Showing papers on "Surface modification published in 2004"

Surface modification of titanium, titanium alloys, and related materials for biomedical applications

Abstract: Titanium and titanium alloys are widely used in biomedical devices and components, especially as hard tissue replacements as well as in cardiac and cardiovascular applications, because of their desirable properties, such as relatively low modulus, good fatigue strength, formability, machinability, corrosion resistance, and biocompatibility. However, titanium and its alloys cannot meet all of the clinical requirements. Therefore, in order to improve the biological, chemical, and mechanical properties, surface modification is often performed. This article reviews the various surface modification technologies pertaining to titanium and titanium alloys including mechanical treatment, thermal spraying, sol–gel, chemical and electrochemical treatment, and ion implantation from the perspective of biomedical engineering. Recent work has shown that the wear resistance, corrosion resistance, and biological properties of titanium and titanium alloys can be improved selectively using the appropriate surface treatment techniques while the desirable bulk attributes of the materials are retained. The proper surface treatment expands the use of titanium and titanium alloys in the biomedical fields. Some of the recent applications are also discussed in this paper.

Physicochemical Properties and Cellular Toxicity of Nanocrystal Quantum Dots Depend on Their Surface Modification

Abstract: Nanocrystal quantum dots (QDs) have been applied to molecular biology because of their greater and longer fluorescence. Here we report the potential cytotoxicity of our characterized QDs modified with various molecules. Surface modification of QDs changed their physicochemical properties. In addition, the cytotoxicity of QDs was dependent on their surface molecules. These results suggested that the properties of QDs are not related to those of QD-core materials but to molecules covering the surface of QDs.

Covalent Functionalization of Single-Walled Carbon Nanotubes for Materials Applications

Abstract: Covalent functionalization of single-walled carbon nanotubes (SWNTs) has significantly expanded the utility of the nanotube structure. Covalent sidewall functionalization has been employed to increase the solubility of these materials, which allows for the manipulation and processing of these otherwise insoluble nanotubes. Increased solubility leads to better dispersion in polymeric systems. Functionalization can be performed selectively wherein the metallic SWNTs react faster than the semiconductors. This has allowed a separation of carbon nanotubes by type. Covalent sidewall functionalization also allows nanotube-based composite formation where the functional group is well mixed with the polymer matrix. This has led to dramatic increases in the modulus of elastomers while retaining their elongation-at-break properties.

