Surface Nanoroughness Research Articles

Nucleate pool boiling heat transfer characteristics of dilute Al2O3–ethyleneglycol nanofluids

Pool boiling heat transfer coefficients of dilute stabilized Al2O3–ethyleneglycol nanofluids as possible coolant fluid are experimentally quantified. The influence of different parameters such as heat flux, heating surface nano-roughness, concentration of nanofluids and fouling resistance on the pool boiling heat transfer coefficient of alumina nanofluids has experimentally been investigated and briefly discussed. Results demonstrated that there are two heat transfer regions with different mechanisms namely free convection and nucleate boiling heat transfer. Studies on the influence of parameter demonstrated that with increasing the heat flux, the pool boiling heat transfer coefficient of nanofluids significantly increases. In contrast, with increasing the concentration of nanofluid, due to the deposition of nanoparticles on the surface, the average roughness of the surface and the heat transfer coefficient dramatically deteriorate, while a significant increase in fouling resistance is reported. Also, studies reveal asymptotic and rectilinear behaviors of fouling resistance parameter in nucleate boiling and free convective domains.

Mechanical properties of UV-waterborne varnishes reinforced by cellulose nanocrystals

There are many instances in the literature of nanocellulose-thermoplastic composites, but there are few studies on coatings reinforced by cellulose nanocrystals (CNCs). The overall objective of this research was to develop organic nanoparticles-reinforced UV-water-based coatings for wood applications and to study the effect, mainly on wear properties, of the final composite coatings. CNC was mixed in the varnishes to improve the mechanical properties of the coatings. One of the key aspects in the technology of nanocomposites remains the dispersion of the nanoparticles within the matrix as well as its affinity with the matrix. To quantify the dispersion, efficient methods of characterization are needed in order to reveal the nanosized particles. In this article, a novel characterization method based on atomic force microscopy was employed to characterize such nanocomposite coatings, by measuring surface nanoroughness, which is clearly correlated with quality of dispersion and mechanical properties. CNC was modified by either alkyl quaternary ammonium bromides or acryloyl chloride. The mechanical properties (abrasion and scratch resistances, hardness and adhesion) were analyzed and compared to the reference varnish without nanoparticles. The modified CNC addition in UV-water-based coatings results in an approximately 30–40% increase in wear resistance (abrasion and scratch), without any loss of appearance.

Understanding improved osteoblast behavior on select nanoporous anodic alumina.

The aim of this study was to prepare different sized porous anodic alumina (PAA) and examine preosteoblast (MC3T3-E1) attachment and proliferation on such nanoporous surfaces. In this study, PAA with tunable pore sizes (25 nm, 50 nm, and 75 nm) were fabricated by a two-step anodizing procedure in oxalic acid. The surface morphology and elemental composition of PAA were characterized by field emission scanning electron microscopy and X-ray photoelectron spectroscopy analysis. The nanopore arrays on all of the PAA samples were highly regular. X-ray photoelectron spectroscopy analysis suggested that the chemistry of PAA and flat aluminum surfaces were similar. However, contact angles were significantly greater on all of the PAA compared to flat aluminum substrates, which consequently altered protein adsorption profiles. The attachment and proliferation of preosteoblasts were determined for up to 7 days in culture using field emission scanning electron microscopy and a Cell Counting Kit-8. Results showed that nanoporous surfaces did not enhance initial preosteoblast attachment, whereas preosteoblast proliferation dramatically increased when the PAA pore size was either 50 nm or 75 nm compared to all other samples (P<0.05). Thus, this study showed that one can alter surface energy of aluminum by modifying surface nano-roughness alone (and not changing chemistry) through an anodization process to improve osteoblast density, and, thus, should be further studied as a bioactive interface for orthopedic applications.

Synthesis of gold microstructures with surface nanoroughness using a deep eutectic solvent for catalytic and diagnostic applications.

