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.     

Surface energy and mechanical behaviour of hardened cement paste

The Bangham equation indicates a direct proportionality between the length change of a porous body and a change of surface energy. In our experiments surface energy of hardened cement paste has been modified by desorbing or adsorbing water molecules. The internal pressure created by surface energy could be directly determined with the help of Mössbauer experiments. Based on these results it is possible to determine to what extent shrinkage or swelling is caused by a change of surface energy. Using Griffith's criterion our findings can explain quantitatively the decrease of stength as a function of increasing water content. Results are in good agreement with other methods of studying surface energy such as experiments to determine van der Waals forces.     

Surface modification of calcium fluoro and hydroxyapatite by 1-octylphosphonic dichloride

The reactivity of the surface of calcium hydroxyapatite (CaHAp) and fluorapatite (CaFAp) was tested and compared by grafting the 1-octylphosphonic dichloride (C₈H₁₇OPCl₂) using a molar ratio x = 2 or 4, x = n(organic)/n(apatite). Successful synthesis was confirmed by different characterisation techniques such as X-ray powder diffraction patterns, IR spectroscopy, MAS-NMR (¹H and ³¹P) and chemical analysis.The difference between their specific surface area (SSA: 57.46 for HAp and 12.09 m²/g for FAp), the percentage of carbon measured after treatment with (C₈H₁₇OPCl₂) and the intensities of IR bands attributed to the grafted moiety suggests that the surface of hydroxyapatite is more reactive than that of fluorapatite.The ³¹P CP-MAS-NMR spectra of treated fluorapatite show a significant change in isotropic signal due to the protonation and deprotonation of superficial phosphate group. This can be explained by the difference in the nature of inorganic material.     

Enhanced in vitro biocompatibility of ultrafine-grained titanium with hierarchical porous surface

Bulk ultrafine-grained Ti (UFG Ti) was successfully fabricated by equal-channel angular pressing (ECAP) technique in the present study, and to further improve its surface biocompatibility, surface modification techniques including sandblasting, acid etching and alkali treatment were employed to produce a hierarchical porous surface. The effect of the above surface treatments on the surface roughness, wettability, electrochemical corrosion behavior, apatite forming ability and cellular behavior of UFG Ti were systematically investigated with the coarse-grained Ti as control. Results show that UFG-Ti with surface modification had no pitting corrosion and presented low corrosion rate in simulated body fluids (SBF). The hierarchical porous surface yielded by surface modification enhanced the ability of UFG Ti to form a complete apatite layer when soaked in SBF and promoted osteoblast-like cells attachment and proliferation in vitro, which promises to have a significant impact on increasing bone-bonding ability and reducing healing time when implanted due to faster tissue integration.     

Microstructure and texture of cementitious porous materials

We have characterized the microstructure of different cementitious materials (white and Portland cement pastes, mortars, concretes) by different magnetic resonance techniques. In particular, we show how the measurement of proton nuclear magnetic spin-lattice relaxation as a function of magnetic field strength (and hence nuclear Larmor frequency) can provide reliable information on the dynamics of proton species at the surface of CSH, the specific surface area and the pore size distribution throughout the progressive hydration of cement-based materials. The measurement does not require any drying temperature modification and is sufficiently fast to be applied continuously during the progressive hydration of the material. Coupling this method with the standard proton nuclear spin relaxation and high-resolution NMR allows us to follow the development of microscale texture within the material.     

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.     

Preparation and in vitro characterization of aerosol-deposited hydroxyapatite coatings with different surface roughnesses

Hydroxyapatite (HA) coatings with different surface roughnesses were deposited on a Ti substrate via aerosol deposition (AD). The effect of the surface roughness on the cellular response to the coating was investigated. The surface roughness was controlled by manipulating the particle size distribution of the raw powder used for deposition and by varying the coating thickness. The coatings obtained from the 1100 °C-heated powder exhibited relatively smooth surfaces, whereas those fabricated using the 1050 °C-heated powder had network-structured rough surfaces with large surface areas and were superior in terms of their adhesion strengths and in vitro cell responses. The surface roughness (R_a) values of the coatings fabricated using the 1050 °C-heated powder increased from approximately 0.65 to 1.03 μm as the coating thickness increased to 10 μm. The coatings with a rough surface had good adhesion to the Ti substrate, exhibiting high adhesion strengths ranging from 37.6 to 29.5 MPa, depending on the coating thickness. The optimum biological performance was observed for the 5 μm-thick HA coating with an intermediate surface roughness value of 0.82 μm.     

