Bioresorbable Fe-based alloys for stent applications processed via laser powder bed fusion
Currently, there is a trend in manufacturing patient-specific implants via laser powder bed fusion (LPBF), a promising additive manufacturing technique. Moreover, combining this technology with bioresorbable metals is attracting increasing attention since the implants provide temporary support for the healing processes of damaged tissue and resorbs after this task is completed. This class of materials overcomes challenges like revision surgery, chronic inflammation or lacking adaptation to growth when the implant is deployed at infancy.
The focus on bioresorbable metallic materials is on magnesium-, iron- and zinc-based systems. Hereby, iron-based alloys are a promising alternative to magnesium alloys since iron is one of the essential elements in the human body, e.g. it is involved in oxygen transport and is a component of metalloproteins. A challenge of iron-based alloys is their slow in vivo corrosion rate, but it can be enhanced by alloying (e.g. with Mn, Pd, S) or applying special manufacturing technologies.
In this study, a novel bioresorbable Fe-30Mn-1C-0.02S alloy [1, 2] is presented, which was processed by LPDF. The occurring rapid solidification during the process results in a fine-grained austenitic microstructure with mainly homogeneous element distribution. In first examination, the properties of bulk FeMnCS SLM samples are presented. Thereby, significantly higher strengths under tensile and compressive load in comparison to those for the as-cast counterpart and a 316L reference steel can be achieved. By potentiodynamic polarization tests in a simulated body fluid (SBF), a moderate corrosion activity could be shown, and immersion tests in SBF indicate a beneficial uniform degradation. After the characterization of bulk samples, SLM-processed FeMnCS stent prototypes were built and subsequently characterized.
The in vitro behavior of Fe-30Mn-1C-0.02S stents was evaluated by cultivation of endothelial cells over two weeks. Both, cell adhesion and viability, were strongly influenced by the formation hydroxyapatite/ iron oxide layer, which was examined via X-ray photoelectron spectroscopy. Furthermore, the influence of stent expansion on the in vitro corrosion was analyzed.
Funding of this project by the DFG under project number HU 2371/1-1 is gratefully acknowledged.