Hydrophilic surface modification of polydimetylsiloxane‐co‐2‐hydroxyethylmethacrylate (PDMS‐HEMA) by Silwet L‐77 (heptamethyltrisiloxane) surface treatment

Biomaterials and their host organism's quintessential place of interaction are the surfaces of materials, as transportation of liquids within microchannels requires hydrophilic surfaces. Modifying the hydrophobic surface of polydimethylsiloxane (PDMS) into a hydrophilic one which can be used in biomaterials remains a big challenge. Herein, PDMS‐hydroxyethylmethacrylate (HEMA) films were prepared by the condensation of PDMS using isophorone diisocyanate as a cross‐linker, followed by the incorporation of HEMA via radical copolymerization. The as‐prepared PDMS‐HEMA films were thereafter hydrophilized via physical treatment with heptamethyltrisiloxane. The surface properties of the obtained PDMS‐HEMA films were characterized in wettability, morphology, topography, swelling, mechanical properties, and protein adsorption. Compared to pristine PDMS‐HEMA as control, the surface wettability, roughness, and protein adsorption of the hydrophilized PDMS‐HEMA films were significantly improved while the films also exhibited excellent optical properties. However, the improvement of the swelling properties remains insignificant, indicating that the interior morphology was still based on the hydrophobic siloxane PDMS. The long‐term hydrophilicity was considered good as no significant hydrophobic recovery was noticeable in a period of 5 months after treatment.     

Stability of monomolecular films of archaebacterial tetraether lipids on silicon wafers: a comparison of physisorbed and chemisorbed monolayers

The monomolecular organisation of symmetric, chemically modified tetraether lipids caldarchaeol-PO(4) was studied using Langmuir film balance, ellipsometry, and atomic force microscopy (AFM). Solid silicon wafer substrates were modified to hydrophobic, hydrophilic, and amino-silanised surfaces; and Langmuir-Blodgett (LB)-films were transferred onto each. LB-caldarchaeol-PO(4) films were subjected to further rinsing with organic solvent and additional physical treatments, to compare their resistance and stability on chemisorbed (amino-silanised) and physisorbed (hydrophobic and hydrophilic) surfaces. The resistance and stability of these monolayer films was characterized by ellipsometry and AFM, and film thickness was determined using ellipsometry. AFM was also employed to observe surface morphology. Monolayer films on hydrophobic surfaces were found to be more resistant to rinsing with organic solvent and additional physical treatments than monolayer films on either amino-silanised or hydrophilic surfaces. The hydrophobic effect with hydrophobic surfaces appears to support the formation of stronger caldarchaeol-PO(4) films on silicon wafer substrates, with increased resistance and stability.     

Self‐assembled silane monolayers: an efficient step‐by‐step recipe for high‐quality,low energy surfaces

Organosilane self‐assembled monolayers (SAMs) are commonly used for modifying a wide range of substrates. Depending on the end group, highly hydrophobic or hydrophilic surfaces can be achieved. Silanization bases on the adsorption, self‐assembly and covalent binding of silane molecules onto surfaces and results in a densely packed, SAM. Following wet chemical routines, the quality of the monolayer is often variable and, therefore, unsatisfactory. The process of self‐assembly is not only affected by the chemicals involved and their purity but is also extremely sensitive to ambient parameters such as humidity or temperature and to contaminants. Here, a reliable and efficient wet‐chemical recipe is presented for the preparation of ultra‐smooth, highly ordered alkyl‐terminated silane SAMs on Si wafers. The resulting surfaces are characterized by means of atomic force microscopy, X‐ray reflectometry and contact angle measurements. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of oxidized silicon (SiOx) surfaces functionalization on real‐time PCR by Lab‐on‐a‐chip microdevices

