling insulator that has been grown on a semiconductor substrate. Sensor response--which is measured as a voltage shift during gas exposure—is governed by the interplay between surface and subsurface-phase chemistry occurring on the metal film. This project will develop an improved understanding of this chemistry and determine the mechanisms by which material properties affect sensor response under conditions relevant to targeted applications.

Functionalized Ionic Liquids for Selective Gas Separations (Prof. Noble) We are using ionic liquids as a liquid membrane phase for gas separations. Ionic liquids have negligible vapor pressure and are thermally stable to high temperatures. The addition of functional complexation sites into the ionic liquid phase, either through covalent attachment to the liquid or as a dopant, can provide enhanced selectivity and flux for gas separations. We plan to evaluate several different ionic liquids and complexing agents for selective gas separations.

Fluidized bed drying for therapeutic proteins (Prof. Randolph) The recent rapid increase in protein-based pharmaceutical products on the market has resulted in new production bottlenecks. The time-intensive lyophilization process, for example, now can comprise up to 40% of the direct production cost for proteins. One alternative to conventional lyophilization is fluidized bed drying. In this process proteins are spray-frozen in liquid nitrogen, then dried at sub-zero temperatures in a fluidized bed. In our project we will measure mass and heat transfer coefficients, and also determine the effects of drying parameters on stability of a model antibody.

Self-assembled surface nanostructures (Profs. Schwartz/Gin) Continued miniaturization of devices will require novel methods for creating organized patterns (e.g. arrays of dots and lines) with length scales of 2-100 nm for use as templates or masks. Self-organized molecular assemblies represent one strategy for creating such patterns. In self-assembled monolayers (SAMs) for example, adsorbate molecules spontaneously assemble on the surface of a particular material to form a well-organized molecular film. The Schwartz group has recently shown that the SAM strategy can be extended to produce molecular films with periodic topographic patterns (with spacings of 2-5 nm) by using molecules with a particular shape. This project will explore the types of patterns that can be produced and how the distance between neighboring features can be predictably varied.

Effect of Photocuring Protocol on Polymer Structure and Properties (Prof. Stansbury) Photocuring is widely used in industrial and biomedical polymer applications as diverse as protective coatings, adhesives, stereolithography, contact lens production and dental fillings. This project will focus on the potential to use photo-induced variations in the polymerization reaction profile as a means to alter polymer density and/or modulus. A student working on this project will photocure dimethacrylate monomers to form crosslinked polymers using a variety of irradiation protocols. Conversion will be controlled and measured. The time dependent characterization of polymer density and modulus for the polymers generated in this manner will then be related to dynamic studies of stress development in these materials.

Synthesis of Passivated Ultrafine Metal Particles Using Atomic Layer Deposition (Prof. Weimer) Ultrafine metal oxalate particles will be used to produce oxidation-resistant metal particles. Decomposition processing of the oxalate precursor will be carried out in a fluidized bed reactor. The resulting metal particles will be coated in-situ with ceramic nanolayers using Atomic Layer Deposition. This technique alters the surface of the particles while keeping their initial bulk properties. Coated particles will be tested at different temperatures to determine their resistance to oxidation using a Thermo-Gravimetric Analyzer. Particles will be characterized using Scanning and Transmission Electron Microscopy, Particle Size Distribution, Surface Area, X-Ray Photoelectron Spectroscopy and Induced-Coupled Plasma Atomic Emission Spectroscopy. Applications for nanocoated particles range from targeted drug delivery and microelectronics to catalysis and environmental control.

		A National Science Foundation REU site program