Devdas Pai

Magnesium incorporated chitosan based scaffolds for tissue engineering applications

Chitosan based porous scaffolds are of great interest in biomedical applications especially in tissue engineering because of their excellent biocompatibility in vivo, controllable degradation rate and tailorable mechanical properties. This paper presents a study of the fabrication and characterization of bioactive scaffolds made of chitosan (CS), carboxymethyl chitosan (CMC) and magnesium gluconate (MgG). Scaffolds were fabricated by subsequent freezing-induced phase separation and lyophilization of polyelectrolyte complexes of CS, CMC and MgG. The scaffolds possess uniform porosity with highly interconnected pores of 50–250 μm size range. Compressive strengths up to 400 kPa, and elastic moduli up to 5 MPa were obtained. The scaffolds were found to remain intact, retaining their original three-dimensional frameworks while testing in in-vitro conditions. These scaffolds exhibited no cytotoxicity to 3T3 fibroblast and osteoblast cells. These observations demonstrate the efficacy of this new approach to preparing scaffold materials suitable for tissue engineering applications.

Electrophoretic deposition of YSZ electrolyte coatings for SOFCs

The main purpose of this study was to create crack-free, thin-film electrolyte coatings for solid oxide fuel cells (SOFCs) at low cost. The electrophoretic deposition (EPD) technique was employed to prepare dense yttria-stabilized zirconia (YSZ) thin films on stainless steel and porous strontium-doped lanthanum manganite (LSM) substrates. The LSM substrates were produced by slurry casting and subsequent sintering. The suspensions of YSZ were prepared in pure acetylacetone, ethanol, and in mixtures of the two. The deposition experiments were performed with the YSZ suspensions in different solvents to examine the effects of the solvent on the EPD behavior. The effects of current density and powder concentration on the EPD rate were also studied. The deposited films were dried at room temperature and then sintered at high temperatures. The microstructures of the sintered coatings were observed with scanning electron microscopy. By using a partially sintered LSM substrate and an optimized set of deposition conditions, dense and continuous YSZ thin-film coatings with thicknesses less than 10 μm were achieved.

Effect of spacer layer thickness on magnetic interactions in self-assembled single domain iron nanoparticles

The magnetic characteristics of iron nanoparticles embedded in an alumina thin film matrix have been studied as a function of spacer layer thickness. Alumina as well as iron nanoparticles were deposited in a multilayered geometry using sequential pulsed laser deposition. The role of spacer layer thickness was investigated by making layered thin film composites with three different spacer layer thicknesses (6, 12, and 18nm) with fixed iron particle size of ∼13nm. Intralayer magnetic interactions being the same in each sample, the variation in coercivity and saturation magnetization is attributed to thickness dependent interlayer magnetic interactions of three types: exchange, strong dipolar, and weak dipolar. A thin film composite multilayer structure offers a continuously tunable strength of interparticle dipole-dipole interaction and is thus well suited for studies of the influence of interaction on the magnetic properties of small magnetic particle systems.

Nanoscratch behaviour, structure and nanoindentation of multilayer TiN/CrN coatings

The nanoscratch behaviour of TiN/CrN nanolaminates has been investigated in the present study. The critical load (LcL) during the loading process characterises the fracture resistance of the coating, whereas that during unloading (LcU), characterises the adhesion strength between the coating and the substrate. For all coatings, the nanoscratch profiles indicate three distinct regimes: elastic deformation, elastic?plastic deformation and delamination with material removal. Multilayer coatings show significantly higher critical loads than monolayer coatings. SEM characterisation indicates the cracking mechanisms are different for monolayer and multilayer coatings explaining why the multilayer coatings withstand higher critical loads.

Systematic studies on NI-YSZ anode material for Solid Oxide Fuel Cell (SOFCs) applications

The characteristics of the Ni/YSZ anode material for the solid oxide fuel cells (SOFCs) were investigated in order to study the relation between the porosity and the conductivity of the cell. The experiments were planned based on a response surface design (central composite design matrix). Porosity and conductivity measurements were performed on the sintered and reduced anode material. The results indicated that the porosity values got decreased by increasing sintering temperature values, while the conductivity values increase with increasing temperature. Higher sintering temperature helped in forming a better Ni-network along the structure, which improved the electrical conductivity of the Ni-YSZ anode cermet.

Nanomaterial-Based Electroanalytical Biosensors for Cancer and Bone Disease

With recent advances in novel nanomaterial development, electroanalytical biosensors are undergoing a paradigm shift. New nanomaterial-based electrochemical biosensors can detect specific biomolecules at previously unattainable ultra-low concentrations. This chapter lists the existing biosensor technologies, describes the mechanisms, and applications of two types of electroanalytical biosensors, and then identifies the barriers in developing these biosensors and concludes by illustrating how nanomaterials can help overcome these limitations. A key feature of the electrochemical impedance sensor is that biomolecules detection can occur in real time without any pre-labeling. Specifically, this chapter summarizes the state of knowledge of the impedance sensor as applied in cancer and bone disease studies, which are clinically relevant.

