Francisco Guitián

Bioeutectic: a new ceramic material for human bone replacement.

In the present work, a new way of obtaining bioactive ceramic materials with eutectic morphology is presented. To this purpose the binary system wollastonite-tricalcium phosphate was selected, taking into account the different bioactivity behaviour of both phases. The material is formed by quasi-spherical colonies composed of alternating radial lamellae of wollastonite and tricalcium phosphate. In in vitro experiments the material presents a high reactivity, with the formation of two well-differentiated zones of hydroxyapatite, one formed by alteration of the eutectic material with solution of the wollastonite into the simulated body fluid and subsequent pseudomorphic transformation of the tricalcium phosphate into hydroxyapatite, and the other, in the last stages of the experiments, by deposition of hydroxyapatite onto the surface of the material. The hydroxyapatite morphology, formed at the beginning of the reaction, is similar to that of porous bone. The method used opens the opportunity to develop a new family of bioactive materials with different constituents, binary or ternary, for which the authors propose the general name of bioeutectics.

Reactivity of a wollastonite–tricalcium phosphate Bioeutectic® ceramic in human parotid saliva

In a previous study, a new ceramic material (Bioeutectic), prepared by slow solidification through the eutectic temperature region of the wollastonite-tricalcium phosphate system, was found to be reactive in a simulated body fluid. In the present study, the reactivity of the Bioeutectic was assessed in human parotid saliva. Samples of the material were soaked for one month in human parotid saliva at 37 degrees C. The experiments showed the formation of two separate zones of carbonate-hydroxyapatite-like phase on the periphery of the samples. The first zone was formed by reaction of the bioeutectic with the saliva and progressed inside the material. The other zone developed on the surface of the bioeutectic by precipitation from the media. The mechanism of carbonate-hydroxyapatite-like phase formation in human parotid saliva appeared to be similar to that of apatite-like phase found in a simulated body fluid.

Differentiation between hydroxyapatite and β-tricalcium phosphate by means of μ-Raman spectroscopy

Abstract We present a comparative study of the Roman spectra of polycrystalline β-tricalcium phosphate (β-TCP) and hydroxyapatite (HA) over their whole optical frequency range. Due to their structural differences, Raman scattering permits to differentiate between these two calcium phosphates, not only through the detection of vibrational modes associated with the OH − group of hydroxyapatite, but also by comparing the bands arising from internal PO 4 3− modes. The widths of the Raman-scattering bands associated with PO 4 3− bond-bending modes and the frequency gap between them are characteristic features that can be used to distinguish between β-TCP and HA. The method is used to identify a HA layer a few microns thick which precipitates on the surface of TCP-wollastonite eutectic soaked in simulated body fluid.

Morphological studies of pseudowollastonite for biomedical application

Pseudowollastonite ceramic (psW) composed of CaO·SiO2 was found to be bioactive in a simulated body fluid environment. The chemical reaction initiated at the material surface resulted in hydroxyapatite (HA)formation. These bone‐bonding properties are essential for securing the necessary physico‐chemical integration of the material with living bone. Materials behaving in this way can be considered for potential biomedical application as bone tissue substitute for a natural bone repair or replacement as implant.

Synthesis and antimicrobial activity of a silver-hydroxyapatite nanocomposite

A silver-hydroxyapatite nanocomposite has been obtained by a colloidal chemical route and subsequent reduction process in H2/Ar atmosphere at 350°C. This material has been characterized by TEM, XRD, and UV-Visible spectroscopy, showing the silver nanoparticles (∼65 nm) supported onto the HA particles (∼130 nm) surface without a high degree of agglomeration. The bactericidal effect against common Gram-positive and Gram-negative bacteria has been also investigated. The results indicated a high antimicrobial activity for Staphylococcus aureus, Pneumococcus and Escherichia coli, so this material can be a promising antimicrobial biomaterial for implant and reconstructive surgery applications.

Mechanism of bone-like formation on a bioactive implant in vivo

The physical and chemical nature of the remodelled interface between the porous A3 glass-ceramic, composed of (wt%): SiO(2) = 54.5; CaO = 15.0; Na(2)O = 12.0; MgO = 8.5; P(2)O(5) = 6.0 K(2)O = 4.0, and the surrounding bone was studied after implantation into rat tibias. The interfaces which developed new bone layer in direct contact with the implants were examined by analytical scanning and transmission electron microscopy after implantation for 6, 8 and 12 weeks. Degradation processes of the implants also encouraged osseous tissue ingrowths into the pores of the material, changing drastically the macro- and microstructure of the implants. The ionic exchange initiated at the implant interface with the physiological environment was essential in the integration process of the implant, through a dissolution-precipitation-transformation mechanism. The interfaces developed non-toxic biological and chemical activities and remained reactive over the 12-week implantation period. These findings were significant as indicative of morphological and chemical integration of the A3 glass-ceramic into the structure of living bone tissue. A3 glass-ceramic could be suitable for the repair or replacement of living bone.

Bioceramics—simulated body fluid interfaces: pH and its influence of hydroxyapatite formation

In the present work a method to determine the pH at bioceramics-simulated body fluid interfaces has been developed. The results obtained with several bioactive silica-based bioceramic materials are used to propose a general mechanism for hydroxyapatite formation.

Transmission electron microscopy of the interface between bone and pseudowollastonite implant

This paper reports on the structural morphology of the interface in vivo between implants composed of bioactive synthetic pseudowollastonite ceramic and bone in rat tibias. Thin sections of the interfaces were examined after 6 and 8 weeks of implantation period in a high resolution transmission electron microscope up to the lattice plane resolution level.

The formation of zircon from amorphous ZrO2 · SiO2 powders

The different factors affecting the mechanism of zircon formation from amorphous ZrO2 · SiO2 powders have been studied. It was shown that zircon was formed by solid state reaction between tetragonal zirconia and silica (amorphous and cristobalite). The previously suggested Hedvall effect associated with the crystallization of amorphous silica into cristobalite did not play any role in this reaction. A high degree of Si-Zr mixing in the starting amorphous powders did not affect the mechanism of zircon formation, but speeded up the reaction rate due to the small particle size of the zirconia and silica particles segregated previously to zircon formation. It was also found that the formation reaction was retarded by the presence of carbonaceous species coming from the alkoxide precursors, which were probably retained at grain boundaries after calcination, acting as a diffusion barrier. These factors can explain the observed differences in the temperatures of zircon formation previously reported.

A New Biocompatible and Antibacterial Phosphate Free Glass-Ceramic for Medical Applications

In the attempt to find valid alternatives to classic antibiotics and in view of current limitations in the efficacy of antimicrobial-coated or loaded biomaterials, this work is focused on the development of a new glass-ceramic with antibacterial performance together with safe biocompatibility. This bactericidal glass-ceramic composed of combeite and nepheline crystals in a residual glassy matrix has been obtained using an antimicrobial soda-lime glass as a precursor. Its inhibitory effects on bacterial growth and biofilm formation were proved against five biofilm-producing reference strains. The biocompatibility tests by using mesenchymal stem cells derived from human bone indicate an excellent biocompatibility.