Evaluation of protein adsorption on atmospheric plasma deposited coatings exhibiting superhydrophilic to superhydrophobic properties

Protein adsorption is one of the key parameters influencing the biocompatibility of medical device materials. This study investigates serum protein adsorption and bacterial attachment on polymer coatings deposited using an atmospheric pressure plasma jet system. The adsorption of bovine serum albumin and bovine fibrinogen (Fg) onto siloxane and fluorinated siloxane elastomeric coatings that exhibit water contact angles (θ) ranging from superhydrophilic (θ < 5°) to superhydrophobic (θ > 150°) were investigated. Protein interactions were evaluated in situ under dynamic flow conditions by spectroscopic ellipsometry. Superhydrophilic coatings showed lower levels of protein adsorption when compared with hydrophobic siloxane coatings, where preferential adsorption was shown to occur. Reduced levels of protein adsorption were also observed on fluorinated siloxane copolymer coatings exhibiting hydrophobic wetting behaviour. The lower levels of protein adsorption observed on these surfaces indicated that the presence of fluorocarbon groups have the effect of reducing surface affinity for protein attachment. Analysis of superhydrophobic siloxane and fluorosiloxane surfaces showed minimal indication of protein adsorption. This was confirmed by bacterial attachment studies using a Staphylococcus aureus strain known to bind specifically to Fg, which showed almost no attachment to the superhydrophobic coating after protein adsorption experiments. These results showed the superhydrophobic surfaces to exhibit antimicrobial properties and significantly reduce protein adsorption.     

Response of osteoclasts to titanium surfaces with increasing surface roughness: an in vitro study

Osteoclasts are responsible for bone resorption and implant surface roughness promotes osseointegration. However, little is known about the effect of roughness on osteoclast activity. This study aims at the characterization of osteoclastic response to surface roughness. The number of osteoclasts, the tartrate-resistant acid phosphatase and matrix metalloproteinase (MMP) activities, the cell morphology and the actin-ring formation were examined on smooth (TS), acid-etched (TA) and sandblasted acid-etched (TLA) titanium and on native bone. Cell morphology was comparable on TA, TLA and bone, actin rings being similar in size on TLA and bone, but smaller on TA and virtually absent on TS. Gelatin zymography revealed increased proMMP-9 expression on TA, TLA, and bone compared to TS. In general, osteoclasts show similar characteristics on rough titanium surfaces and on bone, but reduced activity on smooth titanium surfaces. These results offer some insight into the involvement of osteoclasts in remodeling processes around implant surfaces.     

Cosmetic powder suspensions in compliant, fingerprintlike contacts

Cosmetic powders are regularly employed in skin creams and cosmetic formulations to improve performance and enhance skin feel. A previous study investigated the effect of particle concentration and size on the lubricating properties of powder suspensions in smooth, compliant contacts [Timm et al., Tribol. Int. (2011)]. In this paper the tribological properties of cosmetic powder suspensions are investigated in compliant contacts having model fingerprintlike surface topography. Friction coefficients were measured for a series of powder suspensions with varying particle size and concentration in a polydimethylsiloxane (PDMS)/PDMS contact. A commercial tribometer (MTM, PCS Instruments) was employed to measure friction as a function of rubbing time (20 min), under pure sliding (50 mm/s) and low load (0.5 N) conditions. Compared to results using smooth surfaces, it was clear that surface topography has a pronounced affect on the time-dependent tribological behavior of the cosmetic powder suspensions studied. A two-stage friction coefficient versus time curve was observed. By varying the particle size and concentration it was shown that the duration and magnitude of each stage can be controlled.     

