The concept of piezoelectric energy production is based on energy-harvesting devices using generation materials such as single crystals, ceramics, polymers, and composites. These production systems can harvest wasted environmental energy and convert it essentially into electrical energy. There are different nano- and microscale power harvesters which are increasingly useful for powering mobile electronics and low-power devices, even in hardly accessible areas. Despite many efforts in the development of new materials, the most widely used materials in device applications remain the ceramics of the lead zirconate titanate family, since they still present the higher output performances in the range of milliwatts of generated power.

Energy harvesting from the environment based on electroactive polymers has been increasing in recent years. Ferroelectric polymers are used as mechanical-to-electrical energy transducers in a wide range of applications, scavenging the surrounding energy to power low-power devices. These energy-harvesting systems operate by taking advantage of the piezoelectric, pyroelectric, and magnetoelectric properties of the polymers, harvesting wasted environmental energy and converting it mainly into electrical energy. There have been developed different nano- and micro-scale power harvesters with an increasing interest for powering mobile electronics and low-power devices, including applications in remote access areas. Novel electronic devices are developed based on low-power solutions, and therefore, polymer-based materials represent a suitable solution to power these devices. Among the different polymers, the most widely used in the device application is the poly(vinylidene fluoride) (PVDF) family, due to its higher output performance.

Environmentally resilient antimicrobial coatings are becoming increasingly required for a wide range of applications. For this purpose, nanocomposite thin films of poly(vinylidene fluoride) (PVDF) filled with several types of functionalized nanodiamonds (NDs) were processed by solvent casting. The effects of ND inclusion and functionalization in their morphological, structural, optical, thermal, and electrical properties were evaluated taking into account the type of the nanofiller and a concentration up to 2 wt %. The morphology, structure, and thermal features of the polymer matrix are governed by the processing conditions, and no noticeable changes occurred due to the presence of the ND fillers. The polymer crystallized mainly in the α phase with a crystallinity of ≈60%. In turn, the optical transmittance from 200 to 800 nm and the dielectric constant effectively depended on the ND type and content. The inclusion of the ND particles effectively provided antimicrobial properties to the films, which depended on the ND functionalization. This study thus shows that the incorporation of functionalized NDs into PVDF allows the development of antimicrobial coatings with tailorable optical and dielectric properties, which could be of great importance to face nowadays pandemic crisis scenario.

Flexible and conformable conductive composites have been developed using different polymers, including water-based polyvinylpyrrolidone (PVP), chemical-resistant polyvinylidene fluoride (PVDF), and elastomeric styrene-ethylene-butylene-styrene (SEBS) reinforced with nitrogen-doped reduced graphene oxide with suitable viscosity in composites for printable solutions with functional properties. Manufactured by screen-printing using low-toxicity solvents, leading to more environmentally friendly conductive materials, the materials present an enormous step toward functional devices. The materials were enhanced in terms of filler/binder ratio, achieving screen-printed films with a sheet resistance lower than Rsq < 100 Ω/sq. The materials are biocompatible and support bending deformations up to 10 mm with piezoresistive performance for the different polymers up to 100 bending cycles. The piezoresistive performance of the SEBS binder is greater than double that the other composites, with a gauge factor near 4. Thermoforming was applied to all materials, with the PVP-based ones showing the lowest electrical resistance after the bending process. These conductive materials open a path for developing sustainable and functional devices for printable and conformable electronics.

Bio-based photocurable polymers are increasingly in demand as environmentally friendly materials for advanced applications. Together with functional fillers, these represent a next step for the generation of functional and active smart materials, compatible with additive manufacturing technologies. Herein, acrylated epoxidized soybean oil (AESO) mixed with different amounts of reduced graphene oxide (rGO) up to 6 wt% in order to obtain UV-curable piezoresistive and thermoresistive materials, is reported. It is shown that the addition of rGO to AESO hinders the curing process, but always maintains double bond conversions higher than 50%. Composites are characterized by a good dispersion of micrometric filler clusters. Further, the thermal stabilities are close to 300 degrees C and crosslinking degrees are above 1.75 mmol cm(-3). The Young modulus of the composites decreases with the addition of the rGO fillers, in particular for the higher filler contents, and electrical conductivities up to 0.13 S m(-1) are obtained for the composites with the highest rGO content. UV-curable composites with piezoresistive and thermoresistive responses suitable for applications are thus obtained, characterized by gauge factors around 26 for deformations up to 2% and maximum thermoresistive sensitivity of S = 0.43, values similar to the values obtained for petroleum-based materials.

