Powder Characterisation, Microstructure, and Mechanical Property Evolution of IN625 and IN718 During Selective Laser Melting and Heat Treatment

Additive layer manufacturing is a blanket term for a wide range of processes operating on the same underlying principle. 3D geometry is created by depositing material, layer by layer to create a final 3D geometry. Selective laser melting (SLM) is a branch of additive layer manufacturing, using a laser to fuse a powder bed of metal into each layer. This thesis investigates the SLM process and its application to nickel based superalloy materials, IN625 and IN718. IN625 and IN718 are similar nickel-based superalloys developed for use in aerospace gas turbine engines. In their conventionally manufactured form, these materials have excellent high temperature mechanical properties which make them idea for use in the hot section of gas turbine engines. The aim of this thesis was to investigate how these materials interact with the SLM process and how the material produced can be optimised to improve the range of applications it can be used for. A gap in knowledge regarding a detailed understanding of how the powders morphological and rheological properties influence its ability to be processed by SLM was identified and investigated. A wide range of characterisation methods were implemented with certain important properties being identified to assess a powders processability, namely the particle size distribution and how a significant content of fine particles below 10 μm in size can be detrimental to processability. There is also a lack of a standard powder characterisation methodology specifically for SLM applications. This is addressed with certain methods and measurements being suggested as most promising for wider SLM application. Avalanche flow testing is found to be most applicable to the critical recoating process in SLM and most able to differentiate suitable and unsuitable SLM powders. Following characterisation of the raw material feedstock powder, this thesis also investigates the influence of processing parameters on the microstructure of the material produced by the SLM process. Significant microstructural changes were observed as a result of process parameter changes. This was identified to potentially enable for in-situ modification of material microstructure to suit a manufactured material to its end application. Of the process parameters investigated, laser scan speed was most interesting, suggesting that a faster laser scan speed was able to create a similar microstructure to a much slower one. This was attributed to the reheating effect of the laser beam returning quickly to the adjacent scan line. The validity of this explanation was investigated using a simple, computational thermal model. The result is a new understanding of laser scan speed SLM and its nonlinear relationship with material temperature and microstructure evolution. Finally, post process heat treatments of SLM manufactured IN718 material were investigated. This investigation was in response to a gap in current knowledge regarding heat treatments designed specifically for SLM material. SLM IN718 has been found to have reduced high temperature mechanical properties, specifically stress rupture, which limits its application in demanding environments. In this thesis a range of post process homogenisation heat treatments were investigated, with treatments between 1030 °C and 1060 °C being found to produce material with characteristics consistent with material with excellent stress rupture properties. This novel heat treatment route could provide a method for SLM IM718, and the increased design and geometric freedoms, to be applied in more demanding applications. An evolution of the grain structure in the material was also observed and measured during high temperature homogenisation treatments. This was investigated in the final chapter, and a novel mechanism is suggested for the process of grain coarsening observed. Previously published literature explains similar evolutions as recrystallisation however this did not fit the observations during this thesis. The evolution of grain structure was observed using a process of quasi in-situ electron back scatter diffraction, and a mechanism of grain boundary length reduction, followed by grain growth, is suggested to better fit the observations. It was determined that grains are preferentially selected for growth based on their proximity to a ‘path of least resistance’ of lower angle grain boundaries. The results of this work should benefit industrial users of SLM in the fabrication of Nickel-Based Superalloy material for aerospace applications. The conclusions on powder characterisation offer an insight into available methods to better control and characterise powder feedstock materials for consistent production. Aerospace users especially may find the work regarding post process heat treatments designed specifically for SLM material, to recover lost stress rupture performance, useful in enabling the use of SLM materials, and the design freedom that brings with it, in mor demanding environments than are currently possible

Animal derived antibodies should be considered alongside convalescent human plasma to deliver treatments for COVID-19

Published data on the first 5,000 coronavirus patients to receive plasma shows promise in the United States. However, delivering convalescent plasma therapies in low- and even middle-income countries is both difficult and costly. Here we discuss the advantages and disadvantages of antisera raised in animals that ma

Pancreas Retrieval for Whole Organ and Islet Cell Transplantation

For more than five decades, we have been refining advances in pancreas whole organ and islet cell transplantation as clinical therapies to treat the ever-increasing number of patients suffering from type-1-diabetes. Research and clinical practice have contributed to making both whole organ and cellular transplantation viable therapeutic options for a broader range of patients. Furthermore, both forms of clinical transplantation results have progressively improved, due to the ongoing refinement of organ donation and its various technical processes, combined with the evolution of immunosuppression and patient care now offering excellent long-term treatment for both type-1-diabetes and concomitant renal failure. This chapter provides an overview on how this has been undertaken and achieved over decades to ultimately provide outstanding outcomes on par with other organ transplantation results. Briefly, we cover the history of pancreas retrieval procedures, the importance of donor selection, the intricate processes of the organ donor operation, preservation of the pancreas, and the ideal ways to best improve outcomes for transplantation. Improving and providing the optimal donor and preservation conditions underpinning the success of subsequent whole pancreas or islet transplantation as a safe, effective, and feasible therapeutic option for an increasing number of patients suffering from type-1-diabetes

