Kelly Alvarez

Abstract: The materials (C-ODTi) with different topographical surfaces that possess interstitial oxygen atoms into the host titanium lattice and an upper nanometric surface layer of anatase-TiO2 covered by a carbon thin layer were fabricated in this study. The carbon thin layer on the surface of C-ODTi was composed of amorphous carbon and nano-graphite crystals. In vitro tests, using human bone marrow-derived mesenchymal cells (hBMCs), were performed to check cytotoxicity, examining in particular cell morphology, cell proliferation, cell differentiation, and mineralization capability. After 10 days of culture a higher degree of cell viability was observed on the surface of C-ODTi with an abraded surface. We also observed that hBMCs cultured in direct contact with C-ODTi maintained their capability to express alkaline phosphatase activity (ALP) and formed mineralized nodules similar to the control cultures. Our results demonstrate that the carbon layer coating on the surface of C-ODTi possess better biological response than commercially pure titanium (cp Ti), which was evidenced by the higher proliferation rates of osteoblasts, higher osteo-differentiation and a higher mineralization capability.

Abstract: We investigated the degree of osseointegration in carbon-coated oxygen-diffused titanium implants (C-ODTi) by means of biomechanical tests of the femoral bones of rabbits. C-ODTi possesses interstitial oxygen atoms into the host titanium lattice and an upper nanometric surface layer of anatase-TiO2 covered with 20 nm carbon layer. Interface shear strength was determined by using a transcortical push-out model at 4, 12 and 24 weeks after implantation. Implants with different surfaces were prepared, including a carbon coating and an abrasion treatment. There was a significant improvement in the bone-bonding shear strength for the C-ODTi. The highest shear strength values were observed in the C-ODTi group at 24 weeks and differed significantly from those of the control group at the same experimental time (p < 0.05). After the in vivo evaluation it was concluded that the coating of a carbon layer on the surface of titanium implant was effective for improving the biocompatibility of titanium, which was evidenced by the superior interface shear strength.

Abstract: Dentifrices, such as tooth-paste, are pastes containing insoluble abrasives that aid in the removal of plaque from the teeth and help to polish them. Composite powders contributing to oral hygiene application, i.e., nano-scale MgO crystallite dispersed in CaCO3 grain, were fabricated by the thermal decomposition of dolomite. The composite obtained by heating at 800 °C consisted of CaCO3 grains including 20 nm MgO fine crystallite, being the purpose powder in this study. The antibacterial activity of these powders related to gram-positive and gram-negative bacteria was evaluated in vitro. The thermal decomposition above 800 °C resulted in the mixture of CaO and MgO. Antibacterial activity of the composite enhanced with increasing powder concentration. Though antibacterial action toward Staphylococcus aureus was greater than towards Escherichia coli, the death rate constant was identical in both bacteria. It can be concluded that the obtained composite possesses two functions able to improve the oral hygiene: as a tooth abrasive and as an antibacterial agent.

Abstract: Background: Clinical demands for stronger and faster bone bonding to implants have motivated the development of chemically and topographically modified surfaces capable of chemical bonding. This study presents a new one-step alkali heat treatment performed with a solution containing [Zn(OH)4]2− complex as an alternative to the conventional NaOH solution. Purpose: The objective of this work is to assess the effect of a Zn-modified surface chemistry on bone-implant shear strength using a rabbit model. Materials and Methods: The study was conducted on mechanical-grinded and smooth surfaces of Ti cylindrical implants. The topographical structure, chemical surface composition, and structural properties of the chemically modified titanium surface were studied by scanning electron microscopy, x-ray photoelectron spectroscopy, and x-ray diffractometry. Implant-bone shear strength was evaluated by push-out tests undertaken at 4, 12, and 24 weeks after insertion in rabbit femora. Results: Implants with smooth and rough surfaces chemically-modified with a solution containing [Zn(OH)4]2− complex demonstrated significantly stronger bone fixation than nonmodified implants at all healing times (p < 0.05). Conclusions: The obtained results suggest that biochemical bonding at the bone-implant interface, stimulated by the Zn2+ ion release in combination with mechanical interlocking definitively improved the implant fixation.

Abstract: Bone tissue engineering is an emerging interdisciplinary field in Science, combining expertise in medicine, material science and biomechanics. Hard tissue engineering research is focused mainly in two areas, osteo and dental clinical applications. There is a lot of exciting research being performed worldwide in developing novel scaffolds for tissue engineering. Although, nowadays the majority of the research effort is in the development of scaffolds for non-load bearing applications, primarily using soft natural or synthetic polymers or natural scaffolds for soft tissue engineering; metallic scaffolds aimed for hard tissue engineering have been also the subject of in vitro and in vivo research and industrial development. In this article, descriptions of the different manufacturing technologies available to fabricate metallic scaffolds and a compilation of the reported biocompatibility of the currently developed metallic scaffolds have been performed. Finally, we highlight the positive aspects and the remaining problems that will drive future research in metallic constructs aimed for the reconstruction and repair of bone.