Investigation of surface properties of liquid transition metals: Surface tension and surface entropy

In the present study, surface properties namely surface tension and surface entropy of liquid transition metals have been reported. The surface entropy of liquid Fe, Co and Ni metals has been investigated using the expression derived by Gosh et al. [R.C. Gosh, A.Z. Ziauddin Ahmed, G.M. Bhuiyan, Eur. Phys. J. B 56 (2007) 177]. To describe interionic interaction the pseudopotential approach has been used and radial distribution functions have been determined from the solution of Ornstein-Zernike integral equation. The calculated values of surface tension and surface entropy agree well with experiment. The present study shows that the expression derived by Gosh et al. leads to a good estimation for the surface entropy.     

Effect of electrodeposition modes on surface characteristics and corrosion properties of fluorine-doped hydroxyapatite coatings on Mg-Zn-Ca alloy

The microstructure, morphology and composition highly determine the corrosion resistance and bioactivity of coating. In traditional cathodic electrodeposition process, because of the unfavorable effects of the polarization of concentration difference and H₂ evolution, fluorine-doped hydroxyapatite coating was loose and porous. This coating could not ensure the long-term stability of the Mg alloy implants. In order to improve the corrosion resistance and bioactivity of coating, pulse electrodeposition and H₂O₂ were introduced into the electrodeposition to deposit fluorine-doped hydroxyapatite coating. As a comparative study, microstructure, corrosion resistance properties and bioactivity of traditional cathodic electrodeposition coating and pulse electrodeposition coating were investigated, respectively. The results revealed that nano fluorine-doped hydroxyapatite coating could be prepared by pulse electrodeposition, and the coating was dense and uniform. The potentiodynamic polarization experiment indicated that the dense and uniform coating could effectively protect Mg alloy substrate from corrosion. Immersion testing was performed in simulated body fluid. It was found that pulse electrodeposition coating could more effectively induce the precipitation of Mg²⁺, Ca²⁺ and PO₄³⁻ in comparison with traditional cathodic electrodeposition coating, because the nano phase had comparatively high specific surface area. Thus magnesium alloy coated with fluorine-doped nano-hydroxyapatite coating may be a promising candidate as biodegradable bone implants, and was worthwhile to further investigate the in vivo degradation behavior.     

Microstructure and surface morphology of YSZ thin films deposited by e-beam technique

In present study yttrium-stabilized zirconia (YSZ) thin films were deposited on optical quartz (amorphous SiO₂), porous Ni-YSZ and crystalline Alloy 600 (Fe-Ni-Cr) substrates using e-beam deposition technique and controlling technological parameters: substrate temperature and electron gun power which influence thin-film deposition mechanism. X-ray diffraction, scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to investigate how thin-film structure and surface morphology depend on these parameters. It was found that the crystallite size, roughness and growth mechanism of YSZ thin films are influenced by electron gun power. To clarify the experimental results, YSZ thin-film formation as well evolution of surface roughness at its initial growing stages were analyzed. The evolution of surface roughness could be explained by the processes of surface mobility of adatoms and coalescence of islands. The analysis of these experimental results explain that surface roughness dependence on substrate temperature and electron gun power non-monotonous which could result from diffusivity of adatoms and the amount of atomic clusters in the gas stream of evaporated material.     

Determination of absorption length of CO2 and high power diode laser radiation for ordinary Portland cement and its influence on the depth of melting

The laser beam absorption lengths of CO₂ and a high power diode laser (HPDL) radiation for concrete have been determined. By employing Beer–Lambert’s law the absorption lengths for concrete of CO₂ and a HPDL radiation were 470±22 μm and 177±15 μm, respectively. Indeed, this was borne out somewhat from a cross-sectional analysis of the melt region produced by both lasers which showed melting occurred to a greater depth when the CO₂ laser was used.     