Long‐Range Electrical Contacting of Redox Enzymes by SWCNT Connectors

Abstract: The combination of biological molecules and novel nanomaterial components is of great importance in the process of developing new nanoscale devices for future biological, medical, and electronic applications. The electrical contacting of redox enzymes with electrodes is a subject of extensive research over the last decade, with important implications for developing biosensing enzyme electrodes, biofuel cells and bioelectronic systems. Tethering of redox-relay units to enzymes associated with electrodes, the immobilization of enzymes in redox-polymers, and the reconstitution of apo enzymes on relay-cofactor units associated with electrodes were reported as means to establish electrical communication between redox proteins and electrodes. Recently, the reconstitution of the apo–flavoenzyme glucose oxidase, GOx, with a single Au nanoparticle functionalized with the flavin adenine dinucleotide (FAD) cofactor was reported.The assembly of the Au-nanoparticle/GOx biocatalyst on an electrode led to an effective electrically contacted enzyme electrode. Single-walled carbon nanotubes (SWCNTs) exhibit unique structural, mechanical, and electronic properties, and recent studies have demonstrated the use of SWCNTs in nanodevices and sensors. Several research activities have addressed the generation of biomaterial–SWCNT hybrid systems, protein-linked CNT and nucleic acid-functionalized SWCNT. The oriented assembly of short SWCNT normal to electrode surfaces was accomplished by the covalent attachment of the CNT to the electrode surfaces. This structural alignment of the SWCNTs allows the secondary association of redox-active components to the CNT, and the examination of charge transport through the SWCNT. Herein we wish to report on the structural alignment of the enzyme glucose oxidase, GOx, on electrodes by using SWCNTs as electrical connectors between the enzyme redox centers and the electrode. We demonstrate that the surfaceassembled GOx is electrically contacted to the electrode by means of the SWCNTs, which acts as conductive nanoneedles that electrically wire the enzyme redox-active site to the transducer surface. The effect of the length of the SWCNTon controlling the electrical-communication properties between the enzyme redox center and the electrode is discussed. SWCNTs (Carbolex, Sigma) were first purified by heating the as-received nanotubes in refluxing 3m nitric acid for 24 h and then washing the resulting nanotubes with water by using a 0.6 mm polycarbonate membrane filter (Millipore). The purified long SWCNTs were chemically shortened by oxidation in a mixture of concentrated sulfuric and nitric acids (3:1, 98% and 70%, respectively) that was subjected to sonication for 8 h in an ice/water bath. This procedure yields shortened SWCNTs with a broad length distribution and that have terminal carboxyl functionalities. The shortened SWCNTs were purified by dialysis and filtering. The resulting SWCNTs suspension was further stabilized by sonication for 3 minutes in 1wt% sodium dodecylsulfate (SDS) as surfactant. After some macroscopic particles had settled down, the SWCNTs supernatant dispersion was loaded onto a controlled pore glass (CPG 3000 >, MPG) chromatographic column to perform length fractionation of the SWCNTs and finally dialyzed against a 1wt% Triton X-100 solution. The eluted SWCNTs fractions (ca. 50 fractions) were analyzed by atomic force microscopy (AFM), to determine the length distribution of SWCNTs in each fraction. The average SWCNTs length decreased as the fraction number increased, and the AFM histograms derived from each fraction showed a relative narrow length distribution. Previous studies have shown that the chemical shortening of SWCNTs by strong acids leads to the formation of carboxylic (and phenolic) groups at the nanotube ends (and sidewall defect sites), thus allowing the covalent immobilization of the SWCNTs on surfaces. A 2thioethanol/cystamine mixed monolayer (3:1 ratio) was assembled on an Au electrode and the length fractionalized SWCNTs were coupled to the surface in the presence of the coupling reagent 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) as depicted in Figure 1. The incorporation of 2-thioethanol in the mixed monolayer was anticipated to prevent nonspecific adsorption of the surfactant-protected SWCNTs onto the electrode surface (and presumably to prevent lying of the SWCNT pipes on the surface). Figure 2 shows the AFM images of the 50 nm SWCNTs-modified surfaces upon coupling the CNTs to the modified surface for different time-intervals. Longer coupling times lead to higher surface coverage of the SWCNTs. As illustrated in Figure 2A, isolated needlelike protrusions are clearly seen on the surface after 30 minutes of surface modification, the density of which increases gradually, until a densely packed, needlelike pattern of standing SWCNTs is obtained after five hours of coupling. We could not find by AFM measurements SWCNTs that lie on the surface. There could be as many as eight carboxy groups at each end of the 1.3 nm diameter SWCNT of a (16,0) zigzag structure. Therefore, eight amide bonds could be created between each nanotube and the gold surface, thus leading to a preferred standing conformation of the SWCNTs onto the surface. We found, that the height of the surface-standing nanotubes (determined by AFM) relates directly to the length of the corresponding SWCNTs fraction, although the height measured by AFM is always lower than the length of the free SWCNTs adsorbed on mica surfaces and measured by AFM, [*] F. Patolsky, Y. Weizmann, Prof. I. Willner Institute of Chemistry The Hebrew University of Jerusalem Jerusalem 91904 (Israel) Fax: (+972)2-6527715 E-mail: willnea@vms.huji.ac.il

Adhesively-bonded joints and repairs in metallic alloys, polymers and composite materials: Adhesives, adhesion theories and surface pretreatment

