Keisha B. Walters

The effects of water and microstructure on the mechanical properties of bighorn sheep (Ovis canadensis) horn keratin

The function of the bighorn sheep horn prompted quantification of the various parametric effects important to the microstructure and mechanical property relationships of this horn. These parameters included analysis of the stress-state dependence with the horn keratin tested under tension and compression, the anisotropy of the material structure and mechanical behavior, the spatial location along the horn, and the wet-dry horn behavior. The mechanical properties of interest were the elastic moduli, yield strength, ultimate strength, failure strain and hardness. The results showed that water has a more significant effect on the mechanical behavior of ram horn more than the anisotropy, location along the horn and the type of loading state. All of these parametric effects showed that the horn microstructure and mechanical properties were similar to those of long-fiber composites. In the ambient dry condition (10 wt.% water), the longitudinal elastic modulus, yield strength and failure strain were measured to be 4.0 G Pa, 62 MPa and 4%, respectively, and the transverse elastic modulus, yield strength and failure strain were 2.9 GPa, 37 MPa and 2%, respectively. In the wet condition (35 wt.% water), horn behaves more like an isotropic material; the elastic modulus, yield strength and failure strain were determined to be 0.6G Pa, 10 MPa and 60%, respectively.

SILAC-Based Quantitative Proteomic Analysis of Human Lung Cell Response to Copper Oxide Nanoparticles

Copper (II) oxide (CuO) nanoparticles (NP) are widely used in industry and medicine. In our study we evaluated the response of BEAS-2B human lung cells to CuO NP, using Stable isotope labeling by amino acids in cell culture (SILAC)-based proteomics and phosphoproteomics. Pathway modeling of the protein differential expression showed that CuO NP affect proteins relevant in cellular function and maintenance, protein synthesis, cell death and survival, cell cycle and cell morphology. Some of the signaling pathways represented by BEAS-2B proteins responsive to the NP included mTOR signaling, protein ubiquitination pathway, actin cytoskeleton signaling and epithelial adherens junction signaling. Follow-up experiments showed that CuO NP altered actin cytoskeleton, protein phosphorylation and protein ubiquitination level.

Janus magnetic nanoparticles with a bicompartmental polymer brush prepared using electrostatic adsorption to facilitate toposelective surface-initiated ATRP.

Utilizing the inherent negative charge of mica surfaces, amine-functionalized magnetic nanoparticles (Fe3O4/NH2) were electrostatically adsorbed onto the mica such that surface-initiated ATRP could be used to grow poly(n-isopropylacrylamide) (PNIPAM) from the exposed hemisphere. By reducing the solution pH, a positive charge generated on the mica was used to release the nanoparticles from the substrate. A second ATRP reaction was carried out to grow poly(methacrylic acid) (PMAA) from the initiated surfaces. As a result, the Fe3O4/NH2 core has a polymer shell with one hemisphere PMAA and the other hemisphere PNIPAM-b-PMAA resulting in the PMAA-Fe3O4-PNIPAM-b-PMAA bicompartmental polymer Janus nanoparticles. Elemental and functional group compositions were confirmed using ATR-FTIR, XPS, and EDS. Imaging with AFM, SEM, and TEM showed the evolution of the Janus nanoparticle morphology. This study demonstrates a facile and innovative scheme involving a noncovalent solid protection technique combined with sequential, surface-confined controlled radical polymerizations for the production of multicomponent nanocomposites.

Pickering emulsions stabilized by palygorskite particles grafted with pH-responsive polymer brushes

Poly(2-(diethylamino)ethyl methacrylate (PDEAEMA) was grafted from the surface of palygorskite (PAL) particulates via Cu(0) radical polymerization to form PAL–PDEAEMA nanocomposites. The successful grafting was confirmed by Fourier transform infrared (FT-IR), thermal gravimetric analysis (TGA), and elemental analysis (EA). Water (pH 9)/toluene (W/O) Pickering emulsions stabilized by PAL–PDEAEMA particles were prepared. Spherical emulsion droplets with absorbed small PAL–PDEAEMA aggregates on the interface were observed via scanning electron microscopy (SEM), polarizing optical microscopy (POM) and optical microscopy (OM). The size of the emulsion droplets was decreased with the increase of PAL–PDEAEMA particle concentrations, and reached a limited value at 2 wt%. By changing the pH of water (pH < 3), O/W Pickering emulsions were formed by the same PAL–PDEAEMA particles. Moreover, W/O emulsion–de-emulsion–O/W emulsion transitions can be realized simply by adding HCl/NaOH, which can last at least 7 successive cycles. Therefore, a reversible Pickering emulsion system switched by pH can result on the basis of PAL–PDEAEMA particles.

