Novel method to prepare morphologically rich polymeric surfaces for biomedical applications via phase separation and arrest of microgel particles

We outline here a simple method to prepare polymeric surfaces of controlled surface topography on the micrometer scale, via assembly and arrest of microgel particles, for use in a range of biological applications to modify cell adhesion and spreading. In previous work by other groups, it has transpired that topography on the nanoscale is unlikely to be useful for this purpose, as roughness on this scale is often covered or coated by serum derived proteins during the early stages of cell adhesion and cells can easily bridge nanoscale roughness. Therefore, in our work, we have focused on roughness or topographic variations on the micrometer length scale. The basic idea is to modify the interactions between particles, thereby causing the microgel particles to phase separate into particle-dense and particle-dilute domains and to arrest these domains on the surface. The result is the creation of surfaces with controlled topography. By changing the particle size, it is possible to alter the size of the pores formed and their distribution in the film. Preliminary results show that the system can readily be arrested into a homologous series of such structures (formed from microgel particles of the same size and same chemical structure) with biological implications. At the extremes of this series, large phenotypic differences are observed between cells, ranging (at one end) from localization of the cells in the pores to (at the other end) cells that avoid such localization, and remain extended, growing along the ridges between the pores. This constitutes a sort of cell localization transition on a surface with identical chemical components, where only the morphology has been adjusted.     

Antibacterial metal implant with a TiO2‐conferred photocatalytic bactericidal effect against Staphylococcus aureus

Photocatalysis with anatase Titanium dioxide (TiO₂) under ultraviolet A (UVA) has a well recognized bactericidal effect. There have been a few reports, however, on the effects of photocatalysis on bio‐implant‐related infections. The purpose of present study was to evaluate the photocatalytic bactericidal effects of anatase TiO₂ on Staphylococcus aureus (S. aureus) associated with surgical site infections. TiO₂ films were synthesized on commercially pure titanium substrates and SUS316 stainless steel using a plasma source ion implantation method followed by annealing. The chemical composition of the surface layers was determined using GXRD and XPS. The disks were seeded with cultured S. aureus and exposed to UVA illumination from black light. The bactericidal effect of the TiO₂ films was evaluated by counting the survived colonies statistically. A structural gradient anatase type TiO₂ layer formed on all substrates. The viability of the bacteria on the photocatalytic TiO₂ film coated on titanium was suppressed to 7.0% at 30 minutes and 5.5% at 45 minutes, whereas that on a similarly coated stainless steel was suppressed to 45.8% at 30 minute and 28.6% at 45 minutes (ANOVA: p < 0.05). Complete bacterial inactivation was achieved after 90 minutes on titanium and after 60 minutes on stainless steel. The photocatalytic bactericidal effect of TiO₂ is useful for sterilizing the contaminated surfaces of bioimplants. Copyright © 2008 John Wiley & Sons, Ltd.     

Reduced Graphene Oxide Functionalized with a Luminescent Rare‐Earth Complex for the Tracking and Photothermal Killing of Drug‐Resistant Bacteria

An antibacterial platform based on multifunctional reduced graphene oxide (rGO) that is responsive to near‐infrared (NIR) light has been constructed. By introducing a luminescent Eu³⁺ complex and vancomycin for bacteria tracking into one system, this platform could specifically recognize and light up bacteria. Antibacterial activity of this nanoscale construction under NIR illumination was investigated. Upon illumination with NIR light, this nanoscale architecture generates great heat locally, resulting in the death of drug‐resistant bacteria. These results indicate that the ability of this nanoscale platform to kill drug‐resistant bacteria has great potential for clinical pathogenic bacteria diagnosis and treatment.     

Synthesis of nanoscale titanium dioxide by precipitation using supercritical anti-solvent

The method of synthesis of nanoscale titanium dioxide from organic precursor using supercritical fluid technology was suggested. It was demonstrated that the obtained product consists of amorphous particles with a narrow size distribution. It possesses a high porosity and a large value of specific surface area. The effect of temperature, pressure, and concentration of the titanium(IV) isopropoxide precursor on the average size of TiO₂ nanoparticles has been studied. The method allows preparation of titanium dioxide free from precursor compounds. Complex physico-chemical study of the obtained product has been performed.     

