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Biomedical subjects

M Vallet-Regí

Publications and source records attributed to M Vallet-Regí.

51 records · Page 3Linked to original sources
PubMed2000

Evolution of porosity during in vitro hydroxycarbonate apatite growth in sol-gel glasses.

A bioactive glass of composition (mol %) SiO(2) 58, CaO 36, P(2)O(5) 6 was obtained using the sol-gel method. Changes in porosity during the growth of a hydroxycarbonate apatite (HCA) phase were studied at different stages of the process. The high Ca (II) content led to a higher degree of porosity and enhancement of Ca(2+) released from surface and bulk when the glass was soaked into simulated body fluid (SBF). Saturation of the media (SBF) together with the porosity of the material led to fast growth of HCA on the surface and into the pores.

Apatites↗
PubMed2000

Gentamicin release from hydroxyapatite/poly(ethyl methacrylate)/poly(methyl methacrylate)composites.

In this work the release kinetics of gentamicin sulfate (GEN) in samples composed by hydroxyapatite, poly(methyl methacrylate), and poly(ethyl methacrylate) has been studied. The release study was performed by soaking three samples in simulated body fluid at 37 degrees C; the medium was periodically replaced during 70 days. The concentration of GEN was determined by the o-phtaldialdehyde method. The release profile shows three stages: the first stage, occurring during the first 10 h, corresponds to a fast release (nearly 30% of the drug is released in this period). The second stage is slower and includes from the first 10 h to 16 days, releasing 60% of the total amount of GEN. The final stage is the slowest and it takes from 16 to 70 days (10% of GEN is released). The fraction of released GEN versus square root of time can be fitted to a third order polynomial, corresponding with the model proposed by Cobby et al. (J Pharm Sci 1974;63:725-732). The characterization of the samples after the release study shows that a carbonate hydroxyapatite layer has grown on the whole surface of the composites.

Animals↗
PubMed2000

In vitro bioactivity of glass and glass-ceramics of the 3CaO x P2O5-CaO x SiO2-CaO x MgO x 2SiO2 system.

A glass of nominal composition (wt%) 40.0 CaO-34.5 SiO2-16.5 P2O5-8.5 MgO-0.5 CaF2 has been obtained (G13). The glass showed in vitro bioactivity evidenced by the formation on its surface of a calcium phosphate-rich layer when soaked in a solution with ionic composition analogous to human plasma. By thermal treatments of G13, a glass-ceramic (GC13) containing apatite, diopside, althausite and akermanite as crystalline phases was developed. GC13 as-made did not show in vitro bioactivity. However, after chemical treatment of GC13 with 1 M HCl (GC13-HCl), the in vitro studies showed the formation of an apatite-like layer covering certain areas of the material surface. The influence of both chemical and morphological factors on the in vitro bioactivity has been studied.

Calcium Compounds↗
PubMed1999

Influence of P2O5 on crystallinity of apatite formed in vitro on surface of bioactive glasses.

Two sol-gel glasses with 80 mol % SiO2 were prepared in the system SiO2-CaO-P2O5; the first one had 3 mol% P2O5 in its composition, and the second one was P2O5 free. The in vitro behavior of glasses was studied by soaking them in simulated body fluid for 7 days at 37 degrees C. After the in vitro test, the study by Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, electron diffraction, and transmission electron microscopy showed an apatite-like layer had formed on the surface of both glasses. However, for identical soaking time, the apatite crystals formed on the surface of the glass containing P2O5 in the composition were larger. Therefore, the presence of P2O5 in the sol-gel glass composition promotes the crystal growth of the apatite.

Ceramics↗
PubMed1999

XRD, SEM-EDS, and FTIR studies of in vitro growth of an apatite-like layer on sol-gel glasses.

A glass with a composition (in mole %) of: SiO2 (70), CaO (26), and P2O5 (4) was obtained using a sol-gel method. The in vitro bioactivity of the glass was assessed by determining the changes in surface morphology and composition after soaking in simulated body fluid (SBF) for periods of up to 14 days at 37 degrees C. X-ray diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy, and FTIR analyses of the glass surface after different soaking periods in SBF demonstrated the growth of an apatite-like layer on the glass surface. In the first stage, an amorphous calcium phosphate layer was formed; after 7 days this surface consisted of spheres, with diameters ranging between 2 and 15 microm, composed of needle-like apatite crystallites (250 x 100 nm) with a crystallinity similar to that of a biological apatite.

Apatites↗
PubMed1999

Influence of composition and surface characteristics on the in vitro bioactivity of SiO(2)-CaO-P(2)O(5)-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.

Biocompatible Materials↗
PubMed1999

In vitro calcium phosphate layer formation on sol-gel glasses of the CaO-SiO(2) system.

