A new approach to immobilize poly(vinyl alcohol) on poly(dimethylsiloxane) resulting in low protein adsorption

The hydrophobic characteristics of PDMS and non-specific protein adsorption are major drawbacks for its application in biosensing. Here we have combined surface oxidation by plasma and chemical binding of polyvinyl alcohol (PVA) to obtain long-term stability of hydrophilic PDMS surfaces. Mercaptopropyltrimethoxisilane and aminopropyltrimethoxisilane were used as adhesives between the plasma-oxidized PDMS surface and the PVA, immobilized at room temperature. This approach has allowed for fast, uniform, and very stable modification of the PDMS surface, which maintained a hydrophilic character for as long as 30 days. In addition, the modified hydrophilic surface presented minimized protein adsorption when compared to pristine PDMS. The results obtained in this work are important contributions to the growing field of integrated microfluidic biosensors.     

Biological response of stainless steel surface modified by N2O/O2 glow discharge plasma

Stainless steel wafers were treated with the glow discharge plasma of mixed N₂O and O₂ at different molar ratios at a certain discharge condition to create desirable biological characteristics to the surfaces. It was found that the molar ratio of N₂O to O₂ in the mixture at 1:1 used for plasma surface modification caused high apoptotic percentage. Contact angle measurement showed that the surface of stainless steel samples became very hydrophilic after the plasma modification with a value of 15°-30°. The control stainless steel chips without plasma treatment had a contact angle of 40 ± 2°. The data of Electron Spectroscopy for Chemical Analysis (ESCA) indicated that there was a certain amount of oxynitrites formed on the plasma treated surfaces, which was considered to play an important role to cell apoptosis and anti-clot formation in cell culture tests. The ESCA depth profile of up to 250 Å from the top surface showed the change of elemental compositions within 40-50 Å of the surface by the plasma treatment. The decreased platelet attachment, combined with increased apoptosis in fibroblasts is a distinct combination of biological responses arising from the mixed gas plasma treatment. These initial results suggest it may be of particular use relative to stainless steel stents where decreased platelet attachments are advantageous and induction of apoptosis could limit in-stent restenosis.     

Laser-assisted modification of polystyrene surfaces for cell culture applications

Laser-assisted patterning and modification of polystyrene (PS) was investigated with respect to applications in micro-fluidics and cell culture. For this purpose the wettability, the adsorption of proteins and the adhesion of animal cells were investigated as function of laser- and processing parameters. The change of surface chemistry was characterized by X-ray photoelectron spectroscopy. The local formation of chemical structures suitable for improved cell adhesion was realized on PS surfaces by UV laser irradiation. Above and below the laser ablation threshold two different mechanisms affecting cell adhesion were detected. In the first case the debris deposited on and along laser irradiated areas was responsible for improved cell adhesion, while in the second case a photolytic activation of the polymer surface including a subsequent oxidization in oxygen or ambient air is leading to a highly localized alteration of protein adsorption from cell culture media and finally to increased cell adhesion. Laser modifications of PS using suitable exposure doses and an appropriate choice of the processing gas (helium or oxygen) enabled a highly localized control of wetting. The dynamic advancing contact angle could be adjusted between 2° and 150°. The hydrophilic and hydrophobic behaviour are caused by chemical and topographical surface changes.     

Surface modification of polystyrene with atomic oxygen radical anions-dissolved solution

A novel approach to surface modification of polystyrene (PS) polymer with atomic oxygen radical anions-dissolved solution (named as O⁻ water) has been investigated. The O⁻ water, generated by bubbling of the O⁻ (atomic oxygen radical anion) flux into the deionized water, was characterized by UV-absorption spectroscopy and electron paramagnetic resonance (EPR) spectroscopy. The O⁻ water treatments caused an obvious increase of the surface hydrophilicity, surface energy, surface roughness and also caused an alteration of the surface chemical composition for PS surfaces, which were indicated by the variety of contact angle and material characterization by atomic force microscope (AFM) imaging, field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and attenuated total-reflection Fourier transform infrared (ATR-FTIR) measurements. Particularly, it was found that some hydrophilic groups such as hydroxyl (OH) and carbonyl (CO) groups were introduced onto the polystyrene surfaces via the O⁻ water treatment, leading to the increases of surface hydrophilicity and surface energy. The active oxygen species would react with the aromatic ring molecules on the PS surfaces and decompose the aromatic compounds to produce hydrophilic hydroxyl and carbonyl compounds. In addition, the O⁻ water is also considered as a “clean solution” without adding any toxic chemicals and it is easy to be handled at room temperature. Present method may suit to the surface modification of polymers and other heat-sensitive materials potentially.     

