Characterization of surface‐modified polyalkanoate films for biomedical applications

Poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBHV) films prepared by solvent casting were treated with oxygen, argon, and nitrogen radiofrequency‐generated plasmas. The analysis by attenuated total reflectance infrared spectroscopy and X‐ray absorption near edge spectroscopy of modified surfaces showed an increase of hydroxyl and unsaturated groups, compared with unmodified surfaces. Water contact angles decreased after a short time of exposure (<30 s) for all types of plasma. At long exposure times (>30 s), the water contact angles appeared to be independent of treatment time for nitrogen and argon plasmas, whereas they continuously decreased for films treated with oxygen. HaCaT cultures on nontreated and treated PHBHV films showed that short plasma exposures of 10–20 s improve cell attachment to a greater extent than long exposure times habitually used in polymer surface plasma treatment. The film surface topology did not influence cell attachment. These results illustrate the importance of a detailed characterization of the surface physicochemistry in plasma‐modified substrates designed as part of a strategy to optimize specific cell–biomaterial interactions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal crosslinking of collagen immobilized on poly(acrylic acid) grafted poly(ethylene terephthalate) films

Graft polymerization of acrylic acid onto plasma‐treated poly(ethylene terephthalate) (PET) films was used to prepare surfaces suitable for collagen immobilization by dip‐coating. Such surfaces could be used as matrices for smooth muscle cell cultures in tissue engineering. Contact angle measurements showed that plasma‐treated and grafted PET films undergo considerable surface reorganization during storage under ambient conditions. However, after collagen immobilization the contact angle remained relatively stable. The amount of collagen initially attached to the film surface increased with increasing poly(acrylic acid) graft density, but subsequent washing in water led to significant collagen loss. This loss could nevertheless be substantially reduced by thermal crosslinking of the collagen in the range 110–130 °C. Atomic force microscopy (AFM) observations suggested that the washed crosslinked collagen has a very similar structure to that of the un‐crosslinked collagen. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1874–1880, 2002     

Surface and adhesion properties of poly(ethylene glycol) on polyester(polyethylene terephthalate) fabric surface: Effect of air‐atmospheric plasma treatment

The surface and adhesion properties of different molecular weight poly(ethylene glycol) (PEG) (400, 1500, and 3000 g/mol) on untreated and air‐atmospheric plasma‐treated PET woven fabrics were studied, with the aim of developing durable hydrophilic PET fibrous structures. PEG application was carried out by padding of the PET fabric in aqueous solution of PEG followed by curing and drying. The surface properties of the PEG‐coated PET fabrics were then characterized using wicking test to measure the water contact angle (θ°) and capillary weight (W_c), and using atomic force microscopy (AFM) images in the tapping mode. Results showed that without a prior air‐atmospheric plasma treatment of the PET fabric, the water contact angle decreased and capillary weight increased with the three PEGs, implying an increase in the hydrophilicity of both inner and outer PET fabric fiber surface. Air‐plasma treatment of the PET fabrics before PEG coating increases further the hydrophilicity of the inner fabric fiber surface: the capillary weight was almost doubled in the case of the three PEGs. Best results were obtained with PEG 1500: water contact angle decreasing from 82° to 51°, and the capillary weight increasing from 11 mg to 134 mg. Moreover, wash fastness test at room temperature and at 80°C confirms improved adhesion of PEG‐1500 to the plasma‐treated PET woven fabric surface, while under the same conditions the plasma‐treated PET without PEG loses completely its hydrophilic character. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Hydrophobic and superhydrophobic surfaces fabricated by plasma polymerization of perfluorohexane,perfluoro(2-methylpent-2-ene), and perfluoro(4-methylpent-2-ene)

