Light induced hydrophilicity and osteoblast adhesion promotion on amorphous TiO2

We have studied the effect of the UV induced superhydrophilic wetting of TiO(2) thin films on the osteoblasts cell adhesion and cytoskeletal organization on its surface. To assess any effect of the photo-catalytic removal of adventitious carbon as a factor for the enhancement of the osteoblast development, 100 nm amorphous TiO(2) thin layers were deposited on polyethylene terephthalate (PET), a substrate well known for its poor adhesion and limited wettability and biocompatibility. The TiO(2) /PET materials were characterized by X-ray photoelectron spectroscopy, and atomic force microscopy and their wetting behavior under light illumination studied by the sessile drop method. The amorphous TiO(2) thin films showed a very poor photo-catalytic activity even if becoming superhydrophilic after illumination. The illuminated samples recovered partially its initial hydrophobic state only after their storage in the dark for more than 20 days. Osteoblasts (HOB) were seeded both on bare PET and on TiO(2) /PET samples immediately after illumination and also after four weeks storage in darkness. Cell attachment was much more efficient on the immediately illuminated TiO(2)/PET samples, with development of focal adhesions and cell traction forces. Although we cannot completely discard some photo-catalytic carbon removal as a factor contributing to this cell enhanced attachment, our photodegradation experiments on amorphous TiO(2) are conclusive to dismiss this effect as the major cause for this behavior.

Electrochromic behavior of W(x)Si(y)O(z) thin films prepared by reactive magnetron sputtering at normal and glancing angles

This work reports the synthesis at room temperature of transparent and colored W(x)Si(y)O(z) thin films by magnetron sputtering (MS) from a single cathode. The films were characterized by a large set of techniques including X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), Fourier transform infrared (FT-IR), and Raman spectroscopies. Their optical properties were determined by the analysis of the transmission and reflection spectra. It was found that both the relative amount of tungsten in the W-Si MS target and the ratio O(2)/Ar in the plasma gas were critical parameters to control the blue coloration of the films. The long-term stability of the color, attributed to the formation of a high concentration of W(5+) and W(4+) species, has been related with the formation of W-O-Si bond linkages in an amorphous network. At normal geometry (i.e., substrate surface parallel to the target) the films were rather compact, whereas they were very porous and had less tungsten content when deposited in a glancing angle configuration. In this case, they presented outstanding electrochromic properties characterized by a fast response, a high coloration, a complete reversibility after more than one thousand cycles and a relatively very low refractive index in the bleached state.

Effects of plasma surface treatments of diamond-like carbon and polymeric substrata on the cellular behavior of human fibroblasts

Surface properties play an important role in the functioning of a biomaterial in the biological environment. This work describes the influence of the changes that occurred on diamond-like carbon (DLC) and polymeric substrata by different nitrogen and ammonia plasmas treatments and its effects on the cell proliferation on these materials. All substrata were additionally subjected to the effect of neutral beams of nitrogen atoms and NH species for comparison purposes. Results about the proliferation, viability, and morphology of fibroblasts were correlated with surface chemical composition, surface tension, and topography. It was found that the presence of amine groups on the surface and the surface tension are beneficial factors for the cell growth. Surface roughness in DLC also plays a positive role in favoring cell adhesion and proliferation, but it can be detrimental for some of the treated polymers because of the accumulation of low molecular weight fragments formed as a result of the plasma treatments. Analysis of the overall results for each type of material allowed to define a unique parameter called 'factor of merit' accounting for the influence of the different surface characteristics on the cell deployment, which can be used to predict qualitatively the efficiency for cell growth.

Bacterial adherence on UHMWPE with vitamin E: an in vitro study

Orthopaedic materials may improve its capacity to resist bacterial adherence, and subsequent infection. Our aim was to test the bacterial adherence to alpha-tocopherol (frequently named vitamin E, VE) doped or blended UHMWPE with S. aureus and S. epidermidis, compared to virgin material. Collection strains and clinical strains isolated from patients with orthopaedic infections were used, with the biofilm-developing ability as a covariable. While collection strains showed significantly less adherence to VE-UHMWPE, some clinical strains failed to confirm this effect, leading to the conclusion that VE doped or blended UHMWPE affects the adherence of some S. epidermidis and S. aureus strains, independently of the concentration in use, but the results showed important intraspecies differences and cannot be generalized.

