J. Román

Influence of composition and surface characteristics on the in vitro bioactivity of SiO2−CaO−P2O5−MgO sol-gel glasses

Glasses in the system SiO(2)-CaO-P(2)O(5)-MgO were prepared by the sol-gel method. These glasses featured SiO(2) contents in the range 60-80 mol %, 4 mol % of P(2)O(5), and a CaO/MgO molar ratio of 4. Because of their composition and surface properties, all the glasses showed in vitro bioactivity, as evidenced by the formation of an apatite-like layer on their surface when soaked in an acellular medium with ionic composition similar to human blood plasma. An increase in the CaO content of the glasses also caused an increase in their porosity. Higher porosity facilitated the apatite nucleation on the sample surface during the first days of the in vitro test. On the other hand, those glasses with higher SiO(2) content also showed higher surface area values, as well as higher calcium phosphate layer growth rates. For longer soaking periods, the grown layer was analyzed, revealing a two-phase composition: apatite and whitlockite.

Synthesis of porous hydroxyapatites by combination of gelcasting and foams burn out methods

The biocompatibility and the osteoconductive behavior of hydroxyapatite (OHAp) ceramics are well established. Bioceramics made of OHAp are available in dense and porous form. Recently it has been proved that the volume of bone ingrowth at early times is primarily interconnectivity dependent. A new method for the obtention of porous OHAp ceramics that combine the in situ polymerization (gel casting method) and the foams burn out is proposed. Four polyurethane foams with different cells/cm were used. The foams were fully filled of an OHAp polymerizable suspension that after gelled produced very homogeneous and strong green bodies. After different thermal treatments the green bodies yield porous OHAp ceramics that were a replica of the foams used. Materials used in this work were studied by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), N2 adsorption isotherm, particle size distribution, and Hg porosimetry. Porous pieces of OHAp obtained are constituted by polyhedral-like particles (0.45–1.0 μm) that are surrounded by an interconnected network of pores. A bimodal distribution of the pores size between 30.8–58.6 and 1.0–1.2 μm has been observed. The size of the interconnected pores (30.8–58.6 μm) was controled as a function of the cells/cm of the foam while the volume of the small pores was modified as a function of the sintering time. The presence of pores could promote the bone ingrowth and also could be used to insert different drugs, which makes these porous pieces a potential candidate to be used as non-load-bearing bone implants and as drug delivery systems.

An alternative technique to shape scaffolds with hierarchical porosity at physiological temperature.

The method described in this work, termed GELPOR3D, is characterised by its simplicity of use, low-cost equipment, compositional flexibility, and lack of aggressive or toxic solvents or other thermal treatment. This technique ensures the generation of a three-dimensional network of interconnected pores (300-900 microm); in addition, a random and not necessarily connected porosity is generated, yielding a hierarchical porous architecture from the macro to the molecular scale. The interconnected pores, large enough to ensure an adequate vascularization and new tissue ingrowth, can be obtained by pouring a slurry containing a biodegradable thermogel (such as agarose and gellan) and a ceramic into a mold consisting of a three-dimensional network of rigid filaments. Additional pore distributions in the macropore region can be tailored as a function of the drying/preservation technology (10-100 microm) or the interaction between the inorganic particles coated by the polymeric components (0.1-1 microm). Moreover, porosity in the mesopore range can be created by shaping ceramics such as mesoporous silica or nanocrystalline carbonatehydroxyapatite. In addition to the various bioceramics that have been successfully shaped, this method is flexible enough to allow the introduction of certain substances whose controlled release may help to avoid some negative effects that usually appear with the implantation of a material, i.e. infection, inflammation, etc., or to simplify some of the many steps required for the successful integration of a graft.

Capacitance effects and gaseous adsorption on pure and doped polycrystalline tin oxide

Abstract Conductance and capacitance effects have been studied simultaneously on thin films and ceramics of tin oxide by using d.c. conductance and impedance measurements. Pure SnO2 and SnO2-CuO composite materials were studied. The total resistance of the samples is mainly due to the grain boundaries and the adsorption on these boundaries of gaseous species with high dielectric constant as ethanol leads to a high capacitance value. This capacitance effect is more important in ceramics than in thin films, n-type SnO2-type CuO composite materials exhibit particular capacitance and conductance responses under pollutant gas, due to n–p junctions at the SnO2-CuO interfaces.

