Adjustment of AgCaLa Phases in a FeMn Matrix via LBM for Implants with Adapted Degradation

Abstract

For many applications, implants overtake body function for a certain time. Bioresorbable implants reduce patient burden as they prevent adverse consequences due to remaining implants or operations for removal. Such materials are in clinical use but do not fulfill the requirements of all applications. Iron (Fe) is promising to develop further bioresorbable materials as it offers biocompatibility and good mechanical properties. Alloying, e.g., with manganese (Mn), is necessary to adapt the mechanical behavior and the degradation rate. However, the degradation rate of FeMn is too low. The creation of phases with high electrochemical potential evokes anodic dissolution of the FeMn, increasing the degradation rate. Therefore, silver (Ag), which is insoluble with Fe, has high potential, is biocompatible, and offers antibacterial properties, can be used. Powder-based processes such as laser beam melting (LBM) are favorable to process such immiscible materials. A degradable Ag alloy has to be used to enable the dissolution of Ag phases after the FeMn. This study reports first about the successful processing of FeMn with 5 wt.% of a degradable Ag–calcium–lanthanum (AgCaLa) alloy and enables further targeted adaption due to the gained understanding of the effects influencing the morphology and the chemical composition of the Ag phases.

FeMn with Phases of a Degradable Ag Alloy for Residue-Free and Adapted Bioresorbability

“…Just a small gap with a dimension of 1–3 µm around the Ag and AgCaLa phases has emerged ( Figure 3 d, white arrows). Such gaps have not been present before degradation [ 64 ]. The Ag and AgCaLa phases remain, while the matrix is dissolved, as expected.…”

“…The powders with a nominal particle size between 20 and 63 µm are produced via argon gas atomization. All powders have a suitable particle size distribution that is almost within the desired range and an almost spherical shape with only a few satellites [ 63 , 64 ]. Upright plates with a size of 2.5 × 10 × 12.5 mm³ are manufactured with an SLM 280 HL (SLM Solutions Group AG, Lübeck, Germany) in an argon atmosphere (layer thickness: 50 µm, scanning velocity: 750 mm/s, laser power: 280 W, hatch distance: 110 µm) [ 63 , 64 ].…”

“…All powders have a suitable particle size distribution that is almost within the desired range and an almost spherical shape with only a few satellites [ 63 , 64 ]. Upright plates with a size of 2.5 × 10 × 12.5 mm³ are manufactured with an SLM 280 HL (SLM Solutions Group AG, Lübeck, Germany) in an argon atmosphere (layer thickness: 50 µm, scanning velocity: 750 mm/s, laser power: 280 W, hatch distance: 110 µm) [ 63 , 64 ]. The resulting FeMn matrix is characterized by an austenitic structure and segregations of Mn along with the melt-pool structure of LBM as well as the columnar dendritic solidification structure.…”

“…The AgCaLa phases contain 75.8 wt.-% Ag, 10.6 wt.-% Ca, 5.4 wt.-% La, 5.2 wt.-% Mn, and 3.9 wt.-% O. A detailed characterization of the LBM-processed materials and conventionally processed AgCaLa alloy has been carried out by Krüger et al [ 41 , 63 , 64 ]. In the following, the samples are designated as FeMn, FeMnAg, and FeMnAgCaLa.…”

“…During the subsequent continuous melting process characterized by a small melt pool, a strong melt flow, and rapid melting and solidification, the Ag is incorporated into the bulk material. By the modification of the raw material and the LBM process, the chemical composition and the morphology of the Ag and AgCaLa phases are adaptable [ 22 , 62 , 63 , 64 ]. The raw material for the AgCaLa phases is obtained by conventional alloying and subsequent gas atomization, whereas the final structure and chemical composition of the AgCaLa inside the FeMn matrix are influenced by the LBM process [ 41 , 64 ].…”