There is a great need to improve the biocompatibility of silicon‐based lab‐on‐chip substrate materials for reliable quantitative analysis of biological solutions. These advanced microdevice surfaces need not only be biocompatible but also have surfaces of defined wettability characteristics. The inhibition of biomolecular activity due to microdevice surface interaction is common and can result in inaccurate results or decreased reaction yields. In this work we investigate different techniques for the chemical functionalization of oxidized silicon (SiO_x) surfaces in order to: (i) obtain defined hydrophobic/hydrophilic surfaces; and (ii) increase the efficiency of performing Real‐Time Polymerase Chain Reaction (PCR) on a silicon‐based lab‐on‐chip. Silicon oxide surfaces are functionalized by grafting alkylic chain silanes and poly(ethylene glycol) (PEG) chains to the surfaces, rendering them hydrophobic or hydrophilic. Functionalized surfaces are characterized through contact angle and atomic force microscopy (AFM) measurements, showing stable hydrophobic surfaces with contact angles of 69–78° and layer thicknesses of 11–15 Å and hydrophilic surfaces displaying contact angles of 5–6° and thicknesses of 22–52 Å. PCR experiments carried out directly on bare silicon oxide lab‐on‐chip surfaces show low yields of DNA amplification. Hydrophobic surfaces decrease the inhibition of PCR. Hydrophilic surfaces are a major improvement on the bare silicon oxide exhibiting the same maximum reaction yield as obtained with a standard thermocycler. We have found that the best results are associated with PEG modified surfaces, which prove very suitable for the fabrication of reliable PCR silicon lab‐on‐chips. Copyright © 2011 John Wiley & Sons, Ltd.     

XPS and AES characterization of hydrolysed γ‐mercaptopropyltrimethoxysilane deposited on Al,Zn and Al–43.4Zn–1.6Si alloy‐coated steel

In this paper Al, Zn and Al–43.4Zn–1.6Si (AlZn) alloy‐coated steel have been treated with the organofunctional silane γ‐mercaptopropyltrimethoxysilane (γ‐MPS). The influence of different metal substrates on the structure and composition of the silane films was investigated with XPS and AES. The films were obtained by dipping the substrates in the silane solution followed by a blow‐dry procedure in nitrogen gas. The results show that the surface concentration of the deposited silane is independent of the metal substrate and that the thickness of the silane film is non‐uniform. The AES measurements indicate that the silane film covers the entire substrate surface and XPS analysis of the silane‐treated substrate surfaces at different take‐off angles indicates that the γ‐MPS molecule is randomly orientated. Also, the results show that the silane is well hydrolysed under the solution conditions used. Finally, in the zinc‐containing silane‐metal systems, i.e. the silane‐treated AlZn and Zn substrates, the results indicate that the γ‐MPS molecules can bond to the substrate surfaces via the thiol group of the molecule. Copyright © 2004 John Wiley & Sons, Ltd.     

Probing interfacial interactions of nafion ionomer: Thermal expansion of nafion thin films on substrates of different hydrophilicity/hydrophobicity

Interfacial interactions of Nafion ionomer with superhydrophilic (Pt, Au), hydrophilic (SiO₂), and hydrophobic (graphene, octyltrichlorosilane [OTS]‐modified SiO₂) is investigated, using in situ thermal ellipsometry, by quantification of substrate‐ and thickness‐dependent thermal properties of the ultrathin Nafion films of nominal thickness ranging 25–135 nm. For sub‐50 nm thin Nafion films, the thermal expansion coefficient of films decreased in the order of most hydrophobic to most hydrophilic substrate: OTS > graphene > SiO₂ > Au > Pt, implying weaker interpolymer and polymer–substrate interactions for films on hydrophobic substrates. Expansion coefficient of films on SiO₂, graphene, and OTS‐modified SiO₂ decreased with thickness whereas that of films on Au and Pt substrates increased with thickness. Above ~100 nm of thickness, films on all substrates converged toward a common value representative of bulk Nafion. Thermal transition temperature was found to be higher for films on hydrophilic SiO₂ than that for films on hydrophobic graphene and OTS‐modified SiO₂ but was not discernible for films on Au and Pt substrates. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 343–352     

