Surface modification of poly(ethylene terephthalate) by plasma polymerization of poly(ethylene glycol)

Poly(ethylene glycol) (PEG) was ‘polymerized’ onto poly(ethylene terephthalate) (PET) surface by radio frequency (RF) plasma polymerization of PEG (average molecular weight 200 Da) at a monomer vapour partial pressure of 10 Pa. Thin films strongly adherent onto PET could be produced by this method. The modified surface was characterized by infra red (IR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), cross-cut test, contact angle measurements and static platelet adhesion studies. The modified surface, believed to be extensively cross-linked, however showed all the chemical characteristics of PEG. The surface was found to be highly hydrophilic as evidenced by an interfacial free energy of about 0.7 dynes/cm. AFM studies showed that the surface of the modified PET became smooth by the plasma polymerized deposition. Static platelet adhesion studies using platelet rich plasma (PRP) showed considerably reduced adhesion of platelets onto the modified surface by SEM. Plasma ‘polymerization’ of a polymer such as PEG onto substrates may be a novel and interesting strategy to prepare PEG-like surfaces on a variety of substrates since the technique allows the formation of thin, pin-hole free, strongly adherent films on a variety of substrates.     

Improved impermeability of PET substrates using oxygen and hydrogen plasma

A considerable decrease in permeability of polyethylene terephthalate (PET) films by means of surface plasma treatment in a reactive ion etching system is reported. The effects of oxygen and hydrogen radio frequency plasma on the surface properties of PET polymers are investigated by infrared spectroscopy, scanning electron microscopy (SEM), and X-ray photon spectroscopy (XPS). The surface morphology of the samples has been investigated using SEM and atomic force microscopy (AFM). The optical transmission spectroscopy has been studied further confirming the significant effect of O-plasma. Also the penetration of air through the treated substrates was investigated using a vacuum test. It is found that oxygen and hydrogen plasmas lead to about four-fold reduction in the penetration of air through the PET films, while the effect of hydrogen plasma has been more significant. In addition, oxygen plasma results in a rougher surface as observed both by AFM and SEM analyses. The formation of nanostructures on PET surfaces has been observed at plasma powers of 0.3 W/cm².     

A comparison of reactive plasma pre-treatments on PET substrates by Cu and Ti pulsed-DC and HIPIMS discharges

PET web samples have been treated by magnetically enhanced glow discharges powered using either medium frequency pulse direct current (p-DC) or low frequency high power pulse (HIPIMS) sources. The plasma pre-treatment processes were carried out in an Ar–O₂ atmosphere using either Cu or Ti sputter targets. XPS, AFM and sessile drop water contact angle measurements have been employed to examine changes in surface chemistry and morphology for different pre-treatment process parameters. Deposition of metal oxide onto the PET surface is observed as a result of the sputter magnetron-based glow discharge web treatment. Using the Cu target, both the p-DC and HIPIMS processes result in the formation of a thin CuO layer (with a thickness between 1 and 11 nm) being deposited onto the PET surface. Employing the Ti target, both p-DC and HIPIMS processes give rise to a much lower concentration of Ti (< 5 at.%), in the form of TiO₂ on the PET treated surface. The TiO₂ is probably distributed as an island-like distribution covering the PET surface. Presence of Cu and Ti oxide constituents on the treated PET is beneficial in aiding the adhesion but alone (i.e. without oxygen plasma activation) is not enough to provide very high levels of hydrophilicity as is clear from sessile drop water contact angle measurements on aged samples. Exposure to the plasma treatments leads to a small amount of roughening of the substrate surface, but the average surface roughness in all cases is below 2.5 nm. The PET structure at the interface with a coating is mostly or wholly preserved. The oxygen plasma treatment, metal oxide deposition and surface roughening resulting from the HIPIMS and p-DC treatments will promote adhesion to any subsequent thin film that is deposited immediately following the plasma treatment.     

