Rodrigo Velázquez-Castillo

Interconnected porosity analysis by 3D X-ray microtomography and mechanical behavior of biomimetic organic-inorganic composite materials

Hydroxyapatite-based materials have been used for dental and biomedical applications. They are commonly studied due to their favorable response presented when used for replacement of bone tissue. Those materials should be porous enough to allow cell penetration, internal tissue growth, vascular incursion and nutrient supply. Furthermore, their morphology should be designed to guide the growth of new bone tissue in anatomically applicable ways. In this work, the mechanical performance and 3D X-ray microtomography (X-ray μCT) study of a biomimetic, organic-inorganic composite material, based on hydroxyapatite, with physicochemical, structural, morphological and mechanical properties very similar to those of natural bone tissue is reported. Ceramic pieces in different shapes and several porous sizes were produced using a Modified Gel Casting Method. Pieces with a controlled and 3D hierarchical interconnected porous structure were molded by adding polymethylmethacrylate microspheres. Subsequently, they were subject to a thermal treatment to remove polymers and to promote a sinterization of the ceramic particles, obtaining a HAp scaffold with controlled porosity. Then, two different organic phases were used to generate an organic-inorganic composite material, so gelatin and collagen, which was extracted from bovine tail, were used. The biomimetic organic-inorganic composite material was characterized by Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray Diffraction, Fourier Transform Infrared Spectroscopy and 3D X-ray microtomography techniques. Mechanical properties were characterized in compression tests, obtaining a dramatic and synergic increment in the mechanical properties due to the chemical and physical interactions between the two phases and to the open-cell cellular behavior of the final composite material; the maximum compressive strength obtained corresponds to about 3 times higher than that reported for natural cancellous bone. The pore size distribution obtained could be capable to allow cell penetration, internal tissue in-growth, vascular incursion and nutrient supply and this material has tremendous potential for use as a replacement of bone tissue or in the manufacture and molding of prosthesis with desired shapes.

Synthesis and Characterization of Hydroxyapatite-Based Nanostructures: Nanoparticles, Nanoplates, Nanofibers and Nanoribbons

Material science is taking an increasing important role in bioengineering and biomedical sciences, aiming to develop new systems and materials capable of adapting to the highly demanding environment of a living organism. One of those materials, Hydroxyapatite (HAp), is the principal calcium orthophosphate present in the mineral phase of bone.

Morphological Analysis of Hydroxyapatite Particels Obtained by Different Methods

Material science is playing an increasing role in bioengineering and biomedical sciences, aiming to develop new systems and materials capable of overcoming the highly demanding environment of a living organism. One of those materials, Hydroxyapatite (HAp), is the principal calcium phosphate present in the mineral phase of bone. Hydroxyapatite-based materials have been used for dental and biomedical applications, and the control of morphology and structure at micro and nanoscale levels in the synthesis processes, is crucial for several of those applications. Hydroxyapatite crystalline particles were obtained by the so-called sol-gel technique, in which silica gels induce the formation of apatite particles in a simulated body fluid at nearly 37°C, different chemical additives were used to control morphology and particle size, as previously reported by our group. Recently, the synthesis of HAp particles with similar morphologies obtained by different methods, have been reported by other groups. Differences and similarities in morphologies, as well as in the synthesis processes, are established in the present work, along with a discussion of possible crystal growth and assembly mechanisms, which lead to a better understanding of the particle growth processes, is included. This knowledge could be the basis for further synthesis methods aimed to obtain HAp nanostructures with a crystal preferential orientation.

Mechanical Characterization of Hydroxyapatite-Based, Organic-Inorganic Composites

Hydroxyapatite-based materials have been used for dental and biomedical applications. Newly developed synthesis techniques give cause to a broad field in the study of these materials and industry demands products with better properties day by day. The purpose of the present work was to evaluate the mechanical properties of hydroxyapatite-based (HAp-based), organic-inorganic composites. HAp-based, organic-inorganic composites were obtained by modified gel casting process and organic molecules in a gelatin solution. HAp samples of different sizes and shapes were obtained with controlled micro and macro porosity and then were immersed into several gelatin solutions with different concentrations. X-ray powder Diffraction (XRD), Infra Red (IR) Spectroscopy and Scanning Electron Microscopy (SEM) techniques were used to analyze samples before and after gel casting process in order to assure that chemical and physical properties remains the same after this process. IR Spectroscopy and SEM techniques were used to characterize samples after the introduction of organic phase in order to analyze the final morphology of samples. Mechanical characterization was made in compression mode to samples without and with different concentrations of organic phase in order to establish the optimum conditions in which the highest compressive strength and Young’s modulus is reached.

Morphology Effect of Silver Nanostructures on the Performance of a P3HT

We report the effect of the use of different silver nanostructures (AgNs) layers deposited via dip coating onto a poly(3-hexylthiophene) (P3HT) and solution processable functionalized graphene (SPFGraphene) composite film intended to be used as active layer in BHJ devices. SPFGraphene was added to P3HT in a ratio of 1.5źwt%. The best results were achieved when a layer of silver nano-pseudospheres (AgNPSs) obtained after 10 immersion cycles was used as coating; in this case the highest light trapping and efficiency percent (ź=0.23%) were achieved. This means an increase of ~11.3% in comparison with the efficiency of the noncoated P3HT:SPFGraphene composite. Results also indicate that graphene was successfully functionalized in order to obtain appropriate dispersion in P3HT and that such conjugated polymer remained unaltered after the addition of SPFGraphene. Finally, it can be concluded that the electrical properties of the as-synthesized films are dependent on the shape and concentration of the AgNs deposited via dip coating.