Abstract ：

Electrohydrodynamic printing (EHDP) is capable of fabricating scaffolds that consist of micro/nano scale orientated fibers for three-dimensional (3D) cell culture models and drug screening applications. One of the major hurdles that limit the widespread application of EHDP is the lack of diverse biomaterial inks with appropriate printability and desired mechanical and biological properties. In this work, we blended plant proteins with synthetic biopolymer poly(ε-caprolactone) (PCL) to develop composite biomaterial inks, such as PCL/gliadin and PCL/zein for scaffold fabrication through EHDP. The tensile test results showed that the composite materials with a relatively small amount of plant protein portions, such as PCL/gliadin-10 and PCL/zein-10, can significantly improve tensile properties of the fabricated scaffolds such as Young's modulus and yield stress. These scaffolds were further evaluated by culturing mouse embryonic fibroblasts (NIH/3T3) cells and proven to enhance cell adhesion and proliferation, apart from temporary inhibition effects for PCL/gliadin-20 scaffold at the initial growth stage. After these plant protein nanoparticles were gradually released into culture medium, the generated nanoporous structures on the scaffold fiber surfaces became favorable for cellular attachment, migration, and proliferation. As competent candidates that regulate cell behaviors in 3D microenvironment, such composite scaffolds manifest a great potential in drug screening and 3D in vitro model development.

Keyword ：

Additive manufacturing Composite biomaterials ink Electrohydrodynamics

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Abstract ：

The reduced capabilities of retinal pigment epithelium (RPE) marks early retinal degenerative diseases and leads to blindness. Regenerating a functional RPE monolayer in vitro becomes significant and promise for developing new therapies. Many research activities have been done to develop new materials, structures and fabrication technologies to mimic native RPE structure for cell attachment and subsequent tissue development. Scaffold-based tissue engineering approaches attract intensive investigation, due to their capability and potential in building preclinical models and developing possible treatment for retinal degenerative diseases. Scaffolds in facilitating regeneration of RPE tissue in vitro has been proved by recent studies. Various materials have been applied, such as synthetic polymers, plant or animal extracted proteins, and composite materials. This review outlines the most recent fabrication progresses using these materials for RPE scaffolds, including both in vitro and in vivo trials, and the challenges in building a whole tissue model construct and transplantation. Additive manufacturing technologies at micrometer- and nanometer-scale are proposed as promising methods to build biomimetic RPE scaffolds in the current studies. © 2021 The Authors. Published by Elsevier B.V.

Keyword ：

Aldehydes Biomimetics Fabrication Ophthalmology Scaffolds (biology) Synthetic polymers Tissue Tissue regeneration

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Abstract ：

Significant progress has been made in fabricating porous scaffolds with ultrafine fibers for tissue regeneration. However, the lack of noninvasive tracking methods in vivo makes it impossible to track the fate of such scaffolds in situ. The development of near-infrared region II (NIR-II, 1000-1700 nm) dyes provides the possibility of performing noninvasive visualization with deep-tissue penetration and high spatial resolution in vivo. Herein, we developed a polycaprolactone (PCL) ink containing the small organic NIR-II dye SY-1030 and the fluorescently labeled macromolecular dye SY-COO-PCL and fabricated high-resolution NIR-II active scaffolds via electrohydrodynamic jet (EHDJ) printing. All printed scaffolds subcutaneously implanted in mice were clearly imaged one week after the operation. Compared with scaffolds containing SY-1030, the fluorescence intensity emitted from scaffolds containing SY-COO-PCL can be tracked for up to three weeks. Moreover, the image quality can be optimized by adjusting the dye concentration, laser power, and exposure time. The advantage of such NIR-II active scaffolds is evidenced by the lower dye concentration, longer tracking period, and better in vivo stability. We also demonstrated the biocompatibility and biodegradability of the scaffolds containing SY-COO-PCL over a 3-month period. The developed NIR-II active scaffolds have potential applications in biopolymer implant tracking, tissue reconstruction monitoring, and target-position-based drug delivery. © 2021 American Chemical Society. All rights reserved.

