Hydrogels are popular materials for tissue regeneration. Incorporation of biologically active sub... more Hydrogels are popular materials for tissue regeneration. Incorporation of biologically active substances, e.g. enzymes, is straightforward. Hydrogel mineralization is desirable for bone regeneration. Here, hydro-gels of Gellan Gum (GG), a biocompatible polysaccharide, were mineralized biomimetically with CaCO 3 using a double enzymatic approach. The enzymes urease (U) and carbonic anhydrase (CA) were incorporated in GG hydrogels. Hydrogels were incubated in a mineralization solution containing U substrate (urea) and calcium ions. U converts urea to ammonia (which raises pH) and CO 2. CA catalyses the reaction of CO 2 with water to form HCO 3 À , which undergoes deprotonation to form CO 3 2À , which react with Ca 2+ to form insoluble CaCO 3. All hydrogels containing U+CA were mineralized more with calcite and stiffer than hydrogels containing U. Mineralization with calcite promoted proliferation and spreading of osteoblast-like cells.
Mineralization of hydrogel biomaterials is considered desirable to improve their suitability as m... more Mineralization of hydrogel biomaterials is considered desirable to improve their suitability as materials for bone regeneration. Calcium carbonate (CaCO 3) has been successfully applied as a bone regeneration material, but hydrogel-CaCO 3 composites have received less attention. Magnesium (Mg) has been used as a component of calcium phosphate biomaterials to stimulate bone-forming cell adhesion and proliferation and bone regeneration in vivo, but its effect as a component of carbonate-based biomaterials remains uninvestigated. In the present study, gellan gum (GG) hydrogels were mineralized enzymatically with CaCO 3 , Mg-enriched CaCO 3 and magnesium carbonate to generate composite biomaterials for bone regeneration. Hydrogels loaded with the enzyme urease were mineralized by incubation in mineralization media containing urea and different ratios of calcium and magnesium ions. Increasing the magnesium concentration decreased mineral crystallinity. At low magnesium concentrations calcite was formed, while at higher concentrations magnesian calcite was formed. Hydromagnesite (Mg 5 (CO 3) 4 (OH) 2 .4H 2 O) formed at high magnesium concentration in the absence of calcium. The amount of mineral formed and compressive strength decreased with increasing magnesium concentration in the mineralization medium. The calcium: magnesium elemental ratio in the mineral formed was higher than in the respective mineralization media. Mineralization of hydrogels with calcite or magnesian calcite promoted adhesion and growth of osteoblast-like cells. Hydrogels mineralized with hydromagnesite displayed higher cytotoxicity. In conclusion, enzymatic mineralization of GG hydrogels with CaCO 3 in the form of calcite successfully reinforced hydrogels and promoted osteoblast-like cell adhesion and growth, but magnesium enrichment had no definitive positive effect.
ABSTRACT TiOx−VOx mixed oxides supported SBA-15 catalysts were prepared in a very controlled way ... more ABSTRACT TiOx−VOx mixed oxides supported SBA-15 catalysts were prepared in a very controlled way by the designed dispersion method (MDD) using acetylacetonate complexes. The Ti and V active centers are generated by the MDD of the TiO(acac)2 and VO(acac)2. The process consists of the adsorption and subsequent thermolysis of the Ti−V complexes. A careful selection of synthesis conditions allows us to modify the mutual interaction of the Ti and V centers and the interaction of the active centers with the silica support. The decomposition of the anchored complexes and the conversion of the physisorbed species toward covalently bonded TiOx−VOx surface groups have been studied by using a home-built in-situ IR transmission cell. IR seems to be the most suitable technique to follow the calcination process that is required to understand the reaction mechanism. During the thermal conversion, the Ti−V/acac precursor is converted toward supported mixed oxide. Additional characterization was done by FTIR−PAS, TGA, chemical analysis, as well as XRD, FT-Raman, and N2 adsorption measurements.
... When these precursors are calcined to yield the final catalysts, two mechanisms occur. At tem... more ... When these precursors are calcined to yield the final catalysts, two mechanisms occur. At temperatures less than 200 °C, all hydrogen-bond-interacting ligands leave the surface as acetylacetone (Hacac), consuming a silanol. ...
The use of dimethyldichlorosilane as a coupling agent for the grafting of VOx structures on the M... more The use of dimethyldichlorosilane as a coupling agent for the grafting of VOx structures on the MCM-48 surface, produces a material that is simultaneously hydrophobic (inmiscible with water) and very active (all V-centers are accessible, even for water molecules and the catalytic activity for methanol oxidation has increased). The VOx surface species are grafted by the Molecular Designed Dispersion of VO(acac)2 on the silylated surface, followed by a calcination in air at 450°C. These hydrophobic MCM-48 supported VOx catalysts are stable up to 500°C and show a dramatic reduction in the leaching of the V-centers in aqueous media. Also the structural stability has improved enormously. The crystallinity of the materials does not decrease significantly, even not when the samples are subjected to a hydrothermal treatment at 160°C and 6.1 atm. pressure.
