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1. Tailoring compositionally graded interface of 316L stainless steel to Al12Si aluminum alloy bimetallic structures via Additive Manufacturing

   https://doi.org/doi.org/10.1021/acsami.0c21478  

   Zhang, Yanning; Bandyopadhyay, Amit (February 2021, ACS applied materials interfaces)

   null (Ed.)

   316L stainless steel (SS) to Al12Si aluminum alloy structures were processed, tailoring the compositionally graded interface on a SS 316 substrate using a directed energy deposition (DED)-based additive manufacturing (AM) process. Applying such a compositionally graded transition on bimetallic materials, especially joining two dissimilar metals, could avoid the mechanical property mismatch. This study's objective was to understand the processing parameters that influence the properties of AM processed SS 316L to Al12Si bimetallic structures. Two different approaches fabricated these bimetallic structures. The results showed no visible defects on the as-fabricated samples using 4 layers of Al-rich mixed composition as the transition section. The microstructural characterization showed a unique morphology in each section. Both cooling rate and compositional variations caused microstructural variation. FeAl, Fe2Al5, and FeAl3 intermetallic phases were formed at the compositionally graded transition section. After stress relief heat-treatment of SS 316L/Al12Si bimetallic samples, diffused intermetallic phases were seen at the compositionally graded transition. At the interface, as processed, bimetallic structures had a microhardness value of 834.2 ± 107.1 HV0.1, which is a result of the FeAl3 phase at the compositionally graded transition area. After heat-treatment, the microhardness value reduced to 578.7 ± 154.1 HV0.1 due to more Fe dominated FexAly phase formation. The compression test results showed that the non-HT and HT SS 316L/Al12Si bimetallic structures had a similar maximum compressive strength of 299.4 ± 22.1 MPa and 270.1 ± 27.1 MPa, respectively. 

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2. First synthesis of a unique icosahedral phase from the Khatyrka meteorite by shock-recovery experiment

   https://doi.org/10.1107/S2052252520002729  

   Hu, Jinping; Asimow, Paul D.; Ma, Chi; Bindi, Luca (May 2020, IUCrJ)

   Icosahedral quasicrystals (i-phases) in the Al–Cu–Fe system are of great interest because of their perfect quasicrystalline structure and natural occurrences in the Khatyrka meteorite. The natural quasicrystal of composition Al 62 Cu 31 Fe 7 , referred to as i-phase II, is unique because it deviates significantly from the stability field of i-phase and has not been synthesized in a laboratory setting to date. Synthetic i-phases formed in shock-recovery experiments present a novel strategy for exploring the stability of new quasicrystal compositions and prove the impact origin of natural quasicrystals. In this study, an Al–Cu–W graded density impactor (GDI, originally manufactured as a ramp-generating impactor but here used as a target) disk was shocked to sample a full range of Al/Cu starting ratios in an Fe-bearing 304 stainless-steel target chamber. In a strongly deformed region of the recovered sample, reactions between the GDI and the steel produced an assemblage of co-existing Al 61.5 Cu 30.3 Fe 6.8 Cr 1.4 i-phase II + stolperite (β, AlCu) + khatyrkite (θ, Al 2 Cu), an exact match to the natural i-phase II assemblage in the meteorite. In a second experiment, the continuous interface between the GDI and steel formed another more Fe-rich quinary i-phase (Al 68.6 Fe 14.5 Cu 11.2 Cr 4 Ni 1.8 ), together with stolperite and hollisterite (λ, Al 13 Fe 4 ), which is the expected assemblage at phase equilibrium. This study is the first laboratory reproduction of i-phase II with its natural assemblage. It suggests that the field of thermodynamically stable icosahedrite (Al 63 Cu 24 Fe 13 ) could separate into two disconnected fields under shock pressure above 20 GPa, leading to the co-existence of Fe-rich and Fe-poor i-phases like the case in Khatyrka. In light of this, shock-recovery experiments do indeed offer an efficient method of constraining the impact conditions recorded by quasicrystal-bearing meteorite, and exploring formation conditions and mechanisms leading to quasicrystals. 

