Corrosion behaviour of porous Ti intended for biomedical applications

Abstract

Porous Ti implants are being developed in order to reduce the biomechanical mismatch between the implant and the bone, as well as increasing the osseointegration by improving the bone in-growth. Most of the focus in the literature has been on the structural, biological and mechanical characterization of porous Ti whereas there is limited information on the electrochemical characterization. Therefore, the present work aims to study the corrosion behaviour of porous Ti having 30 and 50 % of nominal porosity, produced by powder metallurgy route using the space holder technique. The percentage, size and distribution of the pores were determined by image analysis. Electrochemical tests consisting of potentiodynamic polarization and electrochemical impedance spectroscopy were performed in 9 g/L NaCl solution at body temperature. Electrochemical studies revealed that samples presented a less stable oxide film at increased porosity, more specifically, the complex geometry and the interconnectivity of the pores resulted in formation of less protective oxide film in the pores.

Influence of macroporosity on NIH/3T3 adhesion, proliferation, and osteogenic differentiation of MC3T3‐E1 over bio‐functionalized highly porous titanium implant material

“…Representative SEM images of as‐etched and bio‐functionalized samples are shown in Figure . Some of the present authors had previously characterized highly porous Ti samples processed under identical conditions . In that work, it was reported that Ti22 and Ti37 samples presented most of the macropores ranging between 50 and 350 μm in size.…”

“…Ti foams having 30 and 50 vol % of nominal porosity were processed by powder metallurgy using space holder technique (hereafter will be given as Ti22 and Ti37, respectively, due to the real porosity values previously measured by image analysis). Ti powders having average size of 25 μm, urea particles under 500 μm, and PVA (0.4 vol %) as binder were used to process highly porous samples.…”

Effect of HAP decomposition on the corrosion behavior of Ti–HAP biocomposites

“…Figure presents the low magnification OM images taken from sintered and polished Ti and Ti–5HAP surfaces. Unreinforced Ti samples presented residual porosity (black dots on Figure a) typical in conventional powder metallurgy . Ti–5HAP composites, on the other hand, presented reasonably homogenous distribution of the HAP particles and/or HAP‐depleted zones (dark phases on Figure b).…”

“…Both curves presented very similar behavior until around 860 °C without any significant dimensional changes. Afterwards, the shrinkage rate increased abruptly for Ti, and presented the maximum values between 1080 and 1220 °C . The curve for Ti–5HAP exhibited a significantly different behavior for temperatures above approx.…”

“…Decomposition of HAP may lead to a porous structure either by the dissolution or pulling out of the brittle phases . This porous structure may affect the corrosion behavior of the composites and, therefore, eventually increase the ion releasing, which is a major concern for metallic implant materials since it can result in severe health complications, as well as failure of the implant . Therefore, this work aims to have a preliminary insight on the effect of HAP decomposition on the electrochemical behavior on Ti–HAP composites.…”