Rosana Zacarias Domingues

Microstructural and mechanical study of zirconia-hydroxyapatite (ZH) composite ceramics for biomedical applications

Abstract Hydroxyapatite is the mineral component of natural hard tissues and, as such, it has been studied extensively as a candidate biomaterial for its use in prosthetic applications. However, the main weakness of this material lies in its poor mechanical strength which makes it unsuitable for load-bearing applications. On the other hand, partially stabilized zirconia has been widely studied on account of its high strength and fracture toughness, and good biocompatibility. Therefore, it is believed that the addition of a particulate zirconia phase to a hydroxyapatite one may lead to an improvement of the mechanical properties of this kind of composite and will not affect its biocompatibility. In this study, two series of zirconia- hydroxyapatite composites, Z4H6 and Z6H4 with 40 and 60 vol.% of zirconia content respectively, were prepared by powder uniaxial pressing at 700 MPa and sintering in air at 1200–1500°C for 3 h. The sintering behavior, microstructural characteristics and mechanical properties were evaluated. Variation of average grain size for the zirconia and hydroxyapatite phases with sintering temperature was observed. Relative densities ranging from 89 to 91% of the theoretical values were reached for the Z6H4 ceramic series and for the Z4H6 sample sintered at 1400°C, although microcracks were present in all specimens sintered at 1400 and 1500°C. Values of ultimate compressive strength, Youngs modulus, micro-Vickers hardness and Poissons ratio near to those for human cortical bone and human tooth (dentine and enamel) were found for almost all samples investigated suggesting that these materials present potential applications as structural implants.

Synthesis and characterization of magnetic nanoparticles coated with silica through a sol-gel approach

This paper investigates the influence of reaction medium pH on silica-coating of magnetite nanoparticles. Magnetite nanoparticles were prepared by means of a reduction-precipitation method using ferric chloride as a starting material, which was partially reduced to ferrous salts by Na2SO3 before alkalinizing with ammonia. The particles were coated by sol-gel method with either ammonia or HCl aqueous solutions for either base- or acid-catalyzed hydrolysis, respectively. Powder X-ray diffraction, Fourier-transform infrared, and Zeta Potential were used for the characterization of oxides and of the coated magnetic nanoparticles. The observed difference of pHIEP in KCl solution for pure silica (2.0), magnetite (5.0), and silica-coated magnetite (2.3) samples confirms that the coating process was effective since the charge surface properties of coated magnetic nanoparticles are close to that of pure silica, even though the Fourier-transform infrared spectra did not evidence the formation of Fe-O-Si bonds.

pH effect on the synthesis of magnetite nanoparticles by the chemical reduction-precipitation method

This work aimed at putting in evidence the influence of the pH on the chemical nature and properties of the synthesized magnetic nanocomposites. Saturation magnetization measurements evidenced a marked difference of the magnetic behavior of samples, depending on the final pH of the solution after reaction. Magnetite and maghemite in different proportions were the main magnetic iron oxides actually identified. Synthesis with final pH between 9.7-10.6 produced nearly pure magnetite with little or no other associated iron oxide. Under other synthetic conditions, goethite also appears in proportions that depended upon the pH of the synthesis medium.

Synthesis and characterization of calcia partially stabilized zirconia-hydroxyapatite powders prepared by co-precipitation method

Abstract It was recently been reported that calcia partially stabilized zirconia can be used as a reinforcement phase in zirconia-hydroxyapatite composites. Composites prepared by a precipitation method lead to the formation of homogeneous powders, easily compacted without addition of other phases. In this work, hydroxyapatite-zirconia composites were prepared by a similar precipitation route previously used. Here, it was lightly modified in relation to steps of addition of precursors reagent solutions. Two powders, having different compositions, were prepared by this method. The modified route led to the formation of a mixture of tetragonal zirconia, t-ZrO 2, monoclinic zirconia, m- ZrO 2 , and calcium zirconium oxide, Ca 0.15 Zr 0.85 O 1.85 , as well as a hydroxyapatite phase. Fine powders with specific surface area of approximately 35 m 2 /g were produced. Textural analyses revealed the presence of multiple generations of agglomerate, for both compositions. Thermal analyses showed the thermal stability of powders which presented weight losses of only 4%, for temperatures from 25 to 1400°C.