Abstract: In the present paper, the following topics are reviewed in detail: (a) the available adhesives, as well as their recent advances, (b) thermodynamic factors affecting the surface pretreatments including adhesion theories, wettability, surface energy, (c) bonding mechanisms in the adhesive joints, (d) surface pretreatment methods for the adhesively bonded joints, and as well as their recent advances, and (e) combined effects of surface pretreatments and environmental conditions on the joint durability and performance. Surface pretreatment is, perhaps, the most important process step governing the quality of an adhesively bonded joint. An adhesive is defined as a polymeric substance with viscoelastic behavior, capable of holding adherends together by surface attachment to produce a joint with a high shear strength. Adhesive bonding is the most suitable method of joining both for metallic and non-metallic structures where strength, stiffness and fatigue life must be maximized at a minimum weight. Polymeric adhesives may be used to join a large variety of materials combinations including metal-metal, metal-plastic, metal-composite, composite-composite, plastic-plastic, metal-ceramic systems. Wetting and adhesion are also studied in some detail in the present paper since the successful surface pretreatments of the adherends for the short- and long-term durability and performance of the adhesive joints mostly depend on these factors. Wetting of the adherends by the adhesive is critical to the formation of secondary bonds in the adsorption theory. It has been theoretically verified that for complete wetting (i.e., for a contact angle θ equal to zero), the surface energy of the adhesive must be lower than the surface energy of the adherend. Therefore, the primary objective of a surface pretreatment is to increase the surface energy of the adherend as much as possible. The influence of surface pretreatment and aging conditions on the short- and long-term strength of adhesive bonds should be taken into account for durability design. Some form of substrate pretreatment is always necessary to achieve a satisfactory level of long-term bond strength. In order to improve the performance of adhesive bonds, the adherends surfaces (i.e., metallic or non-metallic) are generally pretretead using the (a) physical, (b) mechanical, (c) chemical, (d) photochemical, (e) thermal, or (e) plasma method. Almost all pretreatment methods do bring some degree of change in surface roughness but mechanical surface pretreatment such as grit-blasting is usually considered as one of the most effective methods to control the desired level of surface roughness and joint strength. Moreover, the overall effect of mechanical surface treatment is not limited to the removal of contamination or to an increase in surface area. This also relates to changes in the surface chemistry of adherends and to inherent drawbacks of surface roughness, such as void formations and reduced wetting. Suitable surface pretreatment increases the bond strength by altering the substrate surface in a number of ways including (a) increasing surface tension by producing a surface free from contaminants (i.e., surface contamination may cause insufficient wetting by the adhesive in the liquid state for the creating of a durable bond) or removal of the weak cohesion layer or of the pollution present at the surface, (b) increasing surface roughness on changing surface chemistry and producing of a macro/microscopically rough surface, (c) production of a fresh stable oxide layer, and (d) introducing suitable chemical composition of the oxide, and (e) introduction of new or an increased number of chemical functions. All these parameters can contribute to an improvement of the wettability and/or of the adhesive properties of the surface.

Electrochemical and atomic force microscopy study of carbon surface modification via diazonium reduction in aqueous and acetonitrile solutions.

Abstract: Electrochemical reduction of the diazonium salts of 4-nitrobenzene and 4-nitroazobenzene-4‘- has been investigated in aqueous acid and acetonitrile media at carbon surfaces. Using pyrolyzed photoresist films as the substrate, we have examined the deposited films using electrochemistry and atomic force microscopy (AFM). Film thicknesses were measured by scratching through the film with an AFM tip. The procedure employed two AFM cantilevers with different lengths, located on the one device. When the shorter cantilever engages the surface in tapping mode, the longer cantilever (which is not resonating) imbeds into the surface with a constant force. For both modifiers and modification media, film thicknesses increase with deposition time to a limiting value. With equivalent modification conditions, films prepared in aqueous acid medium have lower limiting thicknesses than those prepared in acetonitrile. For nitrophenyl (NP) films, the same trends are found when calculating surface coverages from the charge as...

