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Injection foaming is an method for mass producing lightweight, foamed plastic components with excellent dimensional stability while using less material and energy. In this study, a novel injection foaming method employing supercritical CO2 (scCO2) and water as coblowing agents was developed to produce thermoplastic polyurethane (TPU) components with a uniform porous structure and no solid skin. Various characterization techniques were employed to investigate the cell morphology, crystallization behavior, and static and dynamic mechanical properties of solid injection molded samples, foamed samples using CO2 or water as a single blowing agent, and foamed samples using both CO2 and water as coblowing agents. When compared with CO2 foamed samples, samples produced by the coblowing method exhibited much more uniform cell morphologies without a noticeable reduction in mechanical properties. Moreover, these TPU samples had almost no skin layer, which permitted the free transport of nutrients and waste throughout the samples. Such a mass-produced, skin-free structure is desirable in tissue engineering. In this study, the biocompatibility of the scaffolds was confirmed and the effect of these blowing agents on the TPU foaming behavior was studied. POLYM. ENG. SCI., 54:2947-2957, 2014. © 2014 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

In this study, biomedical thermoplastic polyurethane/graphene oxide (TPU/GO) composite scaffolds were successfully prepared using the thermally induced phase separation (TIPS) technique. The microstructure, morphology, and thermal and mechanical properties of the scaffolds were characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and compression tests. Furthermore, NIH 3T3 fibroblast cell viability on the porous scaffolds was investigated via live/dead fluorescent staining and SEM observation. FTIR and Raman results verified the presence of GO in the composites. SEM images showed that the average pore diameter of the composite scaffolds decreased as the amount of GO increased. Additionally, the surface of the specimens became rougher due to the embedded GO. The compressive modulus of composite specimens was increased by nearly 200% and 300% with the addition of 5% and 10% GO, respectively, as compared with pristine TPU. 3T3 fibroblast culture results showed that GO had no apparent cytotoxicity. However, high loading levels of GO may delay cell proliferation on the specimens. [ABSTRACT FROM AUTHOR]

Novel blended scaffolds combining biobased polylactic acid (PLA) and thermoplastic polyurethane (TPU) were fabricated by thermally induced phase separation (TIPS) using two different solvents. Pure PLA and TPU polymer scaffolds using 1,4-dioxane as the sole solvent exhibited typical ladder-like structures, while blended PLA/TPU scaffolds using the same solvent showed a more uniform microstructure. When de-ionized water was added to the solution as a non-solvent, scaffolds with the mixed solvent showed more open cells and greater interconnectivity. In compression tests, it was found that specimens, including pure PLA, TPU, and blended scaffolds with the mixed solvent, showed a higher compressive modulus than their counterparts that used dioxane as the single solvent. Dynamic mechanical analysis (DMA) was employed to characterize the shape memory properties of the scaffolds. DMA indicated that the shape fixing ratio was highest in the PLA scaffolds, while the shape recovery ratio of the TPU scaffolds was the greatest among the specimens. More interestingly, when the mixed solvent was used, the shape memory property of the blended scaffolds displayed a similar deformation curve to the TPU scaffold. This was due to the presence of the TPU phase and similarity in structure between PLA/TPU and TPU scaffolds when mixed solvent was used. In the degradation test, the blended scaffolds showed a balanced degradation behavior in-between the more easily degraded PLA and the more stable TPU in the phosphate-buffered saline (PBS), and the addition of water to the systems accelerated the degradation process of the specimens. Cell culture results showed that all of the scaffolds had good biocompatibility. [ABSTRACT FROM PUBLISHER]

Rigid thermoplastic polyurethane (TPU)/hydroxyapatite (HA) scaffolds were prepared with micro HA (mHA) and nano HA (nHA) particles, respectively, via the thermally induced phase separation method. The effects of solvent and co-solvent, addition of sodium chloride (NaCl) porogen, and HA particle size were studied together with the morphology, compressive properties, and mineralization behavior of the scaffolds. Depending on the solvent, co-solvent, or porogen used, different porous structures were produced. In particular, a ladder-like morphology was obtained when dioxane (Di) was used as the solvent, whereas an interconnected porous structure was obtained by using dioxane and deionized water (DiW) as co-solvents. Rectangular pores with interconnected channels on the pore walls were achieved by using NaCl crystals as porogens. The TPU/nHA scaffolds showed stronger compressive properties than the TPU/mHA scaffolds and the pure TPU scaffolds. The scaffolds prepared using dioxane and water as co-solvents exhibit the greatest compressive modulus. Furthermore, TPU scaffolds with nHA particles had the ability to form bone apatite when soaked in simulated body fluid (SBF). After being soaked in SBF for 3 weeks, the weight percentage of formed apatite in the TPU/nHA-DiW scaffold was 9.2 %wt of the initial TPU content. Preliminary cytotoxicity tests were conducted using NIH 3T3 fibroblast cells. The high survival rate of these cells and the mineralization behavior suggest biocompatibility and high potential of these composites being used in bone tissue engineering applications. [ABSTRACT FROM AUTHOR]