Fluoropolymer films were deposited on silicon (1 0 0) wafers, glass, epoxy, and hierarchical dual-sized filler epoxy composite surfaces by plasma polymerization of perfluorohexane, perfluoro(2-methylpent-2-ene), and perfluoro(4-methylpent-2-ene). The procedure involved continuous wave plasma-enhanced deposition, followed by a discharge-off period, with the monomer gas feed maintained. Silanization of silicon wafers and glass surfaces with triethoxyvinylsilane was employed to improve plasma fluoropolymer bonding to these substrates. The presence of double bonds in perfluoro(2-methylpent-2-ene) and perfluoro(4-methylpent-2-ene) was found to influence fluoropolymer coating topography, thereby increasing surface roughness in modified glass and epoxy substrates. All fluorocarbons provided a similar level of hydrophobization of flat substrates, exhibited by water contact angles (WCA) of about 110°. Hydrophobization of nanocomposite hierarchical surfaces by plasma polymerization provided superhydrophobic surfaces, with WCA of 160° and contact angle hysteresis below 8°.     

Surface characterization of low‐temperature cascade arc plasma–treated low‐density polyethylene using contact angle measurements

Low‐density polyethylene (LDPE) was treated with a low‐temperature cascade arc plasma torch (LTCAT) of argon with or without adding a reactive gas of oxygen or water vapor. The static sessile droplet method and the dynamic Wilhelmy balance method were employed to perform surface contact angle measurement in order to investigate and characterize the effects of LTCAT treatment on LDPE surfaces. These treatment effects included changes in surface wettability and surface stability and possible surface damage that would create low‐molecular‐weight oligomers on the treated surface. Experimental results indicated that the combination of static and dynamic surface contact angle measurements enabled a comprehensive investigation of these effects of plasma treatment on a polymer surface. Without the addition of a reactive gas, a 2‐s argon LTCAT treatment of LDPE resulted in a stable hydrophilic surface (with a water contact angle of 40°) and little surface damage. The addition of oxygen into argon LTCAT produced a less stable LDPE surface and showed more surface damage. Adding H₂O vapor into argon LTCAT produced an extremely hydrophilic surface (with a water contact angle < 20°) of LDPE but with pronounced surface damage. When compared with conventional radio frequency (13.56 MHz) plasmas, LTCAT treatment provides a much more rapid, effective, and efficient method of surface modification of LDPE. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 2528–2541, 2006     

Creation of superhydrophilic surfaces of paper and board

Corona, flame, atmospheric plasma, and liquid flame spray (LFS) techniques were used to create highly hydrophilic surfaces for pigment-coated paper and board and machine-glossed paper. All the surface modification techniques were performed continuously in ambient atmosphere. The physical changes on the surfaces were characterized by field emission gun-scanning electron microscopy (FEG-SEM), atomic force microscopy and Parker Print-Surf surface roughness. The chemical changes were analysed by X-ray photoelectron spectroscopy. The superhydrophilic surfaces, i.e. contact angle of water (CAW) <10°, were created mainly by modifying the surface chemistry of the paper and board by argon plasma or SiO₂ coating. The nano- and microscale roughness existing on paper and board surfaces enabled the creation of the superhydrophilic surfaces. Furthermore, the benefits and limitations of the surface modification techniques are discussed and compared. For example, the SiO₂ coating maintained its extreme hydrophilicity for at least six months, whereas the CAW of argon plasma-treated surface increased to about 20° already in one day.     

Surface modification of poly(ethylene terephthalate) film by coating with poly(ethylene glycol)‐grafted polystyrene

