Ana Maria Ramos

The present study evaluates the effect of PEG content on the characteristics of poly(lactic-co-glycolic acid)-polyoxyethylene (PLGA-PEG) microspheres loaded with a small molecular weight drug on the polymer matrix degradation behavior of the polymeric matrix and drug release profile. Aclacinomycin A (ACM) was encapsulated in PLGA-PEG microspheres with varying PEG content (0%, 5%, 10%, or 15%) using the oil-in-water solvent evaporation method. Microspheres were obtained with sizes ranging from 45–70 mm, drug loading around 1.3% and encapsulation efficiencies between 48–70%. The produced microspheres were further characterized in terms of degradation behavior and drug release kinetics. The results showed that while PEG content had minimal impact on drug loading and microsphere size, it significantly influenced the degradation behavior of the microspheres and its weight in the release process. In vitro drug release profiles exhibited a three-phase pattern for all PLGA-PEG microspheres with faster and more extensive ACM release compared to PLGA microspheres, being the release improved with the PEG content increase. The Corrigan model was successfully applied to the release data yielding burst-phase kinetic constants (k_b) between 0.082–0.288 and degradation/erosion kinetic constants (k) between 0.054–0.093 day⁻¹, both of which increased with higher PEG content.

Surface cleaning of plastic materials of historical value can be challenging due to the high risk of inducing detrimental effects and visual alterations. As a result, recent studies have focused on researching new approaches that might reduce the associated hazards and, at the same time, minimize the environmental impact by employing biodegradable and green materials. In this context, the present work investigates the effects and potential suitability of dense carbon dioxide (CO₂) as an alternative and green solvent for cleaning plastic materials of historical value. The results of extensive trials with CO₂ in different phases (supercritical, liquid, and vapor) and under various conditions (pressure, temperature, exposure, and depressurization time) are reported for new, transparent, thick poly(methyl methacrylate) (PMMA) samples. The impact of CO₂ on the weight, the appearance of the samples (dimensions, color, gloss, and surface texture), and modifications to their physicochemical and mechanical properties were monitored via a multi-analytical approach that included optical microscopy, Raman and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopies, and micro-indentation (Vickers hardness). Results showed that CO₂ induced undesirable and irreversible changes in PMMA samples (i.e., formation of fractures and stress-induced cracking, drastic decrease in the surface hardness of the samples), independent of the conditions used (i.e., temperature, pressure, CO₂ phase, and exposure time).

Chromogenic reversal films (or color slides) are first-generation positive transparencies. These were used for various purposes, namely as an artistic medium, especially from the 1960s onwards. However, these materials are intrinsically vulnerable to chemical degradation and have poor long-term stability. Although over time significant improvements have been achieved in the stability of chromogenic products, chromogenic dyes are highly susceptible to oxidation and hydrolysis, both induced by light and/or relative humidity and temperature, leading to the fading and shift in the original color balance of the images. During the present investigation, a gap of knowledge regarding chromogenic materials in general, and chromogenic reversal films specifically, was detected. Today, there is still no methodology to identify the dyes present in a specific work and, therefore, to study their chemical mechanism of degradation. From this premise and focused on case studies from the Portuguese artist Ângelo de Sousa (1938–2011), a research study was carried out seeking the characterization of chromogenic dyes. Based on the isolation of the different dyes composing a chromogenic material, several procedures were tested to describe the dyes found in chromogenic reversal films, such as Raman spectroscopy, thin-layer chromatography (TLC), infrared spectroscopy, high-performance liquid chromatography with diode array detector (HPLC-DAD) and coupled with mass spectrometry (HPLC-HRMS). Promising results were achieved with this approach, opening new paths for the understanding of these materials.