Keyword ：

3D printers Biocompatibility Biodegradability Biopolymers Drug delivery Electrohydrodynamics Fluorescence Infrared devices Ink jet printing Mammals Scaffolds (biology) Tissue

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The purpose of this study was to explore the effects of fibre-reinforced composites and onlay restorations on the fracture resistance of the cracked teeth. The experiments were grouped as follows: intact teeth, cracked teeth, crown; onlay; annular ribbond + onlay, laminated ribbond + onlay and fibre post + onlay; annular ribbond + crown, laminated ribbond + crown and fibre post + crown. The maximal Von Mises stress of dentin, the maximal Von Mises stress at the crack, the fracture resistance and fracture pattern under static loading were analysed by single-factor analysis of variance (ANOVA) and post-test by LSD. The annular ribbond + crown had a significant difference in fracture resistance than the crown (P < 0.05). The annular ribbond + onlay had more favourable fractures than crown in fracture pattern, and there were significant differences (P < 0.05). Compared with crown restoration, fibre-reinforced composites and onlay can improve the fracture resistance of the cracked teeth.

Keyword ：

3D finite element cracked tooth fiber-reinforced composite fracture strength onlay

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Abstract ：

Scaffold-based three-dimensional (3D) cell culture systems have gained increased interest in cell biology, tissue engineering, and drug screening fields as a replacement of two-dimensional (2D) monolayer cell culture and as a way to provide biomimetic extracellular matrix environments. In this study, microscale fibrous scaffolds were fabricated via electrohydrodynamic printing, and nanoscale features were created on the fiber surface by simply leaching gliadin of poly(-caprolactone) (PCL)/gliadin composites in ethanol solution. The microstructure of the printed scaffolds could be precisely controlled by printing parameters, and the surface nanotopography of the printed fiber could be tuned by varying the PCL/gliadin ratios. By seeding mouse embryonic fibroblast (NIH/3T3) cells and human nonsmall cell lung cancer (A549) cells on the printed scaffolds, the cellular responses showed that the fiber nanotopography on printed scaffolds efficiently favored cell adhesion, migration, proliferation, and tissue formation. Quantitative analysis of the transcript expression levels of A549 cells seeded on nanoporous scaffolds further revealed the upregulation of integrin-β1, focal adhesion kinase, Ki-67, E-cadherin, and epithelial growth factor receptors over what was observed in the cells grown on the pure PCL scaffold. Furthermore, a significant difference was found in the relevant biomarker expression on the developed scaffolds compared with that in the monolayer culture, demonstrating the potential of cancer cell-seeded scaffolds as 3D in vitro tumor models for cancer research and drug screening. © 2021 American Chemical Society.

Keyword ：

3D printers Bioactivity Biomimetics Cell adhesion Cell culture Cell engineering Cells Diagnosis Diseases Electrohydrodynamics Monolayers Nanotechnology Scaffolds (biology) Tumors

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Abstract ：

Journal bearing is one of the most important components for supporting high speed rotating machinery such as compressors and turbo machines. In recent trends, non-circular journal bearings (lemon bearing, three-lobe bearing, four-lobe bearing, etc.), for their greater load capacity and better stability, have become a superior choice and found wide spread application. In this paper, the nonlinear oil film force is expressed using the dynamic stiffness and damping of 1st-3rd order. And the film thickness and pressure are analyzed using Fourier method, so that the corresponding harmonic components and their deeper connection can be further explored. The paper shows that the nonlinear dynamic performances are connected closely with the bearings' profile, and lays the foundation for expressing the precise nonlinear oil film force.

