pH-Dependent Silica Nanoparticle Dissolution and 1 Cargo Release

The dissolution of microporous silica nanoparticles (NP) in aqueous environments of different biologically relevant pH was studied in order to assess their potential as drug delivery vehicles. Silica NPs, loaded with fluorescein, were prepared using different organosilane precursors (tetraethoxysilane, ethyl triethoxysilane or a 1:1 molar ratio of both) and NP dissolution was evaluated in aqueous conditions at pH 4, pH 6 and pH 7.4. These conditions correspond to the acidity of the intracellular environment (late endosome, early endosome, cytosol respectively) and gastrointestinal tract (‘fed’ stomach, duodenum and jejunum respectively). All NPs degraded at pH 6 and pH 7.4, while no dissolution was observed at pH 4. NP dissolution could be clearly visualised as mesoporous hollows and surface defects using electron microscopy, and was supported by UV–vis, fluorimetry and DLS data. The dissolution profiles of the NPs are particularly suited to the requirements of oral drug delivery, whereby NPs must resist degradation in the harsh acidic conditions of the stomach (pH 4), but dissolve and release their cargo in the small intestine (pH 6–7.4). Particle cores made solely of ethyl triethoxysilane exhibited a ‘burst release’ of encapsulated fluorescein at pH 6 and pH 7.4, whereas NPs synthesised with tetraethoxysilane released fluorescein in a more sustained fashion. Thus, by varying the organosilane precursor used in NP formation, it is possible to modify particle dissolution rates and tune the release profile of encapsulated fluorescein. The flexible synthesis afforded by silica NPs to achieve pH-responsive dissolution therefore makes this class of nanomaterial an adaptable platform that may be well suited to oral delivery applications

TUTORIAL REVIEW Tomographic diffractive microscopy: basics, techniques and perspectives

Tomographic diffractive microscopy (TDM) is an advanced digital imaging technique, which combines the recording of multiple holograms with the use of inversion procedures to retrieve quantitative information on the sample. In this review, we discuss the basic theory of TDM in the framework of electromagnetism and draw a comparison with conventional widefield microscopes. We describe various implementations of TDM, highlighting their power of resolution. Finally, we present some research perspectives for increasing the potential of this promising new imaging modality

ADOÇÃO DE M-LEARNING NO ENSINO SUPERIOR: O PONTO DE VISTA DOS PROFESSORES

This research aim is to investigate the perceptions of professors in higher education settings regarding m-learning and identifying possible enablers and barriers to its adoption. Roger's diffusion of innovations theory is the basis for the content analysis of 12 interviews. Results indicate that while professors recognize m-learning definitions they seem to lack familiarity with the innovation, thus making its adoption for daily teaching activities more difficult.El objetivo de este estudio es investigar las percepciones de los profesores acerca de m-learning, la identificación de lo que puede ayudar y lo que puede inhibir la adopción. A través de análisis de contenido y basado en la teoría de la difusión de las innovaciones de Rogers, fue entrevistado un grupo de doce profesores, tratando de identificar los factores críticos que pueden facilitar (o no) la adopción. Los resultados muestran que si bien en los profesores generales saber la definición de m-learning, parece que todavía no se percibe como una innovación conocida por ellos, lo que puede dificultar su adopción en su actividad docente diaria.O objetivo deste trabalho é investigar as percepções de professores universitários acerca do m-learning, identificando o que pode favorecer e o que pode inibir a sua adoção. Por meio da análise de conteúdo e com base na teoria de difusão de inovações de Rogers, foi entrevistado um grupo com doze docentes, buscando-se identificar fatores críticos que podem facilitar (ou não) a adoção. Os resultados apontam que apesar dos professores em geral conhecerem a definição de m-learning, parece que ele ainda não é percebido como uma inovação bem conhecida por eles, o que pode dificultar sua adoção no cotidiano de suas atividades docentes

Production of photons in a bouncing universe

Using a new non-singular solution,it is shown that the production of photons in dilaton electrodynamics in a cosmological setting is increased if the effect of matter creation on the geometry is taken into account. This increment may be related to the problem of the origin of magnetic fields in the universe.Comment: 7pages, 4 figure

Chilling requirements and dormancy evolution in grapevine buds.

Fluctuations in winter chilling availability impact bud dormancy and budburst. The objective of this work was to determine chilling requirements to induce and overcome endodormancy (dormancy controlled by chilling) of buds in different grape cultivars. "Chardonnay", "Merlot" and "Cabernet Sauvignon" shoots were collected in Veranópolis-RS vineyards in 2010, and submitted to a constant 3 °C temperature or daily cycles of 3/15 °C for 12/12h or 18/6h, until reaching 1120 chilling hours (CH, sum of hours with temperature ≤ 7.2 °C). Periodically, part of the samples in each treatment was transferred to 25 °C for budburst evaluation (green tip). Chilling requirements to induce and overcome endodormancy vary among cultivars, reaching a total of 136 CH for "Chardonnay", 298 CH for "Merlot" and 392 CH for "Cabernet Sauvignon". Of these, approximately 39, 53 and 91 CH are required for induction of endodormancy in the three cultivars, respectively. The thermal regimes tested (constant or alternating) do not influence the response pattern of each cultivar to cold, with 15 °C being inert in the CH accumulation process. In addition, time required to start budburst reduces with the increase in CH, at a rate of one day per 62 CH, without significant impacts on budburst uniformity. Index terms: Chilling hours; endodormancy; budburst; Vitis vinifera