https://www.um.edu.mt/library/oar/handle/123456789/18429 Fri, 17 Apr 2026 16:53:36 GMT 2026-04-17T16:53:36Z https://www.um.edu.mt/library/oar/handle/123456789/143342 Title: On the auxetic potential of synthesizable Calix[4]arene polymers Authors: Cardona, Maria A.; Grima, Joseph N.; Evans, Ken E.; Gatt, Ruben Abstract: Materials exhibiting auxetic behavior have garnered significant interest due to their potential applications across various fields, with synthetic auxetic materials being one such group. Theoretical studies have demonstrated the potential for various organic polymeric systems to exhibit auxetic behavior. However, to date, only a few synthesized molecular systems have shown some degree of auxetic behavior. Among the theoretical classes of molecular systems that have attracted attention are calix[4]arene systems in the “egg-rack” conformation. While the theoretical systems proposed in the literature have been deemed difficult to synthesize, calix[4]arene chemistry has advanced tremendously in recent years. In fact, a number of molecular systems with configurations similar to those predicted to exhibit a negative Poisson’s ratio have been synthesized, albeit with different chemical moieties. Consequently, it is deemed valuable to study the potential of these synthesized systems to exhibit a negative Poisson’s ratio through force-field-based simulations. This study is extended to include theoretical calix[4]arene systems linked by acetylene moieties, which are also potentially synthesizable through known methods. It is suggested that these materials can exhibit auxetic behavior when subjected to on-axis loading in the [001] direction. A detailed mechanistic study of these systems is also conducted. Mon, 01 Jan 2024 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/143342 2024-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/143310 Title: Comparative analysis of N/TERT-1 and N/TERT-2G keratinocyte responses to oxidative stress and immune challenges Authors: Griffin, Sholeem; de Oliveira Mallia, Jefferson; Psakis, Georgios; Attard, Juan; Caruana, Matthias; Gatt, Ruben Abstract: The responses of N/TERT-1 and N/TERT-2G keratinocyte cell lines to oxidative stress and immune challenges were investigated to assess their suitability for dermatological testing. The cell lines were exposed to various stimuli, including PAMPs, DAMPs, H₂O₂, and menadione, to assess cytokine production, oxidative stress markers, cell viability, apoptosis, and membrane integrity. IL-1α, IL-6, IL-8, TNF-α, and TGF-β levels significantly increased in N/TERT-1 cells following exposure to LPS, while N/TERT-2G cells remained unaffected. Both cell lines showed increased production of IL-1α, IL-1β, TNF-α, IL-6, and IL-8 in response to dsDNA and LMW and HMW Poly I:C, although TGF-β significantly decreased only in N/TERT-1 cells. In response to H₂O₂, a dose-dependent increase in cytokine levels was observed in N/TERT-2G, whereas N/TERT-1 did not exhibit a clear dose-dependent response. Markers of oxidative stress, including SOD and GSH, displayed similar patterns in both cell lines, with N/TERT-2G showing slightly higher sensitivity. Lipid peroxidation and mitochondrial membrane potential fluctuations were more pronounced in N/TERT-2G, suggesting greater oxidative stress sensitivity. The baseline GSH levels were higher in N/TERT-1 cells, which may contribute towards the enhanced resilience to oxidative stress. Despite decreased viability in MTT assays following H₂O₂ exposure, the lack of significant changes in cleaved Caspase-3 levels indicated that apoptosis was not the primary mechanism of cell death. These findings highlight the distinct characteristics of N/TERT-1 and N/TERT-2G cells, with N/TERT-1 showing higher baseline resilience to oxidative stress and N/TERT-2G displaying greater sensitivity, particularly to H₂O₂. The study underscores the importance of selecting the appropriate cell line for specific research applications in skin biology and disease modelling, considering the differences in their responses to oxidative and immune challenges. Wed, 01 Jan 2025 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/143310 2025-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/143233 Title: Altering the morphology of graphene aerogels through control of the gelation time and drying method Authors: Mallia, Sean; Xuereb, Matthew Anthony; Gatt, Ruben; Agius Anastasi, Anthea; Vella, Daniel A. Abstract: Graphene aerogels are being increasingly investigated, however, a robust understanding of the effects of synthesis parameters on their morphology and performance remains underdeveloped. This work reports on the successful microstructural control of reduced graphene oxide (rGO) aerogels, prepared via low-temperature hydrothermal reduction of GO, through changes to their gelation time and drying method. Using ascorbic acid as the reducing agent, the hydrogels were allowed to set at three gelation times; until the ‘just-gelled’ state or onset of gelling, for 80 minutes, and for 720 minutes, the latter typically reported in the literature. The hydrogels were then subjected to either freeze drying, or CO2 supercritical drying, followed by a final pyrolysis step. The resulting aerogels were characterised by scanning electron microscopy and micro-Raman spectroscopy. The mechanical properties of the rGO aerogels were assessed under compression loading, whereas their ability to perform in water was assessed by a simple immersion test. The results showed that freeze drying of the just-gelled hydrogels produced aerogels with large and cellular pores, low compressive moduli, and rather poor water stability. Longer gelation times produced denser aerogels with smaller pores and improved water stability. Such results suggest that for the freeze dried aerogels, the gelation time influences the microstructure of the rGO gel – short gelation times lead to weaker, more pliable hydrogels, less resistant to ice crystal growth upon freeze drying. Supercritical drying produced aerogels with randomly oriented nanometrically sized pores, high compressive moduli, and good water stability, irrespective of the gelation time. Thu, 01 Jan 2026 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/143233 2026-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/141213 Title: Exploring hydrodynamic cavitation for citrus waste valorisation in Malta : from beverage enhancement to potato sprouting suppression and water remediation Authors: Psakis, Georgios; Lia, Frederick; Valdramidis, Vasilis P.; Gatt, Ruben Abstract: Introduction: The endorsement of circular economy, zero-waste, and sustainable development by the EU and UN has promoted non-thermal technologies in agro-food and health industries. While northern European countries rapidly integrate these technologies, their implementation in Mediterranean food-supply chains remains uncertain. Aims: We evaluated the usefulness of hydrodynamic cavitation (HC) for valorizing orange peel waste in the fresh orange juice supply chain of the Maltese Islands. Method: We assessed: a) the effectiveness of HC in extracting bioactive compounds from orange peels (Citrus sinensis) in water (35°C) and 70% (v/v) ethanol (−10°C) over time, compared to conventional maceration, and b) the potato sprouting-suppression and biosorbent potential of the processed peel for copper, nitrate, and nitrite binding. Results: Prolonged HC-assisted extractions in water (high cavitation numbers), damaged and/or oxidized bioactive compounds, with flavonoids and ascorbic acid being more sensitive, whereas cold ethanolic extractions preserved the compounds involved in radical scavenging. HC-processing adequately modified the peel, enabling its use as a potato suppressant and biosorbent for copper, nitrate, and nitrite. Conclusion: Coupling HC-assisted bioactive compound extractions with using leftover peel for potato-sprouting prevention and as biosorbent for water pollutant removal offers a straightforward approach to promoting circular economic practices and sustainable agriculture in Malta. Mon, 01 Jan 2024 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/141213 2024-01-01T00:00:00Z