An investigation into interaction between magnesium powder and Ar gas: Implications for selective laser melting of magnesium

Additive Manufactured Magnesium-Based Scaffolds for Tissue Engineering

Additive manufacturing (AM) is an important technology that led to a high evolution in the manufacture of personalized implants adapted to the anatomical requirements of patients. Due to a worldwide graft shortage, synthetic scaffolds must be developed. Regarding this aspect, biodegradable materials such as magnesium and its alloys are a possible solution because the second surgery for implant removal is eliminated. Magnesium (Mg) exhibits mechanical properties, which are similar to human bone, biodegradability in human fluids, high biocompatibility, and increased ability to stimulate new bone formation. A current research trend consists of Mg-based scaffold design and manufacture using AM technologies. This review presents the importance of biodegradable implants in treating bone defects, the most used AM methods to produce Mg scaffolds based on powder metallurgy, AM-manufactured implants properties, and in vitro and in vivo analysis. Scaffold properties such as biodegradation, densification, mechanical properties, microstructure, and biocompatibility are presented with examples extracted from the recent literature. The challenges for AM-produced Mg implants by taking into account the available literature are also discussed.

Biodegradable WE43 Magnesium Alloy Produced by Selective Laser Melting: Mechanical Properties, Corrosion Behavior, and In-Vitro Cytotoxicity

In this work, selective laser melting (SLM) technology was used to prepare Mg-4Y-3Nd-Zr (WE43) alloy. This alloy and production method are promising for the design of biodegradable implants. The aim of this study was to investigate the chemical composition, microstructure, mechanical properties, corrosion behavior in simulated body fluid (SBF), and cytotoxicity of the alloy produced by SLM method and to compare it with conventionally gravity cast reference alloy. Analysis of the surface of the revealed an oxygen content of 7 wt.%. Undesirable unmelted and only partially adhered spherical particles of the starting powder were also found. The microstructure of the material was very fine and consisted of α-Mg dendritic matrix, β-Mg41(Nd, Y)5 intermetallic phase, Y2O3 inclusions, and 0.6 vol.% of residual porosity. The Vickers hardness, compressive yield strength, compressive strength, and maximum compressive strain were 88 HV0.1, 201 MPa, 394 MPa, and 14%, respectively, which are close to the reference values in as-cast. The in vitro corrosion rates determined by immersion and potentiodynamic tests were 2.6 mm/year and 1.3 mm/year, respectively. Cytotoxicity tests indicated good biocompatibility of the 3D-printed alloy.

Biodegradable magnesium alloy WE43 porous scaffolds fabricated by laser powder bed fusion for orthopedic applications: Process optimization, in vitro and in vivo investigation

Laser powder bed fusion (L-PBF) of magnesium (Mg) alloy porous scaffolds is expected to solve the dual challenges from customized structures and biodegradable functions required for repairing bone defects. However, one of the key technical difficulties lies in the poor L-PBF process performance of Mg, contributed by the high susceptibility to oxidation, vaporization, thermal expansion, and powder attachment etc. This work investigated the influence of L-PBF energy input and scanning strategy on the formation quality of porous scaffolds by using WE43 powder, and characterized the microstructure, mechanical properties, biocompatibility, biodegradation and osteogenic effect of the as-built WE43 porous scaffolds. With the customized energy input and scanning strategy, the relative density of struts reached over 99.5%, and the geometrical error between the designed and the fabricated porosity declined to below 10%. Massive secondary phases including intermetallic precipitates and oxides were observed. The compressive strength (4.37–23.49 MPa) and elastic modulus (154.40–873.02 MPa) were comparable to those of cancellous bone. Good biocompatibility was observed by in vitro cell viability and in vivo implantation. The biodegradation of as-built porous scaffolds promoted the osteogenic effect, but the structural integrity devastated after 12 h by the immersion tests in Hank's solution and after 4 weeks by the implantation in rabbits' femur, indicating an excessively rapid degradation rate.

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In vitro and in vivo investigations were performed on WE43 porous scaffolds.

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Reliable fusion quality and dimensional accuracy were achieved.

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The compressive strength and Young modulus ranged 4.37–23.49 and 154.40–873.02 MPa.

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Good biocompatibility and improved osteogenic effect were observed.

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The massive secondary phases as well as the enlarged specific surface resulted to a rapid degradation rate.

