Cell-selective titanium oxide coatings mediated by coupling hafnium-doping and UV pre-illumination

Cell-selective biomaterials, i.e. favoring the functions of gingival cells and simultaneously reducing the adhesion of pathogenic bacteria, is highly desired in dental implants. However, due to the same mechanisms shared in attachment by mammalian and microbial cells, it is hard to increase the functions of the former while acting against the latter. Herein, a cell-selectivity was established on titanium oxide coatings by combining a plasma immersion ion implantation & deposition (PIII) and a UV pre-illumination. The titanium oxide coatings were produced on pure titanium substrates by using a plasma electrolytic oxidation technique and then doped of hafnium (Hf) by using a cathodic arc sourced PIII. The Hf-doped titanium oxide coatings (Hf-PIII groups) were capable of delaying the recombination of UV-illumination generated electron-hole pairs, which decreased the adhesion of bacterial cells at the later period (cultured for 24 h). Titanium oxide coating doped of 4.87 at.% hafnium (Hf) gained the biggest decrease (decreased 52.9% compared to its UV negative counterparts) in bacterial adhesion among the UV positive (UV⁺) groups. This study demonstrates that coupling Hf-doping and UV pre-illumination is promising for improving the cell-selective performance of titanium-based dental implants.     

Fibronectin adsorption on titanium surfaces and its effect on osteoblast precursor cell attachment

The objective of this study was to investigate the adsorption of fibronectin on titanium (Ti) surfaces and the effect of pre-adsorbed fibronectin on osteoblast precursor cell attachment in vitro. Two different concentrations of bovine fibronectin were used in this study. Protein adsorption on Ti surfaces was analyzed using the micro bicinchoninic acid (BCA) protein assay. Cell concentration on Ti and fibronectin pre-adsorbed Ti surfaces after 3 h incubation was analyzed using the Vybrant™ cell adhesion assay. Cell morphology on Ti and fibronectin pre-adsorbed Ti surfaces was observed using scanning electron microscopy (SEM). After 180 min incubation, maximum adsorption of bovine fibronectin on Ti surfaces was observed. Fibronectin adsorption on Ti surfaces was observed to be significantly dependent on the initial concentration and the amount of incubation time. In the presence of 1 mg/ml fibronectin pre-adsorbed on Ti surfaces after 15 min, osteoblast precursor cell attachment on Ti surfaces was observed to be enhanced compared with control Ti surfaces, Ti surfaces pre-adsorbed with 1 mg/ml fibronectin for 180 min, and Ti surfaces pre-adsorbed with 0.1 mg/ml fibronectin for 15 and 180 min. No significant difference in cell attachment was observed between control Ti surfaces, Ti surfaces pre-adsorbed with fibronectin for 180 min, and Ti surfaces pre-adsorbed with 0.1 mg/ml fibronectin for 15 and 180 min. In addition, no differences in cell morphology of the attached osteoblast precursor cells on control Ti surfaces and Ti surfaces pre-adsorbed with fibronectin were observed in this study. It was concluded that an optimum concentration of adsorbed fibronectin on Ti surfaces plays an important role in governing cell attachment.     

Particle-collision and porogen-leaching technique to fabricate polymeric porous scaffolds with microscale roughness of interior surfaces

A facile technique is herein reported to fabricate three-dimensional(3D) polymeric porous scaffolds with interior surfaces of a topographic microstructure favorable for cell adhesion.As demonstration,a well-known biodegradable polymer poly(lactide-co-glycolide)(PLGA) was employed as matrix.Under the porogen-leaching strategy,the large and soft porogens of paraffin were modified by colliding with small and hard salt particles,which generated micropits on the surfaces of paraffin spheres.The eventual PLGA scaffolds after leaching the modified porogens had thus interior surfaces of microscale roughness imprinted by those micropits.The microrough scaffolds were confirmed to benefit adhesion of bone marrow stromal cells(BMSCs) of rats and meanwhile not to hamper the proliferation and osteogenic differentiation of the cells.The insight and technique might be helpful for biomaterial designing in tissue engineering and regenerative medicine.     

