Wearable technologies and flexible electronics have developed rapidly owing to the emergence of cutting-edge cross-disciplines. The flexibility and tunable properties of organic materials enable wearable sensory systems to adapt to complex surface deformations and detect physiological signals sensitively. The demand for high-performance strain sensors, to accurately detect complex movements and environmental changes, in wearable technology has increased notably. However, current sensors primarily detect strain in a single direction, which restricts their effectiveness in detecting multi-directional strains, such as in natural human movements or robotic joints. In this review, we examine the advances and future challenges that may arise in the development of strain sensors that can measure both the magnitude and direction of external tensile strain. Additionally, we examine the sensor materials (platform and sensing materials) required to develop a strain sensor to detect the direction of tension, structural research on strain sensors, and various application fields such as human motion detection and human–machine interaction via system integration. Finally, we discuss the prospects and current challenges involved in the development of direction-selective strain sensors for wearable smart electronic systems or electronic skin. This review should provide a comprehensive reference for future technologies.

Aramid copolymers have garnered significant interest due to their potential applications in extreme environments such as the aerospace, defense, and automotive industries. Recent developments in aramid copolymers have moved beyond their traditional use in high-strength, high-temperature resistant fibers. There is now a demand for new polymers that can easily be processed into thin films for applications such as electrical insulation films and membranes, utilizing the inherent properties of aramid copolymers. In this work, we demonstrate two novel aramid copolymers that are capable of polymerizing in polar organic solvents with a high degree of polymerization, achieved by incorporating flexible bis(4-aminophenoxy) benzene moieties into the chain backbone. The synthesized MBAB-aramid and PBAB-aramid have enabled the fabrication of exceptionally thin, clear films, with an average molecular weight exceeding 150 kDa and a thickness ranging from 3 to 10 μm. The dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) reveal that the thin films of MBAB-aramid and PBAB-aramid exhibited glass transition temperatures of 270.1 °C and 292.7 °C, respectively, and thermal decomposition temperatures of 449.6 °C and 465.5 °C, respectively. The mechanical tensile analysis of the 5 μm thick films confirmed that the tensile strengths, with elongation at break, are 107.1 MPa (50.7%) for MBAB-aramid and 113.5 MPa (58.4%) for PBAB-aramid, respectively. The thermal and mechanical properties consistently differ between the two polymers, which is attributed to variations in the linearity of the polymer structures and the resulting differences in the density of intermolecular hydrogen bonding and pi-pi interactions. The resulting high-strength, ultra-thin aramid materials offer numerous potential applications in thin films, membranes, and functional coatings across various industries.

Lubricants are chemical substances applied between two moving surfaces to reduce frictional forces. Currently, approximately 80% of lubricants available on the market are mineral oils derived from petroleum refining, 8% are synthetic oils, and only a small fraction originates from vegetable oils. Biolubricants, which are derived from animal fats, vegetable oils, or synthetic esters, offer several advantages including biodegradability, non-toxicity, renewability, and rapid decomposition. This study focuses on the production of biolubricants through an epoxidation process using oil extracted from avocado seeds, followed by a ring-opening reaction catalyzed by a heterogeneous catalyst based on activated carbon impregnated with phosphoric acid. The objectives of this research include the characterization of avocado seed oil for its suitability in epoxy compound synthesis, the production of biolubricants using the phosphoric acid-impregnated activated carbon catalyst under various catalyst concentrations, stirring rates, and reaction times, and the subsequent characterization of the produced biolubricant. Analytical evaluations included density, viscosity, kinematic viscosity, and Fourier Transform Infrared Spectroscopy (FT-IR). The biolubricants produced exhibited kinematic viscosities ranging from 20.1401 to 20.9078 cSt and conversion efficiencies between 76.80% and 89.66%. The optimal formulation-using 3% catalyst concentration, a stirring rate of 900 rpm, and a reaction time of 90 minutes-resulted in a biolubricant with a kinematic viscosity of 20.9078 cSt and a conversion rate of 89.66%, met the ISO VG 22 viscosity classification. These results confirm that avocado seed oil is a viable and effective feedstock for the sustainable production of high-quality biolubricants.