Scott Payne

Cobalt ferrite nanoparticles: Achieving the superparamagnetic limit by chemical reduction

An unanticipated superparamagnetic response has been observed in cobalt ferrite materials after thermal treatment under inert atmosphere. Cobalt ferrite particles were prepared via normal micelle precipitation that typically yields CoxFe3−xO4 nanoparticles (x=0.6−1.0). While samples thermally treated under oxygen show majority spinel phase formation, annealing in nitrogen gas yields materials consisting of Co-Fe alloy, FeS, and CoFe2O4 spinel. After thermal treatment, thermomagnetic studies reveal composition-insensitive, but highly treatment-sensitive, saturation magnetization, coercivity, blocking temperature, and Verwey transition temperature dependence. Extremely high saturation magnetization (159 emu/g) with low coercivity (31 Oe) was observed for one of the treated compositions, which drastically deviates from prototypical cobalt ferrite with large magnetocrystalline anisotropy. We attribute such unique magnetic response to Co-Fe alloy coexisting with FeS and CoFe2O4 spinel where the diameter of the...

Vesicular delivery of crystalline calcium minerals to ECM in biomineralized nanoclay composites

The mechanisms of mineralization and new bone formation were explored in newly formed extracellular matrix in a nanoclay based composite. Nanoclay films were prepared by intercalating the clays with amino acids and using the amino acids for mineralization of hydroxyapatite. The biomineralized hydroxyapatite (HAP) inside nanoclay galleries or in situ HAP/clay was further used to make films (substrates) using polycaprolactone (PCL) that were seeded with mesenchymal stem cells in a two-stage seeding process. SEM imaging experiments performed on PCL/in situ HAPclay composite films seeded with human MSCs indicated formation of matrix vesicles. The vesicles appear to emerge from the cells that are adhered to the nanoclay HAP films and also deposited in the extracellular space. Vesicles are also observed to be embedded in the cells or under the surface of cells. Crystalline structures with Ca and P were found inside vesicles. The Ca/P ratios obtained using energy dispersive spectroscopy indicate values ranging from below 0.7 to the stoichiometric HAP value of 1.67. The Ca/P ratios were obtained to be closer to the stoichiometric value for single seeding experiments as compared to the double seeding experiments indicating more new bone formation in double seeding experiments. New bone formation with bone mimetic mineralization is thus observed on the in situ HAP nanoclay PCL samples. Hence the PCL/in situ HAPclay composites besides being osteoinductive are also capable of providing a favorable micro-environment for cell dependent processes involved in bone mineral formation.

Freeze-Fracture of Infected Plant Leaves in Ethanol for Scanning Electron Microscopic Study of Fungal Pathogens

Fungi often are found within plant tissues where they cannot be visualized with the scanning electron microscope (SEM). We present a simple way to reveal cell interiors while avoiding many common causes of artifact. Freeze-fracture of leaf tissue using liquid nitrogen during the 100% ethanol step of the dehydration process just before critical point drying is useful in exposing intracellular fungi to the SEM.

Thin films by metal-organic precursor plasma spray

While most plasma spray routes to coatings utilize solids as the precursor feedstock, metal-organic precursor plasma spray (MOPPS) is an area that the authors have investigated recently as a novel route to thin film materials. Very thin films are possible via MOPPS and the technology offers the possibility of forming graded structures by metering the liquid feed. The current work employs metal-organic compounds that are liquids at standard temperature-pressure conditions. In addition, these complexes contain chemical functionality that allows straightforward thermolytic transformation to targeted phases of interest. Toward that end, aluminum 3,5-heptanedionate (Al(hd)3), triethylsilane (HSi(C2H5)3 or HSiEt3), and titanium tetrakisdiethylamide (Ti(N(C2H5)2)4 or Ti(NEt2)4) were employed as precursors to aluminum oxide, silicon carbide, and titanium nitride, respectively. In all instances, the liquids contain metal-heteroatom bonds envisioned to provide atomic concentrations of the appropriate reagents at th...

Probing electronic structure of biomineralized hydroxyapatite inside nanoclay galleries.

Hydroxyapatite, the most abundant mineral in the human body, is also an important component in design of biomaterials for bone tissue regeneration. Synthetic hydroxyapatite mineralized in the laboratory often does not exhibit the same biological and morphological properties of biogenic hydroxyapatite in human bone. A biomimetic hydroxyapatite structure is synthesized using biomineralization routes inside the clay galleries of montmorillonite clay. Amino acids are used to modify the clay galleries. These amino acids are used to mineralize hydroxyapatite. The molecular interactions between nanoclay, modifiers inside nanoclay (amino acids) and biomineralized hydroxyapatite result in unique morphology, structure and stoichiometry of the biomineralized hydroxyapatite. Prior studies have indicated that this biomineralized hydroxyapatite inside nanoclay galleries is an effective component of tissue engineering bone scaffolds that elicits an optimal biological response from human mesenchymal stem cells. Here, a detailed electron energy-loss spectroscopy (EELS) study is reported that elucidates the differences in hydroxyapatite, biomineralized hydroxyapatite and β-tricalcium phosphate (β-TCP). Comparison of EELS low-loss transitions and energy loss near-edge structure (ELNES) of P-L2,3 edges for these three compounds is done to determine if there are differences in their electronic structures. These changes observed experimentally are compared with prior predictions and simulations using molecular dynamics studies. The simulations predict attractive and repulsive interactions between phosphate, modified MMT clay and aminovaleric acid (amino acid) molecules. Kramers-Kronig analysis is performed on the loss spectra obtained to yield the real and imaginary parts of the dielectric function of the apatites (ε1 and ε 2). We have also used the ε2 spectra obtained to calculate the AC conductivity spectra for the apatites. This study represents a unique experimental probe into molecular interactions in complex biomineralized hydroxyapatite structures. The small changes observed in the energy loss spectra appear to play important biological roles in biomineralized hydroxyapatite such as the ability to differentiate human mesenchymal stem cells into osteoblasts without growth media.