Nanoscale topography reduces fibroblast growth, focal adhesion size and migration-related gene expression on platinum surfaces

Controlling cellular responses on biomaterial surfaces is crucial in biomedical applications such as tissue engineering and implantable prosthetics. Since cells encounter various nanoscale topographic features in their natural environment, it has been postulated that surface nanotopography may be an alternative route to fabricate biomaterials with a desirable cellular response. In this framework, we investigated the responses of primary human fibroblasts to platinum substrates with different levels of surface roughness at the nanoscale. The nanorough surfaces were fabricated by using the glancing angle deposition technique (GLAD). We found that levels of cellular responses depended on the surface roughness and the size of the nanoscale features. We showed that in response to nanotopography cells spread less and have an elongated morphology, displaying signs of actin cytoskeleton impairment and reduced formation of focal adhesion complexes. Although cell growth and adhesion were impaired on the nanorough substrates, cell viability was not affected by topography. To a minor extent our results also indicate that cell migration might be reduced on the nanorough surfaces, since a significantly lower gene expression of migration related genes were found on the roughest surfaces as compared to the flat reference. The results presented here demonstrate that surface nanotopography influences fibroblasts responses on platinum, which may be used to reduce cellular adhesion on platinum implant surfaces such as implantable neural electrodes.     

Mucin coating on polymeric material surfaces to suppress bacterial adhesion

Mucin, a group of large glycoproteins, constitutes one of the major components of mucous which covers the lumenal surfaces of epithelial organs and serves as a physical barrier between the extracellular milieu and the plasma membrane. The molecules have a generic structure consisting of a thread-like peptide backbone with densely packed carbohydrate side chains. Protein and carbohydrate contents are about 30 and 50%, respectively. On hydrophobic materials in aqueous environments the naked parts of mucin’s protein backbone will adhere due to their hydrophobicity, while the carbohydrate side chains are thought to orient themselves away from the surface. This gives the mucin molecules their unique properties as surfactants, i.e. they tend to adsorb to hydrophobic surfaces via protein-surface interactions while they hold water molecules via their hydrophilic oligosaccharide clusters. In the present work, bovine submaxillary gland mucin (BSM) is purified by SEC and subsequently characterized with PAGE. Four polymeric materials, PMMA, silicone, Tecoflex® polyurethane and polystyrene, are selected as coating targets. Contact angle measurements show significant changes in these materials after coating with BSM. Surface concentrations of adsorbed BSM are determined by amino acid analysis and found to correlate well with observed reductions in contact angle. Both Staphylococcus aureus and CNS S. epidermidis are used to contaminate uncoated and BSM coated surfaces of all four materials, demonstrating a correlation between suppression of bacterial adhesion and surface concentration of BSM. Thus, bacterial counts on the coated PMMA, PS, PU and silicone specimens amount to ≈3, 10, 8 and 30% of the counts found on their uncoated counterparts. These results suggest that mucin coatings could profitably be employed to reduce the risk of microbial infections on polymeric biomaterials.     

Corrosion resistance and bioactivity of titanium after surface treatment by three different methods: ion implantation,alkaline treatment and anodic oxidation

The paper compares the effects of various surface modifications, ion implantation, alkaline treatment and anodic oxidation, upon the corrosion resistance and bioactivity of titanium. The chemical composition of the surface layers thus produced was determined by XPS, SIMS and EDS coupled with SEM. The structure of the layers was examined by TEM, and their phase composition by XRD. The corrosion resistance was determined by electrochemical methods after the samples were exposed to the test conditions for 13 h. The bioactivity of titanium was evaluated in a simulated body fluid at a temperature of 37°C after various exposure time.     

Albumin adsorption on unmodified and sulfonated polystyrene surfaces, in relation to cell-substratum adhesion

Albumin is commonly applied for blocking the adsorption of other proteins and to prevent the nonspecific adhesion of cells to diverse artificial substrata. Here we address the question of how effective these albumin properties are--by investigating unmodified and sulfonated polystyrene substrata with distinctly different wettabilities. As clearly shown with (125)I-radioisotopic assays, above a concentration of 10-20 μg/mL, the efficiency of bovine serum albumin (BSA) adsorption became markedly higher on the sulfonated surface than on the unmodified one. This study was assisted with the atomic force microscopy. On the unmodified surface, BSA, adsorbed from sufficiently concentrated solutions, formed a monolayer, with occasional intrusions of multilayered patches. Conversely, the arrangement of BSA on the sulfonated surface was chaotic; the height of individual molecules was lower than on the unmodified polystyrene. Importantly, the adhesion study of LNCaP and DU145 cells indicated that both surfaces, subjected to the prior BSA adsorption, did not completely loose their cell-adhesive properties. However, the level of adhesion and the pattern of F-actin organization in adhering cells have shown that cells interacted with unmodified and sulfonated surfaces differently, depending on the arrangement of adsorbed albumin. These results suggest the presence of some bare substratum area accessible for cells after the albumin adsorption to both types of investigated surfaces.     