Impact of vitronectin concentration and surface properties on the stable propagation of human embryonic stem cells

The standard method for culturing human embryonic stem cells (hESC) uses supporting feeder layers of cells or an undefined substrate, Matrigel(?), which is a basement membrane extracted from murine sarcoma. For stem cell therapeutic applications, a superior alternative would be a defined, artificial surface that is based on immobilized human plasma vitronectin (VN), which is an adhesion-mediating protein. Therefore, VN adsorbed to diverse polymer surfaces was explored for the continuous propagation of hESC. Cells propagated on VN-coated tissue culture polystyrene (TCPS) are karyotypically normal after >10 passages of continuous culture, and are able to differentiate into embryoid bodies containing all three germ layers. Expansion rates and pluripotent marker expression verified that a minimal VN surface density threshold is required on TCPS. Further exploration of adsorbed VN was conducted on polymer substrates with different properties, ranging from hydrophilic to hydrophobic and including cationic and anionic polyelectrolyte coatings. Despite differing surface properties, these substrates adsorbed VN above the required surface density threshold and were capable of supporting hESC expansion for >10 passages. Correlating wettability of the VN-coated surfaces with the response of cultured hESC, higher cell expansion rates and OCT-4 expression levels were found for VN-coated TCPS, which exhibits a water contact angle close to 65°. Importantly, this simple, defined surface matches the performance of the benchmark Matrigel, which is a hydrogel with highly complex composition.     

Development of superhydrophobic polyester fabrics using alkaline hydrolysis and coating with fluorinated polymers

Alkaline hydrolysis is one of the most classic fiber finishing methods, however, its potential as tuning surface superhydrophobicity in mass scale has not been studied much. In this research, fine roughness was formed on the polyester fiber surfaces by alkaline hydrolysis at room temperature and fluorinated polymer mixtures were further coated. The developed superhydrophobic fabrics were evaluated in terms of structural changes, mechanical properties, surface hydrophobicity, and permeability for practical applications. As alkaline hydrolysis treatment time increased, surface roughness was increased as a lot of nano-craters were generated with the decrease of fabrics weight and tensile strength as well. As air pockets formed through nano-craters on the fiber surfaces, static contact angle increased, and shedding angle tended to decrease. In this study, the sample treated with alkaline hydrolysis for 20 minutes showed the highest static contact angle of 167.8±1.3° and lowest shedding angle of 4.4±2.3°. Considering tensile strength loss, however, the 15-minute alkaline hydrolyzed fabrics which showed static contact angle of 162.2±2.7° and shedding angle of 8.8±0.2° was selected as the optimal condition for practical application. The newly developed superhydrophobic fabrics were found to have higher water vapor and air permeability than those of untreated samples. At the same time, fluoropolymer coating played a certain role for tensile strength and water vapor permeability demonstrating the importance of understanding and designing proper fluorinated-compound treatment processes.     

Efficient creation of cellular micropatterns with long-term stability and their geometric effects on cell behavior

Cellular micropatterning with bio-adhesive and nonadhesive areas has attracted increasing interest for the precise design of cell-to-surface attachment in cell biology studies, tissue engineering, cell-based biosensors, biological assays, and drug development and screening. In this paper we describe a simple and efficient method to create a two-dimensional stable cellular microenvironment, which is based on (1) forming a protein-resistant oligo(ethylene glycol) methyl ether methacrylate polymer layer on the substrates via surface-initiated atom transfer radical polymerization; (2) placing a defined photomask on the substrate and exposing the substrate to ultraviolet light; and (3) immersing the patterned surface in a fibronectin solution to form cell-adhesive protein patterns in a cell-resistant background. The resulting surfaces are tailored into cell-adhesive and cell-resistant regions. Three different types of cells (NIH-3T3, PC12, bone marrow-derived mesenchymal stem cells) are seeded on such patterned surfaces to form cellular patterns. The geometric effects on cell behavior are investigated. The long-term stability is tested by NIH-3T3 fibroblasts and mesenchymal stem cells and excellent retention of cellular patterns is observed. The strategy illustrated here offers an efficient way to create a stable, patterned cellular microenvironment, and could be employed in tissue engineering to study the effect of micropatterns on the proliferation and differentiation of cells, and in particular mesenchymal stem cells.     

