C. Fonseca

Corrosion behaviour of commercially pure titanium shot blasted with different materials and sizes of shot particles for dental implant applications

It is well known that the osseointegration of the commercially pure titanium (c.p. Ti) dental implant is improved when the metal is shot blasted in order to increase its surface roughness. This roughness is colonised by bone, which improves implant fixation. However, shot blasting also changes the chemical composition of the implant surface because some shot particles remain adhered on the metal. The c.p. Ti surfaces shot blasted with different materials and sizes of shot particles were tested in order to determine their topographical features (surface roughness, real surface area and the percentage of surface covered by the adhered shot particles) and electrochemical behaviour (open circuit potential, electrochemical impedance spectroscopy and cyclic polarisation). The results demonstrate that the increased surface area of the material because of the increasing surface roughness is not the only cause for differences found in the electrochemical behaviour and corrosion resistance of the blasted c.p. Ti. Among other possible causes, those differences may be attributed to the compressive residual surface stresses induced by shot blasting. All the materials tested have an adequate corrosion and electrochemical behaviour in terms of its possible use as dental implant material.

Corrosion behaviour of titanium in biofluids containing H2O2 studied by electrochemical impedance spectroscopy

Abstract This work aims at studying the electrochemical behaviour of titanium in the presence of an artificial biofluid containing H 2 O 2 , mimicing the situation, where the metal is implanted in the human body and hydrogen peroxide is generated by an inflammatory reaction. A phosphate buffered saline (PBS) solution and two PBS/H 2 O 2 solutions containing 50 and 150 mM of H 2 O 2 were used to simulate the body fluids. The behaviour of the metal was monitored as a function of time by electrochemical impedance spectroscopy (EIS) for three weeks. After one week, the PBS/H 2 O 2 solutions were replaced by fresh PBS solutions in order to simulate the end of the inflammatory process and recovery of the system. All the experiments were carried out at a constant temperature of 37°C. From the simulation of the experimental EIS spectra, it was concluded that the corrosion resistance of titanium is strongly affected by the presence of H 2 O 2 and when the peroxide is removed, the metal displays a sharp resistance increase. Furthermore, the oxides formed in H 2 O 2 are rougher and display higher ionic conductivities than the oxides formed in the absence of peroxide. The study was complemented with potentiostatic experiments and scanning electron microscopy observation of the metal surfaces.

A Novel Dry Active Electrode for EEG Recording

The design and testing of a dry active electrode for electroencephalographic recording is described. A comparative study between the EEG signals recorded in human volunteers simultaneously with the classical Ag-AgCl and dry active electrodes was carried out and the reported preliminary results are consistent with a better performance of these devices over the conventional Ag-AgCl electrodes

Constructing thromboresistant surface on biomedical stainless steel via layer-by-layer deposition anticoagulant.

Multilayer films consisting of polyethylenimine (PEI) and heparin were successfully prepared on biomedical 316L stainless steel surface via electrostatic self-assembly (ESA) of the PEI and heparin. The process of ESA of PEI/heparin was monitored by static contact angle, electrochemical impedance spectroscopy (EIS), reflection adsorption spectroscopy and X-ray photoelectron spectroscopy data. The contact angle and EIS data revealed that the multilayer coating was stable in Tris-HCl (pH 7.35) buffer solution for 21 days. The static platelet adhesion and static clotting time experiments indicated that the PEI/heparin-deposited stainless steel could resist the platelet adhesion and prolong the static clotting time effectively. Such an easy processing and shape-independent method may have good potential for surface modification of cardiovascular devices.

Albumin adsorption on alkanethiols self-assembled monolayers on gold electrodes studied by chronopotentiometry

Chronopotentiometry was used to study the adsorption of human serum albumin (HSA) to self-assembled monolayers with the following terminal functional groups: CH(3), COOH and OH. Surfaces were characterized by X-ray photoelectron spectroscopy, water contact angle measurements and cyclic voltammetry. HSA coverage of the different SAMs was investigated by chronopotentiometry and the total amount of adsorbed protein was determined using radiolabelled albumin. Both techniques have demonstrated that HSA adsorption to the different SAM-modified electrodes increases in the following order: OH<COOH<CH(3)-terminated SAMs. A good correlation between coverage and total amount of HSA adsorbed was observed for long adsorption times (900s).

Characterisation of titanium passivation films by in situ ac impedance measurements and XPS analysis

Abstract Capacitance-potential measurements by ac impedance methods have shown that for polarisations of 0.5 to 0.7 V from the flat band potential, titanium passivation films formed between 0.2 and 2 V (thicknesses ranging from 15 to 100 A) display Mott-Schottky behaviour, with frequency dependent slopes. This study develops a theoretical approach which takes account of the frequency dispersion and allows the determination of flat band potentials, donor densities, and Helmholtz capacitances for the films. The Mott-Schottky behaviour was attributed to the presence of Ti 3+ as the doping element. Experimental evidence for this was obtained from XPS spectra. For films formed above 2 V the linear Mott-Schottky region was difficult to define, and capacitance vs. potential plots resembled the behaviour of amorphous semiconductors.

