Thermoplastic filament Material Extrusion (ME) is one of the most expansive 3D printing processes. Owed to the ME process’s simplicity, low cost of materials, popularity, and flexibility, considerable attention has been devoted to manufacturing specific parts in industries manipulating the polylactic acid (PLA) polymer, such as automotive and biomedical. This work aims to experimentally investigate the material flow and temperature for different layer heights on the surface texture parameters and compression strength of a tailored PLA hexagonal prismatic part. An experimental approach based on L₉ Taguchi’s array and residual analysis (ANOVA) was employed to clarify the parameters’ effects and trends regarding the response variables. The analysis of means showed that the material flow and layer height are critical variables in defining ME parts’ roughness and compression. Based on ANOVA and mean absolute percentage errors (MAPE) results, additive models (ADMO) were used to predict all combinatorial response values. Then, the experimental and the ADMO values feed as trained data for developing a feed-forward back-propagation neural network (FFBP-NN). Three independent experiments confirmed the validity of the proposed methodology resulting in reasonable accuracy of all the performance metrics, making the proposed hybrid-modeling approach adequate for process multi-parameter multi-objective optimization 3D printing cases.

Aquaponics provides an alternative opportunity for the combined production of fish and plants. Most of the essential nutrients required for optimal plant growth can be supplied from the fish feed, except for K and Fe. These nutrients are usually inadequate in fish feed. In this study, red tilapia and rocket plants were co-cultivated in an aquaponics system along with the extra addition of K and Fe. Fish growth, morpho-anatomical characteristics, and K and Fe loading on fish gills were studied. Plant growth parameters were also determined. The addition of Fe and K slightly improved the produced fresh biomass of rocket per unit area and had no impact on tilapia growth and survival. No severe histological alterations in fish gills, liver, and midgut were detected. EDX analysis showed that the addition of K led to the enrichment of this specific ion in fish gills, but no effects of this accumulation were found on other aspects of fish growth and survival.

The present study focuses on the mechanical and viscoelastic characterization of 3D-printed PLA, fabricated in three different printing orientations (0°, 45°, and 90°) and four different nozzle temperatures (210, 220, 230, and 240 °C). By employing a combination of static and dynamic mechanical analysis (DMA) testing, as well as differential scanning calorimetry (DSC) analysis, this work aims to investigate the relationship between processing parameters and the resulting properties of PLA. DSC results showed that higher nozzle temperatures enhance the degree of crystallinity, which in turn affects the mechanical and viscoelastic behavior of PLA. Regardless of the nozzle temperature, the flexural strength decreased as the printing orientation degrees increased. However, it was found that the higher the nozzle temperature, the higher the flexural strength for the same orientation, and the smaller the strength deviations per specimen. DMA results indicated that as the printing orientation increased, glass transition temperature (T_g) values increased while storage modulus values decreased. At the same time, in both cases, by increasing nozzle temperature, an increase in T_g and a respective increase in storage modulus values is observed due to the increase in the degree of crystallinity.

The European seabass is one of the most important species of the Mediterranean, specifically Greece. Individuals with different numbers of vertebrae have been reported. This number ranges from 24 to 26 vertebrae. In this study a sample of 73 individual seabass were collected from fish farms and divided into three age groups. The first group included fingerling individuals, the second group, juvenile individuals and the third group, adult individuals. The number and the length of their vertebrae were measured by radiographs. The individuals were divided into subgroups according to their vertebrae number, and from each one the tenth vertebra was taken. Ca and P levels (%) of each tenth vertebra were measured by X-ray spectroscopy (EDS), and the Ca/P ratio was determined. Vertebrae length, Ca and P levels and Ca/P ratio were compared among age groups and among individuals with different numbers of vertebrae. It was shown that the European seabass’s vertebral column can be divided to three sections—cervical, abdominal and caudal—following the striped bass (Morone saxatilis) model.