A sol-gel derived bioactive fibrous mesh

Nonwoven sheets of bioactive fibers were produced using a sol-gel process. A high velocity spray process was used to prepare fibers of two compositions in the SiO(2)-CaO-P(2)O(5) ternary system. Both discontinuous fibers and dispersed fibers were evaluated. Viscosity and pH of the sol were the two primary processing variables studied. The formation of hydroxy carbonate apatite (HCA) on the surface of the fibers was used to evaluate the kinetics of the bioactivity in a simulated body fluid (SBF). Diffuse reflection infrared fourier transform spectroscopic (DRIFTS) analysis confirmed the presence of HCA (P-O). A homogenous layer of HCA, as observed with SEM (scanning electron microscopy), typically formed after 3-h immersion in the SBF. The concentration of HCA formed was greater for samples richer in silica. The new bioactive fiber sheets produced by this process are chemically more stable than powders or monoliths prepared from similar precursors. Potential applications are as scaffold for both mineralized and nonmineralized structural tissues.

Zeta potential measurement in bioactive collagen

The focus of this work is to show the influence of surface charge on the bioactivity of modified collagen fiber surface. Because silica plays an important role on bone mineralization process, silica obtained by a sol-gel process was used as a surface modification agent. Zeta potential (x) of silica-coated and non-coated samples was measured as a function of pH. It was observed a shift in x vs. pH. The isoelectric point for silica-coated collagen was 6.8, while that of non-treated sample it was near 10. Pure silica has isoelectric point near 2, and the shift observed indicates that at least part of the silica was incorporated onto the surface during the treatment. The ability of samples exposed to biological simulated fluids (SBF) to form a hydroxyapatite layer has been used to recognize bioactive materials. The pH of these biological solutions is about 7.3. It means that treated samples acquire negative charge when in contact with the biological solution and attract ions like Ca2+, HPO42-, and OH- to form HA coatings. Micrographs of chemically treated samples corroborate this assumption. For treated samples, the formation of a coating layer is clear after 5-day immersion in SBF, while pure collagen remains practically unaltered. Fourier Transform Infrared Spectroscopic (FTIR) analyses confirmed that the coating layer has P-O vibration bands near 1060 cm-1 and 600 cm-1 characteristic of hydroxyapatite (HA).

Cerâmicas bioativas: estado da arte

Bioactive glasses undergo corrosion with leaching of alkaline ions when exposed to body fluids. This results in the spontaneous formation of a layer of hydroxyapatite (HA), the mineral component of natural bone, which in turn can induce bone growth in vivo. This paper describes the different types of bioactive glasses, the characterization methods currently used, and the main factors that influence their bioactivity. Nucleation and crystallization, the main mechanisms involved in the formation of hydroxyapatite, Ca10(PO4)6(OH)2, are discussed as a function of the chemical composition and the reactivity of the surface of the material. Finally, promising applications are considered.

Thermosensitive gemcitabine-magnetoliposomes for combined hyperthermia and chemotherapy.

The combination of magnetic hyperthermia therapy with the controlled release of chemotherapeutic agents in tumors may be an efficient therapeutic with few side effects because the bioavailability, tolerance and amount of the drug can be optimized. Here, we prepared magnetoliposomes consisting of magnetite nanoparticle cores and the anticancer drug gemcitabine encapsulated by a phospholipid bilayer. The potential of these magnetoliposomes for controlled drug release and cancer treatment via hyperthermic behavior was investigated. The magnetic nanoparticle encapsulation efficiency was dependent on the initial amount of magnetite nanoparticles present at the encapsulation stage; the best formulation was 66%. We chose this formulation to characterize the physicochemical properties of the magnetoliposomes and to encapsulate gemcitabine. The mean particle size and distribution were determined by dynamic light scattering (DLS), and the zeta potential was measured. The magnetoliposome formulations all had acceptable characteristics for systemic administration, with a mean size of approximately 150 nm and a polydispersity index <0.2. The magnetoliposomes were stable in aqueous suspension for at least one week, as determined by DLS. Temperature increases due to the dissipation energy of magnetoliposome suspensions subjected to an applied alternating magnetic field (AMF) were measured at different magnetic field intensities, and the values were appropriated for cancer treatments. The drug release profile at 37 °C showed that 17% of the gemcitabine was released after 72 h. Drug release from magnetoliposomes exposed to an AMF for 5 min reached 70%.