Preparation of Cellulose Whiskers Reinforced Nanocomposites from an Organic Medium Suspension

Abstract: The purpose of this study was to investigate a new way of processing cellulose whiskers reinforced polymer. A stable suspension of tunicin whiskers was obtained in an organic solvent (N,N-dimethylformamide) without a surfactant addition or a chemical surface modification. Both the high value of the dielectric constant of DMF and the medium wettability of tunicin whiskers were supposed to control the stability of the suspension. The nanocomposite materials were prepared by UV cross-linking using an unsaturated polyether as matrix. The resulting films were characterized by SEM, DSC, and mechanical testing in both the linear and nonlinear domains. The processing technique from a N,N-dimethylformamide suspension was found to be successful and led to materials whose properties are similar to those obtained with aqueous medium. It could be a good alternative to broaden the number of possible polymer matrices and to allow the processing of nanocomposite materials from an organic solvent solution instead of using aqueous suspensions.

Acid/Base-Treated Activated Carbons: Characterization of Functional Groups and Metal Adsorptive Properties

Abstract: Surface modification of activated carbons by various physicochemical methods directs an attractive approach for improvement of heavy metal uptake from aqueous solutions. Activated carbons were modified with HCl and HNO3 optionally followed by NaOH. The effects of surface modifications on the properties of the carbons were studied by the specific surface area, carbon pH, and total acidity capacity as well as by scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The modifications bring about substantial variation in the chemical properties whereas the physical properties remain nearly unchanged. NaOH causes an increase in the content of hydroxyl groups, while the HCl treatment results in an increase in the amount of single-bonded oxygen functional groups such as phenols, ethers, and lactones. The HNO3 modification generates a large number of surface functional groups such as carbonyl, carboxyl, and nitrate groups. The HNO3 modification significantly increases the copper adsorption, while the HCl treatment slightly reduces the copper uptake. Most of the copper ions are adsorbed rapidly in the first 2 h; the adsorption equilibrium is established in around 8 h. An intraparticle diffusion model successfully describes the kinetics of copper adsorption onto the carbons.

Surface functionalization of silicon nanoparticles produced by laser-driven pyrolysis of silane followed by HF-HNO3 etching.

Abstract: CO2 laser induced pyrolysis of silane was used to produce silicon nanoparticles with an average diameter as small as 5 nm at high rates (up to 200 mg/h). Etching these particles with a mixture of hydrofluoric acid (HF) and nitric acid (HNO3) reduces their size and passivates their surface such that they exhibit bright visible photoluminescence (PL). This paper describes the attachment of organic molecules to hydrogen-terminated and hydroxyl-terminated surfaces of these nanoparticles. Stable particle dispersions in various solvents were obtained by treatment of hydrogen-terminated surfaces with octadecene or undecylenic acid and by treatment of hydroxyl-terminated surfaces with octadecyltrimethoxysilane. Transmission electron microscopy showed that the surface-functionalized particles were well dispersed and crystalline. FTIR spectroscopy confirmed the expected reactions of the organic molecules with the particle surfaces. Photoluminescence measurements showed that surface treatment significantly stabilize...

Interior Surface Modification of Bacteriophage MS2

Abstract: An efficient strategy for the interior surface functionalization of MS2 viral capsids is reported, featuring a new hetero-Diels-Alder bioconjugation reaction. After virus isolation, the RNA genome was removed from the spherical particles by exposure to pH 11.8 conditions for a period of 4 h. Following this, 180 tyrosine residues on the interior surface of each "empty" capsid shell were modified by using a site-selective diazonium-coupling reaction. To attach additional functionality, the azo conjugate was reduced with Na2S2O4 to afford an ortho-amino tyrosine derivative. Oxidation of this moiety with NaIO4 produced an o-iminoquinone on the protein surface, which was found to undergo an efficient hetero-Diels-Alder reaction with N-(4-aminophenyl)acrylamide. This four-step procedure can be carried out in under 4 h, reaches high levels of conversion, and yields the desired conjugates in >60% overall yield.

Oriented attachment and membrane reconstitution of His-tagged cytochrome c oxidase to a gold electrode: in situ monitoring by surface-enhanced infrared absorption spectroscopy.

