Tuning the Mechanical and Antimicrobial Performance of a Cu-Based Metallic Glass Composite through Cooling Rate Control and Annealing

The influence of cooling rate on the wear and antimicrobial performance of a Cu52Z41Al7 (at. %) bulk metallic glass (BMG) composite was studied and the results compared to those of the annealed sample (850 °C for 48 h) and to pure copper. The aim of this basic research is to explore the potential use of the material in preventing the spread of infections. The cooling rate is controlled by changing the mould diameter (2 mm and 3 mm) upon suction casting and controlling the mould temperature (chiller on and off). For the highest cooling rate conditions CuZr is formed but CuZr2 starts to crystallise as the cooling rate decreases, resulting in an increase in the wear resistance and brittleness, as measured by scratch tests. A decrease in the cooling rate also increases the antimicrobial performance, as shown by different methodologies (European, American and Japanese standards). Annealing leads to the formation of new intermetallic phases (Cu10Zr7 and Cu2ZrAl) resulting in maximum scratch hardness and antimicrobial performance. However, the annealed sample corrodes during the antimicrobial tests (within 1 h of contact with broth). The antibacterial activity of copper was proved to be higher than that of any of the other materials tested but it exhibits very poor wear properties. Cu-rich BMG composites with optimised microstructure would be preferable for some applications where the durability requirements are higher than the antimicrobial needs

Improving predictability of additively manufactured Ti-6Al-4 V lattices for orthopaedic devices: A parametric and struts angle study

The advancement of metal additive manufacturing has recently enabled the integration of porous lattice regions into orthopaedic devices. Despite the increased utilisation of various metamaterials there remains limited understanding of how to optimise laser process specifically for these geometries. Selective laser melting (SLM) of representative single struts is focused on this study from the perspective of surface properties, mechanical performance, and in-vitro biological response. Specifically, the influence of laser power (100 – 200 W) and speed (2250 – 900 mm/s) and struts angle (20–90°) for a 250μ m strut diameter was explored. Struts built below 45° to the substrate using optimal laser parameters (150 W and 1125 mm/s) were found to exhibit a surface topography that facilitated the highest level of cell adhesion (84.3 cells/mm2) after 24 hrs (p ≤ 0.001). To support this finding, a novel image analysis method was developed to characterise the average roughness across the complete strut profile. An opposite trend was observed for mechanical strength with struts built at above 45° without failure. These findings were brought together in a parameter design map was to guide stakeholders in producing customised biomedical devices, enabling control of key physiochemical properties with the aim of maximising osseointegration

Development of Antibacterial Steel Surfaces Through Laser Texturing

[Abstract] The aim of the present study was to develop novel antibacterial touch surfaces through the laser texturing optimization of stainless steel. A wide range of laser fluence (2.11 J/cm2–5.64 J/cm2) and scanning interval (10 µm–30 μm) parameters were explored. The impact of surfaces with different patterns, wettability, and oxidation states on the antimicrobial behavior of Escherichia coli K-12 and biofilm hyper-producing Acinetobacter baumannii MAR002 was assessed. Modification of laser input enacted topographical changes with high scanning intervals leading to ordered surface patterns, while increasing the laser fluence to 5.64 J/cm2 created larger and less ordered plateaus and valleys. Texturing also drove a transition from a hydrophilic starting surface with a contact angle of 80.67° ± 3.35° to hydrophobic (138°–148°). Antimicrobial analysis and bioluminescence assays of E. coli, alongside biofilm forming test through A. baumannii MAR002 indicated the ability of laser texturing to produce effective bactericidal touch surfaces. No simple correlation was found between wettability and bacterial behavior, revealing that proliferation is dependent on roughness, oxidation, and wettability. For the conditions selected in this study, a laser fluence of 5.64 J/cm2 and a scanning interval of 10 µm showcased the lowest amount of recovered bacteria after 30 min.This research was supported by Project Nos. 592 p-01216A and IJCI-2016-29524 (awarded to A.P.G.), funded by the Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC) and MINECO, respectively. This manuscript is part of Process Design to Prevent Prosthetic Infections (Grant No. EP/P02341X/1)Sociedad Española de Enfermedades Infecciosas y Microbiología Clínica; 592 p-01216AReino Unido. Engineering and Physical Sciences Research Council; EP/P02341X/