The authors wish to make a change to the published paper

Slides de cavalete | Easel slides (1978–1979) is a slide-based artwork by the Portuguese artist Ângelo de Sousa (1938–2011), composed of one-hundred colour slides. Each image was produced by capturing different proportions of red, green, and blue (RGB) lights to obtain colour gradations. The artwork was first presented in the exhibition A Fotografia como Arte/A Arte como Fotografia | Photography as Art/Art as Photography in 1979. Associated with this exhibition, documentary evidence was found during the present study providing specific instruction on how to display the artwork (possibly unknown until now). According to that documentation, the artist wanted the work to be projected on a canvas mounted in an easel with a 19th century semblance, using a slide projector. In the last two exhibitions, carried out in 2017, after the artist had passed, the work was displayed as a digital projection, without the previously mentioned sculptural components. It was considered that this deviation from the first presentation could have led to a misunderstanding of the work. Thus, an exhibition of this artwork was prepared in a room at the Library of Faculdade de Ciências e Tecnologia. This was built as an experimental laboratory, having as one of its important objectives to test the variability of the work projected with a slide projector and a digital projector, following the display setup defined by the artist. For four days, the visitors were shown the work displayed under these two distinct scenarios of presentation. The visitors were also asked to fill out a questionnaire, to capture their perception about the variance of the work. The data obtained in the questionnaire and during the exhibition reinforced the decision to expose Slides de cavalete using the original technology. The public preferred the quality and beauty of the image using the slide projector, highlighting as positive aspects more granularity and warmer hue as well as higher depth of the images. Additionally, the production process behind Slides de cavalete was studied, based on documentation discovered in the artist’s archive and on reproductions, to enrich our perception of the work, in particular the complexity of creating the sfumato effects, and to understand the impact of changing the display technology. The results obtained made it possible to identify the main steps of making these slides, and this knowledge was shared with visitors in a workshop, integrated in this experimental laboratory.

This work aims at understanding the influence of the production processes and materials in the properties and long term behavior of acrylic sheet, i.e., poly(methyl methacrylate) (PMMA), a material generally considered very stable in museum collections. A comparative study was conducted in samples from cast acrylic sheets produced in the early 2000s, from which manufacturing details were known, and samples provided by the artist Lourdes Castro from acrylic sheets she had bought in the 1960s. Transparent and red opaque cast acrylic samples, containing cadmium red pigment, were used. All samples were artificially aged in a solarbox with irradiation λ > 300 nm for a total period of 8000 h, and alterations were followed by a multi-analytical approach which included Raman, infrared (FTIR-ATR) and UV-Vis spectroscopies; gravimetry; size exclusion chromatography (SEC); thermogravimetry (TGA); micro-indentation; colorimetry; and optical microscopy. Not all cast PMMA sheets presented similar stabilities. We have concluded that the production processes (which may include the polymerization conditions, the organic additives and the origin of the monomer) play a more important role in the properties and long-term behavior of these acrylic sheets than the presence of cadmium red and/or the age of the material.

Aiming at contributing to the preservation of black and white (B&W) film-based negatives held by Portuguese archives, four photographic collections from the first half of the twentieth century were selected for study. During the macro assessment of the collections the preservation condition and hues found in photographic negatives from the Elmano Cunha e Costa (ECC) were noticed, distinguishing this collection from the remaining ones. Additional attention was given considering that the ECC collection was formed in a colonial context in the 1930s, while the others were formed on the Portugal mainland. The ECC collection results from an ethnographic survey of Angolan tribes recorded with B&W film-based negatives. In this collection, sets of negatives with pink, lemon yellow, greenish, orange brownish, and red brownish hues were found. To identify the origin of such hues, the image layer was analysed by microscale energy-dispersive X-ray fluorescence (μ EDXRF) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX). Additionally, to assess the base decay and its effect on the formation of hues, the plastic supports were characterized by Fourier transform infrared microscopy (μ FTIR). To complement the assessment of the film-base decay, pH was measured by using combined microelectrodes. The identification of mercury, iodine, chromium, and iron by μ EDXRF allowed correlation of the hues found in the negatives with chemical corrective treatments performed to improve the image quality. SEM-EDX confirmed those results and proved that the elements found were in the photographic emulsion layer. The results obtained are relevant since the hues identified may now be used as markers to indicate the technical work performed on colonial photography. Additionally, the visual and molecular assessment of the negatives’ supports (good to fair condition) allow proposing that the original storage conditions may have had a beneficial contribution to their present condition.