We synthesized highly monodisperse gold microparticles (AuMPs) using a deep eutectic solvent (DES) which composed of choline chloride and malonic acid as both a reaction medium and structure-directing agent. These microparticles exhibit distinctive surface nanoroughness and highly defined diameters that can be precisely controlled over a range of a few micrometers under different reductive conditions. The internal and external structures of the particles are thoroughly investigated by electron microscopy, which is further analyzed in association with their optical properties. We also investigate the gold microparticle concentration-dependent catalytic property employing a reductive reaction of 4-nitrophenol to 4-aminopenol as a model system. Importantly, the gold microparticles are densely functionalized with DNA and reversibly assemble with DNA-gold nanoparticle conjugate probes for the colorimetric detection of target DNA sequences, demonstrating that these novel structures can be utilized as platforms that quickly regulate the optical properties of plasmonic nanoparticles for diagnostic applications.

An insight into the surface properties of calcined kaolinitic clays: The grinding effect

The present work aimed characterizing in a systematic way the surface of metakaolinitic materials produced by calcination of a kaolinitic clay at different temperatures and to study the effect of grinding on the surface properties of metakaolinitic materials. Using X-ray photoelectron spectroscopy, it was found for all materials a Si/Al atomic ratio close to 1, confirming the presence of the 1:1 clay structure. By inverse gas chromatography, an increase of the Lewis basic properties of the surfaces of metakaolinitic materials in comparison to the original clay was found, which was due to the condensation of hydroxyl groups in the structure of the clay. The grinding of the metakaolinitic materials afforded a decrease of the dispersive component of the surface energy (γsd) as well as an increase of the specific interaction with sterically hindered molecules, caused by the diminishing of the materials surface nanoroughness. The Lewis basic properties of the materials surface also increased with grinding. Noticeably, for all studied materials a good inverse relation could be found between the γsd and the specific interaction of trichloromethane (but not with dichloromethane), showing the importance of surface nanoroughness on the adsorption process of bulky molecules.

The influence of surface nanoroughness, texture and chemistry of TiZr implant abutment on oral biofilm accumulation.

The aim of the study was to examine surface nanoroughness, texture and chemistry of dental implant abutment and to investigate how these parameters influence oral biofilm formation in healthy subjects. Eight different nanorough TiZr surfaces were produced by polishing, machining, cathodic polarization and acid etching. Surface topography was examined using field emission scanning electron microscope and a blue light laser profilometer. Surface chemistry was analyzed by secondary ion mass spectrometry and X-ray photoelectron spectroscopy. Surface hydrophilicity was tested by measuring contact angle on the surfaces. A human in vivo study using a splint model was employed to evaluate oral biofilm accumulation on these surfaces. Different surface textures (flat, grooved and irregular) were created with nanoroughness from 29 to 214 nm. Some test surfaces were incorporated with hydrogen by cathodic polarization and/or acid etching with HCl/H(2)SO(4). Nanoroughness (S(a)) positively correlated with microbial adhesion. Biofilm accumulation was less pronounced on flat and grooved than on irregular surfaces. No significant association between hydrogen content or hydrophilicity of the surface and biofilm accumulation was observed. Nanoroughness (< 214 nm) and surface texture influence oral biofilm accumulation independent of surface chemistry and hydrophilicity. Surface hydrogen, which has previously been shown to promote fibroblast growth, does not affect biofilm formation.

Early dentine remineralisation: Morpho-mechanical assessment

ObjectivesThe purpose of this study was to evaluate some physical–mechanical and morphological changes of demineralised dentine at early stages of dentine remineralisation. MethodsExtracted human third molars were sectioned to obtain dentine discs. After polishing the dentine surfaces, three groups were established: (1) untreated dentine – UD, (2) 37% phosphoric acid application for 15s (partially demineralised dentine – PDD) and (3) 10% phosphoric acid for 12h, at 25°C (totally demineralised dentine – TDD). Five different remineralizing fluids were used for 30min: chlorhexidine (CHX), artificial saliva (AS), phosphated solution (PS), ZnCl2 and ZnO solutions. Atomic force microscopy (AFM) imaging/nano-indentation, surface nano-roughness and fibrils diameter were determined. X-ray diffraction (XRD), energy dispersive elemental analyses (EDX) and high resolution scanning electron microscopy analysis (HRSEM) were applied. ResultsPDD and TDD preserved some mineral contents. After demineralisation and immersion in all solutions, width of nanomechanical properties and fibrils was increased, and total nanoroughness was decreased. Peritubular and intertubular dentine were remineralised. ConclusionMineral exists in PA-demineralised dentine matrix and it is important since it may work as a constant site for further nucleation. The dentine surface remineralisation process may be stimulated as early as 30min in abiotic conditions, with a pH ranging from 7.0 to 7.5. Clinical significanceThe existence of enzymes and remineralising factors within the dentine matrix may facilitate early dentine remineralisation under favourable conditions. This process should be stimulated by new reparative materials.