Novel guests for porous columnar thin films: the switchable perchlorinated trityl radical derivatives

TiO(2) and SiO(2) porous thin films consisting of tilted nanocolumns prepared by glancing angle evaporation (GLAD) have been infiltrated with guest derivatives belonging to the family of perchlorinated trityl radicals, novel guest molecules presenting an open-shell electronic configuration associated with paramagnetism, fluorescence, and electroactivity. The main driving forces for infiltration from aqueous solutions of the carboxylate-substituted radical derivatives are the electrostatic interactions between their negative charge and the net positive charges induced on the film pores. Positive charges on the internal surface of the films were induced by either adjusting the radical solution pH at values lower than the point of zero charge (PZC) of the oxide or passivating the nanocolumns oxide surface with a positively charged aminosilane. The infiltrated composite thin films are robust and easy to handle thanks to the physical protection exerted by the film columns. They also keep the multifunctionality of the used guests, as confirmed by electron paramagnetic resonance (EPR), UV-vis spectroscopy, and fluorescence spectroscopy. To prove the electroactivity of the infiltrated porous films, a porous TiO(2) host layer was supported onto conductive indium tin oxide (ITO). By application of an appropriate redox potential, the guest radical molecules have been reversibly switched from their open-shell electronic configuration to their diamagnetic state and hence changed their optical properties. On the basis of these results, it is herein proposed that the appropriate surface functionalization of the pore internal surface of GLAD thin films can be used to prepare novel radical-oxide composite thin films usable for the development of robust switchable electrically driven photonic and magnetic devices.

Surface functionalization, oxygen depth profiles, and wetting behavior of PET treated with different nitrogen plasmas

Polyethylene terephthalate (PET) plates have been exposed to different nitrogen containing plasmas with the purpose of incorporating nitrogen functional groups on its surface. Results with a dielectric barrier discharge (DBD) at atmospheric pressure and a microwave discharge (MW) at reduced pressure and those using an atom source working under ultrahigh vacuum conditions have been compared for N(2) and mixtures Ar + NH(3) as plasma gases. The functional groups have been monitored by X-ray Photoemission Spectroscopy (XPS). Nondestructive oxygen and carbon depth profiles for the plasma treated and one month aged samples have been determined by means of the nondestructive Tougaard's method of XPS background analysis. The surface topography of the treated samples has been examined by Atomic Force Microscopy (AFM), while the surface tension has been determined by measuring the static contact angles of water and iodomethane. It has been found that the DBD with a mixture of Ar+NH(3) is the most efficient treatment for nitrogen and amine group functionalization as determined by derivatization by reaction with chlorobenzaldehyde. It is also realized that the nitrogen functional groups do not contribute significantly to the observed increase in surface tension of plasma treated PET.

Supported Ag-TiO(2) core-shell nanofibres formed at low temperature by plasma deposition

Ag-TiO(2) nanofibres (about three microm long and 30-150 nm thick) formed by a single-crystalline silver wire (20-30 nm thick) and an external layer of amorphous TiO(2) of variable thickness are prepared at 403 K by oxygen plasma activation of a silver substrate followed by plasma deposition of TiO(2). Thicker fibres of anatase crystallites surrounding the silver wire were prepared when plasma deposition was carried out at 523 K. The fibres have been analysed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray photoemission spectroscopy (XPS). The plasmon losses of the silver core wire have been characterized by electron energy loss spectroscopy in the TEM microscope. Based on the experimental evidence, a new volcano-type mechanism of formation of these core-shell fibres is proposed, whereby the effect of the plasma and the high mobility of the silver would be key factors determining their morphology and dimensions.