Claudia García

Effect of Some Physical-Chemical Variables in the Synthesis of Hydroxyapatite by the Precipitation Route

The synthetic hydroxyapatite is a very useful material for numerous applications in medicine as a biomaterial. One of the most economic manufacturing process is the precipitation route. In the present work, synthetic hydroxyapatite was prepared using the precipitation route, starting with aqueous solutions of calcium nitrate (Ca(NO3).4H2O ) and ammonium phosphate (H2(PO4)NH4). The effects of physical-chemical variables such as pH, temperature, time of agitation, ageing time and heat treatment of the mixture were evaluated. The characterization of the samples obtained in different conditions made possible to conclude about the optimal values of the studied variables for the synthesis of this material in laboratory conditions.

Electrochemical evaluation of resistance to localised corrosion of vitreous coatings containing particles applied on metallic substrates for biomedical applications

CrCoMo alloys are generally known to be highly resistant to corrosion-induced failures and to spontaneously form passive oxide films when immersed in physiological environments. The stresses resulting from the use of the prosthesis can cause fracture and abrasion of the oxide film that covers the surface. This can result in crevice corrosion, with the corresponding decrease in pH leading to severe attack. Protective coatings deposited onto the metals would minimise the release of metallic ions from the substrate and the incorporation of bioactive particles would enable the adhesion to the bone tissue. This work describes the electrochemical behavior of CrCoMo alloys (F75) as cast, covered by a hybrid silica coating obtained by sol‐gel. The silica sol‐gel coating contains bioactive glass ceramic and vitreous particles of the system CaO‐ SiO2‐P2O5 previously obtained by fusion, crystallization and milling. The performance of the alloy with and without coating is evaluated in simulated body fluid (SBF) pH 7.31 at 37 jC. As cobalt base alloys are susceptible to crevice attack, coated pieces are also tested in SBF acid solution (pH 0.7) in order to simulate the acidic media and the high chloride concentrations that develop when a crevice is formed. The electrochemical behavior has been evaluated by potenciodynamic polarization and electrochemical impedance spectroscopy. It was found that for both pH conditions the samples coated with double layer of glass ceramic particles showed lower passive current densities than those with monolayers. The coating improves the protection potential of the base material in the neutral solution. Besides, in the acidic solution, all the samples remain passive but the protection potential shifts to potentials more active than those measured in the neutral SBF. D 2002 Elsevier Science B.V. All rights reserved.

Enhancing low cost stainless steel implants: bioactive silica-based sol-gel coatings with wollastonite particles

A hybrid organic-inorganic sol-gel coating with the addition of wollastonite particles is used as a potential solution to improve performance of low cost AISI 316L stainless steel. This work is focused on characterising the coatings by studying their synthesis and deposition, electrochemical, and in vitro and in vivo response. The coated implants presented in vitro Ca/P-rich apatitic precursors phases on their surface and acceptable electrochemical behaviour. The in vivo response regarding bone formation seems to be excellent either with the implant in contact with bone marrow, in contact with the endostium or in contact with the trabecular bone. The bioactive and regenerative responses of bone tissue to the TEOS-MTES-wollastonite system over-compensate the coating deterioration reaction, making these coatings as a good way to improve osseo-integration of stainless steel for long term use implants.

Genotoxicity Effects of Ceramic Coatings Applied on Metallic Substrates Using Single Cell Gel Electrophoresis Assay In Vitro

Sol-Gel coatings are a good choice for protection and bioactivation of metals used as dentistry and standard surgical implant materials. These films should both prevent degradation of the substrates by wear or corrosion, and bioactivate the material for inducing the formation of a hydroxyapatite (HA) rich layer onto the material surface, thereby permitting a natural bonding to living tissues. The aim of this work was to estimate the clastogenicity in vitro by Single Cell Gel lectrophoresis Assay (SCGE) or “comet” assay of coatings of TiN applied by magnetron sputtering and of hybrid layers obtained by Sol-Gel containing glass, glass-ceramic and HA particles on stainless steel AISI 304. Six test specimens were prepared: AISI 304 Stainless Steel coated with an hybrid silica single film (SF), applied by sol-gel process, AISI 304 SS coated with double film with bioactive glass (DFG), glass-ceramics (DFGC) and HA (DFHA) particles, AISI 304 SS coated with TiN multi films (MFTiN) applied by PVD and bare AISI 304 SS (304SS). Significantly lower DNA migration (p>0.005) was observed in the cells of the cultures corresponding to the samples coated with SF, DFG, DFGC, DFHA and MFTiN respect to the bare 304 SS. The comparison between negative control and the same coated samples did not reveal any statistically significant difference (p>0.005) in clastogenicity in vitro evaluated by SCGE.

Comparative Study of Two Methods of Drying an Electro-Porcelain Paste

A comparative analysis between two methods of drying ceramics (microwave and conventional) was done based on the results of the Bigot curves of an electro-porcelain paste used as an insulator element in high-voltage circuits. The study was conducted on ceramic bars molded at 300, 600, and 900 kPa and, as expected, it was found that the higher the pressure, the lower the shrinkage and the smoother moisture profiles. The microwave technique proved to be a much more efficient method of drying ceramics because the results were always better: the volumetric shrinkage was lower (less defects), it required half the time to dry an object (less pollution and costs), and it produced a more uniformly dried piece (the residual moisture content was better distributed throughout the object). Additionally, the mechanical properties of microwave-dried bars were 20% better and the dielectric strength intensity was slightly higher than that of conventionally dried samples.