Abstract: A novel concept is introduced for the oriented incorporation of membrane proteins into solid supported lipid bilayers. Recombinant cytochrome c oxidase solubilized in detergent was immobilized on a chemically modified gold surface via the affinity of its histidine-tag to a nickel-chelating nitrilo-triacetic acid (NTA) surface. The oriented protein monolayer was reconstituted into the lipid environment by detergent substitution. The individual steps of the surface modification, including (1) chemical modification of the gold support, (2) adsorption of the protein, and (3) reconstitution of the lipid bilayer, were followed in situ by means of surface-enhanced infrared absorption spectroscopy (SEIRAS) and accompanied by normal-mode analysis. The high surface sensitivity of SEIRAS allows for the identification of each chemical reaction process within the monolayer at the molecular level. Finally, full functionality of the surface-tethered cytochrome c oxidase was demonstrated by cyclic voltammetry after binding of the natural electron donor cytochrome c.

Direct-write laser micromachining and universal surface modification of PMMA for device development

Abstract: The use of direct-write laser micromachining on poly(methyl methacrylate) (PMMA) to fabricate microfluidic chip has the potential for fast prototyping and production. However, the advantage has been diminished by the rugged surface and the limited surface chemistry modification available. To overcome this problem, we have developed a flexible and economic pipeline including PMMA micromachining, surface smoothness improvement, and a universal surface modification for introduction of various functional groups. The micromachining is accomplished by a commercial laser scriber, to which a user designed computer drawing is sent directly for grooving. The typical trench width is 140m while the aspect ratio up to more than 7 is easily achieved. Smooth surface is obtained after a one-step thermal annealing treatment after machining. The chemical modification is performed by a simple reduction reaction followed by the widely used organosilane chemistry to introduce diverse functional groups such as perfluoroalkyl (–C nF2n+2), amino (–NH2), and sulfhydryl (–SH) for surface passivation or further biomolecule immobilization. The surface smoothness after thermal annealing has been examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM) to be comparable to pristine surface. The surface chemistry modification has been confirmed by attenuated total reflectance–Fourier transform infrared spectroscopy (ATR–FTIR) and X-ray photoelectron spectroscopy (XPS). The whole procedure provides a very efficient micromachining platform to fabricate PMMA microfluidic chip for both prototyping and production. © 2003 Elsevier B.V. All rights reserved.

Improvement in the Luminescence Properties and Processability of LaF3/Ln and LaPO4/Ln Nanoparticles by Surface Modification

Abstract: The surface of lanthanide(III)-doped LaPO4 nanoparticles was modified by reaction with an alcohol, leading to a covalent bond between the ligand and the particle surface. The surface of lanthanide(III)-doped LaF3 nanoparticles was modified to alter the solubility of the nanoparticles and study the influence of surface effects on the luminescence of lanthanide ions doped in the nanoparticles. The coordinated organic ligands can be modified by a quantitative exchange reaction in solution or by using functionalized ligands during the synthesis. Variation of the ratio of ligand to core reagents had a significant influence on the size of the nanoparticles. Smaller nanoparticles were formed with a higher ligand ratio. The optical properties of these nanoparticles show a strong dependence on nanoparticle size, indicating the influence of quenching probably by CH and OH groups at or near the surface of the nanoparticle cores. The luminescence lifetime of LaF3/Eu nanoparticles varied from 6.5 to 7.4 ms for nanoparticles with an average size of 7.1 to 8.4 nm. A significant reduction of the quenching from the surface of the nanoparticles was obtained by the synthesis of core-shell nanoparticles, in which a shell of LaF3 was grown epitaxially around the doped core nanoparticles. This leads to an increase in the luminescence lifetime of the Eu3+ ion and the observation of emissions from the 5D2 energy level, in addition to emissions from the 5D1 and 5D0 levels. The quantum yield of LaF3/Ce,Tb nanoparticles could be increased from 24 to 54% by the growth of a LaF3 shell around the nanoparticles.