Synthesis and characterisation of titanium pyridine- and pyrimidine-thiolates and their application as precursors to titanium disulfide

The reaction of TiCl₄ with pyridine- and pyrimidine-thiol has been investigated. Reaction of TiCl₄ with 3 equiv. of 2-mercaptopyridine and 3 equiv. of tert-butylpyridine in toluene at room temperature resulted in the formation of the tris(pyridine-2-thiolate) complex [TiCl(SC₅H₄N)₃] (1). The related reaction between TiCl₄ with 3 equiv. of 2-mercaptopyrimidine and 3 equiv. of tert-butylpyridine in toluene at room temperature resulted in the isolation of the complex [TiCl(SC₄H₃N₂)₃] (2). Compound 2 has been characterised by X-ray crystallography. Low pressure CVD of 1 and 2 produced brown/gold films of TiS₂/TiO₂ on glass substrates at 550 and 600 °C.     

Fabrication and biocompatibility of cell outer membrane mimetic surfaces

The surface design used for improving biocompatibility is one of the most important issues for the fabrication of medical devices.For mimicking the ideal surface structure of cell outer membrane,a large number of polymers bearing phosphorylcholine(PC) groups have been employed to modify the surfaces of biomaterials and medical devices.It has been demonstrated that the biocompatibility of the modified materials whose surface is required to interact with a living organism has been obviously improved by introducing PC groups.In this review,the fabrication strategies of cell outer membrane mimetic surfaces and their resulted biocompatibilities were summarized.     

A potential flower-like coating consisting of calcium-phosphate nanosheets on titanium surface

A potential calcium-phosphate fl ower-like nanocoating were coated onto the titanium surface in an easy approach. It has high surface area, low cytotoxicity as well as promising cell affi nity, which makes it a potential alternative modifi cation method for titanium surface.     

Formation and recovery of a cell sheet by a particle monolayer with the surface roughness

We studied the topographical effect of roughness displayed by a closely packed particle monolayer on formation of a cell monolayer (cell sheet). Particle monolayers were prepared by Langmuir-Blodgett deposition using particles, which were 527nm (SA053) and 1270nm (SA127) in diameter. Human umbilical vein endothelial cells (HUVECs) were seeded at a high density (2.0 x10(5)cells/cm(2)) onto particle monolayers. It was found that cells gradually became into contact with adjacent cells on the SA053 monolayer and the formed cell sheet could be readily detached from the particle monolayer by gentle pipetting. On the other hand, cells adhering onto the tissue culture polystyrene (TCPS) and the SA127 particle monolayer were difficult to peel off. At a low cell seeding density (5.0x10(4)cells/cm(2)), pre-coating with bovine plasma fibronectin (FN) allowed cell growth on an SA053 particle monolayer, and a confluent monolayer was able to be peeled as a cell sheet from the particle monolayer just by pipetting. By immunostaining of human fibronectin, we found that fibronectin was secreted and concentrated onto the substrate side of a cell sheet. The obtained cell sheet adhered and grew on the TCPS again within 20min.     

Effect of preparative conditions on the surface characteristics of mixed zirconium and titanium oxides

The surface characteristics of mixed zirconium and titanium oxides prepared from different starting materials are investigated. One mode of preparation entailed the use of zirconium sulfate and titanium oxysulfate as starting materials and ammonium hydroxide as precipitating agent. The produced oxides were washed to different extents to obtain samples with different sulfate content. A second preparative mode used zirconium oxychloride and titanous chloride as starting materials also with ammonium hydroxide as precipitating agent. The oxidation of the titanous to the titanic form for these oxides was carried out by means of oxygen gas. Resulting samples were heat treated at 400 °C and 600 °C, and textural characteristics determined from the adsorption of N₂ at 77 K, complemented by infrared and thermal studies. The samples precipitated from the oxychloride and chloride salts of zirconium and titanium, as well as those precipitated from the sulfate and oxysulfate salts and washed free of the sulfate ions displayed quite similar textural characteristics. The unheated samples and those heat-treated at 400 °C were mesoporous, with some microporosity, and relatively large surface areas in the order of 200–300 m²/g. Heat treatment to 600 °C led to a relative decrease in surface area, in the order of 100 m²/g, and to the disappearance of microporosity. The mixed zirconium and titanium oxides with a sulfate content of ≈17% displayed significantly lower surface areas, smaller than 10 m²/g, with a prevalence of micro and mesoporosity. Infrared and thermal studies indicated the presence of differently bounded sulfato groups, which seem to have a blocking effect on the pores, resulting in the observed smaller surface areas.     

