PET Membranes Research Articles

Characterizations of heavy ion irradiated PET membranes

Various characterizations were used to study the effect of heavy-ion irradiation on a poly(ethylene terephthalate) (PET) membrane. Our study made use of various dynamic and thermal measurements with the aim of understanding the chemical change in the material induced by heavy-ion irradiation. The analyses included DMA, tensile measurement, DSC and micro-FT-IR. The overall structure change in the PET polymer was investigated as a function of the Xe-ion fluence in the range from 3 × 10 3 to 3 × 10 9 ions/cm 2. Based on some mechanical measurements such as tensile analysis and a dynamic test, the heavy-ion irradiated PET membranes exhibited a significant change in cross-linking. We believe that the secondary electron induced by a collision between the irradiated ion and the constituent atoms of the membrane material form the cross-linking. The polymer chain scissions and structure degradations are expected to occur at higher ion fluence. Also, a slight change in the structure, such as amorphization, has been shown by DSC and the micro-FT-IR test.

Human fibroblast culture on a crosslinked dermal porcine collagen matrix

The use of a novel porcine-derived collagen biomaterial as a dermal tissue engineering matrix was examined. The matrix is derived from porcine dermis, and is processed to retain the native collagen (Type 1) and elastin structure. Human primary fibroblasts were cultured on the matrix to examine its potential for creating a dermal replacement. Attachment of fibroblasts on the collagen was compared to tissue culture plastic and PET membranes. Cell proliferation was assessed using the MTT assay and DAPI staining. For seeding densities of 5×10 4 and 1×10 5 cells cm −2, PET and plastic demonstrated >95% attachment of seeded numbers after 3 h. The collagen matrix reached levels >80% after 3–4 h with no influence of the seeding density. Matrix samples with perforating pores of 40 μm diameter were also studied. After 216 h culture in static culture, with media replacement every 3 days, the final cell numbers reached 2.1×10 5 (perforated) and 2.0×10 5 cells cm −2 (unperforated). In comparison fibroblast culture in a perfusion bioreactor, with continuous media replacement, reached 2.3×10 5 (unperforated) and 2.5×10 5 cells cm −2 (perforated) after 216 h.

Optical and electronic characterization on polymeric membranes

This work is dedicated to the optical and electronic characterization of poly(ethylene terephthalate) (PET) membranes, which are extensively used in many practical applications. Spectroscopic ellipsometry (SE) from 1.5 to 6.5 eV was applied to probe the dielectric function ( ε( ω)) of industrially supplied PET membranes and to reveal their optical anisotropy. Two characteristic features were observed at ∼5.0 and 6.1 eV, attributed to electronic transitions occurred in specific chemical bonds of the PET macromolecule. Through the appropriate fitting analysis it was obtained the geometrical structure of the membrane; consisting of a thick amorphous layer with a crystalline-like layer on top of it, formed during treatment processes. Using Fourier transform infrared (FT–IR) SE it was also extracted the spectral dependence of the ε( ω) in IR energy range by taking into account the contribution of the PET’s vibrational modes, and this it was found to be in an excellent agreement with the SE results.

Covalent grafting of fibronectin and asialofetuin at surface of poly(ethylene terephthalate) track-etched membranes improves adhesion but not differentiation of rat hepatocytes.

The adhesion and differentiation of rat hepatocytes onto track-etched poly(ethylene terephthalate) (PET) membranes were studied. Native or [3H]methylated fibronectin (FN) or asialofetuin (ASF) were immobilized onto oxidized PET membranes, preactivated or not with carbodiimide (WSC). Radiochemical assay and ELISA indicated that upon washing in SDS or in serum-containing medium, significantly less FN was released from WSC-activated membranes that from unactivated ones. These differences were abolished when the NH2 functions of FN were fully acetylated, suggesting that part of FN was covalently grafted on WSC-activated PET. Although weaker, a comparable effect was observed with ASF. Hepatocytes adhered faster on membranes on which FN was grafted than adsorbed, reaching values comparable to collagen-coated PET; after 24 h these differences decreased. Experiments with cycloheximide or at 4 degrees C suggested that this results from secretion of extracellular matrix adsorbing on PET. Phase I or II biotransformation activities of cells cultured for 1-4 days on FN-, ASF-, or collagen-treated substrates were not significantly different. These results indicate that stable immobilization of FN (covalent grafting) onto PET membranes significantly accelerates adhesion of hepatocytes but does not affect their differentiation. This may result from a progressive surface reconditioning by neosynthesized extracellular matrix.