Influence of surface topography and pore architecture of alkali-treated titanium on in vitro apatite deposition

Alkali-treated titanium surfaces have earlier shown to induce bone-like apatite deposition. In the present study, the effect of surface topography of two-dimensional and pore architecture of three-dimensional alkali-treated titanium substrates on the in vitro bioactivity was investigated. Titanium plates with a surface roughness of R_a = 0.13 μm, 0.56 μm, 0.83 μm, and 3.63 μm were prepared by Al₂O₃ grit-blasting. Simple tetragonal and face-centered Ti6Al4V scaffolds with spatial gaps of 450-1100 μm and 200-700 μm, respectively, were fabricated by a three-dimensional fiber deposition (3DFD) technique. After alkali treatment, the titanium plates with a surface roughness of R_a = 0.56 μm were completely covered with hydroxyapatite globules after 7 days in simulated body fluid (SBF), while the coverage of the samples with other surface roughness values remained incomplete. Similarly, face-centered Ti₆Al₄ scaffolds with spatial gaps of 200-700 μm exhibited a full surface coverage after 21 days in SBF, while simple tetragonal scaffolds with spatial gaps of 450-1100 μm were only covered for 45-65%. This indicates the importance of surface topography and pore architecture for in vitro bioactivity.     

A 43Ca and 13C NMR study of the chemical interaction between poly(ethylene-vinyl acetate) and white cement during hydration

⁴³Ca and ¹³C NMR methods were used to study the chemical interaction of poly(ethylene–vinyl acetate) (PEVAc) admixture in commercial-grade white cement. From ⁴³Ca NMR it is shown both that PEVAc induces modest changes in the hydrated cement structure, and that hydrated commercial cement is significantly more complex than models that have been used for its structure in past work. The ¹³C NMR results show that the PEVAc hydrolysis occurs early in the cement hydration acceleration period, with a rate well-fit by an exponential decay using a time constant of 6±1 days.     

Influence of the hydrothermal temperature and pH on the crystallinity of a sputtered hydroxyapatite film

Hydroxyapatite (HA) was coated onto titanium substrates using radio frequency sputtering, and the sputtered films were crystallized under hydrothermal conditions at 110-170 °C at pH values of 7.0 and 9.5. The crystallite size, the remnant film thickness, and the surface morphology of the films were observed using X-ray diffraction, energy dispersive X-ray spectroscopy, and scanning electron microscopy, respectively.The crystallite size increased with the process temperature, and reached 123.6 nm (pH 9.5 and 170 °C) after 24 h. All of the crystallite sizes of the film treated at pH 9.5 were higher than those treated at pH 7.0 at each process temperature. The film treated at pH 9.5 retained more than 90% of the initial film thickness at any process temperature. The ratio of the film treated at pH 7.0 did not reached 90% at less than 150 °C, and tended to increase with the process temperature.     

Fabrication of hydroxyapatite and TiO2 nanorods on microarc-oxidized titanium surface using hydrothermal treatment

AC-type microarc oxidation (MAO) and hydrothermal treatment techniques were used to enhance the bioactivity of commercially pure titanium (CP-Ti). The porous TiO₂ layer fabricated by the MAO treatment had a dominant anatase structure and contained Ca and P ions. The MAO-treated specimens were treated hydrothermally to form HAp crystallites on the titanium oxide layer in an alkaline aqueous solution (OH-solution) or phosphorous-containing alkaline solution (POH-solution). A small number of micro-sized hydroxyapatite (HAp) crystallites and a thin layer composed of nano-sized HAps were formed on the Ti-MAO-OH group treated hydrothermally in an OH-solution, whereas a large number of micro-sized HAp crystallites and dense anatase TiO₂ nanorods were formed on the Ti-MAO-POH group treated hydrothermally in a POH-solution. The layer of bone-like apatite that formed on the surface of the POH-treated sample after soaking in a modified simulated body fluid was thicker than that on the OH-treated samples.     