Single-layered porous silica films on polyethylene terephthalate substrates for antireflection coatings

Single-layered porous silica films were prepared on polyethylene terephthalate (PET) substrates as antireflection coatings for efficient, large-scale flexible optoelectronic devices. Cetyltrimethylammonium bromide (CTAB)-templated synthesis was employed to form porous silica films. Without using high temperature treatment, CTAB was removed by washing in water to create a porous structure in the films. To spin-coat on PET substrates, contact angle between silica sol and PET surface was measured to optimize the molar ratio of the solution. Pore size and surface sharpness were estimated using atomic force microscope data. The average reflectance of as-prepared AR coatings on PET substrates was ≤ 2%.     

Differentiation of human mesenchymal stem cells on plasma-treated polyetheretherketone

Polyetheretherketone (PEEK) generally exhibits physical and chemical characteristics that prevent osseointegration. To activate the PEEK surface, we applied oxygen and ammonia plasma treatments. These treatments resulted in surface modifications, leading to changes in nanostructure, contact angle, electrochemical properties and protein adhesion in a plasma power and process gas dependent way. To evaluate the effect of the plasma-induced PEEK modifications on stem cell adhesion and differentiation, adipose tissue-derived mesenchymal stem cells (adMSC) were seeded on PEEK specimens. We demonstrated an increased adhesion, proliferation, and osteogenic differentiation of adMSC in contact to plasma-treated PEEK. In dependency on the process gas (oxygen or ammonia) and plasma power (between 10 and 200 W for 5 min), varying degrees of osteogenic differentiation were induced. When adMSC were grown on 10 and 50 W oxygen and ammonia plasma-treated PEEK substrates they exhibited a doubled mineralization degree relative to the original PEEK. Thus plasma treatment of PEEK specimens induced changes in surface chemistry and topography and supported osteogenic differentiation of adMSC in vitro. Therefore plasma treated PEEK holds perspective for contributing to osseointegration of dental and orthopedic load-bearing PEEK implants in vivo.     

Deposition of cellular fibronectin and desorption of human serum albumin during adhesion and spreading of human endothelial cells on polymers

More insight into the mechanism of adhesion of human endothelial cells (HEC) on to polymeric surfaces may lead to the development of improved small-diameter vascular grafts. HEC suspended in 20% human serum-containing culture medium adhere and spread well on moderately water-wettable polymers such as tissue culture polystyrene (TCPS). Earlier it was demonstrated that during adhesion and spreading of HEC on TCPS, cellular fibronectin is deposited on to this surface. It was postulated that fibronectin deposition is accompanied by desorption of adsorbed serum proteins, e.g. human serum albumin (HSA). The amounts of adsorbed (cellular) fibronectin and HSA on TCPS surfaces pretreated for 1 h with solutions of human serum (ranging from 0.01%–20%), were determined after incubation of these surfaces for 6 h with HEC in culture medium and after incubation with culture medium without cells. Protein adsorption was determined by means of a two-step enzyme-immunoassay (EIA). HEC adhesion and spreading on TCPS resulted in a significant deposition of fibronectin irrespective of the serum concentration in the solution used for the pretreatment of TCPS. The deposition of cellular fibronectin on to TCPS, pretreated with human serum, was accompanied by displacement of adsorbed HSA. Desorption of HSA from TCPS was only detectable with the EIA at serum concentrations ranging from 0.01%–1%. Using¹³¹-l-labelled HSA as tracer protein; it could, however, be demonstrated that HSA was also displaced from TCPS, pretreated with solutions of higher serum concentrations. Pretreatment of the hydrophobic vascular graft material PET (poly(ethylene terephthalate); Dacron) and of FEP (fluoroethylenepropylene copolymer; a Teflon-like polymer) with a solution containing 20% human serum resulted in a reduced adhesion of HEC compared to uncoated surfaces. We suggest that this may be caused by a poor displacement of adsorbed serum proteins from these hydrophobic surfaces by cellular fibronectin. This may explain why HEC normally fail to adhere on to prosthetic surfaces.     