Reproducible Biofilm Cultivation of Chemostat-Grown Escherichia coli and Investigation of Bacterial Adhesion on Biomaterials Using a Non-Constant-Depth Film Fermenter

Biomaterials-associated infections are primarily initiated by the adhesion of microorganisms on the biomaterial surfaces and subsequent biofilm formation. Understanding the fundamental microbial adhesion mechanisms and biofilm development is crucial for developing strategies to prevent such infections. Suitable in vitro systems for biofilm cultivation and bacterial adhesion at controllable, constant and reproducible conditions are indispensable. This study aimed (i) to modify the previously described constant-depth film fermenter for the reproducible cultivation of biofilms at non-depth-restricted, constant and low shear conditions and (ii) to use this system to elucidate bacterial adhesion kinetics on different biomaterials, focusing on biomaterials surface nanoroughness and hydrophobicity. Chemostat-grown Escherichia coli were used for biofilm cultivation on titanium oxide and investigating bacterial adhesion over time on titanium oxide, poly(styrene), poly(tetrafluoroethylene) and glass. Using chemostat-grown microbial cells (single-species continuous culture) minimized variations between the biofilms cultivated during different experimental runs. Bacterial adhesion on biomaterials comprised an initial lag-phase I followed by a fast adhesion phase II and a phase of saturation III. With increasing biomaterials surface nanoroughness and increasing hydrophobicity, adhesion rates increased during phases I and II. The influence of materials surface hydrophobicity seemed to exceed that of nanoroughness during the lag-phase I, whereas it was vice versa during adhesion phase II. This study introduces the non-constant-depth film fermenter in combination with a chemostat culture to allow for a controlled approach to reproducibly cultivate biofilms and to investigate bacterial adhesion kinetics at constant and low shear conditions. The findings will support developing and adequate testing of biomaterials surface modifications eventually preventing biomaterial-associated infections.

Investigation of static and dynamic wetting transitions of UV responsive tunable wetting surfaces

Ultraviolet (UV) radiation responsive surfaces, with tunable wetting properties, are fabricated by spin casting polystyrene/titania nanocomposite dispersion in tetrahydrofuran on silicon substrates. The prepared samples are found hydrophilic due to the presence of the water miscible solvent. Upon annealing, as the solvent evaporates, samples become superhydrophobic due to presence of hydrophobic polystyrene and formation of nano and micro scale surface roughness due to titania nanoparticles. Effect of different annealing temperatures and time on resulting wettability is investigated. Photocatalytic property of titania is exploited to make transition from superhydrophobic to hydrophilic state upon UV exposure. Subsequently, upon annealing again at elevated temperatures for sufficient time, the UV exposed hydrophilic samples recover their superhydrophobicity showing transition from hydrophilic to superhydrophobic state. Detailed static and dynamic study of these reversible transitions, between superhydrophobic and hydrophilic states, due to UV exposure and annealing is presented in this article.

Flow-Induced Aggregation and Breakup of Particle Clusters Controlled by Surface Nanoroughness

Interactions between colloidal particles are strongly affected by the particle surface chemistry and composition of the liquid phase. Further complexity is introduced when particles are exposed to shear flow, often leading to broad variation of the final properties of formed clusters. Here we discover a new dynamical effect arising in shear-induced aggregation where repeated aggregation and breakup events cause the particle surface roughness to irreversibly increase with time, thus decreasing the bond adhesive energy and the resistance of the aggregates to breakup. This leads to a pronounced overshoot in the time evolution of the aggregate size, which can only be explained with the proposed mechanism. This is demonstrated by good agreement between time evolution of measured light-scattering data and those calculated with a population-balance model taking into account the increase in the primary particle nanoroughness caused by repeated breakup events resulting in the decrease of bond adhesive energy as a function of time. Thus, the proposed model is able to reproduce the overshoot phenomenon by taking into account the physicochemical parameters, such as pH, till now not considered in the literature. Overall, this new effect could be exploited in the future to achieve better control over the flow-induced assembly of nanoparticles.

