Polysaccharide surface engineering of poly(D, L-lactic acid) via electrostatic self-assembly technique and its effects on osteoblast growth behaviours

The objective of this study was to surface modify the poly (D, L-lactic acid) (PDLLA) films and assess the effects of the modified surfaces on the functions of osteoblasts cultured in vitro. A layer-by-layer (LBL) self assembly technique, was used leading to the formation of multilayers on the PDLLA film surfaces. Chitosan (Chi) and poly (styrene sulfonate, sodium salt) (PSS) were utilized as polycation and polyanion in this study, respectively. The layer structure was investigated by using X-ray photoelectron spectroscopy (XPS) and water contact angle measurement, respectively. XPS analysis displayed the presence of chitosan on PDLLA surface. A full coverage of coating with PSS/Chi layers was achieved on the PDLLA surface only after the deposition layers of PEI/(PSS/Chi)₂. These results showed that PDLLA films could be modified with PSS/Chi pairs which may affect the biocompatibility of the modified PDLLA films. To confirm this hypothesis, cell proliferation, cell viability as well as alkaline phosphtase activity of osteoblasts on layer-by-layer modified PDLLA films as well as control samples were investigated in vitro. The proliferation of osteoblasts on modified PDLLA films was found to be greater than that on control (p < 0.05 and p < 0.01) after 1, 4 and 7 days culture, respectively. Cell viability measurement showed that the PSS/Chi modified PDLLA films have higher cell viability (p < 0.01) than control. Osteoblast differentiation function (ALP) on LBL-modified PDLLA film was found significantly higher (p < 0.01) than that of virgin PDLLA films. These data suggests that PSS/Chi pair was successfully employed to surface modify PDLLA film via a layer-by-layer technique, and enhanced its cell biocompatibility.     

Surface modification of titanium substrates with silver nanoparticles embedded sulfhydrylated chitosan/gelatin polyelectrolyte multilayer films for antibacterial application

To develop Ti implants with potent antibacterial activity, a novel “sandwich-type” structure of sulfhydrylated chitosan (Chi-SH)/gelatin (Gel) polyelectrolyte multilayer films embedding silver (Ag) nanoparticles was coated onto titanium substrate using a spin-assisted layer-by-layer assembly technique. Ag ions would be enriched in the polyelectrolyte multilayer films via the specific interactions between Ag ions and –HS groups in Chi-HS, thus leading to the formation of Ag nanoparticles in situ by photo-catalytic reaction (ultraviolet irradiation). Contact angle measurement and field emission scanning electron microscopy equipped with energy dispersive X-ray spectroscopy were employed to monitor the construction of Ag-containing multilayer on titanium surface, respectively. The functional multilayered films on titanium substrate [Ti/PEI/(Gel/Chi-SH/Ag) _n /Gel] could efficiently inhibit the growth and activity of Bacillus subtitles and Escherichia coli onto titanium surface. Moreover, studies in vitro confirmed that Ti substrates coating with functional multilayer films remained the biological functions of osteoblasts, which was reflected by cell morphology, cell viability and ALP activity measurements. This study provides a simple, versatile and generalized methodology to design functional titanium implants with good cyto-compatibility and antibacterial activity for potential clinical applications.     

Corrosion resistance of biodegradable polymeric layer-by-layer coatings on magnesium alloy AZ31

Biocompatible polyelectrolyte multilayers (PEMs) and polysiloxane hybrid coatings were prepared to improve the corrosion resistance of biodegradable Mg alloy AZ31. The PEMs, which contained alternating poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH), were first self-assembled on the surface of the AZ31 alloy substrate via electrostatic interactions, designated as (PAH/PSS)₅/AZ31. Then, the (PAH/PSS)₅/AZ31 samples were dipped into a methyltrimethoxysilane (MTMS) solution to fabricate the PMTMS films, designated as PMTMS/(PAH/PSS)₅/AZ31. The surface morphologies, microstructures and chemical compositions of the films were investigated by FE-SEM, FTIR, XRD and XPS. Potentiodynamic polarization, electrochemical impedance spectroscopy and hydrogen evolution measurements demonstrated that the PMTMS/(PAH/PSS)₅/AZ31 composite film significantly enhanced the corrosion resistance of the AZ31 alloy in Hank’s balanced salt solution (HBSS). The PAH and PSS films effectively improved the deposition of Ca-P compounds including Ca₃(PO₄)₂ and hydroxyapatite (HA). Moreover, the corrosion mechanism of the composite coating was discussed. These coatings could be an alternative candidate coating for biodegradable Mg alloys.     