A comparative study of wool fibre surface modified by physical and chemical methods

The wool scale present on the fibre surface gives rise to certain unwanted effects such as felting and poor wettability in textile wet processing. In general practice, the removal of scale was done either by surface modification through physical/chemical degradation of scale or by deposition of a polymer on the scale. In modern treatment, combination of both methods is usually carried out. Since the deposition of a polymer on the fibre surface depends much on the surface characteristic of the fibre, therefore, the surface property of modified fibre is an important factor for polymer application. On the other hand, the surface modification methods may also result in improved hydrophilicity of fibre. The present paper investigated the surface physico-chemical properties of wool fibre under the influence of different surface modification treatments: (i) low temperature plasma (LTP) treatment with nitrogen gas and (ii) chlorination. The surface physico-chemical properties of the LTP-treated and chlorinated wool fibres were studied which included contact angle measurement with different solvents, determination of critical surface tension and surface free energy. Experimental results showed that these selected properties were altered after the surface modification treatments. In addition, a polymer was deposited in the treated wool fabrics and scanning electron microscope was used for assessing the surface morphology.     

Effects of nanometric roughness on surface properties and fibroblast's initial cytocompatibilities of Ti6Al4V

Titanium alloy (Ti6Al4V) has widespread medical applications because of its excellent biocompatibility. Its biological responses can further be enhanced by polishing and passivation. Unfortunately, preparing titanium alloy samples of nanometric roughness is by far much more difficult than preparing those of micrometric roughness, and numerous investigations on roughness induced effects are all focused on micrometric scales. For the remedy, we investigate, at nanometric scale, the influence of roughness on surface properties and biological responses. Six groups of Ti6Al4V with average roughness (R(a)) values of 2.75-30.34 nm are prepared. The results indicated that nanometric roughness of samples change the wettability and amphoteric OH groups. The contact angles monotonically decrease from 2.75 to 30.34 nm and the rougher surfaces lead to higher wettability. The in vitro cell-culture studies, using Murine NIH-3T3 fibroblasts, showed the spindle-shaped morphology on rougher surface compared to round∕spherical morphology on smoother surface. A cytodetacher is employed to quantitatively measure the initial adhesion force of fibroblasts to specimen. The adhesion strength of fibroblasts, ranging from 55 to 193 nN, is significantly influenced by the nanometric roughness while the surface is within the range of 2.75-30.34 nm R(a) roughness, and the adhesion strength appeared stronger for rougher surface. The cell number on the smoother surface is higher than on the rougher surface at 5-day culture. The studies indicated that nanometric roughness would alter the surface properties and further influence cell morphology, adhesion strength, and proliferation.     

Highly Durable and Robust Superhydrophobic/Superoleophilic Cotton Fabric with Well-designed Roughness for Oil/Water Separation

Herein we report a simple and reproducible method for fabricating highly durable and robust superhydrophobic and superoleophilic cotton fabrics via simultaneous radiation-induced graft polymerization of glycidyl methacrylate and subsequent chemical modifications with aminopropyltriethoxysilane and hexamethyldisilazane. The chemical structure and the surface topography of the pristine and the modified cotton fabrics were investigated in detail by ATR-FTIR, XPS, and ²⁹Si NMR, and a grafting layer was successfully immobilized onto the surface of the cotton fabric by forming covalent bonds. Multi-dimensional surface roughness was created by combining micro-sized fibers of the cotton fabric, nanoscaled protuberances of the grafting chain, and molecular level spherical projection points of silicon methyl. The superhydrophobic cotton fabric exhibited long-term stability, ultra-high durability and robustness, and maintained its properties even after 25 wash cycles. The fabric also showed excellent water repellency with a water contact angle of 153 ° and a high efficiency of oil/water separation (98 %). The superhydrophobic/superoleophilic cotton fabric developed in the present work exhibits important potential applications in superhydrophobic textiles and oil/water separation.     

Robust Water-Repellent Treatment of Cotton Fabrics with Polysiloxane Modified via Thiol-Ene Click Reaction

A facile and inexpensive way to prepare self-crosslinkable poly(dimethylsiloxane) (PDMS) for superhydrophobic treatment of cotton fabrics is reported in the study. Through thiol-ene click reaction between mercaptopropyltrimethoxysilane (MPTMOS) and vinyl-containing poly(dimethylsiloxane) (VPDMS), PDMS-g-TMOS can be simply and quickly synthesized. The trimethoxysilane group of PDMS-g-TMOS can react with hydroxyl group on cotton fabric and other -Si(OCH₃)₃ groups. The synthesized polysiloxane (PDMS-g-TMOS) was identified by FT-IR and ¹H-NMR. The morphology of the treated cotton fabric was observed by SEM and XPS was used to analyze the elemental composition on the surface of cotton fabric. The analysis results indicated that the surface was fully covered with PDMS. Due to the low surface energy of PDMS and the rough surfaces of cotton fabric, the optimized water contact angle (WCA) and sliding angle were respectively 154°±0.4° and 14°±0.5°, indicating superhydrophobicity. Moreover, water spray test (AATCC Test Method 22-2010) was also applied to evaluate the water repellency of treated cotton fabric and a score of 90 was assigned according to AATCC Test Method 22-2010. The durability of treated cotton fabric was tested by 50 laundering cycles. The resultant WCA barely decreased and the score of water spray test dropped from 90 to 80, showing the reasonable wash durability.     

