Why does the human body not reject titanium alloys? Why does it repel other metals?

The metals put into the human body in medicine are titanium alloys, titanium is the only kind of metal that the human body will not reject, why not reject? Does titanium have anything to do with body composition?

Let's talk about it today
First, the so-called rejection is when the immune system recognizes the foreign protein, which is labeled by antibodies, and then triggers an inflammatory response in which immune cells gather, eat and degrade the foreign cells and the virus.

In addition, the main danger of metals in the body is the corrosion of metals by body fluids, and some metal ions + may be cytotoxic.
The biggest advantage of titanium is that at normal temperature, air and water can form a high-quality oxide film, completely prevent titanium ions + into the body, titanium oxide film in the body is almost completely not corroded, which is the so-called tissue compatibility.

Not only in the human body, in the strong acid and alkali environment of the chemical industry, in the strong salt corrosion environment of the deep sea industry, only titanium alloys can play the heavy responsibility of structural metals and resist corrosion in various harsh environments.

In fact, the metal tantalum + and niobium are similar to titanium in the biological body, but they are more expensive than titanium, and the mechanical processing performance is not necessarily better, so they are not used much.

Let's clarify, titanium alloy is widely used in the human body because
1. Biological compatibility:
The biocompatibility of titanium alloys is mainly due to the titanium oxide layer that can be naturally formed on its surface. This oxide film is very stable and can effectively prevent the release of metal ions into the body, thus reducing the immune response. The inert nature of the titanium oxide layer means that it hardly reacts with biological tissues or bodily fluids in the body, which further reduces the possibility of rejection and inflammation.

2. Density/Mechanical properties:
The strength and toughness of titanium alloy make it an ideal orthopedic implant material with a density similar to that of human bone. These physical properties are similar to human bone and help reduce stress mismatches between implants and bone.

3. Corrosion resistance:
Titanium alloys have extremely high corrosion resistance in the human body. This is because the titanium oxide layer prevents direct contact between body fluids and the metal, reducing corrosion and preventing the release of metal ions.

4. Non-magnetic:
The non-magnetic nature of titanium alloys means that the implants do not interfere with diagnostic procedures such as magnetic resonance imaging (MRI).

Because of these properties of titanium alloy, human cells will grow along titanium alloy and eventually "grow" together with titanium alloy.