Background and motivation
The number of total hip arthroplasties implanted per year was estimated at 700,000 worldwide in 2002. Here, the procedures are not limited to a first-time implantation of an endoprosthesis. Due to the increasing age of the total population, approximately 20% of the procedures were performed for a change of prosthesis. Especially for young patients this is usually unavoidable in the course of life, so that a better integration of the prosthesis is associated with fewer interventions and consequently less health risks. Three factors, among others, are relevant for the design of an endoprosthesis and its long-term, sustainable as well as successful implementation:

• Biocompatibility of the materials used
• Biomechanical stability by aiming for load distributions between bone and prosthesis that are close to the natural state in order to avoid stress-shielding (the body's own degredation of unused bone material)
• Stability of the anchorage in the bone through ingrowth of new bone tissue into the prosthesis

Diatoms are marine microorganisms that occur in thousands of different forms in the world's oceans and are characterized by filigree, highly porous but still strong and resistant structures. The potential of corresponding bio-inspired design principles could already be used for different areas, so that, for example, crash-relevant components with better impact values at lower weight could be developed. Due to their low density and unique lightweight shell structures that are insensitive to variable dynamic loads, corresponding design principles are a promising model and predestined for the development of bio-inspired open porous structures that can be used in the optimized design of endoprosthesis.

Objective and approach
The initial aim of this project is to develop a method for AI-supported structuring of compression and crack growth specimens in order to enable the successful structuring of endoprostheses in follow-up projects in the long term. The focus here is on bio-inspired, open-pored diatom structures that promote bone ingrowth. At the same time, realistic loads are to be considered in order to support the most accurate stress distribution possible in the long term. The structures are created from biocompatible, corrosion-resistant materials using additive manufacturing in a powder bed-based selective laser melting (PBSLM) process at IWT. Mechanical testing, modelling of crack initiation and failure of the structures, and analysis of the test specimens also take place here.
In this way, on the one hand, KIKI develops a compression specimen optimized with respect to lightweight construction and stress, which can bear stresses comparable to the natural condition in a femur without excessively unloading the surrounding bone. On the other hand, an AI-supported development process of bio-inspired structures is being developed. The combination of both points represents the basis for the development of bio-inspired endoprostheses, which will be addressed in the following.
In this way, the KIKI project contributes to strengthening Bremen as an important location for additive manufacturing in medical technology.

Role of the AWI
Within the project, bio-inspired open pore structures and design concepts will be generated at AWI using innovative software and parametric model generation. The principles will be developed in such a way that they can be used in a highly variable manner, consider design properties relevant for endoprosthesis, and enable optimization in terms of weight, porosity, strength, and manufacturability. Mainly, construction principles of diatoms are derived and abstracted for this purpose. In the following step, a database will be created on the basis of the designs created and the results of the mechanical analysis of the test specimens. This is the basis for a new AI tool to be developed. In the design process of the bio-inspired mechanical specimens, this tool will support the selection of appropriate diatom structures.