Salil Desai

Material and process selection in product design using decision-making technique (AHP)

This paper presents a design for manufacture (DFM) paradigm by applying a flexible decision-making technique, the analytic hierarchy process (AHP). A material and process selection engine (MPSE) that integrates multiple criteria is presented to assist designers and customers make judicious selections. The new approach applies an analytical hierarchy process to allocate weights (order ranking) to the respective alternatives and has been found to provide good results. This determines the most effective alternative to the overall goal of material and process selection. This DFM-AHP adaptation provides flexibility to include multiple criteria for making design decisions and can be applied to the design of a variety of products. [Received: 11 November 2009; Revised: 25 August 2010; Accepted: 27 November 2010]

Metallic and Ceramic Biomaterials: Current and Future Developments

This chapter discusses the different types of biomaterials used for medical applications. Metallic, ceramic and nanomaterial based biomaterials are classified and described based on their physical and biocompatibility properties. Various applications of these biomaterials are discussed. State-of-the-art in biomaterial research is also introduced.

Direct writing of polymeric coatings on magnesium alloy for tracheal stent applications.

This paper investigates the direct-write inkjet method for depositing multi-layer coatings of biodegradable polymers on magnesium alloy surface. Immersion studies were conducted on Poly(lactic-co-glycolic) acid (PLGA), polycaprolactone (PCL), and poly-ester urethane urea (PEUU) coatings to determine the corrosion behavior of different samples based on their varying degradation properties. Using the inductively coupled plasma spectroscopy, a reduction in magnesium ion concentration was observed from the polymer-coated samples indicative of the lower corrosion rates as compared to the uncoated Mg substrate. Findings also showed correlation between the release of the magnesium ions and the health of fully differentiated normal human bronchial epithelial (NHBE) cells via evaluation of key biomarkers of inflammation and toxicity, cyclooxygenase-2 (COX-2) and lactate dehydrogenase (LDH), respectively. The induction of COX-2 gene expression was proportional to the increase in magnesium exposure. In addition, the release of higher magnesium content from uncoated and PCL polymer coated samples resulted in lower LDH activity based on the favorable response of the NHBE cells. PEUU and PLGA polymer coatings provided good barrier layer corrosion protection. This research evaluates candidate polymer coatings as a source for therapeutic agents and barrier layer to control the corrosion of magnesium alloys for tracheal applications.

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.

Computational fluid dynamics analysis of a direct write manufacturing process

This paper investigates the microdroplet generation mechanism in a direct write manufacturing process. A continuous inkjet (CIJ) method is utilised to deposit conductive nano particulate materials which can be used for building functionally gradient micro-sized features and devices. The spatial and temporal complexity of this process requires a computational modelling methodology to complement its experimental development. A CFD model is developed that is further validated using an ultra-high speed photography experimental setup. Input parameters such as fluid pressure, excitation frequency and voltage of the piezoelectric disc within the CIJ print head are varied to obtain trends for droplet volume and velocity. The dynamic pressure fluctuations due to acoustic waves generated during the piezoelectric disc excitation are studied. The effect of excitation parameters on satellite droplet formations is explained. These findings can be useful for the fabrication of freeform miniaturised devices in three dimensional spaces.

Molecular dynamics modeling of water nanodroplet spreading on topographically patterned silicon dioxide and silicon nitride substrates

This article reports the investigation of the spreading behavior of a nanodroplet in a droplet-based scalable nanomanufacturing process using Molecular Dynamics (MD) modeling and simulation. The objective of the study is to understand the effect of substrate topology on the wetting behavior of nanodroplets at the molecular level. A water nanodroplet spreading on silicon dioxide (SiO2) and silicon nitride (Si3N4) substrates with different topologies was studied. A migration of the SiO2–water system from a hydrophilic to hydrophobic interaction was observed with an increase in the aspect ratio of the patterns. In contrast, for the Si3N4–water system the fluid–structural interaction shifted from a hydrophobic to hydrophilic behavior for patterns with corresponding higher aspect ratios. The MD models were validated using molecular kinetic theory. This research provides a foundation for extending the functional range of substrate and solvent combinations by manipulating the substrate topology. The results of this work are expected to serve in the effective control of the hydrophobic/hydrophilic nature of the substrates and therefore aid in the prediction of nanofeature deposition in droplet-based micro/nanomanufacturing processes.