Abstract: Although titanium has been successful as an orthopedic or dental implant material, performance problems still persist concerning implant–bone interfacial bonding strength. In this study a novel oxygen-diffused titanium (ODTi), fabricated by introducing oxygen into the titanium crystal lattice by thermal treatment, was investigated. The fabricated material is the result of a surface modification made on commercially pure titanium (cp Ti) previously coated with poly(vinyl alcohol) (PVA) by means of a thermal treatment performed at 700°C in an ultra-pure argon atmosphere. The thermal treatment at 700°C led to the formation of an anatase TiO2 film on the cp Ti surface and a concentration gradient of oxygen into titanium. The surface of the fabricated ODTi consisted of an outer nanometric layer of anatase TiO2 and an inner nanometric layer of Ti2Ox (x<1) in which the oxygen is in solid solution with the titanium metal. It was found that ODTi possesses in vitro apatite formation ability after being soaked into simulated body fluid (SBF) solution. This apatite formation ability is attributed to the presence of the anatase TiO2 outermost surface layer and to abundant hydroxyl groups (–OH) formed on the ODTi surface after immersion in SBF.

Abstract: The microstructural features, shape memory behavior and mechanical properties of Ni-Mn based alloys were investigated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermal cycling test under various stresses. The transformation temperatures shifted toward lower temperatures when adding a third element into the Ni-Mn system. The addition of 10 at. pct Fe increased considerably the mechanical properties exhibiting still high transformation temperatures. However, it was found that in NiMn40Fe10 alloy the martensitic transformation is not thermoelastic in nature. The mechanism of this transformation and the crystallography of Ni-Mn(50-x)-Fex (x = 5,7,10,20 at. pct) alloys is presented.

Abstract: The bone response to lotus-type porous nickel-free stainless steels implants was investigated using Sprague-Dawley rats. The implants were inserted in the femora and tibiae of rats (n = 60) and bone formation inside the pores of the implants was followed up to 12 weeks. Bone ingrowth in transverse histological sections was calculated using an image analysis program. Shear strength of the bone–implant interface was evaluated by the push-out test. Histological examination showed that bone grew into apparent direct contact with the implant surface and into the pores, which sizes were between 70–650 μm. At 12 weeks, maximum compressive shear strengths of 24 ± 1 MPa were obtained; these values are substantially higher than the typical shear strength achieved by porous-coated materials. These results clearly indicate that lotus-type porous structure allowed bone cells and tissue to invade the implant throughout superficial porous spaces, which resulted in an efficient biological fixation responsible for the mechanical stability at the implantation site.

Abstract: In order to produce powder samples of Zn-doped MgO, the precursors, MgO and ZnO, were mixed in a molar ratio higher than 1.86 and subsequently treated at 1200 °C for 5 h in air atmosphere. With increasing Zn content in MgO, the lattice constant increased linearly, and the optical absorption intensity increased in the wavelength ranging from 200 to 400 nm. Antibacterial activity of the obtained powder samples was examined by colony count method using Escherichia coli and Staphylococcus aureus. In the antibacterial tests, it was found that the antibacterial activity enhanced with increasing Zn content in MgO. Antibacterial action toward S. aureus was greater than that toward E. coli, irrespective of the Zn content in MgO. From these results, the enhancement of the antibacterial activity could be related with the optical absorption of Zn-doped MgO.

Abstract: Corrosion behaviour of three austenitic Lotus-type porous high nitrogen Ni-free stainless steels exposed to an acidic chloride solution has been investigated by electrochemical tests and weight loss measurements. Polarization resistance indicates that the corrosion rate of Lotus-type porous high nitrogen Ni-free stainless steels is an order of magnitude lower than that of Lotus-type porous 316L stainless steel in acidic environment. The localised corrosion resistance of the investigated high nitrogen Ni-free stainless steels, measured as pitting potential, Eb, also resulted to be higher than that of type 316L stainless steel. The influences of porous structure, surface finish and nitrogen addition on the corrosion behaviour were discussed.

Abstract: Lotus-type porous Fe–25 wt.%Cr, Fe–23 wt.%Cr–2 wt.%Mo alloys and type AISI 446 stainless steel were fabricated by continuous zone melting technique in pressurized hydrogen and helium gas. The porosity of the samples varied in the range 44–48% and the mean pore size values obtained (145–374 μm) are in the biomedical field desired range. The fabricated Lotus-type porous nickel-free stainless steel was nitrided at high temperature up to the nitrogen concentration of 1.0 wt.% and this amount resulted to be sufficient for maintaining almost single-phase austenitic structure at room temperature. The combination of very small magnetic susceptibility, light weight, mechanical properties close to the human cortical bone, together with the known good enough corrosion resistance of high nitrogen nickel-free stainless steel, makes this Lotus-type porous Fe–Cr–N alloys very attractive for bone implant applications.