Covalent grafting of fibronectin and asialofetuin at surface of poly(ethylene terephthalate) track‐etched membranes improves adhesion but not differentiation of rat hepatocytes

The adhesion and differentiation of rat hepatocytes onto track-etched poly(ethylene terephthalate) (PET) membranes were studied. Native or [3H]methylated fibronectin (FN) or asialofetuin (ASF) were immobilized onto oxidized PET membranes, preactivated or not with carbodiimide (WSC). Radiochemical assay and ELISA indicated that upon washing in SDS or in serum-containing medium, significantly less FN was released from WSC-activated membranes than from unactivated ones. These differences were abolished when the NH2 functions of FN were fully acetylated, suggesting that part of FN was covalently grafted on WSC-activated PET. Although weaker, a comparable effect was observed with ASF. Hepatocytes adhered faster on membranes on which FN was grafted than adsorbed, reaching values comparable to collagen-coated PET; after 24 h these differences decreased. Experiments with cycloheximide or at 4°C suggested that this results from secretion of extracellular matrix adsorbing on PET. Phase I or II biotransformation activities of cells cultured for 1–4 days on FN-, ASF-, or collagen-treated substrates were not significantly different. These results indicate that stable immobilization of FN (covalent grafting) onto PET membranes significantly accelerates adhesion of hepatocytes but does not affect their differentiation. This may result from a progressive surface reconditioning by neosynthesized extracellular matrix. © 1996 John Wiley & Sons, Inc.

Chemical Assays of End-groups Displayed on the Surface of Poly(ethylene terephthalate) (PET) Films and Membranes by Radiolabeling

Poly(ethylene terephthalate) BET) films and track-etched microporous membranes naturally display, on their surfaces, reactive chain-ends, i.e. carboxyl and hydroxyl functions. These were assayed by suitable activation (reaction with carbodiimide and tosyl chloride, respectively), followed by coupling with H-3-lysine and liquid scintillation counting of the sample-associated radioactivity. Values ranging between 5 and 30 pmol/cm(2) (open surface) of labeled end-groups were obtained, depending on the physico-chemical nature of the samples. Basic hydrolysis enriched the PET films with both types of endings (15-25 pmol/cm(2)). Reduction of films with the NaBH4-catechol complex in tetrahydrofuran enriched their surfaces with hydroxyl groups. However, this procedure was not readily applicable to the surface modification of membranes; we observed an erosion effect that was confirmed by scanning electron microscope analyses. In contrast with the reduction process, the oxidation with KMnO4 in 1.2 N H2SO4 could be easily applied to the modification of either films or membranes; their surfaces were significantly enriched with carboxyl groups (15-50 pmol/cm(2)). This surface modification strategy has been used for the covalent coupling of adhesive proteins on PET membranes developed as supports for cell cultivation.

The covalent grafting of fibronectin at the surface of poly(ethylene terephthalate) track-etched membranes improves adhesion of rat hepatocytes

[H-3]methylated fibronectin (FN) has been immobilized on the surface of poly(ethylene terephthalate) track-etched membranes (PET), carboxylated and then activated or not with water-soluble carbodiimide (WSC). Upon washing in 10% SDS or in the nutritive medium used for hepatocytes cultivation (supplemented with 15% newborn calf serum), respectively, 76% and 43% of [H-3]FN are released from the unactivated PET membranes and those WSC activated. This difference is almost totally abolished when the -NH2 functions of FN have been fully acetylated, to impair their reaction with activated -COOH groups. These results strongly suggest that part of FN is covalently grafted to the activated -COOH of PET but that, in addition, FN is also adsorbed on this surface. Rat hepatocytes were inoculated on PET membranes on which FN had been adsorbed and/or grafted. Image analysis clearly indicates that, during the first hours of culture, the FN immobilization on WSC activated, carboxylated PET membranes, significantly favours the adhesion of hepatocytes. After 24 h, the difference between these substrates decreases, probably due to the reconditioning of the PET surface by extracellular matrix constituents secreted by the hepatocytes. Our results confirm that the nature of the protein-polymer interaction strongly affects cell behaviour.

Permeation of gases through poly (ethylene terephthalate) membranes metallized with palladium

The permeation of He, H 2, CO 2, Ar and N 2 at 50°C through poly(ethylene terephthalate) (PET) membranes metallized with Pd layers ranging from 125 to 1000 Å in thickness was studied. It was found that the Pd layers act as gas barriers which reduce the rate of gas transfer through the polymer with up to more than one order of magnitude. The fact that the Pd layers failed to be perfect gas barriers was attributed to the presence of defects in the structure of the Pd layers and to additional gas diffusion through preferential diffusion paths along grain boundaries. A particular case is represented by the permeation of H 2. Since H 2 is able to dissolve into the Pd layers it permeates not only through the defects of the layers but also through the layers themselves. The experimental results show that catalytic activity of Pd in dissociating H 2 molecules determines the permeation rate of H 2 through the metallized PET membranes.

The influence of thickness and condensation rate on the resistivity of evaporated aluminum films

The permeation of He, H2, CO2, Ar and N2 at 50°C through poly(ethylene terephthalate) (PET) membranes metallized with Pd layers ranging from 125 to 1000 Å in thickness was studied. It was found that the Pd layers act as gas barriers which reduce the rate of gas transfer through the polymer with up to more than one order of magnitude. The fact that the Pd layers failed to be perfect gas barriers was attributed to the presence of defects in the structure of the Pd layers and to additional gas diffusion through preferential diffusion paths along grain boundaries. A particular case is represented by the permeation of H2. Since H2 is able to dissolve into the Pd layers it permeates not only through the defects of the layers but also through the layers themselves. The experimental results show that catalytic activity of Pd in dissociating H2 molecules determines the permeation rate of H2 through the metallized PET membranes.