Aachen, March 12, 2025 – The Chair Digital Additive Production (DAP) at RWTH Aachen University, in collaboration with project partners within the reACT alliance, is researching a novel approach to the patient-specific design of bioresorbable implants. Particularly for Critical Size Bone Defects, such as in long bones, the combination of Additive Manufacturing, automated design configuration, and bioresorbable zinc-magnesium alloys aims to create new possibilities for significantly reducing the side effects of conventional implant therapies.

Bone defects caused by accidents, congenital malformations or tumour resection require complex reconstructive procedures. These procedures often result in a significant health burden for patients and high costs for healthcare systems. Permanent implants, such as titanium, can increase the risk of fracture due to stress shielding and often require follow-up surgery for removal. The development of innovative materials and design methods is therefore essential to improve both clinical and socio-economic outcomes.

Additive Manufacturing as a Key Technology

Additive manufacturing offers almost limitless design possibilities, making it an ideal technology for the development of patient-specific implants. Within the reACT alliance, researchers are developing an algorithm-based design configurator for long bone defects. This tool automatically generates optimised implant designs based on patient-specific parameters such as defect geometry, age, bone density and weight. At the same time, the design is adapted for powder bed laser beam (PBF-LB) fabrication with metallic materials such as zinc-magnesium alloys.

Automated Patient-Specific Implant Design: The Design Configurator

A design configurator is an algorithm that integrates logical, mathematical and geometric operations to generate an implant design that meets functional requirements. In the first step, segmented CT data of the defect site defines the geometric design space for the implant (Figure 1).

In the next step, adaptive lattice structures are generated within the design space to ensure uniform resorption of the implant (Figure 2). By varying the geometry and arrangement, new tissue growth is encouraged and degradation products can be efficiently removed. In addition, the implant structure is tailored to the patient-specific biomechanical loads, minimising the risk of refracture.

Optimal Material Properties: Development of a Zinc-Magnesium Alloy

Zinc and magnesium alloys are considered promising materials for resorbable bone implants. While pure zinc (Zn) has favourable degradation properties, it lacks the mechanical strength required for use in implants. Magnesium (Mg), on the other hand, is already used in orthopaedic implants due to its bone-like mechanical properties. However, it degrades too quickly in certain applications, and gas formation can occur in moist tissue environments.

An extensive alloy screening of different compositions, ranging from pure zinc to Zn8Mg alloys, identified a ZnMg alloy with ≤1 wt% magnesium as the optimal composition for bone replacement applications.

First Demonstrator: Implant for a Critical Long Bone Defect

A first demonstrator implant has already been successfully manufactured by additive manufacturing. The implant design was customised to the specific defect size and bone structure of the patient, generating a cylindrical design space. Various lattice structure geometries were automatically incorporated into this space. These geometries can already be adjusted in terms of arrangement, unit cell size and strut diameter (Figure 3).

With this innovative approach, the reACT alliance is contributing to the realisation of the next generation of patient-specific, bioresorbable implants – with the aim of improving clinical outcomes and reducing the burden on healthcare systems. The design configurator methodology can also be adapted for other applications such as spinal cages and maxillofacial implants.

Project Partners in the reACT Alliance (Vertical 3):

• Meotec GmbH
• Medical Magnesium GmbH
• Fibrothelium GmbH
• University Hospital Aachen
• Fraunhofer Institute for Laser Technology (ILT)
• RWTH Aachen – Chair Digital Additive Production (DAP)

The reACT alliance (“Resorbable Medical Solutions from the Aachen Technology Region,” funding code: 03RU1U173C) is part of the “RUBIN – Regional Entrepreneurial Alliances for Innovation” program, funded by the German Federal Ministry of Education and Research (BMBF).