Volume 16, Issue 5

The aim of this work was to develop bioresorbable, asymmetric membranes for guided bone regeneration (GBR). Two resorbable polymers – polylactide (PLA) and polycaprolactone (PCL) were used in fabrication process. Two different manufacturing methods were applied: electrospinning in the case of PLA and freeze-drying of PCL. Mechanical properties, stability in a water environment and biocompatibility of fabricated membranes were evaluated. Microstructure [scanning electron microscopy (SEM)] of the membranes was assessed in terms of level of porosity, as well as size and shape of the pores. Study showed that combination of electrospinning and freeze-drying methods allows biocompatible PLA/PCL bi-phasic materials of appropriate mechanical properties and diverse microstructure to be produced, that should on the one hand prevent soft tissue growth, and on the other hand be a suitable scaffold for the growth of bone cells.

The esophagus is a tubular multi-layer organ that carries the food bolus and liquids from the mouth to the stomach. Esophageal prostheses and scaffolds should have the appropriate mechanical and strain properties in the longitudinal and circumferential directions. A novel bi-layered esophageal prosthesis was produced using knitted tubular silk fabric and a coating of polyurethane (PU) nanofibers. The optimization process was performed in two steps. First, 12 different tubular structures of knitted silk fabrics were produced and mechanical properties were measured in both directions. The mechanical properties were optimized using an artificial neural network (ANN) and a genetic algorithm (GA) and the optimum knitted structure was produced as a substrate for coating with PU nanofibers. In second step, 20 different samples were produced by electrospinning the PU nanofibers at different process conditions (collector speed, feeding rate) on the optimized structure of the knitted fabric. Finally, the elastic properties of the bi-layered tubular structures were measured and optimized by the ANN and GA methods. Results presented show that the optimized structure of the esophageal prosthesis had proper mechanical properties similar to the esophagus. Such a structure can be used as a substitute in esophageal disorders.

In this investigation, we studied the effect of the cavity air pressure on the replication of micro-patterns in injection molding. When pressure is applied to the cavity air, the pressure at the flow front is also increased and thus the overall pressure gradient in the polymer melt is lowered. Therefore, the melt flow in the cavity becomes slower providing more time for the polymer melt to fill the patterns on the cavity surface resulting in the improvement of replication of the microscopic pattern. We carried out experiments for molds with a macroscopic pattern (ribs) and a microscopic pattern on the surface. In order to evaluate the quality of replication, we measured the filling heights of patterns with different ratio of the cavity air pressure to the injection pressure. The results showed that the application of cavity pressure helps the replication of patterns both for macroscopic and microscopic scales.

Mineral fillers (MFs) have been widely employed for polymer hybrid composites to enhance mechanical properties for the past few decades. In this study, we explored structural impacts of kaolin and talc on the mechanical, heat-resistant, rheological and flame retardant (FR) properties of the polycarbonate (PC) composites. The incorporation of these fillers into the polymer matrix enhanced mechanical properties like flexural and tensile modulus while elongation at break, impact strength and melt flow index (MFI) were reduced as a function of filler concentration. The heat deflection temperature (HDT) was slightly increased with increasing talc content. Infiltration of even 5 phr fillers dramatically enhanced the flame retardancy. Talc showed somewhat higher mechanics and FR characteristic, compared to kaolin. These PC/filler hybrid composites with enhanced mechanics and flame retardancy would be useful for a specific application by tailoring their ratios.

Bubble growth during polymeric foam production by a physical nucleating agent is a result of rapid gas phase separation in a polymer/gas solution media. The dynamics of bubble growth is thought to be influenced by the material properties and processing conditions. However, the degree of effectiveness of each parameter has not been evaluated in earlier studies. In this work, a simplified single bubble growth in a polymeric media was modeled to specify the critical parameters affecting the bubble growth phenomenon. The predicted bubble growth profile was compared with some experimental data reported in the literature. The model was able to predict the observed bubble growth profile with acceptable precision. Therefore, it was applied to investigate the effect of each physical property of the polymer, i.e. viscosity, surface tension and diffusion coefficient as well as processing conditions, i.e. temperature and pressure release rate on the bubble growth profile. Furthermore, the impact of each factor was clarified.

Several tough and flexible fluorinated polyamide-imide films were prepared from trimellitic anhydride chloride and 2,2′-bis(trifluoromethyl)benzidine through a facile one-pot in-situ silylation method. By incorporating fluorinated side groups, the solubility of the prepared polyamide-imide was greatly enhanced. Meanwhile, due to their linear chain configuration and the existence of hydrogen bonding, the prepared polyamide-imide films revealed high tensile strength, high tensile modulus, high glass transition temperature (Tg) and most interestingly, very low coefficient of thermal expansion (CTE) of 11 ppm/°C. Copolymerization with pyromellitic dianhydride (PMDA) led to an extremely low CTE of 4 ppm/°C which should be among the lowest values available for soluble polyamide-imides. The optical homogeneity and stress homogeneity of the obtained polyamide-imide films were also tested. After non-contact with substance and thermal treatment at 300°C, they revealed a better optical homogeneity and stress homogeneity than that of the commercially available Kapton polyimide (PI) films, with a PV value of 0.915 λ and RMS value of 0.163 λ. Thus, these colorless and soluble polyamide-imide films simultaneously possessing promising optical imaging performance are good candidates as novel diffractive membrane optical system architectures.

In this study, poly (1-vinylimidazole)-iron(III) [PVIm-Fe(III)] complex was investigated along with adsorption behavior of bovine serum albumin (BSA). The cross-linked PVIm-Fe(III) was synthesized in supercritical carbon dioxide by using N,N′-methylenebisacrylamide (BIS) as a cross-linker. The obtained products were analyzed using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS) analysis. The results reveal that iron ion is complexed by coordination with basic (-N) functional groups of 1-vinylimidazole successfully. The effects of the operating pressure, the ratio of iron and cross-linker concentration were investigated. A fine and yellow powder was obtained at high yield and crosslinking degrees at 20 MPa, 70°C. Additionally, the property of PVIm-Fe(III) complexes in terms of BSA adsorption has been studied, and the higher adsorption capacity was 660 mg/g.

This article reports the synthesis of novel diamines as chain extenders for the improvement of thermal and mechanical properties of polyurethane (PU). Three novel diamine, 1,2-di(p-aminophenoxy)ethane (BAE), 1,2-di(p-aminophenoxy)propane (BAP) and 2,2-bis(p-(p-aminophenoxy)phenyl)propane (BAPP) were synthesized as chain extenders. Formation of diamines and their reaction with PU prepolymer was analyzed by using Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy. The conversion of the free isocyanate group (NCO) into a urethane-urea group was confirmed through the disappearance of the isocyanate peak at 2244 cm -1 . The thermogravimetric analysis (TGA) reveals the thermal stabilization effect of urethane-urea hard segments of the polyurethane system. From the SAXS investigations, the hard segment inter-domain spacing ( d ) was calculated, which was 24 nm for the reference sample, and 25, 26, and 28.5 nm for the synthesized PU systems. Mechanical test shows an increase in the Young’s modulus and yield strength with BAE and BAP diamines, while BAPP diamine based systems reveal lower modulus values as compared to the reference sample.