Super-hydrophilic coatings based on silica nanoparticles

This work focuses on the use of silica nanoparticles for producing durable, transparent, and super-hydrophilic coatings on painted surfaces. Two methods were studied in detail: bottom-up approach using layer-by-layer (LbL) assemblies of hydroxylated SiO2 nanoparticles, and top-down approach based on hybrid polymer/silica nanoparticles coatings. Of the two approaches studied, only the hybrid polymer/SiO2 nanocomposite coatings containing 50–90%wt. SiO2 exhibited durable super-hydrophilic surface properties less than 5° water contact and sliding angles. In the latter case, a unique micrometer-sized cracking pattern was developed. The LbL-assembled SiO2 coatings showed a gradual degradation over time from the initial super-hydrophilic properties, indicated by the increase of the contact angles from less than 5o to greater than 30o after accelerated aging. To investigate the effect of environmental exposure on developing hydrophilicity, a variety of analytical methods were employed such as: atomic force microscopy, scanning electron microscopy, optical microscopy, and Fourier transform infrared. Experimental results and associated modeling indicated that the combination of micro- and nano-surface roughness and the surface chemical composition were the dominant factors affecting the durability of the hydrophilic attributes of the coatings containing silica nanoparticles.

Poly(azobenzene acrylate-co-fluorinated acrylate) Spin-Coated Films: Influence of the Composition on the Photo-Controlled Wettability

The wetting properties of spin-coated films of copolymers based on azobenzene and fluorinated units have been investigated. The copolymers, denoted as poly(Azo-co-AcRf6), have been synthesized by free-radical polymerization of different proportions of acrylate monomers bearing either an azobenzene group or a semifluorinated side chain. The UV-visible spectroscopy analysis of the different spin-coating films through a cycle of UV and visible light irradiation indicates the reversible trans-cis isomerization of azobenzene groups. Simultaneously, atomic force microscopy shows that surface roughness does not exceed 1 nm. Advancing and receding contact angles of water and diiodomethane have been measured before and after UV photoirradiation of the different surfaces. In particular, a decrease in the advancing contact angles has been observed upon trans-cis isomerization of azobenzene groups. Switching variations up to 50° have been evidenced without any introduction of surface nanoroughness. Surface free-energy evaluations have been deduced from these measurements, including dispersive and polar components. The results show that, through surface composition and UV photoirradiation, a large range of surface free-energies can be obtained, from 7 to 46 mN·m(-1).

Physical vapor deposited titanium thin films for biomedical applications: Reproducibility of nanoscale surface roughness and microbial adhesion properties

The surface topography is of great importance for the biological performance of titanium based implants since it may influence the initial adsorption of proteins, cell response, as well as microbial adhesion. A recently described technique for the preparation of titanium thin films with an adjustable surface roughness on the nanometer scale is the physical vapor deposition (PVD). The aims of this study were to statistically evaluate the reproducibility of nanorough titanium thin films prepared by PVD using an atomic force microscopy (AFM) based approach, to test the microbial adhesion in dependence of the nanoscale surface roughness and to critically discuss the parameters used for the characterization of the titanium surfaces with respect to AFM microscope settings. No statistically significant differences were found between the surface nanoroughnesses of the PVD prepared titanium thin films. With increasing surface nanoroughness, the coverage by Escherichia coli decreased and the microbial cells were increasingly patchy distributed. The calculated roughness values significantly increased with increasing AFM scan size, while image resolution and pixel density had no influence on this effect. Our study shows that PVD is a suitable tool to reproducibly prepare titanium thin films with a well-defined surface topography on the nanometer scale. These surfaces are, thus, a suitable 2D model system for studies addressing the interaction between surface nanoroughness and the biological system. First results show that surface roughness even on the very low nanometer scale has an influence on bacterial adhesion behavior. These findings give new momentum to biomaterials research and will support the development of biomaterials surfaces with anti-infectious surface properties.

