Flexible PCL tube scaffolds by winding of micro-extruded filaments

An important requirement for tissue engineering scaffolds is matching of the functional me-chanical properties to their natural tissue counterpart. Specifically for arteries this comprises the elastic re-sponse of the vessel wall to blood pressure. Human aorta has a low elastic modulus when compared to some FDA-approved synthetic polymer materials frequently used in tissue engineering. The current research en-deavours to expand the existing production technology of 3D plotting to winding of micro-extruded filaments in order to obtain flexible polymer tubes with continuous fibre. Tube scaffolds are manufactured by conven-tional 3D plotting and by winding. Their structure and quasi-static mechanical properties are evaluated and compared to human aorta. Winded tubes are found to be far more suitable for application as a blood vessel scaffold than their 3D plotted counterparts

Production of syndiotactic polystyrene powder for part manufacturing through SLS

Selective laser sintering (SLS) is a well-established additive manufacturing (AM) process. While AM originally found its use as rapid prototyping technique, it is nowadays more and more considered for the production of actual end-use parts. A widely acknowledged hindrance in the evolution of this technology is the limited range of materials available for processing with SLS, making the application window rather small. Introducing new materials with the correct morphology and thermal requirements for SLS could broaden this window and give rise to new products. This research aims at identifying such promising materials, considering the relevant requirements for selecting and processing a new material. Considered foremost within this manuscript is the processability of syndiotactic polystyrene from pellet form into spherical particles of 50-90 μm without significantly changing their properties. Regarding processing methods, the focus of this work is on solution based techniques (single phase precipitation, emulsion precipitation) instead of more conventional mechanical processing methods (ball milling) as these are believed to be more accessible and more suitable as a precursor step for a wide range of processing technique

Preparation and electrochemical performance of hollow activated carbon fiber self-supported electrode for supercapacitor

Hollow activated carbon fiber (HACF) with high specific surface area and high charge storage capability was prepared by pre-oxidation, carbonization and KOH-activation from polyacrylonitrile (PAN). HACF was used as self-supported working electrode directly without any binder and conductive agent. The effect of the activation time on specific surface area of HACF was studied intensively. The results show that the specific surface area of HACF increased with the increase of activation time from 0.5 h to 1.5 h, and then decreased with further increase of activation time. Highest specific surface area of 1873 m(2)g(-1) and micropore volume of 0.61 cm(3)g(-1) were obtained in HACF activated for 1.5 h. Electrochemical properties of HACF can be improved with increase of activation time, but excessive activation results in the decrease of specific surface area and increase of internal resistance of HACF. The self-supported electrode of HACF possesses a large specific capacitance of 323 F g(-1) at 0.05 A g(-1) and 216 F g(-1) at 1 A g(-1). Therefore, HACF can be a promising self-supported electrode for high performance supercapacitors

Elegant design of carbon nanotube foams with double continuous structure for metamaterials in a broad frequency range

Carbon nanotube (CNT) foams with negative permittivity and permeability are successfully prepared by chemical vapor deposition (CVD) and post-treatment. A double negative metamaterial in the 1-1000 MHz frequency range with double continuous structure results by effectively compounding the CNT foam with a polymer material, i.e. epoxy or nanosilver silicone resin. The negative permeability is specifically attributed to the three-dimensional CNT interactions as clear from the study of the relation of the material microstructure and the macroscopic measurements. Compared to CNT foam/epoxy composites, CNT foam/nanosilver/silicone composites have a lower permeability but a more excellent electrical conductivity or permittivity. It is also shown that the carbon source time during CVD and post-pressurization can be adjusted to allow for both negative permittivity and permeability. This contribution highlights a convenient method to obtain a metamaterial in a much larger frequency range (ca. 1 to 1000 MHz) than the state-of-the-art. It thus supports the expansion of the application range of metamaterials and simplifies their preparation, which is of great significance for the wider use of these materials

The Effect of Injection Moulding Temperature on PET Particles/Fibrils in Blends and MFCs

The microfibrillar composites of polypropylene (PP)/poly(ethylene terephthalate) (PET) have been prepared by twin-screw extrusion, followed by cold drawing. The employed stretch ratio was 4. Further processing was done by injection moulding at three different processing temperatures (210ºC, 230ºC, 280ºC) on PP/PET blends with wt% 70/30 Samples were subjected to extensive characterization in each step of MFC preparing. Fourier Transform Infrared (FTIR) spectroscopy was employed to determine the nature of the interaction between the polymers in the composites.. Thermogravimetric Analysis (TGA) were used to investigate degradation of polymers. The crystallization, melting behaviour and the crystallization morphology were investigated by Dynamic Scanning Calorimetry (DSC) and Polarized Optical Microscopy (POM). Influence of processing temperature on morphology was investigated by using Scanning Electron Microscopy (SEM). The observations from the fracture surfaces were discussed and compared with the mechanical properties, and the results have shown a significant influence of the injection moulding temperature on the morphology development and mechanical properties

Evaluating the exit pressure method for measurements of normal stress difference at high shear rates

A challenge for polymer rheology is the reliable determination of shear dependent first normal stress difference (N-1 values) at high shear rates (>10 s(-1)). Here, we evaluate the correctness of the commonly applied exit pressure method focusing on polypropylene and high and low density polyethylene melts at 200 degrees C. It is demonstrated that the linear extrapolation of pressure values toward the die exit, which is a key step in the application of the exit pressure method, is affordable to determine N-1 values despite that these extrapolated exit pressure values are characterized by a relative deviation of 25%-40%. The validity of the exit pressure method is further supported by an excellent match with rheological data from the Laun rule (exponent close to 0.7) and a representative simulation of extrudate swelling data in the width and height direction, considering tuned parameters for the Phan-Thien-Tanner constitutive model. Also, the absence of a significant viscous heating effect near the die exit is highlighted based on numerical analysis. (c) 2020 The Society of Rheology

The influence of draw ratio on morphology and thermal properties of MFCs based on PP and PET

The main goal of this study is to investigate the influence of draw ratio on morphology and properties in microfibrillar composites (MFCs). In situ MFCs based on polypropylene (PP) and poly(ethylene terephthalate) (PET) have been prepared at the weight ratio of 80/20 by twin-screw extrusion, followed by cold drawing and injection moulding. In order to study the differences in MFCs caused by draw ratio, the samples were prepared at different ratios and subjected to extensive characterization in each step of the MFC preparation process. The morphology of MFC and influence of draw ratio were investigated by using Scanning Electron Microscopy (SEM). The thermal decomposition of the polymers in MFCs was studied by Thermogravimetric Analysis (TGA), the melting and crystallization behaviour by Dynamic Scanning Calo-rimetry (DSC)

Methods for improved flexural mechanical properties of 3D-plotted PCL-based scaffolds for heart valve tissue engineering

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