3D printing with amorphous metals
Amorphous metals are versatile because they have exceptional properties. They are extraordinarily hard, but also very elastic. It should be a contradiction, but not with materials like these. Amorphous metals, or metallic glasses, have a disordered internal structure. This is because they are cooled rapidly from the molten state, which prevents the formation of an ordered crystal structure. The result is an amorphous, non-crystalline solid in which the atoms remain in a largely disordered state.
In addition to exceptional strength and elasticity, the unusual structure of amorphous metals also makes them resistant to corrosion and wear. They are ideal for medical applications such as heavy duty scalpels and minimally invasive surgical instruments. In the future, they will also be used to make implants for use in the human body. When subjected to pressure and tension, they behave almost like human bones, with which they share a similar modulus of elasticity. This means that they are less rigid than other materials and therefore better able to withstand the loads that the bones must bear.
These new materials are also ideal for implants. They are just as biocompatible as the current material of choice, titanium or its Ti6Al4V alloy. The human body has a high tolerance for amorphous metal implants.
New alloys from additive manufacturing
Hanau, Germany-based Heraeus Amloy is currently working on new alloys for use in the manufacture of medical implants. “Zirconium-based alloys are suitable for medical applications,” said Eugen Milke, innovation manager at Heraeus Amloy. “We already have a biocompatible zirconium alloy, Amloy-ZR02, certified according to ISO 10993-5 and ISO 10993-12 standards.
According to Milke, there is also a demand for titanium alloys in the medical sector: “Titanium is a proven material for medical components such as bone implants and artificial heart pacemakers, so we are also working on titanium alloys in this moment. “
The development team uses an additive manufacturing process to produce the actual components. Heraeus Amloy has specially modified the composition of Amloy-ZR02 for this purpose. In a joint project with laser specialists from TRUMPF, the company is investigating the use of the TruPrint 2000 3D printer to industrially produce amorphous metal components.
An innovative process meets an innovative material
3D printer and new lightweight materials make a perfect team. The laser creates structures only where they are needed to fabricate the part. This saves material and weight, even with large and complex components. The process has little heat input, which is a key requirement for production with amorphous metals. With a diameter of only 55 m, the laser beam creates only a small weld pool. The heat is therefore quickly dissipated, ensuring that the critical cooling rate of 200 Kelvin per second is met. This prevents the molten metal from crystallizing. The narrow focus of the beam also enables the production of complex structures with a high surface quality and degree of detail.
Klaus Parey, Managing Director of TRUMPF Additive Manufacturing, is confident: “Amorphous metals offer great potential for many industries. They are particularly suitable for applications in medical engineering, which is one of the most important sectors of additive manufacturing. We therefore believe that this collaboration is an excellent opportunity for us and our industrial 3D printers to make new inroads in this key market. “Jürgen Wachter, Director of Heraeus Amloy, said:” This combination of innovative materials and additive manufacturing has the potential to revolutionize medical practice. By working in close collaboration with the clinics, it will be possible to use 3D printers to produce implants precisely adapted to each patient.
Implants from the 3D printer
In order to realize this vision, the two partners signed a research project at the Medical University of Graz. Launched in October 2019, the manufacture of clinical additives for medical applications (CAMed) is funded by the Austrian Federal Ministry for Climate Action, Environment, Energy, Mobility, Innovation and Technology (BMK), the Austrian Federal Ministry of Digital and Economic Affairs (BMDW) and by the Steierische Wirtschaftsförderungsgesellschaft (SFG), the business development agency of the Austrian federal state of Styria. CAMed studies the complete process chain for the additive manufacturing of implants personalized for each patient. Besides areas such as computer modeling, data processing and various finishing processes, the project also focuses on new materials and production methods.
Specifically, this means using 3D printers to produce custom rib implants and plate implants for the treatment of physical injuries. The potential is enormous, especially with complex bone fractures. With the implants currently on the market, for example radial plate implants or other implants for trauma surgery, big compromises are often necessary. For starters, there are only a few basic implant sizes available. For injuries of bodily origin or following a tumor, improvisation is therefore necessary. This means that the surgeon has to bend the metal implant by hand until it has the right shape and then secure it to the bone with screws. Sometimes it stays firmly attached; sometimes less. Indeed, an implant is subjected to constant stress. A rib implant, for example, needs to perform about eight million breaths per year. This often results in a stress fracture or loosening of the fixation to the sternum, thus requiring additional intervention. At present, there is no alternative.
In addition, in order to promote the healing process after surgery, the bone with the implant must be stabilized but also requires regular movement. This is the case with the plate implant used to fix the humerus, the bone in the upper arm, where conventional implants quickly encounter their limits.
In contrast, 3D printing can provide custom implants made from amorphous materials that have the necessary strength but are also flexible enough to resist and cushion the necessary movement. At the same time, the additive manufacturing process can also create a porous surface texture which promotes the rooting of bone tissue in the implant. If a smooth surface is required, in order to facilitate subsequent removal of the implant, this method can also produce a surface quality of one micrometer without the need for finishing. It’s better than most other materials. In addition, if an even smoother surface is required, a surface roughness as low as Ra 0.05 to 0.08 m can be achieved with a milling machine.
Almost like a human bone
As part of the CAMed project, Heraeus is currently testing the AMLOY-ZR02 alloy. This consists of 65 percent zirconium, 16 percent copper, 12 percent nickel, 4 percent aluminum and 3 percent titanium. With a density of 6.6 g / cm³, this new alloy is heavier than the titanium alloys conventionally used in medical implants. However, the design freedom afforded by the use of an additive manufacturing process means that less material is required, resulting in weight savings of up to 20%. Likewise, a flexural strength of 2000 MPa and a tensile strength of 1700 MPa make the implants thinner than usual. In addition, with a modulus of elasticity of 85 GPa, it is closer to human bone (17-21 GPa) than titanium. If the goal is a combination of flexibility and strength, the new AMLOY alloy is ideal for the fabrication of plate implants, as these can then be made thinner than with titanium. It also encourages the healing process.
Completely new applications
The first results of the CAMed project are very promising. As such, additively manufactured implants, tailored to each patient and possessing exceptional material properties, are now a very real prospect. Other applications such as prosthetic implants and heart valves are also possible. With their exceptional properties, amorphous metals are extremely versatile and will allow many new applications, especially in the field of medical engineering.