Kakoli Das

TiO2 nanotubes on Ti: Influence of nanoscale morphology on bone cell–materials interaction

Ti being bioinert shows poor bone cell adhesion with an intervening fibrous capsule. Ti could be made bioactive by several methods including growing in situ TiO2 layer on Ti-surface. TiO2 nanotubes were grown on Ti surface via anodization process and the bone cell-material interactions were evaluated. Human osteoblast cell attachment and growth behavior were studied using an osteoprecursor cell line for 3, 7, and 11 days. An abundant amount of extracellular matrix (ECM) between the neighboring cells was noticed on anodized nanotube surface with filopodia extensions coming out from cells to grasp the nanoporous surface of the nanotube for anchorage. To better understand and compare cell-materials interactions, anodized nanoporous sample surfaces were etched with different patterns. Preferential cell attachment was noticed on nanotube surface compare to almost no cells in etched Ti surface. Cell adhesion with vinculin adhesive protein showed higher intensity, positive contacts on nanoporous surface and thin focal contacts on the Ti-control. Immunochemistry study with alkaline phosphatase showed enhanced osteoblastic phenotype expressions in nanoporous surface. Osteoblast proliferation was significantly higher on anodized nanotube surface. Surface properties changed with the emergence of nanoscale morphology. Higher nanometer scale roughness, low contact angle and high surface energy in nanoporous surface enhanced the osteoblast-material interactions. Mineralization study was done under simulated body fluid (SBF) with ion concentration nearly equal to human blood plasma to understand biomimetic apatite deposition behavior. Although apatite layer formation was noticed on nanotube surface, but it was nonuniform even after 21 days in SBF.

Surface Coatings for Improvement of Bone Cell Materials and Antimicrobial Activities of Ti Implants

Ti surface was modified to simultaneously improve bone cell materials and antimicrobial activities. Titanium surface was first anodized in sodium fluoride and sulfuric acid electrolytic solution to form titania nanotube on the surface to improve the biocompatibility of the surface. Silver was electrodeposited on the titania nanotube surface at 5 V. Silver added titania nanotube surface was tested for compatibility with bone-cell materials interactions using human osteoblast bone cells. The antibacterial effect was studied using Pseudomonas aeruginosa. Our results show that silver-treated titania nanotube surface may provide antibacterial properties to prevent implants against postoperative infections without interference to the attachment and proliferation of bone tissue on titanium, which is commonly used in dental and orthopedic surgical procedures.

Application of fused deposition in controlled microstructure metal‐ceramic composites

Purpose – Al‐alumina interconnected phase composites were processed using the direct fused deposition process. These materials with tailored microstructures can find applications as structural materials with gradient properties.Design/methodology/approach – In this process, feedstock material with fused silica as a starting material was compounded at a high shear mixer and then extruded as a filament using a single screw extruder. Extruded filaments were used with a commercial fused deposition modeler, FDM 1650, to process controlled porosity green ceramic structures. Porous green ceramic preforms were subjected to binder removal and sintering cycles in furnace air. Controlled porosity sintered ceramic structures were infiltrated with Al 5052 metal by pressureless reactive metal infiltration to form an in situ Al‐alumina structured composite.Findings – The main advantage for this approach is to control distribution of both metal and ceramic phases in the composite. During metal infiltration good bonding w...

Shock Wave Synthesis of Titanium Silicide (Ti5Si3) Part I: Effects of Impact Velocity, Milling Time and Compact Density

Ti‐Si systems undergo exothermic reactions, which can be used for self‐propagating high temperature synthesis (SHS) of starting powders. Using plate impact loading, titanium silicide (Ti5Si3) samples were synthesized in the present work. Effects of compact density, impact velocity, milling time were studied. Ti and Si powders were first ball‐milled in molar ratios of (Ti5Si3) and then compacted. Powders were ball‐milled for different time periods, 24h, 100h and 190h, and then compacted for different theoretical densities, 40%, 45%, 50% and 60%. Four rectangular cells were machined in a Cu target and these cells were filled with ball‐milled powders. Targets were impacted at different velocities, 250 m/s, 350 m/s and 450 m/s. All samples were recovered after the impact loading and analyzed. Phase analysis, microstructural analysis, microhardness measurements were carried out with recovered samples. Results indicate that lower compact density, higher milling time and higher shock velocity produced higher rea...

Shock Wave Synthesis of Titanium Silicide (Ti5Si3) Part II: Effect of Ceramic Fillers

Ti‐Si systems undergo exothermic reactions, which can be used for self‐propagating high temperature synthesis (SHS) of starting powders. Titanium silicide (Ti5Si3) powders were mixed with a ceramic‐filler and shock‐compressed in plate impact experiments. Effect of ceramic filler concentrations was examined. Mullite was used as an inert ceramic filler in different weight percentage (10, 20, 30) and mixed with ball‐milled (pre‐alloyed Ti5Si3) powders. Four rectangular cells were machined in a Cu target and these cells were filled with composite powders. Targets were impacted at different velocities, 250 m/s, 350 m/s and 450 m/s. All samples were recovered after impact loading and analyzed. Changes in impact velocity had a significant effect on the reaction kinetics. Increasing filler materials and decreasing milling time reduced the rate of reaction. Increasing mullite content decreased the reaction kinetics, but reduced the residual porosity in the dense compacts. Increase in mullite content also increased...