Tailoring the wettability of nanocrystalline TiO2 films

The water contact angle (WCA) of nanocrystalline TiO₂ films was adjusted by fluoroalkylsilane (FAS) modification and photocatalytic lithography. FAS modification made the surface hydrophobic with the WCA up to ∼156°, while ultraviolet (UV) irradiation changed surface to hydrophilic with the WCA down to ∼0°. Both the hydrophobicity and hydrophilicity were enhanced by surface roughness. The wettability can be tailored by varying the concentration of FAS solution and soaking time, as well as the UV light intensity and irradiation time. Additionally, with the help of photomasks, hydrophobic-hydrophilic micropatterns can be fabricated and manifested via area-selective deposition of polystyrene particles.     

Surface modification of polyester to produce a bacterial cellulose-based vascular prosthetic device

The surface of medical grade polyesters was modified to impart hydrophilic character for attachment to bacterial synthesized cellulose to produce a vascular prosthetic device. The polyesters were treated with UV/ozone, air plasma, and nitrogen plasma for various lengths of time. The unmodified and modified surfaces were analyzed by X-ray photoelectron spectroscopy (XPS) and advancing contact angle measurements. The surfaces were then coated with bacterial produced cellulose to study adhesion properties through tensile testing (peel testing). UV/ozone and plasma treatment XPS results indicated an increase in the oxygen concentration in the form of CO(H) on the treated polyester surfaces. The treatment time to reach steady state in the case of air and nitrogen plasmas took the order of seconds, while 7 min and longer were required for UV/ozone treatment. Peel strength tests to measure adhesion of modified polyester to cellulose reached their maximum values when the CO(H) concentrations were at the highest level. It was also at this level that the contact angle measurements showed no further decrease.     

Modification of the surface properties of polyimide films using polyhedral oligomeric silsesquioxane deposition and oxygen plasma exposure

Topographically rich surfaces were generated by spray-coating organic solutions of a polyhedral oligomeric silsesquioxane, octakis(dimethylsilyloxy)silsesquioxane (POSS), on Kapton^® HN films and exposing them to radio frequency generated oxygen plasma. Changes in both surface chemistry and topography were observed. High-resolution scanning electron microscopy indicated substantial modification of the POSS-coated polyimide surface topographies as a result of oxygen plasma exposure. Water contact angles varied from 104° for unexposed POSS-coated surfaces to ∼5° for samples exposed for 5 h. Modulation of the dispersive and polar contributions to the surface energy was determined using van Oss Good Chaudhury theory. Changes in surface energy are related to potential adhesive interactions with lunar dust simulant particles.     

Surface modification of polyethylene terephthalate with albumin and gelatin for improvement of anticoagulation and endothelialization

The surfaces of polyethylene terephthalate (PET) were modified by oxygen plasma-induced and ultraviolet (UV)-assisted acrylic acid (AAc) grafting polymerization, and the carboxyl (COOH) groups on the PET surface was 5.29 × 10⁻⁹mol/cm². Then using the COOH as reacting sites, the molecules of gelatin and bovine serum albumin (BSA) were further co-immobilized on the PET surface. The modified PET surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and surface chemical quantitative analysis. The results showed that the molecules of gelatin and albumin were immobilized on the PET surface. The concentration of gelatin on the gelatin-immobilized PET surface was 2.02 μg/cm². For the gelatin-immobilized PET surface, the human umbilical vein endothelial cells (HUVECs) culture attachment and proliferation ratios were improved, but the anticoagulation became worse proved by platelet adhesion test in vitro and the lactate dehydrogense (LDH) test. After further co-immobilization of albumin with gelatin biomolecules on the PET surface (PET-Gel-BSA), the percent of platelet adhesion in vitro decreased 28% than that on the gelatin-immobilized PET surface, and the cell density on the PET-Gel-BSA film (1.08 × 10⁵ cells/cm²) was significantly higher than that on the control PET surface. This investigation tries to find a method which can construct the anticoagulant surface before the endothelium formation and also accelerate the endothelialization of polymer surface.     

