Centre for Environmental and Marine Studies

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Publications

Insights on Ultrafiltration-Based Separation for the Purification and Quantification of Methotrexate in Nanocarriers

Publication . Marques, Sara S.; Ramos, Inês I.; Fernandes, Sara; Barreiros, Luisa; Lima, Sofia A. C.; Reis, Salette; Domingues, M. Rosário M.; Segundo, Marcela A.

The evaluation of encapsulation efficiency is a regulatory requirement for the characterization of drug delivery systems. However, the difficulties in efficiently separating nanomedicines from the free drug may compromise the achievement of accurate determinations. Herein, ultrafiltration was exploited as a separative strategy towards the evaluation of methotrexate (MTX) encapsulation efficiency in nanostructured lipid carriers and polymeric nanoparticles. The effect of experimental conditions such as pH and the amount of surfactant present in the ultrafiltration media was addressed aiming at the selection of suitable conditions for the effective purification of nanocarriers. MTX-loaded nanoparticles were then submitted to ultrafiltration and the portions remaining in the upper compartment of the filtering device and in the ultrafiltrate were collected and analyzed by HPLC-UV using a reversed-phase (C18) monolithic column. A short centrifugation time (5 min) was suitable for establishing the amount of encapsulated MTX in nanostructured lipid carriers, based on the assumption that the free MTX concentration was the same in the upper compartment and in the ultrafiltrate. The defined conditions allowed the efficient separation of nanocarriers from the free drug, with recoveries of >85% even when nanoparticles were present in cell culture media and in pig skin surrogate from permeation assays.

2020-04Journal article

Open access

Morphodynamics of an Embayed Beach in Majorca Island

Publication . Abreu, Tiago; Parreño-Mas, Benjamín; Pinto-Faria, José

Cala Millor Beach is located in Mallorca Island and is a small sandy beach, embedded in a rocky bay. It remained generally in a state of equilibrium but, in the 60s, the urbanistic area began to develop towards the beach, interfering with the natural sediment transport of the bay. The seabed is covered by native vegetation known as Posidonia Oceanica, playing an important role in the morphodynamic system. This vegetation is responsible for the lamination of the waves through energy dissipation. To characterize the local dynamics, the SMC program (System of Coastal Modelling) is employed to study sediment transport trends and to evaluate morphological evolutions in the short term. The results seem to support the observed problem, resulting from an imbalance of sediment transport due to the drift from north to south. Moreover, the results support the idea that the morphological variations can be significantly attenuated in the presence of Posidonia Oceanica. This is of great importance for coastal management since the influence of the vegetation can be assessed, improving our knowledge on the coastal morphology and enabling to identify ways to protect the beach.

2019Conference object

Open access

Analysis of Nonlinear Wave Parameters on Ofir Sandy Beach (NW Portugal)

Publication . Abreu, Tiago; Silva, Paulo A.; Baptista, Paulo; Pais-Barbosa, Joaquim; Fernández-Fernández, Sandra; Ferreira, Caroline; Matos, João

The characterization of wave transformation processes in the nearshore is of paramount importance when it comes to assessing storm and flooding impacts, sediment transportation and deposition, harbors safety or design of coastal protective structures. This study analyzes nonlinear wave parameters on Ofir sandy beach. This beach is located along the northwest Portuguese coast which is a highly energetic coast exposed to waves generated far away in the Atlantic Ocean. Despite the existence of rocky outcrops in the nearshore and intertidal zones at the study site, reducing the wave energy that reaches the beach, the study site exhibits pronounced erosive processes. Field observations of six near-bottom pressure records collected at the intertidal zone help to characterize the evolution of wave nonlinearities which are directly associated with sediment transport mechanisms. Data results show that there is an interrelation between the characteristics of the waves and the local morphology. It is also possible to ascertain, more clearly, the level of asymmetry present in the waves propagated at different depths, contributing to a better understanding of the local morpho-hydrodynamics.

2019Conference object

Open access