The therapeutic potential of sialylated fragment crystallizable (Fc) domains of human IgG

Pathogens frequently use multivalent binding to sialic acid to infect cells or to modulate immunity through interactions with human sialic acid-binding immunoglobulin-type lectins (Siglecs). Molecules that interfere with these interactions could be of interest as diagnostics, anti-infectives or as immune modulators. This review describes the development of molecular scaffolds based on the crystallizable fragment (Fc) region of immunoglobulin (Ig) G that deliver high-avidity binding to innate immune receptors, including sialic acid-dependent receptors. The ways in which the sialylated Fc may be engineered as immune modulators that mimic the anti-inflammatory properties of intravenous polyclonal Ig or as blockers of sialic-acid-dependent infectivity by viruses are also discussed

Choice of Host Cell Line Is Essential for the Functional Glycosylation of the Fc Region of Human IgG1 Inhibitors of Influenza B Viruses

Abs are glycoproteins that carry a conserved N-linked carbohydrate attached to the Fc whose presence and fine structure profoundly impacts on their in vivo immunogenicity, pharmacokinetics, and functional attributes. The host cell line used to produce IgG has a major impact on this glycosylation, as different systems express different glycosylation enzymes and transporters that contribute to the specificity and heterogeneity of the final IgG-Fc glycosylation profile. In this study, we compare two panels of glycan-adapted IgG1-Fc mutants expressed in either the human endothelial kidney 293-F or Chinese hamster ovary–K1 systems. We show that the types of N-linked glycans between matched pairs of Fc mutants vary greatly and in particular, with respect, to sialylation. These cell line effects on glycosylation profoundly influence the ability of the engineered Fcs to interact with either human or pathogen receptors. For example, we describe Fc mutants that potently disrupted influenza B–mediated agglutination of human erythrocytes when expressed in Chinese hamster ovary–K1, but not in human endothelial kidney 293-F cells

IgE-tailpiece associates with α-1-antitrypsin (A1AT) to protect IgE from proteolysis without compromising its ability to interact with FcεRI

Several splice variants of IgE exist in human plasma, including a variant called IgE-tailpiece (IgE-tp) that differs from classical IgE by the replacement of two carboxy-terminal amino acids with eight novel residues that include an ultimate cysteine. To date, the role of the secreted IgE-tp isoform in human immunity is unknown. We show that levels of IgE-tp are raised in helminth-infected donors, and that both the classical form of IgE (IgE-c) and IgE-tp interact with polymers of the serine protease inhibitor alpha-1-antitrypsin (A1AT). The association of IgE-tp with A1AT polymers in plasma protects the antibody from serine protease-mediated degradation, without affecting the functional interaction of IgE-tp with important receptors, including FcεR1. That polymers of A1AT protect IgE from degradation by helminth proteases may explain why these common and normally non-disease causing polymorphic variants of A1AT have been retained by natural selection. The observation that IgE can be complexed with polymeric forms of A1AT may therefore have important consequences for our understanding of the pathophysiology of pulmonary diseases that arise either as a consequence of A1AT-deficiency or through IgE-mediated type 1 hypersensitivity responses

Glycan-independent binding and internalization of human IgG to FCMR, its cognate cellular receptory

IgM is the first antibody to be produced in immune responses and plays an important role in the neutralization of bacteria and viruses. Human IgM is heavily glycosylated, featuring five N-linked glycan sites on the μ chain and one on the J-chain. Glycosylation of IgG is known to modulate the effector functions of Fcγ receptors. In contrast, little is known about the effect of glycosylation on IgM binding to the human Fcμ receptor (hFCMR). In this study, we identify the Cμ, omain of IgM as the target of hFCMR, and show that binding and internalization of IgM by hFCMR is glycan-independent. We generated a homology-based structure for hFCMR and used molecular dynamic simulations to show how this interaction with IgM may occur. Finally, we reveal an inhibitory function for IgM in the proliferation of T cells

A common theme in interaction of bacterial immunoglobulin-binding proteins with immunoglobulins illustrated in the equine system

