When reporting surface quality, the roughest surface is a reference for the measurements. In LPBF due to recoil pressure and scan movement, asymmetric surface is shaped, and surface roughness has different values in different measurement orientations. In this research, the influence of the laser powder bed fusion (LPBF) process parameters on surface tension and roughness of Ti-6AI-4 V parts in three orientations are investigated. To improve the mechanical properties, heat treatment was carried out and added to the designed matrix to generate a comprehensive data set. Taguchi design of experiment was employed to print 25 samples with five process parameters and post-processing. The effect and interaction of the parameters on the formation of surface profile comprising tension, morphology and roughness in various directions have been analysed. The main contribution of this paper is developing a model to approximate the melting pool temperature and surface tension based on the process parameters. Other contributions are an analysis of process parameters to determine the formation and variation of surface tension and roughness and explain the governing mechanisms through rheological phenomena. Results showed that the main driving factors in the variation of surface tension and formation of the surface profile are thermophysical properties of the feedstock, rheology and the temperature of the melting pool. Also, the results showed that while the value of surface tension is the same for each test case, morphology and the value of roughness are different when analysing the surface in perpendicular, parallel and angled directions to laser movement.

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Purpose The purpose of this study is, to compare laser-based additive manufacturing and subtractive methods. Laser-based manufacturing is a widely used, noncontact, advanced manufacturing technique, which can be applied to a very wide range of materials, with particular emphasis on metals. In this paper, the governing principles of both laser-based subtractive of metals (LB-SM) and laser-based powder bed fusion (LB-PBF) of metallic materials are discussed and evaluated in terms of performance and capabilities. Using the principles of both laser-based methods, some new potential hybrid additive manufacturing options are discussed. Design methodology approach Production characteristics, such as surface quality, dimensional accuracy, material range, mechanical properties and applications, are reviewed and discussed. The process parameters for both LB-PBF and LB-SM were identified, and different factors that caused defects in both processes are explored. Advantages, disadvantages and limitations are explained and analyzed to shed light on the process selection for both additive and subtractive processes. Findings The performance of subtractive and additive processes is highly related to the material properties, such as diffusivity, reflectivity, thermal conductivity as well as laser parameters. LB-PBF has more influential factors affecting the quality of produced parts and is a more complex process. Both LB-SM and LB-PBF are flexible manufacturing methods that can be applied to a wide range of materials; however, they both suffer from low energy efficiency and production rate. These may be useful when producing highly innovative parts detailed, hollow products, such as medical implants. Originality value This paper reviews the literature for both LB-PBF and LB-SM; nevertheless, the main contributions of this paper are twofold. To the best of the authors’ knowledge, this paper is one of the first to discuss the effect of the production process (both additive and subtractive) on the quality of the produced components. Also, some options for the hybrid capability of both LB-PBF and LB-SM are suggested to produce complex components with the desired macro- and microscale features.

Extracellular matrix (ECM) molecules play significant roles in regulating b-cell function and viability within pancreatic islets by providing mechanical and biological support, stimulating cell survival, proliferation, and their endocrine function. During clinical islet transplantation, the b-cell's ECM environment is degraded by enzymatic digestion. Literature suggests that interactions between islet cells and ECM molecules, such as fibronectin (FN), collagen type IV (Col4), and laminin (LN), are essential for maintaining, or stimulation of islet function and survival, and can effect differentiation and proliferation of the endocrine cells. It is also thought that three-dimensional (3D) culture of b-cells can improve glucose responsiveness by providing a specific niche, in which cells can interact with each other in a more natural manner. Conventional suspension cultures with b-cells results generally in a heterogeneous population with small and large aggregates, in which cells experience different nutrient diffusion limitations, negatively affecting their physiology and function. In this study, we have explored the effect of FN, Col4, and LN111 on INS1E insulinoma cells by using microcontact printing (mCP) to investigate whether a controlled environment and aggregate dimensions would improve their endocrine function. Using this method, we produced a pattern of well-defined circular spots of FN, Col4, and LN111 on polydimethylsiloxane with high spatial resolution. Cell seeding of the INS1E cells on these ECM protein spots resulted in the formation of 3D b-cell aggregates. We show that these INS1E aggregates have very reproducible dimensions, and that the cell culture method can be easily adjusted, leading to a highly accurate way of forming 3D b-cell aggregates on an ECM-functionalized substrate. In addition, we show that ECM molecules can act as anchoring points for b-cells on an otherwise non-cell-adherent material, and this can improve both the endocrine function and viability. We found a significant increase in the secretion of insulin by INS1E cells cultured on mCP FN and Col4 substrates, in comparison to cells that were growing in monolayers on substrates without ECM molecules. Moreover, INS1E cells growing on circular ECM spots in a 3D manner showed improved endocrine function in comparison to their two-dimensional counterparts.

To effectively apply microwell array cell delivery devices their biodegradation rate must be tailored towards their intended use and implantation location. Two microwell array devices with distinct degradation profiles, either suitable for the fabrication of retrievable systems in the case of slow degradation, or cell delivery systems capable of extensive remodeling using a fast degrading polymer, were compared in this study. Thin films of a poly(ethylene glycol)-poly(butylene terephthal

Transplanting islets into a patient's portal vein is currently the most promising method to treat type one diabetes. However, the long-term efficiency of this method has only been demonstrated in a small number of the treated patients. In the majority of patients, the treatment ultimately fails and they will still suffer from labile blood glucose control. Although it is known that multiple factors play an important role in the loss of donor cells, such as the immediate blood mediated inflammatory response, allo and auto immune reaction, poor revascularization and high levels of glucose, lipids and immunosuppressive drugs. Another factor, which more recently is being studied, is the effect of islet isolation, which can induced damage to the β-cell's microenvironment. Specifically, in order to isolate islets the pancreas is perfused with collagenase, this leads to enzymatic digestion of the islets extra cellular matrix causing loss of the general extracellular matrix (ECM) network architecture, and supportive ECM molecules. Another important factor, is insufficient rapid vascularization after transplantation leading to poor mass transport of oxygen and nutrients to the metabolically very active β-cells leading to cell stress, apoptosis and loss of function. The ECM in islets consists predominantly of a basement membrane associated with the dense microvasculature surrounding the endocrine cells. Consequently, it is expected that islet transplantation can be significantly improved by re-establishing the islet microenvironment. Here, we review the state-of-the-art in engineering islet microenvironments, and provide a comprehensive understanding of the relationship between pancreatic islet cells and its surrounding microenvironment within the islet. Additionally, we highlight the progress and challenges related to the biological, biochemical, and biophysical aspects of engineering the islet micro-environment for transplantation purposes.

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