Contact angle analysis of low-temperature cyclonic atmospheric pressure plasma modified polyethylene terephthalate

Polyethylene terephthalate (PET) films are modified by cyclonic atmospheric pressure plasma. The experimentally measured gas phase temperature was around 30 °C to 90 °C, indicating that this cyclonic atmospheric pressure plasma can treat polymers without unfavorable thermal effects. The surface properties of cyclonic atmospheric pressure plasma-treated PET films were examined by the static contact angle measurements. The influences of plasma conditions such as treatment time, plasma power, nozzle distance, and gas flow rate on the PET surface properties were studied. It was found that such cyclonic atmospheric pressure plasma is very effective in PET surface modification, the reduced water contact angle was observed from 74° to less than 37° with only 10 s plasma treatment. The chemical composition of the PET films was analyzed by X-ray photoelectron spectroscopy (XPS). Atomic force microscopy (AFM) was used to study the changes in PET surface feature of the polymer surfaces due to plasma treatment. The photoemission plasma species in the continuous cyclone atmospheric pressure plasma was identified by optical emission spectroscopy (OES). From OES analysis, the plasma modification efficiency can be attributed to the interaction of oxygen-based plasma species in the plasma with PET surface. In this study, it shows a novel way for large scale polymeric surface modification by continuous cyclone atmospheric pressure plasma processing.     

Plasma processing for surface optical modifications of PET films

The plasma interaction with the surface produces modifications of its chemical structure or morphology. Surface modifications through cold plasma occur, thanks to the high plasma reactivity and ability to affect the surface of materials.The present work shows the surface modification of polyethylene terephthalate (PET) films after the exposure both to low-pressure plasma (film deposition by plasma enhanced chemical vapour deposition) and to an atmospheric pressure dielectric barrier discharge (surface etching). After plasma treatment we have analysed the effect on the PET surface.For the atmospheric pressure plasma-treated samples, contact angle and atomic force microscope analysis enable us to determine roughness changes. For the low-pressure plasma samples, contact angles and Fourier transform infrared absorption spectroscopy analysis are used to estimate the chemical composition of the deposition and focused ion beam analysis to collect the image and calculate the thickness of plasma deposition.Both plasma treatments (film deposition and etching) cause changes in optical properties as indicated by reflectivity measurements.     

Electric properties and surface characterization of transparent Al-doped ZnO thin films prepared by pulsed laser deposition

We grew 2 wt.% Al-doped ZnO (AZO) films on 5.08 cm-diameter polymer substrates at room temperature by the pulsed laser deposition (PLD) technique added the beam-rastering function. The structural properties, surface morphology, resistivity, mobility and chemical bonding states of AZO/polymer films were measured. The structuring of polymer surface by atmospheric plasma can occur at nm scales and can influence adhesion, optical and wettability properties of the materials. With increasing plasma treatment power, surface hydrophilicity and roughness for PET and PES polymer increased, respectively.     

Surface modification and characterization of indium–tin oxide for organic light-emitting devices

We used various treatment methods such as ethanol treatment, sodium hydroxide solution treatment, sulfur acid treatment, and oxygen plasma treatment to modify the surface of indium–tin oxide (ITO) substrates for organic light-emitting devices (OLEDs). The surface properties of the treated ITO substrates were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), contact angle, surface energy measurements, four-point probe, X-ray Diffraction (XRD) and ultraviolet-visible spectrophotometer. The results showed that the ITO surface properties were closely related to the treatment methods, and the oxygen plasma is more efficient than other treatments as it leads to smoother surface, better surface stoichiometry, higher work function and surface energy, lower sheet resistance, and higher transmission of the ITO substrates. Moreover, small molecular organic light-emitting devices (SMOLEDs) using different treated ITO substrates as anodes were fabricated and investigated. It was found that surface treatment of ITO substrates has influence upon the injection current, the turn-on voltages of light emission, luminance, efficiency and lifetime. Oxygen plasma treatment on the ITO substrate yields the highest performance of SMOLEDs due to the improvement of interface formation and electrical contact of the ITO substrate with the small molecular material blend in the SMOLEDs.     

