A state-of-the-art review on recent advances in the fabrication and characteristics of magnesium-based alloys in biomedical applications

Magnesium(Mg)and its alloys have recently gained increasing attention in the biomedical field as promising biodegradable materials with harmless degradation products.Magnesium-based alloys have a wide range of biomedical applications because of their outstanding biocompatibility and unique mechanical properties.Widespread use of Mg-based biomedical devices eliminates the need for post-healing biomaterial removal surgery and minimizes the negative consequences of the implantation of permanent biomaterials,including stress shielding and undesired metal ion release in the body.This paper provides a literature review on the properties and manufacturing methods of Mgbased alloys for biomedical applications,including orthopedic implants,cardiovascular applications,surgical wires and staplers,and antitumor activities.Each application of Mg-based biomaterials is investigated from a biological perspective,including matching functional properties,biocompatibility,host tissue responses,and anti-microbial strategies,along with potential additive manufacturing technologies for these applications.Finally,an outlook is presented to provide recommendations for Mg-based biomaterials in the future.

Recent progress and perspectives in additive manufacturing of magnesium alloys

Magnesium alloys remain critical in the context of light-weighting and advanced devices. The increased utilisation of magnesium(Mg)each year reveals growing demand for its Mg-based alloys. Additive manufacturing(AM) provides the possibility to directly manufacture components in net-shape, providing new possibilities and applications for the use of Mg-alloys, and new prospects in the utilisation of novel physical structures made possible from ‘3D printing’. The review herein seeks to holistically explore the additive manufacturing of Mg-alloys to date, including a synopsis of processes used and properties measured(with a comparison to conventionally prepared Mg-alloys). The challenges and possibilities of AM Mg-alloys are critically elaborated for the field of mechanical metallurgy.

Review on laser directed energy deposited aluminum alloys

Lightweight aluminum(Al)alloys have been widely used in frontier fields like aerospace and automotive industries,which attracts great interest in additive manufacturing(AM)to process high-value Al parts.As a mainstream AM technique,laser-directed energy deposition(LDED)shows good scalability to meet the requirements for large-format component manufacturing and repair.However,LDED Al alloys are highly challenging due to their inherent poor printability(e.g.low laser absorption,high oxidation sensitivity and cracking tendency).To further promote the development of LDED high-performance Al alloys,this review offers a deep understanding of the challenges and strategies to improve printability in LDED Al alloys.The porosity,cracking,distortion,inclusions,element evaporation and resultant inferior mechanical properties(worse than laser powder bed fusion)are the key challenges in LDED Al alloys.Processing parameter optimizations,in-situ alloy design,reinforcing particle addition and field assistance are the efficient approaches to improving the printability and performance of LDED Al alloys.The underlying correlations between processes,alloy innovation,characteristic microstructures,and achievable performances in LDED Al alloys are discussed.The benchmark mechanical properties and primary strengthening mechanism of LDED Al alloys are summarized.This review aims to provide a critical and in-depth evaluation of current progress in LDED Al alloys.Future opportunities and perspectives in LDED high-performance Al alloys are also outlined.

Development of Micro Selective Laser Melting:The State of the Art and Future Perspectives

Additive manufacturing(AM)is gaining traction in the manufacturing industry for the fabrication of components with complex geometries using a variety of materials.Selective laser melting(SLM)is a common AM technique that is based on powder-bed fusion(PBF)to process metals;however,it is currently focused only on the fabrication of macroscale and mesoscale components.This paper reviews the state of the art of the SLM of metallic materials at the microscale level.In comparison with the direct writing techniques that are commonly used for micro AM,micro SLM is attractive due to a number of factors,including a faster cycle time,process simplicity,and material versatility.A comprehensive evaluation of various research works and commercial systems for the fabrication of microscale parts using SLM and selective laser sintering(SLS)is conducted.In addition to identifying existing issues with SLM at the microscale,which include powder recoating,laser optics,and powder particle size,this paper details potential future directions.A detailed review of existing recoating methods in powder-bed techniques is conducted,along with a description of emerging efforts to implement dry powder dispensing methods in the AM domain.A number of secondary finishing techniques for AM components are reviewed,with a focus on implementation for microscale features and integration with micro SLM systems.

Picosecond Laser Surface Texturing of a Stavax Steel Substrate for Wettability Control

In this investigation,a picosecond laser was employed to fabricate surface textures on a Stavax steel substrate,which is a key material for mold fabrication in the manufacturing of various polymer products.Three main types of surface textures were fabricated on a Stavax steel substrate:periodic ripples,a two-scale hierarchical two-dimensional array of micro-bumps,and a micro-pits array with nanoripples.The wettability of the laser-textured Stavax steel surface was converted from its original hydrophilicity into hydrophobicity and even super-hydrophobicity after exposure to air.The results clearly show that this super-hydrophobicity is mainly due to the surface textures.The ultrafast laserinduced catalytic effect may play a secondary role in modifying the surface chemistry so as to lower the surface energy.The laser-induced surface textures on the metal mold substrates were then replicated onto polypropylene substrates via the polymer injection molding process.The surface wettability of the molded polypropylene was found to be changed from the original hydrophilicity to superhydrophobicity.This developed process holds the potential to improve the performance of fabricated plastic products in terms of wettability control and easy cleaning.

