Polyethylene Terephthalate Matrices Research Articles

Fabrication and characterization of phase change material composite fibers with wide phase-transition temperature range by co-electrospinning method

An innovative electrospun form-stable phase change composite material is fabricated by combining binary fatty acid eutectics of capric-lauric acid (CA-LA) and capric-palmitic acid (CA-PA) as the phase change materials (PCMs) and polyethylene terephthalate (PET) as the supporting matrix. The encapsulated PCM composite fibers are produced by co-electrospinning of different fibers at various PCM-to-PET ratios of 50/100, 70/100, 100/100 and 120/100. Thermal behavior and characteristics of individual fatty acids, fatty acid eutectics and composite fibers as well as the structural morphology of the composite fibers are characterized by differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Scanning electron microscopy images revealed that the average diameter of the composite fibers is slightly increased by increasing the PCM contents. Comparison of FT-IR plots for fatty acids and PET with those of composite fibers containing PCMs clearly indicates that no chemical reaction occurred between PCM and PET matrices. In addition, thermogravimetric analysis results have shown that composite fibers have two steps of degradation which correspond to decomposition of PCM molecular chains and PET structure, respectively. Moreover, DSC results have indicated that enthalpy of composite fibers is improved by increasing PCM contents while no considerable change is observed in phase-transition temperature. Compared to previous studies, the present fabricated co-electrospun composite fibers offer wider phase-transition temperature range (−9 to 34°C) and higher enthalpy values even with lower amounts of PCM. Therefore, these composite fibers are very promising for use in near ambient storage and retrieval energy systems.

A preliminary investigation on reinforced double layer Nafion membranes for high temperature PEFCs application

Double layer recast Nafion® membranes reinforced using a polyethyleneterephthalate (PET) support were developed for PEFCs application at Tcell>110°C, low humidification and pressure. The investigation of chemical–physical properties suggested a probable interaction between PET and Nafion matrices. Electrochemical tests in a 25cm2 H2/air PEFC between 80 and 140°C were carried using a pure Nafion as a reference. A short time test supplied an average stable current density of about 400mAcm−2 (0.5V) for reinforced membrane against an unstable trend of reference. High current densities of 530mAcm−2 and 330mAcm−2 (0.6V) were obtained for N-PET at unusual temperatures (130–140°C).

Multiwalled carbon nanotube-coated polyethylene terephthalate fibrous matrices for enhanced neuronal differentiation of mouse embryonic stem cells.

The next-generation of tissue scaffolds should incorporate 3-D structures with nanofeatures. Fibrous polyethylene terephthalate (PET) matrices have been widely studied as tissue engineering scaffolds, but their performance is limited by the lack of nanotopography. Carbon nanotubes can provide nanoscale structures similar to those present in natural extracellular matrices in vivo, but are difficult to use as 3-D scaffolds for tissue engineering. In this study, multiwalled carbon nanotubes (MWCNTs) were used to coat and provide nanofeatures on the surface of PET membranes and fibers. The effects of MWCNTs on the cellular functions of mouse embryonic stem (mES) cells cultured on the nanoengineered PET surface and 3-D scaffolds were investigated. In general, MWCNTs promoted cell adhesion and proliferation of mES cells while maintaining excellent cell viability in the growth medium. Neuronal differentiation was also significantly enhanced when cells were cultured in the differentiation medium. Different cell morphologies were observed in the presence of MWCNTs. Cells were stretched and well spread out in MWCNT-coated PET scaffolds, whereas cells were sporadically distributed in non-coated PET scaffolds. Furthermore, more filopodia were formed in MWCNT-coated PET matrices, suggesting increased interactions between scaffolds and cells. Also, neuronal cells differentiated from mES cells in the 3-D nanoengineered PET scaffolds formed extensive nerve networks around each fiber and neurite bridges between fibers. These findings suggest that MWCNTs can provide nanofeatures on PET fibrous matrices and enhance their performance as 3-D nanoengineered tissue engineering scaffolds.

Three-dimensional culture of human mesenchymal stem cells in a polyethylene terephthalate matrix

Polyethylene terephthalate (PET) was used as the scaffold material to support the proliferation of human mesenchymal stem cells (hMSCs). The cells were cultured either statically in multi-wells or in a spinner flask agitated at 80 rpm for up to 20 days. To optimize the cell expansion condition, effects of the initial cell density and basic fibroblast growth factor (bFGF) were examined. During culture, cell growth and metabolism were tested. After 20 days, cells were harvested and surface markers were identified and quantified with flow cytometry. The results showed that hMSCs seeded at the lowest density gave the highest expansion fold. hMSCs grown in porous three-dimensional (3D) matrices displayed significantly different characteristics in terms of their proliferation and metabolism. PET matrices with 3D space could sustain cell proliferation for a long time. In addition, a low concentration (5 ng mL−1) of bFGF significantly enhanced the expansion of hMSCs in PET. Cell attachment and distribution in PET matrices were studied with confocal laser microscopy and scanning electron microscopy, which also confirmed cell proliferation. Furthermore, most of the cells in PET matrices were CD29, CD44 and CD105 positive, and CD34, CD45 and CD14 negative, confirming that hMSCs cultured in 3D PET matrices can be expanded and maintained in their undifferentiated state for at least 20 days without subculturing.

