1,721,041 research outputs found
Formation of defined microporous 3D-structures starting from cross-linked hydrogels
No full textA new and simple technique was developed to obtain polysaccharide (hyaluronane, alginate and carboxymethylcellulose) -based hydrogels with a defined porous morphology. The technique consists of stratifying a cross-linked hydrogel on a filter with known pore diameter. CO2 bubbles, produced by the addition of HCl to a porogen salt NaHCO3, are forced to pass through the filter, and they induce the hydrogel to assume a porous morphology. The presence and distribution of pores was confirmed by scanning-electron microscopy (SEM). A strict correspondence was found between the porosity of the filter and the pore diameter in the hydrogels. Water uptake measurements showed a decreased amount of water taken up by the porous hydrogels compared with the native hydrogels, due to a compacting of the material. An explanation of the porous material properties of Hyal hydrogel was given on the basis of FTIR spectra.
The role of fibronectin in cell adhesion to spiral patterned TiO2 nanoparticles
No full textSpiral micropatterned surfaces of decreasing dimensions were produced by photo-immobilising a photoreactive hyaluronan (Hyal) derivative on TiO2 nanoparticles. The microstructured surfaces were characterised by both SEM and AFM analysis. The behaviour, of both endothelial cells (HCAEC) and tumoral mouse fibroblasts (NIH3T3) on the patterned surfaces was evaluated. HCAEC adhered only to the TiO2 nanoparticles avoiding the contact with Hyal. NIH3T3 adhered to and covered completely the TiO2 spiral and prolonging the culture time also the photo-immobilised Hyal. The role of fibronectin to mediate cell adhesion to the TiO2 pattern surfaces was evaluated by experiments with blocked fibronectin membrane receptors on both HCAEC and NIH3T3. The results showed the absence of any adhering cells. Thus, fibronectin seemed to be the only key protein in mediating cell adhesion to these TiO2 substrates
Thermodynamic behavior of complexes with 5,6-membered condensed chelate rings. 1,4,8-Triazaoctane
No full textThe enthalpies of the reactions between NH2(CH2)2NH(CH2)3NH2 and Ni2+, Cu2+, and Zn2+ in 0.5M KNO3 at 25° were detd. by direct calorimetric titrations and previously reported free energy values were used to calc. the corresponding entropy values. Complexes formed contained a system of condensed 5- and 6-membered chelate rings and had higher heats of formation than corresponding complexes of NH2(CH2)2NH(CH2)2NH2 (5,5-ring size sequence) and NH2(CH2)3NH(CH2)3NH2 (6,6-ring size sequence.). Addn. of a 2nd mol. of ligand to the complex depended on steric factors
The immobilization of titania nanoparticles on hyaluronan films and their photocatalytic properties
No full textWe have developed a method to bind titania nanoparticles onto hyaluronic films (HA) photoimmobilized on silanized glass. Titania nanoparticles were deposited on the HA films from commercially available dispersions by casting and dip-coating methods at various pHvalues. XPS was used to monitor the deposition of titania and to estimate the surface coverage of the nanoparticles. The topography of the titania-modified HA films was investigated by means of AFM. XPS results indicate that the titania surface coverage depends on the preparation method and the pH of the dispersion. We found that the maximum titania nanoparticle surface coverage was obtained by the casting method with the formation of aggregates and multilayers of particles. The titania surface coverage for the surfaces prepared
by the dip-coating method is pH-dependent. The surfaces prepared at pH 2 show a surface coverage of 65% and a rather uniform distribution of particles. We found that titania nanoparticles are anchored in a stable way to the HA substrate in a phosphate buffer solution (PBS) and that the interaction between the HA and the titania is through the carbonyl group of
carboxylates and amidic groups of the polymer. AFM images clearly show that titania nanoparticles are uniformly distributed over the HA films. By measuring the average diameter
and the average height of the nanoparticles deposited on HA films it appears that the particles are partially embedded in the polysaccharide films. The results of the study on the photobleaching of methylene blue indicate that the characteristic photocatalytic activity of titania is maintained when the nanoparticles are anchored to the HA substrate
Hyaluronic acid and sulfated hyaluronic acid in aqueous solution: effect of the sulfation on the protonation and complex formation with Cu2+ and Zn2+ ions
No full textThe behaviour of hyaluronic acid (Hyal) and sulfated hyaluronic acid (HyalS) in aqueous solution
was investigated in terms of protonation and complex formation by thermodynamic and spectroscopic
techniques. The presence of the scarcely protonable sulfate groups in the polymer chain provided the HyalS
molecule with a more rigid structure in aqueous solution, allowing this polysaccharide to remain in the
stretched conformation even after neutralisation of the carboxylate moieties. The presence of the sulfate
groups also increases the basic character of the COO– group. Both Hyal and HyalS were able to form complexes
with Cu2+ and Zn2+ ions in aqueous solution. The metal ion has a preferential binding site on these polysaccharides,
providing a precise stoichiometry for the metal ion complex. The sulfate groups were not
directly involved in the coordination of the metal ion, and the stoichiometry of the complex species is not
