Mitun Das

In situ synthesized TiB-TiN reinforced Ti6Al4V alloy composite coatings: microstructure, tribological and in-vitro biocompatibility.

Wear resistant TiB-TiN reinforced Ti6Al4V alloy composite coatings were deposited on Ti substrate using laser based additive manufacturing technology. Ti6Al4V alloy powder premixed with 5wt% and 15wt% of boron nitride (BN) powder was used to synthesize TiB-TiN reinforcements in situ during laser deposition. Influences of laser power, scanning speed and concentration of BN on the microstructure, mechanical, in vitro tribological and biological properties of the coatings were investigated. Microstructural analysis of the composite coatings showed that the high temperature generated due to laser interaction with Ti6Al4V alloy and BN results in situ formation of TiB and TiN phases. With increasing BN concentration, from 5wt% to 15wt%, the Youngs modulus of the composite coatings, measured by nanoindentation, increased from 170±5GPa to 204±14GPa. In vitro tribological tests showed significant increase in the wear resistance with increasing BN concentration. Under identical test conditions TiB-TiN composite coatings with 15wt% BN exhibited an order of magnitude less wear rate than CoCrMo alloy-a common material for articulating surfaces of orthopedic implants. Average top surface hardness of the composite coatings increased from 543±21HV to 877±75HV with increase in the BN concentration. In vitro biocompatibility and flow cytometry study showed that these composite coatings were non-toxic, exhibit similar cell-materials interactions and biocompatibility as that of commercially pure titanium (CP-Ti) samples. In summary, excellent in vitro wear resistance, high stiffness and suitable biocompatibility make these composite coatings as a potential material for load-bearing articulating surfaces towards orthopaedic implants.

Microstructure and thermo mechanical properties of a talc doped stoneware composition containing illitic clay

The influence of talc on the thermo mechanical properties and microstructure of a stoneware composition containing illitic clay has been studied. It has been observed that there is an optimum addition of talc/feldspar combination to reach proper vitrification at a relatively lower temperature. The addition of 3 mass% talc resulted in increased flexural strength (69.7 MPa at 1200 °C), decreased water absorption value (0.28%) and increased relative density (94.83%). Decrease in residual quartz content with progressive addition of talc led to decrease in percent thermal expansion upto 3 mass% talc addition, beyond which reverse trend was observed due to increased proportion of the high expansion glassy phase. Addition of talc had little effect on the mullite content of the fired body. The decrease of sintering temperature of bodies containing more than 3 mass% talc led to enlargement of pores which is responsible for decrease in the fired MOR of the matured specimens.

Laser surface modification of 316 L stainless steel with bioactive hydroxyapatite

Laser-engineered net shaping (LENS™), a commercial additive manufacturing process, was used to modify the surfaces of 316 L stainless steel with bioactive hydroxyapatite (HAP). The modified surfaces were characterized in terms of their microstructure, hardness and apatite forming ability. The results showed that with increase in laser energy input from 32 J/mm(2) to 59 J/mm(2) the thickness of the modified surface increased from 222±12 μm to 355±6 μm, while the average surface hardness decreased marginally from 403±18 HV0.3 to 372±8 HV0.3. Microstructural studies showed that the modified surface consisted of austenite dendrites with HAP and some reaction products primarily occurring in the inter-dendritic regions. Finally, the surface-modified 316 L samples immersed in simulated body fluids showed significantly higher apatite precipitation compared to unmodified 316 L samples.

Microstructure and corrosion behavior of laser processed NiTi alloy

Laser Engineered Net Shaping (LENS™), a commercially available additive manufacturing technology, has been used to fabricate dense equiatomic NiTi alloy components. The primary aim of this work is to study the effect of laser power and scan speed on microstructure, phase constituents, hardness and corrosion behavior of laser processed NiTi alloy. The results showed retention of large amount of high-temperature austenite phase at room temperature due to high cooling rates associated with laser processing. The high amount of austenite in these samples increased the hardness. The grain size and corrosion resistance were found to increase with laser power. The surface energy of NiTi alloy, calculated using contact angles, decreased from 61 mN/m to 56 mN/m with increase in laser energy density from 20 J/mm(2) to 80 J/mm(2). The decrease in surface energy shifted the corrosion potentials to nobler direction and decreased the corrosion current. Under present experimental conditions the laser power found to have strong influence on microstructure, phase constituents and corrosion resistance of NiTi alloy.

Effect of hydroxyapatite particle size, morphology and crystallinity on proliferation of colon cancer HCT116 cells.

