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Tubular esophageal scaffolds with fiber diameter ranging from 13.9±1.7 μm to 65.7±6.2 μm were fabricated from the highly elastic poly( l -lactide-co-ε-caprolactone) (PLC) via a melt-drawing method. The morphology, crystallinity, thermal and mechanical properties of the PLC fibers were investigated. They were highly aligned and have a uniform diameter. PLC is found to be semicrystalline consisting of α- and β- lactide (LA) crystals. The crystallinity increases up to 16.8% with increasing melt-drawing speeds due to strain-induced crystallization. Modulus and strength increases while ductility decreases with an increase in crystallinity of the PLC samples. Moisture will not degrade the overall tensile properties but affect its tangent modulus at the low strain. L929 cells are able to attach and proliferate on the scaffolds very well. The cells seeded on the scaffolds show normal morphology with >90% cell viability after 6 days of culture. These results demonstrate that the PLC fibrous scaffold has good potential for use in esophageal tissue engineering application. [ABSTRACT FROM AUTHOR]

Tissue engineering aims to produce patient-specific biological substitutes in an attempt to circumvent the limitations of existing clinical treatments for damaged tissue or organs. The main regenerative tissue engineering approach involves transplantation of cells onto scaffolds. The scaffold attempts to mimic the function of the natural extracellular matrix, providing a temporary template for the growth of target tissues. Scaffolds should have suitable architecture and strength to serve their intended function. This paper presents a comprehensive review of the fabrication methods, including conventional, mainly manual, techniques and advanced processing methods such as rapid prototyping (RP) techniques. The potential and challenges of scaffold-based technology are discussed from the perspective of RP technology. [Copyright &y& Elsevier]

In this study, laser powder bed fusion (L-PBF), also known as selective laser melting (SLM), was used to fabricate samples of titanium-tantalum (TiTa) alloys with 0, 10, 30 and 50 wt% of tantalum using in-situ alloying. As-fabricated samples comprised of randomly-dispersed pure tantalum particles in a titanium-tantalum matrix. Porosity and unmelted tantalum particles of the samples were revealed using an optical microscope (OM). The microstructure of the alloys were determined by combination of field emission scanning electron microscopy (FE-SEM), electron back scatter diffraction (EBSD) and X-ray diffraction (XRD). The mechanical properties of the alloys were investigated with tensile and Vickers hardness tests. To ascertain the suitability of these alloys as biomaterials, Ti50Ta scaffolds with 60% porosity were characterized biologically. This study further shows that porous TiTa scaffolds fabricated using L-PBF are biocompatible with comparable biological results and manufacturability as Ti6Al4V and commercially pure titanium, based on the results obtained from cell culture with human osteosarcoma cell line SAOS-2. [ABSTRACT FROM AUTHOR]

Abstract Selective laser melting (SLM) is a powder bed fusion additive manufacturing (AM) technique that produces three-dimensional (3D) parts by fusing metallic powders with a high-energy laser. SLM involves numerous process parameters that may influence the properties of the final parts. Hence, establishing the effect of the SLM processing parameters is important for producing parts of high quality. In this study, titanium-tantalum alloy was fabricated by SLM using a customized powder blend to achieve in situ alloying. The influence of processing parameters on the microstructure and properties such as relative density, microhardness and surface roughness was investigated. The results show that fully dense titanium-tantalum parts can be obtained from SLM. With laser power of 360 W, scan speed of 400 mm/s, powder layer thickness of 0.05 mm and hatch spacing of 0.125 mm, the titanium-tantalum alloy produced by SLM has relative density of 99.85 ± 0.18%. Despite the variation in process parameters, titanium-tantalum shows laminar β grains in random directions in both xy and yz-plane from optical microscope (OM) analysis in all the parts produced. This observation is further confirmed using x-ray diffraction (XRD). Graphical abstract Unlabelled Image Highlights • Titanium-tantalum (TiTa) alloy were fabricated using selective laser melting (SLM) • TiTa alloy formed using SLM from powder mixture • In-situ alloying is proved to be feasible with SLM • Laser power and scan speed have significant effect on the part quality of SLM TiTa [ABSTRACT FROM AUTHOR]

Bioprinting provides a fully automated and advanced platform that facilitates the simultaneous and highly specific deposition of multiple types of skin cells and biomaterials, a process that is lacking in conventional skin tissue-engineering approaches. Here, we provide a realistic, current overview of skin bioprinting, distinguishing facts from myths. We present an in-depth analysis of both current skin bioprinting works and the cellular and matrix components of native human skin. We also highlight current limitations and achievements, followed by design considerations and a future outlook for skin bioprinting. The potential of bioprinting with converging opportunities in biology, material, and computational design will eventually facilitate the fabrication of improved tissue-engineered (TE) skin constructs, making bioprinting skin an impending reality. [ABSTRACT FROM AUTHOR]