Cationized albumin-biocoatings for the immobilization of lipid vesicles

Tethered lipid membranes or immobilized lipid vesicles are frequently used as biomimetic systems. In this article, the authors presented a suitable method for efficient immobilization of lipid vesicles onto a broad range of surfaces, enabling analysis by quantitative methods even under rigid, mechanical conditions-bare surfaces such as hydrophilic glass surfaces as well as hydrophobic polymer slides or metal surfaces such as gold. The immobilization of vesicles was based on the electrostatic interaction of zwitterionic or negatively charged lipid vesicles with two types of cationic chemically modified bovine serum albumin (cBSA) blood plasma proteins (cBSA-113 and cBSA-147). Quantitative analysis of protein adsorption was performed as the cBSA coatings were characterized by atomic force microscopy, surface zeta potential measurement, fluorescence microscopy, and surface plasmon spectroscopy, revealing a maximal surface coverage 270-280?ng/cm(2) for 0.02 mg/ml cBSA on gold. Small unilamellar vesicles as well as giant unilamellar vesicles (GUVs) were readily immobilized (～15?min) on cBSA coated surfaces. GUVs with 5-10 mol% negatively charged 1,2,-dipalmitoyl-sn-glycero-3-phosphoglycerol remained stable in liquid for at least 5 weeks.     

Oriented, multimeric biointerfaces of the L1 cell adhesion molecule: an approach to enhance neuronal and neural stem cell functions on 2-D and 3-D polymer substrates

This article focuses on elucidating the key presentation features of neurotrophic ligands at polymer interfaces. Different biointerfacial configurations of the human neural cell adhesion molecule L1 were established on two-dimensional films and three-dimensional fibrous scaffolds of synthetic tyrosine-derived polycarbonate polymers and probed for surface concentrations, microscale organization, and effects on cultured primary neurons and neural stem cells. Underlying polymer substrates were modified with varying combinations of protein A and poly-D-lysine to modulate the immobilization and presentation of the Fc fusion fragment of the extracellular domain of L1 (L1-Fc). When presented as an oriented and multimeric configuration from protein A-pretreated polymers, L1-Fc significantly increased neurite outgrowth of rodent spinal cord neurons and cerebellar neurons as early as 24 h compared to the traditional presentation via adsorption onto surfaces treated with poly-D-lysine. Cultures of human neural progenitor cells screened on the L1-Fc/polymer biointerfaces showed significantly enhanced neuronal differentiation and neuritogenesis on all protein A oriented substrates. Notably, the highest degree of βIII-tubulin expression for cells in 3-D fibrous scaffolds were observed in protein A oriented substrates with PDL pretreatment, suggesting combined effects of cell attachment to polycationic charged substrates with subcellular topography along with L1-mediated adhesion mediating neuronal differentiation. Together, these findings highlight the promise of displays of multimeric neural adhesion ligands via biointerfacially engineered substrates to "cooperatively" enhance neuronal phenotypes on polymers of relevance to tissue engineering.     