Synthesis, structure and gas sensitivity properties of pure and doped SnO2

Polycrystalline SnO2 showing small particle size has been synthesized by means of pyrolysis in a tubular furnace of an aerosol produced by ultrahigh-frequency spraying of a solution. Pd nanoparticles have also been dispersed on the surface of cassiterite grains. In both cases, three solution precursors have been used: chloride, oxalate and sulfate. An SEM study indicates that two kinds of textures are obtained depending on the precursor solution: hollow spherical particles or quasi-spherical grain agglomerates. Cold pressing and annealing modify such morphologies. Conductance G = f(T) curves were studied from 50 to 500 °C under pure air (G = G0), 80 ppm ethanol or 300 ppm CO. G = f(T) curves under polluted air show different behaviors. Most of them show a pronounced maximum and corresponding sensitivity S = (G - G0)/G0 varies between 10 and 390.

Adducts of bis(8-quinolinate) oxovanadium(IV) with organic bases

Abstract We report the synthesis and study of bis(8-quinolinol) oxovanadium(IV) adducts with pyridine and substituted pyridines. These complexes were identified by IR and electronic spectra, magnetic susceptibility measurements and analytical data. The relation between the basicity of the pyridines and the VO stretching frequency has also been studied. The effects of steric hindrance and the inductive effects exercised by the functional groups, amino and methyl of the pyridine, in the formation of the adducts are discussed.

Control of the pore architecture in three-dimensional hydroxyapatite-reinforced hydrogel scaffolds

Abstract Hydrogels (gellan or agarose) reinforced with nanocrystalline carbonated hydroxyapatite (nCHA) were prepared by the GELPOR3D technique. This simple method is characterized by compositional flexibility; it does not require expensive equipment, thermal treatment, or aggressive or toxic solvents, and yields a three-dimensional (3D) network of interconnected pores 300–900 μm in size. In addition, an interconnected porosity is generated, yielding a hierarchical porous architecture from the macro to the molecular scale. This porosity depends on both the drying/preservation technology (freeze drying or oven drying at 37 ○C) and on the content and microstructure of the reinforcing ceramic. For freeze-dried samples, the porosities were approximately 30, 66 and below 3% for pore sizes of 600–900 μm, 100–200 μm and 50–100 nm, respectively. The pore structure depends much on the ceramic content, so that higher contents lead to the disappearance of the characteristic honeycomb structure observed in low-ceramic scaffolds and to a lower fraction of the 100–200-μm-sized pores. The nature of the hydrogel did not affect the pore size distribution but was crucial for the behavior of the scaffolds in a hydrated medium: gellan-containing scaffolds showed a higher swelling degree owing to the presence of more hydrophilic groups.

Kinetic studies by DSC on the thermal decomposition of calcium oxalate

Abstract In the present paper, we have studied the kinetics of the thermal decomposition of calcium oxalate monohydrate, using a new method of kinetic study employing data obtained from differential scanning calorimetry, as previously proposed by us. Initial products and those obtained following decomposition have been identified by infrared spectroscopy and X-ray powder diffraction. A comparison between the results obtained in this paper and those reported in the literature has also been made.

Role of acid attack in the in vitro bioactivity of a glass-ceramic of the 3CaO.P2O5-CaO.SiO2-CaO.MgO.2SiO2 system.

A non-bioactive glass-ceramic (GC13) that contains hydroxyapatite (Ca5(PO4)3OH), diopside (CaMg(SiO3)2) and althausite (Mg2 PO4OH) as crystalline phases has been obtained by thermal treatment of a parent bioactive glass (G13) of nominal composition (wt%) 40.0 CaO-34.5 SiO2-16.5 P2O5-8.5 MgO-0.5CaF2. To induce bioactivity, GC13 was chemically treated with 1 M HCl for different periods of time. After chemical etching the in vitro studies showed formation of an apatite-like surface layer. In this article the influence of etching time both on the surface composition of the glass-ceramic and on the growth rate of the apatite layer is studied. It is concluded that the presence of hydroxyapatite in the glass-ceramic, associated to microstructural fluctuations, can favour apatite deposition in vitro.

Suppression of anoikis by collagen coating of interconnected macroporous nanometric carbonated hydroxyapatite/agarose scaffolds

Three dimensional interconnected macroporous (pore diameter: 600-800 μm) hydroxyapatite/agarose disks have been evaluated in this study as potential bone regeneration scaffolds. With this purpose, the adhesion and proliferation of human Saos-2 osteoblasts on this biomaterial were analyzed. As an index of cell function, the following parameters were measured: cell morphology, viability, cell size/complexity, cell cycle, reactive oxygen species (ROS) content, and lactate dehydrogenase (LDH) release. The existence of anoikis induced by inappropriate contacts between the cell and the scaffold has been detected by scanning electron microscopy, confocal microscopy, and flow cytometry. The intracellular nitric oxide content has been also measured as potential inducer of anoikis. The positive effects of previous scaffold coating with type I collagen on osteoblast adhesion as well as the collagen protection against anoikis have been demonstrated in this study.