Improved proliferation of human osteosarcoma cells on oxygen plasma treated polystyrene

Polystyrene (PS) foils were exposed to oxygen plasma in order to improve the ability of human osteosarcoma cells (HOS) proliferation. Plasma was created in an electrodeless radio-frequency (RF) discharge in pure oxygen. Plasma treatment time of 30 s allowed for saturation of the surface with oxygen rich functional groups. Incubation of proteins from cell culture media was studied versus incubation time for untreated and plasma treated PS by X-ray photoelectron spectroscopy (XPS). Then HOS cells were cultivated according to a standard procedure, applied on the PS substrates and incubated. The proliferation was studied qualitatively by optical microscopy, scanning electron microscopy (SEM) and quantitatively by MTT assay. All techniques revealed significant differences in HOS cells proliferation on untreated and oxygen plasma treated PS. The differences were most pronounced after 24 h of incubation when the cells have already stared to proliferate on plasma treated PS, while they were still in quiescence on untreated PS. The confluency was achieved till the 6th day on plasma treated PS, while on untreated PS such confluency has never been achieved. The cell viability assay revealed that HOS cells grew better on plasma treated PS for various incubation times. Similar trend was observed regarding the adhesion of proteins. They adhered better on plasma treated PS causing better environment for further cell proliferation. The results clearly show that oxygen plasma treatment allows for much better proliferation of HOS cells on plasma treated PS as compared to the untreated PS substrates.     

涤纶材料表面类金刚石薄膜的沉积及其抗菌性能研究

采用乙炔等离子体浸没离子注入与沉积(PIII-D)，对医用涤纶(PET)缝合环材料进行表面改性，Raman光谱、X射线光电子能谱(XPS)和衰减全反射傅立叶变换红外光谱(ATR-FTIR)的分析结果表明：在涤纶材料表面有效地沉积了一层类金刚石(DLC)薄膜。原子力显微镜(AFM)的图像分析进一步证明表面平均粗糙度从58．9nm降低到11．2mm。细菌粘附实验结果证明沉积了类金刚石薄膜的表面对5种细菌——金黄色葡萄球菌(SA)、表皮葡萄球菌(SE)、大肠杆菌(EC)、绿浓杆菌(PA)和白色念殊菌(CA)的粘附均有明显抑制作用，其中从培养时间为15h的吸附情况比较来看，金黄色葡萄球菌的粘附率降低了70％．表皮葡萄球菌降低了86%。     

Lubricant‐Infused PET Grafts with Built‐In Biofunctional Nanoprobes Attenuate Thrombin Generation and Promote Targeted Binding of Cells

New surface coatings that enhance hemocompatibility and biofunctionality of synthetic vascular grafts such as expanded poly(tetrafluoroethylene) (ePTFE) and poly(ethylene terephthalate) (PET) are urgently needed. Lubricant‐infused surfaces prevent nontargeted adhesion and enhance the biocompatibility of blood‐contacting surfaces. However, limited success has been made in incorporating biofunctionality onto these surfaces and generating biofunctional lubricant‐infused coatings that both prevent nonspecific adhesion and enhance targeted binding of biomolecules remains a challenge. Here, a new generation of fluorosilanized lubricant‐infused PET surfaces with built‐in biofunctional nanoprobes is reported. These surfaces are synthesized by starting with a self‐assembled monolayer of fluorosilane that is partially etched using plasma modification technique, thereby creating a hydroxyl‐terminated fluorosilanized PET surface. Simultaneously, silanized nanoprobes are produced by amino‐silanizing anti‐CD34 antibody in solution and directly coupling the anti‐CD34‐aminosilane nanoprobes onto the hydroxyl terminated, fluorosilanized PET surface. The PET surfaces are then lubricated, creating fluorosilanized biofunctional lubricant‐infused PET substrates. Compared with unmodified PET surfaces, the designed biofunctional lubricant‐infused PET surfaces significantly attenuate thrombin generation and blood clot formation and promote targeted binding of endothelial cells from human whole blood.     