An addressable antibody nanoarray produced on a nanostructured surface

The ability to address specific nanoscale features is required to produce diverse biological nanoarrays or perform local assembly using biological building blocks and is an important unsolved problem in nanotechnology. In this work, we describe the use of a novel nanofabricated gold surface, with regions of distinct topography and chemical functionalities, to solve this problem. First, nanoarrays of IgG antibodies were produced by selective immobilization in nanoholes on the surface. The smallest feature size was determined by the hole size (fwhm 90 nm) and not surface diffusion. Using holes of 300 nm diameter, we selectively addressed specific features in the array by nanopipet delivery of a functional antibody, anti-IgG. To our knowledge, this is the first example of addressing specific biologically functional features on a surface at the nanoscale.     

Does the nanometre scale topography of titanium influence protein adsorption and cell proliferation?

To investigate the influence of titanium films with nanometre scale topography on protein adsorption and cell growth, three different model titanium films were utilized in the present study. The chemical compositions, surface topographies and wettability were investigated by using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and water contact angle measurement, respectively. The films share the same surface chemistry but exhibit different topographies on a nanometre scale. Thus, they act as model systems for biological studies regarding surface topography effects. The films were obtained by varying the deposition rate and the film thickness, respectively. These films displayed nanometre scale surface roughness (root mean square roughness, R_rms) from 2 to 21 nm over areas of 50 μm × 50 μm, with different grain sizes at their surfaces. Albumin and fibrinogen adsorption on these model titanium films were performed in this study. Bicinchoninic acid assay was employed to determine the amount of adsorbed protein on titanium film surfaces. No statistically significant differences, however, were observed for either albumin or fibrinogen adsorption between the different groups of titanium films. No statistically significant influence of surface roughness on osteoblast proliferation and cell viability was detected in the present study.     

Effect of surface topography on the anodization of titanium

The influence of surface topography and electrolyte composition on the anodization of titanium was investigated. The growth of the anodic oxides layer and the impedance response of the electrode/electrolyte interface were studied by means of ac-voltammetry, and the surface topography before and after anodization was visualized by atomic force microscopy. It was observed that the final topographic features and the instability phenomenon during the anodization of titanium were dependent on the surface finishing and on the nature of the anions in the electrolyte. In particular, it appears that rougher surfaces lead to a more homogeneous anodic film, while polished ones form an irregular morphology. The presence of sulfates is enhancing the breakdown of the film.     

一步水热合成铜纳米颗粒负载二氧化钛复合纳米管及其可见光催化活性

采用一步水热法合成了Cu纳米粒子负载二氧化钛纳米管材料. 利用透射电子显微镜(TEM)、X射线衍射仪(XRD)、能谱仪(EDS)等对材料的相组成、形貌以及形成过程进行了研究. 制得的Cu-TiO₂复合纳米材料长度约为100 nm, 直径10-15 nm, 其上负载的Cu纳米粒子尺寸约为5 nm. BET比表面积测试表明实验制备的Cu-TiO₂复合纳米管的比表面积为154.67 m²·g^-1. 通过调节水热反应时间和钛前驱体种类, 研究了该复合纳米管材料的形成机制. 结果表明: 非晶态的钛源对于成功一步合成Cu-TiO₂复合纳米管至关重要. 同时, 实验中观察到铜纳米粒子的尺寸随水热反应时间延长而减小(反奥氏陈化过程), 这一现象有助于纳米粒子的可控合成.紫外-可见吸收光谱表明该复合纳米管在350-800 nm范围内有较强的吸收, 并在550-600 nm范围观察到Cu的表面等离子激元吸收带. Cu-TiO₂界面处形成的肖特基势垒有助于加快光生载流子的输运, 提高光生电子-空穴对的分离效率. 光催化实验表明Cu-TiO₂复合纳米管在可见光下具有较高的催化活性.     

Silver nanoparticles as antimicrobial agent: a case study on E. coli as a model for Gram-negative bacteria

The antimicrobial activity of silver nanoparticles against E. coli was investigated as a model for Gram-negative bacteria. Bacteriological tests were performed in Luria-Bertani (LB) medium on solid agar plates and in liquid systems supplemented with different concentrations of nanosized silver particles. These particles were shown to be an effective bactericide. Scanning and transmission electron microscopy (SEM and TEM) were used to study the biocidal action of this nanoscale material. The results confirmed that the treated E. coli cells were damaged, showing formation of "pits" in the cell wall of the bacteria, while the silver nanoparticles were found to accumulate in the bacterial membrane. A membrane with such a morphology exhibits a significant increase in permeability, resulting in death of the cell. These nontoxic nanomaterials, which can be prepared in a simple and cost-effective manner, may be suitable for the formulation of new types of bactericidal materials.     

