Nanopartículas para liberação controlada de substâncias indutoras da fertilidade de peixes reofílicos.

Abstract

Fish are the taxonomic group that has shown the greatest increase in the number of species threatened with extinction. To prevent extinction, ex situ reproduction is an alternative to increase the number of individuals of these species, allowing their reintroduction into nature. However, migratory fish, such as rheophilic species, do not reproduce in captivity due to the lack of environmental stimuli necessary for sexual maturation. To replicate the effects of migration, hormonal stimuli can be used through dopamine antagonist drugs, which act by blocking dopamine inhibition, promoting the production of GnRH, a hormone that leads to sexual maturation. The focus of this study was to investigate the feasibility of mesoporous silica nanoparticles (MSNs) as controlled-release systems for dopamine antagonists. The nanoparticles were synthesized using the modified Stöber method, with different concentrations of water and surfactant, resulting in non-crystalline nanospheres of varying sizes (230, 420, and 720 nm) and different specific surface areas (ranging from 955 to 1585 m²/g). Various adsorption parameters were evaluated using dyes, achieving maximum adsorption in a solution of rhodamine B (40 mg/L) at pH 5, 20°C, and with 20 mg of adsorbent. Under these conditions, a maximum adsorption capacity of 42.64 mg/g was achieved with the 420 nm MSNs, which also had the highest specific surface area, indicating that porosity significantly affects the material's adsorptive potential. The tests showed that pH is the variable that most strongly influences adsorption, and its ideal value can be estimated through the Zeta potential of the adsorbent and adsorbate solutions. The adsorption kinetics followed the pseudo-second-order model, indicating that the process is governed by valence interactions between the adsorbent and the adsorbate, with efficiency maximized by large Zeta potential differences. The release kinetics were best fitted to the Korsmeyer-Peppas model, indicating that the predominant release mechanism occurs through diffusion, following Fick's laws. A rapid initial release was observed in the first hours, followed by a reduced and prolonged rate that extended up to seven days. The initial release rate was influenced by the size of the nanoparticles, being faster when larger nanoparticles were used. The studied particles demonstrated significant potential as controlled-release mechanisms due to their high and rapid adsorption combined with a slow and sustained release of the adsorbate.