Covalent Bonding of Organic Molecules to Cu and Al Alloy 2024 T3 Surfaces via Diazonium Ion Reduction

Abstract: Cu surfaces and polished aluminum alloy 2024 T3 substrates were derivatized at open-circuit potential with aryl diazonium salts in both aprotic and aqueous media. Raman spectroscopy confirmed the presence of a derivatized film on the substrates before and after exposure to boiling water and sonication in acetone. Two different Cu substrate surfaces were prepared and used for X-ray photoelectron spectroscopy (XPS) analysis of the derivatization results. One surface was native oxide Cu, predominantly in the form of Cu 2 O, and one surface was predominantly Cu 0 . Results of the XPS analysis indicate the presence of both a Cu-O-C linkage and a Cu-C covalent bond between the aryl ring and the Cu substrate, and a high coverage of the organic layer. XPS results also indicate the formation multilayers on both types of Cu surfaces with different percentages of azo coupling within the multilayers on the two surfaces. Applications of a covalently bonded organic film on copper and alloy surfaces include adhesion promotion, corrosion protection, and possibly inhibition of oxygen reduction.

Surface modification and characterization of magnetic polymer nanospheres prepared by miniemulsion polymerization.

Abstract: A novel and effective protocol for the surface modification and quantitative characterization of magnetic polymeric nanospheres prepared by miniemulsion polymerization is reported. Composite nanospheres consisting of polymer-coated iron oxide nanoparticles were prepared by the miniemulsion polymerization of methyl methacrylate and divinylbenzene in the presence of magnetic fluid. Surface modification reaction of the magnetic polymer with poly(ethylene glycol) (PEG) was employed to obtain a hydrophilic hydroxyl-group-functionalized magnetic nanospheres. An affinity dye, Cibacron blue F3G-A (CB), was then coupled covalently to prepare a magnetic nonporous affinity adsorbent. The morphology and magnetic property of the polymer nanospheres obtained were examined by transmission electron microscopy and a vibrating sample magnetometer. The contents of surface groups modified were quantitatively measured by using diffusive reflectance Fourier transform infrared spectroscopy on the basis of a linear relationship ...

Functionalization of mesoporous silica for lipase immobilization: Characterization of the support and the catalysts

Abstract: A support for enzyme immobilization was prepared by functionalization of mesoporous silica with octyltriethoxysilane. The features of the surface enables the adsorption of lipase from Candida antarctica B via strong hydrophobic interactions, enhancing the stability of the adsorbed enzyme molecules. Derivatives with a high enzyme loading (200 mg protein/g of silica) can be obtained due to the high porosity and surface properties of the support while the immobilization occurs in a monolayer fashion. The lack of inactive enzyme aggregates, together with the high enzyme loading, are responsible for the high catalytic activity achieved by these species. Derivatives were prepared with different lipase loading, and the activities were tested and compared to the commercial derivative Novozym 435. The stability of the catalyst and hence its industrial applicability were tested by performing subsequent reaction cycles of acylation of ethanolamine with lauric acid in acetonitrile. Conversion was quantitative even after 15 reaction cycles.

Tailoring the Surface and Solubility Properties of Nanocrystalline Titania by a Nonaqueous In Situ Functionalization Process

Abstract: The reaction between titanium tetrachloride and benzyl alcohol in the presence of enediol ligands such as dopamine and 4-tert-butylcatechol provides a simple nonaqueous route to in situ surface functionalization of titania nanoparticles. The as-prepared precipitates are resoluble either in water or in organic solvents, depending on the ligand used. The surface chemistry of the 4-tert-butylcatechol-functionalized particles dissolved in dimethylformamide was analyzed by 1H NMR measurements revealing the presence of adsorbed 4-tert-butylcatechol, in addition to benzyl alcohol and water. Although the reaction temperatures of 70 or 80 °C are relatively low, XRD and HRTEM investigations give evidence that the as-synthesized nanoparticles are highly crystalline. Ultracentrifugation analysis of dopamine-functionalized titania nanoparticles dissolved in water shows a particle size distribution of approximately 3.5−8 nm with the peak maximum at 5.5 nm. Furthermore, the UV−vis detector system of the ultracentrifuge ...