1 Overview
As stainless steel for biomedical equipment, in addition to good mechanical properties, physicochemical properties and processability, it should have excellent biocompatibility and physiological corrosion resistance.
Biocompatibility refers to the ability of a material used in a living organism to elicit an appropriate host response to produce an effective effect in a particular application. Characterize the biological properties of the material and determine the interaction of the material with the living host system. This interaction includes both host and material reactions. A series of in vivo and ex vivo evaluation experiments must be conducted to ensure the safety of biomaterials for clinical applications.
Stainless steel is a biocompatible metal material that does not come into contact with living organisms' tissues and whose properties and functions are not affected by them.
The human implantation of stainless steel also requires.
(1) No biological reactions.
(2) No toxicity or metastatic reaction.
3) Anti-thrombotic.
4) Wear and abrasion resistance.
5) High corrosion fatigue.
High-performance stainless steel for medical devices requires high surface quality and dimensional accuracy with good toughness, corrosion resistance and functionality.
In the selection of biomedical and high performance medical devices, the role of alloying elements must be fully understood, and the FAO and WHO classify the role of trace elements in the human body into three categories.
(1) The human body must have the elements I, Fe, Zn, Se, Cu, Mo, Cr, Co a total of eight kinds.
(2) Five species of Mn, Si, Ni, B, V that may be necessary for the human body.
（3) Trace elements that are potentially toxic but may have essential functions in low doses, such as F, Pb, Cd, Hg, As, Al, Li, Sn, etc.
The main elements in stainless steel are Fe, Cr, Ni, Mo, Cu, as well as Si, Mn, Co and other harmless elements, which is why stainless steel is widely used in this field. As for high-strength stainless steel containing Al (e.g. 17-7PH, PH15-7Mo, PH14-8Mo, PH13-8Mo, etc.), use Cu-reinforced stainless steel (e.g. 17-4PH, 15-5PH, etc.) as little or no use as possible. Free-cutting stainless steel containing Pb should also be used sparingly in favour of free-cutting stainless steel containing Se.
2 Stainless steel for biomedical use
(1) The commonly used AISI 316L and 317L are listed in ISO 5832 and 7153 standards, which have good biocompatibility and integrative properties.
(2) The development of Ni-free austenitic stainless steels Cr18Mn14Mo3Nl and Cr21Mn22Mo1Nl in some populations, especially a small minority of women, who are allergic to Ni. China has also developed Cr17Mn14Mo2N0.6 and 03Cr17Mn12.5Mo2.5Cu1.5N0.4 instead of 316L and 317L.
（3) Cr20Ni20Co20Mo4P alloy for artificial joints.
（4) Nanosilver-coated stainless steel that is conducive to bone implant engagement and less susceptible to infection.
3 Stainless steel for high performance medical devices
(1) Mostly applicable to martensitic stainless steel, ferritic stainless steel, such as: 2Cr13, 3Cr13, 7Cr17, 8Cr17, 9Cr18Mo and 9Cr18MoV, etc.
(3) Different types of stainless steel containing Cu and Ag antibacterial.
（4) Functional stainless steel (e.g. non-magnetic, soft magnetic, damping, etc.)
（5) 304Cu2Wo.6 Antibacterial stainless steel.
4 Specific uses of stainless steel
（1) Artificial joints, internal fixation devices for fractures.
（2) Dental implants, orthodontics, dental implants and auxiliary instruments.
(3) Cardiovascular system; implantation of electrodes, sensor housing and leads, artificial heart valves, endovascular stents, etc..
（4) Artificial ears, artificial eye wires, etc..
(5) Structural and functional parts of high-performance medical devices.
5 New processes and technologies for the direct production of stainless steel components for biomedical and high-performance medical devices
Because the stainless steel products required in this field, especially the shape of the key components is very complex, dimensional accuracy, surface quality requirements are very high, the use of traditional production processes often do not meet the technical requirements, and the low yield, high cost and have to adopt new processes, new technologies, such as injection molding technology is the first choice, and 3D printing technology is also gradually entering the field.
In short, in high-end manufacturing, the injection molding process is the best choice for parts with particularly complex shapes, high precision requirements, very large output (1 million pieces), difficult to produce by other processes, or high material consumption and light weight that can be produced with very low yield.
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