affected by the presence of these groups. However, by increasing the negative charge on the polymer chain,
the sulfate groups are responsible for the electrostatic attraction of the metal ion
Fibrinogen conformation and platelet reactivity in relation to material-blood interaction: effect of stress hormones
No full textThe performance of many biomaterials in hemocompatibility tests is altered when blood is drawn from
stressed subjects. A salient physiological response during stress is one in which hormones are released into
plasma by the hypothalamo-pituitary-adrenal axis. We investigated the influence of basal and stress levels
of epinephrine and â-endorphin on the conformation of fibrinogen (Fbg), both in saline solution (under
physiological conditions) and after its adsorption to polyethylene (PE), by FT-IR spectroscopy. Moreover,
as Fbg is one of the major mediators of platelet adhesion, the behavior of platelets in contact with PE was
also evaluated as a function of the two different hormone concentrations. Epinephrine was found to affect
Fbg conformation and to increase platelet adhesion to PE at stress level. Basal and stress levels of â-endorphin
did not significantly affect the Fbg conformation and only induced adhesion of isolated platelets to the PE
surface. A direct relationship was therefore found between Fbg conformation and platelet behavior. The
response of platelets was affected by the stress status of donors through the influence of epinephrine on Fbg
conformation
A novel strategy to obtain a hyaluronan monolayer on solid substrates
No full textThe aim of this study was to find a novel simple method to obtain polysaccharide ultrathin layers on solid substrates to investigate the interaction between the surface and the biological environment. A Hyaluronan (Hyal) monolayer with a well-defined chemistry was obtained by exploiting the capability of organosilanes to spontaneously adhere onto glass surfaces. A silane alkylic chain was conjugated with Hyal, and the derivatized polysaccharide was allowed to spontaneously adhere onto a glass surface. The elemental analysis of the modified polysaccharide demonstrated that one out of five disaccharide units was conjugated with the alkyl silane chain, corresponding to a substitution degree of the carboxylate groups of similar to 20%. The film of the modified polysaccharide was characterized by means of X-ray photoelectron spectroscopy (XPS), water contact angle, and atomic force microscopy (AFM) measurements. XPS analysis demonstrated that we obtained a Hyal layer with a thickness of about 2.0 nm corresponding to a Hyal monolayer. The Hyal-coated surfaces appeared to be rather smooth and highly hydrophilic and showed significant resistance to nonspecific cell adhesion
The role of Fibrinogen conformation on platelets activation
No full textAbstract
Platelet adhesion and activation induced by fibrinogen (Fbg) coating on polysaccharide layers of hyaluronic acid (Hyal) and its sulfated derivative (HyalS) were analyzed. Hyal or HyalS was coated and grafted on the glass substrate using a photolithographic method. The Fbg coating was achieved by two different routes: the immobilization of Fbg by means of covalent bond to the polysaccharide layers and the mere adsorption of Fbg to Hyal and HyalS surfaces. Platelet adhesion and activation to the surfaces were evaluated using, respectively, scanning electron microscopy (SEM) and quantifying the release of Platelet Factor 4 by ELISA. The method used for the coating of the surfaces with the Fbg influenced the platelet response. In fact, platelet adhesion and activation took place on surfaces covered by bound Fbg but not on those containing adsorbed Fbg. To explain this difference, the molecular mechanism involved in the Fbg--platelet interaction was investigated blocking platelet membrane receptors by monoclonal antibodies. Because the interaction between Fbg and the GPIIb/IIIa platelet membrane receptor was the only molecular pathway involved, Fbg conformation after the interaction (adsorption or binding) with the Hyal and the HyalS chains and the role of serum proteins adsorbed on the Fbg containing surfaces were accurately analyzed. Both adsorbed and bound Fbg prevented the adsorption of further serum proteins; consequently, a direct interaction between Fbg and platelets was supposed and the different platelet behavior was ascribed to the different conformational changes that occurred after the adsorption and the chemical binding of the Fbg to the Hyal and HyalS surfaces
Novel carboxymethylcellulose-based microporous hydrogels suitable for drug delivery
No full textSeveral materials capable of acting as structures for controlled release were analysed for the fabrication of matrices. Among those used, hydrophilic polysaccharides appeared to be the most suitable materials. Carboxymethylcellulose (a semi-synthetic polysaccharide) was chemically cross-linked with a 60% and 90% cross-linking degree in order to obtain hydrogels and utilised as matrix for the realisation of controlled drug release systems. The morphology of the gels was changed in order to obtain a microporous structure with different porosity (14, 30 and 40 μm). The obtained porous matrices were characterised in terms of pore density, dimension and swelling behaviour. The influence of both the pore dimension and technique of loading on the release kinetics was analysed. By increasing the pore dimension the release of ibuprofen-lysin was slower. Inducing the microporous structure after the loading of the hydrogel with the drug resulted in a slower release. © VSP 2004
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