Characterization of surface modified polyester fabric

Woven polyethylene terephthalate (PET) fabric has been used in the construction of vascular grafts and sewing ring of prosthetic heart valves. In an effort to improve haemocompatibility and tissue response to PET fabric, a fluoropolymer, polyvinylidine fluoride (PVDF), was coated on PET fabric by dip coating technique. The coating was found to be uniform and no significant changes occurred on physical properties such as water permeability and burst strength. Cell culture cytotoxicity studies showed that coated PET was non-cytotoxic to L929 fibroblast cell lines. In vitro studies revealed that coating improved haemocompatibility of PET fabric material. Coating reduced platelet consumption of PET fabric by 50%. Upon surface modification leukocyte consumption of PET was reduced by 24%. About 60% reduction in partial thromboplastin time (PTT) observed when PET was coated with PVDF. Results of endothelial cell proliferation studies showed that surface coating did not have any substantial impact on cell proliferation. Overall results indicate that coating has potential to improve haemocompatibility of PET fabric without affecting its mechanical performance.     

A ZnO/PET assembly study: Optimization and investigation of the interface region

Zinc oxide thin films are deposited on polyethylene terephthalate (PET) by r.f. magnetron sputtering process from a ceramic target in oxygen–argon plasmas. Structural studies show that the thin films are highly oriented along the (0 0 2) direction of the würtzite phase when the oxygen partial pressure is lower than 0.2 Pa. The crystallinity is accentuated when the oxygen partial pressure of the sputtering gas is increased from 0 to 0.02 Pa. The composition of the films determined by Rutherford backscattering spectrometry (RBS) varies in a wide range and it is necessary to add a few amount of oxygen in the plasma composition to establish the stoichiometry. The oxygen partial pressure is found to influence also the microstructure and consequently the density of the coatings.Various cold plasmas are used to treat the polymer surface before the deposition of zinc oxide films. Wettability measurements show an increase in the polar component of the PET surface free energy whatever the nature of the plasma used for the treatment. This increase is more obvious with the carbon dioxide plasma. XPS examinations of the CO₂ plasma treated PET surface in optimized conditions show a functionalisation of the polymer surface. The carbon dioxide plasma treatments of PET surface are found to enhance the peeling energy. The adhesion level depends also on the sputtering parameters, mainly the oxygen partial pressure and the r.f. power which influence the coating properties. The zinc oxide/PET interface is studied by XPS at the different stages of deposition and at various take-off angles. AFM observations show a regular growth of zinc oxide layers with smooth topographies on PET films. The different findings obtained from C1s, O1s, Zn2p3/2, Zn3p peaks and Auger Zn L₃M_4.5M_4.5 peak are corroborated and discussed. New chemical bonds between the polymer and the further coming zinc oxide thin layer are evidenced.     

Textured surface boron-doped ZnO transparent conductive oxides on polyethylene terephthalate substrates for Si-based thin film solar cells

Textured surface boron-doped zinc oxide (ZnO:B) thin films were directly grown via low pressure metal organic chemical vapor deposition (LP-MOCVD) on polyethylene terephthalate (PET) flexible substrates at low temperatures and high-efficiency flexible polymer silicon (Si) based thin film solar cells were obtained. High purity diethylzinc and water vapors were used as source materials, and diborane was used as an n-type dopant gas. P-i-n silicon layers were fabricated at ~ 398 K by plasma enhanced chemical vapor deposition. These textured surface ZnO:B thin films on PET substrates (PET/ZnO:B) exhibit rough pyramid-like morphology with high transparencies (T ~ 80%) and excellent electrical properties (Rs ~ 10 Ω at d ~ 1500 nm). Finally, the PET/ZnO:B thin films were applied in flexible p-i-n type silicon thin film solar cells (device structure: PET/ZnO:B/p-i-n a-Si:H/Al) with a high conversion efficiency of 6.32% (short-circuit current density J_SC = 10.62 mA/cm², open-circuit voltage V_OC = 0.93 V and fill factor = 64%).     