Self-assembly of a tripodal pseudorotaxane on the surface of a titanium dioxide nanoparticle

This paper describes the self-assembly of a heterosupramolecular system consisting of a tripodal viologen, adsorbed at the surface of a titanium dioxide nanoparticle, that threads a crown ether to form a pseudorotaxane. The viologen, a 1,1'-disubstituted-4,4'-bipyridinium salt with a rigid tripodal anchor group, has been synthesized. This viologen is adsorbed at the surface of a titanium dioxide nanoparticle in solution. As intended, this tripodal viologen is both oriented normal to and displaced from the surface of the nanoparticle and threads a crown ether to form the heterosupramolecular complex. The threading of the crown ether by the tripodal viologen to form the above pseudorotaxane complex at the surface of a titanium dioxide nanoparticle has been studied by (1)H NMR, optical absorption spectroscopy, and cyclic voltammetry.     

Nitrogen oxide activation on the surfaces of titanium carbide and titanium nitride

The mechanism of NO activation on the surfaces of crystalline titanium monocarbide and titanium mononitride has been studied within the framework of semiempirical SCF LCAO NDDO method. The adsorption has been shown to be accompanied by electron density transfer from the crystal surface to the adsorbate molecule. Stronger activation of the NO molecule is observed on the TiC surface as compared with that on TiN surface.     

Surface modification of titanium with thermally treated polydimethylsiloxane coating and the effect on resin to titanium adhesion

In this study, titanium surface modification by a thermal treatment using a polydimethylsiloxane (PDMS) coating was investigated. The surfaces of four titanium samples were surface treated by polishing, sandblasting, and coating with a PDMS with a thermal treatment at 800 and 1100 °C. The titanium surfaces were characterized by X‐ray photoelectron spectroscopy (XPS) and atomic force microscopy. The effect of the surface treatments on adhesion of resin to titanium was assessed by shear adhesion strength test. XPS analysis showed that there was a change of elemental composition of titanium surfaces after surface treatment. Binding energy shifts for Si2p and O1s were observed after sandblasting and thermally treated PDMS. Therefore, chemical states of Si and O were changed. Atomic force microscopy analysis revealed that the surface topography of the Ti samples was different, and surface roughness was increased after sandblasting and thermal treatment of PDMS coating. Shear adhesion strength test results showed that the adhesion between resin and titanium is affected by the treatment temperature of PDMS coating. The highest adhesion is obtained at 1100 °C (14.7 ± 1.57 MPa). Copyright © 2014 John Wiley & Sons, Ltd.     

A novel dual surface modification on titanium in dental use: Characterization and topography

This laboratory study aimed to compare, contrast, and evaluate the effect of a novel dual surface modification method on the adhesion strength of resin composite cement to titanium. C.p.-2 grade titanium samples were silica-coated, etched with HNO₃(69vol %) or a blend of HCl (35vol %) and H₃PO₄ (85vol %), for 1 h at 80°C. Surface roughness was measured by surface roughness profilometry, topographic analysis by scanning electron microscopy (SEM), atomic force microscopy (AFM), and surface analyses by energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS). Silanization of all specimens was carried out after SEM, EDX, and AFM analysis, before enclosed mold microshear bond strength testing (EM-μSBS). Adhesion strengths were measured after artificial ageing: 1 day, 1 week, 4 weeks, and 8 weeks by EM-μSBS testing and failure mode analysis by optical microscopy. Polished titanium was used as a control. The highest surface roughness was observed in titanium samples treated with silica-coating + HCl-H₃PO₄ etching. The elemental composition confirmed the presence of Ti, O, C, with Si and Al in samples treated with silica-coating. A gradual decrease in EM-μSBS values was observed in all titanium samples with adhesive and cohesive failure modes. The novel dual surface modification method applied in this study suggests that silica-coating + HCl-H₃PO₄etching strongly affects titanium surface topography and roughness. The presence of Si on silica-coated surface modified titanium before silanization with an experimental silane has a positive effect on the EM-μSBS of titanium samples treated with silica-coating only or silica-coating + HNO₃ etching.     

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.     