A glass with a composition of SiO(2) 80% and CaO 20% (in mol %) was prepared by the sol-gel method, and its in vitro bioactivity was studied by soaking it in simulated body fluid (SBF) at 37 degrees C. The formation of a calcium phosphate layer on the glass was analyzed by determining the ionic concentrations in solution and by studying the surface of the glass with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and electron diffraction (ED) after it had been in SBF for varying periods of time. The composition of this bioactive glass, formed of only two components, allowed us to monitor the formation process of the hydroxycarbonate apatite (HCA) layer. The bioactive behavior of this glass indicates that the presence of phosphorous in the glass composition is not an essential requirement for the development of a HCA layer. In this case, the layer is formed because of the phosphorous present in the in vitro assay solution.

Biocompatible Materials↗
PubMed1998

Preparation, characterization, and in vitro release of ibuprofen from AI2O3/PLA/PMMA composites.

The preparation, characterization, and in vitro release of Ibuprofen from Al2O3, poly(L-lactic acid) (PLLA), and polymethylmethacrylate (PMMA) composites are described. The release process of the anti-inflammatory drug after the immersion of composites in a buffered solution is analyzed. The rate of Ibuprofen release is related to the crystalline or amorphous form of the drug. The presence of a ceramic component, alpha-Al2O3, and a biodegradable polymer, PLLA, facilitates both Ibuprofen crystallization and drug release. In addition, these composite systems modulate the release of the stereoisomers R(-) and S(+) of the drug.

Aluminum Oxide↗
PubMed1997

Ibuprofen release from hydrophilic ceramic-polymer composites.

Two composite systems composed of alpha-Al2O3/poly(methyl methacrylate) (PMMA)/poly(vinyl pyrrolidone) (PVP)/ibuprofen or alpha-Al2O3/PMMA/co-vinyl pyrrolidone-methyl methacrylate/ibuprofen were prepared by free radical polymerization. These systems were characterized by spectroscopic techniques and thermogravimetric and differential thermal analyses. The hydration behaviour of composites with different hydrophilic characters was analysed after the immersion of the composites in buffered solution at pH 7.4 and 37 degrees C. The swelling of the composites depends strongly on the content of the hydrophilic component and is controlled by the presence of the ceramic component. The release of the anti-inflammatory drug, ibuprofen, from the composites in buffered solution was followed by UV spectroscopy and the results obtained indicated that the components of the composites influenced the rate of release of the drug, without the classical 'burst' effect observed frequently with hydrophilic systems.

Aluminum Oxide↗
PubMed1997

TiO2-polymer composites for biomedical applications.

Composite hydrogels of poly(acrylic acid) (PAA) and poly-(methyl metacrylate) (PMMA) reinforced with a bioceramic, TiO2, have been prepared by reactive moulding from a mixture of the bioceramic with PMMA beads and acrylic acid. Cylindrical specimens with various TiO2-polymer compositions, but a constant 3:1 PAA/PMMA ratio were obtained, and their corresponding swelling behavior was followed at pH = 7.0 and pH = 8.0 in buffered solution at 37 degrees C. The composition and structure of the composites prepared was studied by thermogravimetry, 1H-NMR spectroscopy and scanning electron microscopy. The composites prepared present a considerable consistency, even in hydrated media, since their swelling behavior is rather sensitive to the pH of the media. Specific polar interactions of the carboxylic groups of the hydrophilic polymer component PAA with the surface of TiO2 particles, modulate the behavior of the composites against the hydration processes at different pH.

Acrylic Resins↗
PubMed1996

Composite biomaterials based on ceramic polymers. I. Reinforced systems based on Al2O3/PMMA/PLLA.

Composite biomaterials with good mechanical response and a partially biodegradable character were prepared by the free radical polymerization of mixtures of alpha-Al2O3, low-molecular-weight but crystalline poly(L-lactic acid) (PLLA), and methyl methacrylate (MMA). Cylindrical specimens prepared with different composition were characterized by thermogravimetry, calorimetry, 1H-NMR spectroscopy, and x-ray diffraction (XRD). The in vitro biodegradative process was studied in different media, following variations of the pH, gravimetric weight loss of the specimens, and crystalline domain change by XRD after immersion in pure water and buffered solutions at pH 4.0 and pH 8.0 for 90 days. Formation of a relatively porous structure with good cohesion after the biodegradative treatment (confirmed by SEM) was observed. These systems can be considered for applications in orthopedic surgery as filling biomaterials and even as control drug-delivery systems.

Aluminum Oxide↗
PubMed1995

Order-disorder in T, T', and T* phase: superconductors and related materials.

After reviewing microstructural studies on superconducting materials showing T, T', and T* structural types, results are presented on the microstructure of some n-type superconductors and related materials prepared with accurate control of the oxygen stoichiometry. Electron microscopy is used to describe the ordering of interstitial oxygen defects in T-type La2NiO4 + delta leading to the formation of the n = 2 term of a homologous series with the general formula La8nNi4nO16n + 1. Structural transitions and superstructure formation in the Pr2-x-yCexSryCuO4-delta system are reported, where T, T', and T* phases are isolated as a function of both Ce and Sr content.

Electric Conductivity↗