The increasing need for wearable and portable electronics and the necessity to provide a continuous power supply to these electronics have shifted the focus of scientists toward harvesting energy from ambient sources. Harvesting energy from ambient sources, including solar, wind, and mechanical energies, is a solution to meet rising energy demands. Furthermore, adopting lightweight power source technologies is becoming more decisive in choosing renewable energy technologies to power novel electronic devices. In this regard, piezoelectric nanogenerators (PENGs) based on polymer composites that can convert discrete and low-frequency irregular mechanical energy from their surrounding environment into electricity have attracted keen attention and made considerable progress. This review highlights the latest advancements in this technology. First, the working mechanism of piezoelectricity and the different piezoelectric materials will be detailed. In particular, the focus will be on polymer composites filled with lead-free BaTiO₃ piezoceramics to provide environmentally friendly technology. The next section will discuss the strategies adopted to enhance the performance of BaTiO₃-based polymer composites. Finally, the potential applications of the developed PENGs will be presented, and the novel trends in the direction of the improvement of PENGs will be detailed.

Piezoelectric polymer composites, particularly polyvinylidene fluoride (PVDF) blended with barium titanate (BT), show promise for wearable technologies as both energy harvesters and haptic actuators. However, these composites typically exhibit limited electromechanical coupling and insufficient β-phase formation. This study presents a novel approach using ionic liquids (ILs) to enhance PVDF-based piezoelectric composite performance. Through solution-casting methods, we examined the effect of IL concentration on the structural, mechanical, and piezoelectric properties of PVDF/BT composites. Results demonstrate that the use of IL significantly improves β-phase crystallization in PVDF while enhancing electrical properties and mechanical flexibility, which are key requirements for effective energy harvesting and haptic feedback applications. The optimized composites show a 25% increase in β-phase content, enhanced flexibility, and a 100% improvement in piezoelectric voltage output compared to other more conventional PVDF/BT systems. The IL-modified composite exhibits superior piezoelectric response, generating an output voltage of 9 V and an output power of 40.1 µW under mechanical excitation and a displacement of 138 nm when subjected to 13 V peak-to-peak voltage, making it particularly suitable for haptic interfaces. These findings establish a pathway toward high-performance, flexible piezoelectric materials for multifunctional wearable applications in human–machine interfaces.

This paper presents the design and fabrication of Fil3D-Hand, a humanoid robotic hand with five fingers integrating nanocomposite filament strain sensors to monitor finger movements. The objective is to replicate the functionality of the human hand through an affordable design, with potential applications in humanoid robotics and prosthetic rehabilitation. Based on the investigation of the human hand’s anatomical structure and existing robotic hands, the mechanical design of Fil3D-Hand is elaborated. The kinematics analysis and finger workspace are formulated and illustrated using the Denavit-Hartenberg (D-H) convention and numerical simulations. The proposed design features 17 degrees of freedom, weighs 2.4 kg (including the forearm and 12 servo motors), and achieves a fabrication cost of less than $350. The Fil3D hand’s size is approximately 1.2 the size of the real human hand, allowing for enhanced versatility while maintaining a naturalistic appearance. This design strategy ensures a cost-effective, tendon-driven underactuated mechanism, utilizing servo motors for precise control of finger joints. It also integrates 14 filament strain sensors for accurate monitoring of finger positions. Experimental results demonstrate the performance of these sensors, revealing a highly linear correlation ( $$ R^2 = 0.9964 $$R 2 = 0.9964 ) between the finger’s proximal angles and the strain sensor resistance, guaranteeing precise real-time monitoring of finger movements. Evaluation of the Fil3D-Hand’s performance highlights its excellent grasping capabilities, showcasing its potential in practical applications.