# Poly(\(\varepsilon\)-caprolactone)-Ionic Liquid Composite as Piezoionic Mechanical Sensor
## 1 Introduction  
Electronic waste (e-waste) production is caused by discarded electronic devices and electrical equipment that have reached the end of their useful life or are no longer wanted by their owners. E-waste encompasses a wide range of electronic products, from consumer electronics, like smartphones and laptops, to large appliances, industrial equipment, and more. The proliferation of electronic devices in modern society has led to a significant increase in an e-waste generation. Rapid technological advancements and shorter product lifespans contribute to this issue and determine substantial environmental challenges. Many electronic devices contain hazardous materials such as lead, mercury, cadmium, and flame retardants [1]. When not properly managed, these toxins can leach into the soil and water, causing pollution, harm to ecosystems, and health risks for both humans and animals. Extended producer responsibility (EPR) programs hold manufacturers responsible for the end-of-life management of their products [2]. These programs incentivize manufacturers to design products with recycling and environmental impact in mind. A way that can help mitigate the environmental and health risks associated with e-waste and promote a more sustainable approach to electronic device usage and disposal has been adopted through transient electronics [3; 4; 5]. Transient electronics is a captivating and cutting-edge field that has garnered significant attention in recent years within the realm of advanced materials and electronics research. This emerging technology promises groundbreaking applications by designing electronic systems that, unlike their conventional counterparts, intentionally degrade and disappear after fulfilling their purpose. Drawing inspiration from the natural world, where everything has a limited lifespan, transientelectronics emulate this ephemeral concept, offering a wide array of potential applications in medicine, environmental monitoring, and data security. The literature surrounding transient electronics is a rich tapestry of scientific exploration, spanning disciplines such as materials science, electronics, and bioengineering [6; 7; 8; 9; 10]. In the intriguing world of transient electronics, researchers endeavor to create devices that can exist only briefly, leaving no trace behind, thereby challenging our conventional notions of electronics. In this scenario, biodegradable polymers occupy a prominent place, and among them polycaprolactone (PCL), a biodegradable and biocompatible polyester with various applications, has found its use in sensors due to its unique properties [4; 11; 12]. Due to its flexibility and ease of processing, PCL has been used in producing strain gauges [13], pressure sensors [12], biomechanical sensors [14], tactile sensors [15], biodegradable sensors, and smart fabrics [16]. The use of PCL in mechanical sensors offers versatility, biocompatibility, and biodegradability, making it a promising material for a wide range of sensing applications in industries such as healthcare, robotics, and environmental monitoring. Its ability to be tailored to specific mechanical and environmental requirements makes it an attractive choice for sensor development. PCL has been widely used in the realization of mechanical sensors due to its favorable mechanical properties and biocompatibility [17; 18; 19; 20]. PCL exhibits high mechanical strength, making it suitable for applications in tissue engineering and regenerative medicine [17; 19; 20]. It is well tolerated in vivo and has been used in various biomedical applications [18]. PCL also degrades at a rate compatible with bone regeneration, making it suitable for bone tissue engineering [19]. In the field of bionanocomposites, PCL has been grafted onto microfibrilated cellulose to enhance the mechanical properties of the composite material [21]. The grafting of PCL onto cellulose allows for the preparation of thermormable bionanocomposites with good mechanical strength [21].