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

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

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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MFC concept as a possible solution for closed-loop recycling of food packaging trays

Flexible plastic films from food packaging trays make up one of the largest fractions of the plastic waste stream and recycling is one of the most important actions to deal with this fraction, reducing the impact of these plastics on the environment. However, the recyclability of multi-layered films is not straightforward and in most of the cases these fractions are landfilled or incinerated. Recycling of discarded mixed polymers without previous separation often results in low mechanical properties which have lead researchers to investigate novel solutions for recycling. In this research, the concept of microfibrillar composites (MFCs) was investigated aiming to upcycle mixed polymer waste streams. A blend based on polypropylene (PP) and poly(ethylene terephthalate) (PET) at a weight ratio of 80/20 PP/PET was studied. The final step of the MFC processing was conducted using a conical twin screw extrusion. The morphological results confirmed the presence of PET microfibrils in the composites, leading to an improvement in mechanical properties such as in the tensile yield strength and strain at break. Subsequently, the MFC samples were successfully moulded into trays via thermoforming

Uses and Misuses of the Black-Litterman Model in Portfolio Construction

The Black-Litterman model has gained popularity in applications in the area of quantitative equity portfolio management. Unfortunately, many recent applications of the Black-Litterman to novel aspects of quantitative portfolio management have neglected the rigor of the original Black-Litterman modelling. In this article, we critically examine some of these applications from a Bayesian perspective. We identify three reasons why these applications may create losses to investors. These three reasons are: (1) Using a prior without anchoring the prior to an equilibrium model, (2) Using a prior and an equilibrium model that conflict with one another, and (3) Ignoring the implications of the estimation error of the variance-covariance matrix. We also quantify the loss first analytically, and also numerically based on historical data on 10 major world stock market indices. Our conservative estimate of the loss is around a 1% reduction in the annualized return of the portfolio

High-Temperature Series Analysis of the Free Energy and Susceptibility of the 2D Random-Bond Ising Model

We derive high-temperature series expansions for the free energy and susceptibility of the two-dimensional random-bond Ising model with a symmetric bimodal distribution of two positive coupling strengths J_1 and J_2 and study the influence of the quenched, random bond-disorder on the critical behavior of the model. By analysing the series expansions over a wide range of coupling ratios J_2/J_1, covering the crossover from weak to strong disorder, we obtain for the susceptibility with two different methods compelling evidence for a singularity of the form $\chi \sim t^{-7/4} |\ln t|^{7/8}$, as predicted theoretically by Shalaev, Shankar, and Ludwig. For the specific heat our results are less convincing, but still compatible with the theoretically predicted log-log singularity.Comment: 19 pages, 6 Postscript figure