Thermoplastic polyurethane is a commonly used polymer in our daily lives. Microcellular injection molding (a.k.a. MuCell) is an emerging method capable of mass-producing thermoplastic polyurethane foams with tunable microstructures and properties. This study investigated the effects of four main processing parameters—namely, plasticizing temperature, carbon dioxide (CO2) content, injection volume, and injection speed—on microcellular injection molded thermoplastic polyurethane ASTM tensile test bars. Property variables of interest included the cell diameter, cell density, skin layer thickness, and Young’s modulus. Influence sequences of parameters on each variable were obtained via the orthogonal array test method. It was found that the CO2 content primarily affected the cell diameter and cell density, whereas the temperature mainly influenced the skin layer thickness and Young’s modulus. Surface fitting of each dependent variable was done by combining its two most influential parameters from the experiment data. The value of each property variable within the processing window could then be predicted from the fitted surface. In addition, microcellular injection molding of thermoplastic polyurethane was simulated by a commercial software package, and the simulated results confirmed the reliability of the cell diameter prediction. [ABSTRACT FROM PUBLISHER]

Microcellular injection molding is capable of fabricating light weight, dimensionally stable plastic parts while using less material and energy. Two kinds of blowing agents, namely, supercritical nitrogen and expandable thermoplastic microspheres, were employed to produce foamed polylactic acid parts. The surface characteristics were evaluated with a two-dimensional surface roughness analyzer and a three-dimensional white-light interferometer surface profiler. Through surface roughness comparisons, injection molded American Society for Testing Material tensile test bars with expandable thermoplastic microspheres exhibited better surface quality than their supercritical nitrogen counterparts. The tensile properties of injection molded polylactic acid tensile bars with nitrogen and expandable thermoplastic microspheres at various weight concentrations were investigated. The results showed that the polylactic acid/nitrogen parts possessed a better Young’s modulus and tensile strength. The microstructure on the fractured cross-sectional surfaces was characterized using a scanning electron microscope. As reflected by the testing results, the cell microstructure – such as cell size and cell density, and multi-layered structure with a foamed core sandwiched by skin layers – played an important role in the surface quality and mechanical properties. In addition, while an appropriate expandable thermoplastic microspheres content had a positive effect on the cell microstructure and weight reduction, too high of a concentration of expandable thermoplastic microspheres adversely affected the tensile properties and surface roughness of the microcellular polylactic acid tensile test bars. [ABSTRACT FROM PUBLISHER]

Microcellular injection molding is capable of fabricating light weight, dimensionally stable plastic parts while using less material and energy. Two kinds of blowing agents, namely, supercritical nitrogen and expandable thermoplastic microspheres, were employed to produce foamed polylactic acid parts. The surface characteristics were evaluated with a 2D surface roughness analyzer and a 3D white-light interferometer surface profiler. Through surface roughness comparisons, injection molded ASTM tensile test bars with expandable thermoplastic microspheres exhibited better surface quality than their supercritical nitrogen counterparts. The tensile properties of injection molded polylactic acid tensile bars with nitrogen and expandable thermoplastic microspheres at various weight concentrations were investigated. The results showed that the polylactic acid/nitrogen parts possessed a better Young’s modulus and tensile strength. The microstructure on the fractured cross-sectional surfaces was characterized using a scanning electron microscope. As reflected by the testing results, the cell microstructure—such as cell size and cell density, and multi-layered structure with a foamed core sandwiched by skin layers—played an important role in the surface quality and mechanical properties. In addition, while an appropriate expandable thermoplastic microsphere content had a positive effect on the cell microstructure and weight reduction, too high of a concentration of expandable thermoplastic microsphere adversely affected the tensile properties and surface roughness of the microcellular polylactic acid tensile test bars. [ABSTRACT FROM PUBLISHER]

Abstract: Polylactic acid (PLA) and thermoplastic polyurethane (TPU) are two kinds of biocompatible and biodegradable polymers that can be used in biomedical applications. PLA has rigid mechanical properties while TPU possesses flexible mechanical properties. Blended TPU/PLA tissue engineering scaffolds at different ratios for tunable properties were fabricated via twin screw extrusion and microcellular injection molding techniques for the first time. Multiple test methods were used to characterize these materials. Fourier transform infrared spectroscopy (FTIR) confirmed the existence of the two components in the blends; differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) confirmed the immiscibility between the TPU and PLA. Scanning electron microscopy (SEM) images verified that, at the composition ratios studied, PLA was dispersed as spheres or islands inside the TPU matrix and that this phase morphology further influenced the scaffold's microstructure and surface roughness. The blends exhibited a large range of mechanical properties that covered several human tissue requirements. 3T3 fibroblast cell culture showed that the scaffolds supported cell proliferation and migration properly. Most importantly, this study demonstrated the feasibility of mass producing biocompatible PLA/TPU scaffolds with tunable microstructures, surface roughnesses, and mechanical properties that have the potential to be used as artificial scaffolds in multiple tissue engineering applications. [Copyright &y& Elsevier]

Abstract: A series of controlled-rheology polypropylenes (CRPPs) were prepared through reactive extrusion of polypropylene (PP) and dicumyl peroxide (DCP). Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) were used to evaluate the ability of three different kinds of nucleating agents (NAs), E3B, WBG-II, and TMB-5, to induce β-crystals in the CRPPs. The results indicate that TMB-5 shows the best nucleation effect and can induce the highest relative content of β-crystals. For the effect of DCP content on the β-crystal of CRPP, it was found that with 0.3wt% TMB-5 incorporated, the critical DCP content emerged at 0.1wt%. For the effect of NA content on the β-crystal of CRPPs, the total β-crystallinity index and relative β-crystal content were found to reach a maximum value at a content of 0.5wt% β-NA, with a 0.1wt% DCP content incorporated. [Copyright &y& Elsevier]