The technology of 3D printing has become one of the most effective methods of creating various parts, such as those used for fast prototyping. The most important aspect of 3D printing is the selection and application of the appropriate material, also known as filament. The current review concerns mainly the description of the mechanical and physical properties of the different filaments and the possibilities of improving those properties. The review begins with a short description of the development of 3D printing technology. Next, the basic characteristics of thermoplastics used in the fused filament fabrication (FFF) are discussed, namely polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), and polyethylene terephthalate glycol (PETG). According to modern concepts, the printed parts can be reinforced with the use of different kinds of fibers, namely synthetic fibers (carbon, glass, aramid) or natural fibers (wood, flax, hemp, jute). Thus, the impact of such a reinforcement on the performance of FFF composites is also presented. The current review, unlike other works, primarily addresses the problem of the aging of parts made from the thermoplastics above. Environmental conditions, including UV radiation, can drastically reduce the physical and mechanical properties of printed elements. Moreover, the current review contains a detailed discussion about the influence of the different fibers on the final mechanical properties of the printed elements. Generally, the synthetic fibers improve the mechanical performance, with documented increases in tensile modulus reaching, for instance, 700% for carbon-fiber-reinforced ABS or over 15-fold for continuous aramid composites, enabling their use in functional, load-bearing components. In contrast, the natural ones could even decrease the stiffness and strength (e.g., wood–plastic composites), or, as in the case of flax, significantly increase stiffness (by 88–121%) while offering a sustainable, lightweight alternative for non-structural applications.

The technology of 3D printing has become one of the most effective methods of creating various parts, such as those used for fast prototyping. The most important aspect of 3D printing is the selection and application of the appropriate material, also known as filament. The current review concerns mainly the description of the mechanical and physical properties of the different filaments and the possibilities of improving those properties. The review begins with a short description of the development of 3D printing technology. Next, the basic characteristics of thermoplastics used in the fused filament fabrication (FFF) are discussed, namely: polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), and polyethylene terephthalate glycol (PETG). According to modern con-cepts, the printed parts can be reinforced with the use of different kinds of fibers, namely: synthetic fibers (carbon, glass, aramid) or natural fibers (wood, flax, hemp, jute). Thus, the impact of such a reinforcement on the performance of FFF composites is also presented.

The study aimed to determine the effect of acute, one-time physical effort performed under different environmental temperature conditions on erythrocyte deformability in healthy young men. This exploratory randomized parallel-group study involved 30 men randomly assigned to an experimental group exercising at −10 °C in a climatic chamber and a control group exercising under thermoneutral outdoor conditions. Erythrocyte deformability was assessed using the elongation index (EI), reflecting erythrocyte elasticity and the ability to pass through microcirculation vessels. Participants performed an incremental 20 m shuttle run test. Venous blood samples were collected before and immediately after exercise, and erythrocyte deformability was analyzed using a Lorrca analyzer across a shear stress range of 0.30–60.00 Pa. A two-factor repeated-measures analysis of variance was applied. An increase in EI after exercise was observed in both groups, predominantly at higher shear stress values, indicating enhanced erythrocyte deformability under conditions of increased shear forces. However, the magnitude of post-exertion changes differed between groups. At lower shear stress levels (0.30 Pa and 0.58 Pa), EI tended to decrease after exercise. These findings indicate that a single bout of physical effort influences erythrocyte deformability, while the potential effects of cold exposure on this response remain uncertain and warrant further investigation.

Background: Exercise in the cold is an attractive option for many athletes. Erythrocyte aggregation, as one of the main rheological parameters, constitutes an important indicator of microcirculation and oxygen transport capacity in the human body. Acute exercise and environmental cold may alter erythrocyte aggregation. We compared immediate hematological, aggregation, metabolic, and hormonal responses to progressive shuttle run exercise in a cold chamber and outdoors. Methods: This exploratory parallel-group analysis included 30 young healthy male students allocated to exercise in a climatic chamber at −10 °C (n = 15) or outdoors at 18 °C (n = 15). Blood was collected before and immediately after exercise. Group × time interactions were assessed using repeated-measures ANOVA and within-group comparisons used Bonferroni adjustment. Results: Erythrocyte amplitude of aggregation (AMP) showed a significant group × time interaction (p = 0.0014). In the paired analysis, the between-group difference in AMP change was −3.24 au (pointwise 95% CI −5.12 to −1.36). Lactate showed a nominal interaction (p = 0.016). Within the experimental group, red blood cell count, hemoglobin, hematocrit, mean corpuscular volume, aggregation index (AI) and lactate increased, whereas AMP and aggregation half-time (T½) decreased (all p < 0.001). Estimated plasma-volume change did not differ significantly between settings. Conclusions: Exercise in the cold-chamber setting was associated with a greater reduction in the optical aggregation amplitude. Further studies are needed to clarify the contribution of temperature and the physiological significance of these changes.