Effects of baicalin-modified poly(D,L-lactic acid) surface on the behavior of osteoblasts

In the present study, the functions of rat calvaria osteoblasts on baicalin-modified poly(D,L-lactic acid) (PDLLA) films were investigated in vitro. The surface characteristics of surfaces (both modified and control) were investigated by water contact angle measurement and electron spectroscopy for chemical analysis (ESCA). Cell morphologies on these surfaces were examined by scanning electron microscopy (SEM). Cell adhesion and proliferation were used to assess cell growth on the modified and control surfaces. The MTT assay was used to determine cell viability and alkaline phosphatase (ALP) activity was performed to evaluate differentiated cell function. Compared to control films, cell attachment of osteoblasts on baicalin-modified PDLLA film was significantly higher (P<0.05 and P<0.01) after 6 h and 8 h culture, and cell proliferation was also significantly greater (P<0.05 and P<0.01) at the end of 4th and 7th day, respectively. The MTT assay suggested that the cell viability of osteoblasts cultured on baicalin-modified PDLLA film was significantly higher (P<0.05) than that seeded on the control. Meanwhile, the ALP activity of osteoblasts cultured on modified films was also considerably enhanced (P<0.01) compared to that found on control. These results revealed that the biocompatibility PDLLA could be improved by surface modification with baicalin.     

Immobilization of poly (ethylene imine) on poly (l-lactide) promotes MG63 cell proliferation and function

Poly (ethylene imine) (PEI) is a polycation widely used for DNA transfection to cells but also applied as primary polycation for layer-by-layer (LBL) assembly of polyelectrolytes. The aim of the present study was to investigate the effect of modification with PEI on the biocompatibility of poly (l-lactide) (PLLA) films. PEI with different molecular weight was immobilized on PLLA by either adsorption or covalent binding. Cell morphologies, immuno-fluorescence staining, cell proliferation by lactate dehydrogenase assay and cell differentiation by alkaline phosphatase assay were utilized to assess the biocompatibility of the modified PLLA using osteoblast cell line MG63. Results revealed that PEI modification remarkably improved cell adhesion, viability, proliferation and function compared with plain PLLA. Hence, PEI-modified PLLA is acceptable as transfection vehicle for engineering of bone and other tissues, or as primary layer to allow LBL assembly to generate biomimetic surface coatings.     

Kinetics of Carbonization of Titanium Alloys in a Carbon-Oxygen-Containing Medium

We investigate the kinetics of saturation of surface layers of VT1-0 and OT4 titanium alloys in the process of carbonization from graphite in an atmosphere of argon at temperatures of 900 and 1000°C for 1–15 h. We revealed the formation of a deep hardened zone for long-holding times. The redistribution of oxygen in the case of dissociation of a surface oxide film promotes the formation of complex TiC _x O _y -type compounds based on titanium carbide, which additionally harden surface layers.     

Oxidation behavior of (Ti1 − xAlx)N films perpared by r.f. reactive sputtering

(Ti, Al)N films have drawn much attention as alternatives for TiN coatings, which are oxidized easily in air above 500 °C. We have investigated the effect of Al content on the oxidation resistance of (Ti_{1 − x}Al_x)N films prepared by r.f. reactive sputtering.(Ti_{1 − x}Al_xN films (O ≤ x ≤ 0.55) were deposited onto fused quartz substrates by r.f. reactive sputtering. Composite targets with five kinds of Al-to-Ti area ratio were used. The sputtering gas was Ar (purity, 5 N) and N₂ (5 N). The flow rate of Ar and N₂ gas was kept constant at 0.8 and 1.2 sccm, respectively, resulting in a sputtering pressure of 0.4 Pa. The r.f. power was 300 W for all experiments. Substrates were not intentionally heated during deposition. The deposited films (thickness, 300 nm) were annealed in air at 600 900 °C and then subjected to X-ray diffractometer and Auger depth profiling.The as-deposited (Ti_{1 − x}Al_x)N films had the same crystal structure as TiN (NaCl type). Al atoms seemed to substitute for Ti in lattice sites. The preferential orientation of the films changed with the Al content of the film, x. Oxide layers of the films grew during annealing and became thicker as the annealing temperature increased. The thickness of the oxide layer grown on the film surface decreased with increasing Al content in the film. For high Al content films an Al-rich oxide layer was grown on the surface, which seemed to prevent further oxidation. All of the films, however, were oxidized by 900 °C annealing, even if the Al content was increased up to 0.55.     