Interpretation of protein adsorption: surface-induced conformational changes

Protein adhesion plays a major role in determining the biocompatibility of materials. The first stage of implant integration is the adhesion of protein followed by cell attachment. Surface modification of implants (surface chemistry and topography) to induce and control protein and cell adhesion is currently of great interest. This communication presents data on protein adsorption (bovine serum albumin and fibrinogen) onto model hydrophobic (CH(3)) and hydrophilic (OH) surfaces, investigated using a quartz crystal microbalance (QCM) and grazing angle infrared spectroscopy. Our data suggest that albumin undergoes adsorption via a single step whereas fibrinogen adsorption is a more complex, multistage process. Albumin has a stronger affinity toward the CH(3) compared to OH terminated surface. In contrast, fibrinogen adheres more rapidly to both surfaces, having a slightly higher affinity toward the hydrophobic surface. Conformational assessment of the adsorbed proteins by grazing angle infrared spectroscopy (GA-FTIR) shows that after an initial 1 h incubation few further time-dependent changes are observed. Both proteins exhibited a less organized secondary structure upon adsorption onto a hydrophobic surface than onto a hydrophilic surface, with the effect observed greatest for albumin. This study demonstrates the ability of simple tailor-made monochemical surfaces to influence binding rates and conformation of bound proteins through protein-surface interactions. Current interest in biocompatible materials has focused on surface modifications to induce rapid healing, both of implants and for wound care products. This effect may also be of significance at the next stage of implant integration, as cell adhesion occurs through the surface protein layer.     

In situ adsorption studies of a 14-amino acid leucine-lysine peptide onto hydrophobic polystyrene and hydrophilic silica surfaces using quartz crystal microbalance, atomic force microscopy, and sum frequency generation vibrational spectroscopy

The adsorption of a 14-amino acid amphiphilic peptide, LK14, which is composed of leucine (L, nonpolar) and lysine (K, charged), on hydrophobic polystyrene (PS) and hydrophilic silica (SiO2) was investigated in situ by quartz crystal microbalance (QCM), atomic force microscopy (AFM), and sum frequency generation (SFG) vibrational spectroscopy. The LK14 peptide, adsorbed from a pH 7.4 phosphate-buffered saline (PBS) solution, displayed very different coverage, surface roughness and friction, topography, and surface-induced orientation when adsorbed onto PS versus SiO2 surfaces. Real-time QCM adsorption data revealed that the peptide adsorbed onto hydrophobic PS through a fast (t < 2 min) process, while a much slower (t > 30 min) multistep adsorption and rearrangement occurred on the hydrophilic SiO2. AFM measurements showed different surface morphologies and friction coefficients for LK14 adsorbed on the two surfaces. Surface-specific SFG spectra indicate very different ordering of the adsorbed peptide on hydrophobic PS as compared to hydrophilic SiO2. At the LK14 solution/PS interface, CH resonances corresponding to the hydrophobic leucine side chains are evident. Conversely, only NH modes are observed at the peptide solution/SiO2 interface, indicating a different average molecular orientation on this hydrophilic surface. The surface-dependent difference in the molecular-scale peptide interaction at the solution/hydrophobic solid versus solution/hydrophilic solid interfaces (measured by SFG) is manifested as significantly different macromolecular-level adsorption properties on the two surfaces (determined via AFM and QCM experiments).     

Two-dimensional Monte Carlo simulations of ionic and nonionic silane self-assembly on hydrophilic surfaces

Aqueous chemistries have recently been shown to be useful for the deposition of hydrophobic films of nonionic and cationic silanes on hydrophilic substrates for the prevention of stiction in MEMS. The Monte Carlo method is used to simulate in two dimensions the self-assembly of silane films on a hydrophilic surface. We investigate the impact of charged group in cationic silane on the overall structure of the films. We characterize the film structure with spatial pair correlations at each molecular layer of the deposited films. The simulations reveal long-range correlations for the film of cationic silanes. Based on our two-dimensional simulations, we report an average "most probable" structure for the films of nonionic and cationic silanes.     

