Chandan Pulletikurthi

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.

Towards a Better Corrosion Resistance and Biocompatibility Improvement of Nitinol Medical Devices

Haemocompatibility of Nitinol implantable devices and their corrosion resistance as well as resistance to fracture are very important features of advanced medical implants. The authors of the paper present some novel methods capable to improve Nitinol implantable devices to some marked degree beyond currently used electropolishing (EP) processes. Instead, a magnetoelectropolishing process should be advised. The polarization study shows that magnetoelectropolished Nitinol surface is more corrosion resistant than that obtained after a standard EP and has a unique ability to repassivate the surface. Currently used sterilization processes of Nitinol implantable devices can dramatically change physicochemical properties of medical device and by this influence its biocompatibility. The Authors’ experimental results clearly show the way to improve biocompatibility of NiTi alloy surface. The final sodium hypochlorite treatment should replace currently used Nitinol implantable devices sterilization methods which rationale was also given in our previous study.

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.

Utility of magneto-electropolished ternary nitinol alloys for blood contacting applications

The thrombogenicity of a biomaterial is mainly dependent on its surface characteristics, which dictates its interactions with blood. Surface properties such as composition, roughness wettability, surface free energy, and morphology will affect an implant materials hemocompatibility. Additionally, in the realm of metallic biomaterials, the specific composition of the alloy and its surface treatment are important factors that will affect the surface properties. The utility of magneto-electropolished (MEP) ternary Nitinol alloys, NiTiTa, and NiTiCr as blood contacting materials was investigated. The hemcompatibility of these alloys were compared to mechanically polished (MP) metallic biomaterial counterparts. In vitro thrombogenicity tests revealed significantly less platelet adherence on ternary MEP Nitinol, especially MEP NiTi10Ta as compared to the MP metals (p < 0.05). The enhanced anti-platelet-adhesive property of MEP NiTi10Ta was in part, attributed to the Ta2 O5 component of the alloy. Furthermore, the formation of a dense and mixed hydrophobic oxide layer during MEP is believed to have inhibited the adhesion of negatively charged platelets. In conclusion, MEP ternary Nitinol alloys can potentially be utilized for blood-contacting devices where, complications resulting from thrombogenicity can be minimized.

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.