Using Graphene Oxide to Enhance the Barrier Properties of Poly(lactic acid) Film

The ultra‐thin (polyethyleneimine/graphene oxide)_n [(PEI/GO)_n]multilayer films on poly(lactic acid) (PLA) were constructed via the layer‐by‐layer assembly. Here, the electrostatic interactions between PEI and GO were used to obtain the nanoscale composite membrane of (PEI/GO)_n on the surface of PLA film. With the number of assembling layers increased, the oxygen permeability (PO₂) of PLA film decreased substantially. As a 0.06 wt% GO solution was used with only four layers, the PO₂ decreased from 53.8 to 0.377 × 10^?4 cm³/m²/d/Pa, only 0.7% of the original PLA film. At the same time, the coated PLA film also presented a good transparency and better mechanical properties. It is a novel way to use GO on biodegradable packaging materials. Copyright © 2014 John Wiley & Sons, Ltd.     

The microstructure and wettability of the TiOx films synthesized by reactive DC magnetron sputtering

Different chemical state of titanium oxide films were deposited on commercially pure Ti (CP Ti) by reactive DC magnetron sputtering under different oxygen flow rates to examine a possibility of their applications to endovascular stents. The chemical composition and crystal structure of the obtained films were analyzed by XPS and XRD, respectively. In dependence on the deposition parameters employed, the obtained films demonstrated different mixture of anatase TiO₂, Ti₂O₃, TiO and Ti. The wettability of the films was measured by the water contact angle variation. By formation of titanium oxide film on CP Ti, contact angle was decreased. In order to modify and control the surface wettability, the resultant TiO_x films were etched subsequently by different plasma. The wettability was influenced by etched process according to the decreased contact angle values of etched TiO_x film. Furthermore, TiO_x films became highly hydrophilic by ultraviolet (UV) irradiation, and returned to the initial relatively hydrophobic state by visible-light (VIS) irradiation. The wettability of the TiO_x film was enabled to convert between hydrophilic and hydrophobic reversibly by alternative UV and VIS irradiation. By adjusting deposition parameter and further modification process, the wettability of the TiO_x films can be changed freely in the range of 0–90°.     

Backscattering analysis of the successive layer structures of titanium silicides

Solid state reactions of titanium thin films with silicon and with SiO₂ were studied using a backscattering technique. For the Ti-Si system layers of TiSi₂, TiSi and Ti₅Si₃ were detected in the temperature range 500–600°C. For the Ti-SiO₂ system layers of TiO_x and Ti₅Si₃ were formed in the temperature range 700–900°C. At temperatures above 1000°C the oxygen in the film disappeared and silicon was found to reach the film surface. A surface structure of concentric circular rings was observed.     

Low-voltage characteristics of MgO-CaO films as a protective layer for AC plasma display panels by e-beam evaporation

The MgO-CaO composites films were prepared by e-beam evaporation to improve both operating voltages and memory coefficient of a protective layers for AC plasma display panels (PDPs). The effects of CaO addition to the conventional MgO films on both the electrical properties and the structural changes of the Mg_1–xCa_xO thin films deposited on the slide glass substrates were investigated. Atomic force microscopy (AFM) results revealed that the Mg_0.8Ca_0.2O film had a very rough surface due to the formation of a second phase on the surface. By adding controlled amount of CaO, the Mg-Ca-O films showed a firing voltage of 176 V that is lower than that of the conventional 100% MgO film. The deposition rates of 40–100 nm/min were obtained as a function of [CaO/(MgO+CaO)] ratio of the evaporation source materials.     

