Luci Cristina de Oliveira Vercik

Dental Implants: Surface Modification of cp-Ti Using Plasma Spraying and the Deposition of Hydroxyapatite

The commercial pure titanium (cp-Ti) is currently being used with great success in dental implants. In this work we investigate how the cp-Ti implants can be improved by modifying the metal surface morphology, on which a synthetic material with properties similar to that of the inorganic part of the bone, is deposited to facilitate the bone/implant bonding. This synthetic material is the hydroxyapatite, HA, a calcium phosphate ceramic. The surface modification consists in the application of a titanium oxide (TiO 2 ) layer, using the thermal aspersion - plasma spray technique, with posterior deposition of HA, using the biomimetic method. The X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) and Diffuse Reflectance Infrared Fourier Transform (DRIFT) techniques have been used for characterizing phases, microstructures and morphologies of the coatings. The TiO 2 deposit shows a mixture of anatase, rutilo and TiO 2-x phases, and a porous and laminar morphology, which facilitate the HA deposition. After the thermal treatment, the previously amorphous structured HA coating, shows a porous homogeneous morphology with particle size of about 2-2.5 μm, with crystallinity and composition similar to that of the biological HA.

Synthesis and characterisation of gold nanoparticles using Mentha piperita leaf extract: a green, non-toxic and rapid method

Eco-friendly synthesis of gold nanoparticles (AuNPs) using Mentha piperita leaf extract was addressed in this work. Different extract concentrations (0.5, 1.0 and 1.5% w/v) were used for the synthesis of AuNPs. Reaction rate increased with temperature and leaf extract concentration; however, prolonged heating might affect negatively the AuNPs synthesis. AuNPs in colloid state were synthesised in acid pH (between 2.5 and 3.1), with potentials for charged surface between –21.8 and –24.1 mV, these colloids were highly stable for a storage time of four weeks. Bioreduction has generated AuNPs with spherical and triangular shape and size range between 3–26 nm for all concentrations of leaf extract, indicating a weak dependence of the nanoparticle size on extract concentrations. The present work, thus, offers a simple, rapid and non-toxic process for the synthesis of AuNPs that would potentially be used in different areas such as foods, cosmetic, medicine, electronics and polymer science.

A new conductometric biosensor based on horseradish peroxidase immobilized on chitosan and chitosan/gold nanoparticle films

Abstract A new conductometric biosensor was developed and characterized; the biosensor was based on horseradish peroxidase that was deposited in chitosan and chitosan/AuNPs films. The biosensors were characterized by scanning electron microscopy and current-voltage curves. Current-voltage curves in biosensors showed that the electrical conductivity and bistability in biosensors can be modulated by horseradish peroxidase. Horseradish peroxidase catalyzed the reduction of H2 O2 to H2 O with the oxidation of the prosthetic group (Fe3+) in the enzyme to Fe4+=O. Conductometric signal in the biosensors increased with the gradual increase of H2 O2 concentration, and it was due to the H2 O2 reduction. Linear hydrogen peroxide detection was observed for a concentration between 0 and 15 mm. The results proved that these biosensors could have promising industrial applications, due to its rapid and sensitive H2 O2 detection.

Evaluation of the antimicrobial activity and cytotoxic effect of hydroxyapatite containing Brazilian propolis

The aim of this work was to produce hydroxyapatite powder (HA) containing the dry extract of green and red propolis, and to evaluate the possible bactericidal activity of these materials over a short period of time through a fast release system. The ethanolic extracts of green and red propolis (EEP) were incorporated into the material by spray drying. After release tests, powders containing dry EEP were characterized regarding the content of total phenolics and flavonoids. Material characterization was undertaken by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The antimicrobial activity was evaluated by plate colony counting, minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) against Staphylococcus aureus (S. aureus). The cytotoxicity of the materials was determined by the neutral red incorporation method. The materials showed apparently spherical morphology, indicating a decrease in the degree of agglomeration with the addition of propolis. Characteristic HA and propolis functional groups were observed in the FTIR. The materials showed a higher release of phenolics and lower amounts of flavonoids when compared to the EEP, with the higher amounts of flavonoids observed for HA with red propolis. A bactericidal effect was observed for all materials within the interval of 0.5 and 1 h, showing lower inhibitory activity (MIC) and higher bactericidal activity (MBC) when compared to the EEP, with the best results attributed to HA with red propolis. The IC50 values (which is the concentration needed to inhibit cell growth by 50%) obtained from the cytotoxicity assay for HA with the green and red propolis lay between MIC and MCB. Considering these results, it is suggested that HA and propolis may be used as a possible antimicrobial agent, inhibiting the growth of S. aureus, although further in vivo biocompatibility should be investigated before using this material as a medical device with bactericidal potential.

