Microstructural, biomechanical and biocompatibility studies of porous Ti-Nb-Zr alloys fabricated by powder metallurgy

Abstract

This thesis presents a study on microstructural, biomechanical, and in vitro studies of Ti-Nb-Zr alloys fabricated by powder metallurgy with the space holder technique. This work aims to fabricate Ti-xNb (x:10, 20, and 30; at.%), Ti-20Zr (at.%) and Ti-xNb-10Zr (x: 10, and 20; at.%) alloys with different porosities used as a load-bearing implant that can mimic bone structure. Microstructural analysis was performed by using various methods including scanning electron microscopy, energy dispersive spectroscopy, electron backscatter diffraction and X-ray diffraction. Corrosion performance was assessed via electrochemical polarisation tests, while mechanical behaviour was determined by uniaxial compressive tests. In vitro studies such as cell viability and proliferation, adhesion potential, and genotoxicity were examined by performing MTT assay, scanning electron microscopy, fibronectin adsorption, and plasmid-DNA interaction assay. Results revealed that the alloys could be divided into low and highly porous categories, with porosities ranging from 21% to 29% and 43% to 58%, respectively. The alloys exhibited irregularly shaped open pores with a uniform pore size distribution, allowing for cell ingrowth. Adding a space holder effectively adjusted the porosity characteristics of the alloys achieved. As foreseen, porosities dramatically diminished the mechanical performance of the alloys. The ultimate compressive strengths ranged from 618 MPa to 1376 MPa for low porous alloys and from 48 MPa to 356 MPa for highly porous alloys. Moreover, potentiodynamic polarisation revealed that the alloys had passivation behaviour, protecting against corrosion attacks in Hank’s Balanced Salt Solution. Ti-xNb and Ti-xNb-10Zr alloys contained hcp α-Ti and bcc β-Ti phases with primary niobium phase, while Ti-20Zr alloys exhibited hcp α-Ti and distorted hcp αʹ-Ti phase structures. Biological evaluations of the alloys studied met the biocompatibility criteria required for orthopaedic biomaterial use. Microscopic examination of L929 and Saos-2 cell lines increased cell adherence and proliferation at a high density due to migration of the pores.