A generation of piezoresistive sensors (force or deformation) fully processed by printing technologies is increasingly being implemented in applications due to advantages as a large-area application, simple device, integration, and high flexibility. This work reports the development of a fully printed piezoresistive (5 × 5 sensor) matrix in which an organic thin-film transistor (OTFT) is placed in each sensor to allow the readout of each sensor independently and thus reducing the crosstalk between individual sensors. The manufacturing was carried out using inkjet printing for the deposition of materials in a thin layer stacked on top of each other to obtain functional OTFTs. The piezoresistive nanocomposite sensors, based on multiwalled carbon nanotubes within an elastomeric styrene-ethylene-butadiene-styrene (SEBS) polymer matrix, were fabricated by screen printing. The fabrication and characterization of both OTFT and sensors are presented and discussed in detail. The inkjet-printed OTFTs (width/length channel ratio of ∼130) show a drain-source current (IDS) of 150 μA with a gate-source voltage of −40 V. Gauge factors of up to 5.9 were obtained for the sensors, resulting in a current variation of 1.5 μA. This corresponds to about 0.7% of the total IDS in a deformation cycle

There is a large current need for new and improved approaches to treat chronic diseases such as non-neurogenic bladder diseases, the solution to prevent urethritis or inflammation of the urethral meatus being to slide a catheter along the urethra. In order to improve this procedure, it would be advantageous to place sensors in the catheter, allowing to monitor forces and deformation along the process. This work reports on a new generation of functional, sustainable piezoresistive sensors for their implementation in catheter medical devices. Composite films based on polyether block amide with varying contents of multiwalled carbon nanotubes (MWCNTs) as fillers have been produced with MWCNT contents up to 5 wt%. Further, their morphological, thermal, mechanical, electrical and piezoresistive functional response have been evaluated. Composite materials with suitable filler dispersion have been obtained, with a maximum electrical conductivity of 9 × 10&lt;sup&gt;−3&lt;/sup&gt; S.m&lt;sup&gt;−1&lt;/sup&gt; for the samples with the highest filler content of 5 wt% of MWCNT, the percolation threshold is between 1 and 2 wt% MWCNT content. All composites show appropriate piezoresistive behavior, with the gauge factor (GF) ranging between 0.5 and 1.5. At a maximum deformation of 5 mm, a composite with 3 wt% of MWCNT dip-coated on a catheter demonstrates an exceptional GF ∼ 4.5. Additionally, an electrical system was developed to demonstrate the suitability of the self-sensing catheter for practical applications, by detecting bending deformations in real time. This work shows that these sustainable polymer-based nanocomposites can be used in the biomedical industry due to their excellent piezoresistive characteristics.

From scientific and technological points of view, poly(vinylidene fluoride), PVDF, is one of the most exciting polymers due to its overall physicochemical characteristics. This polymer can crystalize into five crystalline phases and can be processed in the form of films, fibers, membranes, and specific microstructures, being the physical properties controllable over a wide range through appropriate chemical modifications. Moreover, PVDF-based materials are characterized by excellent chemical, mechanical, thermal, and radiation resistance, and for their outstanding electroactive properties, including high dielectric, piezoelectric, pyroelectric, and ferroelectric response, being the best among polymer systems and thus noteworthy for an increasing number of technologies. This review summarizes and critically discusses the latest advances in PVDF and its copolymers, composites, and blends, including their main characteristics and processability, together with their tailorability and implementation in areas including sensors, actuators, energy harvesting and storage devices, environmental membranes, microfluidic, tissue engineering, and antimicrobial applications. The main conclusions, challenges and future trends concerning materials and application areas are also presented.

Multifunctional composites for deformation sensing applications have been developed by solvent casting based on polycarbonate (PC) and polylactic acid (PLA) reinforced with carbon nanotubes (CNT). Composites shows homogeneous filler dispersion and low percolation threshold at 0.1 and 0.06 wt% CNT content for PLA and PC, respectively. The maximum electrical conductivity obtained for the larger filler contents is two order of magnitude higher for PLA composites than for PC ones, showing that the matrix influences the electrical properties of the composites. With respect to the mechanical characteristics, the samples show a maximum strain near 40% and 2.75% for composites with 0.25 and 1 wt% CNT content for PC and PLA, respectively, decreasing for larger filler contents. Concerning the piezoresistive response, 4‐point‐bending experiments from 0.1 to 5 mm, lead to a Gauge Factor (GF) of ≈1 for PC, showing that the piezoresistive response if determined by the geometrical response. On the other hand, PLA composites show GF of ≈3, revealing also intrinsic contributions, due to the variation of the filler network upon material deformation. The resistance variation upon mechanical bending deformation shows linear response for the composites near the percolation threshold and above, for both composites. A proof‐of‐concept of the functional sensing response for applications is achieved by measuring the bending deformation of an endoscope, showing that the developed sensors can determine the bending orientation and intensity, as predicted by the simulation model applied to the endoscope