Biomedical subjects

Eduardo Saiz

Publications and source records attributed to Eduardo Saiz.

9 recordsLinked to original sources

PubMed2006

Freeze casting of hydroxyapatite scaffolds for bone tissue engineering.

Although extensive efforts have been put into the development of porous scaffolds for bone regeneration, with encouraging results, all porous materials have a common limitation: the inherent lack of strength associated with porosity. Hence, the development of porous hydroxyapatite scaffolds has been hindered to non-load bearing applications. We report here how freeze casting can be applied to synthesize porous scaffolds exhibiting unusually high compressive strength, e.g. up to 145 MPa for 47% porosity and 65 MPa for 56% porosity. The materials are characterized by well-defined pore connectivity along with directional and completely open porosity. Various parameters affecting the porosity and compressive strength have been investigated, including initial slurry concentration, freezing rate, and sintering conditions. The implications and potential application as bone substitute are discussed. These results might open the way for hydroxyapatite-based materials designed for load-bearing applications. The biological response of these materials is yet to be tested.

Bone and Bones↗

PubMed2006

Sintering and robocasting of beta-tricalcium phosphate scaffolds for orthopaedic applications.

beta-Tricalcium phosphate (beta-TCP) scaffolds with designed, three-dimensional (3-D) geometry and mesoscale porosity have been fabricated by direct-write assembly (robocasting) techniques. Concentrated beta-TCP inks with suitable viscoelastic properties were developed to enable the fabrication of the complex 3-D structures. A comprehensive study of the sintering behavior of TCP as a function of the calcium content in the starting powder was also carried out, and the optimal heat treatment for fabricating scaffolds with dense beta-TCP rods has been determined. Such analysis provides clues to controlling the microstructure of the fabricated structures and, therefore, enabling the fabrication by robocasting of TCP scaffolds with tailored performance for bone tissue engineering applications.

Biocompatible Materials↗

PubMed2006

Functionally graded bioactive coatings: reproducibility and stability of the coating under cell culture conditions.

This work sought to provide a basic protocol for treatment of functionally graded bioactive glass coatings (FGC) that reliably adhere to titanium alloy (Ti6Al4V) prior to in vivo evaluation. The effect of the fabrication process on glass structure and reproducibility of the coating's properties, and the effect of cell culture conditions on the integrity of the coating were assessed. The structure of FGCs was compared to that of the as cast glass used as a top coating. X-ray diffraction (XRD) showed that the fabrication process resulted in 5.9+/-3.0 vol.% crystallization, while glass as cast was amorphous. Glass as cast and coatings behaved similarly in simulated body fluid (SBF): an amorphous layer rich in phosphate formed, and it crystallized, over 4 weeks, into apatite-like mineral (Fourier transform infrared spectroscopy (FTIR), XRD, scanning electron microscopy (SEM)). Reproducibility of the fabrication process was tested from three batches of coatings by measuring thickness and crystallinity. MC3T3-E1.4 mouse pre-osteoblast cells were cultured and induced to mineralize on FGCs, either as made or pre-conditioned in SBF. The sub-surface glass silica network in FGCs was compromised by cell culture conditions. A crystalline phosphate was formed during pre-conditioning (XRD, FTIR, and SEM). SBF-pre-conditioning stabilized the coatings. Thus incubation in SBF is recommended to produce a stable coating.

3T3 Cells↗

PubMed2006

Freezing as a path to build complex composites.

Materials that are strong, ultralightweight, and tough are in demand for a range of applications, requiring architectures and components carefully designed from the micrometer down to the nanometer scale. Nacre, a structure found in many molluscan shells, and bone are frequently used as examples for how nature achieves this through hybrid organic-inorganic composites. Unfortunately, it has proven extremely difficult to transcribe nacre-like clever designs into synthetic materials, partly because their intricate structures need to be replicated at several length scales. We demonstrate how the physics of ice formation can be used to develop sophisticated porous and layered-hybrid materials, including artificial bone, ceramic-metal composites, and porous scaffolds for osseous tissue regeneration with strengths up to four times higher than those of materials currently used for implantation.

Biocompatible Materials↗

PubMed2005

Spreading of viscous liquids at high temperature: silicate glasses on molybdenum.

The spreading of Si-Ca-Al-Ti-O glasses on molybdenum has been investigated. By controlling the oxygen activity in the furnace, spreading can take place under reactive or nonreactive conditions. As the nucleation of the reaction product under reactive conditions is slow in comparison to the spreading kinetics, in both cases the glass front moves on the metal surface with similar spreading velocities. Spreading can be described using a molecular dynamics model where the main contribution to the wetting activation energy comes from the viscous interactions in the liquid. Enhanced interfacial diffusions in low-oxygen activities (reactive cases) form triple-line ridges that can pin the wetting front and cause a stick-slip motion.

