# Poly(\(\varepsilon\)-caprolactone)-Ionic Liquid Composite as Piezoionic Mechanical Sensor
## 1 Introduction
Furthermore, PCL has been utilized in the fabrication of 3D printed mechanochromic materials, which can change color in response to mechanical stimuli [22]. PCL containing a chain-centered spiropyran has been 3D printed and explored for its mechano-responsive characteristics, demonstrating its potential for use in prototype force sensors [22]. In the context of nanofiber scaffolds, electrospun PCL nanofibers have been combined with bioceramics to improve the mechanical characteristics of the scaffold and enhance the osteogenic differentiation of stem cells [23]. This combination of PCL nanofibers and bioceramics has been used to increase the mechanical strength of the nanofibrous scaffold [23]. Overall, PCL has been extensively utilized in the realization of mechanical sensors due to its favorable mechanical properties, biocompatibility, and ability to be incorporated into various composite materials and scaffolds. Ionic liquids (ILs) are a class of liquid salts that are composed entirely of ions, which comprise both positively charged cations and negatively charged anions. Unlike traditional salts like sodium chloride, which have high melting points and are typically solid at room temperature, ionic liquids remain in a liquid state at or near room temperature. They exhibit a unique combination of properties that make them valuable in various scientific, industrial, and technological applications [24; 25; 26; 27]. They have excellent thermal stability, resisting decomposition at high temperatures, low vapor pressures (they do not readily evaporate, making them useful in closed systems), and properties that can be finely tuned by selecting specific cations and anions, thus allowing for customization based on the desired application. Moreover, many ionic liquids are non-flammable or have low flammability, making them safer than some organic solvents. The term \"piezoionic effect\" denotes a phenomenon observed, for instance, when blending a polymer matrix with an ionic liquid. In such materials, mechanical deformation or stress can induce ion movement, leading to ionic conductivity. Though not as widely acknowledged as conventional piezoelectric materials, recent research [28; 29] has brought attention to the piezoionic effect. These sensors have garnered interest for a range of uses, such as in human-machine interfaces for medical robotics [30], as wearable sensors to track human movements [31], and as strain sensors as well as energy harvesters [32]. Their dis tinct benefits include self-powered signal generation and the ability to detect the direction of an applied load, positioning them as compelling options for wearable electromechanical sensing applications [33]. The piezoelectric effect creates ion concentration variances under pressure, resembling the signal production and transmission in biological systems like cell membranes. This makes them well suited for biomimetic sensor applications [34]. Additionally, piezoelectric sensors have been proven to operate effectively across a broad spectrum of both steady and fluctuating applied pressures, making them capable of capturing physiological data in various static and dynamic scenarios [35]. The piezoionic effect closely resembles the redistribution of the ion concentration in natural mechanoreceptor cell membranes when they are externally stimulated, offering a promising pathway for developing biomimetic mechanoreceptors [36]. Electrospinning is a versatile and widely used technique for producing polymeric membranes with a range of applications, including filtration, tissue engineering, drug delivery, and more [37; 38; 39]. It involves the use of an electric field to create ultrafine polymer fibers that are collected on a substrate to form a membrane. Electrospinning offers precise control over membrane properties, including fiber diameter and pore size, making it a valuable technique for tailoring membranes for specific applications. In recent years, our research has focused on the study of \"green\" composites comprised of bacterial cellulose and ionic liquids.