Hip question: The "brain" for a 3D printer will help print a prosthesis with the desired properties

Russian engineers have created a 3D printer control program that allows you to print hip joint heads from two metals at once. Their combination makes it possible to manufacture implants with different properties that can be customized for a specific patient. The technology also allows doctors to control the manufacturing process and, if necessary, adjust it to the clinical situation. According to experts, this is a significant step towards improving the quality of medical devices, the demand for which in Russia reaches about 320 thousand per year. However, they note that from the point of view of practical application, there are certain issues due to the high cost of this solution.

Two-metal printing

Specialists of Peter the Great St. Petersburg Polytechnic University have developed a program that allows manufacturing the head of a hip arthroplasty from two metals using 3D printing using a digital model. The system controls the 3D printer during the laser melting of cobalt-chromium-molybdenum alloy and stainless steel.

The combination of materials makes it possible to create implants tailored to the individual characteristics of the patient. In addition, the program visualizes the layered formation of the product, which allows engineers and doctors to adjust its properties depending on the clinical situation, the expected load and the condition of human bone tissue.

— The endoprosthesis head has an external and an internal zone. The first one is in contact with the cup all the time, so it must be firm and wear-resistant. However, when we increase these values, the material becomes more brittle, so it is better to make the inner part more plastic. In our case, steel is more ductile, and the alloy is harder. By changing the ratio, we can change the properties of the prosthesis. For example, taking into account the fact that the patient leads a mobile lifestyle or, possibly, is overweight," said Arseniy Repnin, a leading researcher at the Structural and Functional Materials Research and Educational Center at the Institute of Mechanical Engineering, Materials and Transport at St. Petersburg State University.

The program monitors critical parameters of material fusion in real time: laser power, scanning speed, etc. This makes it possible to form a monolithic prosthesis structure from two dissimilar metals with minimal risk of pores and microcracks forming at their interface.

It takes about five hours to print one endoprosthesis head. The scientists used a Russian-made printer for this, which also manufactures parts for aviation, robotics, etc. Since the technology is intended for medical use, its effectiveness will have to be confirmed by preclinical and clinical studies. At the same time, other metals can be used as materials. Theoretically, scientists are able to increase their number to three or four, but due to the increasing complexity and cost of production, this will be justified only for solving highly specialized tasks.

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According to the developers, the technology they have created opens the way to a fundamentally new approach in the creation of metal products.

— We are used to choosing the material from the catalog first, and then making the part from it. Now it becomes possible to develop the material itself, taking into account the parameters of a specific part and its operating conditions. The adaptive capabilities of the program make it possible to transfer this approach to a wide variety of fields: aircraft construction, energy, automotive industry — wherever there is a need for combined properties, this technology can find application," said Arseniy Repnin.

Promising technology

The technology is promising, as it translates 3D-printing of implants from the logic of "one alloy for the whole part" into the logic of a functionally delimited design, said Danil Anisimov, a researcher at Motorika ORTHO. In his opinion, this is especially important for the endoprosthesis head.

— Cobalt-chromium-molybdenum concentrates in the friction zone, where wear resistance and corrosion resistance are critical, and medical steel acts as a structural base. Both alloys have been well studied in print and are recognized as biocompatible, which reduces regulatory risks. In endoprostheses, the junction of metals is especially important: due to the difference in melting temperatures (about 100 degrees), thermal gradients arise, which give stresses and microdefects," he said.

Fine-tuning for a clinical task and more predictable quality due to a program that controls printing parameters and visualizes layer-by-layer formation will help to avoid these defects. An additional effect is saving expensive cobalt-chromium alloy. So far, one bimetallic bundle has been worked out, but the base for scaling to other alloys and types of implants has already been laid, the expert emphasized.

— The technology is promising from the point of view of scientific research, it can be considered a breakthrough. Today, 3D printing usually uses only one material, whereas in this development we are talking about the simultaneous use of two. This is a step forward, this has never happened before. However, from the point of view of practical implementation, there are still issues, primarily related to the high cost of such technology," said Andrey Nikolaenko, director of the Research Institute of Bionics and Personalized Medicine at Samara State Medical University of the Ministry of Health of the Russian Federation (SamSMU), market expert at NTI Helnet.

According to Professor Nikolai Zagorodny, head of the Department of Traumatology and Orthopedics at RUDN University, there is no particular need to improve the head of the hip joint, since it practically does not wear out, and the polyethylene components of the implant become unusable. Although, in general, the need for prosthetics in the Russian Federation is great. About 320 thousand products are needed per year, the expert noted. As a rule, operations are necessary for people with osteoarthritis and after fractures.