Bioluminescent magnetic nanoparticles as potential imaging agents for mammalian spermatozoa

BackgroundNanoparticles have emerged as key materials for developing applications in nanomedicine, nanobiotechnology, bioimaging and theranostics. Existing bioimaging technologies include bioluminescent resonance energy transfer-conjugated quantum dots (BRET-QDs). Despite the current use of BRET-QDs for bioimaging, there are strong concerns about QD nanocomposites containing cadmium which exhibits potential cellular toxicity.ResultsIn this study, bioluminescent composites comprised of magnetic nanoparticles and firefly luciferase (Photinus pyralis) are examined as potential light-emitting agents for imaging, detection, and tracking mammalian spermatozoa. Characterization was carried out using infrared spectroscopy, TEM and cryo-TEM imaging, and ζ-potential measurements to demonstrate the successful preparation of these nanocomposites. Binding interactions between the synthesized nanoparticles and spermatozoon were characterized using confocal and atomic/magnetic force microscopy. Bioluminescence imaging and UV–visible-NIR microscopy results showed light emission from sperm samples incubated with the firefly luciferase-modified nanoparticles. Therefore, these newly synthesized luciferase-modified magnetic nanoparticles show promise as substitutes for QD labeling, and can potentially also be used for in vivo manipulation and tracking, as well as MRI techniques.ConclusionsThese preliminary data indicate that luciferase-magnetic nanoparticle composites can potentially be used for spermatozoa detection and imaging. Their magnetic properties add additional functionality to allow for manipulation, sorting, or tracking of cells using magnetic techniques.

Fetuin-A adsorption and stabilization of calcium carbonate nanoparticles in a simulated body fluid

Fetuin-A is a serum glycoprotein identified as a calcification inhibitor, and a key player in bone formation and human metabolic processes. A study on binding mechanisms of Fetuin-A with calcium carbonate nanoparticles in a simulated body fluid (DMEM) environment is presented. Observed interactions between Fetuin-A and the CaCO3 nanoparticles reveal an initial adsorption process, followed by a stabilization stage, and then a solubilization period for the Fetuin-A/CaCO3 complex. FTIR and XPS are used to monitor functional group and elemental composition changes during the initial adsorption process between Fetuin-A and the CaCO3 nanoparticles. Distinctive Fetuin-A/CaCO3 complex structures-also known as mineralo-protein particles-are imaged with TEM and SEM. DLS and UV-Vis methods are used to further characterize the in situ binding mechanisms. Results of this study can guide the design of complex organic-inorganic hybrid materials, improve current drug delivery methods, and provide insight in monitoring and controlling interactions between Fetuin-A and external calcium ions.

Electromagnetic induction by ferrofluid in an oscillating heat pipe

Thermal-to-electrical energy conversion was demonstrated using an oscillating heat pipe (OHP) filled with ferrofluid and equipped with an annular-type solenoid. The OHP was subjected to a 100 °C axial temperature difference allowing the ferrofluid to passively oscillate through the solenoid, thus accomplishing electromagnetic induction. The measured solenoid voltage consisted of aperiodic pulses with dominant frequencies between 2 and 5 Hz and peak-to-peak amplitudes approaching 1 mV. Despite exposure to the thermal and phase change cycling within the OHP, nanoparticle morphologies and magnetic properties of the ferrofluid remained intact. This energy harvesting method allows for combined thermal management and in-situ power generation.

Rheological characterization of mammalian lung mucus

Mammalian lung mucus is a complex fluid that demonstrates non-linear viscoelastic responses, strain-stiffening at low and strain-softening at large strain values, as measured using large amplitude oscillatory shear (LAOS) experiments. The mechanical properties of lung mucus reported here can be linked to high-strain rate physiological processes, such as coughing, and can guide drug delivery development.

pH Responsive Behavior of Fe3O4@PDEA-PEGMA Core-Shell Hybrid Magnetic Nanoparticles

Fe3O4@PDEA-PEGMA core-shell magnetic nanoparticles were prepared via surface-initiated atom transfer radical polymerization (ATRP). First, an ATRP initiator was immobilized onto the surface of Fe3O4 magnetic nanoparticles, then poly[2-(diethylamino)ethyl methacrylate] (PDEA) and poly(poly[(ethylene glycol) monomethacrylate]) (PEGMA) were grafted from the surface of the magnetic nanoparticles in succession. Each step of the reactions gave distinctive thermogravimetric analysis curves. Polymer shells cleaved from Fe3O4 core were measured by gel permeation chromatography, while its molecular weight was found to increase with successive polymerization (with a polydispersity of approximately 1.3–1.4). The architecture of the core-shell nanoparticles was confirmed by transmission electron microscopy. The Fe3O4@PDEA-PEGMA hybrid magnetic nanoparticles formed stable dispersions in H2O at low pH (pH < 6) and precipitated out at high pH (pH > 6). This pH transition behavior was also observed in dynamic light scattering experiments.

Constant pH simulations of pH responsive polymers

Polyacidic polymers can change structure over a narrow range of pH in a competition between the hydrophobic effect, which favors a compact state, and electrostatic repulsion, which favors an extended state. Constant pH molecular dynamics computer simulations of poly(methacrylic acid) reveal that there are two types of structural changes, one local and one global, which make up the overall response. The local structural response depends on the tacticity of the polymer and leads to different cooperative effects for polymers with different stereochemistries, demonstrating both positive and negative cooperativities.