The M protein of Streptococcus equi subsp. equi known as fibrinogen-binding protein (FgBP) is a cell wall-associated protein with antiphagocytic activity that binds IgG. Recombinant versions of the seven equine IgG subclasses were used to investigate the subclass specificity of FgBP. FgBP bound predominantly to equine IgG4 and IgG7, with little or no binding to the other subclasses. Competitive binding experiments revealed that FgBP could inhibit the binding of staphylococcal protein A and streptococcal protein G to both IgG4 and IgG7, implicating the Fc interdomain region in binding to FgBP. To identify which of the two IgG Fc domains contributed to the interaction with FgBP, we tested two human IgG1/IgA1 domain swap mutants and found that both domains are required for full binding, with the CH3 domain playing a critical role. The binding site for FgBP was further localized using recombinant equine IgG7 antibodies with single or double point mutations to residues lying at the CH2-CH3 interface. We found that interaction of FgBP with equine IgG4 and IgG7 was able to disrupt C1q binding and antibody-mediated activation of the classical complement pathway, demonstrating an effective means by which S. equi may evade the immune response. The mode of interaction of FgBP with IgG fits a common theme for bacterial Ig-binding proteins. Remarkably, for those interactions studied in detail, it emerges that all the Ig-binding proteins target the CH2-CH3 domain interface, regardless of specificity for IgG or IgA, streptococcal or staphylococcal origin, or host species (equine or human)

IS ONLINE VIDEO-BASED EDUCATION AN EFFECTIVE METHOD TO TEACH BASIC SURGICAL SKILLS TO STUDENTS AND SURGICAL TRAINEES? A SYSTEMATIC REVIEW AND META-ANALYSIS

BACKGROUND: Online education has been increasingly utilized over the past decades. The COVID-19 pandemic accelerated the transition of conventional face-to-face curricula to online platforms, with limited evidence for its teaching efficacy. This systematic review aims to assess the effectiveness of online video-based education compared with standard conventional education in teaching basic surgical skills to surgical trainees and students undergoing medical training. METHODS: We performed a literature search in Embase, Medline, Cochrane CENTRAL and Scopus from inception until February 2022. Studies included were randomised controlled trials (RCTs) and observational studies. We included randomised controlled trials only for meta-analysis. The primary outcome was surgical skill proficiency. The secondary outcomes were participant perception, confidence and satisfaction. Two authors independently assessed the search results for eligibility, extracted the data and assessed the risk of bias using the Cochrane Risk of Bias tool 2. Where appropriate, we performed random effects meta-analyses of the pooled study data to calculate a standardized mean difference. RESULTS: A total of 11 studies met the inclusion criteria totaling 715 participants; 603 were included in qualitative analysis and 380 in meta-analysis. All included studies were assessed as having a low risk of bias. The majority of studies found no significant difference between conventional and video-based education in teaching basic surgical skills, three studies found video-based education was superior and one study found conventional education was superior. There was no statistically significant difference in skill proficiency between the two groups (standardized mean difference of -0.02 (95% CI: -0.34, 0.30); p=0.90). Video-based education results in an equivalent improvement in confidence and satisfaction rates. Additional benefits of video-based education include convenience, accessibility and efficiency. CONCLUSIONS: Basic surgical skills can be taught as effectively through online video-based education as conventional teaching methods. Online education should be utilized as an adjunct to medical curricula beyond the COVID-19 era

An Analysis of the Binding Characteristics of a Panel of Recently Selected ICAM-1 Binding Plasmodium falciparum Patient Isolates.

The basis of severe malaria pathogenesis in part includes sequestration of Plasmodium falciparum-infected erythrocytes (IE) from the peripheral circulation. This phenomenon is mediated by the interaction between several endothelial receptors and one of the main parasite-derived variant antigens (PfEMP1) expressed on the surface of the infected erythrocyte membrane. One of the commonly used host receptors is ICAM-1, and it has been suggested that ICAM-1 has a role in cerebral malaria pathology, although the evidence to support this is not conclusive. The current study examined the cytoadherence patterns of lab-adapted patient isolates after selecting on ICAM-1. We investigated the binding phenotypes using variant ICAM-1 proteins including ICAM-1Ref, ICAM-1Kilifi, ICAM-1S22/A, ICAM-1L42/A and ICAM-1L44/A using static assays. The study also examined ICAM-1 blocking by four anti-ICAM-1 monoclonal antibodies (mAb) under static conditions. We also characterised the binding phenotypes using Human Dermal Microvascular Endothelial Cells (HDMEC) under flow conditions. The results show that different isolates have variant-specific binding phenotypes under both static and flow conditions, extending our previous observations that this variation might be due to variable contact residues on ICAM-1 being used by different parasite PfEMP1 variants