Long term hydrophilic coating on poly(dimethylsiloxane) substrates for microfluidic applications

Poly(dimethylsiloxane) (PDMS) has been used extensively for microfluidic components and as substrates for biological applications. Since the native nature of PDMS is hydrophobic it requires a functionalization step for use in conjunction with aqueous media. Commonly, oxygen plasma treatment is used for the formation of hydrophilic groups on the surface. However, the hydrophilic nature of these surfaces is short lived and the surfaces quickly revert back to their original hydrophobic state. In this work, branched-polyethylenimine (b-PEI) was used for long term modification of plasma treated PDMS surface. Contact angle, X-ray photoelectron spectroscopy (XPS) and Atomic force microscopy (AFM) were used for characterization of the modified surfaces and their stability with time was studied. The results obtained demonstrate that comparatively higher stability, hydrophilic, positively charged surfaces can be obtained after b-PEI treatment. These b-PEI treated PDMS surfaces can be used as fluidic channels for the separation of molecules as well as a substrate for the adherence of bio-molecules or biological cells.     

Protein immobilization capacity and covalent binding coverage of pulsed plasma polymer surfaces

Three carbon surfaces were deposited using pulsed plasma enhanced chemical vapour deposition method: a low and a high nitrogen-containing plasma polymer surfaces and a diamond-like carbon surface. The surfaces were analysed using both X-ray photoelectron spectroscopy (XPS) technique and the enzyme-linked immunosorbent assay (ELISA) method combining with sodium dodecyl sulphate (SDS) cleaning to investigate the capacity and covalent binding of the immobilized proteins. A good correlation was found on quantification of remaining protein after SDS cleaning using the ELISA method and the XPS technique. All surfaces had similar initial capacity of protein attachment but with large different resistance to SDS cleaning. The analysis showed that the high nitrogen-containing plasma polymer was the best biocompatible material due to its highest resistance to SDS cleaning, i.e. with the highest quantity (∼80%) of proteins bound covalently.     

Surface modification with fibronectin or collagen to improve the cell adhesion

Objective

The surface of biomaterials plays a critical role in determining bioactivity. The aim of this study was to evaluate the cell adhesion and proliferation of ADSCs on the surface of biomaterial which is modified with fibronectin or collagen.

Materials and methods

Adipose-derived stromal cells (ADSCs) were obtained from SD rats, expanded in culture, and seeded onto scaffold surface-modified with fibronectin or collagen. To characterize cellular attachment, cells were incubated on scaffold for 1 and 2 h and then counted the cells attached onto the scaffold. The MTT assay was chosen to evaluate the proliferation at days 1, 4, 7 and 14. After 7 d of culture, scanning electron microscope was chosen to observe cell morphology and attachment of ADSCs on the scaffolds.

Results

Attachment at 1 and 2 h of cells on scaffold modified with fibronectin was significantly greater than in control, but not with collagen. The MTT assay revealed that ADSCs proliferation tendency was nearly parallel to that in control. The scanning electron microscope (SEM) showed that ADSCs in experiment expanded thoroughly and excreted much extracellular materials.

Conclusions

Surface modification with fibronectin or collagen can enhance the attachment of cultured ADSCs on the scaffold, but it had not evident effect to proliferation.     

Characterization of diamond (1 0 0) surface with oxygen termination

Ab initio density functional theory (DFT) was employed to study reconstructions of diamond (1 0 0) surfaces in the presence of hydrogen, oxygen and hydroxyl. Clean and (2 × 1):1H surfaces are taken as reference. The properties of oxidization diamond surfaces with several adsorption structures, namely, O-on-top (OT) site, O-bridge (BR) site, hydroxyl (-OH), hydroxyl/hydroxyl, OT/hydroxyl, BR/hydroxyl have been considered. The calculated results indicate that the BR model is much more stable than the OT model, and the most energetically favorable structures of oxygenated surfaces are those with chemisorbed hydroxyl (-OH) group. Furthermore, the stability of the structures is also discussed from the point of HOMO-LUMO gap. Analysis of electronic structures shows that the presence of hydrogen induces surface conductivity whereas oxygen weakens it.     

