Hybrid MMCs are a new class of materials that exhibit superior characteristics and functional response when compared to monolithic alloys and mono-reinforced MMCs, and thus have tremendous potential for widespread application in modern industrial and engineering applications. Since the manufacturing fraternity is proliferating, a cyclic evaluation of understanding the behavior of hybrid MMCs and their evolution is needed. Therefore, to address this necessity, this paper presents a detailed review of hybrid MMC manufacturing methods, materials (matrix and reinforcement) used, physicomechanical, tribological, and corrosion properties, and challenges associated with hybrid MMCs. This retrospective investigation presents the state of the art of hybrid MMC materials in the categories involving matrix materials and their alloys, ceramics reinforcements and secondary reinforcements, and the applications and formation of microstructures. This paper also discussed the overview and the status of various matrix and reinforcement materials in manufacturing hybrid MMCs using different fabrication methods. Further, the significant challenges associated with the fabrication of hybrid MMCs using different manufacturing methods, such as distribution of reinforcement, wettability, and other common limitations identified in the literature, are presented. This paper provides a broad-spectrum attitude on hybrid MMCs techniques, challenges, and future research directions.

The advent of Metal fibers has led to the development of different fiber-reinforced composite systems via different manufacturing methodologies. Utilizing Metal fibers as a single reinforcement can create completely new materials with unique physical structures and a synergistic effect on many properties. Steel, aluminum, titanium, and copper are examples of Metal fibers used in industries such as aerospace, marine, automotive, and structural applications. Moreover, the possibility of combining various material systems (Metal fibers - traditional fibers) to create hybrid composites allows for unlimited variation in cost and performance. In general, Metals are available in the form of sheets as Metal fiber Metal laminate (FML), or as Metal fibers in the form of fine wires, and mesh fibers. Investigation of fine wires and mesh fibers is still limited in the literature compared to the sheet Metal form. Therefore, this work focuses on reviewing the processing techniques, properties, and applications of fine wires and mesh Metals. In this paper, the application, methods of production, and several types and forms of Metal fiber were described in detail. Moreover, the properties and applications of Metal fibers reinforced polymer composite materials have been reviewed. The application of Metalized fibers and the hybridization of Metal fibers with synthetic and natural fibers reinforced polymer composites are also reviewed. To conclude, the potential of fine wires and mesh fiber forms, which are partially explored, seems to have excellent mechanical, thermal, and other material properties. Steel fiber is the most common Metal fiber used due to its cost-effectiveness, availability in different forms, and high performance despite its heavy weight.

Ionic Polymer Metal composites (IPMC) are smart materials that consist of two parts, Metal, and elastomer. Functionally, IPMCs are a group of electroactive polymers that, due to their special structure, are a suitable option for use as sensors and soft actuators with low excitation voltage. When used as an actuator, in addition to the excitation voltage, IPMC bending is affected by intrinsic and environmental factors. One of the serious challenges in the practical application of IPMC is the prediction of the "Back-Relaxation effect". The term back-relaxation effect is a term used for the gradual reduction of IPMC bending and return to the cathode side under constant voltage excitation. In this research, the effect of back-relaxation on the bending behavior of IPMC has been modeled in three dimensions with Comsol software, for the first time. The comparison of the results with the practical test data indicates high accuracy of 93% of the modeling in predicting displacement, which also confirms other important performance information such as concentration changes and stress distribution in the material. Using this model to predict IPMC behavior will be very cost-effective in terms of time and cost compared to practical tests.

   Intrinsically conducting polymers (ICPs) have revolutionized materials science with their versatile applications in electronics, sensors, and energy storage. This review explores the synthesis, properties, and applications of polypyrrole (PPy) and its hybrid nanocomposites with Metal oxides, emphasizing advancements in electrical conductivity, stability, and performance. PPy, a prominent conducting polymer, is synthesized through chemical polymerization or electrochemical methods and exhibits high conductivity and mechanical flexibility. Doping PPy with Metal oxides like nickel oxide (NiO) and tungsten oxide (WO3) enhances its properties for various applications. PPy-NiO composites show improved conductivity and dielectric properties, while PPy-WO3 composites demonstrate superior electrochemical performance in supercapacitors. This review highlights recent advancements in synthesizing and characterizing these composites, including X-Ray Diffraction (XRD), Ultraviolet-Visible Spectroscopy (UV-VIS), and Raman Spectroscopy. The findings underscore the potential of PPy-Metal oxide composites in advancing technologies such as energy storage, corrosion protection, and sensor development.