Solvent-cast 3D printing of magnesium scaffolds

Biodegradable porous magnesium (Mg) scaffolds are promising for application in the regeneration of critical-sized bone defects. Although additive manufacturing (AM) carries the promise of offering unique opportunities to fabricate porous Mg scaffolds, current attempts to apply the AM approach to fabricating Mg scaffolds have encountered some crucial issues, such as those related to safety in operation and to the difficulties in composition control. In this paper, we present a room-temperature extrusion-based AM method for the fabrication of topologically ordered porous Mg scaffolds. It is composed of three steps, namely (i) preparing a Mg powder loaded ink with desired rheological properties, (ii) solvent-cast 3D printing (SC-3DP) of the ink to form scaffolds with 0 °/ 90 °/ 0 ° layers, and (iii) debinding and sintering to remove the binder in the ink and then get Mg powder particles bonded by applying a liquid-phase sintering strategy. A rheological analysis of the prepared inks with 54, 58 and 62  vol% Mg powder loading was performed to reveal their viscoelastic properties. Thermal-gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), carbon/sulfur analysis and scanning electron microscopy (SEM) indicated the possibilities of debinding and sintering at one single step for fabricating pure Mg scaffolds with high fidelity and densification. The resulting scaffolds with high porosity contained hierarchical and interconnected pores. This study, for the first time, demonstrated that the SC-3DP technique presents unprecedented possibilities to fabricate Mg-based porous scaffolds that have the potential to be used as a bone-substituting material. STATEMENT OF SIGNIFICANCE: Biodegradable porous magnesium scaffolds are promising for application in the regeneration of critical-sized bone defects. Although additive manufacturing (AM) carries the promise of offering unique opportunities to fabricate porous magnesium scaffolds, current attempts to apply the AM approach to fabricating magnesium scaffolds still have some crucial limitations. This study demonstrated that the solvent-cast 3D printing technique presents unprecedented possibilities to fabricate Mg-based porous scaffolds. The judicious chosen of formulated binder system allowed for the negligible binder residue after debinding and the short-time liquid-phase sintering strategy led to a great success in sintering pure magnesium scaffolds. The resulting scaffolds with hierarchical and interconnected pores have great potential to be used as a bone-substituting material.

Effect of Laser Parameters on Processing of Biodegradable Magnesium Alloy WE43 via Selective Laser Melting Method

The global aim of the theme of magnesium alloy processing by the selective laser melting technology is to enable printing of replacements into the human body. By combining the advantages of WE43 magnesium alloy and additive manufacturing, it is possible to print support structures that have very similar properties to human bones. However, printing magnesium alloy parts is very difficult, and the printing strategies are still under development. Knowledge of weld deposit behaviour is needed to design a complex printing strategy and still missing. The main aim of the manuscript is the find a stable process window and identify the dependence of the weld deposit shape and properties on the laser power and scanning speed. The range of the tested parameters was 100–400 W and 100–800 mm/s for laser power and scanning speed. The profilometry and light microscopy were used to verify the continuity and shape evaluation. The microhardness and EDX analysis were used for the detailed view of the weld deposit. The manuscript specifies the weld deposit dimensions, their changes depending on laser power and scanning speed, and the continuity of the weld tracks. The stable weld deposits are made by the energy density of 5.5–12 J/mm². Thin walls were also created by layering welds to determine the surface roughness scattering (Ra 35–60) for various settings of laser power and scanning speed.

Additive manufacturing of magnesium alloys

Magnesium alloys are a promising new class of degradable biomaterials that have a similar stiffness to bone, which minimizes the harmful effects of stress shielding. Use of biodegradable magnesium implants eliminates the need for a second surgery for repair or removal. There is a growing interest to capitalize on additive manufacturing's unique design capabilities to advance the frontiers of medicine. However, magnesium alloys are difficult to 3D print due to the high chemical reactivity that poses a combustion risk. Furthermore, the low vaporization temperature of magnesium and common biocompatible alloying elements further increases the difficulty to print fully dense structures that balance strength and corrosion requirements. The purpose of this study is to survey current techniques to 3D print magnesium constructs and provide guidance on best additive practices for these alloys.

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A review of additive manufacturing of magnesium alloys for biomedical applications.

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Examined challenges associated with vaporization and porosity.

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Surveyed multiple AM processes and the role of process parameters on print quality and performance.