Comparison of the enthalpic relaxation of poly(lactide–<i>co</i>‐glycolide) 50:50 nanospheres and raw polymer

Bailey, Nicola; Sandor, Maryellen; Kreitz, Mark; Mathiowitz, Edith

doi:10.1002/app.11109

Cited by 17 publications

(16 citation statements)

References 17 publications

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“…The weight fractions of the PS segment (78 %), the azo chromophores (8 %), the mesogenic side chains (12 %), and the remaining hydroxyl-ethyl ester segments (2 %) were calculated from 1 H NMR spectra. The block copolymers showed two glass transitions; the first one appeared only during the first heating cycle due to enthalpic relaxation [17] of the photoaddressable unit in the temperature range of the polyHEMA block at 49°C, whereas the second one at 99°C was ascribed to the PS block. SEC measurements of the injection-molded polymer blends showed a peak above the detection limit of 2 × 10 6 g mol -1…”

Section: Methodsmentioning

confidence: 95%

Polymer Blends with Azobenzene‐ Containing Block Copolymers as Stable Rewritable Volume Holographic Media

et al. 2007

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Volume holography is a promising technology for high-capacity optical data storage. [1,2] When utilizing the entire volume of a medium instead of only its surface, capacities above one terabyte on a memory medium the size of a compact disc are theoretically possible. Recent developments in the field of holographic storage materials and advances in storage techniques and technology are summarized in review articles by Ashley et al. [3] and Hesselink et al. [4] Although there are still material challenges, write-once media seem to be fairly advanced. In search of rewritable media, many studies have been performed on photorefractive crystals and organic glasses. [1,4] Manufacturing single crystals of the required size is very expensive, and a major drawback of the organic photorefractive materials is the requirement of very high electric field strengths. With increasing material thickness, the voltage necessary for creating the field becomes difficult to handle. A different potential class of rewritable media are polymers containing photoaddressable azobenzene chromophores.[5] Many studies have been performed on azobenzene-containing polymer films with thicknesses in the range of 0.5-10 lm. [3,6] However, the preparation of the thick samples required for multiplexing with sufficiently low optical density remains difficult to achieve. Because the absorption coefficient depends on the wavelength, it is in principle possible to tune a laser with an adjustable wavelength (e.g., a dye laser) to the very edge of the absorption band. [7] If writing is to be performed at a wavelength where fixed-wavelength, solid-state lasers are available (515 or 532 nm), however, a concept that allows for diluting the chromophores is required. So far, the best results have been reported by Minabe et al. with a homogeneous polymer blend based on an azobenzene-containing polymer and a similar but nonabsorbing polymer. [8] In a sample of 250 lm thickness, a set of 20 data pages were successfully inscribed; yet, the individual holograms were not completely spatially overlapping. The important issues of stabilizing the inscribed data and rewritability were not addressed. We use a different concept of controlling the optical density, by using block copolymers that contain azobenzene side groups in one block. Block copolymers with less than 15 vol % of one component form spherical microphases with typical diameters in the range of 10-20 nm. Thus, we can macroscopically dilute the chromophores while, at the same time, keeping them in a local confinement. The latter is important for the stability of the inscribed information. In an earlier paper, we have already reported the formation of individual holographic gratings in 10 lm thick films of a material that contained azobenzene and nonabsorbing three-ring mesogenic side groups in the minority phase.[9] In the confined geometry, the presence of a cooperative effect of the side groups was demonstrated. The mesogenic side groups were reoriented together with the chromophores; furthermore, in materia...

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Section: Methodsmentioning

confidence: 95%

Polymer Blends with Azobenzene‐ Containing Block Copolymers as Stable Rewritable Volume Holographic Media

et al. 2007

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“…The transformation was clearly visible and was accompanied by an appreciable enthalpic relaxation associated with aging of the polymer. 42 Therefore, the onset point and inflection point were both reported. In the second heating scan, the glass transitions of PLGA were not visible, due to the melting peak of PCL.…”

Section: Methodsmentioning

confidence: 99%

Biomolecule Gradient in Micropatterned Nanofibrous Scaffold for Spatiotemporal Release

et al. 2012

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Controlled molecule release from scaffolds can dramatically increase the scaffold ability of directing tissue regeneration in vitro and in vivo. Crucial to the regeneration is precise regulation over release direction and kinetics of multiple molecules (small genes, peptides, or larger proteins). To this end, we developed gradient micropatterns of electrospun nanofibers along the scaffold thickness through programming the deposition of heterogeneous nanofibers of poly(ε-caprolactone) (PCL) and poly(D,L-lactide-co-glycolide) acid (PLGA). Confocal images of the scaffolds containing fluorophore-impregnated nanofibers demonstrated close matching of actual and designed gradient fiber patterns; thermal analyses further showed their matching in the composition. Using acid-terminated PLGA (PLGAac) and ester-terminated PLGA (PLGAes) to impregnate molecules in the PCL-PLGA scaffolds, we demonstrated for the first time their differences in nanofiber degeneration and molecular weight change during degradation. PLGAac nanofibers were more stable with gradual and steady increase in the fiber diameter during degradation, resulting in more spatially confined molecule delivery from PCL-PLGA scaffolds. Thus, patterns of PCL-PLGAac nanofibers were used to design versatile controlled delivery scaffolds. To test the hypothesis that molecule-impregnated PLGAac in the gradient-patterned PCL-PLGAac scaffolds can program various modalities of molecule release, model molecules, including small fluorophores and larger proteins, were respectively used for time-lapse release studies. Gradient-patterns were used as building blocks in the scaffolds to program simultaneous release of one or multiple proteins to one side or, respectively, to the opposite sides of scaffolds for up to 50 days. Results showed that the separation efficiency of molecule delivery from all the scaffolds with a thickness of 200 μm achieved >88% for proteins and >82% for small molecules. In addition to versatile spatially controlled delivery, micropatterns were designed to program sequential release of proteins. The hierarchically structured materials presented here may enable development of novel multifunctional scaffolds with defined 3D dynamic microenvironments for tissue regeneration.

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“…Rapid cooling below the glass transition temperature (T g ) of the polymer results in a glassy state with high structural energy compared to the equilibrium state (Allison, 2008;White, 2006). When such a rapidly quenched polymer is stored at temperatures up to 30-40 • C below its T g , the polymer chains gradually relax (due to molecular mobility) to attain their thermodynamic equilibrium state (Bailey et al, 2002;Liu et al, 2009;White, 2006). This phenomenon is referred to as physical ageing or structural relaxation.…”

Section: Introductionmentioning

confidence: 97%

Effect of physical ageing on the performance of dexamethasone loaded PLGA microspheres

Rawat

Burgess

2011

International Journal of Pharmaceutics

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Comparison of the enthalpic relaxation of poly(lactide–co‐glycolide) 50:50 nanospheres and raw polymer

Cited by 17 publications

References 17 publications

Polymer Blends with Azobenzene‐ Containing Block Copolymers as Stable Rewritable Volume Holographic Media

Polymer Blends with Azobenzene‐ Containing Block Copolymers as Stable Rewritable Volume Holographic Media

Biomolecule Gradient in Micropatterned Nanofibrous Scaffold for Spatiotemporal Release

Effect of physical ageing on the performance of dexamethasone loaded PLGA microspheres

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