Assessment by XPS and electrochemical techniques of two molecular organosilane films prepared on stainless‐steel surfaces

The ability of silane groups to chemosorb on mechanically polished stainless‐steel surfaces has been investigated. Accordingly, tridecafluoro‐1,1,2,2‐tetrahydrooctyltrichlorosilane and the tridecafluoro‐1,1,2,2‐tetrahydrooctyltriethoxysilane, two organosilanes of similar chain length terminated with hydrophobic non‐reactive functions, have been tested as probe molecules. X‐ray photoelectron spectroscopy characterization, optical microscopy imaging, electrochemistry and contact angle measurements have been performed to characterize bare and modified samples. Results reported in this work show the influence of time of immersion and coupling agent reactive group on self‐assembled monolayer formation. It emerges that silanization by triethoxysilanes in millimolar solutions is not suitable for producing chemically bonded organic films with high density. Copyright © 2004 John Wiley & Sons, Ltd.     

Surface immobilization of fibronectin-derived PHSRN peptide on functionalized polymer films – Effects on fibroblast spreading

The Pro-His-Ser-Arg-Asn (PHSRN) sequence in fibronectin is a second cell-binding site that synergistically affects Arg-Gly-Asp (RGD). The PHSRN peptide also induces cell invasion and accelerates wound healing. We report on the surface immobilization of PHSRN by spontaneous adsorption on polysiloxane thin films which have different surface free energy characteristics. Low-surface energy (hydrophobic) polysiloxane and the corresponding high-surface energy (hydrophilic) surfaces obtained by UV–ozone treatments were used as adsorbing substrates. The peptide adsorption process was investigated by quartz crystal microbalance with dissipation monitoring and atomic force microscopy. Both adsorption kinetics and peptide rearrangement dynamics at the solid interface were significantly different on the surface-modified films compared to the untreated ones. Fibroblast cells cultures at short times and in a simplified environment, i.e., a medium-free solution, were prepared to distinguish interaction events at the interface between cell membrane and surface-immobilized peptide for the two cases. It turned out that the cell-adhesive effect of immobilized PHSRN was different for hydrophobic compared to hydrophilic ones. Early signatures of cell spreading were only observed on the hydrophilic substrates. These effects are explained in terms of different spatial arrangements of PHSRN molecules immobilized on the two types of surfaces.     

Micro-morphological investigations on wettability of Al-incorporated c-Si thin films using statistical surface roughness parameters

The tunable surface properties of Al-incorporated c-Si and/or homogeneous c-Si (i.e., absorber layer) thin films are investigated with the help of 3D surface topography, statistical analysis, and contact angle measurement. The absorber layers are developed by ion irradiation on c-Al/a-Si films, which results the crystallization of Si in bilayer films, and the top unreacted Al layers were chemically etched off by wet selective etching. The 3D surface topography and statistical analysis is performed on the atomic force microscopy images of the absorber film surface. The analyses suggest that the surfaces are highly complex and irregular isotropic. The surface roughness and irregularity is found to be decreasing with increasing ion fluence. Variation of contact angle with statistical parameters suggest that the wettability of the absorber surface strongly depends on the surface statistical parameters. The surfaces are hydrophobic in nature, and hydrophobicity is found to decrease with increasing ion fluence. The hydrophobic nature of low reflective absorber surface suggests that the film may be useful as a photon absorber layer for advance solar cell applications.     

Vapour-growth of Sn on stearic acid molecular layers

Tin metal was vacuum deposited at room temperature on to Langmuir–Blodgett (LB) films with surfaces of either hydrophilic head groups or hydrophobic tail groups. Different growth modes on different surfaces of the LB films were observed with an atomic force microscope. Fine Sn particles deposited on the hydrophobic surface were uniform in size and similar in shape, but on the hydrophilic surface large Sn particles were observed. Chemical interactions between organic functional groups and deposited metal seems critical for the manner of crystal growth. The possibility of control over the crystallization of metals using two-dimensionally assembled organic molecules is demonstrated.     