Modification of titanium phosphate precipitated from titanylsulfate

The titanium phosphate-synthesized sol–gel method was subjected to the mechanochemical treatment in a planetary ball mill Pulverisette 6 in air or water environment or the hydrothermal treatment at 873 K or 1073 K. The properties of such modified/treated samples were examined using the XRF, XRD, TGA, static light scattering, FTIR Raman and adsorption/desorption of N₂ methods. The mechanochemical treatment of xerogel samples leads to a small decrease in water contents in the sample, but the structure remains amorphous. Additionally, during milling of the sample aggregation of titanium phosphate particles and a decrease in specific surface area were observed. The hydrothermal treatment of the xerogel sample leads to a crystal product composed of titanium oxide phosphate hydrate, titanium oxide phosphate and titanium dioxide. The TGA analysis confirms the presence of titanium oxide phosphate hydrate. The hydrothermally treated titanium phosphate samples are monodispersed and have a larger specific surface area than the initial sample.

     

Electropolishing of pure metallic titanium in a deep eutectic solvent

This work presents a facile and efficient electropolishing of metallic titanium (Ti) in the relatively eco-friendly electrolyte of deep eutectic solvent (DES) using a mixture of choline chloride-propylene glycol (1 mol ChCl: 2 mol PG). The electropolishing process of metallic titanium was performed under potentiostatic condition (10 V for 40 min) at room temperature. Surface topography and morphology were investigated using scanning electron microscope (SEM) and atomic force microscopy (AFM). The promising electropolishing provides a shiny and mirror-like surface with an average surface roughness (Ra) of 37.92 nm from the parent metallic Ti with a roughness of 455.60 nm. The surface passivation after electropolishing is of the most likely acceptable mechanism for removing microscope roughness. The proposed electropolishing in the present DES electrolyte is a promising strategy for making mirror-like surface (surface resistive against corrosion) of biomedical metallic titanium.     

Block copolymer micelles as switchable templates for nanofabrication

Block copolymer inverse micelles from polystyrene-block-poly-2-vinylpyridine (PS-b-P2VP) deposited as monolayer films onto surfaces show responsive behavior and are reversibly switchable between two states of different topography and surface chemistry. The as-coated films are in the form of arrays of nanoscale bumps, which can be transformed into arrays of nanoscale holes by switching through exposure to methanol. The use of these micellar films to act as switchable etch masks for the structuring of the underlying material to form either pillars or holes depending on the switching state is demonstrated.     

Modeling of wetting: a study of nanowetting at rough and heterogeneous surfaces

Molecular dynamics simulations were performed to study the behavior of nanoscale water droplets at solid surfaces. Simulations of droplets on heterogeneous patterned surfaces show that the relative sizes of the domains and the droplets play an important role as do the interactions between the solid and the liquid, particularly when the domain width is comparable to the droplet radius. For pillar surfaces, a transition is observed between the Wenzel and the Cassie and Baxter regimes with increasing pillar height. The effects of pillar width and the gap between the pillars were also examined. The simulations show clearly the importance of the detailed topography and composition of the solid surface.     

Influence of nanotopography on phospholipid bilayer formation on silicon dioxide

We have investigated the effect of well-defined nanoscale topography on the 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid vesicle adsorption and supported phospholipid bilayer (SPB) formation on SiO2 surfaces using a quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). Unilamellar lipid vesicles with two different sizes, 30 and 100 nm, were adsorbed on pitted surfaces with two different pit diameters, 110 and 190 nm, as produced by colloidal lithography, and the behavior was compared to results obtained on flat surfaces. In all cases, complete bilayer formation was observed after a critical coverage of adsorbed vesicles had been reached. However, the kinetics of the vesicle-to-bilayer transformation, including the critical coverage, was significantly altered by surface topography for both vesicle sizes. Surface topography hampered the overall bilayer formation kinetics for the smaller vesicles, but promoted SPB formation for the larger vesicles. Depending on vesicle size, we propose two modifications of the precursor-mediated vesicle-to-bilayer transformation mechanism used to describe supported lipid bilayer formation on the corresponding flat surface. Our results may have important implications for various lipid-membrane-based applications using rough or topographically structured surfaces.     

Protein adsorption and surface patterning

Surface patterning has become an important discipline of biologically oriented surface science over the past decades. Many methods have been developed that allow the formation of patterns on the micro- and nanoscale. This Opinion discusses the role of protein adsorption in patterning technologies, highlighting how it can be used as an integrated part of the patterning process, how it can be controlled by patterns with appropriate properties, and how it may lead to disruption of formed patterns if not properly accounted for. Recent examples from literature are used to emphasize some of the most interesting developments in the field, such as novel surface chemistries only allowing specific protein adsorption, directed self-sorting adsorption of proteins on patterned surfaces, and control of protein adsorption through nanopatterning.