Optimizing the antimicrobial performance of metallic glass composites through surface texturing

In the present work, we analyse the influence of laser texturing on the physicochemical and bactericidal properties of Cu55Zr40Al5 Bulk Metallic Glass Composite (BMGC) to develop novel antimicrobial touch surfaces. Laser ablation was employed to increase the average roughness of BMGC samples from 0.08 ± 0.02 μm to 3.07 ± 0.96 μm using a maximum laser fluence of 2.82 J/cm2. This treatment also influenced surface chemistry causing the formation of CuO, CuO2, ZrO2, more prominent as the laser fluence was increased. Alongside chemical and topographic changes, the initial contact angle of the as-cast sample was found to increase from 85.81° to angles between 105.72° and 126.17° after texturing. The influence of these modifications on the antimicrobial performance of all rapidly solidified alloys was studied with Escherichia coli K12 modified to drive lux expression. Luminescence measurements revealed a reduction in bacterial growth as the laser fluence applied was risen. This increase in bactericidal effect as laser fluence rose was corroborated with recovery tests, which showed an increase in log reduction of E. coli K12 from 1.10 (for as-cast sample) to 2.16 (textured at 2.82 J/cm2) after 4 h of contact. Variations in bacterial morphology were observed with SEM imaging, specifically, a length increase of E. coli cells from 2 μm up to 20 μm could be observed in cells deposited on the textured surfaces. Deposited bacteria on laser treated samples revealed loss of membrane integrity, which along the aforementioned morphological changes suggest both external and DNA damage in all ablated samples. These findings reveal the possibility of tailoring the antimicrobial behaviour of BMGCs through laser texturing, which could be used as novel touch surfaces to tackle nosocomial infections along antibiotic resistance

Antimicrobial and wear performance of Cu-Zr-Al metallic glass composites

The antimicrobial and wear behaviour of metallic glass composites corresponding to the Cu50+x(Zr44Al6)50-x system with x=(0, 3 and 6) has been studied. The three compositions consist of crystalline phases embedded in an amorphous matrix and they exhibit crystallinity increase with increasing copper content, i.e., decrease of the glass-forming ability. The wear resistance also increases with the addition of copper as indirectly assessed from H/Er and H3/Er2 parameters obtained from nanoindentation tests. These results are in agreement with scratch tests since for the alloy with highest Cu content, i.e., Cu56Zr38.7Al5.3, reveals a crack increase, lower pile-up, prone adhesion wear in dry sliding and higher scratch groove volume to pile-up volume. Samples with higher Cu content revealed higher hydrophilicity. Time-kill studies revealed higher reduction in colony-forming units for E. coli (gram-negative) and B. subtilis (gram-positive) after 60 min of contact time for the Cu56Zr38.7Al5.3 alloy and all the samples achieved a complete elimination of bacteria in 250 min

Stakeholder Perspectives on the Current and Future of Additive Manufacturing in Healthcare

Additive manufacturing (AM) technologies have disrupted many supply chains by making new designs and functionalities possible. The opportunity to realize complex customized structures has led to significant interest within healthcare; however, full utilization critically requires the alignment of the whole supply chain. To offer insights into this process, a survey was conducted to understand the views of different medical AM stakeholders. The results highlighted an agreement between academics, designers, manufacturers, and medical experts, that personalization and design control are the main benefits of AM. Interestingly, surface finish was consistently identified as an obstacle. Nevertheless, there was a degree of acceptance that post-processing was necessary to achieve appropriate quality control. Recommendations were made for extending the use of in situ process monitoring systems to support improved reproducibility. Variations in the future vision of AM were highlighted between stakeholder groups and areas of interest for development noted for each stakeholder. Collectively, this survey indicates that medical stakeholders agree on the capabilities of AM but have different priorities for its implementation and progression. This highlights a degree of disconnection among the supply chain at a ground level; thus, collaboration on AM specific standards and enhancement of communication between stakeholders from project inception is recommended

Selective Laser Melting of Ti-6Al-4V Lattices:Case Study on a Spinal Cage Prosthesis