Particle zips: vertical emulsion films with particle monolayers at their surfaces

Vertical emulsion films with particle monolayers at their surfaces have been studied by direct microscope observations. The effects of particle wettability and surface coverage on the structure and stability of water films in octane and octane films in water have been investigated. Monodisperse silica particles (3 microm in diameter) hydrophobized to different extents have been used. It is found that the structure and stability of emulsion films strongly depend on the film type (water-in-oil or oil-in-water), the particle contact angle, the interactions between particles from the same and the opposite monolayer, and the monolayer density. Stable films are observed only when the particle wettability fulfills the condition for stable particle bridges--in agreement with the concept that hydrophilic particles can give stable oil-in-water emulsions, whereas hydrophobic ones give water-in-oil emulsions. In the case of water films with dilute disordered monolayers at their surfaces, the hydrophilic particles are expelled from the film center toward its periphery, giving a dimple surrounded by a ring of particles bridging the film surfaces. In contrast, the thinning of octane films with dilute ordered monolayers at their surfaces finally leads to the spontaneous formation of a dense crystalline monolayer of hydrophobic particles bridging both surfaces at the center of the film. The behaviors of water and octane films with dense close-packed particle monolayers at their surfaces are very similar. In both cases, a transition from bilayer to bridging monolayer is observed at rather low capillary pressures. The implications of the above finding for particle stabilized emulsions are discussed.     

Sugar‐fiber Imprinting to Generate Microgrooves on Polymeric Film Surfaces for Contact Guidance of Cells

Anisotropic surface topography is known to induce the contact guidance of cells, and facile and biocompatible approaches of the physical modification of the pertinent matrix surfaces are thus meaningful for biomaterials. Herein, we put forward a sugar‐fiber imprinting technique to generate microgrooves on hydrophobic polymers demonstrated by the poly(lactic‐co‐glycolic acid) (PLGA) films. Microgrooves were conveniently generated after removing sugar fibers simply by water. The resulting locally anisotropic microgrooves were confirmed to elongate the cells cultured on the surface.     

水溶性聚合物和两亲聚合物——10.两亲聚合物PAMC_(16)S的自组装有序膜

用自组装技术在金(纯金和经阳极氧化的金)表面上获得了新型两亲聚合物PAMC_(16)S的有序膜。用接触角测试,XPS谱和电化学分析等方法对自组装膜进行了表征。根据膜表面的润湿性,金表面的自组装膜是疏水的,亲水的磺酸基团连于金表面,而疏水的碳氢链从表面伸展出。XPS实验结果支持金表面上单层膜的疏水结构。聚合物单层膜复盖的金电极起到含有针孔缺陷的阻膈型电极的作用。单层膜在法拉第反应中显示很强的吸附稳定性,说明聚合物LB膜在潜在应用中有其特有的特点。     

Cooperativity in the adsorption of cellulose ethers and fibrinogen at liquid-solid interfaces

The possibility of reducing fibrinogen adsorption to solid surfaces by competitive adsorption of cellulose ethers (EHEC, HEC) was investigated. The surface concentration of fibrinogen adsorbed onto hydrophilic and hydrophobic (methylized) glass was measured with an enzyme-linked immunosorbent assay. The immunoassay was calibrated by ellipsometry, using the initial mass transport limitation of adsorption for calculations of the maximum amount of adsorbed protein.At a hydrophobic surface, the presence of cellulose polymers caused a decrease of the adsorption of fibrinogen. The hydrophobic EHEC (cloud point 35°C) was most efficient and abolished surface-adsorption of the protein.At a hydrophilic surface, positive cooperativity was seen between fibrinogen and cellulose polymers. The hydrophilic HEC (cloud point >100°C) gave the most prominent effect.The results indicate that the affinity between a water soluble polymer or protein and a solid surface is not the only factor determining surface adsorption. The finding that there may be both positive and negative cooperativity in the adsorption of polymers shows the importance of polymer compatibility in layers of adsorbed polymers.     

