Titanium Grade 23 (Ti6Al4V ELI) in orthopedics
Highly pure titanium powder for perfect osseointegration in spine and hip implants.
1. Introduction: The metal that the body does not reject
When it comes to hip joints, spinal cages or skull plates, the human body only accepts the absolute best. The industry's standard titanium (Ti6Al4V Grade 5) is already excellent, but in orthopedic medical technology, its even purer form is used: Titanium Grade 23, also known as Ti6Al4V ELI (Extra Low Interstitials).
Grade 23 metal 3D printing (particularly PBF-LB and EBM) has revolutionized the manufacturing of patient-specific implants.
What does “ELI” (Extra Low Interstitials) mean?
Interstitial elements are tiny atoms (such as oxygen, nitrogen, carbon and iron) that sneak into the spaces (interstitials) of the titanium crystal lattice. Although they make standard titanium harder, they also make it more brittle. With Titanium Grade 23 (ELI), the proportion of these foreign atoms (especially oxygen) in the powder is kept extremely low. The result is a material that is extremely fracture tough, damage tolerant and highly biocompatible.
2. Osseointegration: When bone and metal fuse
The biggest problem with conventional CNC-milled implants is their smooth surface. The bone adheres poorly to them, which in the long term leads to loosening of the implant (aseptic loosening).
Through 3D printing with Ti6Al4V ELI, implants can be constructed in such a way that their surface consists of highly complex, open-pored lattice structures (trabecular lattices). These structures perfectly mimic the spongy architecture of human bones (cancellous bone). The bone does not recognize the implant as a foreign body, but rather physically grows into the printed titanium grid - a process called osseointegration. The implant and the person become one.
3. Solve the stress shielding problem
Bones need stress to stay healthy (Wolff's law). When you place a solid, CNC-machined titanium implant into a leg, the titanium is much stiffer (higher modulus of elasticity) than the surrounding bone. The titanium takes on the entire load, the bone becomes unemployed and regresses (stress shielding).
Using 3D printing and Ti6Al4V ELI, engineers can adjust the density of the lattice structure so that the implant has exactly the same mechanical stiffness as the patient's bone. The load is shared fairly and the bone is preserved.
4. Strict specifications for powder handling (MDR / FDA)
Titanium is extremely reactive (affinous for oxygen). Every melting process in the 3D printer and every sieving process in powder recycling carries the risk that the titanium will absorb oxygen from the air.
If the extremely pure Ti6Al4V ELI powder (Grade 23) absorbs too much oxygen, it exceeds the permissible limits and turns into normal Grade 5 titanium - or becomes so brittle that it becomes unusable. Therefore, medical technology authorities (FDA in the USA, MDR in Europe) require complete protocols about the oxygen levels in the installation space and often strictly limit how often the titanium powder can be reused (reused).
5. Conclusion: Tailor-made for life
Ti6Al4V ELI in 3D printing is the perfection of medical materials science. The combination of the superior ductility of the ELI material and the geometric freedom of the PBF process (for creating ingrowing bone structures) now enables operations and reconstructions in bone cancer or trauma patients that were considered pure science fiction 15 years ago.