The masks have always been mentioned as an effective tool against environmental threats. They are considered as protective equipment to preserve the respiratory system against the non-desirable air droplets and aerosols such as the viral or pollution particles. The aerosols can be pollution existence in the air, or the infectious airborne viruses initiated from the sneezing, coughing of the infected people. The filtration efficiency of the different masks against these aerosols are not the same, as the particles have different sizes, shapes, and properties. Therefore, the challenge is to fabricate the filtration masks with higher efficiency to decrease the penetration percentage at the nastiest conditions. To achieve this concept, knowledge about the mechanisms of the penetration of the aerosols through the masks at different effective environmental conditions is necessary. In this paper, the literature about the different kinds of face masks and respiratory masks, common cases of their application, and the advantages and disadvantages of them in this regard have been reviewed. Moreover, the related mechanisms of the penetration of the aerosols through the masks are discussed. The environmental conditions affecting the penetration as well as the quality of the fabrication are studied. Finally, special attention was given to the numerical simulation related to the different existing mechanisms.

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In this study, polyurethane‐films loaded with diclofenac were used to analyze the drug release kinetics and mechanisms. For this purpose, the experimental procedures were developed under static and dynamic conditions with different initial drug loads of 10, 20, and 30%. In the dynamic condition, to better simulate the biological flow, drug release measurements were investigated at flow rates of 7.5 and 23.5 ml/s. These values indicate the flow rate of the internal carotid artery (ICA) for a normal state of a body and for a person during the exercise, respectively. The experimental data were analyzed and adjusted by Higuchi, Korsmeyer–Peppas, First‐order, zero‐order, and Peppas–Sahlin models in order to understand the mechanisms contributed. Finally, drug release mechanisms were specified by investigating the model correlation coefficients. Experimental results showed that increasing the flow rate and initial drug loads enhance drug liberation. In addition, the rate of release is more influenced by the drug dosage in the static state. The analysis revealed that diffusion, burst, and osmotic pressure are the principal mechanisms contributed. Moreover, Fickian type was the dominant mechanism at all duration of release. However, it was discovered using Peppas–Sahlin model that the contribution of the diffusion mechanism decreases with increasing flow rate and initial dosage. Furthermore, the tests at different drug dosages showed that the number of stages in medication release profile is independent of the flow rate and the medicine percentage. One can conclude that the drug release kinetic in static state is more influenced by drug dosage compared with dynamic state.

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The effect of molecular weight on the crystallization behavior of poly(lactic acid) (PLA) both isothermally and non‐isothermally was studied using differential scanning calorimetry and polarized optical microscopy. Two distinct crystal forms (α and α′) were investigated under normal conditions of crystallization for different molecular weights. Using microscopy, the growth rate of spherulites was measured and the nucleation rate was estimated. Heterogeneous nucleation and morphology with a variant α and α′ forms have been proposed. Spherulites from low molecular mass PLA contained more interlamellar amorphous phase. In addition, the results showed more rapid crystallization of α′ than the α form in isothermal conditions.

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Impellers are referred to as a core component of turbomachinery. The use of impellers in various applications is considered an integral part of the industry. So, increased performance and the optimization of impellers have been the center of attention of a lot of studies. In this regard, studies have been focused on the improvement of the efficiency of rotary machines through aerodynamic optimization, using high-performance materials and suitable manufacturing processes. As such, the use of polymers and polymer composites due to their lower weight when compared to metals has been the focus of studies. On the other hand, methods of the manufacturing process for polymer and polymer composite impellers such as conventional impeller manufacturing, injection molding and additive manufacturing can offer higher economic efficiency than similar metal parts. In this study, polymeric and polymer composites impellers are discussed and conclusions are drawn according to the manufacturing methods. Studies have shown promising results for the replacement of polymers and polymer composites instead of metals with respect to a suitable temperature range. In general, polymers showed a good ability to fabricate the impellers, however in more difficult working conditions considering the need for a substance with higher physical and mechanical properties necessitates the use of composite polymers. However, in some applications, the use of these materials needs further research and development.

Additive manufacturing (AM) has attracted a lot of attention in the industry and studies due to the ability to fabricate parts in different sizes and shapes along with economic costs. Among the different three-dimensional (3D) printing methods, stereolithography (SLA) is becoming an important method. The objective of this work is to investigate the effect of different sub-build orientations of an acrylate-based 3D printing SLA rapid-prototyping photosensitive resin concerning UV and thermal post-curing on the thermal and mechanical properties. Key role of polymerization as a determining factor in the final mechanical and thermal properties was shown. The results indicate turning the mechanical properties of cured resin by different sub-build orientations. Furthermore, post-curing process was performed in order to complete the curing of unreacted monomers. The results show the important effect of thermal post-curing on the mechanical properties. In addition, a polymerization up to 98% for thermal curing at 80 C was achieved. In addition, the maximum tensile strength for the maximum amount of polymerization was for sub-building orientation of 45 , 0 , and 90 .