Abstract: The corrosion behavior of three kinds of austenitic high nitrogen Lotus-type porous Ni-free stainless steels was examined in acellular simulated body fluid solutions and compared with type AISI 316L stainless steel. The corrosion resistance was evaluated by electrochemical techniques, the analysis of released metal ions was performed by inductively coupled plasma mass spectrometry (ICP-MS) and the cytotoxicity was investigated in a culture of murine osteoblasts cells. Total immunity to localized corrosion in simulated body fluid (SBF) solutions was exhibited by Lotus-type porous Ni-free stainless steels, while Lotus-type porous AISI 316L showed very low pitting corrosion resistance evidenced by pitting corrosion at a very low breakdown potential. Additionally, Lotus-type porous Ni-free stainless steels showed a quite low metal ion release in SBF solutions. Furthermore, cell culture studies showed that the fabricated materials were non-cytotoxic to mouse osteoblasts cell line. On the basis of these results, it can be concluded that the investigated alloys are biocompatible and corrosion resistant and a promising material for biomedical applications.

Abstract: The localized corrosion behavior of high nitrogen Ni-free and Ni-reduced austenitic stainless steels in L929 mouse fibroblasts and cell culture medium (Eagle's minimum essential medium (MEM) supplemented with 10% fetal bovine serum (FBS)) was evaluated by electrochemical techniques in an electrochemical cell culture corrosion cell. The positive effect of nitrogen alloying was evidenced. The examined high nitrogen Ni-free and Ni-reduced alloys resulted to be immune to pitting corrosion even in the presence of cells. Cell culture studies showed that high nitrogen lotus-type porous Ni-free and Ni-reduced stainless steels were non-cytotoxic to mouse fibroblasts cell line. In this sense, they represent a better alternative to other conventional stainless steels. ©2007 COPYRIGHT ECS - The Electrochemical Society Permalink: http://dx.doi.org/10.1149/1.2812436

Abstract: Lotus-type porous Fe-25wt.%Cr and Fe-23wt.%Cr-2Wt.%Mo alloys were fabricated by continuous zone melting technique in pressurized hydrogen gas. After applying a high temperature nitriding treatment, the fabricated Lotus-type porous nickel-free stainless steel absorbed larger amount of nitrogen compared with non-porous alloy of the same composition since the surface area exposed to the gas is larger in the porous samples. In the Lotus-type porous Fe-25wt.%Cr and Fe-23wt.%Cr-2Wt.%Mo alloys the nitrogen concentration after the nitriding achieved was approximately 1.2 wt. %. Only austenite peaks were detected in the profile of both Fe-Cr-N alloys after the nitriding treatment. Neither CrN nor Cr2N were identified by XRD in any specimen after the nitriding.

Abstract: The search for ideal materials for bone substitution has been a challenge for many decades. Numerous natural and synthetic materials have been studied. For this application, exoskeletons of coral have been considered a good alternative given its tendency to resorption, biocompatibility and similarity to the mineral bone phase. Very few studies of these materials consider a detailed analysis of the structure-property relationship. The purpose of this work was to carry out the microstructural characterization of a coralline species named Acropora palmata and the determination of the mechanical and physicochemical properties. Measurements of hardness, compressive strength, bulk density and apparent porosity were performed. From these results it was determined that this marine coral species could be an alternative xenograft due to its mechanical properties and osteoconductive nature

Abstract: In this study novel oxygen-infused titanium, fabricated by introducing oxygen by heat treatment into the titanium crystal lattice was investigated. In vitro tests were performed to check cytotoxicity, examining cell morphology, cell proliferation and alkaline phosphatase activity. In vivo experiments involved implantation of cylindrical implants into a rabbit femoral bone. Interface shear strength was determined using a transcortical push-out model at 4 and 12 weeks after implantation. After the in vitro and in vivo evaluation it was concluded that the applied thermochemical treatment is effective for improving the biocompatibility of titanium, which was evidenced by the higher proliferation rates of osteoblasts, higher osteodiferentiation capability and superior interface shear strength.

Abstract: Lotus-type porous Ni-free stainless steels with long straight pores aligned parallel to the solidification direction were fabricated by continuous zone melting technique. Ni-free stainless steel is defined here as a steel with a nickel content of at most　0.3 wt.%　Ni, which also meets the medically indicated requirements for the absence of nickel. In this paper, an overview of the characterization results relevant to potential medical applications of this Lotus-type porous Ni-free stainless steel is given. Measured material properties include magnetic properties, compressive yield strength, Young’s modulus and pitting corrosion resistance in several environments. Biological tests were performed in order to elucidate if the fabricated material effectively could be used as a biomaterial. In vitro osteoblasts cell spreading and proliferation assays were done. Additionally, in vivo test was performed to evaluate bone tissue response to Lotus-type porous Ni-free austenitic stainless steel using Sprague-Dawley rats for 12 weeks of implantation time. No apparent adverse reactions were noted on or around the implanted material. On the contrary, bone ingrowth with significantly direct bone-contacts was found inside the porous spaces.

Abstract: Based on preliminary results obtained using Lotus-type porous AISI 304 stainless steel [1], this study focuses on further and detailed biocompatibility evaluation of austenitic Lotus-type porous Ni-free stainless steel as a biomaterials candidate. The aim of the present study was to evaluate the osseointegration, extent of bone ingrowth and the implant fixation strength of Lotus-type porous Ni-free stainless steels in the tibia bone of young adult male Sprague-Dawley rats after 12 weeks of implantation time.