Colloids and Surfaces a Physicochemical and Engineering Aspects, May 22, 1995
The surface modification reaction of silica gel with aminoorganosilanes proceeds in two steps. Fo... more The surface modification reaction of silica gel with aminoorganosilanes proceeds in two steps. For both the reaction step and the curing step, the chemical and physical interactions of the silane molecules with the silica surface have been modelled.From ethanol leaching tests, the reaction phase interaction, in dry conditions, may be characterized as 22% proton transfer, 10% hydrogen bonding and 68%
Hydrogels are popular materials for tissue regeneration. Incorporation of biologically active sub... more Hydrogels are popular materials for tissue regeneration. Incorporation of biologically active substances, e.g. enzymes, is straightforward. Hydrogel mineralization is desirable for bone regeneration. Here, hydro-gels of Gellan Gum (GG), a biocompatible polysaccharide, were mineralized biomimetically with CaCO 3 using a double enzymatic approach. The enzymes urease (U) and carbonic anhydrase (CA) were incorporated in GG hydrogels. Hydrogels were incubated in a mineralization solution containing U substrate (urea) and calcium ions. U converts urea to ammonia (which raises pH) and CO 2. CA catalyses the reaction of CO 2 with water to form HCO 3 À , which undergoes deprotonation to form CO 3 2À , which react with Ca 2+ to form insoluble CaCO 3. All hydrogels containing U+CA were mineralized more with calcite and stiffer than hydrogels containing U. Mineralization with calcite promoted proliferation and spreading of osteoblast-like cells.
Mineralization of hydrogel biomaterials is considered desirable to improve their suitability as m... more Mineralization of hydrogel biomaterials is considered desirable to improve their suitability as materials for bone regeneration. Calcium carbonate (CaCO 3) has been successfully applied as a bone regeneration material, but hydrogel-CaCO 3 composites have received less attention. Magnesium (Mg) has been used as a component of calcium phosphate biomaterials to stimulate bone-forming cell adhesion and proliferation and bone regeneration in vivo, but its effect as a component of carbonate-based biomaterials remains uninvestigated. In the present study, gellan gum (GG) hydrogels were mineralized enzymatically with CaCO 3 , Mg-enriched CaCO 3 and magnesium carbonate to generate composite biomaterials for bone regeneration. Hydrogels loaded with the enzyme urease were mineralized by incubation in mineralization media containing urea and different ratios of calcium and magnesium ions. Increasing the magnesium concentration decreased mineral crystallinity. At low magnesium concentrations calcite was formed, while at higher concentrations magnesian calcite was formed. Hydromagnesite (Mg 5 (CO 3) 4 (OH) 2 .4H 2 O) formed at high magnesium concentration in the absence of calcium. The amount of mineral formed and compressive strength decreased with increasing magnesium concentration in the mineralization medium. The calcium: magnesium elemental ratio in the mineral formed was higher than in the respective mineralization media. Mineralization of hydrogels with calcite or magnesian calcite promoted adhesion and growth of osteoblast-like cells. Hydrogels mineralized with hydromagnesite displayed higher cytotoxicity. In conclusion, enzymatic mineralization of GG hydrogels with CaCO 3 in the form of calcite successfully reinforced hydrogels and promoted osteoblast-like cell adhesion and growth, but magnesium enrichment had no definitive positive effect.
ABSTRACT TiOx−VOx mixed oxides supported SBA-15 catalysts were prepared in a very controlled way ... more ABSTRACT TiOx−VOx mixed oxides supported SBA-15 catalysts were prepared in a very controlled way by the designed dispersion method (MDD) using acetylacetonate complexes. The Ti and V active centers are generated by the MDD of the TiO(acac)2 and VO(acac)2. The process consists of the adsorption and subsequent thermolysis of the Ti−V complexes. A careful selection of synthesis conditions allows us to modify the mutual interaction of the Ti and V centers and the interaction of the active centers with the silica support. The decomposition of the anchored complexes and the conversion of the physisorbed species toward covalently bonded TiOx−VOx surface groups have been studied by using a home-built in-situ IR transmission cell. IR seems to be the most suitable technique to follow the calcination process that is required to understand the reaction mechanism. During the thermal conversion, the Ti−V/acac precursor is converted toward supported mixed oxide. Additional characterization was done by FTIR−PAS, TGA, chemical analysis, as well as XRD, FT-Raman, and N2 adsorption measurements.
... When these precursors are calcined to yield the final catalysts, two mechanisms occur. At tem... more ... When these precursors are calcined to yield the final catalysts, two mechanisms occur. At temperatures less than 200 °C, all hydrogen-bond-interacting ligands leave the surface as acetylacetone (Hacac), consuming a silanol. ...
The use of dimethyldichlorosilane as a coupling agent for the grafting of VOx structures on the M... more The use of dimethyldichlorosilane as a coupling agent for the grafting of VOx structures on the MCM-48 surface, produces a material that is simultaneously hydrophobic (inmiscible with water) and very active (all V-centers are accessible, even for water molecules and the catalytic activity for methanol oxidation has increased). The VOx surface species are grafted by the Molecular Designed Dispersion of VO(acac)2 on the silylated surface, followed by a calcination in air at 450°C. These hydrophobic MCM-48 supported VOx catalysts are stable up to 500°C and show a dramatic reduction in the leaching of the V-centers in aqueous media. Also the structural stability has improved enormously. The crystallinity of the materials does not decrease significantly, even not when the samples are subjected to a hydrothermal treatment at 160°C and 6.1 atm. pressure.
Colloids and Surfaces a Physicochemical and Engineering Aspects, May 22, 1995
The surface modification reaction of silica gel with aminoorganosilanes proceeds in two steps. Fo... more The surface modification reaction of silica gel with aminoorganosilanes proceeds in two steps. For both the reaction step and the curing step, the chemical and physical interactions of the silane molecules with the silica surface have been modelled.From ethanol leaching tests, the reaction phase interaction, in dry conditions, may be characterized as 22% proton transfer, 10% hydrogen bonding and 68%
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