Gradients in surface nanotopography used to study platelet adhesion and activation

Gradients in surface nanotopography were prepared by adsorbing gold nanoparticles on smooth gold substrates using diffusion technique. Following a sintering procedure the particle binding chemistry was removed, and integration of the particles into the underlying gold substrate was achieved, leaving a nanostructured surface with uniform surface chemistry. After pre-adsorption of human fibrinogen, the effect of surface nanotopography on platelets was studied. The use of a gradient in nanotopography allowed for platelet adhesion and activation to be studied as a function of nanoparticle coverage on one single substrate. A peak in platelet adhesion was found at 23% nanoparticle surface coverage. The highest number of activated platelets was found on the smooth control part of the surface, and did not coincide with the number of adhered platelets. Activation correlated inversely with particle coverage, hence the lowest fraction of activated platelets was found at high particle coverage. Hydrophobization of the gradient surface lowered the total number of adhering cells, but not the ratio of activated cells. Little or no effect was seen on gradients with 36nm particles, suggesting the existence of a lower limit for sensing of surface nano-roughness in platelets. These results demonstrate that parameters such as ratio between size and inter-particle distance can be more relevant for cell response than wettability on nanostructured surfaces. The minor effect of hydrophobicity, the generally reduced activation on nanostructured surfaces and the presence of a cut-off in activation of human platelets as a function of nanoparticle size could have implications for the design of future blood-contacting biomaterials.

The influence of surface nanoroughness of electrospun PLGA nanofibrous scaffold on nerve cell adhesion and proliferation

Electrospun nanofibrous scaffolds in neural tissue engineering provide an alternative approach for neural regeneration. Since the topography of a surface affects the microscopic behaviour of material; the creation of nanoscale surface features, which mimic the natural roughness of live tissue, on polymer surfaces can promote an appropriate cell growth and proliferation. In this research, a unique PLGA nanofibrous structure was fabricated without any post-electrospinning treatment. Scaffolds were prepared in two general groups: cylindrical and ribbon-shaped electrospun fibres, with smooth and rough (porous and grooved) surfaces. The experiments about nerve cell culture have demonstrated that the nanoroughness of PLGA electrospun scaffolds can increase the cell growing rate to 50% in comparison with smooth and conventional electrospun scaffolds. SEM and AFM images and MTT assay results have shown that the roughened cylindrical scaffolds enhance the nerve growth and proliferation compared to smooth and ribbon-shaped nanofibrous scaffolds. A linear interaction has been found between cell proliferation and surface features. This helps to approximate MTT assay results by roughness parameters.

Femtosecond laser treatment of 316L improves its surface nanoroughness and carbon content and promotes osseointegration: An in vitro evaluation

Cell-material surface interaction plays a critical role in osseointegration of prosthetic implants used in orthopedic surgeries and dentistry. Different technical approaches exist to improve surface properties of such implants either by coating or by modification of their topography. Femtosecond laser treatment was used in this study to generate microspotted lines separated by 75, 125, or 175μm wide nanostructured interlines on stainless steel (316L) plates. The hydrophobicity and carbon content of the metallic surface were improved simultaneously through this method. In vitro testing of the laser treated plates revealed a significant improvement in adhesion of human endothelial cells and human bone marrow mesenchymal stem cells (hBM MSCs), the cells involved in microvessel and bone formation, respectively, and a significant decrease in fibroblast adhesion, which is implicated in osteolysis and aseptic loosening of prostheses. The hBM MSCs showed an increased bone formation rate on the laser treated plates under osteogenic conditions; the highest mineral deposition was obtained on the surface with 125μm interline distance (292±18mg/cm2 vs. 228±43mg/cm2 on untreated surface). Further in vivo testing of these laser treated surfaces in the native prosthetic implant niche would give a real insight into their effectiveness in improving osseointegration and their potential use in clinical applications.

