Plain metallic biomaterials:opportunities and challenges

The‘plainification of materials’has been conceptualized to promote the sustainable development of materials.This perspective,for the first time in the field of biomaterials,proposes and defines‘plain metallic biomaterials(PMBs)’with demonstrated research and application case studies of pure titanium with high strength and toughness,and biodegradable,fine-grained and high-purity magnesium.Then,after discussing the features,benefits and opportunities of PMBs,the challenges are analyzed from both technical and regulatory aspects.Regulatory perspectives on PMB-based medical devices are also provided for the benefit of future research,development and commercialization.

Electrochemical Corrosion Behavior and Mechanical Response of Selective Laser Melted Porous Metallic Biomaterials

The porous metallic biomaterials have attracted significant attention for implants because their lower young's modulus matches the human bones, which can eliminate the stress shielding effect and facilitate the growth of bone tissue cells. The porous metallic biomaterials fabricated by selective laser melting (SLM) have broad prospects, but the surface of the SLM-built porous structure has been severely adhered with unmelted powders, which affects the forming accuracy and surface quality. The porous metallic biomaterials face the corrosion problem of complex body fluid environments during service, so their corrosion resistance in the human body is extremely important. The surface quality will affect the corrosion resistance of the porous metallic biomaterials. Therefore, it is necessary to study the effect of post-treatment on the corrosion resistance of SLMed samples. In this work, the mechanical response and the electrochemical corrosion behavior in simulated body fluid of diamond and pentamode metamaterials Ti-6Al-4V alloy fabricated by SLM before and after sandblasting were studied. After sandblasting, the mechanical properties of the two porous metallic biomaterials were slightly improved, and the self-corrosion potential and pitting potential were more negative;meanwhile, the self-corrosion current density and passive current density increased, indicating that its corrosion performance decreased, and the passive film stability of sandblasted samples got worse.

Preface to SPECIAL ISSUE: Advances in Metallic Biomaterials

Metallic biomaterials,especially advances in various biodegradable metallic materials and porous or open-cellular metallic materials having important applications as orthopaedic and other biomedical implants or appliances,have become the focus of many research groups worldwide.This Special Issue themed on"Advances in

Additive manufacturing and 3D printing of metallic biomaterials

The advancements of 3D printing technology have been combined with the use of metallic biomaterials to cre-ate devices and products for the biomedical field.3D printing has been a revolutionary process that makes the fabrication of metallic biomedical devices highly specific and simultaneously easier than other fabrication methods.The purpose and overall function of each medical device created is dependent on the type of metal used along with its fabrication method.In this review paper,the major characteristics of metallic biomaterials,includ-ing iron,magnesium,zinc,titanium,cobalt,and stainless steel,will be discussed.Major considerations of these metallic biomaterials include degradation rate,biocompatibility,and mechanical properties will be addressed.Importantly,various additive manufacturing processes will be described.Depending on the 3D printing method and the use of specific alloys,these properties can be altered to optimize their functionality for purposes such as bone implants,stents,and other devices.

Topology optimization of microstructure and selective laser meltingfabrication for metallic biomaterial scaffolds

The precise design and fabrication of biomaterial scaffolds is necessary to provide a systematic study for bone tissue engineering. Biomaterial scaffolds should have sufficient stiffness and large porosity. These two goals generally contradict since larger porosity results in lower mechanical properties. To seek the microstructure of maximum stiffness with the constraint of volume fraction by topology optimization method, algorithms and programs were built to obtain 2D and 3D optimized microstructure and then they were transferred to CAD models of STL format. Ti scaffolds with 30% volume fraction were fabricated using a selective laser melting （SLM） technology. The architecture and pore shape in the metallic biomaterial scaffolds were relatively precise reproduced and the minimum mean pore size was 231μm. The accurate fabrication of intricate microstructure has verified that the SLM process is suitable for fabrication of metallic biomaterial scaffolds.

Bioactive glass coatings on metallic implants for biomedical applications

Metallic implant materials possess adequate mechanical properties such as strength,elastic modulus,and ductility for long term support and stability in vivo.Traditional metallic biomaterials,including stainless steels,cobalt-chromium alloys,and titanium and its alloys,have been the gold standards for load-bearing implant materials in hard tissue applications in the past decades.Biodegradable metals including iron,magnesium,and zinc have also emerged as novel biodegradable implant materials with different in vivo degradation rates.However,they do not possess good bioactivity and other biological functions.Bioactive glasses have been widely used as coating materials on the metallic implants to improve their integration with the host tissue and overall biological performances.The present review provides a detailed overview of the benefits and issues of metal alloys when used as biomedical implants and how they are improved by bioactive glass-based coatings for biomedical applications.

Bulk Metallic Glasses: MRI Compatibility and Its Correlation with Magnetic Susceptibility

Several bulk metallic glasses （BMGs） were selected to in vitro assess their magnetic resonance imaging （MRI） compatibility with agarose gel as a phantom, in terms of the extent of susceptibility artifacts in magnetic resonance image. The investigated metals include the Au49Ags.sPd2.3Cu26.9Si16.3, Zr61Ti2Cu2sA112, Cu50.4Nis.0Ti31Zr13 and Ti47Cu38Zr7.5Fe2.5Sn2Si1Ag2, together with pure titanium （CP-Ti） and Co-28Cr-6Mo alloy （ASTM-F799） for comparison. The artifact extent in MR images was quantitatively characterized according to the total volume in reconstructed 3D images with a series of slices under acquisition by fast spin echo （FSE） sequence and gradient echo （GRE） sequence. As indicated, artifact severity of the BMGs is much less than that of the CoCrMo alloy. The AuAgPdCuSi BMG manifested the smallest arti- fact among the four BMGs, while the TiCuZrFeSnSiAg BMG is comparative to the CP-Ti. The MRI compatibility of BMGs is ranked as a sequence of the Au-, Zr-, Cu- and Ti-based alloys. Dependence of material mag- netic susceptibility on artifact extent is also the case of the BMGs, even though it does not follow a simple linear relationship within a range of △χv = 30-180 ppm. These findings are of interest to reveal that the BMGs are potentially applied in the fields associated with an interventional MRI for MRI-guided surgeries.