A tetravalent dengue nanoparticle stimulates antibody production in mice

BackgroundDengue is a major public health problem worldwide, especially in the tropical and subtropical regions of the world. Infection with a single Dengue virus (DENV) serotype causes a mild, self-limiting febrile illness called dengue fever. However, a subset of patients experiencing secondary infection with a different serotype progresses to the severe form of the disease, dengue hemorrhagic fever/dengue shock syndrome. Currently, there are no licensed vaccines or antiviral drugs to prevent or treat dengue infections. Biodegradable nanoparticles coated with proteins represent a promising method for in vivo delivery of vaccines.FindingsHere, we used a murine model to evaluate the IgG production after administration of inactivated DENV corresponding to all four serotypes adsorbed to bovine serum albumin nanoparticles. This formulation induced a production of anti-DENV IgG antibodies (p < 0.001). However, plaque reduction neutralization assays with the four DENV serotypes revealed that these antibodies have no neutralizing activity in the dilutions tested.ConclusionsOur results show that while the nanoparticle system induces humoral responses against DENV, further investigation with different DENV antigens will be required to improve immunogenicity, epitope specicity, and functional activity to make this platform a viable option for DENV vaccines.

Coating Nanomagnetic Particles for Biomedical Applications

Magnetic particles with dimensions ranging from the nanometer to the micrometer scales are being used in an increasing number of medical applications, since the mid-1970s. The most important properties of magnetic particles for clinical diagnostics and medical therapies are clearly nontoxicity, biocompatiblilty, injectability, and high-level accumulation in the target tissue or specific organ, being strictly and spatially confined to the planned region of the internal body (Ito et al., 2005). The unique feature of NMPs to be guided by an external magnetic field has been used in magnetic resonance imaging (MRI), tissue repair, hyperthermia, drug delivery, and in cell separation (Duguet et al., 2006; Gupta & Gupta, 2005; Gupta et al., 2007; Mccarthy et al., 2007). For these biomedical applications, magnetic particles exhibiting superparamagnetic behavior at room temperature are preferred because they do not retain any magnetism after removal of the magnetic field. For NMPs, this behavior can be explained by their extraordinarily reduced sizes (Morup et al., 1976; Pfannes, 1997). The magnetization relaxation depends on KV/kT (Gupta & Gupta, 2005; Gupta et al., 2007) in which K is the particle anisotropy constant, V is particle volume, k is Boltzmann’s constant and T is temperature. At a certain reduced size (volume), KV becomes comparable to the thermal energy kT. As a result, the magnetization of the particle fluctuates rapidly from one direction to another due to the thermal agitation, leaving no net magnetic moment. At this magnetic stage, the particle is said to be superparamagnetic (Xu & Sun, 2007). Fig. 1 shows a magnetization curve obtained by Andrade et al for a NMPs with particle size of 7 nm (Andrade et al., 2009). This shows that a particle can be magnetized under an external magnetic field (H), reaching a maximum moment (M) when the field is strong enough. However, there is no remnant magnetic moment, i.e. without an external magnetic field, the net moment of the particle is randomized to zero. Therefore, these superparamagnetic nanoparticles are very useful for biomedical applications as they are not subject to strong magnetic interactions in the dispersion and are readily stabilized in physiological conditions (Gupta & Gupta, 2005; Neuberger et al., 2005; Sonvico et al., 2005).