Sinter AM

All three Sinter-AM processes share the common feature that they begin with an additive shaping process. This results in so-called green parts, where the metal powder is held in shape using a binder system.

Depending on the process and binder system, the additively manufactured green parts exhibit different strengths, which are always lower than the final strengths achieved after sintering.

Between the sintering and shaping processes, a debinding step is always carried out to remove the binder system used for shaping. The debinding process can vary depending on the method but always concludes with a thermal process.

Following debinding, the sintering process takes place, during which the metal powder is densified, and the fundamental material properties are established.

The production of bioresorbable implants with graded properties was the goal of the VIP+ project BioMag3D, funded by the German Federal Ministry of Education and Research (BMBF). In a consortium with the Helmholtz Centre Hereon, Fraunhofer IAPT further developed piston-based material extrusion (pMEX) in order to process the magnesium alloy Mg4.5Gd in the form of a metal injection molding (MIM) feedstock and use it to manufacture implants that dissolve in a controlled manner after implantation in the body. Magnesium is particularly well suited for this purpose because it reacts in the aqueous, physiological environment of the body to form magnesium hydroxide and other soluble magnesium salts, which are absorbed or excreted by the organism.

By combining Hereon's expertise in materials science in the field of magnesium sintering with IAPT's expertise in additive process development, it was possible to validate the process route for manufacturing resorbable implants and examine its reproducibility and process stability. In addition to process optimization, the work also included the development of a workflow for the integration and design of graded hollow structures within the implant geometry, as well as methods for geometric and microstructural characterization and for determining degradation rates.

The results showed that the developed magnesium implants have the potential to become the next generation of advanced, bioresorbable implants. The targeted design of the internal porosity allows both the stiffness and the degradation rate to be adjusted locally, enabling individualized and functionally optimized implant solutions for regenerative medicine.

What are the advantages of this process?

• Elimination of follow-up surgery to remove the implant: Reduction of surgical risks and stress for the patient.
  
  
• Support of the natural healing process: The implant only performs a stabilizing function until the tissue or bone has regenerated sufficiently. Magnesium ions have an osteoinductive effect and stimulate bone cell activity.
  
  
• Reduction of long-term foreign body reactions: Since the implant is completely resorbed, no permanent foreign materials remain in the body.
  
  
• Prevention of stress shielding effects: The elastic properties of magnesium are similar to those of bone, thus preventing bone loss due to unnatural load distribution.
  
  
• Biocompatible degradation products: Magnesium ions and hydroxides are excreted via the metabolism and can even have a positive effect on the organism in some cases.
  
  
• Radiological advantages: Good visibility in CT and MRI, but without the image artifacts of titanium.
  
  
• Market potential: The combination of functional stability, biocompatibility, and degradability opens up new medical applications.