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3. A Mechanistic Perspective on the Mechanochemical Method To Reduce Carbonyl Groups with Stainless Steel and Water

   https://doi.org/10.1002/ejoc.202300149  

   Mokhtar, Mennatullah_M; Andersen, Joel_M; Kister, Ethan_A; Hopkins, Jordan_X; Estier, Tom; Hamilton, Fiona; Guan, Hairong; Mack, James; Haley, Rebecca_A (May 2023, European Journal of Organic Chemistry)

   Abstract Mechanochemistry through high‐speed ball milling has become an increasingly popular method for performing organic transformations. This newfound interest in high‐speed ball milling is in part driven by the benefit of performing reactions in the absence of solvent. Mechanochemical reactions are often conducted in stainless‐steel vials with stainless‐steel balls. Since stainless steel is made of several readily oxidizable metals (Fe, Cr, and Ni), reduction reactions using water as a hydrogen source were explored using a temperature‐controlled mixer mill. Mechanistic studies suggest that the reduction proceeds via a single electron transfer (SET) pathway, with iron and nickel being essential components for the reaction. 

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4. Developing Bioactive-Nanograined Metals With Bacterial Biofilm Inhibition Properties For Orthopedic Devices

   Kelkar, Shaunak; Saleh, Bahram; Yusa, Fumie; Suzuki, Yohei; Komatsu, Takafumi; Webster, Thomas (January 2021, Orthopaedic Research Society)

   null (Ed.)

   INTRODUCTION: Orthopedic implants are important therapeutic devices for the management of a wide range of orthopedic conditions. However, bacterial infections of orthopedic implants remain a major problem, and not an uncommon one, leading to an increased rate of osteomyelitis, sepsis, implant failure and dysfunction, etc. Treating these infections is more challenging as the causative organism protects itself by the production of a biofilm over the implant’s surface (1). Infections start by the adhesion and colonization of pathogenic bacteria such as Staphylococcus aureus (SA), Staphylococcus epidermidis (SE), Escherichia coli (E. coli), Methicillin-Resistant Staphylococcus aureus (MRSA), and Multi-Drug Resistant Escherichia coli (MDR E. coli) on the implant’s surfaces. Specifically, Staphylococcus comprises up to two-thirds of all pathogens involved in orthopedic implant infections (2). However, bacterial surface adhesion is a complex process influenced by several factors such as chemical composition, hydrophobicity, magnetization, surface charge, and surface roughness of the implant (3). Considering the intimate association between bacteria and the implant surface, we measured the effect of stainless-steel surface properties on bacterial surface attachment and subsequent formation of biofilms controlling above mentioned factors. METHODS: The prominent bacteria responsible for orthopedic implant infections (SA, SE, E. coli, MRSA, and MDR E. coli) were used in this study. We were able to control the grain size of medical grade 304 and 316L stainless steel without altering their chemical composition (grain size range= 20μm-200nm) (4). Grain size control affected the nano-topography of the material surfaces which was measured by an Atomic Force Microscope (AFM). Grain sizes, such as 0.2, 0.5, 1, 2, 3, 9, and 10 μm, were used both polished and non-polished. All the stainless-steel samples were cleaned by treating with acetone and ethanol under sonication. Triplicates of all polished and non-polished samples with different grain sizes were subjected to magnetization of DM, 0.1T, 0.5T, and 1T, before seeding them with the bacteria. Controls were used in the form of untreated samples. Bacterial were grown in Tryptic Soy Broth (TSB). An actively growing bacterial suspension was seeded onto the stainless-steel discs into 24-well micro-titer plates and kept for incubation. After 24 hours of incubation, the stainless-steel discs were washed with Phosphate Buffer Saline (PBS) to remove the plankton bacteria and allow the sessile bacteria in the biofilm to remain. The degree of development of the bacterial biofilms on the stainless-steel discs were measured using spectrophotometric analysis. For this, the bacterial biofilm was removed from the stainless steel by sonication. The formation of biofilms was also determined by performing a biofilm staining method using Safranin. RESULTS SECTION: AFM results revealed a slight decrease in roughness by decreasing the grain size of the material. Moreover, the samples were segregated into two categories of polished and non-polished samples, in which polishing decreased roughness significantly. After careful analysis we found out that polished surfaces showed a higher degree for biofilm formation in comparison to the non-polished ones. We also observed that bacteria showed a higher rate for biofilm formation for the demagnetized samples, whereas 0.5T magnetization showed the least amount of biofilm formation. After 0.5T, there was no significant change in the rate of biofilm formation on the stainless-steel samples. Altogether, stainless steel samples containing 0.5 μm and less grainsize, and magnetized with 0.5 tesla and stronger magnets demonstrated the least degree of biofilm formation. DISCUSSION: In summary, the results demonstrate that controlling the grain size of medical grade stainless steel can control and mitigate bacterial responses on, and thus possibly infections of, orthopedic implants or other implantable devices. The research was funded by Komatsuseiki Kosakusho Co., Ltd (KSJ: Japan) SIGNIFICANCE/CLINICAL RELEVANCE: Orthopedic implants that more than 70% of them are made of metals (i.e., stainless steel, titanium, and cobalt-chromium alloys) are failing through loosening and breakage due to their limited mechanical properties. On the other hand, the risk of infection for these implants and its financial burden on our society is undeniable. We have seen that our uniformly nanograined stainless steel shows improved mechanical properties (i.e., higher stiffness, hardness, fatigue) as compared to conventional stainless steel along with the reduction of biofilm formation on its surface. These promising results made us to peruse the development of nanograined titanium and cobalt-chromium alloys for resolving the complications of orthopedic implants. 