Subcellular topological effect of particle monolayers on cell shapes and functions

We studied topological effects of subcellular roughness displayed by a closely packed particle monolayer on adhesion and growth of endothelial cells. Poly(styrene-co-acrylamide) (SA) particles were prepared by soap-free emulsion copolymerization. Particle monolayers were prepared by Langmuir–Blodgett deposition using particles, which were 527 (SA053) and 1270 nm (SA127) in diameter. After 24-h incubation, cells tightly adhered on a tissue culture polystyrene dish and randomly spread. On the other hand, cells attached on particle monolayers were stretched into a narrow stalk-like shape. Lamellipodia spread from the leading edge of cells attached on SA053 monolayer to the top of the particles and gradually gathered to form clusters. This shows that cell–cell adhesion became stronger than cell–substrate interaction. Cells attached to SA127 monolayer extended to the reverse side of a particle monolayer and engulfed particles. They remained immobile without migration 24 h after incubation. This shows that the inhibition of extensions on SA127 monolayer could inhibit cell migration and cell proliferation. Cell growth on the particle monolayers was suppressed compared with a flat TCPS dish. The number of cells on SA053 gradually increased, whereas that on SA127 decreased with time. When the cell seeding density was increased to 200,000 cells cm⁻², some adherent cells gradually became into contact with adjacent cells. F-actin condensations were formed at the frame of adherent cells and the thin filaments grew from the edges to connect each other with time. For the cell culture on SA053 monolayer, elongated cells showed a little alignment. Cells showed not arrangement of actin stress fibers but F-actin condensation at the contact regions with neighboring cells. Interestingly, the formed cell monolayer could be readily peeled from the particle monolayer. These results indicate that endothelial cells could recognize the surface roughness displayed by particle monolayers and the response was dependent on the pitch of particle monolayers.     

Efficient hydrophobization and solvent microextraction for determination of trace nano-sized silver and titanium dioxide in natural waters

Hydrophobic silver and titanium (IV) oxide nanoparticles (commercial Ag and TiO₂ NPs with average particle sizes of 17 and 19 nm, respectively) were quantitatively transferred into organic phase in natural water samples. Five NP surface modification and solvent extraction agents (reagents) types, mercaptocarboxylic acid, alkylamine, mediator solvent, extraction solvent, and surfactant, were investigated and optimized with three-level orthogonal array design (OAD), an OA₂₇ (3¹³) matrix. The most favorable reagents and experimental conditions were then examined. The best extraction efficiencies of 78.6 and 73.7% were obtained for 1 mg L⁻¹ citrate-stabilized Ag and TiO₂ NPs, respectively, with 0.5 mM of 11-mercaptoundecanoic acid, 1.5 mM of octadecylamine, 1 mL of methanol, 150 μL of cyclohexane, 0.05 mM of tetra-n-octylammonium bromide, pH = 8.0, adsorption time of 2 h, sonication time of 3 min, and centrifugation time of 10 min. Enrichment factors were 97 and 83, for Ag and TiO₂ NPs, respectively. The optimum extraction conditions were successfully applied to genuine water samples at spiking levels of 2–100 μg L⁻¹ of Ag and TiO₂ NPs. The relative recoveries of (69.0–85.1)% and (61.5–78.5)% were obtained for Ag and TiO₂ NPs, respectively. The extracted surface-modified NPs were characterized with transmission electron microscopy, selected area electron diffraction, energy-dispersive X-ray, ultraviolet–visible, and Fourier transform infrared spectroscopic techniques. Based on the results, efficient ligand exchange and acid–base pair formation were observed on the NP surface without significant change in its original properties. The organic phase was microwave digested, and analyzed with inductively coupled plasma (ICP) optical emission spectroscopy and ICP mass spectrometry (ICP-MS). Detection limits of ICP-MS analyses of Ag and TiO₂ NPs were 0.02 and 0.07 μg L⁻¹, respectively.     

Spectral force analysis using atomic force microscopy reveals the importance of surface heterogeneity in bacterial and colloid adhesion to engineered surfaces

Coatings developed to reduce biofouling of engineered surfaces do not always perform as expected based on their native properties. One reason is that a relatively small number of highly adhesive sites, or the heterogeneity of the coated surface, may control the overall response of the system to initial bacterial deposition. It is shown here using an approach we call spectral force analysis (SFA), based on force volume imaging of the surface with atomic force microscopy, that the behavior of surfaces and coatings can be better understood relative to bacterial adhesion. The application of vapor deposited TiO₂ metal oxide increased bacterial and colloid adhesion, but coating the surface with silica oxide reduced adhesion in a manner consistent with SFA based on analysis of the “stickiest” sites. Application of a TiO₂-based paint to a surface produced a relatively non-fouling surface. Addition of a hydrophilic layer coating to this surface should have decreased fouling. However, it was observed that this coating actually increased fouling. Using SFA it was shown that the reason for the increased adhesion of bacteria and particles to the hydrophilic layer was that the surface produced by this coating was highly heterogeneous, resulting in a small number of sites that created a stickier surface. These results show that while it is important to manufacture surfaces with coatings that are relatively non-adhesive to bacteria, it is also essential that these coatings have a highly uniform surface chemistry.     

