Aug 30 2012
By their very nature, devices designed for medical uses must meet extremely stringent design and fabrication criteria. In a world increasingly focused on lawsuits and retribution claims for injury or damage caused by medical malpractice anything that comes into contact with or surgically implanted within the human body must perform exactly as designed, without fail.
The design and fabrication process for medical devices poses some of the most challenging material science questions and engineering problems for the medical industry to overcome. With such broad applications, medical devices come in all shapes and sizes to perform a raft of different jobs and therefore a diverse range of materials are employed by scientists and engineers to help meet the most stringent of design specifications.
Stainless steel is one of the most commonly used materials in the manufacture of medical devices, and in particular Stainless Steel 304.
For further information on this grade: Stainless Steel 304
Stainless Steel 304 - Properties used in Medical Devices
Stainless Steel 304 is regarded the world over as one of the most suitable materials for the manufacture of medical devices for all sorts of applications. In fact, it is the most common stainless steel used in the world today. No other grade of stainless steel comes in so many forms, finishes and with such diverse applications. Stainless Steel 304 Properties offer unique material characteristics at a competitive price point, thus making it the logical choice for medical device specification.
The typical chemical composition of Stainless Steel 304 is highlighted in Table 1.
Typical Chemical Composition of Stainless Steel 304 for Medical Devices
Table 1. Typical Chemical Composition of Stainless Steel 304
18.0 - 19.5
8.0 - 10.5
A high corrosion resistance and low carbon content are key factors that mak Stainless Steel 304 suitable for medical applications over and above other grades of Stainless steel. The reassurance that medical devices won't chemically react with bodily tissue, cleaning products used to sterilise and the hard, reptitive wear that many medical devices are subjected to, means that Stainless 304 is the perfect material for hospitals, surgeries and paramedic applications etc.
Typical Mechanical Properties of Stainless Steel 304 for Medical Devices
Table 2. Mechanical Properties of Stainless Steel 304
Not only does Stainless Steel 304 offer high strength, it is also extremely workable, with the ability to be deep drawn into shape without the need for annealing, making 304 perfect for the manufacture of bowls, sinks, pans and a range of different medical vessels and hollow ware.
There are also a number of different versions of Stainless Steel 304 with improved material properties for specific applications such as 304L, the low carbon version, used in heavy guage situations where high strength welds are required. Medical equipment may incorporate 304L where welds are required to withstand a range of impacts, prolonged periods of stress and or strain etc. Stainless 304L is also a CryogenicSteel, which means it can be used in applications where the product is required to operate at incredibly cold temperatures. For extremely corrosive environments, 304L also offers a greater resistance to intergranular corrosion, than similar grades of stainless.
The combination of low yield strength and high elongation potential, means that 304 Stainless steel is great for forming into complex shapes without the need for annealing.
If the medical application requires a harder or stronger stainless steel, 304 can be work hardened through Cold working. In an annealed state 304 and 304L are extremely ductile and can be formed, bent, deep drawn or fabricated easily. However, 304 does harden quickly and may require further annealling to improve ductility for further work.
Medical Applications for Stainless Steel 304
Stainless steel 304 is widely used in all sorts of industrial and domestic applications. Within the medical device industry, 304 is used where high corrosion resistance, good formability, strength, manufacturing precision, reliability and hygiene is of particular importance.
Stainless Steel 304 offers a number of advantages:
- Diverse Application - can be used for all types of medical devices - economies of scale - reducing raw material costs.
- Rust Proof - reduces the risk of infection from rust and other surface imperfections caused by oxidation.
- High Corrosion Resistance
- Antibacterial poperties
- It does not stain - so it can be cleaned and re-used many times in the medical field.
- Non Magnetic - perfect for operating theatres or implants within the body
- High heat resistance
- Once work-hardened Stainless Steel 304 will keep its shape.
Medical / Surgical Stainless steel
For surgical stainless steel, specific grades of Stainless steel - 316 and 316L are predominantly used. By alloying the elements Chromium, Nickel and Molybdenum Stainless steel offers the material scientist and surgeon some uniquely reliable qualities.
- Chromium - heightens the materials scratch resistance and corrosion resistance - perfect for cleaning and sterilization.
- Nickel - provides an extremely smooth and polishable surface - fine details required for machinging precision, high quality products etc. Also important for hygiene.
- Molybdenum - provides hardness after forming and is great for sharp cutting edges - scalpel
Note - In some rare cases the bodies immune system has been known to have an adverse reaction (both cutaneous and systematic) to the nickel content in some stainless steels. In cases like this, Titanium may be used as a substitute for Stainless Steel. However, with Titanium comes a more costly solution. Often, Stainless steel is used for temporary implants and the more expensive, titanium may be used for permanent implants.
For example, the following list summarizes some possible medical device applications for stainless steel:
- Precision stainless steel tubing
- Orthopaedic implants (Predominantly 316 / 316L)
- Artificial heart valves (Predominantly 316 / 316L)
- Bone fixation
- Mandrels / tools
- Chemical containers / Hazardous waste containers
- Wire coils
- Wire forms
- Speciality guide wires
- Screws / prostheses / plates
- Medical needles
- Medical syringes
- Sensor probes
- Otolaryngology ear scope nozzles
- Sinks / bowls / surfaces / trays / knives
References and further reading: