Protein adsorption and biomimetic mineralization behaviors of PLL-DNA multilayered films assembled onto titanium

Titanium and its alloys are frequently used as surgical implants in load bearing situations, such as hip prostheses and dental implants, owing to their biocompatibility, mechanical and physical properties. In this paper, a layer-by-layer (LBL) self-assembly technique, based on the polyelectrolyte-mediated electrostatic adsorption of poly-l-lysine (PLL) and DNA, was used to the formation of multilayer on titanium surfaces. Then bovine serum albumin (BSA) adsorption and biomimetic mineralization of modified surfaces were studied. The chemical composition and wettability of assembled substrates were investigated by X-ray photoelectron spectroscopy (XPS), fluorescence microscopy and water contact angle measurement, respectively. The XPS analysis indicated that the layers were assembled successfully through electrostatic attractions. The measurement with ultraviolet (UV) spectrophotometer revealed that the LBL films enhanced ability of BSA adsorption onto titanium. The adsorption quantity of BSA on the surface terminated with PLL was higher than that of the surface terminated with DNA, and the samples of TiOH/P/D/P absorbed BSA most. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) showed that samples of assembled PLL or/and DNA had better bioactivity in inducing HA formation. Thus the assembling of PLL and DNA onto the surface of titanium in turn via a layer-by-layer self-assembly technology can improve the bioactivity of titanium.     

Room-temperature-adsorption behavior of acetic anhydride on a TiO2(1 1 0) surface

We have studied the adsorption structure of acetic anhydride on a TiO₂(1 1 0) surface using XPS (X-ray photoelectron spectroscopy), LEED (low energy electron diffraction) and HREELS (high resolution electron energy loss spectroscopy) to determine the origins of the unique adsorption properties of carboxylic acids on a TiO₂(1 1 0) surface. The C 1s XPS data indicated that the saturation carbon amount of adsorbed acetic anhydride was 12 ± 3% larger than that of the adsorbed acetic acid. LEED showed p(2 × 1) weak spots for the acetic anhydride adsorbed surface. The HREELS spectra revealed the dissociative adsorption of acetic anhydride. Based on these findings, we concluded that the neutralization of the bridging oxygen atoms associated with the dissociative adsorption is necessary for the stable adsorption of carboxylates on the 5-fold Ti sites.     

Adsorption of silane and methylsilane on gold surfaces

The adsorption of silane and methylsilane on the (1 1 0) and polycrystalline surfaces of gold is examined using vibrational electron energy loss spectroscopy (VEELS), angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) and X-ray photoelectron spectroscopy (XPS). Adsorption of silane onto the Au(1 1 0) surface at low temperatures is dissociative and yields an SiH₂ and possibly also SiH₃ surface species. Further dissociation occurs at room temperature to yield adsorbed SiH, which is tilted on the surface, with complete dissociation to Si occurring by 110 °C. The similarity in the UP spectra for silane adsorbed on the polycrystalline sample suggests that the same surface species are present over that temperature range. Above 200 °C, spectral changes suggest rearrangement of the Si atoms, which, by 350 °C, have diffused into the bulk. Adsorption of methylsilane onto the (1 1 0) surface at low temperatures initially produces adsorbed CH₃SiH or CH₃SiH₂, with undissociated methylsilane physisorbing at higher exposures. By room temperature, desorption and decomposition leaves (or direct adsorption yields) only adsorbed CH₃Si. After further heating, the hydrogen-carbon bonds of the CH₃ group break to leave an adsorbed SiC species. On the polycrystalline surface, methylsilane adsorption is the same at low temperatures as on (1 1 0). In contrast to the latter, though, the UP spectra indicate that direct exposures at room temperature yield adsorbed Si or SiC initially, with CH₃Si again adsorbing at higher exposures. Upon further heating to 330 °C, little if any methyl-groups remain on the surface and the Si has started to diffuse into the bulk.     

Plasma treatment of carbon fibers: Non-equilibrium dynamic adsorption and its effect on the mechanical properties of RTM fabricated composites

The effect of oxygen plasma treatment on the non-equilibrium dynamic adsorption of the carbon fabric reinforcements in RTM process was studied. 5-Dimethylamino-1-naphthalene-sulfonylchloride (DNS-Cl) was attached to the curing agent to study the change of curing agent content in the epoxy resin matrix. Steady state fluorescence spectroscopy (FS) analysis was used to study this changes in the epoxy resin at the inlet and outlet of the RTM mould, and XPS was used to study the chemical changes on the carbon fiber surfaces introduced by plasma treatment. The interlaminar shear strength (ILSS) and flexural strength were also measured to study the effects of this non-equilibrium dynamic adsorption progress on the mechanical properties of the end products. FS analysis shows that the curing agent adsorbed onto the fiber surface preferentially for untreated carbon fiber, the curing agent content in the resin matrix maintain unchanged after plasma treatment for 3 min and 5 min, but after oxygen plasma treatment for 7 min, the epoxy resin adsorbed onto the fiber surface preferentially. XPS analysis indicated that the oxygen plasma treatment successfully increased some polar functional groups concentration on the carbon fiber surfaces, this changes on the carbon fiber surfaces can change the adsorption ability of carbon fiber to the resin and curing agent. The mechanical properties of the composites were correlated to this results.     

XPS study of protein adsorption onto nanocrystalline aluminosilicate microparticles

X-ray photoelectron spectroscopy (XPS) was used to study the interaction of two different sized proteins, bovine serum albumin (BSA) and fibrinogen, with an aluminosilicate system containing yttrium and iron that is a potential biomaterial. Serum albumin and fibrinogen are two major plasma proteins and the most relevant proteins adsorbed on the surface of biomaterials in blood contact.The aluminosilicate samples were incubated for several exposure times, up to 24 h, in simulated body fluid enriched with BSA, and in buffered fibrinogen solution. Time dependence of proteins adsorption onto surface of the investigated samples is reflected by the evolution of the new N 1s photoelectron peak and by the modification of C 1s core-level spectra recorded from the samples immersed in protein solution.     

Effects of surface microstructure of hydroxyapatite on protein adsorption and biological performance of osteoblasts

The aim of this study was to investigate the effect of surface microstructure on the serum protein adsorption and the biological performance of osteoblasts cultured in vitro, when seeded onto the surface of ceramics with different grain size: conventional HA, micron-sized HA and nano-sized HA. Sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to comparatively analyze the protein adsorption solution. The content of alkaline phosphatase (ALP) was determined, and then by using wash way method, the adhesion ability was tested. XPS tests indicated that the content of N on the surface was significant different between the three groups (P < 0.05). SDS-PAGE analysis indicated that all the materials in these three groups could adsorb a large amount albumin, while the material in the nHA group adsorbed more albumin than the other groups. There were significant differences among them on the levels of osteoblast proliferation and adhesion in vitro. The biocompatibility of nHA is the best and of conventional HA is the worst.     

Adsorption and decomposition of NO on K-deposited Pd(1 1 1)

The adsorption and decomposition of NO on a K-deposited Pd(1 1 1) surface were investigated using X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, and temperature-programmed desorption. For the K-deposited Pd(1 1 1) surface, two different NO adsorption sites were observed in addition to the Pd site. On the clean Pd(1 1 1) surface, the adsorption of NO was purely molecular and reversible, but on the K-deposited surface, the adsorbed NO decomposed at two different temperatures, 530 and 610 K. These results indicate that the NO adsorption and decomposition sites were newly created by the deposition of K onto the Pd(1 1 1) surface.     

Surface bioactivity modification of titanium by CO2 plasma treatment and induction of hydroxyapatite: In vitro and in vivo studies

Since metallic biomaterials used for orthopedic and dental implants possess a paucity of reactive functional groups, bioactivity modification of these materials is challenging. In the present work, the titanium discs and rods were treated with carbon dioxide plasma and then incubated in a modified simulated body fluid 1.5SBF to obtain a hydroxyapatite layer. Surface hydrophilicity of samples, changes of surface chemistry, surface morphologies of samples, and structural analysis of formed hydroxyapatite were investigated by contact angle to water, X-ray photoelectron spectrometer (XPS), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and X-ray diffraction (XRD). The results demonstrated that hydrophilicity of titanium surface was improved and hydroxyl groups increased after modification with carbon dioxide plasma treatment. The hydroxyl groups on the surface of titanium were the richest after carbon dioxide plasma treatment under the condition of 20 W for less than 30 s. The hydroxyapatite formability of titanium surface was enhanced by carbon dioxide plasma pretreatment, which was attributed to the surface chemistry. MC3T3-E1 cell as a model cell was cultured on the Ti, CPT-Ti and CPT/SBF-Ti discs in vitro, and the results of the morphology and differentiation of the cell showed that CPT/SBF-Ti was the highest bioactive. The relative parameters of the new bone around the Ti and CPT/SBF-Ti rods including bone mineral density (BMD), a ratio of bone volume to total volume (BV/TV), trabecular thickness (Tb.Th.) and trabecular number (Tb.N.) were analyzed by a micro-computed tomography (micro-CT) after 4-, 8- and 12-week implantation periods in vivo. The results indicated that the CPT/SBF-Ti was more advantageous for new bone formation.     

Effect of gun current on the microstructure and crystallinity of plasma sprayed hydroxyapatite coatings

Hydroxyapatite (HA) is a bioactive material because its chemical structure is close to the natural bone. Its bioactive properties make it attractive material in biomedical applications. Gas tunnel type plasma spraying (GTPS) technique was employed in the present study to deposit HA coatings on SUS 304 stainless steel substrate. GTPS is composed of two plasma sources: gun which produces internal low power plasma (1.3-8 kW) and vortex which produces the main plasma with high power level (10-40 kW). Controlling the spraying parameters is the key role for spraying high crystalline HA coatings on the metallic implants. In this study, the arc gun current was changed while the vortex arc current was kept constant at 450 A during the spraying process of HA coatings. The objective of this study is to investigate the influence of gun current on the microstructure, phase crystallinity and hardness properties of HA coatings. The surface morphology and microstructure of as-sprayed coatings were examined by scanning electron microscope. The phase structure of HA coatings was investigated by X-ray diffraction analysis. HA coatings sprayed at high gun current (100 A) are dense, and have high hardness. The crystallinity of HA coatings was decreased with the increasing in the gun current. On the other hand, the hardness was slightly decreased and the coatings suffer from some porosity at gun currents 0, 30 and 50 A.     

A novel graded bioactive high adhesion implant coating

One method to increase the clinical success rate of metal implants is to increase their bone bonding properties, i.e. to develop a bone bioactive surface leading to reduced risks of interfacial problems. Much research has been devoted to modifying the surface of metals to make them become bioactive. Many of the proposed methods include depositing a coating on the implant. However, there is a risk of coating failure due to low substrate adhesion. This paper describes a method to obtain bioactivity combined with a high coating adhesion via a gradient structure of the coating. Gradient coatings were deposited on Ti (grade 5) using reactive magnetron sputtering with increasing oxygen content. To increase the grain size in the coating, all coatings were post annealed at 385 °C. The obtained coating exhibited a gradual transition over 70 nm from crystalline titanium oxide (anatase) at the surface to metallic Ti in the substrate, as shown using cross-section transmission electron microscopy and X-ray photoelectron spectroscopy depth profiling. Using scratch testing, it could be shown that the adhesion to the substrate was well above 1 GPa. The bioactivity of the coating was verified in vitro by the spontaneous formation of hydroxylapatite upon storage in phosphate buffer solution at 37 °C for one week.The described process can be applied to implants irrespective of bulk metal in the base and should introduce the possibility to create safer permanent implants like reconstructive devices, dental, or spinal implants.     

Surface chemistry of (2,4-dimethylpentadienyl)(ethylcyclopentadienyl)Ru on polycrystalline Ta

The adsorption and desorption of (2,4-dimethylpentadienyl)(ethylcyclopentadienyl)Ru [DER] on polycrystalline Ta have been studied by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). DER exposures to Ta at 140 K result in primarily molecular adsorption and desorption, while a minor surface reaction occurs at defect sites. Monolayer DER desorbs between 278 and 297 K with increasing coverage, exhibiting a first order, zero coverage desorption energy of 2.3 eV. Multilayer DER desorbs between 272 and 263 K, most likely with fractional order kinetics, and exhibits a zero coverage desorption energy of 0.9 eV. XPS Ru 3d binding energies increase with increasing coverage due to core hole screening in the monolayer regime and increasing sample charging as the DER overlayer becomes thicker in the multilayer regime. DER exhibits a three-dimensional (3D) “hit and stick” growth mode in which random 3D structures form due to the lack of adsorbate mobility at 140 K. DER exposures to Ta between 298 and 773 K result in minor decomposition resulting primarily in adsorbed hydrocarbon species on the surface. When the Ta is pre-covered with atomic iodine, DER dissociation is significantly decreased while adsorption is increased.     