The aim of the present work is to chemically and physically characterize the synthesized Hydroxyapatite (HAp) micro and nanoparticles and to explore the inhibitory effect of nano-HAps on the in vitro growth of human colon cancerous cells HCT116. HAp powder was synthesized using three different routes to achieve micro and nanosized powders, with different morphologies and crystallinity. The synthesized powders were characterized using X-ray diffraction, FTIR spectroscopy and scanning electron microscope. The results showed that the average crystallite size of HAp powder varies from 11nm to 177nm and respective crystallinity of powder found to be in the range of 0.12 and 0.92. The effect of these physico-chemical properties of HAp powders on human colon cancer HCT116 cells inhibition was determined in vitro. It was found that decreasing the HAp powder crystallite size between 11nm and 22nm significantly increases the HCT116 cell inhibition. Our results demonstrate that apart from HAp powder size their crystallinity and morphology also play an important role in cellular inhibition of human colon cancer cells.

Fabrication of Biomedical Implants using Laser Engineered Net Shaping (LENS

There has been significant research, understanding of musculoskeletal disorders, but the development of suitable bone replacement materials for load-bearing applications is still lacking. Commercially available load-bearing implants/materials differ significantly from the natural host tissues in several aspects such as macro/microstructures, mechanical, physical and chemical properties. These differences limit the effectiveness of implants’ biological repair capability and longevity. One approach to enhance the cellular response and tissue integration of metal implants is to design and fabricate novel porous biomaterials that closely resemble the architecture and properties of natural bone tissue. In this article, we review application of Laser Engineered Net Shaping (LENS™) - an additive manufacturing process developed at Sandia National Laboratories, in developing materials/structures for load bearing implant application to enhance their in vivo life time. It has been established that LENS™ process is capable of fabricating near net shaped metallic implants with tailored porosity that can eliminate stress shielding issue associated with fully dense implants. Similarly, LENS™ is a potential technique to create compositionally and/or structurally graded implants. Further, functionally graded hard coatings have been developed via LENS™ to minimize the wear induced osteolysis. Finally, mono-block or unitized structures such as functionally graded CoCrMo or TiB-TiN coating on porous Ti6Al4V can also be fabricated using LENS™. In summary, the combination of novel designs and freeform fabrication capability of LENS process might have significant effect on development of novel implants/structures using varieties of metallic/ceramic biomaterials with tailored mechanical and biological properties.

Current advances in enhancement of wear and corrosion resistance of titanium alloys – a review

Titanium alloys have created a biomedical revolution in the past three decades and several research works are being carried out globally to combat the day to day challenges posed by the biomedical industries to meet the needs of a patient-friendly implant. Enhancement of corrosion and wear resistance of titanium alloys serve as the major treat for the stability of implant material after implantation. These problems could be overcome through various objectives, one among them being alloying titanium with non-toxic β-stabilizer elements to both increase the surface-related properties and improve biocompatibility. Other objectives include surface engineering methods such as coating, oxidation, nanograined surface and laser texturing. Overall, in this article an attempt has been made to bring out the current advances in the development of highly stable Ti-alloys with superior corrosion and wear resistance through various processes has been reviewed in detail.

Additive Manufacturing of Co-Cr-Mo Alloy: Influence of Heat Treatment on Microstructure, Tribological, and Electrochemical Properties

Co-Cr-Mo alloy samples, fabricated using Laser Engineered Net Shaping – a laser based additive manufacturing technology, have been subjected heat treatment to study its influence on microstructure, wear and corrosion properties. Following L9 Orthogonal array of Taguchi method, the samples were solutionized at 1200oC for 30, 45 and 60 min followed by water quenching. Ageing treatment was done at 815oC and 830oC for 2, 4 and 6 h. Heat treated samples were evaluated for their microstructure, hardness, wear resistance and corrosion resistance. The results revealed that highest hardness of 512 ± 58 Hv and wear rate of 0.90 ± 0.14 × 10-4 mm3/N.m can be achieved with appropriate post-fabrication heat treatment. ANOVA and grey relational analysis on the experimental data revealed that the samples subjected to solution treatment for 60 min, without ageing, exhibit best combination of hardness, wear and corrosion resistance.

Synthesis of boron nitride from boron containing poly(vinyl alcohol) as ceramic precursor

A ceramic precursor, prepared by condensation reaction from poly(vinyl alcohol) (PVA) and boric acid (H3BO3) in 1:1, 2:1 and 4:1 molar ratios, was synthesized as low temperature synthesis route for boron nitride ceramic. Samples were pyrolyzed at 850°C in nitrogen atmosphere followed by characterization using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD).

Understanding compressive deformation behavior of porous Ti using finite element analysis

In the present study, porous commercially pure (CP) Ti samples with different volume fraction of porosities were fabricated using a commercial additive manufacturing technique namely laser engineered net shaping (LENS™). Mechanical behavior of solid and porous samples was evaluated at room temperature under quasi-static compressive loading. Fracture surfaces of the failed samples were analyzed to determine the failure modes. Finite Element (FE) analysis using representative volume element (RVE) model and micro-computed tomography (CT) based model have been performed to understand the deformation behavior of laser deposited solid and porous CP-Ti samples. In vitro cell culture on laser processed porous CP-Ti surfaces showed normal cell proliferation with time, and confirmed non-toxic nature of these samples.