[Paper Review] Microstructure, mechanical properties, corrosion resistance and cytocompatibility of WE43 Mg alloy scaffolds fabricated by laser powder bed fusion for biomedical applications

M. Li, Felix Benn+7 more|arXiv (Cornell University)|Oct 8, 2020

Magnesium Alloys: Properties and Applications42 references8 citations

TL;DR

This study investigates laser powder bed fusion (LPBF) fabrication of open-porous WE43 Mg alloy scaffolds for biomedical implants, demonstrating that strut diameter and post-processing heat treatments significantly influence microstructure, mechanical properties, and corrosion resistance. The lowest corrosion rates (2–3 mm/year) were achieved in as-printed and solution-treated scaffolds, further reduced to ~0.1 mm/year via plasma electrolytic oxidation (PEO), while PEO-coated scaffolds enabled sustained cell proliferation due to improved biocompatibility.

ABSTRACT

Open-porous scaffolds of WE43 Mg alloy with a body-center cubic cell pattern were manufactured by laser powder bed fusion with different strut diameters. The geometry of the unit cells was adequately reproduced during additive manufacturing and the porosity within the struts was minimized. The microstructure of the scaffolds was modified by means of thermal solution and ageing heat treatments and was analysed in detail by means of X-ray microtomography, optical, scanning and transmission electron microscopy. Moreover, the corrosion rates and the mechanical properties of the scaffolds were measured as a function of the strut diameter and metallurgical condition. The microstructure of the as-printed scaffolds contained a mixture of Y-rich oxide particles and Rare Earth-rich intermetallic precipitates. The latter could be modified by heat treatments. The lowest corrosion rates of 2-3 mm/year were found in the as-printed and solution treated scaffolds and they could be reduced to ~0.1 mm/year by surface treatments using plasma electrolytic oxidation. The mechanical properties of the scaffolds improved with the strut diameter: the yield strength increased from 8 to 40 MPa and the elastic modulus improved from 0.2 to 0.8 GPa when the strut diameter increased from 275 μm to 800 μm. Nevertheless, the strength of the scaffolds without plasma electrolytic oxidation treatment decreased rapidly when immersed in simulated body fluid. In vitro biocompatibility tests showed surface treatments by plasma electrolytic oxidation were necessary to ensure cell proliferation in scaffolds with high surface-to-volume ratio.

Motivation & Objective

• To develop WE43 Mg alloy scaffolds using laser powder bed fusion for load-bearing biomedical implants.
• To investigate the influence of strut diameter and heat treatments on microstructure and mechanical behavior.
• To evaluate corrosion resistance in simulated body fluid and optimize it via surface treatments.
• To assess in vitro cytocompatibility and determine the necessity of surface modifications for cell proliferation.

Proposed method

• Open-porous scaffolds with body-centered cubic unit cells were fabricated via laser powder bed fusion using WE43 Mg alloy powder.
• Strut diameters were varied from 275 µm to 800 µm to study size-dependent mechanical and corrosion responses.
• Thermal solution and aging heat treatments were applied to modify the microstructure and precipitate phases.
• X-ray microtomography, optical, scanning, and transmission electron microscopy were used to analyze microstructure and porosity.
• Corrosion rates were measured in simulated body fluid (SBF) under various conditions including PEO surface treatment.
• In vitro cytocompatibility was evaluated on scaffolds with and without PEO coating to assess cell proliferation.

Experimental results

Research questions

• RQ1 How does strut diameter affect the yield strength and elastic modulus of LPBF-fabricated WE43 Mg scaffolds?
• RQ2 What is the impact of solution and aging heat treatments on the microstructure and corrosion resistance of as-printed WE43 Mg scaffolds?
• RQ3 Can plasma electrolytic oxidation (PEO) treatment significantly reduce corrosion rates in WE43 Mg scaffolds?
• RQ4 Does PEO coating enable sustained cell proliferation on high surface-area WE43 Mg scaffolds?
• RQ5 What is the relationship between microstructure evolution and mechanical performance in heat-treated WE43 Mg scaffolds?

Key findings

• Yield strength increased from 8 MPa to 40 MPa and elastic modulus from 0.2 GPa to 0.8 GPa as strut diameter increased from 275 µm to 800 µm.
• The as-printed scaffolds exhibited a microstructure containing Y-rich oxide particles and rare earth-rich intermetallic precipitates, which were modified by heat treatments.
• Corrosion rates of 2–3 mm/year were observed in as-printed and solution-treated scaffolds, reduced to ~0.1 mm/year after plasma electrolytic oxidation (PEO) treatment.
• Scaffolds without PEO treatment showed rapid strength degradation upon immersion in simulated body fluid, indicating poor stability in physiological environments.
• PEO-coated scaffolds supported sustained cell proliferation, confirming that surface treatment is essential for biocompatibility in high surface-to-volume ratio scaffolds.
• X-ray microtomography confirmed minimal internal porosity within struts, indicating high geometric fidelity in LPBF-fabricated scaffolds.