On the stability of the polymer brushes formed by adsorption of ionomer complexes on hydrophilic and hydrophobic surfaces

We have studied the effect of normal forces and shear forces on the stability and functionality of a polymer brush layer formed upon adsorption of polymeric micelles on hydrophilic and hydrophobic surfaces. The micelles consist of oppositely charged polyelectrolyte blocks (poly(acrylic acid) and poly(N-methyl 2-vinyl pyridinium iodide), and a neutral block (poly(vinyl alcohol)) or neutral grafts (poly(ethylene oxide)). The strength of the attachment of the micellar layers to various substrates was evaluated with Atomic Force Microscopy. Flow cell experiments allowed for the evaluation of long-term stability of coatings in lateral flow. Fixed angle optical reflectometry was used to quantify protein (BSA) adsorption on the micellar layers after their exposure to flow. The results show that adsorbed micellar layers are relatively weakly attached to hydrophobic surfaces and much stronger to hydrophilic surfaces, which has a significant impact on their stability. Adsorbed layers maintain their ability to suppress protein adsorption on hydrophilic surfaces but not on hydrophobic surfaces. Due to the relatively weak attachment to hydrophobic surfaces the structure of adsorbed layers may easily be disrupted by lateral forces, such that the complex coacervate-brush structure no longer exists.     

Time‐of‐flight SIMS characterization of hydrolysed organofunctional and non‐organofunctional silanes deposited on Al,Zn and Al–43.4Zn–1.6Si alloy‐coated steel

In this paper Al, Zn and Al–43.4Zn–1.6Si (AlZn) alloy‐coated steel have been treated with the organofunctional silane γ‐mercaptopropyltrimethoxysilane (γ‐MPS) and the non‐organofunctional silane 1,2‐bis(triethoxysilyl)ethane (BTSE). Also, a two‐step treatment of metal substrates was performed: the metal substrates were treated with the BTSE silane followed by a γ‐MPS treatment. The influence of metal substrate and the pH value of the silane film properties were investigated using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The results show that the BTSE silane is fully hydrolysed but the γ‐MPS silane is not. The presence of negative ions of the type HSi_xO_y^? indicates that both types of silane films are highly cross‐linked via Si–O–Si bonds. The two‐step treatment gave a γ‐MPS silane layer on top of the BTSE silane layer but the thickness of the total silane film become thinner than for a single BTSE film, indicating that some of the BTSE is dissolved during the γ‐MPS deposition step. Furthermore, the ToF‐SIMS results show that the thiol group of the γ‐MPS silane is oxidized. Finally, no major influence, either in the positive or the negative mass spectra, from the different metal substrates could be detected for the silane films investigated. Copyright © 2003 John Wiley & Sons, Ltd.     

Specific Cell Surface Protein Imaging by Extended Self-Assembling Fluorescent Turn-on Nanoprobes

Visualization of tumor-specific protein biomarkers on cell membranes has the potential to contribute greatly to basic biological research and therapeutic applications. We recently reported a unique supramolecular strategy for specific protein detection using self-assembling fluorescent nanoprobes consisting of a hydrophilic protein ligand and a hydrophobic BODIPY fluorophore in test tube settings. This method is based on recognition-driven disassembly of the nanoprobes, which induces a clear turn-on fluorescent signal. In the present study, we have successfully extended the range of applicable fluorophores to the more hydrophilic ones such as fluorescein or rhodamine by introducing a hydrophobic module near the fluorophore. Increasing the range of available fluorophores allowed selective imaging of membrane-bound proteins under live cell conditions. That is, overexpressed folate receptor (FR) or hypoxia-inducible membrane-bound carbonic anhydrases (CA) on live cell surfaces as cancer-specific biomarkers were fluorescently visualized using the designed supramolecular nanoprobes in the turn-on manner. Moreover, a cell-based inhibitor-assay platform for CA on a live cell surface was constructed, highlighting the potential applicability of the self-assembling turn-on probes.