Papers by Author: Elena Landi

Abstract: Proper thermal treatments allowed to modify the number of surface Ca2+ able to coordinate water molecules on the surface of hydroxyapatite (HA) nanoparticles surrounded by an amorphous layer. Despite the consequent significant difference in the first hydration level between untreated and treated HA, the amount of adsorbed BSA, used as a model protein, remained essentially unchanged and the native structure of adsorbed protein was retained (as indicated by mid-IR ATR). Near-IR spectroscopy evidenced that adsorbed proteins should be in direct contact with surface Ca2+ through a displacement of H2O molecules by charged acidic residues. In agreement with a previous study that evidenced the heterogeneity of surface Ca2+ ions in terms of Lewis acidity, it was then proposed that the adsorption of BSA on such nano-HA should be ruled by some feature of the local structure of surface Ca2+ sites, prevailing on the total number of cationic sites exposed and the related features of the first hydration layer.

Abstract: A novel foaming method of design and synthesis of porous Carbonate-apatite/gelatine composite scaffolds is proposed for biomedical applications. Two different suspensions, one constituted by a biomimetic inorganic phase (B-CHA) and the second by a protein (gelatine), are mixed, foamed, lyophilized and, in some cases, cross-linked to stabilize the organic phase. Chemical, morphological and mechanical features of the scaffolds are evaluated. The samples have chemical composition, compressive and flexural strengths and Young modulus values in the range of trabecular bone ones. A high interconnected porosity (about 90%) showing a micro- to macrosize distribution, that is needed for osteoconduction and vascolarization processes in vivo, is also detected.

Abstract: The preparation and characterization of an inorganic/organic composite scaffold is proposed in this paper. The substrate was realized by the polymerization of an electroconductive polymer, namely polypyrrole PPy, into an hydroxyapatite HAp porous support. The PPy/HAp composite was characterized by XRD, Hg porosimetry measurements, SEM-EDS and electrochemical test. The results pointed out that the PPy polymer entered into the HAp whole pores moving through the interconnected paths of the hydroxyapatite matrix. The PPy thin film doped with heparin maintained its electrochemical characteristics even in the ceramic support.

Abstract: The present work deals with the preparation and characterization of ceramic composites for the substitution of load-bearing bone portions, made of hydroxyapatite (HA) and bioactive β- calcium silicate (β-Ca2SiO4) as a reinforcing phase. The composite materials were prepared by Fast Hot-Pressing technique (FHP), which allowed the rapid sintering of monolithic ceramics at temperatures up to 1500 °C, well above the commonly adopted temperatures for sintering of hydroxyapatite (1200-1300 °C), in order to achieve the densification of the reinforcing phase also. XRD analysis reported no formation of secondary phases other than HA and β-Ca2SiO4, after FHP cycles. Flexural strength tests were performed on selected samples sintered at different temperatures: the composite materials exhibited increased mechanical resistance compared to samples constituted of HA only. These preliminary results confirmed that composites of HA and β- Ca2SiO4 are promising for the development of bioactive load-bearing ceramic bone substitutes.

Abstract: The present work describes the development of biomimetic materials for osteochondral tissue substitution and repair, which can be the start for a revolution in the classical procedures of orthopedic surgery. Performing biomineralization process, we succeeded to prove that biological system store and process information at the molecular level. The substitute consist in three layers: the lower layer, mimicking bone tissue, is formed by HA/Collagen (70/30)wt; the intermediate layer, mimicking the tade-mark, is formed by HA/Collagen (40/60)wt; and the upper layer, mimicking the cartilagineous layer, is formed by Collagen containing Hyaluronic Acid. In vivo tests performed on small and large size animals should that: the bony portion well integrate and gradually are reabsorbed in contact with femoral bone in rabbit. The osteochondral substitute showed the ability to repair defect in osteochondral lesion opened in horses knee and differently stimulate cells thanks to the different chemico-morphological-microstructural features of the scaffold layer.

Abstract: Hydroxyapatite powders characterized by substitutions of Mg2+, SiO4 4-, CO3 2- ions in biological like amounts, in the crystallographic site of calcium and phosphates, ions in biological like amounts, in the crystallographic site of calcium and phosphorus, were successfully prepared by synthesis in aqueous medium. The chemico-physical properties of the powders were investigated through several analytical techniques, among them: XRD, FTIR, TG-DTA, ICP-OES, HR-TEM. The entering of silicon in the HA structure progressively reduces its crystallinity, as also carbonate ions do. Silicate and carbonate ions can enter simultaneously into the HA structure, in biological-like amounts, although they compete for the occupation of the phosphate site. Solubility tests, carried out at physiological conditions, reveal an increased calcium release in the HA powders containing silicon compared to the silicon-free HA.

Abstract: In this work, we studied the surface/water interaction properties of a pure calcium hydroxyapatite (HA) and their modifications as a consequence of the partial Ca2+/Mg2+ (MHA) substitution by means of IR spectroscopy and microcalorimetry of adsorbed water. IR data indicated that water molecules in direct contact with the surface of HA are coordinated to surface cations and experience H-bond significantly stronger than in liquid water. The heats of adsorption associated to such interactions are very high, being twice-triple the heat of liquefaction of water. Interestingly, water experiences H-bond higher than in its bulk liquid state also in the second layer. Finally the entering in the material of Mg2+ ions was shown to significantly affect the affinity of the material toward water and the properties of its hydration layers.

Abstract: The incorporation of magnesium ions into the hydroxyapatite structure, which is of great interest for the developing of artificial bone, was performed starting from a wet chemical synthesis using magnesium chloride as Mg source. Different doping extents were attempted, four powders were produced and characterized in term of morphology, composition, solubility, thermal resistance,etc. in comparison with stoichiometric HA. In vitro tests with mesenchimal stem cells (MSCs) and human osteoblast like cells MG-63 cells were performed with the powder characterized with a biological-like doping of 5%Mg. The same powder was used, in form of granules, to carry out in vivo test by filling a defect in the femur on New Zealand White rabbits. All the tests showed better performance of the Mg doped apatite compared to stoichiometric HA, in agreement with the chemico-physical features of the material.

Abstract: A series of synthetic apatites bulk samples, characterized by different atomic substitutions were polarized by field of 1 and 2 kV·cm-1 at 300 °C. The thermally stimulated depolarization currents (TSDC) were measured and the stored electric charge density evaluated. The recent development in the synthesis of non-stoichiometric HA powders, whose chemical composition resembles that of the natural bone, is promising for the realization of improved biomimetic implants for bone substitution; therefore, electrical polarization applied on the ceramic pieces could further enhance the already strong bioactivity of these materials. The depolarization processes in the various material were evaluated by the Arrhenius’ method and related with the corresponding chemical features; finally, SEM observations of some polarized samples immersed in SBF at 37 °C revealed a wide growth of HA particles within a few days in all the investigated materials.