Puneet Gill

A Comparative Biocompatibility Analysis of Ternary Nitinol Alloys

Nitinol alloys are rapidly being utilized as the material of choice in a variety of applications in the medical industry. It has been used for self-expanding stents, graft support systems, and various other devices for minimally invasive interventional and endoscopic procedures. However, the biocompatibility of this alloy remains a concern to many practitioners in the industry due to nickel sensitivity experienced by many patients. In recent times, several new Nitinol alloys have been introduced with the addition of a ternary element. Nevertheless, there is still a dearth of information concerning the biocompatibility and corrosion resistance of these alloys. This study compared the biocompatibility of two ternary Nitinol alloys prepared by powder metallurgy (PM) and arc melting (AM) and critically assessed the influence of the ternary element. ASTM F 2129-08 cyclic polarization in vitro corrosion tests were conducted to evaluate the corrosion resistance in phosphate buffered saline (PBS). The growth of endothelial cells on NiTi was examined using optical microscopy.

Surface modification of Ni–Ti alloys for stent application after magnetoelectropolishing

The constant demand for new implant materials and the multidisciplinary design approaches for stent applications have expanded vastly over the past decade. The biocompatibility of these implant materials is a function of their surface characteristics such as morphology, surface chemistry, roughness, surface charge and wettability. These surface characteristics can directly influence the materials corrosion resistance and biological processes such as endothelialization. Surface morphology affects the thermodynamic stability of passivating oxides, which renders corrosion resistance to passivating alloys. Magnetoelectropolishing (MEP) is known to alter the morphology and composition of surface films, which assist in improving corrosion resistance of Nitinol alloys. This work aims at analyzing the surface characteristics of MEP Nitinol alloys by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The wettability of the alloys was determined by contact angle measurements and the mechanical properties were assessed by Nanoindentation. Improved mechanical properties were observed with the addition of alloying elements. Cyclic potentiodynamic polarization tests were performed to determine the corrosion susceptibility. Further, the alloys were tested for their cytotoxicity and cellular growth with endothelial cells. Improved corrosion resistance and cellular viability were observed with MEP surface treated alloys.

Cytotoxicity of Metal Ions Released from Nitinol Alloys on Endothelial Cells

Most implantable medical devices are expected to function in the body over an extended period of time. Therefore, immersion tests under simulated conditions can be useful for assessing the amount of metal ions released in situ. In this investigation, dissolved ions from as-received binary and ternary Nitinol alloys in cell culture media were periodically measured under static and dynamic conditions. Endothelial cells were grown in aliquots of culture media obtained and the effect of dissolved ions on cell proliferation and viability of endothelial cells (HUVEC) was studied by cytotoxicity assays. The concentration of metal ions in the media was measured by inductively coupled plasma mass spectrometry.

Cytotoxicity of Ni from Surface-Treated Porous Nitinol (PNT) on Osteoblast Cells.

The leaching of nickel from the surface of porous Nitinol (PNT) is mainly dependent on its surface characteristics, which can be controlled by appropriate surface treatments. In this investigation, PNT was subjected to two surface treatments, namely, water-boiling and dry-heating passivations. Phosphate buffer saline (PBS) solutions obtained from cyclic potentiodynamic polarization tests on PNT were employed to assess the cytotoxicity of Ni contained therein on osteoblast cells by Sulforhodamine B (SRB) assay. In addition, similar concentrations of Ni were added exogenously to cell culture media to determine cytotoxic effects on osteoblast cells. The morphologies of the untreated and the surface-treated PNTs were examined using SEM and AFM. Furthermore, growth of human osteoblast cells was observed on the PNT surfaces.

Characterization and Degradation Behaviour of Anodized Magnesium-Hydroxyapatite Metal Matrix Composites

Recently, magnesium (Mg) alloys have inspired a significant amount of attention from researchers all over the world for implant applications due to their light weight, mechanical integrity and degradation behaviour. The major concerns with Mg implants are its rapid and non-uniform degradation, which can increase the risk of leached ions and can cause premature failure. In this study, Mg based alloys/metal matrix composites (MgZnCa/HA) were mechanically and electrochemically (anodized) surface treated. In-vitro corrosion tests revealed that the addition of hydroxyapatite (HA) and anodizing, stabilizes the corrosion process and lowers hydrogen evolution. Evidence of reduced degradation was provided by the presence of a relatively smooth surface morphology after corrosion. Furthermore, exposure of leached ions on osteoblast cells indicated good cytocompatibility.

Submerged Jet Mixing of Non-Newtonian Fluids in a Waste Tank

Unsteady jet mixing of Non-Newtonian fluids was investigated in order to develop a mixing correlation for treatment of stored radioactive waste prior to disposal. The radioactive waste was simulated by using carbopol mixtures, which possess both Newtonian and Non-Newtonian fluid rheological characteristics. A particle image velocimetry (PIV) technique with high spatial and temporal resolution was used to measure jet axial velocity, vector field velocity, and mixing properties of the carbopol mixtures. The relationship between the decaying jet axial velocity, tank geometry, fluid rheology and initial jet velocity were determined. A mathematical correlation was developed to estimate jet velocity in submerged jet-agitated tanks using the Buckingham Pi theorem and Dimensionless Numbers that influence the jet velocity and agitation in the tank.Copyright

Corrosion Behavior of Electropolished and Non-electropolished Ternary Nitinol Alloys

Electropolishing is a common technique for rendering a smooth mirror-like surface finish to implant materials. It is also known to improve a material’s corrosion resistance. A current method to evaluate the corrosion resistance of biomedical implants is based on in-vitro corrosion tests (ASTM F2129-08). Cyclic polarization tests were conducted at 37 °C using phosphate buffer saline (PBS) as an electrolyte to evaluate the corrosion resistance of electropolished and non-electropolished Ni-Ti-Cu and Ni-Ti-Cr alloys. The effects of electropolishing on break down potential (Eb) and the difference between break down potential and rest potential (Er), which is equivalent to the resistance to pitting corrosion were evaluated.