The Selective Laser Melting (SLM) fabrication process is complex and it is crucial to understand the phenomena that will occur to better control it. In this paper, an FE model on SLM that considers powder-to-solid transition together with an effective method to achieve volume shrinkage and material removal has been created. Experiments were conducted to validate the model. A detailed discussion on the progression of the melt pool and the rate of temperature change has been made. Parametric study with the laser power and scan speed as variables has been conducted to identify their relationships with the melt dimensions, melting and evaporation of powder and rates of temperature change. [ABSTRACT FROM AUTHOR]

The microstructures and the mechanical properties, including fatigue crack growth (FCG) and mode I fracture toughness (K IC), of in-situ alloyed Ti41Nb (wt.%) fabricated using the laser powder bed fusion (LB-PBF) were investigated. A small hatch spacing - fast scanning strategy was utilized for obtaining parts with minimum porosity and unmelted Nb particle combination. The mesostructure of the fabricated blocks comprises columnar grains with alternating Nb-poor regions (NPRs), which occur due to the short residence time of materials in the melt that limits the melting and diffusion of Nb, and matrix layers. Extensive ω iso precipitates were noted in the microstructure, which were attributed to the large-build related heat accumulation during the LB-PBF process that stems from the combination of large sample size and high energy density input. Consequently, ductility of the as-built parts was low. The FCG rate at high ∆K was strongly influenced by the layers of NPR and hence depend on the orientation whereas the near-threshold FCG rate was strongly influenced by the local slip systems ahead of the crack tip. Significant anisotropy in K IC , a result of the crack deflection by the NPR/matrix interfaces, was observed. The mesostructure induced toughening mechanism improves the fracture toughness of the resultant alloy despite its brittle failure response. The potential of in-situ alloying to induce toughening through the mesostructure control was discussed. [Display omitted]. [ABSTRACT FROM AUTHOR]

Diabetes is a severe chronic disease worldwide. In various types of diabetes, the pancreatic beta cells fail to secrete sufficient insulin, at some point, to regulate blood glucose levels. Therefore, the replacement of dysfunctional pancreas, islets of Langerhans, or even the insulin-secreting beta cells facilitates physiological regulation of blood glucose levels. However, the current lack of sufficient donor human islets for cell replacement therapy precludes a routine and absolute cure for most of the existing diabetes cases globally. It is envisioned that tissue engineering of a bioartificial pancreas will revolutionize regenerative medicine and the treatment of diabetes. In this review, we discuss the anatomy and physiology of the pancreas, and identify the clinical considerations for engineering a bioartificial pancreas. Subsequently, we dissect the bioengineering problem based on the design of the device, the biomaterial used, and the cells involved. Last but not least, we highlight current tissue engineering challenges and explore potential directions for future work. Insufficient donor human islets and diminished survival of transplanted islets prevent the use of islet transplantation as a routine means to counter diabetes and confer insulin independence. While hormone infusion pumps are being improved to provide good glycemic control in diabetic patients, the availability of a physiological bioartificial pancreas can potentially provide a competitive solution for diabetes. Bioartificial pancreas involves both acellular (bioprinted hydrogels/polymers) and cellular (beta cells and supplementary cells) components to recapitulate the functions of the pancreas in insulin secretion and glycemic control. Vascularized bioartificial pancreas can be populated with stem cell-derived beta cells and supplemented with accessory cells to achieve desired islet integrity and function. Currently, multiple designs of bioartificial pancreas are studied in preclinical and clinical settings. Proper material design and biological considerations will improve the success of bioartificial pancreas for regenerative medicine in diabetes. [ABSTRACT FROM AUTHOR]

In this research contribution, effort is taken to monitor the crack initiation and crack propagation of three-dimensional (3D) printed corrugated sandwich structures using acoustic emission technique. Vertical pillars were introduced in between the existing sinusoidal wave-like corrugations to improve the load bearing capacity of these structures. The vertical pillared corrugated structures were 3D printed with single and multi-material combinations in the facesheet and tested for their indentation resistance. To monitor the exact invisible crack initiation and crack propagation in the 3D printed corrugated structures, a highly-sensitive acoustic emission (AE) testing method was introduced. The resulting AE data points during testing illustrated a cluster of low amplitude data points from 40 to 65 dB indicating invisible crack initiations. High amplitude points up to 95 dB indicated visible cracks propagating until the end of specimen failure. Prevalent failure mechanism for single material (type A) specimens was found to be shear cracking of facesheets with micro steps and failure mechanism of multimaterial (type B) specimens were found to be delamination and shear cracking of multimaterial layers. Load bearing capacity was maximum at 2.14 ± 0.3 kN for type A specimens under a flat indenter with a displacement of 2.12 ± 0.4 mm. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) technique allows the creation of parts with a high degree of design complexity by building three-dimensional (3D) parts layer-by-layer. Many of the current restrictions of design for manufacturing (DFM) as well as design for assembly (DFA) are no longer applicable for AM due to the lack of needs for tooling. Instead, it is critical to establish the manufacturing limits and design guidelines to achieve optimal production outcomes. This can be achieved through manipulation of process parameters. The purpose of this paper is to establish a systematic methodology for investigating the process capability of material jetting AM techniques by using specially designed benchmark artifacts. In this study, three customized benchmarks were designed to characterize and establish the process capability of material jetting AM techniques. Each of the benchmarks was designed for different purposes. Using a benchmark, metrological studies were conducted to determine the effect of process parameters on the dimensional accuracy of fabricated part. The design limitations on special features such as thin walls and assembly-free parts fabricated using different build orientations were also evaluated. [ABSTRACT FROM AUTHOR]