Novel Multipin Electrode Cap System for Dry Electroencephalography

Current usage of electroencephalography (EEG) is limited to laboratory environments. Self-application of a multichannel wet EEG caps is practically impossible, since the application of state-of-the-art wet EEG sensors requires trained laboratory staff. We propose a novel EEG cap system with multipin dry electrodes overcoming this problem. We describe the design of a novel 24-pin dry electrode made from polyurethane and coated with Ag/AgCl. A textile cap system holds 97 of these dry electrodes. An EEG study with 20 volunteers compares the 97-channel dry EEG cap with a conventional 128-channel wet EEG cap for resting state EEG, alpha activity, eye blink artifacts and checkerboard pattern reversal visual evoked potentials. All volunteers report a good cap fit and good wearing comfort. Average impedances are below 150xa0kΩ for 92 out of 97 dry electrodes, enabling recording with standard EEG amplifiers. No significant differences are observed between wet and dry power spectral densities for all EEG bands. No significant differences are observed between the wet and dry global field power time courses of visual evoked potentials. The 2D interpolated topographic maps show significant differences of 3.52 and 0.44xa0% of the map areas for the N75 and N145 VEP components, respectively. For the P100 component, no significant differences are observed. Dry multipin electrodes integrated in a textile EEG cap overcome the principle limitations of wet electrodes, allow rapid application of EEG multichannel caps by non-trained persons, and thus enable new fields of application for multichannel EEG acquisition.

Biocompatibility and Calcification of Bovine Pericardium Employed for the Construction of Cardiac Bioprostheses Treated With Different Chemical Crosslink Methods

The use of biological materials in the construction of bioprostheses requires the application of different chemical procedures to improve the durability of the material without producing any undesirable effects. A number of crosslinking methods have been tested in biological tissues composed mainly of collagen. The aim of this study was to evaluate the in vitro biocompatibility, the mechanical properties, and in vivo calcification of chemically modified bovine pericardium using glutaraldehyde acetals (GAAs) in comparison with glutaraldehyde (GA) treatment. Homsys tests showed that the most cytotoxic treatment is GA whereas GAA treatments showed lower cytotoxicity. Regarding the mechanical properties of the modified materials, no significant differences in stress at rupture were detected among the different treatments. Zeta-Potential showed higher negative values for GA treatment (-4.9 +/- 0.6 mV) compared with GAA-0.625% (-2.2 +/- 0.5 mV) and GAA-1% (-2.2 +/- 0.4 mV), which presented values similar to native tissue. Similar results were obtained for calcium permeability coefficients which showed the highest values for GA treatment (0.12 +/- 0.02 mm(2)/min), being significantly lower for GAA treatments or non-crosslinked pericardium. These results confirmed the higher propensity of the GA-treated tissues for attraction of calcium cations and were in good agreement with the calcification degree obtained after 60 days implantation into young rats, which was significantly higher for the GA group (22.70 +/- 20.80 mg/g dry tissue) compared with GAA-0.625% and GAA-1% groups (0.49 +/- 0.28 mg/g dry tissue and 3.51 +/- 3.27 mg/g dry tissue, respectively; P < 0.001). In conclusion, GAA treatments can be considered a promising alternative to GA treatment.

Modelling of the impedance behaviour of an amorphous semiconductor schottky barrier in high depletion conditions. Application to the study of the titanium anodic oxide/electrolyte junction

Abstract A mathematical model to describe the impedance behaviour of the amorphous semiconductor Schottky barrier in the high band bending region is proposed. The model is based on the admittance theory of the amorphous silicon Schottky barrier and it is valid in the polarisation region where the semiconductor displays a Mott—Schottky like behaviour. We have applied the model to the characterisation of very thin (10–44 nm) amorphous oxides formed electrochemically on titanium. The calculated parameters are shown to be in good agreement with those obtained from the classical (low band bending) amorphous silicon Schottky barrier theory for the same oxides. A comparative discussion on the advantages and handicaps of each model is carried out.

Poly(Trimethylene Carbonate-co-ε-Caprolactone) Promotes Axonal Growth

Mammalian central nervous system (CNS) neurons do not regenerate after injury due to the inhibitory environment formed by the glial scar, largely constituted by myelin debris. The use of biomaterials to bridge the lesion area and the creation of an environment favoring axonal regeneration is an appealing approach, currently under investigation. This work aimed at assessing the suitability of three candidate polymers – poly(ε-caprolactone), poly(trimethylene carbonate-co-ε-caprolactone) (P(TMC-CL)) (11∶89 mol%) and poly(trimethylene carbonate) - with the final goal of using these materials in the development of conduits to promote spinal cord regeneration. Poly(L-lysine) (PLL) coated polymeric films were tested for neuronal cell adhesion and neurite outgrowth. At similar PLL film area coverage conditions, neuronal polarization and axonal elongation was significantly higher on P(TMC-CL) films. Furthermore, cortical neurons cultured on P(TMC-CL) were able to extend neurites even when seeded onto myelin. This effect was found to be mediated by the glycogen synthase kinase 3β (GSK3β) signaling pathway with impact on the collapsin response mediator protein 4 (CRMP4), suggesting that besides surface topography, nanomechanical properties were implicated in this process. The obtained results indicate P(TMC-CL) as a promising material for CNS regenerative applications as it promotes axonal growth, overcoming myelin inhibition.