Surface modification of calcium carbonate: radical graft polymerization of vinyl monomers onto calcium carbonate surface initiated by azo groups introduced onto the surface

—The preparation of calcium carbonate modified by 12-hydroxystearate groups and the grafting of polymers onto the surface by the polymerization of vinyl monomers initiated by azo groups introduced onto the surface were investigated. The preparation of calcium carbonate modified by 12-hydroxystearate was achieved by the reaction of calcium chloride with sodium carbonate containing a small amount of sodium 12-hydroxystearate. The introduction of azo groups onto calcium carbonate was successfully achieved by the direct condensation of the carboxyl group of 4,4'-azobis(4-cyanopentanoic acid) with 12-hydroxystearate groups on the modified calcium carbonate using N,N'-dicyclohexylcarbodiimide as a condensing agent. It was found that the radical polymerization of vinyl monomers, such as methyl methacrylate (MMA), styrene, and N-vinylcarbazole (NVC), was initiated by azo groups introduced onto the surface, and the corresponding polymers were grafted onto the surface based on the propagation of polymer from the surface: the percentage of grafting of polyMMA, polystyrene, and polyNVC reached 5.7, 9.5 and 3.5%, respectively, at 70°C. The percentage of grafting was found to decrease with decreasing monomer concentration. The wettability of calcium carbonate surface was found to turn from hydrophilic to hydrophobic by the grafting of polymers.     

Mechanics of plasma exposed spin-on-glass (SOG) and polydimethyl siloxane (PDMS) surfaces and their impact on bond strength

Silicone polymer (PDMS), widely used for micro-fluidic and biosensor applications, possesses an extremely dynamic surface after it is subjected to an oxygen plasma treatment process. The surface becomes extremely hydrophilic immediately after oxygen plasma exposure by developing silanol bond (SiOH), which promotes its adhesion to some other surfaces like, silicon, silicon dioxide, glass, etc. Such a surface, if left in ambient dry air, shows a gradual recovery of hydrophobicity. We have found an identical behavior to occur to surfaces coated with a thin continuous film of SOG (methyl silsesquioxane). The chemistry induced by oxygen plasma treatment of a spin-on-glass (SOG) coated surface provides a much higher density of surface silanol groups in comparison to precleaned glass, silicon or silicon dioxide substrates thus providing a higher bond strength with polydimethyl siloxane (PDMS). The bonding protocol developed by using the spin coated and cured SOG intermediate layer provides an universal regime of multi level wafer bonding of PDMS to a variety of substrates. The paper describes a contact angle based estimation of bond strength for SOG and PDMS surfaces exposed to various combinations of plasma parameters. We have found that the highest bond strength condition is achieved if the contact angle on the SOG surface is less than 10°.     

Role of reactive gas in atmospheric plasma for cell attachment and proliferation on biocompatible poly ?-caprolactone film

This paper reports the surface modification of a biocompatible poly ?-caprolactone (PCL) film treated by atmospheric cold plasma (ACP) with reactive gases. The change in wettability and surface morphology of the PCL film after the plasma treatment with the reactive gases (Ar, H₂, N₂ and O₂) were determined using contact angle and surface roughness measurements. The chemical bonding states and molecular vibration modes of the activated organic groups on the polymer surface were examined by X-ray photoelectron spectroscopy and Fourier-transformation infrared techniques. The surface of the ACP-treated PCL films was also examined for their in vitro cell attachment and proliferation using human prostate epithelial cells (HPECs). The increase in the hydrophobicity of the Ar + H₂ plasma-treated PCL film resulted in a lower cell loading in the initial step of cell culture as well as a decrease in the level of cell attachment and proliferation compared with the pristine film. However, the hydrophilic properties of the Ar + N₂, Ar and Ar + O₂ plasma-treated PCL film improved the adhesion properties. Therefore, the Ar + N₂, Ar and Ar + O₂ plasma-treated PCL films showed a better cell distribution and growth than that of the pristine PCL film. The ACP-treated PCL film is potentially useful as a suitable scaffold in biophysics and bio-medical engineering applications.     