Cu adsorption on pyrite (1 0 0): Ab initio and spectroscopic studies

Surface optimised S 2p photoelectron spectra show that both surface S²⁻ monomers and (S-S)²⁻ dimers are present at pyrite (1 0 0) fracture surfaces. In order to determine which sulfur species are involved in Cu adsorption, fresh pyrite surfaces were exposed to Cu²⁺ in solution. The S 2p spectra suggest that both types of S surface species are involved in the mechanism of Cu adsorption (activation). Ab initio density functional theory was used to model Cu adsorbed onto pyrite (1 0 0) to support the interpretation of the spectroscopy. Mulliken population analysis confirms the charge distribution suggested by the core line shifts as observed in the photoelectron spectra. The ab initio calculations were consistent with a two-coordinate bond between Cu(I), a surface S monomer and a surface S dimer.     

X-ray photoelectron spectroscopy study of the growth kinetics of biomimetically grown hydroxyapatite thin-film coatings

Hydroxyapatite (HA) thin-film coatings grown biomimetically using simulated body fluid (SBF) are desirable for a range of applications such as improved fixation of fine- and complex-shaped orthopedic and dental implants, tissue engineering scaffolds and localized and sustained drug delivery. There is a dearth of knowledge on two key aspects of SBF-grown HA coatings: (i) the growth kinetics over short deposition periods, hours rather than weeks; and (ii) possible difference between the coatings deposited with and without periodic SBF replenishment. A study centred on these aspects is reported. X-ray photoelectron spectroscopy (XPS) has been used to study the growth kinetics of SBF-grown HA coatings for deposition periods ranging from 0.5 h to 21 days. The coatings were deposited with and without periodic replenishment of SBF. The XPS studies revealed that: (i) a continuous, stable HA coating fully covered the titanium substrate after a growth period of 13 h without SBF replenishment; (ii) thicker HA coatings about 1 μm in thickness resulted after a growth period of 21 days, both with and without SBF replenishment; and (iii) the Ca/P ratio at the surface of the HA coating was significantly lower than that in its bulk. No significant difference between HA grown with and without periodic replenishment of SBF was found. The coatings were determined to be carbonated, a characteristic desirable for improved implant fixation. The atomic force and scanning electron microscopies results suggested that heterogeneous nucleation and growth are the primary deposition mode for these coatings. Primary osteoblast cell studies demonstrated the biocompatibility of these coatings, i.e., osteoblast colony coverage of approximately 80%, similar to the control substrate (tissue culture polystyrene).     

A study of Ga layers on Si(1 0 0)-(2 × 1) by SR-PES: Influence of adsorbed water

Results for deposition and thermal annealing of gallium on the Si(1 0 0)-(2 × 1) surface achieved by synchrotron radiation photoelectron spectroscopy (SR-PES) and low energy electron diffraction (LEED) are presented. In addition to deposition of Ga on a clean surface, the influence of water adsorption on the arrangement of gallium atoms was also studied. The results on Ga deposition at a higher temperature (490 °C) are consistent with a Ga ad-dimer model showing equivalent bond arrangement of all Ga atoms for coverages up to 0.5 ML. The deposition onto a surface with adsorbed water at room temperature led to a disordered gallium growth. In this case gallium atoms bind to silicon dimers already binding fragments of adsorbed water. A subsequent annealing of these layers leads to a surface structure similar to the Ga-(2 × 2), however, it is less ordered, probably due to the presence of silicon oxides formed from water fragments.     

Self-assembled organic templates for the selective adsorption of gold nanoparticles into confined domains

A simple procedure for the fabrication of submicron-sized functional organic templates is demonstrated. Native silicon samples are partially coated in millimolar octadecyltrichlorosilane (OTS) solutions. After coating, atomic force microscopy (AFM) reveals islands with diameters ranging from 0.6 to 1 μm. The hydrocarbon chains of the self-assembled silane entities within these islands subsequently are chemically functionalized following a robust preparation scheme. X-ray photoelectron spectroscopy (XPS) and water contact angle measurements were used for characterization. After functionalization, alkylsiloxane islands provide a versatile means to direct the deposition of nanoscopic components. In particular, citrate-stabilized gold nanoparticles (d = 16 ± 2 nm) are shown to selectively adsorb onto aminated islands, whereas adsorption on areas between these islands is negligible.     