The poly(ethylene glycol) (PEG)‐grafted styrene (St) copolymer, which was formed as a nanosphere, was used as an agent to modify the surface of poly(ethylene terephthalate) (PET) film. The graft copolymer was dissolved into chloroform and coated onto the PET film by dip–coating method. The coated amount depends on the content ratios of PEG and St, the solution concentration, and the coating cycles. The graft copolymers having a low molecular weight of PEG‐ or St‐rich content was fairly stable on washing in sodium dodecyl sulfate (SDS) aqueous solution. It was confirmed that the PET surface easily altered its surface property by the coating of the graft copolymers. The contact angles of the films coated with the graft copolymers were very high (ca. 105–120°). The coated film has good antistatic electric property, which agreed with PEG content. The best condition of coating is a one‐cycle coating of 1% (w/v) graft copolymer solution. The coated surface had water‐repellency and antistatic electric property at the same time. The graft copolymer consisted of a PEG macromonomer; St was successfully coated onto PET surfaces, and the desirable properties of both of PEG macromonomer and PSt were exhibited as a novel function of the coated PE film. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1524–1530, 1999     

Hydrophobic recovery of repeatedly plasma-treated silicone rubber. Part 1. Storage in air

Silicone rubber is used for a wide variety of biomedical and industrial applications due to its good mechanical properties, combined with a hydrophobic surface. Frequently, however, it is desirable to alter the surface hydrophobicity of silicone rubber. Often this is done by plasma treatments but the effects are usually transient. In this study, surfaces of medical grade silicone rubber have been repeatedly modified by means of oxygen, argon, carbon dioxide, and ammonia RF plasma treatments with a 24 h time interval in between treatments. Treated samples were stored in air prior to surface characterization by water contact angle measurements, X-ray photoelectron spectroscopy (XPS), streaming potential measurements, and profilometry for surface roughness. The carbon percentage of the surfaces decreased after plasma treatment, while the silicon and oxygen percentages increased irrespective of the plasma used. The formation of Si-O-Si bridges between siloxane chains after plasma treatment was demonstrated by the appearance of a new component in the Si_2p peak but the degree to which this occurred differed per gas. Streaming potential measurements in a 10 mM potassium phosphate buffer indicated a more negatively charged surface for treated samples compared to untreated samples (-23.3 mV at pH 7.0). Surface roughness increased slightly for repeatedly plasma-treated samples from R_A = 0.35 μm to R_A = 0.46 μm, while scanning electron microscopy showed the presence of several 'cracks' spanning the surface after repeated treatment. Argon, carbon dioxide, and ammonia plasmas significantly reduced the advancing water contact angle from 115° to 58°, 72°, and 85°, respectively, on a more permanent basis (especially when the treatments were repeated after recovery). Oxygen plasma effects on water contact angles generally disappeared within 5 h, also after repeated treatment.     

Surface hydrophobization of CNF films by roll-to-roll HMDSO plasma deposition

Cellulosic films are typically sensitive towards moisture which limits their industrial applicability. In this study the films made from cellulose nanofibrils (CNF) were surface silylated with hexamethyldisiloxane (HMDSO) by roll-to-roll plasma deposition. The effects on surface hydrophobicity were clear and indisputable. Water contact angles of non-modified and plasma-deposited CNF films were 23° and 103°, respectively. As a result of surface silylation the relative polarity decreased from 46.8% to 0.6%. Surface hydrophobicity correlated well with the plasma deposition line speeds (0.5, 5, and 10 m/min) and the water vapor barrier properties. Silylation also decreased the oxygen transmission rates both at 50% and 80% relative humidity as compared to non-modified CNF films. All films were completely impermeable to olive oil and intact in contact with castor oil, toluene, and n-heptane or mixtures of them. The developed surface hydrophobization method can be exploited in strengthening the position of cellulosic films in high performance film applications.     

Residual reactivity for surface grafting of acrylic acid on argon glow-discharged poly(ethylene terephthalate) (PET) films