Centrifugal seeding of mammalian cells in nonwoven fibrous matrices

Three-dimensional (3D) cell cultures have many advantages over two-dimensional cultures. However, seeding cells in 3D scaffolds such as nonwoven fibrous polyethylene terephthalate (PET) matrices has been a challenge task in tissue engineering and cell culture bioprocessing. In this study, a centrifugal seeding method was investigated to improve the cell seeding efficiency in PET matrices with two different porosities (93% and 88%). Both the centrifugal force and centrifugation time were found to affect the seeding efficiency. With an appropriate centrifugation speed, a high 80-90% cell seeding efficiency was achieved and the time to reach this high seeding efficiency was less than 5 min. The seeding efficiency was similar for matrices with different porosities, although the optimal seeding time was significantly shorter for the low-porosity scaffold. Post seeding cell viability was demonstrated by culturing colon cancer cells seeded in PET matrices for over 5 days. The centrifugal seeding method developed in this work can be used to efficiently and uniformly seed small fibrous scaffolds for applications in 3D cell-based assays for high-throughput screening.

Modifications of nonwoven polyethylene terephthalate fibrous matrices via NaOH hydrolysis: Effects on pore size, fiber diameter, cell seeding and proliferation

A simple NaOH treatment method was developed for fabricating nonwoven fibrous matrices of polyethylene terephthalate (PET) with predictable porosity, pore size, and fiber diameter. Matrices with various porosities (90–97%), fiber diameters (13.5–25 μm), and pore sizes (54–65 μm) were prepared by treating with 1N NaOH at 70 °C for up to 120 h, resulting in up to 70% hydrolysis of the PET polymer. The hydrolysis of PET polymer by NaOH was found to follow a second-order kinetics with respect to the fiber surface area. Accordingly, mathematical models were developed to predict matrix porosity, fiber diameter, and apparent pore size of the PET matrices. The exponential decay coefficient of PET polymer was found to be 0.0147 h −1. The matrices were used to study the effects of pore size and fiber diameter on cell seeding and proliferation. The seeding study demonstrated that cell adhesion on PET fibers can be enhanced, largely due to the increased surface roughness of the PET fibers. Decreasing the fiber diameter increases the surface curvature of the fibers and decreases available surface area for cell attachment, which, however, only resulted in a small decrease in the cell growth rate.

Electronic conductance of ion implanted and plasma modified polymers

The authors used the plasma immersion ion implantation and deposition technique to modify polyethylene terephthalate (PET) and by using conductive atomic force microscope, the spatial distribution of ∼10nm size titanium nanoclusters embedded in PET matrices were observed. The I-V plots showed typical metal-semiconductor junction conductivity between the conductive tip and the surface. In addition, the authors also measured the temperature dependent conductivity and fitted it well to the Mott law, which implied that the conductance arose from electron hopping process. Such technique to create the surface structure of metal/polymer nanocomposites may open an alternative way for plastic nanoelectronics.

Effects of mixing intensity on cell seeding and proliferation in three‐dimensional fibrous matrices

Nonwoven fibrous matrices have been widely used in cell and tissue cultures because their three-dimensional (3-D) structures with large surface areas and pore spaces can support high-density cell growth. Although cell adherence and growth on 2-D surfaces have been thoroughly investigated, very little is known for cells cultured in 3-D matrices. The effects of mixing intensity on cell seeding, adherence, and growth in fibrous matrices were thus investigated. Chinese Hamster Ovary and osteosarcoma cells were inoculated into nonwoven polyethylene terephthalate matrices by dynamic and static seeding methods, of which the former was found to be superior in seeding efficiency and cell distribution in the matrices. Dynamic seeding increased seeding efficiency from approximately 40% to more than 90%. When higher mixing intensities were applied, both cell attachment and detachment rates increased. Cell attachment was transport limited, as indicated by the increased attachment rate with increasing the mass transfer coefficient of the cells. Meanwhile, cell detachment from the 3-D matrix can be described by the Bell model. The effects of matrix pore size on cell adherence and proliferation were also investigated. In general, the smaller pore size is favorable to cell attachment and proliferation. Further analysis revealed that the interaction between mixing intensity and pore size played a vital role in hydrodynamic damage to cells, which was found to be significant when the Kolomogorov eddy size was smaller than the matrix pores. Increasing mixing intensity also increased oxygen transfer, decreased the lactate yield from glucose, and improved cell growth.