多晶硅表面周期性微结构的激光制备与性能研究

为了减小多晶硅表面入射光的反射率,提高太阳能电池的光电效率,利用紫外纳秒激光器在多晶硅表面制备不同深度、不同间距的微凹坑点阵绒面,研究织构形貌对反射率及光电转换效率的影响.通过激光频率的改变实现微凹坑深度的变化,通过微凹坑排布方式的改变实现微凹坑间距的变化;使用光纤光谱仪测量多晶硅表面反射率并通过激光共聚焦显微镜观察微...     

The effects of process gas type on the surface condition of high-power diode laser-treated ordinary Portland cement

This paper examines the effects of using O₂, Ar and He process gasses during the treatment of the ordinary Portland cement (OPC) surface of concrete with a high-power diode laser (HPDL). The study revealed that, depending on the shield gas used, distinct difference existed in the surface condition of the concrete after HPDL treatment. In particular, the use of O₂ as the shield gas was seen to result in glazes with far fewer microcracks and porosities than those generated with either Ar or He shield gases. Such differences were found to be due to the smaller O₂ gas molecules dissolving molecularly into the open structure of the HPDL-generated glaze on the OPC surface of concrete and react with the glass network to increase the fluidity of the melt. This in turn was also seen to affect the cooling rate and therefore the tendency to generate microcracks.     

Effect of laser-remelting of surface cracks on microstructure and residual stresses in 12Ni maraging steel

The paper presents the results of a study on possible application of laser-remelting to repair of narrow and comparatively deep cracks at the surface of highly thermo-mechanically loaded parts made of 12% Ni hot-working maraging tool steel. Laser-remelting of maraging steel is, due to very good weldability and flexibility of the process, very prospective for repair of fatigued surfaces of parts made of this steel at which the presence of surface microcracks may be observed. In addition to the efficiency of crack remelting, the influence of laser-remelting on the heat-affected zone in terms of its microstructure and residual stresses was also studied. The microstructure in the laser-remelted track is cellular/dendritic. In the heat-affected zone surrounding the laser-remelted track, the microstructure varies considerably. A microstructure analysis revealed, in the heat-affected zone, five microstructural zones and sub-zones. Residual stresses measured after laser-remelting are with reference to gradual through-depth changing of the stresses favourable.     

Nanoscale characterization of the interface between bone and hydroxyapatite implants and the effect of silicon on bone apposition

Silicon plays an important role in bone mineralization and formation and is therefore incorporated into a wide variety of medical implants and bone grafts used today. The significance of silicon (Si) can be understood through an analysis of the mechanisms of bone bonding to calcium containing biomaterials and through comparisons of hydroxyapatite (HA) and silicon-substituted hydroxyapatite (Si–HA). The addition of Si to HA causes a decrease in grain size that subsequently affects surface topography, dissolution–reprecipitation rates and the bone apposition process. Through the use of high-resolution transmission electron microscopy (HR-TEM) studies, the interactions between bone and silicon hydroxyapatite (Si–HA) at interfaces are reviewed and related to their impact on bone apposition and ultimately the performance of medical implants.     

Microstructure performance and formation mechanism of laser alloying rare earth oxides modified nanocrystalline layer on TA7

Nanoscale particles (NP) were observed in a Ni60–Ag–Si₃N₄–Y₂O₃ laser alloying (LA) layer on a TA7 titanium alloy, NP usually locate on the grain boundaries, which are able to block the motion of dislocation in a certain extent. Such layer mainly consisted of γ-Ni, TiN, γ-(Fe, Ni), TiAg and lots of amorphous phases. The wear resistance of such layer with laser scanning speed 3 mm/s was better than that of a LA layer with 6 mm/s, which was mainly ascribed to an uniform microstructure and less defect of layer. The high laser scanning speed made the existing time of laser molten pool be shorter than before, favoring the formation of a fine microstructure. However, the defects, such as pores were produced in LA layer (higher scanning speed), decreasing the wear resistance.