Effect of gallium on the electrical properties and photoresponse of CuIn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>2</Subscript> films

Semiconducting films of CuIn_{1 − x} Ga _x Se₂ solid solutions have been produced on CdS by selenizing metallic layers in flowing nitrogen. We have optimized the film growth conditions and investigated the structure, electrical properties, energy band structure, and photoconversion quantum efficiency of the films. With increasing gallium content, the band gap of the CuIn_{1 − x} Ga _x Se₂ (x = 0, 0.2, 0.25, 0.30) films increases, reaching 1.27 eV. The films are potentially attractive for use in high-efficiency solar cells.     

Distribution of interstitial impurities in titanium-vanadium alloys after holding in liquid lithium

The distribution of interstitial impurities between liquid lithium and solid titanium-alloyed vanadium is investigated. It is shown that titanium alloying of vandium intensifies nitrogen and carbon transport from lithium into the solid metal. At the same time, the concentration of oxygen in the surface layers of the specimens increases as a result of penetration of lithium and formation of complex oxides of the Me _x Li _y O _z type. Increase in the titanium content leads to an increase in the carbon concentration on the surface and to the formation of protective carbon films that inhibit the diffusion of interstitial impurities into deep-seated layers.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 5, pp. 56–60, September–October, 1993.     

On the mechanism of carbon monoxide oxidation on the surface of gold nanoclusters supported on titanium oxide

The process of carbon monoxide (CO) oxidation on the surface of a system comprising nanodimensional gold clusters deposited onto thin films of titanium oxide of variable stoichiometry formed on a Re(1000) single crystal surface has been studied by methods of thermodesorption, IR, and X-ray photoelectron spectroscopy. It is established that oxygen contained in titanium oxide plays an important role in the conversion of CO into CO₂. The efficiency of this process on the Au/TiO _x (x < 2) system surface is significantly higher that that on the Au/TiO₂ system.     

The effect of amorphous silicon capping on titanium during TiSi2 formation by RTA

Thin film reactions of the Ti/(1 0 0)Si structure and the amorphous-Si/Ti/(1 0 0)Si structure are performed by rapid thermal annealing (RTA) in argon at temperatures of 500–800° C. Auger depth profiling shows that the as-deposited titanium film of the Ti/(1 0 0)Si structure and the as-deposited amorphous silicon (a-Si) film of the a-Si/Ti/(1 0 0)Si structure exhibit a roughly exponential oxygen distribution decreasing from the surface when exposed to air. An electronic spectroscopy for chemical analysis (ESCA) shows that the oxygen in the a-Si film forms Si0₂ and the oxygen in the titanium film forms titanium oxide. For the Ti/(1 0 0)Si structure, the oxygen tends to be redistributed uniformly throughout the titanium film near the onset of silicide formation during RTA. As silicide formation progresses, the redistributed oxygen is snowplowed back toward the surface owing to oxygen solubility difference between Ti and TiSi₂. Consequently, the oxygen concentration in the unreacted titanium layer increases. This increased oxygen concentration retards the silicide growth even though there remains an unreacted titanium layer. The oxygen redistribution in the titanium film correlates well with the rapid increases in the sheet resistance near the onset of silicide formation. When a-Si is sputter-deposited sequentially on the titanium film without breaking the vacuum, the oxygen in a-Si is not redistributed during RTA. Thus there is no rapid increase in the sheet resistance, and the saturated sheet resistance is lower than that of Ti/(1 0 0)Si structure. The reason is that the conversion of deposited titanium film into TiSi₂ is made completely because the a-Si film on the titanium film prevents oxygen infiltration into the titanium film.     

