Why does titanium have a high affinity for the human body?

The main reason for the frequent use of titanium in the human body is the biocompatibility of titanium and the surface-modified bioactive surfaces. Surface characteristics that affect biocompatibility are surface properties spatial site resistance, binding sites and hydrophobicity (wetting). These features are optimised to produce the desired cellular response. Some medical implants as well as parts of surgical instruments are coated with titanium nitride. Titanium is considered the best biocompatible metal due to its resistance to corrosion by body fluids, biological inertness, osseointegration ability and high fatigue limit. Titanium's ability to withstand the harsh environment of the body is a result of the natural formation of a protective oxide film in the presence of oxygen. The oxide film adheres strongly, is insoluble and chemically impermeable, preventing the metal from reacting with its surroundings. It is thought that titanium's bone healing ability stems from the high dielectric constant of its surface oxide, which does not denature proteins. Titanium's ability to physically bond to bone makes it superior to other materials that require the use of adhesives to stay attached. Titanium implants last longer and require greater force to break the bonds that attach them to the body than alternatives. The surface properties of biomaterials play an important role in determining the cellular response (cell adhesion and proliferation) to the material. Titanium's microstructure and high surface energy allow it to induce angiogenesis, which contributes to the bone healing process. Depending on its oxidation state, titanium can have many different standard electrode potentials. Solid titanium has a standard electrode potential Materials with higher standard electrode potentials are easier to reduce and make better oxidisers. Solid titanium prefers oxidation, making it a better reducing agent. Titanium passivates naturally, forming an oxide film which becomes uneven and polarised with exposure to the physical environment. Over time, this leads to increased adsorption of hydroxyl groups, lipoproteins and glycolipids. Adsorption of these compounds alters the interaction of the material with the body and can improve biocompatibility. In titanium alloys such as titanium-zirconium and titanium-niobium, the zirconium and niobium ions released due to corrosion are not released into the patient's body but are added to the passivation layer. The alloying elements in the passivation layer add a degree of biocompatibility and corrosion resistance, depending on the original alloy composition of the host metal prior to corrosion. By increasing the wettability, the implant can reduce the time required for bone healing by allowing cells to bind more readily to the implant surface. Titanium wetting can be altered by optimising process parameters such as temperature, time and pressure. Titanium having a stable oxide layer consisting primarily of titanium dioxide results in improved wettability of the implant in contact with physiological fluids.