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The aim of the present contributionis to prepare a functionalizedbioactive glass potentially useful as prosthetic material, but alsoable to release organic molecules in response to a change of the pHenvironment. By this approach it is possible to develop devices whichcan be used for a triggered drug release in response to specific stimuli;this is an attractive research field, in order to avoid either systemicand/or local toxic effects of drugs. In particular, in the presentpaper we report data related to the development of a new formulationof bioactive glasses, their functionalization with organic moleculesto obtain a pH-sensitive bond, their physicochemical characterizationand in vitro bioactivity in simulated biological fluids (SBF), andorganic molecule delivery tests at different pH. The glass functionalization,by means of a covalent reaction, allows us to produce a model of pH-responsivebioactive biomaterial: when it is exposed to specific pH changes,it can favor the release of the organic molecules directly at thetarget site. Cysteamine and 5-aminofluorescein are used as model moleculesto simulate a drug. The materials, before and after the differentfunctionalization steps and in vitro release tests at different pH,have been characterized by means of different experimental techniquessuch as X-ray powder diffraction (XRPD), Raman, FTIR and fluorescencespectroscopies, N2adsorption, thermogravimetric (TGA)and elemental analysis. [ABSTRACT FROM AUTHOR]

In the field of implantation, the delivery and/or immobilization of biomolecules developing a specific action on bone mineralization has attracted great attention in the last few years. In fact, a wide spectrum of enzymes and proteins have been grafted with different methods onto/within implanted materials. Bioactive glasses and glass-ceramics, due to their tailorable properties in terms of chemical composition, reactivity, and easiness of manufacturing, represent good scaffolds for enzyme immobilization. These biomaterials are well known for their peculiar surface reactivity promoting, when contacted with real or simulated body fluids, the formation of an hydroxy-carbonate apatite layer. The aim of the present contribution has been to immobilize, viaa covalent linkage, an enzyme on the glass surface through the formation of self-assembled monolayers (SAMs), in order to obtain a stable bio-conjugate useful as a material bio-implantable into the human body. The innovation of this study resides in the use of a new method of protein immobilization on the glass surface. Unlike other works, in which a preliminary silanization process has often been used, the introduction of gold nanoparticles (AuNPs) in the glass composition allowed us to exploit the easy SAMs formation process on the AuNPs dispersed in the bioactive glass matrix and, consequently, to immobilize an enzyme (soybean peroxidase, SBP, in the present case) on the SAMs. A thorough characterization of the materials, at different steps of the functionalization process, has been also reported, together with in vitroactivity tests of immobilized SBP, compared with merely adsorbed SBP, and cytotoxicity tests using human osteoblast (MG-63) cells. Overall, a new bio-conjugate material, able to maintain its activity over time and to decrease the oxidative stress when in contact with MG-63 cells, has been obtained. [ABSTRACT FROM AUTHOR]

Curcumin, an active ingredient in the traditional Ayurvedic herbal remedy [Curcuma longaL.], is nowadays also employed in western medicine for its pleiotropic activities, ranging from anticancer to its free radical scavenger ability. These features are related to curcumin's function as a metal chelator, especially being selective for hard Lewis acids, such as Ga3+which has interesting pharmacological activities. We report the synthesis and characterization of bioactive gel and mesoporous Ga-containing phospho-silicate glasses loaded with curcumin, in which, for the first time, the design of novel drug delivery systems takes advantage of coordination chemistry. In particular, it was found that: (i) there is a direct correlation between the external surface area and the amount of loaded curcumin; (ii) the presence of Ga3+species on the surface increases the quantity of drug molecules uploaded and slows down their release in the biological medium (SBF), hinting a coordination-like interaction between curcumin and the surface metal ions; (iii) curcumin molecules released in the SBF solution stabilize Ga3+ions, avoiding their precipitation. [ABSTRACT FROM AUTHOR]

It is demonstrated here that bioactive glasses containing Au nanoparticles (AuNPs) can be selectively functionalized with small molecules carrying either amino or thiol groups by simply varying the temperature and pH of the functionalization batch. The results evidence the following. (i) At room temperature (RT), no functionalization of Au-free glass occurs, whereas in the case of glasses containing AuNPs, stable linkages form only with amino groups, as in this condition Au does not bind with either thiol or hydroxyl groups. The RT functionalization with cysteine and cystine confirms the preferential functionalization through the amino groups, while the -SH groups are oxidized to S−S bridges. (ii) The functionalization with cysteine and cystine, compared at pH = 5, 9, and 12, is shown not to take place at pH = 5 and to be hindered by the glass matrix dissolution at pH = 12 (with consequent release of AuNPs), while the best results are obtained at pH = 9. (iii) For the effect of reaction temperature, at 4 °C it is possible to obtain a strong Au−S interaction, whereas at RT, a weak Au−N linkage is formed. These results should allow production, in a selective way, of different bonds exhibiting different strengths and, consequently, different release times in solution, with a wide range of possible applications (for instance, weak Au−N bonds in the case of drug delivery, strong Au−S bonds in protein immobilization). [ABSTRACT FROM AUTHOR]

A new melted bioactive system containing gold nanoparticles (AuNPs) was prepared exploiting a post-synthesis thermal treatment that allows one to modify crystal phases and nature, shape and distribution of the gold species in the glass-ceramic matrix as evidenced by UV-visible spectroscopy, transmission electron microscopy and powder X-ray diffraction analysis. In human MG-63 osteoblasts the presence of Au(n)(+) species caused an increase of lactate dehydrogenase leakage and malonyldialdehyde production, whereas Hench's Bioglass HAu-600-17 containing only AuNPs did not cause any effect. In addition, HAu-600-17 caused in vitro hydroxyapatite formation and an increase of specific surface area with a controlled release of gold species; this material is then suitable to be used as a model system for the controlled delivery of nanoparticles.

Bioactive glasses containing gold nanoparticles (AuNPs) have been synthesized via the sol-gel route using HAuCl(4) x 3 H(2)O as gold precursor. The formation process of AuNPs was studied as a function of the thermal treatment, which induces nucleation of Au particles and influences their nature, optical properties, shape, size, and distribution. The physicochemical characterization indicates that the sample treated at 600 degrees C presents the best characteristics to be used as a bioactive material, namely high surface area, high amount of AuNPs located at the glass surface, presence of micropores, and abundant surface OH groups. In the case of samples either aged at 60 degrees C or calcined at 150 degrees C, AuNPs just begin their formation, and at this stage the gel is not completely polymerized and dried yet. A thermal treatment at higher temperatures (900 degrees C) causes the aggregation of AuNPs, forming "AuMPs" (i.e., Au microparticles) in a densified glass-ceramic material with low surface area, absence of pores, and low number of surface OH groups. These features induce in the glass-ceramic materials treated at high-temperatures a lower bioactivity (evidenced by SBF reaction), as compared with that exhibited by the glass samples treated at 600 degrees C.