Adsorption of 1,2-diaminoethane on ZnO thin films from p-xylene

The interaction of 1,2-diaminoethane (DAE) with ZnO thin films prepared by electrodeposition and magnetron sputtering was investigated by X-ray photoelectron spectroscopy (XPS). The samples were exposed to organic solution of 0.5 M DAE-p-xylene in an Ar atmosphere glove box (O₂ and H₂O <5 ppm), directly connected to the XPS analysis chamber by an anaerobic and anhydrous transfer system. A clear interaction of DAE with the ZnO surface is evidenced by the presence of a high intensity N1s peak at BE = 399.5 ± 0.2 eV and C1s at BE = 286.3 ± 0.2 eV which are attributed to C-N bonding. The atomic ratio C:N was very close to 1:1 consistent with the molecular, non-dissociative adsorption of DAE on the ZnO layer. No significant difference in adsorption of DAE was observed for three different ZnO surfaces despite slight differences in their acid/base properties as evidenced by the O/OH ratio. The results are interpreted in terms of adsorption on Brönsted acid sites. A uniform layer model was used to approximate the DAE film thickness, which was found to be around 10 Å on three studied samples. The N1s and C1s_B signals were observed to decrease on sample exposure to vacuum and/or X-ray irradiation and additional N1s_B peak appeared at lower binding energy at around 398.5 ± 0.2 eV. This is interpreted by the desorption and modification of DAE, indicating low stability of the adsorbed state on ZnO. The exposure to water of the sample with adsorbed DAE causes a significant decrease of the N1s_A and C1s_B peak intensities attributed to the adsorbed DAE molecule, demonstrating the instability of the DAE-ZnO interface in water.     

Photoelectron spectroscopy study of oxygen adsorption on Mo2C(0 0 0 1)

Oxygen adsorption on the α-Mo₂C(0 0 0 1) surface has been investigated with X-ray photoelectron spectroscopy and valence photoelectron spectroscopy utilizing synchrotron radiation. It is found that oxygen adsorbs dissociatively at room temperature, and the adsorbed oxygen atoms interact with both Mo and C atoms to form an oxycarbide layer. As the O-adsorbed surface is heated at ≧800 K, the C-O bonds are broken and the adsorbed oxygen atoms are bound only to Mo atoms. Valence PES study shows that the oxygen adsorption induces a peculiar state around the Fermi level, which enhances the emission intensity at the Fermi edge in PES spectra.     

Adsorption of octadecyltrichlorosilane on mesoporous SBA-15

Adsorption of octadecyltrichlorosilane (OTS) on mesoporous SBA-15 has been studied by using Brunauer-Emmett-Teller (BET) surface area analysis, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermo-gravimetric analysis (TGA) techniques. BET surface area analysis shows decrease of surface area from 930 to 416 m²/g after OTS adsorption. SEM pictures show close attachment of SBA-15 particles. EDAX measurements show increase of carbon weight percentage and decrease of oxygen and silicon weight percentage. XPS results closely support EDAX analysis. FTIR spectra shows presence of methyl (-CH₃) and methylene (-CH₂) bands and oriented OTS monolayer on SBA-15. Thermo-gravimetric analysis shows that the OTS adsorbed on SBA-15 are stable up to a temperature of 230 °C and that the OTS monolayers decompose between 230 and 400 °C.     

The catalytic reduction of NO by H2 on Ru(0 0 0 1): Observation of NHads species

Adsorption of NO and the reaction between NO and H₂ were investigated on the Ru(0 0 0 1) surface by X-ray photoelectron spectroscopy (XPS). Surface composition was measured after NO adsorption and after the selective catalytic reduction of nitric oxide with hydrogen in steady-state conditions at 320 K and 390 K in a 30:1 mixture of H₂ and NO (total pressure = 10⁻⁴ mbar). After steady-state NO reduction, molecularly adsorbed NO in both the linear on-top and threefold coordinations, NH_ads and N_ads species were identified by XPS. The coverage of the NH_ads and N_ads species was higher after the reaction at 390 K than the corresponding values at 320 K. Strong destabilisation of N_ads by O_ads was detected. A possible reaction mechanism is discussed.     

Coordination-dependent valence state of Sm adsorbed on Cu(1 0 0) and (1 1 0) studied by STM and XPS

Geometric and electronic structures of Sm adlayers on Cu(1 0 0) and (1 1 0) were studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). The present results, in addition to the previous results for Sm/Cu(1 1 1) [Y. Nakayama, H. Kondoh, T. Ohta, Surf. Sci. 552 (2004) 53], indicate that the valence state of Sm adsorbed on Cu surfaces is determined by Sm-Sm and Sm-Cu coordination numbers. We propose that the valence state of the adsorbed Sm atoms can be explained by a simple thermodynamic equation including the coordination numbers.