Astrocyte Growth and Glial Cell Line-Derived Neurotrophic Factor Secretion in Three-Dimensional Polyethylene Terephthalate Fibrous Matrices

The ability of human astrocytes grown in nonwoven fibrous matrices to produce glial cell line-derived neurotrophic factor (GDNF) was studied. GDNF has the ability to selectively nourish and regenerate dopaminergic neurons and thus can provide a new treatment of Parkinson's disease. Compressed polyethylene terephthalate (PET) fabrics (porosity, 88.8%; mean pore diameter, 64 microm), treated with boiling NaOH, was effective in supporting high-density growth of astrocytes with stable GDNF production over the entire period of 18 days studied. Treatment of PET with NaOH renders the fiber surface more hydrophilic, thereby facilitating attachment and spreading of cells, whereas matrix compression allows cells to grow along and also between the fibers of these matrices to a higher density. The average production of GDNF by cells grown in these matrices (approximately 2 cm in diameter) was 21.7 pg/mL x day, with an average high concentration of 64.6 pg/mL, which is well above the effective concentration of 40 pg/mL. This work shows promise in culturing astrocytes in PET matrices as the first step in developing a potential implantable tissue-engineering device for treating patients with Parkinson's disease.

Toughening of polyethylene terephthalate/amorphous copolyester blends with a maleated thermoplastic elastomer

AbstractThe toughening of polyethylene terephthalate (PET)/amorphous copolyester (PETG) blends using a maleic anhydride grafted mixture (TPEg) of polyethylene‐octene elastomer and a semicrystalline polyolefin plastic (60/40 by weight) was examined. The TPEg was more effective in toughening PETG than PET, although the dispersion qualities of the TPEg particles in PET and PETG matrices were very similar. At the fixed TPEg content of 15 wt %, replacing partial PET by PETG resulted in a sharp brittle‐ductile transition when the PETG content exceeded the PET content. Before the transition, PET/PETG blends were not toughened with the TPEg of 15 wt %, whereas after the transition, the PET/PETG blends with 15 wt % of TPEg, similar to the PETG/TPEg (85/15) binary blend, maintained a super‐tough level. The impact‐fractured surfaces of the PET/PETG/TPEg blends were also evaluated. When PETG content was lower than PET content, the ternary blend showed a brittle feature in its impact‐fractured surface, similar to the PET/TPEg (85/15) binary blend. While PETG content exceeded PET content, however, the impact‐fractured surface of the ternary blend was very similar to that of PETG/TPEg (85/15) binary blend, exhibiting intensive cavitation and massive matrix shear yielding, which were believed to be responsible for the super‐tough level of the blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 797–805, 2003

Thermal compression and characterization of three-dimensional nonwoven PET matrices as tissue engineering scaffolds

Nonwoven fibrous matrices have been widely used as scaffolds in tissue engineering, and modification of microstructure of these matrices is needed to organize cells in three-dimensional space with spatially balanced proliferation and differentiation required for functional tissue development. The method of thermal compression of nonwoven polyethylene terephthalate (PET) fabrics was developed and key parameters of temperature, pressure, and compression duration were evaluated in this study. The permanent deformation was obtained at elevated temperature under pressure and the viscoelastic compressional behaviors were observed, characterized by a distinct apparent modulus change in glass transition temperature region. A liquid extrusion method was further employed to analyze both pore size and its distribution for matrices with porosity ranging from 84 to 93%. It is also found that a more uniformly distributed pore size was resulted from thermal compression and the isotropic nature of nonwoven fabrics was preserved because of the proportional reduction of the pore by compression. The thermally compressed fabric matrices with two different pore sizes (15 and 20 μm in pore radius) were used to culture human trophoblast ED 27 and NIH 3T3 cells. It was found that cells cultured in the different pore-size PET matrices had different cell spatial organization and proliferation rates. The smaller pores in the matrix allowed cells to spread better and proliferate faster, while cells in the larger pores tended to form large aggregates and had lower proliferation rate. The thermal compression technique also can be applied to other synthetic fibrous matrices including biodegradable polymers used in tissue engineering to modify the microstructure according to their viscoelastic properties.

Effects of pore size in 3-D fibrous matrix on human trophoblast tissue development.

The effects of pore size in a 3-D polyethylene terephthalate (PET) nonwoven fibrous matrix on long-term tissue development of human trophoblast ED27 cells were studied. Thermal compression was used to modify the porosity and pore size of the PET matrix. The pore size distributions in PET matrices were quantified using a liquid extrusion method. Cell metabolic activities, estradiol production, and cell proliferation and differentiation were studied for ED27 cells cultured in the thermally compressed PET matrices with known pore structure characteristics. In general, metabolic activities and proliferation rate were higher initially for cultures grown in the low-porosity (LP) PET matrix (porosity of 0.849, average pore size of 30 microm in diameter) than those in the high-porosity (HP) matrix (porosity of 0.896, average pore size of 39 microm in diameter). However, 17beta-estradiol production and cell differentiation activity in the HP matrix surpassed those in the LP matrix after 12 days. The expression levels of cyclin B1 and p27kip1 in cells revealed progressively decreasing proliferation and increasing differentiation activities for cells grown in PET matrices. Also, difference in pore size controlled the cell spatial organization in the PET matrices and contributed to the tissue development in varying degrees of proliferation and differentiation. It was also found that cells grown on the 2-D surface behaved differently in cell cycle progression and did not show increased differentiation activities after growth had stopped and proliferation activities had lowered to a minimal level. The results from this study suggest that the 3-D cell organization guided by the tissue scaffold is important to tissue formation in vitro.