The wettability of poly(ethylene terephthalate) (PET) films in water was significantly improved upon exposure to argon glow discharge. Depending upon the lengths of glow-discharge exposure, the water contact angle (CA) of the untreated film (73.1° ± 0.1°) was reduced to between 33.7° and 41.0° on the argon glow-discharged films. Wettability decay was observed during the initial few days. Depending upon the treatment time, the water CA stabilized 4–7 days after the treatment and the extent of the wettability decay ranged from 4.3° to 7.6°. The residual reactivity of the glow-discharged surfaces was captured by exposing the glow-discharged PET to acrylic acid in the liquid and vapor phases. Optimal water CAs of 54.0° and 41.9° were achieved in the liquid-phase and the vapor-phase exposures, respectively. Wettability decay of these acrylic acid-grafted PET surfaces was very small (0°–1.9°) for the liquid-phase reactions and negligible (0.3°–0.6°) for the vapor-phase reactions. The near absence of wettability decay or the greater stability of the grafted surfaces suggested the almost complete dissipation of the residual reactivity through reactions with acrylic acid. Surface morphology of the untreated as well as the acrylic acid-grafted PET surfaces were examined and detailed by scanning electron microscopy.     

Solvent- and glow-discharge-induced surface wetting and morphological changes of poly(ethylene terephthalate) (PET)

The effects of argon glow discharge and selected organic solvents on the surface wettability of poly(ethylene terephthalate) (PET) and on the wettability decay of glow discharged PET films were studied. Glow discharge in argon (30 W/1 min) drastically reduced the initial water contact angle (CA) measurement of PET from 67.0 to 26.2°. The glow-discharge-induced wetting, however, decayed during the first 7 days and stabilized at 33.1°. Treatments in dimethyl sulfoxide, dimethyl formamide, pyrdine, and water at 80°C caused some improvement in surface wettability as shown by decreases of water CAs in the range of 53–56°. When the solvent and glow discharge treatments were applied consecutively on PET, additive effects on improving surface wettability were observed. The stabilized water CAs of the solvent-and-glow-discharged films ranged from 25.0 to 32.1° depending upon the solvent type. The solvent treatments prior to glow discharge either reduced the extent of CA decay or the time taken to reach stabilization on PET films. Scanning electron microscopic evaluation showed no difference between the solventtreated and the untreated PET surfaces, but a finely etched surface was observed on the glow discharged PET at a 40,000 magnification and above. The distinctly different surface of the DMSO-and-glow-discharged PET indicated that morphological changes on PET surface were induced by the solvent.     

Effects of argon plasma treatment on surface characteristic of photopolymerization PEGDA–HEMA hydrogels

The aim of this research was to determine the influence of argon plasma treatment condition on the surface properties of poly(ethylene glycol) diacrylate (PEGDA)–hydroxyethly methacrylate hydrogel films, a kind of scaffold materials for tissue engineering. The changes of surface properties have been evaluated by contact angles, X‐ray photoelectron spectra (XPS), and scanning electron microscopy (SEM). From the contact angle measurements of different liquids, the surface free energy of the hydrogel was calculated according to approaches by Owens–Wendt–Kaelble. Results showed that the contact angle of the hydrogel to water decreased remarkably after argon plasma treatment, which was caused by the changes in morphology (SEM images) and chemical composition (XPS results) of the argon plasma‐treated surface. The surface free energy increased with the increase of the argon plasma treated time and power, and these increasing was mainly due to the increase of polar component. The XPS results confirmed that plasma oxidation reaction produced oxygen‐containing functional groups onto the surface. This functional group played an important role in increasing the hydrophilic properties of the hydrogel. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effects of aromatic groups in polymer chains on plasma surface modification

Three polyester films with different repeating units—poly(lactic acid) (PLA), poly(ethylene terephthalate) (PET), and poly(oxybenzoate‐co‐oxynaphthoate) (PBN)—were modified by plasma, and the way in which the chemical compositions of the polymer chains influenced the plasma modification was investigated with contact‐angle measurements and X‐ray photoelectron spectroscopy (XPS). There were large differences in the compensated rates of weight loss among the three polyester films when they were exposed to Ar and O₂ plasmas. The PLA film showed the highest rate for weight loss of the three films, and the PBN film showed the lowest rate. The PET and PBN film surfaces were modified to become more hydrophilic by either argon or oxygen plasma. However, the PLA film surface was not made more hydrophilic by the plasmas. XPS spectra showed that the PLA film surface was not modified in its chemical composition, but the PBN film surface was modified in its chemical composition to form C? O groups in the PBN polymer chains. The reason that the PLA film surface was not modified but the PBN film surface was modified was examined. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 96–103, 2003     

