Researchers at IMDEA Materials Institute have conducted the first electrochemical comparison of how fabrication method and surface treatment affect corrosion in bioabsorbable metals, with implications for designing safer, longer-lasting biodegradable implants. Published in Surface and Coatings Technology, the study could inform the design of safer, longer-lasting implants by revealing how additive manufacturing and extrusion affect magnesium and zinc bioalloys.
The team, working in collaboration with the Helmholtz-Zentrum Hereon Institute of Surface Science and Meotec GmbH, tested WE43 magnesium and Zn1Mg zinc alloys produced via extrusion and Laser Powder Bed Fusion (LPBF). Using electrochemical testing in buffered saline, they found that LPBF samples corroded significantly faster than extruded counterparts.
“For these materials, this is the first time that these two manufacturing techniques have been compared in terms of corrosion resistance,” said first author Guillermo Domínguez, who conducted part of the research during a stay at Hereon as part of the Horizon Europe BIOMET4D project.
Key findings and results
In the study, LPBF parts exhibited significantly higher corrosion rates than their extruded counterparts. For example, LPBF WE43 degraded at 11.85 mm/year, nearly four times faster than the extruded version at 3.42 mm/year. The Zn1Mg alloy showed a similar trend, with LPBF samples corroding at 2.70 mm/year, compared to 0.98 mm/year for extruded.
This disparity was attributed to microstructural differences. LPBF WE43 contained yttrium oxide particles, likely inherited from the powder feedstock, which disrupted the formation of stable, protective corrosion layers. The Zn1Mg LPBF samples showed a fine eutectic structure with a higher volume of intermetallic Mg₂Zn₁₁, exacerbating microgalvanic corrosion.
The researchers then applied a PEO surface treatment, which significantly improved corrosion resistance across all samples. The corrosion rate in LPBF Zn1Mg, for instance, dropped from 2.70 mm/year to 0.30 mm/year, surpassing even the extruded counterpart. This was linked to a denser PEO coating and higher phosphorus content in the LPBF samples, promoting formation of protective phosphate phases.
In contrast, PEO-treated LPBF WE43 samples still performed worse than the extruded ones, due to uneven oxide layer thickness and microstructural heterogeneities in the LPBF material. SEM images revealed cracks and localized degradation in these regions, highlighting the limitations of PEO when applied to inhomogeneous LPBF microstructures.
“These results underscore the importance of optimizing both the manufacturing method and post-processing treatment,” said lead author Guillermo Domínguez. “In particular, LPBF zinc alloys show strong potential when paired with phosphorus-rich PEO coatings.”
The study was conducted as part of the Horizon Europe BIOMET4D project, focused on smart biodegradable metallic implants, with contributions from Helmholtz-Zentrum Hereon and Meotec GmbH. Electrochemical testing was supported by Dr. Carsten Blawert’s group at Hereon. Additional support came from the BIOFUN3D project on zinc-based scaffolds for additive manufacturing.
Advancements in biomedical implant printing
Surface treatments are playing an increasingly critical role in enhancing the performance of 3D printed biomedical implants. Recent work by Himed compared different abrasive blasting media for titanium implants, highlighting how surface roughness and cleanliness can influence osseointegration and implant longevity. As additive manufacturing expands in regulated sectors, companies like Croom Medical are also integrating tailored surface properties into platforms like their new tantalum 3D printing system, designed specifically for orthopedic applications.
Meanwhile, zinc-based alloys are emerging as promising candidates for biodegradable implants. A recent review of zinc biomaterials emphasized their potential in load-bearing medical devices thanks to controllable degradation rates and biocompatibility. Developments in high-resolution metal printing technologies such as Lithography-based Metal Manufacturing (LMM), adopted by Azoth 3D, further open new pathways for producing complex geometries in resorbable metals, with surface quality and microstructure control remaining key to optimizing performance in vivo.
These findings align with broader trends in biomedical implant development, where surface treatments like PEO are increasingly critical for enhancing the performance of 3D printed metals.
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Featured image shows SEM images of degraded PEO treated surfaces in the PDP tests. Image via IMDEA Materials.