Development and Characterization of Hydroxyapatite Containing Silver by Precipitation and Immersion Methods

The use of bone substitutes for recovery of lost function is a constant search within the medical field. So biomaterials have received a very large attention from the scientific community, including the materials the basis of calcium phosphate. Hydroxyapatite (HA) has been studied as apart from representing the natural constitution of the mass of bones and teeth in 30 to 70 %, has properties of bioactivity and osteoconductivity, encouraging and assisting the growth of bone tissue. In contrast, bacterial infections can arise after implantation causing the loss of functionality in the short and medium term. Several alternatives are being tested, usually associated with the use of conventional antibiotics incorporated into biomaterials. An alternative to antibiotics would be use such metals that possess antibacterial properties. Silver (Ag) is known as a bactericidal metal and so gained a prominent place among the studies as an important ally in the control of post-surgical infections. This work aimed to synthesize, characterize and evaluate the antimicrobial effect of the addition of silver ions into hydroxyapatite. The hydroxyapatites containing silver were obtained by the precipitation method in aqueous solution containing AgNO3 and by immersing the powder after the precipitation process in aqueous solutions containing AgNO3. At this stage of the work, were analyzed and characterized the crystalline phases and the ionic groups present in HA, HA precipitates with Ag and immersed in a solution of Ag. X-ray diffraction (XRD) spectra showed that regardless of the method used, precipitation (room temperature or 90°C) or by immersion, the metallic Ag was present in the structure of HA. Additionally, it was observed that the peaks indicated in the XRD pattern for HA corresponding to the diffraction pattern of plugs JPCDS 09-0432 (Joint Committee on Powder Diffraction Standards). No peaks related to the phases being observed β-TCP and CaO, respectively, indicating that the conditions adopted for obtaining HA Ag, only HA phase is present and that methods, precipitation and immersion are efficient to occur doping of HA with Ag

Electronic transport in organic memories of chitosan with gold nanoparticles

Abstract The effect of gold nanoparticles (AuNPs) on the electronic transport in chitosan and chitosan/AuNPs films was experimentally and theoretically studied. The electronic properties (current-voltage curves) relative to the transport in the organic bulk in films were fitted to various models: space-charge limited current (SCLC), trap-charge limited current (TCLC) and scaling rule. However, it was found that the TCLC model, ITCLC(V)αVl+1 and scaling rule, I(V)α(V-VT)ξ, describes better the electronic transport in chitosan and chitosan/AuNPs films. Current-voltage (I-V) curves showed an increasing conductivity with the AuNPs concentration. In addition, a bistable behavior was observed in chitosan/AuNPs films and it was attributed to the electron capture in the AuNPs. The results reported in this paper indicate that the electronic conductivity and bistable behavior in chitosan/AuNPs films could be controlled by the AuNPs incorporation on the chitosan matrix.

Development of Gelatin/HA Membranes

The aim of this work is to develop membranes of gelatin/hydorxyapatite composite for using as mechanical barrier. Membranes with 4% of gelatin and 0.5-3% of hydroxyapatite were studied. The composite was obtained by heterogeneous co-precipitation method. X-ray diffractometry showed the formation of a pure phase of hydroxyapatite with excellent crystallinity. Using atomic force microscopy, the distribution of crystals of hydroxyapatite in the gelatin matrix was observed, with nanoparticles of about 50-100nm in a homogeneous mixture. After crosslinking process with glutaraldehyde at different concentrations (0.5, 1, 1.5 and 2%), a significant decrease of the swelling behavior was observed due to the increase of the amount of triple helix in the samples, which increases their stability in aqueous solution.

Hydroxyapatite Nucleation on Modified Silicon Surface for Use in Biosensors

In this work, we explore the deposition of single-phase and uniform HA coatings on a crystalline silicon surface of microelectronic quality. The used methodology includes an NaOH treatment to produce the silanization of Si surface and a modified biomimetic technique, using sodium silicate solution (SS) as nucleant agent, for apatite-based coating formation. The sodium silicate solution (SS) demonstrated to be effective for the calcium phosphate layer formation, but the treatment can reduce the induction to obtain a uniform surface coating of HA. This suggests that, among the factors that determine nucleation of calcium phosphate on silicon, surface electrical charge could play a key role.