RSM-based optimisation for the processing of nanoparticulate SOFC anode material

The relationship between porosity and electronic conductivity of a Nickel-Yttria Stabilised Zirconia (Ni/YSZ) material was investigated using the Response Surface Methodology (RSM) technique. This advanced material is intended for use as the anode of a Solid Oxide Fuel Cell (SOFC). Tests were structured around a central composite design of experiments matrix. Ni/YSZ specimens were fabricated via a powder processing route, using precursor powders of nickel oxide (NiO) and YSZ, mixed with graphite that acts as a pore former. Porosity and conductivity measurements were performed on the material in the as-sintered stage as well as after the reduction process. Statistical analysis was performed using selected process parameters (sintering temperature and amount of graphite pore former) as input variables and porosity and conductivity as outputs. The contour plots obtained from the RSM technique were used to study the trend of porosity and conductivity. The results indicate that the porosity values decrease significantly beyond a certain sintering temperature, while the electronic conductivity increases significantly. A super-imposed porosity-conductivity contour plot was used to determine the optimal region for the desired porosity volume and conductivity value.

Process Optimization Studies on Ni-YSZ Anode Material for Solid Oxide Fuel Cell Applications

The characteristics of the Ni/YSZ anode material for the solid oxide fuel cells (SOFCs) were investigated in order to study the relation between the porosity and the conductivity of the cell. The nano-sized Yittria Stabilized Zirconia (YSZ) (∼ 60 nm), Nickel Oxide (NiO) (∼ 40 nm) and graphite (∼ 40 nm) particles were used as the raw materials. The graphite particles act as a pore former. The experiments were planned based on a response surface design (central composite design matrix). The graphite content and the sintering temperatures were varied based on the design chart, while the other variables like NiO/YSZ ratio, ball milling time, powder compaction pressure and reduction temperature values were fixed. Porosity and conductivity measurements were performed on the sintered and reduced anode material. The results indicated that the porosity values got decreased by increasing sintering temperature values, while the conductivity values were on the reverse scale. The conductivity values increase with increasing temperature. The scanning electron microscope (SEM) images showed that the sintering temperature had a visible impact on the microstructure. At elevated temperature, the microstructure showed visible particle growth and it formed a better Ni-network along the structure, compared to samples sintered at lower temperature. It is believed that the enhanced Ni-network at elevated temperature helps to increase the electrical conductivity of the Ni-YSZ anode cermet.© 2007 ASME

A Four Cell Decomposition Model for Unbalanced Woven Fabric Composites Subjected to Thermal-Mechanical Loading

The stress and strain fields predicted at a global structural level are unable to determine the damage and failure mechanisms at the constituent level and the resulting stiffness degradation. To establish a mapping relation between the global and constituent response parameters, a new four-cell micromechanics model has been developed for an unbalanced weave subjected to a thermal-mechanical loading. The thermal-mechanical mapping relations at different microstructural levels are derived based on the multicell homogenization, intercell compatibility conditions, and energy methods. The dual-function micromechanics model can not only characterize the effective thermal-mechanical properties of the unbalanced weave at a given constituent damage, but can also compute the stress and strain at each constituent. The calculated constituent stress and strain can be used in a mechanism-driven failure criterion to predict the failure mode, failure sequence, and the synergistic interaction that leads to global stiffness degradation and the final rupture. The accuracy and the dual function of the developed micromechanics model are demonstrated with its application to a balanced plain weave, an unbalanced plain weave, and failure mode simulation of a tensile coupon test.

Ionic Liquids Incorporating Nanomaterials as Lubricants for Harsh Environments

Ionic liquids are salts that are liquid at ambient temperatures, and they produce virtually no hazardous vapors. As lubricating liquids, ionic liquid lubricants are of interest for reducing wear in circumstances where conventional lubricants are impractical such as in aerospace applications and high temperature vacuum bearings. The synthetic flexibility of ionic liquids allows control of the liquidous temperature range, good polymer compatibility, and high thermal stability. In this paper, a variety of ionic liquids were synthesized to build a library for testing. The liquids were thermally characterized by DSC and TGA, and mechanically characterized by pin-on-disk and 4-ball testing. Several chiral ionic liquids were synthesized as candidates for MEMS testing. The chiral nature of the liquids should help prevent crystallization in MEMs applications. Additionally, nanomaterials incorporated into the lubricants imparted lower friction coefficients and enhanced thermal stability.Copyright