Bio-Implant Corrosion: Fab Method & Surface Key, Study Finds

The quest for safer, more reliable bio-implants has taken a leap forward, thanks to researchers at IMDEA Materials, Helmholtz-Zentrum Hereon Institute of Surface Science, and Meotec GmbH. Their groundbreaking study delves into how the manufacturing process and surface treatments affect corrosion in bioabsorbable metallic alloys , specifically, magnesium (Mg) and zinc (Zn) based materials intended to dissolve harmlessly within the body after fulfilling their purpose.

Published in Surface and Coatings Technology, the research marks the first head-to-head comparison of corrosion resistance between two key manufacturing methods: extrusion and Laser Powder Bed Fusion (LPBF), a type of additive manufacturing. The focus was on WE43 magnesium alloy and Zn1Mg zinc alloy, both promising candidates for biodegradable implants.

“To our knowledge, this is the first time that these two manufacturing techniques have been compared in terms of corrosion resistance for these materials,” stated Guillermo Domínguez, the study’s lead author. The findings could have significant implications for the longevity and safety of medical implants, from bone screws to cardiovascular stents.

Debate Overview:

The central question revolves around optimizing the degradation rate of bioabsorbable metals. Too fast, and the implant might lose its structural integrity prematurely. Too slow, and it risks causing long-term inflammation or interfering with tissue regeneration. The study explores two key factors influencing this delicate balance: manufacturing method and surface treatment.

Key Arguments:

• Manufacturing Matters: The study revealed that LPBF-fabricated samples generally corroded faster than their extruded counterparts. This difference stems from microstructural variations introduced during the manufacturing process.
• WE43 Magnesium Alloy: In WE43, the accelerated corrosion in LPBF samples was linked to the presence of yttrium oxide particles. These particles disrupt the formation of a protective corrosion layer, making the material more susceptible to degradation.
• Zn1Mg Zinc Alloy: For Zn1Mg, the higher corrosion rate in LPBF samples was attributed to an increased volume of eutectic phases , microscopic regions where two elements solidify together. These phases create numerous tiny galvanic cells, accelerating localized corrosion.
• Surface Treatment is Crucial: To combat the increased corrosion, the researchers employed plasma electrolytic oxidation (PEO), a surface treatment that forms a protective oxide layer.
• PEO’s Variable Impact: The PEO treatment generally improved corrosion resistance across all samples. However, its effectiveness varied depending on the material and manufacturing method. Notably, PEO-treated LPBF Zn1Mg samples actually outperformed extruded ones.

The team’s findings highlight the complex interplay between material composition, manufacturing technique, and surface treatment. The results suggest that a “one-size-fits-all” approach won’t work for bioabsorbable implants. Instead, engineers will need to carefully tailor the manufacturing process and surface treatment to achieve the desired degradation rate for each specific application.

“To enhance corrosion resistance, a PEO process was applied to the samples,” Domínguez explained. “This treatment formed the expected oxide layer that improved protection across all tested materials compared to their untreated counterparts.” The key, it seems, lies in understanding how the manufacturing process impacts the formation and properties of this protective layer.

Interestingly, further analysis revealed that the superior performance of PEO-treated LPBF Zn1Mg was due to the formation of phosphorus-rich protective layers. These layers, formed during the surface modification process, stabilized the protective oxide layer, making it more resistant to corrosion. It seems that a slight typo in the layering process actually benefited the corrosion process.

The experimental work was conducted by Domínguez during a research stay at the Helmholtz-Zentrum Hereon Institute of Surface Science, facilitated by the Horizon Europe BIOMET4D project, coordinated by IMDEA Materials Institute. Meotec GmbH, a project partner, fabricated the samples. Access to advanced electrochemical testing equipment at Hereon, through collaboration with Dr. Carsten Blawert’s Department of Functional Surfaces, was also instrumental to the study.

Unresolved Questions:

While the study provides valuable insights, several questions remain:

• What is the long-term biocompatibility of the corrosion byproducts released from these materials? Further research is needed to assess the potential impact on surrounding tissues.
• Can the LPBF process be optimized to minimize the formation of yttrium oxide particles in WE43 or eutectic phases in Zn1Mg? This could involve fine-tuning the laser parameters or modifying the alloy composition.
• Are there alternative surface treatments that could provide even better corrosion protection, particularly for WE43 magnesium alloy?

These are just some of the questions that researchers will need to address as they continue to refine and improve bioabsorbable metallic alloys. The ultimate goal is to develop implants that are not only strong and durable but also biocompatible and capable of degrading at a predictable rate.

The implications of this research extend beyond the laboratory. For patients awaiting innovative medical solutions, this study offers a glimpse into the future of bio-implants. One patient advocate, speaking anonymously on a Facebook group for those awaiting joint replacement surgery, wrote, “This is a story we need to tell,” emphasizing the importance of informing the public about advancements that could directly impact their health and well-being.

Another user commented on X.com: “Progress! But I’m still nervous about metal dissolving inside me,” highlighting the need for ongoing research and transparency to address patient concerns. Further studies focusing on the human body will be paramount.

By carefully controlling how these materials are manufactured and treated, researchers can optimize their behavior inside the body, reducing risks and improving patient outcomes. The road ahead is complex, but the potential rewards , safer, longer-lasting, and more effective bio-implants , are well worth the effort. Finding the right balance between creation and corrosion.