Olga García

5-Fluorouracil release from copolymeric hydrogels of itaconic acid monoester. I. Acrylamide-co-monomethyl itaconate.

The aim of this work was to test the application of new copolymeric poly (acrylamide-co-monomethyl itaconate) (A/MMI) hydrogels to 5-fluorouracil (5-FU) release. Three different compositions of copolymers have been studied, 90A:10MMI 75A:25MMI and 60A:40MMI. The equilibrium swelling degree in saline solution was between 76 and 80% depending on the copolymer composition. 5-FU, as the sodium salt, was trapped in the gels by including it in the feed mixture of polymerization. The swelling kinetics of the hydrogels in saline solution were studied at four temperatures, and the diffusion coefficient and the activation energy of the process were obtained. The 5-FU release as a function of temperature and disc load was studied; the diffusion coefficient and the activation energy of the release process were also obtained. The diffusion studies follow Ficks second law.

Enhancement of laser properties of pyrromethene 567 dye incorporated into new organic–inorganic hybrid materials

Abstract The incorporation of pyrromethene 567 dye into newly synthesized organic–inorganic hybrid materials, laser photostabilities were demonstrated, which are, to the best of our knowledge, the highest achieved to date for both inorganic and hybrid matrices doped with pyrromethene dyes. These results evidence that, in order to reach the necessary photostability for a solid-state dye laser being competitive with liquid dye lasers, hybrid matrices combine advantageous properties of inorganic materials, such as a high thermal dissipation capability, without losing the benefits of organic polymers.

Amplified spontaneous emission and optical gain measurements from pyrromethene 567--doped polymer waveguides and quasi-waveguides.

Amplified spontaneous emission from planar waveguides and quasi-waveguides based on Pyrromethene 567-doped poly(methyl methacrylate) thin films deposited onto quartz and glass substrates is investigated. Films with different thickness were prepared and pumped optically at 532 nm with pulses of up to 8 MW/cm(2). Pump thresholds for the onset of ASE emission, optical gains and losses were assessed. Net gain coefficients were estimated by fitting the data provided by variable stripe length measurements with a theoretical expression which takes into account saturation. In this way, net gain coefficients of up to 56 +/- 9 cm(-1) at a pump intensity of 5.3 MW/cm(2) for quasi-waveguides and up to 20.6 +/- 2.7 cm(-1) at a pump intensity of 3.4 MW/cm2 for waveguides, were obtained. Loss coefficients in the waveguides were estimated to be 3.8 +/- 0.4 cm-1 and 6.1 +/- 1.3 cm(-1) for 15 microm and 5 microm thick films, respectively. The results obtained seem to indicate a stronger self-mode-restriction capability in the quasiwaveguides than in conventional total internal-reflection waveguides.

Cytarabine trapping in poly(2-hydroxyethyl methacrylate) hydrogels: drug delivery studies

The release of cytarabine (ara-c) from poly(2-hydroxyethyl methacrylate) hydrogels cross-linked with different amounts of ethyleneglycol dimethacrylate (EGDMA) has been studied. The drug (range 5-25 mg) was trapped in polymer discs by including it in the feed mixture of polymerization. The drug delivery was followed by HPLC. The release was in accordance with Fickian behaviour. Total release of ara-C was reached after between 3 and 7 days depending on the percentage of EGDMA in the gels. A constant release rate of ara-C from the hydrogels was obtained, the time depending on the degree of cross-linking of the gels: 22 h for gels with 0.5% EGDMA, 32 h for gels with 5% EGDMA and 42 h for gels with 7% EGDMA; the amount of ara-C released being 50%, 80% and 85%, respectively, of the drug load of the gel discs. An increase of the release rate with the disc load was observed for each sort of hydrogel. Neither during the loading of the gels nor right through the drug release was degradation of ara-C observed.

Organo-modified silica aerogels and implications for material hydrophobicity and mechanical properties

Two types of organo-modified silica gels, with the organic groups trimethoxymethylsilane (TRIMOS) and 3-(trimethoxysilyl)propyl methacrylate (TMSPMA), have been synthesized. The wet gels were dried by supercritical evacuation of the solvent. The materials with enhanced performance were those hybridized with TRIMOS and dried above the critical conditions of methanol. Such aerogels were found to be hydrophobic with mechanically improved properties whilst still maintaining the characteristic transparency of pure silica aerogels. The condensation degree and the number of superficial hydroxyl groups were determined from solid-state 29Si-NMR spectroscopy. Mechanical properties were measured using nanoindentation.