Oxygen plasma modification of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) film surfaces for tissue engineering purposes

Plasma glow‐discharge application is known as a technique to coat or modify the surfaces of various materials. In this study, the influence of oxygen rf‐plasma treatment on surface and bulk properties of a biological polyester, poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), were studied by determining water content and water contact angle, and by using X‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The plasma‐treated films absorbed more water than the untreated film, and the absorbance increased with the total power applied. The water contact angles decreased and O/C atomic ratio increased on treatment, indicating that the material became more hydrophilic due to increases in the oxygen‐containing functional groups on the surface of the polymer. A direct relation could be observed when the O/C ratio was plotted against the total power applied (treatment duration × treatment power). SEM revealed a visual record of surface modification, the extent of which increased with increased total power. It was thus possible to alter the surface chemistry and relevant properties of the polymer film using oxygen plasma as a tool. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1285–1289, 2003     

Effect of oxygen plasma treatment on non-thrombogenicity of diamond-like carbon films

The non-thrombogenicity of oxygen-plasma-treated DLC films was investigated as surface coatings for medical devices. DLC films were deposited on polycarbonate substrates by a radio frequency plasma enhanced chemical vapor deposition method using acetylene gas. The deposited DLC films were then treated with plasma of oxygen gas at powers of 15 W, 50 W, and 200 W. Wettability was evaluated by water contact angle measurements and the changes in surface chemistry and roughness were examined by X-ray photoelectron spectroscopy and atomic force microscope analysis, respectively. Each oxygen-plasma-treated DLC film exhibited a hydrophilic nature with water contact angles of 11.1°, 17.7° and 36.8°. The non-thrombogenicity of the samples was evaluated through the incubation with platelet-rich plasma isolated from human whole blood. Non-thrombogenic properties dramatically improved for both 15 W- and 50 W-oxygen-plasma-treated DLC films. These results demonstrate that the oxygen plasma treatment at lower powers promotes the non-thrombogenicity of DLC films with highly hydrophilic surfaces.     

Surface modification of nylon 6 films treated with an He/O2 atmospheric pressure plasma jet

To investigate the effect of the gas composition of the plasma treatment on the surface modification of an atmospheric pressure plasma jet (APPJ), nylon 6 films were treated with APPJ with pure helium (He), He + 1% oxygen (O₂), and He + 2% O₂, respectively. Atomic force microscopy showed increased surface roughness, whereas X‐ray photoelectron spectroscopy revealed increased oxygen contents after the plasma treatments. The plasma‐treated samples had lower water contact angles and higher T‐peel strengths than the control. The addition of a small amount of O₂ to the He plasma increased the effectiveness of the plasma treatment in the polymer surface modification in terms of surface roughness, surface oxygen content, etching rate, water contact angle, and bonding strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Surface modification of poly(vinylidene fluoride) film by remote Ar, H2, and O2 plasmas

The surface modification of poly(vinylidene fluoride) (PVDF) film induced by remote Ar, H₂, and O₂ plasmas have been investigated using contact angle measurement, X-ray photoelectron spectroscopy, and scanning probe microscope. The contact angle of water shows an improvement in the PVDF surface wettability during short plasma exposure time. Three remote plasmas treated PVDF sheet surfaces occurred dehydrofluorination and oxidation reactions simultaneously. Remote hydrogen plasma was the most effective in defluorination reactions and remote oxygen plasma was unfavorable to abstract fluorine atoms.     