Water-soluble, cyclodextrin-functionalized semiconductor nanocrystals: Preparation and pH-dependent aggregation and emission properties

Using peramino-functionalized β-cyclodextrin molecules for phase.transfer of hydrophobic CdSe multishell nanocrystals into water, we obtained hydrophilic nanoparticles with high quantum yield (up to 50%). At pH > 9, the aqueous solution of these nanocrystals remained stable for several months. The nanoparticles showed a strong influence of the pH of the aqueous solution on the emission of the nanocrystals: the quantum yield varied reversible from ∼10% at pH=6 to ∼50% at pH=14, an effect which according to particle size characterization by dynamic light-scattering and asymmetric flow field-flow fractionation has mainly been attributed to reversible partial aggregation of the hydrophilic nanocrystals at lower pH-values. Additionally, prolonged irradiation in the presence of oxygen led to a strong enhancement of the photoluminescence intensity of the nanocrystals.     

Modifications of AISI 1045 steel by picosecond Nd:YAG laser at 266 nm; comparison with 532 and 1064 nm pulses

Interaction of Nd:YAG laser, operating at 266 nm wavelength and a pulse duration of 40 ps, with AISI 1045 steel was studied. Surface damage threshold was estimated to be 0.14 J/cm². The steel surface modification was studied at the laser fluence of ∼1.0 J/cm². The energy absorbed from Nd:YAG laser beam is partially converted to thermal energy, which generates a series of effects, such as melting, vaporization of the molten material, shock waves, etc. The following AISI 1045 steel surface morphological changes and processes were observed: (i) intensive damage of the target in the central zone of irradiated area; (ii) appearance of periodic surface structures at nano-level, with periodicity in agreement with the used wavelength; (iii) reduction of oxygen concentration in irradiated area; and (iv) development of plasma in front of the target. Generally, interaction of laser beam with AISI 1045 steel (at 266 nm) results in a near-instantaneous creation of damage, meaning that large steel surfaces can be modified in short times.     

Wood surface functionalization by means of low-pressure air plasma

Low-pressure plasma treatments in an radio frequency (RF) discharge of air have been used on the surface of wood to stimulate polar function groups onto pine and beach surfaces to enhance the wettability and activation. The effects of plasma treatments on the morphology and wettability of surfaces were characterized by using static contact angle measurements, attenuated total reflection Fourier transform infrared spectroscopy and scanning electron microscopy. A clear increase in the surface energy of the wood surface due to air plasma treatment was observed. The surfaces became highly hydrophilic when woods were exposed for 5 s or longer to the plasma discharge. The wettability of wood surface can be improved when oxygen functionalities were generated, which can be achieved directly in O-containing plasma or via post plasma reaction. A small reduction in the surface energy of the treated wood after 12 days of aging showed that the plasma-induced cross-linking in the surface of the wood was not the dominant phenomenon.     

Wetting behavior of magnesite and dolomite surfaces

Magnesite and dolomite are salt-type minerals that show similar chemical composition and flotation behavior due to same crystal structure, and sparingly soluble nature. The surface properties of minerals play a major role in determining their separation from each other in processes such as flotation. During flotation process, selectivity problem arises between magnesite and associated gangue minerals such as dolomite. There is a close relationship between floatability of minerals and their contact angles. Therefore, surface hydrophobicity of magnesite and dolomite minerals was investigated by contact angle measurements in the absence and presence of flotation reagents.Magnesite and dolomite show hydrophilic properties and they have got a small contact angle (magnesite ∼10.4° and dolomite ∼6.6°) in distilled water in the absence of any surfactant. The contact angle values at the magnesite and dolomite surfaces remained at 9.7°-10.9° in the presence of petroleum sulphonates (R825 and R840) while sodium oleate affected hydrophobicity of magnesite, and the contact angle value increased up to 79°. The contact angle value of 39° at dolomite surface was obtained in the solution of sodium oleate, respectively.     

The research on the interfacial compatibility of polypropylene composite filled with surface treated carbon fiber

Dielectric barrier discharges (DBD) in ambient air are used on carbon fiber to improve the fiber surface activity. Carbon fibers with length of 75 μm are placed into the plasma configuration. The interaction between modified carbon fibers and polypropylene (PP) was studied by three-point bending (TPB) test. The chemical changes induced by the treatments on carbon fiber surface are examined using X-ray photoelectron spectroscopy (XPS). XPS results reveal that the carbon fiber modified with the DBD at atmospheric pressure show a significant increase in oxygen and nitrogen concentration. These results demonstrate that the surface of the carbon fiber is more active and hydrophilic after plasma treatments using a DBD operating in ambient air.