This paper describes the design, fabrication and characterization of a microchannel-based strain sensor using flexible material. The work explores the use of additive manufacturing, also known as 3D printing, to fabricate the sensor in easy and cost-effective way. It is shown that 3D printing can print complex designs with ease and fabricate objects with embedded features. Microchannels with dimension of 500 μm diameter are printed within the sensor structure and filled with conductive silver nanoparticle ink. The fabricated device is checked for printability and design valve adherence using optical microscope and micro-CT. The printed sensor is capable of measuring normal (orthogonal to channels) and in-plane (parallel to channels) tensile forces and is tested using a custom-built test rig. [ABSTRACT FROM AUTHOR]

The present study employs fast scanning speeds to fabricate high-density stainless steel 316L (SS316L) parts via selective laser melting (SLM). It aims to improve the production rate while maintaining a low porosity for the SLM-built parts. Density values of > 99% were recorded for all the fabricated samples in this study. The scanning speed of the laser could be much improved due to the use of 380 W power laser. The overall build rate in this study is supposed to be enhanced by ~ 72% as compared to commonly used processing parameters. Detailed microstructural characterization was carried out in order to obtain an in-depth understanding of the microstructure of SLM-built SS316L. The microhardness of built parts is between 213 and 220 HV, which is much higher than that of the standard annealed counterpart of ~ 155 HV. This study provides an insight on how to improve SLM build rates without any loss of parts' density and mechanical properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • Formulas to predict the shore hardness and compressive modulus were developed. • The machine learning technique outperforms the surface response method by 3.5%. • The multi-layer model can mimic material properties ranging from 20A to 65A. Polyjet, a material jetting 3D printing technique, has been widely used for the fabrication of patient-specific anatomical models owing to the toolless fabrication technique and its ability to print multiple materials in a single part. Although the fabrication of anatomical models with high dimensional accuracy has been demonstrated, 3D printed anatomical models with tissue-mimicking properties have not been realized. In this study, a composite layering design was used to tune the shore hardness and compressive modulus of the Polyjet-printed parts in an attempt to mimic the properties of human tissues. 216 specimens (with 72 combinations of design parameters) were printed and tested to develop the material library for the anatomical models. An analytical model was developed to estimate the effective compressive modulus and shore hardness of the composite laminate. A neural network was used to learn the multi-dimensional relationship between the design parameters and mechanical properties. The 5-33-2 network size is found to be the optimum neural network structure with a mean square error of 0.98% for the compressive modulus, lower than the traditional response surface method model. A genetic algorithm was used to search the design space for the most optimum design parameters for the targeted effective shore hardness. [ABSTRACT FROM AUTHOR]

A parametric experimental study on the role played by the power (P), velocity (V L) and profile (top-hat or Gaussian) of the laser on the porosity, inclusion content and microstructural evolution of in-situ alloyed laser powder bed fusion (LPBF) manufactured Ti34Nb was conducted. For this, alloys were printed with three sets of processing parameters, in which the above-mentioned parameters were varied but the energy density was held constant. A detailed tomographic and microstructural investigation of these alloys was followed by tensile tests. Observations of melt pools in the single tracks and single stripes were complemented by thermal finite element method (FEM) simulations that studied their evolution. Results show that a top-hat laser profile combined with high P (> 650 W), high V L (> 650 mm/s) and short stripe width scanning strategy forms a large single stripe melt pool that moves slowly and has a low aspect ratio. The large and slow melt pool allows Nb to melt efficiently and minimizes its unmelted content while the low melt pool aspect ratio prevents keyholing that can otherwise result in porosity. These melt pool attributes also favor the formation of a columnar β-Ti microstructure with a strong {100} texture, which has the ideal combination of strength and elastic modulus. The mechanisms of microstructural evolution were explained and the scope of this parameter optimization principle was discussed in the context of further improving the properties of this alloy. Image, graphical abstract [ABSTRACT FROM AUTHOR]