Jonas Schmidt

This study characterizes the mechanical behavior of Ti‐6Al‐4V lattice structures manufactured using laser powder bed fusion (PBF‐LB/M) for application in endoprostheses. Additive manufacturing enables creating customized orthopedic implants with complex geometries that combine mechanical stability with biological integration. The choice of biocompatible Ti‐6Al‐4V, together with the incorporation of lattice structures, offers improved mechanical performance, corrosion resistance, and bone ingrowth. A critical step toward the clinical adoption of such additively manufactured lattice structures is their thorough mechanical characterization, the central focus of this work. To this end, three test methods are employed to assess macroscopic mechanical response and damage tolerance: uniaxial compression, fourpoint bending and crack propagation tests. The results show that the mechanical properties depend on the lattice topology and surface finish. In particular, TPMS‐based architectures (Triply Periodic Minimal Surfaces) exhibit superior fatigue crack propagation behavior, which is attributed to a more homogeneous stress distribution. In static testing, the SplitP TPMS (SPP) and Honeycomb (HCG) structures achieve the best balance of high stiffness (up to 27 GPa) and compressive strength (up to 249 MPa). These experimentally validated data form a crucial basis for subsequent artificial intelligence (AI)‐based structural optimization to maximize the long‐term mechanical reliability of implants under physiological loads.

This study investigates the effect of carbon on the mechanical and functional properties of an additively manufactured Fe-32Mn-6Si-5Cr-0.5Nb-xC alloy. A base alloy was processed using laser powder bed fusion, and the carbon content was altered during manufacturing using a nanoparticle dispersion-based in situ re-alloying approach. This method enabled an increase in carbon content from 0.06 wt.-% to 0.15 wt.-% and 0.23 wt.-%, respectively. The three resulting alloys were analysed both in the as-built condition and after heat treatments, including direct artificial ageing, as well as solution annealing and subsequent artificial ageing. While the different heat treatment states led to distinct microstructures, the carbon content affected the microstructure only after the additional heat treatments. Here, a higher carbon content led to an increase in the volume fraction of precipitates. Mechanical and functional properties were analysed under compression loading and subsequent unconstrained thermal activation. Depending on the carbon content and, more significantly, the heat treatments, the mechanical and functional properties could be tuned in a wide range. The highest mechanical strength was achieved through direct ageing, while a carbon content of 0.06 wt.-% in combination with solution annealing and ageing led to the highest recovery strain of up to 80%.

Shape memory alloys exhibit unique properties ideal for functionally integrated components, such as actuators. While commonly used Ni-Ti alloys are well established, especially in biomedicine and aerospace, their high cost limits wider applications. Fe-based shape memory alloys present an affordable alternative, suitable for diverse applications, with a larger thermal hysteresis but lower recovery strain. Nonetheless, their functional properties can be enhanced through optimized processing methods like laser powder bed fusion and adjustments to their alloy composition. In the present study, laser powder bed fusion was used for modifying the composition and microstructure of a Fe-30Mn-6Si-5Cr alloy. For this purpose, laser parameters were varied to evaporate up to 47.3% of the initial Mn in the manufacturing process. In this context, the amount of Mn evaporated was dependent on both the line energy and more considerably on the volume energy density introduced in the manufacturing process. Subsequently, the impact of the resulting compositional changes on the microstructure was analyzed, and the functional properties were visualized using a demonstrator. Lowering the Mn content below 24.1% led to a higher degree of ferrite in the otherwise austenitic microstructure. This also affected the functional properties. These findings highlight the potential of laser-based additive manufacturing for modifying the composition and microstructure of shape memory alloys in situ and, thus, tailoring their functional properties.

BACKGROUND: There are certain issues using saliva as a sample for steroid hormone analysis in clinical diagnostics. Therefore, it is important to test whether currently available assays are suitable for this approach in a routine laboratory. OBJECTIVES: The analytical performance of two commercially available immunoassays was compared under routine conditions. In addition, salivary steroid hormone levels were compared with serum levels. METHODS: Saliva and serum samples were collected from healthy subjects. Afterwards, the concentration of cortisol, testosterone, progesterone and estradiol in saliva was measured by using the ADIVA Centaur® XP platform and commercially available manual ELISA kits. Serum levels of the selected steroid hormones were determined by using the ADVIA Centaur® platform. RESULTS: Currently, the ADVIA Centaur® XP platform cannot be used for the quantification of steroid hormones in saliva due to an insufficient calibration range. Commercially available ELISA kits on the other side are well suitable for this application. CONCLUSIONS: There are commercially available immunoassays which are sensitive enough for the determination of steroid hormones from saliva and can be used under routine conditions. However, the interpretation of salivary steroid hormone levels stays a challenging task due to the large variability of the results.