Biomedical prostheses are artificial devices suitable for the replacement of missing or inefficient parts of the body, implanted to reduce the anatomical or functional deficiency, and sometimes also applied for aesthetic purposes. Despite this type of medical devices represents today a very innovative sector from the medical and engineering point of view, some issues, inherent to the interaction between human body and the external hosts must be considered. It is important that the weight and porosity of the prosthesis respect the patient’s physiological equilibrium which permit an appropriate osseointegration where needed. A typical solution is a lattice structure, which can be manufactured by Additive Manufacturing techniques which, as known, permit to build complex geometries in comparison with other processing routes. Lattice structure are typically characterized by both stiffness and strength significantly lower than the full part of the structure. Generally, for this reason, the lattices are applied to the low-stress areas, leaving a portion of solid sufficient to transmit the loads involved, or in such a way to guarantee the desired flexibility of the part-itself. During the design of lattices some limitations regarding their printability must be considered, such as the minimum printable dimension and the necessary support parts. A Design of Experiment analysis was conducted to identify the optimal parameters to manufacture a spinal cage with negligible porosity via laser powder bed fusion using Ti6Al4V alloy.</p

Wear rate at RT and 100 °C and operating temperature range of microalloyed Cu50Zr50 shape memory alloy

The effect of microalloying with Co on the wear rate and on the operating temperature range of Cu50Zr50 shape memory alloy against 304 stainless steel counterface has been investigated by studying the mass loss and wear behaviour of Cu50Zr50, Cu49.5Zr50Co0.5 and Cu49Zr50Co1 at. % at room temperature (RT) and 100 °C. For the alloys tested at 15 N, maximum wear resistance is achieved at RT for the alloy with 0.5 at. % Co compared to the parent Cu50Zr50 at. % alloy. This is mostly attributed to the effect of Co in promoting stress-induced martensitic transformation (i.e., work-hardening). For wear tests at 100 °C (100 °C plus friction temperature for 1 h), the mass loss is higher than that at RT since martensite partly reverts into soft austenite through an isothermal process. In addition, the alloys are more prone to oxidation with formation of thick oxide layers that can easily get fragmented and detached from the surface thus resulting is higher mass loss than at RT. The effect of Co in promoting martensitic transformation is negligible when testing at 100 °C, since the stress-induced martensite partly reverts into austenite and the thick oxide layer formed on the surface not only masks the effect of the underlaying substrate for it can also easily detach upon wear

Repeated exposure of nosocomial pathogens to silver does not select for silver resistance but does impact ciprofloxacin susceptibility

The rise of antimicrobial resistant bacteria coupled with a void in antibiotic development marks Antimicrobial Resistance as one of the biggest current threats to modern medicine. Antimicrobial metals are being developed and used as alternative anti-infectives, however, the existence of known resistance mechanisms and limited data regarding bacterial responses to long-term metal exposure are barriers to widespread implementation. In this study, a panel of reference and clinical strains of major nosocomial pathogens were subjected to serial dosage cycles of silver and ciprofloxacin. Populations exposed to silver initially showed no change in sensitivity, however, increasingly susceptibility was observed after the 25th cycle. A control experiment with ciprofloxacin revealed a selection for resistance over time, with silver treated bacteria showing faster adaptation. Morphological analysis revealed filamentation in Gram negative species suggesting membrane perturbation, while sequencing of isolated strains identified mutations in numerous genes. These included those encoding for efflux systems, chemosensory systems, stress responses, biofilm formation and respiratory chain processes, although no consistent locus was identified that correlated with silver sensitivity. These results suggest that de novo silver resistance is hard to select in a range of nosocomial pathogens, although silver exposure may detrimentally impact sensitivity to antibiotics in the long term. Statement of significance: The adaptability of microbial life continuously calls for the development of novel antibiotic molecules, however, the cost and risk associated with their discovery have led to a drying up in the pipeline, causing antimicrobial resistance (AMR) to be a major threat to healthcare. From all available strategies, antimicrobial metals and, more specifically, silver showcase large bactericidal spectrum and limited toxic effect which coupled with a large range of processes available for their delivery made these materials as a clear candidate to tackle AMR. Previous reports have shown the ability of this metal to enact a synergistic effect with other antimicrobial therapies, nevertheless, the discovery of Ag resistance mechanisms since the early 70s and limited knowledge on the long term influence of silver on AMR poses a threat to their applicability. The present study provides quantitative data on the influence of silver based therapies on AMR development for a panel of reference and clinical strains of major nosocomial pathogens, revealing that prolonged silver exposure may detrimentally impact sensitivity to antibiotics