Highly photocatalytic activity of metallic hydroxide/titanium dioxide nanoparticles prepared via a modified wet precipitation process

Surface modification is one important approach to increase the photocatalytic activity of TiO₂. By using a modified wet precipitation process, novel M(OH)_x/TiO₂ nanoparticles were synthesized, where M(OH)_x represents ferric or cupric hydroxide. The prepared M(OH)_x/TiO₂ powders were characterized with XRD, FT-IR, BET, UV–vis DRS, and TGA, and were observed to yield high photocatalytic ability by using methyl orange (MO) as a model compound of organic pollutants to be degraded. Due to the accelerating effects of the new photocatalyst, the half-time of MO during its photocatalytic degradation at pH 6.0 over M(OH)_x/TiO₂ was decreased from 332 min for unmodified neat TiO₂ to 63 min for Fe(OH)₃/TiO₂ and 65 min for Cu(OH)₂/TiO₂, respectively. The enhancing effects of M(OH)_x/TiO₂ was further observed in a wide composition range with various M/Ti atomic ratios in the photocatalysts and in a wide pH range of the MO solution from 3 to 7. This enhancing effect is mainly attributed to the increased trapping of the photogenerated electron by the higher valence sites (Fe(III) or Cu(II)) in the hydroxide layer near the M(OH)_x/TiO₂ interface and the enriched surface hydroxyl groups which accept photogenerated holes to yield more hydroxyl radicals.     

Force measurements on cell repellant and cell adhesive alginic acid coated surfaces

The atomic force microscope (AFM) was used to acquire force versus distance curves between the cantilever tip and samples bearing a surface overlayer of covalently linked alginic acid. The alginic acid coating resists cell-adhesion in in vitro experiments involving a normal and a tumor cell line. However, the surface becomes cell adhesive when alginic acid coated samples are subjected to glow discharge treatment. Force curves show in both cases the typical features resulting from the interaction between the cantilever tip and a hydrophilic, compressible polymer overlayer, suggesting that in both cases a diffuse interface with water exists. Following some recent findings on oligoethyleneglycol-terminated self-assembled-monolayers, it is suggested that conformational and molecular aspects of hydrophilic surface layers, rather than steric repulsion effects, could play a significant role in the mechanism that controls resistance to bio-adhesion.     

生物材料与细胞相互作用及表面修饰

生物材料用作人工细胞外基质(ECMs)在组织工程中起重要作用。生物材料表面的拓扑结构、亲水／疏水平衡、自由能、电荷状况、化学基团和生物特异性识别对材料／细胞相互作用有较大影响。生物材料表面与细胞的相互作用主要是细胞膜表面受体与生物材料表面配体间的相互分子识别,因此采用仿生修饰生物材料表面以提高细胞亲和性和特异性识别。本文对生物材料与细胞相互作用及表面修饰的技术方法进行了介绍。     

Synthesis, characterization, and ethylene polymerizations of various N-O chelated mono Cp titanium complexes

Various mono Cp^∗ type titanium mononuclear complexes (1-5) and dinuclear complexes (6 and 7) containing non-Cp type chelate ligand, picolinate group, which has multi-binding sites of N and O atoms were synthesized and fully characterized by ¹H and ¹³C NMR spectroscopy, mass spectroscopy, elemental analysis, and X-ray diffraction study. The 1 and 2/MMAO catalytic systems for ethylene polymerization exhibited a moderate activity and gave the polyethylenes with broad molecular weight distributions.     

Modification of silica surfaces by grafting of alkyl chains. II-Characterization of silica surfaces by inverse gas-solid chromatography at finite concentration

Summary Model compounds, resulting from the surface esterification of fumed and precipitated silicas with methanol or hexadecanol, have been characterized by inverse gassolid chromatography at finite concentration. Surface treatments are shown to result in a decrease of adsorbate-adsorbent interactions (hexadecylated silicas are indeed virtually unable to exchange any specific interaction with a solute) and with an improvement of the energetic homogeneity of the materials. Results obtained suggest moreover that the distribution of surface silanol groups on precipitated silicas is not the same as on fumed silicas of identical surface area.