Direct writing of bio‐functional coatings for cardiovascular applications

The surface modification of metallic biomaterials is of critical importance to enhance the biocompatibility of surgical implant materials and devices. This article investigates the use of a direct-write inkjet technique for multilayer coatings of a biodegradable polymer (polyester urethane urea (PEUU)) embedded with an anti-proliferation drug paclitaxel (Taxol). The direct-write inkjet technique provides selective patterning capability for depositing multimaterial coatings on three-dimensional implant devices such as pins, screws, and stents for orthopedic and vascular applications. Drug release profiles were studied to observe the influence of drug loading and coating thickness for obtaining tunable release kinetics. Platelet deposition studies were conducted following ovine blood contact and significant reduction in platelet deposition was observed on the Taxol loaded PEUU substrate compared with the unloaded control. Rat smooth muscle cells were used for cell proliferation studies. Significant reduction in cell growth was observed following the release of anti-proliferative drug from the biopolymer thin film. This research provides a basis for developing anti-proliferative biocompatible coatings for different biomedical device applications.

Computational modeling of nanodroplet evaporation for scalable micro-/nano-manufacturing

This article focuses on the Molecular Dynamics (MD) modeling and simulation of a droplet-based scalable micro-/nano-manufacturing process. In order to aid precise control of the nanodroplet deposition on substrates, it is important to study its evaporation dynamics. Water and acetone are used as candidate fluids for the simulation based on the differences in their densities and volatilities. The MD simulations describe the effects of ambient conditions and fluid properties on the vaporization of the nanodroplets. Physical drop size reductions, volume slices at the cross section, and root mean square deviations are evaluated for different time scales and temperature ranges. The MD results show different evaporation rates and varied molecular dispersion patterns outside the droplet core region. These results are validated using standard molecular density values and a theoretical evaporation model for the respective fluids at given ambient conditions. This research provides a systematic understanding of droplet evaporation for predicting size variations in the nanoscale regime. These results are applicable to a direct-write droplet-based approach for depositing different nanopatterns on substrates.

Understanding conductivity in a composite resin with Single Wall Carbon Nanotubes (SWCNTs) using design of experiments

This paper investigates the effect of different factors that influence the electrical conductivity of a polymer based composite matrix loaded with Single Wall Carbon Nanotubes (SWCNTs). A design of experiment approach was employed to identify the significant factors such as composite processing method, SWCNT orientation and SWCNT weight percentages within a polysulphide resin. Preliminary electrical conductivity measurements indicated that the DC conductivity of the SWCNT dispersed polysulphide composite increases with the weight percentage of the SWCNT. Electrical conductivity data also varied based on the measurement location in the experiments. SEM studies indicated a variation in the distribution and orientation of SWCNT that changes the local electrical conductivity and were used to confirm the findings from the design of experiments. This combinatorial approach can assist in the design of polymer composites that are light weight, cost-effective and with enhanced electrical properties.

Multiphysics Modeling of a Piezoelectric Bimorph Disc in a Direct Write Fabrication Process

This paper investigates the behavior of the Piezoelectric (PZT) Bimorph disc within a Direct Write Fabrication Process. A modified Continuous Inkjet Print (CIJ) method is utilized to deposit a variety of conductive nano particulate materials for building miniaturized devices that can sustain harsh environments. Typical example includes the fabrication of electronic devices that are subject to severe fluctuations to temperature gradients. The spatial and temporal complexity of the novel CIJ based microfabrication process necessitates a computational solution to complement its experimental development. The interaction of three fields namely; electrostatic, structural and fluidic in the CIJ head are captured within a single Multiphysics model. A fluid-structure interaction (FSI) algorithm is used to capture the interaction of the PZT disc with the ink media. The effects of input parameters such as pressure, frequency and voltage on the PZT disc displacement are studied. Further, their effects on the transient pattern of the PZT displacement are explained. The findings from this research can be utilized to control the PZT disc displacements which, ultimately can be used to obtain an optimized and consistent drop break up for high precision printing.Copyright