Artificial discs are made from a combination of medical-grade metals and specialized plastics, engineered to replicate the movement and cushioning of a natural spinal disc. The most common materials are cobalt-chromium-molybdenum alloy for the metal endplates and ultra-high-molecular-weight polyethylene for the cushioning core, though titanium, stainless steel, and newer polymers also play important roles depending on the device.
Metal Endplates: Cobalt-Chromium and Titanium
The top and bottom plates of most artificial discs are made from metal alloys that anchor into the vertebrae above and below. Cobalt-chromium is the most widely used. It contains roughly 5 to 7 percent molybdenum and has about twice the stiffness of titanium, giving it excellent resistance to the repetitive loading your spine endures every day. During manufacturing, a chromium-oxide film forms on its surface, which makes it highly resistant to corrosion inside the body and reduces the risk of immune reactions.
Cobalt-chromium also produces less wear debris than titanium when used as a bearing surface, meaning fewer microscopic particles are released into surrounding tissue over time. This matters because wear particles can trigger inflammation. In laboratory testing, metal-on-metal lumbar disc prototypes generated wear rates as low as 6.2 cubic millimeters per million movement cycles, and design refinements like adjusting carbon content and surface geometry brought those numbers down further.
Titanium is the other major metal in disc replacement. It is lighter, more flexible, and its stiffness is closer to that of bone, which can reduce stress at the bone-implant boundary. Titanium is often used for the outer coating of endplates rather than the bearing surface itself. The Mobi-C cervical disc, for example, uses cobalt-chromium plates for structural strength but applies a titanium plasma spray coating on the surfaces that contact bone. This coating significantly improves how quickly and firmly bone grows into the implant. Animal studies have shown that plasma-sprayed titanium increases both the amount of new bone attachment and the force required to dislodge the implant, with the most critical bonding happening in the first 6 to 12 weeks after surgery.
Many devices add a layer of hydroxyapatite on top of the titanium spray. Hydroxyapatite is a mineral that makes up a large portion of natural bone, so it acts as a biological welcome mat, encouraging your vertebrae to bond directly with the implant rather than forming scar tissue around it.
The Plastic Core: Medical-Grade Polyethylene
Between the metal endplates sits a core or insert made from ultra-high-molecular-weight polyethylene, a dense plastic that has been used in joint replacements for over four decades. It is tough, durable, and biologically inert, meaning it does not provoke a reaction from your immune system. In an artificial disc, this polyethylene insert is what allows smooth gliding movement between the two metal plates.
Newer versions of this plastic are crosslinked using radiation, which rearranges the molecular chains to dramatically improve wear resistance. Clinical studies have confirmed that these crosslinked polyethylenes wear down far less than conventional versions. One tradeoff is that crosslinking can make the material slightly more brittle, but second-generation formulations infused with vitamin E have solved much of this problem. Vitamin E stabilizes the plastic against long-term oxidation (the slow chemical breakdown that can make polyethylene stiff and fragile over years inside the body) while maintaining the improved wear performance.
In the Mobi-C cervical disc, the polyethylene insert is mobile, meaning it can slide slightly between the upper and lower plates. The insert’s top surface contacts a curved metal surface while its bottom rests on a flat one, and small stops on the lower plate keep the insert from shifting too far. This design distributes forces more evenly and allows a more natural range of motion.
PEEK and Elastomeric Alternatives
Not all artificial discs follow the metal-on-plastic formula. Some newer designs use polyetheretherketone, commonly called PEEK, a high-performance polymer that offers two distinct advantages. First, its stiffness is much closer to natural bone than metal is, which may reduce the risk of the implant slowly sinking into the vertebra over time. Second, PEEK is radiolucent, meaning it does not block X-rays. This allows surgeons to clearly see the bone and surrounding tissue on imaging after surgery, something that metal implants can obscure.
Another category uses elastomeric cores made from polycarbonate urethane, a flexible rubber-like polymer bonded between titanium endplates. These “viscoelastic” designs behave more like a natural disc because the core compresses and rebounds under load, absorbing shock the way your original disc’s gel-like center once did. Traditional ball-and-socket designs allow rotation but do not truly cushion compressive forces. Viscoelastic implants aim to restore both movement and shock absorption across all directions of spinal motion.
Cervical vs. Lumbar Material Demands
The cervical spine (neck) and lumbar spine (lower back) place very different demands on an artificial disc. Lumbar discs bear significantly more weight, since they support the entire upper body, so lumbar implants tend to be larger and require materials with higher fatigue resistance. Cervical discs experience less compressive force but need to accommodate a wider range of rotational movement.
Despite these differences, the core material palette is similar. Both regions use cobalt-chromium, titanium, and polyethylene in various combinations. The main variations are in size, geometry, and how the components interact. A lumbar viscoelastic disc like the Freedom Lumbar Disc uses an elastomeric core bonded to titanium alloy endplates, while its cervical counterpart adapts the same concept with a polycarbonate urethane core and a textured titanium surface coated in hydroxyapatite to suit the smaller, more mobile cervical vertebrae.
Metal Sensitivity and Material Selection
Between 10 and 15 percent of the general population has some degree of skin sensitivity to metals, with nickel being the most common trigger at around 14 percent. Cobalt and chromium can also cause reactions. Among people who have already received joint implants, the rate of contact sensitivity may be as high as 25 percent.
If you have a known metal allergy, your surgeon will typically choose titanium-based components, which contain only trace amounts of nickel. For patients with severe sensitivities, ceramic bearing surfaces or carbon fiber components are alternatives, though they are less widely available. Allergy testing before surgery is straightforward and can prevent complications like persistent pain, swelling, or skin reactions that occasionally occur when a sensitized patient receives a cobalt-chromium implant.
Experimental Hydrogel Materials
Researchers are actively developing hydrogels as a potential next-generation disc material. These are three-dimensional polymer networks that absorb and hold large amounts of water, closely mimicking the water-rich nucleus pulposus at the center of a natural disc. Because of their high water content, hydrogels can compress and rebound under load in a way that rigid metal-and-plastic designs cannot fully replicate.
Composite hydrogels, which blend different polymers together, allow engineers to tune the material’s stiffness, degradation rate, and biological activity. Some formulations can interact with surrounding tissue to encourage healing, and early laboratory work has produced hydrogel scaffolds that restore the biomechanical properties of a degenerated disc while reducing re-herniation rates in animal models. These materials remain investigational, but they represent a fundamentally different approach: rather than replacing the disc with a mechanical joint, hydrogels aim to restore something closer to the disc’s original biological function.