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Abstract ：

The stable working condition of high speed, heavy loaded rotating machinery depends strongly on the stability provided by the journal bearing. Tilting pad journal bearings (TPJB) are widely used under such situation due to their inherent stability performance. However, because of the complexity of the TPJB structure, obtaining a reliable prediction of the journal bearing's dynamic characteristics has always been a challenging task. In this paper, a theoretical analysis has been done to investigate the dynamic performance of a 4 pad TPJB with ball-in-socket pivot, emphasizing on the frequency dependency due to pivot flexibility. The analytical model containing the complete set of dynamic coefficients of the TPJB is built and the pivot stiffness is calculated and used to evaluate the equivalent dynamic coefficients of the bearing. In general, at lower perturbation frequency, the equivalent stiffness and damping increase with frequency. While for higher perturbation frequency, the dynamic coefficients are nearly independent of the frequency. Moreover, the results also show the limit value of the dynamic characteristics of the TPJB when the perturbation frequency is set to 0(+) and infinity.

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Abstract ：

As one of the most important components in a rotor-bearing system, journal bearings provide proper support and damping to the rotor so that it can run both smoothly and efficiently and keep stable under different working conditions. As the rotating speed of the rotor growing faster and load getting heavier, the traditional cylinder journal bearing can no longer meet the demand of stabilizing the rotor, so different kinds of non- circular journal bearings were invented, such as elliptical bearing, multi lobe bearing, wave bearing and etc., to provide better stability and greater load capacity. However, these kinds of non- circular bearings were mostly designed by experience of the engineers, and also the current hydrodynamic bearing design methodology still depends on empirical design. There lacks of corresponding theoretical foundation. In order to develop a theoretical method for bearing designing, an innovative analyzing approach needs to be carried out to explore the mechanism of the bearings and its performance. In this paper, a new approach is presented focusing on the profile of each bearing and their film thickness. A universal mathematical expression for different types of non circular bearings has been put forward based on the Fourier series theory. The influence of periodic harmonics of film thickness on the static performance of non-circular bearings of finite length is studied for incompressible lubricant. The results show that the film thickness can always be expanded into a Fourier series, and the harmonic components of film pressure can be obtained by solving the Reynolds equation. Finally, the relation between the k-th order harmonic component H-0,H-k and the corresponding static pressure component P-0,P-k is established. This new investigation can be used to improve the non-circular bearing designing methodology with theoretical guidance.

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Abstract ：

Two multileaf gas foil journal bearings with backing bump foils and one set of gas foil thrust bearings were designed, fabricated, and used in a 100 kW class microturbine simulated rotor system to ensure stability of the system. Meanwhile, a preliminary test rig had been built to verify the simulated system stability. The rotor synchronous and subsynchronous responses were well controlled by using of the gas foil bearings. It is on the multileaf gas foil bearings with backing bump foils that the test was conducted and verified for the first time in open literatures. The success in the experiments shows that the design and fabrication of the rotor and the gas foil bearings can provide a useful guide to the development of the advanced high speed rotating machinery.

Keyword ：

gas foil bearing Microturbine rotordynamics simulated rotor

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Abstract ：

High-speed and heavy-loaded rotating machinery require accurate prediction of rotor's response and stability, which can be characterized by the static and dynamic coefficients of the bearing support. In this paper, a theoretical study has been done to investigate the performance of a fixed-tilting pad journal bearing with ball-in-socket pivot. The analytical model is established with the flexibility of the pad pivot and turbulent effect of the oil film both taken consideration. Under such situation, the pad pivot elastic deformation and its stiffness are calculated using Hertz Contact Theory for various operating points of the rotor-bearing system. The finite element method is adopted to simulate the static coefficients of the fixed-tilting pad bearing, obtaining its oil film pressure distribution varied with the bearing eccentricity ratio. The corresponding dynamic stiffness and damping of the oil film are solved using partial derivative method. In addition, a special interest is put in investigating the effect of the series complex stiffness of the oil film and pad pivot, according to which, the equivalent dynamic characteristics are obtained. The results show that the relation between these two factors are complex and interactive, both of which have a significant influence on the static and dynamic performance of the bearing.

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