Journal Article↗

PubMed2004

Colloid formation at waste plume fronts.

Highly saline and caustic tank waste solutions containing radionuclides and toxic metals have leaked into sediments at U.S. Department of Energy (DOE) facilities such as the Hanford Site (Washington state). Colloid transport is frequently invoked to explain migration of radionuclides and metals in the subsurface. To understand colloid formation during interactions between highly reactive fluids and sediments and its impact on contaminant transport, we simulated tank waste solution (TWS) leakage processes in laboratory columns at ambient and elevated (70 degrees C) temperatures. We found that maximum formation of mobile colloids occurred at the plume fronts (hundreds to thousands times higher than within the plume bodies or during later leaching). Concentrations of suspended solids were as high as 3 mass %, and their particle sizes ranged from tens of nanometers to a few micrometers. Calcium carbonate is always one of the dominant phases of the plume front colloids, while the other phases varied with solution pH and temperature. During infiltration of the leaked high-Na+ waste solution, rapid and completed Na+ replacement of exchangeable Ca2+ and Mg2+ from the sediment caused accumulation of these divalent cations at the moving plume front. Precipitation of supersaturated Ca2+/Mg2+-bearing minerals caused dramatic pH reduction atthe plume front. In turn, the reduced pH caused precipitation of other minerals. This understanding can help predict the behavior of contaminant trace elements carried by the tank waste solutions and could not have been obtained through conventional batch studies.

Adsorption↗

PubMed2004

Atomic dynamics and Marangoni films during liquid-metal spreading.

Despite its apparent simplicity, spreading of liquid metals at high temperatures has defied description and generalization. Wetting at high temperature is usually accompanied by interdiffusion and chemical reaction, but the forces that drive reactive spreading and the mechanisms that control its kinetics have been very poorly understood. The unsolved challenge has been to link macroscopic measurements such as the dynamic contact angle or the speed of a moving liquid front to phenomena occurring at the microscopic and even atomic level in the vicinity of the triple solid-liquid-vapour junction. We have taken a big step towards meeting this challenge. Our systematic analysis of the spreading of metal-metal systems with varying degrees of mutual solubility allows us to report on the fundamental differences between the mechanisms controlling spreading of organic liquids and liquid metals and on formation of Marangoni films driven by surface-tension gradients in high-temperature systems.

Computer Simulation↗

PubMed2004

The influence of novel bioactive glasses on in vitro osteoblast behavior.

Implant success requires a direct bond between bone and implant surface. Bioinert implants, such as titanium alloys, are commonly plasma-spray-coated with a bone-bonding, bioactive material such as hydroxyapatite. Such coatings tend to be chemically and topographically inhomogeneous without reproducible properties. A family of bioactive glasses that can be enameled and reliably adheres to titanium alloy has been developed. In this study the cytocompatibility of two of these glass compositions was tested in the as-cast condition. The effects of these glasses on the early and late events of osseous tissue formation in vitro were determined with MC3T3-E1.4 mouse osteoblast-like cells. MC3T3-E1.4 cells were cultured on glasses containing 55 and 50 wt % SiO(2), with titanium alloy (Ti6Al4V) and tissue culture polystyrene as controls. Cellular adhesion and proliferation, and alkaline phosphatase activity were studied over 5 to 15 days in culture. Qualitative and quantitative assays of mineralization were conducted. The osteoblast-like cells showed increased proliferation when grown on a bioactive glass containing 50 wt % silica. However, the adhesion, differentiation and mineralization behavior were similar on both glass compositions used in this study. These bioactive glasses proved to be cytocompatible substrata for osteoblast-like cell culture, and yielded higher cellular proliferation than titanium alloy.

Alkaline Phosphatase↗

PubMed2003

A new approach to mineralization of biocompatible hydrogel scaffolds: an efficient process toward 3-dimensional bonelike composites.

As a first step toward the design and fabrication of biomimetic bonelike composite materials, we have developed a template-driven nucleation and mineral growth process for the high-affinity integration of hydroxyapatite with a poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogel scaffold. A mineralization technique was developed that exposes carboxylate groups on the surface of cross-linked pHEMA, promoting high-affinity nucleation and growth of calcium phosphate on the surface, along with extensive calcification of the hydrogel interior. Robust surface mineral layers a few microns thick were obtained. The same mineralization technique, when applied to a hydrogel that is less prone to surface hydrolysis, led to distinctly different mineralization patterns, in terms of both the extent of mineralization and the crystallinity of the apatite grown on the hydrogel surface. This template-driven mineralization technique provides an efficient approach toward bonelike composites with high mineral-hydrogel interfacial adhesion strength.

Biocompatible Materials↗