Silicon-containing organic matrices as hosts for highly photostable solid-state dye lasers

Modified polymeric matrices incorporating silicon atoms in their structure and doped with lasing dyes have been synthesized and demonstrated to render improved laser performance. When transversely pumped at 532nm, highly stable laser operation with reasonable, not-optimized efficiencies was obtained. Materials were prepared where dyes pyrromethene 567 and pyrromethene 597 emitted laser radiation with no sign of degradation in the laser output, albeit with some oscillations, after 100 000pump pulses in the same position of the sample at 10Hz repetition rate.

Highly photostable solid-state dye lasers based on silicon-modified organic matrices

We report on the synthesis, characterization, and physical properties of modified polymeric matrices incorporating silicon atoms in their structure and doped with laser dyes. When the silicon-modified organic matrices incorporated pyrromethene 567 (PM567) and pyrromethene 597 (PM597) dyes as actual solid solutions, highly photostable laser operation with reasonable, nonoptimized efficiencies was obtained under transversal pumping at 532nm. At a pump repetition rate of 10Hz, the intensity of the laser emission remained at the level or above the initial lasing intensity after 100 000 pump pulses in the same position of the sample, corresponding to an estimated accumulated pump energy absorbed by the system of 518 and 1295GJ∕mol for PM567 and PM597, respectively. When the pump repetition rate was increased to 30Hz, the laser emission of dye PM567 decreased steadily and the output energy fell to one-half its initial value after an accumulated pump energy of 989 GJ/mol. Dye PM597 demonstrated a remarkable phot...

Laser performance of pyrromethene 567 dye in solid polymeric matrices with different cross-linking degrees

We report on the laser action of pyrromethene 567 (PM567) incorporated into copolymers of methyl methacrylate (MMA) with different methacrylic and acrylic cross-linking monomers: ethyleneglycol dimethacrylate, trimethylolpropane trimethacrylate, tetraethyleneglycol diacrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate (PETRA). The vol/vol proportion of the different co-monomers in each copolymer formulation was systematically varied, and the effect of each composition on the lasing properties of PM567 was evaluated. The laser samples were transversely pumped at 534 nm with 5.5 mJ/pulse from a frequency doubled Q-switched Nd:KGW laser. Lasing efficiencies of up 26% and good stability with a drop of the initial laser output of 30% after 100 000 pump pulses at 5 Hz in P(MMA:PETRA 95:5) were demonstrated.

Influence of degree of crosslinking on 5-fluorouracil release from poly(2-hydroxyethyl methacrylate) hydrogels.

Controlled release of 5-fluorouracil (5-FU) from poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels with three different degrees of crosslinking is reported. The swelling kinetic of PHEMA hydrogels in water was studied at different disc thicknesses and temperatures, and the diffusion coefficient and activation energy of the process were obtained. The gels were loaded with 5-FU by immersing them in concentrated aqueous solutions of the drug. The 5-FU release was studied as a function of temperature, disc thickness, disc load and degree of crosslinking of the gels; the diffusion coefficient and activation energy of the release process were also obtained.

Controlled release of cytarabine from poly(2-hydroxyethyl methacrylate-co-N-vinyl-2-pyrrolidone) hydrogels

Controlled release of cytarabine (ara-C) from poly(2-hydroxyethyl methacrylate-co-N-vinyl-2-pyrrolidone) [p(HEMA-co-VP)] hydrogels cross-linked with ethylene glycol dimethacrylate (EGDMA) is reported. Three compositions of copolymer, each one with a different cross-linking degree, have been studied: H50/VP50, H75/VP25, and H80/VP20. Ara-C (5-25 mg by disc) was trapped in the gels by including it in the polymerization feed mixture. The ara-C release time was between 1 day from H50/VP50/E0.5 discs and 16 days from H80/VP20/E15 discs. In all cases there is a time period for which the drug release rate is constant.