The medical industry continues to develop less invasive surgical procedures, which improves patient care. 3D printing/additive manufacturing often plays a big role in enabling these less invasive procedures.
One example involves back pain treatments. Minimally invasive technical components made of plastic or metal can be implanted in the body. For spinal surgery patients and surgeons, these implants can be a blessing. Behind these implants lies a combination of design, functionality and a great deal of manufacturing expertise.
Spine cages are implants for leveling and relieving the pressure on the spine caused by spinal stenosis or other degenerative disease. Typically, both the cage and the screws used to secure the cage to the spinal column are made of Titanium.
However, in some cases, the titanium component negatively affects the bone structure due to the rigidity of the cage. The implants typically have a significantly lower elasticity than bone.
More recently, cages are being made of PEEK (polyetheretherketone), a biocompatible material suitable even for allergy sufferers. PEEK is a high-performance plastic with compression properties or elasticity rivaling that of bone. In addition, PEEK components cause no issues with magnetic resonance imaging and are thus easy to locate by the surgeon through imaging.
One of the disadvantages of PEEK spine cages, though, is their inability to be integrated into the bone structure. If these cages have been in a body a long time, they tend to move from the original position.
A solution to this issue came about using additive manufacturing, specifically the LaserCUSING additive laser melting method from Concept Laser. This method combines the strengths – and eliminates the weaknesses – of traditional titanium or PEEK components for spine cage applications.
A laser-melted component can offer the biocompatibility of titanium with the desired elasticity of a plastic material in a single product. Laser-melted spine cages can have a very complicated geometry, which, with partially different density distributions (embedded web-like structures), gives titanium parts the same elasticity as a PEEK solution.
Laser-melted cages can also be affordably manufactured in various dimensions depending on the anatomy of the patient, allowing for custom manufacturing.
The Tsunami Medical Srl, in Modena, Italy, is a developer of spinal implants and has been working with additive manufacturing to develop custom spinal cages. According to CEO Stefano Caselli, laser-melted cages represent “a true innovation that combines material-specific advantages such as biocompatibility that enables the cages to be embedded into the bone structure, and elasticity that is customized for the human body.”
A Tsunami innovation is the “lobster spacer,” which is a self-spreading spacer that can be used between intervertebral discs in surgical spinal column reconstruction. The spreading mechanism consists of a gearbox with a central screw and side gears that spreads apart two wings. Creating lobster spacers with perfectly aligned surfaces is possible thanks to the LaserCUSING process, using an Mlab cusing R system from Concept Laser. Its highly smooth nearly polished surface ensures significantly less excrescence in the tissue.
A remarkable aspect of the manufacturing technology, according to Caselli, is the ability to produce multiple copies of this complex, movable part at the same time. “LaserCUSING gives us time and cost advantages, and is also much easier, under cleanroom conditions, than conventional manufacturing strategies. In addition, machine solutions from Concept Laser provide excellent performance and a high level of safety when working with reactive materials such as titanium or titanium alloys.”
Disc prosthesis as a single component
When it comes to component design, additive manufacturing can open up entirely new directions. One innovation that resulted from the opportunities offered by LaserCUSING at Tsunami is the development of a custom disc prosthesis that acts as a vertebral spacer to strengthen the spine. It consists of an upper shell and a lower shell connected by a double spring. The shells’ surface is designed to fit perfectly into the vertebral plate. The double spring is made of titanium with a silicone core for damping the movement of the spring. The design and spacing dimensions can be adjusted precisely to the patient’s anatomy in accordance with the surgeon’s specifications. The highlight of this innovative solution: the disc prosthesis is manufactured in a “one-shot” process using laser melting technology, a solution that eliminates the need for downstream assembly processes.
The disc prosthesis ensures 360-degree freedom of movement, providing enormous support to the patient’s mobility. Optimum elasticity is ensured by the double spring and enhanced through the silicone core. Noted Caselli, “From a design standpoint, the disc prosthesis as a product idea is the direct result of the geometric freedom and functional integration offered by the LaserCUSING method. Conventional manufacturing methods don’t work for this kind of solution. Additive manufacturing complements our expertise in spinal column reconstruction by offering a multitude of new options. The solution is also very flexible: we can adjust the dimensions to a patient’s specific anatomical profile.”