Deepak Rajput

Solution-cast high-aspect-ratio polymer structures from direct-write templates.

This letter presents a novel strategy for template synthesis of polymer structures with laser machined substrates. User-designed patterns of submicrometer holes with aspect ratios >10:1 and depths >10 μm were produced by focusing 160 fs, 5.2 μJ laser pulses on the surface of fused silica with a high numerical aperture microscope objective. Some holes were enlarged by chemical etching. Polymer solutions were cast into the templates to create high-aspect-ratio polymer structures using replication. Engineered polymer structures prepared by this unique method are useful for a number of applications such as high surface area electrodes and biological substrates.

Cell interaction study method using novel 3D silica nanoneedle gradient arrays

Understanding cellular interactions with culture substrate features is important to advance cell biology and regenerative medicine. When surface topographical features are considerably larger in vertical dimension and are spaced at least one cell dimension apart, the features act as 3D physical barriers that can guide cell adhesion, thereby altering cell behavior. In the present study, we investigated competitive interactions of cells with neighboring cells and matrix using a novel nanoneedle gradient array. A gradient array of nanoholes was patterned at the surface of fused silica by single-pulse femtosecond laser machining. A negative replica of the pattern was extracted by nanoimprinting with a thin film of polymer. Silica was deposited on top of the polymer replica to form silica nanoneedles. NIH 3T3 fibroblasts were cultured on silica nanoneedles and their behavior was studied and compared with those cultured on a flat silica surface. The presence of silica nanoneedles was found to enhance the adhesion of fibroblasts while maintaining cell viability. The anisotropy in the arrangement of silica nanoneedles was found to affect the morphology and spreading of fibroblasts. Additionally, variations in nanoneedle spacing regulated cell-matrix and cell-cell interactions, effectively preventing cell aggregation in areas of tightly-packed nanoneedles. This proof-of-concept study provides a reproducible means for controlling competitive cell adhesion events and offers a novel system whose properties can be manipulated to intimately control cell behavior.

Cast carbide-metal composite components via laser based solid freeform fabrication

Tungsten-titanium-carbon base alloys are a promising candidate material for high performance propulsion systems, given their ability to form carbide-metal composites having a fine microstructure consisting of a dispersion of hard titanium carbide particles within a tough tungsten rich metal matrix. These high temperature, non-eroding materials can be produced by laser melting mixtures of tungsten and titanium carbide powders. The fabrication of cast carbide-metal composite components via laser based solid freeform fabrication techniques is currently being explored at the Center for Laser Applications (CLA) at the University of Tennessee Space Institute (UTSI). The microstructure and hardness of the fabricated cast carbide-metal composite components are presented in this paper.Tungsten-titanium-carbon base alloys are a promising candidate material for high performance propulsion systems, given their ability to form carbide-metal composites having a fine microstructure consisting of a dispersion of hard titanium carbide particles within a tough tungsten rich metal matrix. These high temperature, non-eroding materials can be produced by laser melting mixtures of tungsten and titanium carbide powders. The fabrication of cast carbide-metal composite components via laser based solid freeform fabrication techniques is currently being explored at the Center for Laser Applications (CLA) at the University of Tennessee Space Institute (UTSI). The microstructure and hardness of the fabricated cast carbide-metal composite components are presented in this paper.

The tower nozzle solid freeform fabrication technique

Purpose – The purpose of this paper is to develop a simple, easy to implement powder delivery strategy for solid freeform fabrication (SFF) processing.Design/methodology/approach – A specially designed “tower nozzle” located at the center of the processing area dispenses the feedstock powders continuously and uniformly onto the processing area, where powders accumulate progressively as a flat powder bed. During the dispensing, powders are selectively consolidated by melting and solidification using a laser beam which was scanned in a predefined pattern using a galvo‐mirror scan head.Findings – Experiments performed with AISI H13 steel show that the tower nozzle powder delivery strategy is suitable for SFF processing.Practical implications – Both powder delivery and laser consolidation are performed simultaneously and without interruption with simple apparatus. No powder delivery scrapers or rollers are used.Originality/value – The main characteristics of a prototype tower nozzle and the typical processing...

Transition metal coatings on graphite via laser processing

Graphite is a high temperature structural material due to its low specific gravity and high strength along with exceptional chemical and physicomechanical properties. However, graphite and other carbon materials suffer high temperature oxidation and are easily eroded by particle and gas streams. One of the ways to improve these properties is by making adherent protective coatings on carbon materials. The adherence of the coatings depends on their wettability and the difference in the values of their coefficient of thermal expansion with that of the carbon material. The transition metals have outstanding ability to combine strongly with carbon due to their partly-filled d-orbitals and ability to form strong covalent bonds. Hence, transition metals can be used to make coatings on graphite. In this paper we have deposited titanium, zirconium, and niobium coatings on graphite using a fiber laser. The coatings have been characterized using scanning electron microscope (SEM), Knoop’s hardness, X-ray diffraction, and secondary ion mass spectrometer (SIMS). A one-dimensional finite element heat transfer model of titanium coating on graphite was prepared and experimentally validated.Graphite is a high temperature structural material due to its low specific gravity and high strength along with exceptional chemical and physicomechanical properties. However, graphite and other carbon materials suffer high temperature oxidation and are easily eroded by particle and gas streams. One of the ways to improve these properties is by making adherent protective coatings on carbon materials. The adherence of the coatings depends on their wettability and the difference in the values of their coefficient of thermal expansion with that of the carbon material. The transition metals have outstanding ability to combine strongly with carbon due to their partly-filled d-orbitals and ability to form strong covalent bonds. Hence, transition metals can be used to make coatings on graphite. In this paper we have deposited titanium, zirconium, and niobium coatings on graphite using a fiber laser. The coatings have been characterized using scanning electron microscope (SEM), Knoop’s hardness, X-ray diffraction...