Characterization of ZnO structures by optical and X-ray methods

ZnO thin films doped by Ga and In as well as multilayer structures of ZnO/Al2O3 have been investigated by X-ray fluorescence, Raman spectrometry, spectroscopic ellipsometry and vacuum ultra violet reflectometry. Systematic changes in the optical properties have been revealed even for Ga concentrations below 1%. The Raman active phonon mode of Ga doping at 580cm−1 shows a correlation with the Ga concentration. Optical models with surface nanoroughness correction and different parameterizations of the dielectric function have been investigated. There was a good agreement between the dielectric functions determined by the Herzinger–Johs polynomial parameterization and by direct inversion. It has been shown that the correction of the nanoroughness significantly influences the accuracy of the determination of the layer properties. The band gap and peak amplitude of the imaginary part of the dielectric function corresponding to the excitonic transition changes systematically with the Ga-content and with annealing even for low concentrations.

Comparative measurements on atomic layer deposited Al2O3 thin films using ex situ table top and mapping ellipsometry, as well as X-ray and VUV reflectometry

In this study we compare the thicknesses and optical properties of atomic layer deposited (ALD) Al2O3 films measured using table top and mapping ellipsometry as well as X-ray and optical reflectometry. The thickness of the films is varied in the range of 1–50nm. ALD samples are used as references with well-controlled composition and thickness, as well as with a good lateral homogeneity. The homogeneity is checked using mapping ellipsometry. Optical models of increasing complexity were developed to take into account both the top (surface roughness on the nanometer scale) and bottom interfaces (buried silicon oxide and interface roughness). The best ellipsometric model was the one using a single interface roughness layer. Since the techniques applied in this work do not measure in vacuum, organic surface contamination even in the sub-nanometer thickness range may cause an offset in the measured layer thicknesses that result in significant systematic errors. The amount of surface contamination is estimated by in situ reflectometry measurement during removal by UV radiation. Taking into account the surface contamination the total thicknesses determined by the different methods were consistent. The linearity of the total thickness with the number of atomic layer deposition cycles was good, with an offset of 1.5nm, which is in good agreement with the sum of thicknesses of the interface layer, surface nanoroughness, and contamination layer.

Synergistic effect of released dexamethasone and surface nanoroughness on mesenchymal stem cell differentiation

Stem cells can alter their shapes and functions in response to the physical cues at the cell-substrate interface or the chemical signals in the culture environment. In this study, the surface nanoroughness, as a physical cue in the form of the beads-on-string features on polymer nanofibers, was fabricated through an electrospinning technology, and simultaneously dexamethasone (DEX), an osteogenic differentiation factor as a chemical signal, was incorporated into these nanofibers during this process. The morphology of the DEX-loaded nanofibers was observed with scanning electron microscopy (SEM). In vitro DEX release was carried out in PBS over a period of 29 days. The combination of the physical and chemical signals was also used to investigate the differentiation capability of rat bone marrow mesenchymal stem cells (rBMSCs) through SEM and fluorescence microscopy observation, alkaline phosphatase (ALP) activity assay, Alizarin Red S staining, quantification of mineral deposition and quantitative real-time PCR analysis. The results indicate that the DEX gradually released into the culture medium played a dominant role in promoting rBMSCs' differentiation towards osteoblast-like cells, and the surface nanoroughness could play a supporting role in the differentiation. Therefore, this DEX-loaded polymer nanofiber scaffold with moderate surface nanoroughness has great potential application in bone tissue regeneration.

Nanostructured magnesium has fewer detrimental effects on osteoblast function

Efforts have been made recently to implement nanoscale surface features on magnesium, a biodegradable metal, to increase bone formation. Compared with normal magnesium, nanostructured magnesium has unique characteristics, including increased grain boundary properties, surface to volume ratio, surface roughness, and surface energy, which may influence the initial adsorption of proteins known to promote the function of osteoblasts (bone-forming cells). Previous studies have shown that one way to increase nanosurface roughness on magnesium is to soak the metal in NaOH. However, it has not been determined if degradation of magnesium is altered by creating nanoscale features on its surface to influence osteoblast density. The aim of the present in vitro study was to determine the influence of degradation of nanostructured magnesium, created by soaking in NaOH, on osteoblast density. Our results showed a less detrimental effect of magnesium degradation on osteoblast density when magnesium was treated with NaOH to create nanoscale surface features. The detrimental degradation products of magnesium are of significant concern when considering use of magnesium as an orthopedic implant material, and this study identified a surface treatment, ie, soaking in NaOH to create nanoscale features for magnesium that can improve its use in numerous orthopedic applications.