Titanium biocompatibility
Titanium is considered the most biocompatible metal due to its resistance to corrosion from bodily fluids, bio-inertness, capacity for osseointegration, and high fatigue limit.
Titanium's ability to withstand the harsh bodily environment is a result of the protective oxide film that forms naturally in the presence of oxygen.
The oxide film is strongly adhered, insoluble, and chemically impermeable, preventing reactions between the metal and the surrounding environment.
[citation needed] It has been suggested that titanium's capacity for osseointegration stems from the high dielectric constant of its surface oxide, which does not denature proteins (like tantalum, and cobalt alloys).
[3] Its ability to physically bond with bone gives titanium an advantage over other materials that require the use of an adhesive to remain attached.
Titanium implants last longer and much higher forces are required to break the bonds that join them to the body compared to their alternatives.
[4] The surface properties of a biomaterial play an important role in determining cellular response (cell adhesion and proliferation) to the material.
Titanium's microstructure and high surface energy enable it to induce angiogenesis, which assists in the process of osseointegration.
Titanium naturally passivates, forming an oxide film that becomes heterogeneous and polarized as a function of exposure time to bodily environments.
In titanium alloys such as Ti-Zr and Ti-Nb, zirconium and niobium ions that are liberated due to corrosion are not released into the patient's body, but rather added to the passivation layer.
[11] where D = 8.83 × 10−7 cm2⋅s−1 is the diffusion coefficient of the BSA molecule at 310 K, d = 7.2 nm is the "diameter" of the proteinwhich is equivalent to twice the Stokes radius, NA = 6.023 × 1023 mol−1 is the Avogadro constant, and c* = 0.23 g⋅L−1 (3.3 μM) is the critical bulk supersaturation concentration.
[4] Wetting of titanium can be modified by optimizing process parameters such as temperature, time, and pressure (shown in table below).
Titanium with stable oxide layers predominantly consisting of TiO2 result in improved wetting of the implant in contact with physiological fluid.
Titanium alloys are susceptible to hydrogen absorption which can induce precipitation of hydrides and cause embrittlement, leading to material failure.
[15] "Hydrogen embrittlement was observed as an in vivo mechanism of degradation under fretting-crevice corrosion conditions resulting in TiH formation, surface reaction and cracking inside Ti/Ti modular body tapers.
A coating consisting of trimers and pentamers increased the bone-implant contact area by 75% when compared to the current clinical standard of uncoated titanium.