Facile fabrication of superhydrophobic cotton fabric from stearyl methacrylate modified polysiloxane/silica nanocomposite

The stearyl methacrylate modified polysiloxane/nanocomposite was synthesized by graft copolymerization between stearyl methacrylate modified polysiloxane with pendent epoxy groups and amino-functionalized nano silica. Then it was utilized to fabricate the superhydrophobic cotton fabric by one-step method. The structures, chemical compositions, thermal properties, surface morphology and wettability were characterized by Fourier Transform Infrared Spectrum (FT-IR), X-ray photoelectron spectroscopy (XPS), Thermo-gravimetric analyzer (TGA), Scanning electron microscopy (SEM) and Static contact angle analyzer. Results showed that a hydrophobic polysiloxane film and many nano-scaled tubercles were coated on the surface of the treated cotton fabrics plus their inherent microscaled roughness, which were the reasons why cotton fabric changed from hydrophilicity to hydrophobicity. In addition, with increase of the amount of nanocomposite, hydrophobicity of the treated cotton fabric would be enhanced; water contact angle of this fabric could attain 157°, which was higher than 141.5° reached by the fabric treated with stearyl methacrylate modified polysiloxane. The superhydrophobic cotton fabric also possessed favorable washing durability. On the other hand, its air permeability, color and softness would not be influenced instead.     

Fabrication of superhydrophobic cellulose/chitosan composite aerogel for oil/water separation

Superhydrophobic cellulose and chitosan composite aerogel (SCECS) is fabricated through a novel and simple approach for the first time. During the preparation of cellulose and chitosan composite aerogel (CECS), chitosan is selfassemble into number micron-diameter particles on the surface of aerogel, which is similar to the micromorphology of a lotus leaf. Based on the rough surface, CECS is modified by sodium stearate through electrostatic interaction and ion exchange. Water contact angles of 156° are obtained for superhydrophobic aerogel. SCECS can remove various oils from water and with absorption capacities of 10 g/g for oil. Furthermore, the special structure of a non-porous of surface and porous layer of internal is benefit to separate surfactant-stabilized water-in-oil emulsions under gravity.     

Green composites. I. physical properties of ramie fibers for environment-friendly green composites

The surface topography, tensile properties, and thermal properties of ramie fibers were investigated as reinforcement for fully biodegradable and environmental-friendly ‘green’ composites. SEM micrographs of a longitudinal and cross-sectional view of a single ramie fiber showed a fibrillar structure and rough surface with irregular cross-section, which is considered to provide good interfacial adhesion with polymer resin in composites. An average tensile strength, Young’s modulus, and fracture strain of ramie fibers were measured to be 627 MPa, 31.8 GPa, and 2.7 %, respectively. The specific tensile properties of the ramie fiber calculated per unit density were found to be comparable to those of E-glass fibers. Ramie fibers exhibited good thermal stability after aging up to 160°C with no decrease in tensile strength or Young’s modulus. However, at temperatures higher than 160°C the tensile strength decreased significantly and its fracture behavior was also affected. The moisture content of the ramie fiber was 9.9%. These properties make ramie fibers suitable as reinforcement for ‘green’ composites. Also, the green composites can be fabricated at temperatures up to 160°C without reducing the fiber properties.     

Effect of fiber length on mechanical behavior of coir fiber reinforced epoxy composites

Fiber reinforced polymer composites have played a dominant role for a long time in a variety of applications for their high specific strength and modulus. The fiber which serves as a reinforcement in reinforced plastics may be synthetic or natural. To this end, an investigation has been carried out to make use of coir, a natural fiber abundantly available in India. Natural fibers are not only strong and lightweight but also relatively very cheap. The present work describes the development and characterization of a new set of natural fiber based polymer composites consisting of coconut coir as reinforcement and epoxy resin as matrix material. The developed composites are characterized with respect to their mechanical characteristics. Experiments are carried out to study the effect of fiber length on mechanical behavior of these epoxy based polymer composites. Finally, the scanning electron microscope (SEM) of fractured surfaces has been done to study their surface morphology.     

Enzymatic surface modification of polyacrylonitrile and its copolymers: Effects of polymer surface area and protein adsorption