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5. NanoSUS (Ultra Fine Grained Stainless-Steel) for Orthopedic Implants

   Bahram Saleh, Ada Vernet-Crua (February 2021, Orthopaedic Research Society)

   Statement of Purpose: Orthopedic implants are important therapeutic devices for the management of a wide range of orthopedic conditions. However, bacterial infections of orthopedic implants remain a major problem, and not an uncommon one, leading to an increased rate of osteomyelitis, sepsis, implant failure and dysfunction, etc. Treating these infections is more challenging as the causative organism protects itself by the production of a biofilm over the implant’s surface (1). Infections start by the adhesion and colonization of pathogenic bacteria such as Staphylococcus aureus (SA), Staphylococcus epidermidis (SE), Escherichia coli (E. coli), Methicillin-Resistant Staphylococcus aureus (MRSA), and Multi-Drug Resistant Escherichia coli (MDR E. coli) on the implant’s surfaces. Specifically, Staphylococcus comprises up to two-thirds of all pathogens involved in orthopedic implant infections (2). However, bacterial surface adhesion is a complex process influenced by several factors such as chemical composition, hydrophobicity, magnetization, surface charge, and surface roughness of the implant (3). Considering the intimate association between bacteria and the implant surface, we measured the effect of stainless-steel surface properties on bacterial surface attachment and subsequent formation of biofilms controlling above mentioned factors. Method: The prominent bacteria responsible for orthopedic implant infections (SA, SE, E. coli, MRSA, and MDR E. coli) were used in this study. We were able to control the grain size of medical grade 304 and 316L stainless steel without altering their chemical composition (grain size range= 20μm-200nm) (4). Grain size control affected the nano-topography of the material surfaces which was measured by an Atomic Force Microscope (AFM). Grain sizes, such as 0.2, 0.5, 1, 2, 3, 9, and 10 μm, were used both polished and non-polished. All the stainless-steel samples were cleaned by treating with acetone and ethanol under sonication. Triplicates of all polished and non-polished samples with different grain sizes were subjected to magnetization of DM, 0.1T, 0.5T, and 1T, before seeding them with the bacteria. Controls were used in the form of untreated samples. Bacterial were grown in Tryptic Soy Broth (TSB). An actively growing bacterial suspension was seeded onto the stainless-steel discs into 24-well micro-titer plates and kept for incubation. After 24 hours of incubation, the stainless-steel discs were washed with Phosphate Buffer Saline (PBS) to remove the plankton bacteria and allow the sessile bacteria in the biofilm to remain. The degree of development of the bacterial biofilms on the stainless-steel discs were measured using spectrophotometric analysis. For this, the bacterial biofilm was removed from the stainless steel by sonication. The formation of biofilms was also determined by performing a biofilm staining method using Safranin. Results: AFM results revealed a slight decrease in roughness by decreasing the grain size of the material. Moreover, the samples were segregated into two categories of polished and non-polished samples, in which polishing decreased roughness significantly. After careful analysis we found out that polished surfaces showed a higher degree for biofilm formation in comparison to the non-polished ones. We also observed that bacteria showed a higher rate for biofilm formation for the demagnetized samples, whereas 0.5T magnetization showed the least amount of biofilm formation. After 0.5T, there was no significant change in the rate of biofilm formation on the stainless-steel samples. Altogether, stainless steel samples containing 0.5 μm and less grainsize, and magnetized with 0.5 tesla and stronger magnets demonstrated the least degree of biofilm formation. Conclusion: In summary, the results demonstrate that controlling the grain size of medical grade stainless steel can control and mitigate bacterial responses on, and thus possibly infections of, orthopedic implants or other implantable devices. The research was funded by Komatsuseiki Kosakusho Co., Ltd (KSJ: Japan) 

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