Analysis of the corrosion performance of binder jet additive manufactured magnesium alloys for biomedical applications

Binder jet printing(BJP)is a state-of-the-art additive manufacturing technique for producing porous magnesium structures.Porous MgZn-Zr based BJP samples were assessed for corrosion performance in simulated body fluids by electrochemical and hydrogen evolution measurements.The corrosion rates of the BJP specimens were significantly higher than solid controls,even after accounting for their larger surface areas,suggesting that the BJP microstructure is detrimental to corrosion performance.X-ray computed tomography revealed nonuniform corrosion within the porous structure,with corrosion products forming on the pore walls.Impregnating the pores with hydroxyapatite or polymers greatly improved the corrosion resistance of the BJP samples.

Digital manufacturing of personalized magnesium implants through binder jet additive manufacturing and automated post machining

While magnesium(Mg)is a promising material for personalized temporary implants,the lack of a digital manufacturing solution for Mg implants impedes its potential progress.This study introduces a hybrid manufacturing process that integrates binder jet additive manufacturing with automated dry post-machining to enable end-to-end digital manufacturing of personalized Mg implants.Spherical cap-shaped Mg implants were additively manufactured through binder jetting.These implants were placed on graphite flakes during sintering as a potential non-reactive support material,allowing unrestricted shrinkage of 15.2%to a relative density of 87%.Microstructural and dimensional analysis revealed consistent interconnected porous microstructures with a shrinkage distortion within±0.2 mm of the original digital drawing.High-speed dry milling of the sintered samples,assessed via an orthogonal cutting test,identified the optimized cutting parameters.A three-step machining process for automated 5-axis machining,along with clamping strategies,referencing,and an adaptive plug-in,were successfully implemented.The automated dry machining on binder-jet printed Mg implants resulted in an average roughness of<1.3μm with no defects.In summary,this work introduces a robust digital manufacturing solution to advance the transformative landscape of Mg implants and scaffolds.©2024 Chongqing University.Publishing services provided by Elsevier B.V.on behalf of KeAi Communications Co.Ltd.

Smart window of large transparency-tuning capacity

Windows are one of the least energy-efficient components of a building.It allows energy to escape,leading to high cooling demand in summer and energy loss in winter.Sunlight and temperature in the building also affect people's health,comfort,and even productivity.As a result,controlling the heat and light entering the building dynamically is critical for improving the comfort of building occupants and reducing energy consumption.In this work,we develop a tunable smart window based on transparent dielectric elastomer actuators(DEAs)as an alternative solution to sunlight and temperature control.The transparency-tuning is achieved by creating wrinkles in a soft elastomer film made of waterborne polyurethane(WPU).The actuation mechanism is based on highly transparent dielectric elastomer actuators that use all solid-state stretchable transparent conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/(PEDOT:PSS/WPU)as compliant electrodes.The modulation range of the smart tunable window with direct viewing is achieved to be 35%to 90%,which is one of the largest among existing tunable windows.At the low-transparency state,the window can also effectively block the heat and decrease the temperature rise to 2℃over 200 s,while the ambient temperature rises by 6℃with direct sunlight.We anticipate that this transparency-tuning mechanism is potentially useful for privacy protection,smart glass,projector screens,displays,and camouflage.The heat isolation feature also has the potential to reduce carbon emissions and improve the sustainability of buildings and greenhouses.

4D printing for future manufacturing

Additive manufacturing(AM),also called three-dimensional(3D)printing,offers disruptive design freedom and manufacturing flexibility due to the layer-wise incremental formation manner of components.Advancements in AM techniques provide unique advantages and feasibilities for overcoming challenges arising from fabricating parts with complexities in geometry,materials,and properties.

Femtosecond laser-induced surface wettability modification of polystyrene surface

In this paper, we demonstrated a simple method to create either a hydrophilic or hydrophobic surface. With femtosecond laser irradiation at different laser parameters, the water contact angle (WCA) on polystyrene’s surface can be modified to either 12.7° or 156.2° from its original WCA of 88.2°. With properly spaced micro-pits created, the surface became hydrophilic probably due to the spread of the water droplets into the micro-pits. While with properly spaced micro-grooves created, the surface became rough and more hydrophobic. We investigated the effect of laser parameters on WCAs and analyzed the laser-treated surface roughness, profiles and chemical bonds by surface profilometer, scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). For the laser-treated surface with low roughness, the polar (such as C—O, C=O, and O—C=O bonds) and non-polar (such as C—C or C—H bonds) groups were found to be responsible for the wettability changes. While for a rough surface, the surface roughness or the surface topography structure played a more significant role in the changes of the surface WCA. The mechanisms involved in the laser surface wettability modification process were discussed.

PMMA-Based Microsphere Mask for Sub-wavelength Photolithography

The authors present a polymethyl methacrylate(PMMA)-based,reusable microsphere mask used in the laser sub-wavelength photolithography.In order to overcome the diffraction limit to achieve nano-structuring using l-|im laser wavelength,the photolithography technique was conventionally characterized by applying a one-off monolayer of silica microspheres serving as Mie scatterers.Addressing the major limitation of this technique,which was that the monolayer of microspheres must be prepared on the sample surface prior to fabrication,the proposed hot press approach could firmly fuse the 1silica microspheres to the PMMA base without the use of adhesives.The PMMA-based microsphere mask could hence reduce the amount of work for the monolayer preparation and was proven reusable for at least 20 times without damage to top or bottom surfaces.Using the mask,dimples that were 0.7 pm in diameter and 40 nm in depth were produced on tool steel by a single pulse of picosecond laser irradiation.