Grafting of gold nanoparticles on polyethyleneterephthalate using dithiol interlayer

Two different procedures of grafting of polyethyleneterephthalate (PET), modified by plasma treatment, with gold nanoparticles (nanospheres) are studied. In the first procedure the PET foil was grafted with biphenyl-4,4′-dithiol and subsequently with gold nanoparticles. In the second one the PET foil was grafted with gold nanoparticles previously coated by the same dithiol. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and electrokinetic analysis were used for characterization of the polymer surface at different modification steps. Gold nanoparticles were characterized by ultraviolet–visible spectroscopy. The first procedure was found to be more effective. It was proved that the dithiol was chemically bonded to the surface of the plasma activated PET and it mediates subsequent grafting of the gold nanoparticles.     

冷等离子体处理对涤纶纤维表面性能的影响

采用冷等离子体技术处理涂纶纤维,利用ESCA分析了冷等离子体处理前后的纤维表面元素组成,官能团类型的变化,通过比较处理前后浸润性,涂纶纤维／环氧复合材料的层间剪切强度,研究了冷等离子处理对涤纶纤维表面性质的影响,结果表明：绦纶纤维经冷等离子处理后表面含氧的极性基团增加,纤维表面的浸润性显著改善,涤纶纤维／环氧复合材料界面性能增强。     

Silk fibroin immobilization on poly(ethylene terephthalate) films: Comparison of two surface modification methods and their effect on mesenchymal stem cells culture

Silk fibroin (SF) has played a curial role for the surface modification of conventional materials to improve the biocompatibility, and SF modified poly(ethylene terephthalate) (PET) materials have potential applications on tissue engineering such as artificial ligament, artificial vessel, artificial heart valve sewing cuffs dacron and surgical mesh engineering. In this work, SF was immobilized onto PET film via two different methods: 1) plasma pretreatment followed by SF dip coating (PET-SF) and 2) plasma-induce acrylic acid graft polymerization and subsequent covalent immobilization of SF on PET film (PET-PAA-SF). It could be found that plasma treatment provided higher surface roughness which was suitable for further SF dip coating, while grafted poly(acrylic acid) (PAA) promised the covalent bonding between SF and PAA. ATR-FTIR adsorption band at 3284 cm^? 1, 1623 cm^? 1 and 1520 cm^? 1 suggested the successful introduction of SF onto PET surface, while the amount of immobilized SF of PET-SF was higher than PET-PAA-SF according to XPS investigation (0.29 vs 0.23 for N/C ratio). Surface modified PET film was used as substrate for mesenchymal stem cells (MSCs) culture, the cells on PET-SF surface exhibited optimum density compared to PET-PAA-SF according to CCK-8 assays, which indicated that plasma pretreatment followed by SF dip coating was a simple and effective way to prepare biocompatible PET surface.     

Enhanced adhesion of osteoblastic cells on polystyrene films by independent control of surface topography and wettability

We independently controlled surface topography and wettability of polystyrene (PS) films by CF₄ and oxygen plasma treatments, respectively, to evaluate the adhesion and proliferation of human fetal osteoblastic (hFOB) cells on the films. Among the CF₄ plasma-treated PS films with the average surface roughness ranging from 0.9 to 70 nm, the highest adhesion of hFOB cells was observed on a PS film with roughness of ~ 11 nm. When this film was additionally treated by oxygen plasma to provide a hydrophilic surface with a contact angle less than 10°, the proliferation of bone-forming cell was further enhanced. Thus, the plasma-based independent modification of PS film into an optimum nanotexture for human osteoblast cells could be appplied to materials used in bone tissue engineering.