Medical implants in orthopaedic, cardiovascular, and dental applications face numerous challenges. Inside the body, they encounter constant mechanical stress from weight-bearing and movement, as well as the chemical environment of bodily fluids.
Implant material must be chemically non-reactive and biocompatible, strong, fatigue-resistant, corrosion-resistant, and durable. These properties ensure that implants such as hip replacements, cardiovascular stents, or dental screws remain safe, reliable, and comfortable throughout a patient’s life.
If the material is not of high quality and sufficient strength, mechanical stress can lead to metal fatigue or fracture, and wear between moving implant parts or against bone can create debris particles, potentially provoking inflammation and pain. Chemical corrosion from body fluids that are rich in salts, proteins, and enzymes can corrode poor-quality steel, releasing metal ions that irritate tissues or cause toxicity.
High performance stainless steel for medical implants
Surgical-grade stainless steels are alloyed to be especially resistant to rust and wear. The most widely used grade is 316L stainless steel, a low-carbon, molybdenum-bearing alloy renowned for its use in implants. The “L” in 316L indicates extra low carbon (<0.03%), which improves corrosion resistance by preventing carbide precipitates at grain boundaries. High chromium (~17–19%) forms a protective oxide film that prevents rusting, and added molybdenum (~2–3%) improves resistance to pitting and crevice corrosion from chlorides. Lastly, nickel (~13–15%) stabilises the austenitic structure and enhances toughness and formability. It’s also non-magnetic, which is beneficial for compatibility with MRI diagnostics.
Implant-grade 316L can also be further refined to meet stringent medical standards (ASTM F138/F139 and ISO 5832-1). Alleima® 316LVM stands for “316L Vacuum Melted”, a high-purity variant of 316L stainless steel that undergoes specialised melting processes to achieve improved cleanliness and structural homogeneity. It retains all the beneficial chemistry of standard 316L but with significantly reduced impurities and inclusions such as oxygen, sulphur, and phosphorus, which can form non-metallic inclusions or brittle phases. Alleima 316LVM process involves melting in an electric arc furnace, followed by vacuum arc remelting to produce a uniformly distributed microstructure. This manufacturing process yields steel with very high fatigue strength, with no internal weak spots where a crack can easily start, which is vital for load-bearing implants such as hip and knee replacements or spinal rods.
Vacuum-melted 316LVM is also essentially ferrite-free, which improves corrosion resistance. Ferrite (a magnetic iron phase) in stainless steel can be more prone to corrosion in certain conditions; by avoiding it, 316LVM maximises its resistance to general and intergranular corrosion.
The importance of surface finishing
Even with a superior alloy, the surface finishing of an implant plays an important role in both wear resistance and biocompatibility. A smooth, defect-free surface reduces friction between moving parts or between the implant and tissue, reducing the generation of wear particles and minimising the risk of inflammation. A polished surface also eliminates microscopic crevices where corrosion could initiate or bacteria could colonise. Implants with mirror-like finishes on articulating surfaces also produce less wear against their counterparts and help the implant last longer.
Engineers and designers therefore must pay attention not only to alloy selection but also to processes such as electropolishing, passivation, and surface coating to maximise these properties on the final device. Vacuum-melted steels such as 316LVM provide engineers with an advantage with their high purity and fine microstructure, which makes it easier to achieve a high-gloss polish.
Rigorous testing and standards compliance
Alleima® 316LVM meets the requirements of standards such as ASTM F139 and ISO 5832-1, and it complies with FDA regulations for implant materials. Alleima undertakes comprehensive testing and quality control for every batch of implant-grade alloy, starting with metallurgical analysis that uses microscopy and chemical analysis to verify that the steel’s purity and microstructure meet the strict criteria. Mechanical testing follows, which includes tensile tests to confirm strength, hardness tests to ensure proper strength/toughness balance.
Specialised tests according to ASTM/ISO standards such as the intergranular corrosion test are conducted to certify the material won’t suffer sensitisation or grain-boundary corrosion after processing.
Partners in high-performance steel
Using inferior steel can lead to corrosion, inflammation, or mechanical failure, putting patients at risk. High‑performance steel such as Alleima® 316LVM provides the biocompatibility, strength, and durability that implants need to function flawlessly under stress, wear, and corrosive conditions.
To find out more, download the whitepaper below.