Silica Sol-Gel Patterned Surfaces Based on Dip-Pen Nanolithography and Microstamping: A Comparison in Resolution and Throughput

Fabrication of patterns on silicon and gold via Dip-Pen Nanolithography (DPN) using silica sol as ink and the combination of DPN, soft lithography, and silica sol-gel to transfer patterns from silicon and gold to stainless steel were assessed. In addition, a comparison in terms of throughput and resolution of both protocols was performed. Optical, scanning electron and atomic force microscopy were used to characterize the patterns. Silica sol showed high resolution but low throughput when used to pattern directly on gold and silicon using DPN. The combination of DPN, silica sol-gel and soft lithography showed high throughput and resolution. The present experimental methodology was useful to create patterns on a surface and transfer them to another surface of interest, which may serve as a biomaterial surface modification model.

APLICACIÓN DE LA MICROSCOPÍA HOLOGRÁFICA DIGITAL EN TRANSMISIÓN PARA LA CARACTERIZACIÓN DEL ESPESOR DE RECUBRIMIENTOS DELGADOS

I n this work an experimental optical system of digital holographic microscopy is implemented to measure thicknesses of thin films. The three-dimensional surface reconstruction was achieved as a phase contrast image obtained through computational processing of digital holograms. These images allow quantitative measurements of thin films thicknesses. This technique was applied to measure silica depositions bioactivated with particles of wollastonite produced by means of sol-gel technique. The depositions were made through dip-coating method with different velocities and using 10% p/p of wollastonite particles dispersed into the silica sol.

A novel approach to create an antibacterial surface using titanium dioxide and a combination of dip-pen nanolithography and soft lithography

Soft lithography and Dip-Pen Nanolithography (DPN) are techniques that have been used to modify the surface of biomaterials. Modified surfaces play a role in reducing bacterial adhesion and biofilm formation. Also, titanium dioxide has been reported as an antibacterial substance due to its photocatalytic effect. This work aimed at creating patterns on model surfaces using DPN and soft lithography combined with titanium dioxide to create functional antibacterial micropatterned surfaces, which were tested against Streptococcus mutans. DPN was used to create a master pattern onto a model surface and microstamping was performed to duplicate and transfer such patterns to medical-grade stainless steel 316L using a suspension of TiO2. Modified SS316L plates were subjected to UVA black light as photocatalytic activator. Patterns were characterized by atomic force microscopy and biologically evaluated using S. mutans. A significant reduction of up to 60% in bacterial adhesion to TiO2 -coated and -micropatterned surfaces was observed. Moreover, both TiO2 surfaces reduced the viability of adhered bacteria after UV exposure. TiO2 micropatterned demonstrated a synergic effect between physical and chemical modification against S. mutans. This dual effect was enhanced by increasing TiO2 concentration. This novel approach may be a promising alternative to reduce bacterial adhesion to surfaces.

Solvothermal Synthesis of Magnesium Oxide-Substituted Hydroxyapatite Nanoparticles as Antibacterial Nanomaterial for Biomedical Applications

In order to generate bactericidal effects in the oral cavity, several alternatives have been studied, including the use of silver nanoparticles but presents problems such as toxicity and low biocompatibility. From human-inspired systems, the antibacterial efficiency of the hydroxyapatite nanoparticles depends strongly on the type of composites and nanoparticles size. Several types of hydroxyapatite nanoparticles and their derivatives have received much attention for their antibacterial potential effect, including magnesium oxide nanoparticles. The purpose of this research was to produce a biocompatible antimicrobial compound of nanoparticles of hydroxyapatite doped with magnesium oxide to generate antibacterial effects in the oral cavity. The solvothermal method was used to produce hydroxyapatite nanoparticles doped with magnesium oxide. Antibacterial activity of as synthesized nanopowders against cariogenic Streptococcus mutans was tested by the CLSI disk-diffusion method. As result of this research, hydroxyapatite doped with magnesium nanoparticles (nHAMg) were successfully synthetized by the solvothermal method where in structural characterization indicates magnesium substitution and FTIR analysis gives a broader spectrum of the nHAMg when compared to pure nHA and crystallite size of nHA decreased. Furthermore, results of antibacterial assays showed that nHAMg allow to inhibit the grown of S. mutans by showing a halo of inhibition around the discs. Moreover, this antibacterial activity is enhanced by the addition of silver ion in an amount below to known toxic concentration, showing a synergetic effect that can further potentiate even more these HA nanoparticles. This work demonstrates that solvothermal method is a promising synthesis way for producing antibacterial hydroxyapatites nanoparticles for biomedical applications such as oral tissue regeneration.

Recubrimientos sol-gel con partículas de wollastonita sobre acero inoxidable 316l

El acero inoxidable AISI 316L es el biomaterial mas utilizado para la fabricacion de implantes temporales, pero estos presentan limitaciones para implantes permanentes, debido a la liberacion de iones metalicos. Una estrategia para minimizar la liberacion de iones, es la modificacion superficial de los implantes metalicos por medio de recubrimientos inorganicos ceramicos o vitreos aplicados por el metodo sol-gel. En el presente trabajo, se depositaron recubrimientos con particulas de wollastonita producidos por la tecnica sol-gel sobre acero inoxidable. Se evaluaron la estabilidad de las suspensiones y la biocompatibilidad de los recubrimientos mediante ensayos in Vitro en fluido fisiologico simulado (SBF).