Electrical and optical properties of reactive sputtered TiO x thin films for uncooled IR detector applications

Nanostructured titanium oxide (nano-TiO _x ) thin films for uncooled IR detectors were fabricated by dc reactive magnetron sputtering and post-deposition annealed in oxygen atmosphere. The crystalline structure and surface morphology were characterized by glancing incidence X-ray diffraction (GIXRD) and field emission scanning microscopy. The results of GIXRD measurements indicate that TiO _x thin film deposited at room temperature is amorphous. A mixture of anatase and rutile nanocrystalline structure phase were present in oxygen annealed TiO _x thin film. A weak absorption peak around 438 cm^?1 corresponding to Ti–O stretching vibration is observed by Fourier transform infrared spectroscopy with annealed TiO _x thin film. The X-ray photoelectron spectra reveals Ti³⁺ and Ti⁴⁺ ions are coexisting in TiO _x films. The optical spectra of the films indicate that the optical absorption edge of the nano-TiO _x film exhibits a red shift compared to the as-deposited film. Furthermore, compared to bulk TiO _x , a blue shift was observed in both of the deposited and annealed films due to quantum size effect. The dependence of resistivity on temperature reveals both the absolute value of temperature coefficient of resistivity (TCR) and activation energy of TiO _x thin film increase significantly after annealing in oxygen.     

Study of the polyelectrolyte multilayer thin films' properties and correlation with the behavior of the human gingival fibroblasts

The relation between fibroblast cell behavior and wettability parameters of different polyelectrolyte multilayers (PEM) was investigated. To this end, three types of film ending with polycations or polyanions were selected: poly(l-lysine)/poly(l-glutamic acid) (PGA/PLL)₅ and (PGA/PLL)₅–PGA, hyaluronan/PLL (HA/PLL)₅ and (HA/PLL)₅–HA, and poly(styrene sulfonate)/poly(allylamine hydrochloride) (PSS/PAH)₁₀ and (PSS/PAH)₁₀–PSS. The film roughness and thickness were measured by AFM and optical waveguide lightmode spectroscopy (OWLS). Surface free energy (SFE), polar (acid, basic and acid–basic) and dispersive components of SFE were determined using the Van Oss approach by dynamic contact angle (DCA) measurements. Cell adhesion was quantified by fluorescent labeling using an image analysis system. Cell morphology was analyzed by scanning electron microscopy (SEM) and phase contrast microscopy. Cell proliferation was followed over a seven day period. Fibroblast adhesion and proliferation were strongly dependent on film type. SEM observations of cells on the different films agreed with the proliferation and adhesion tests.     

Interface structure of sputter deposited CNx film on silicon substrate

Amorphous carbon nitride (CN_x, x = 0.05) films were reactively sputtered on Si(100) substrate, and the interface structure was studied by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). In cross-sectional TEM a gray interlayer about 5 nm thick between the bulk CN_x film and silicon substrate is observed, and the interface is dense. A little Si impurity (< 1 at.%) is revealed in the films deposited for short time (7 s and 17 s) by XPS measurement. The in-depth XPS analyses indicate that there exists an interlayer with Si impurity above, and a sub-surface layer with C and N below the original surface of silicon substrate. The two layers have different chemical composition and bonding state.     

Absorbing TiOx thin film enabling laser welding of polyurethane membranes and polyamide fibers

Abstract

We report on the optical properties of thin titanium suboxide (TiO_x) films for applications in laser transmission welding of polymers. Non-absorbing fibers were coated with TiO_x coatings by reactive magnetron sputtering. Plasma process parameters influencing the chemical composition and morphology of the deposited thin films were investigated in order to optimize their absorption properties. Optical absorption spectroscopy showed that the oxygen content of the TiO_x coatings is the main parameter influencing the optical absorbance. Overtreatment (high power plasma input) of the fiber surface leads to high surface roughness and loss of mechanical stability of the fiber. The study shows that thin substoichiometric TiO_x films enable the welding of very thin polyurethane membranes and polyamide fibers with improved adhesion properties.     

Nitridation of the sol-gel derived TiO2 coating films and the infrared ray reflection

The titanium nitride coating film was prepared on the SiO₂ glass substrate by ammonolysis of titanium dioxide coating film formed by sol-gel method. The X-ray diffraction (XRD) pattern indicated that it is cubic titanium nitride with a lattice parameter,a _o, of 0.4231 nm. The obtained titanium nitride is non-stoichiometric (TiN _x x≤ 1) because the value, 0.4231 nm, is smaller than the stoichiometric one (0.4240 nm). The coating film show very high infrared (i.r.) reflectance in the wavelength region of 2–8 μm.