Biopolymer brushes grown on PDMS contact lenses by in situ atmospheric plasma-induced polymerization

It is critical for silicone based-contact lens development by improving surface characterization to prevent protein adsorption. In this paper, the silicone (polydimethylsiloxane, PDMS) contact lenses were modified by varied molecular weights of poly(ethylene glycol) methacrylate (PEGMA, Mw 360 and 500 Da) polymer brushes by in situ atmospheric plasma-induced surface copolymerization. After PDMS contact lenses were homogenously immersed in PEGMA monomer solutions, varied gases (oxygen, nitrogen, and argon) with the atmospheric plasma were employed in the process of polymerization. The characterizations of PEGMA polymer brushes modified on the PDMS contact lenses would be evaluated by atomic force microscopy, FT-IR spectroscopy, X-ray photoelectron spectroscopy, and contact angle test. The results show that the hydrophilicity of the PEGMA polymer brush-modified surface is obviously improved. The contact angle of PEGMA-modified surface decreases about 20°–40° by varied atmospheric plasma (O₂, N₂, and Ar gases), compared to the pristine lenses. Importantly, the hydrophilicity of the PEGMA polymer brush-modified surface could be retained beyond 2 weeks. PEGMA-modified PDMS contact lenses also display superior anti-protein (fibrinogen and human serum bovine) adsorption ability. Therefore, immobilization of PEGMA polymer brushes by in situ atmospheric plasma-induced polymerization would be a great and rapid method to enhance the hydrophilicity and anti-protein adsorption ability in the PDMS contact lenses.     

XPS/AFM study of the PET surface modified by oxygen and carbon dioxide plasmas: Al/PET adhesion

The formation of the interface between aluminium and O₂ or CO₂ plasma-modified poly(ethylene terephthalate) (PET) has been investigated by X-ray photoelectron spectroscopy (XPS). As demonstrated by the changes in the C 1s, O 1s, and A1 2p core level spectra upon A1 deposition, the metal was found to react preferentially with the original ester, with the plasma-induced carboxyl and carbonyl groups to form interfacial complexes. The phenyl ring at the modified PET surface was seen to be involved in the formation of the interface, but to a lesser extent. This confirms the high reactivity of the oxygen-containing groups towards the deposited A1 atoms. The adhesion between A1 and the plasma-modified PET films was evaluated by means of a 180° peel test. A considerable (up to ten times) improvement in adhesion was achieved by plasma treatment of the PET substrate, but for either plasma gas the adhesion strength was found to depend strongly on the plasma power and treatment time. The results are discussed in terms of the concentration of oxygen-containing groups at the polymer surface, the surface topography, and the possible presence of low-molecular-weight materials at the metal-polymer interface.     

Effect of plasma treatment of polymeric tape carriers on wetting behaviour of aqueous ceramic tape casting slurry

Due to environmental and health aspects, aqueous ceramic slurries are preferred to traditional organic solvent systems in tape casting. An important obstacle associated with the high surface energy of water is poor wetting of aqueous ceramic slurries on polymeric tape carriers. Therefore, we measured the contact angles of an aqueous epoxy-based ceramic slurry on polyethylene terephtalate (PET), polypropylene (PP), polymethyl methacrylate (PMMA), and aluminium-coated polyethylene terephtalate (PET-Al) films and investigated approaches to improving their wetting. We evaluated the effect of plasma treatment of the tape carrier surface on the wetting behaviour and compared it with the effect of adding non-ionic amphiphilic surfactants to the ceramic slurry. The treatment of the tape carrier surface by low-temperature plasma substantially improved the wetting behaviour of aqueous ceramic slurry. The lowest contact angle of 31° was obtained on the PET film. Although the addition of non-ionic surfactants improved both the wetting behaviour of the slurry and the detachment of the polymeric carrier from the ceramic tape even better than the plasma treatment of the carrier surface did, the plasma-treated carriers still present a useful alternative to the surfactants. In the case of the plasma-treated PET carrier the surfactants could be fully eliminated and potential drawbacks related to the use of surfactants could be prevented.