Polyacrylonitrile (PAN) is a widely used polymer in the textile industry. PAN contains cyano groups on the surface due to which it possess low hydrophilicity and limits its application. Thus, there is a need to modify the functional groups on the surface of PAN for its industrial demand to improve moisture uptake, dyeability with ionic dyes, without affecting mechanical properties. A number of strategies such as chemical treatment, plasma treatment, enzymatic treatment etc. have been applied for the surface modification of polymer but enzymatic treatment are advantageous over plasma treatment and chemical treatment. In enzymatic treatment, reaction is limited to polymer surface only, and provides milder condition with less damage to polymer. In present study, it was found that enzyme system of Amycolatopsis sp.IITR215 was effective enzyme system for modification of surface nitrile groups of polyacrylonitrile. PAN powder was treated with the cell free extract of Amycolatopsis sp.IITR215 and it was found that the nitrile metabolizing enzymes of this strain were efficiently able to transform -CN to -COOH groups present on the surfaces of PAN powder. The formation of carboxyl group was quantified by ammonia released and dye binding assay. Further, confirmation of carboxyl group on polymer was done by FTIR and XPS. This study indicates that, specific adsorption of enzyme probably plays an important role in the enzymatic surface modification of polymer.     

Surface modification of poly(L-lactic acid) with biomolecules to promote endothelialization

Rapid endothelialization is important for biodegradable blood-contacting devices not only to prevent thrombosis but also to prevent degradation debris from entering the bloodstream and causing further complications. Here the authors report a three-step surface modification method, by which biomolecules, such as gelatin and chitosan, are covalently immobilized on the surface of plasma-treated poly(L-lactic acid) (PLLA) via -COOH groups introduced by acrylic acid grafting polymerization. Surface characterization techniques, including x-ray photoelectron spectroscopy, contact angle measurement, and colorimetric methods for surface density of functional groups, proved the feasibility and stability of this surface modification method. Surface wettability was increased by biomolecules immobilization. The -COOH surface density was measured to be 4.17±0.15?μmol/cm(2), the and amount of gelatin immobilized was 4.8?μg/cm(2). Human umbilical vein endothelial cell was used during in vitro study at seeding density of 10(4)?cells/cm(2). PLLA-gAA-gelatin surface was found to enhance cell adhesion, spreading, focal adhesion formation, and proliferation significantly. Chitosan-modified PLLA shows marginally improvement in cell adhesion and proliferation. Endothelialization was achieved within 7 days on both modified PLLA surfaces. In conclusion, this work demonstrates the feasibility of the surface modification method, and its ability to promote complete endothelialization for cardiovascular applications.     

Effects of ferric chloride on structure, surface morphology and combustion property of electrospun polyacrylonitrile composite nanofibers

In this work, the pure polyacrylonitrile (PAN) nanofibers and PAN/FeCl₃ composite nanofibers were prepared by an electrospinning process. Electrospinning solution properties including viscosity, surface tension and conductivity, had been measured and combined with the results of Scanning electron microscopy (SEM), Atomic force microscope (AFM) and Micro Combustion Calorimeter (MCC) to investigate the effects of FeCl₃ on the structure, surface morphology and combustion property of electrospun PAN nanofibers, respectively. It was found from SEM images that the diameters of composite nanofibers were decreased with the addition of FeCl₃, which was attributed predominantly to the increased conductivity of the polymer solutions compared to viscosity and surface tension. The AFM analyses revealed that the surface morphology of electrospun nanofibers changed from smooth and wrinkle-like structure (without FeCl₃) to rough and ridge-like structure (with FeCl₃). The results characterized by MCC showed that the loading of FeCl₃ decreased the heat release rate (HRR) and improved the combustion property of composite nanofibers.     

Dorsal and ventral stimuli in cell-material interactions: effect on cell morphology

Cells behave differently between bidimensional (2D) and tridimensional (3D) environments. While most of the in vitro cultures are 2D, most of the in vivo extracellular matrices are 3D, which encourages the development of more relevant culture conditions, seeking to provide more physiological models for biomedicine (e.g., cancer, drug discovery and tissue engineering) and further insights into any dimension-dependent biological mechanism. In this study, cells were cultured between two protein coated surfaces (sandwich-like culture). Cells used both dorsal and ventral receptors to adhere and spread, undergoing morphological changes with respect to the 2D control. Combinations of fibronectin and bovine serum albumin on the dorsal and ventral sides led to different cell morphologies, which were quantified from bright field images by calculating the spreading area and circularity. Although the mechanism underlying these differences remains to be clarified, excitation of dorsal receptors by anchorage to extracellular proteins plays a key role on cell behavior. This approach--sandwich-like culture--becomes therefore a versatile method to study cell adhesion in well-defined conditions in a quasi 3D environment.