As medicine has become more advanced and our understanding of the early symptoms of illnesses continues to grow, there has been a demand in recent years for new technology committed to healthcare that can sense and monitor the functioning of complex biological systems without causing undesired responses. Similarly, materials that can efficiently transduce signals for remote sensing are needed to connect and synchronize human activities with the environment through new digital technologies [[1], [2], [3]]. However, conventional health monitoring techniques typically depend on massive machinery and qualified medical staff, which require expensive and complicated monitoring. The introduction of wearable health monitoring technologies has effectively resolved these issues [[4], [5], [6]] because it can collect real-time physical data from the user, evaluate their health, and provide personalized medical suggestions based on data analysis, wearable monitoring systems are crucial for medical treatment, preventing illness, and control. Signal conversion and recording play a critical role in the health monitoring process, as they establish the accuracy of the data received by the user. Thus, one area of great interest to academics is the manufacture of sensors with consistent performance. Consumer wearable health monitoring devices, such as smartwatches and smart glasses, include internal sensors formed by semiconductor methods based on rigid substrates. This makes it difficult for the sensors to conform to the surface of the human body, which reduces wearing comfort [1,7].

The ongoing research for synthetic methods that combine the flexibility and compositional diversity of polymeric matrices and gels with the properties of photonic, conductive, and semi-conductive materials is driven by the growing popularity of flexible electronics (Li et al., 2023, 2024). Many of them, like bioinspired and biomimetic materials, allude to the complex hierarchical composition and organization observed in biological structures [8,9]. Creating biocompatible materials with a controllable life cycle for these devices is one of their biggest obstacles once the primary function of the device is completed [10]. Their limited capacity to gather vital signs, specifically blood oxygen levels, body temperatures, and pulses, makes it difficult for them to adjust to more complex and customized medical settings. Furthermore, there is a significant Young's modulus difference between the surface of human skin and these rigid sensors. When an individual performs significant motions, rigid sensors tend to separate from the body surface, which can result in erroneous data collection [11]. Thus, creating a sensor that is completely flexible and stretchy is essential to building a wearable health monitoring system. There are still several scientific and technological obstacles in the way of stretchable device preparation, even with the latest developments. Thus far, two distinct methods have been proposed for implementing stretchability into supercapacitors: (I) From a material standpoint, active materials can be deposited or compounded with an elastic polymer substrate and conductive fillers to form stretchable electrodes [1,12,13]. (II) From the perspective of structural design, the electrodes can be made using a geometric structure that has been specially formed, like helical [14,15], spring [16], wrinkle [17], and honeycombed [18] geometries. As a result of the additional inert component, there will be a decrease in energy density at the device level and an increase in internal resistance. Activated carbon and synthetic pseudo-capacitive materials are examples of traditional granular materials whose applicability is restricted due to their huge aspect ratio, which is required to convert them into ultra-thin self-supporting films. The other problem is that electrode materials are inherently stiff. The mismatches in mechanics between the electrodes and gel electrolytes can lead to significant concentrations of stress at the contact surfaces, which might potentially result in sliding and delamination during stretching [[19], [20], [21]].

Stretchable conductor materials are in high demand due to the rapid development of flexible electronic technologies including, soft robotics, artificial electronic skins, wearable devices, and health monitoring systems [[22], [23], [24], [25]]. Researchers are paying more attention to conductive hydrogels because of their remarkable biocompatibility, low cost, excellent conductivity, and tunable mechanical characteristics [26]. The field of biomedicine has a lot of potential for these hydrogels as well. Conductive hydrogels are now employed in actuators, sensors, and flexible energy storage devices [27,28] (Hunag et al., 2025). However, hydrogels lose their flexibility and conductivity when they contain a lot of water because it causes them to evaporate at high temperatures or even room temperature, and to condense at low temperatures [29]. Researchers have looked at adding organic solvents like glycerin and ethylene glycol, which have good anti-freezing and moisturizing qualities, to hydrogels to resolve the problem of temperature stability [25,30,31]. This method successfully extends the hydrogels' service life. Polyacrylic acid hydrogels, for example, exhibit exceptional mechanical and electrical conductivity when dissolved in a mixture of glycerin and water. The gels continue to show almost 1000 % cracked strain at −50 °C, and after 7 days at ambient temperature, the gel's stable performance is sustained due to the superior water retention capability of the glycerin molecules [31]. However, after 30 days of testing, the gel gradually loses its water molecules, which makes it less conductive and brittle.

Ionic liquids are organic salts in liquid form that are made up of cations and anions. They have strong thermal stability, great electrical conductivity, and are non-volatile [32]. Ionogels, which have a greater electrical conductivity and temperature resistance than volatile hydrogels and are intriguing candidates to replace them in flexible batteries, soft robotics, and energy storage devices, may be manufactured by immobilizing them in a three-dimensional gel network [30,33,34]. Ionic liquids' expensive price and possible cytotoxicity have, however, restricted their use [35]. To address the shortcomings of ionic liquids, researchers are concentrating on developing new, environmentally friendly solvent alternatives. Deep eutectic solvents (DESs) are a novel liquid combination that combines hydrogen bond donors and acceptors to produce; it was discovered in 2003 by Abbott et al. (2003). Similar to ionic liquids, DES has strong conductivity, low volatility, and thermal stability [36]. However, it also has non-toxicity, affordability, simplicity, and biodegradability of manufacture, which makes it a “green” ionic liquid [37]. Researchers have used DES to make unique gels known as eutectogels [26,38]. But the majority of these gels that are being researched now are not very tough or strong; therefore, they can only be used as solid electrolytes if great ductility is not needed [39]. Even though some studies have replaced the solvent in eutectogels to improve their mechanical qualities [35], the conductivity of the gels has been significantly decreased. Thus, creating eutectogels with superior mechanical and electrical characteristics is still difficult, particularly for applications using flexible sensors [40].

Eutectogel-based flexible devices have great promise for advancements in the field of materials science. Strength, toughness, conductivity, self-healing, and hydrophobicity are just a few of the special qualities that these devices have to offer [10,41]. Eutectogels are perfect for several applications, from biomedical devices to wearable electronics, because of these exceptional properties. Eutectogels may be incorporated with flexibility into both thin-film and bulk applications through the use of specific electrode nanostructures [42,43]. Apart from their intended applications, eutectogels exhibit remarkable biocompatibility and resemblance to the natural extracellular matrix [44]. Because of this, they are ideal for use in biomedical applications such as bioreactors, specialized separation systems, and self-regulating and site-specific drug delivery systems. Additionally, eutectogels are perfect for tissue engineering applications because they can imitate extracellular matrix components more accurately than can be achieved with traditional methods [45,46]. Eutectogel-made flexible devices have the potential to transform several fields and enhance the lives of a broad spectrum of human beings. Because of their outstanding efficiency and flexibility, eutectogels are a potential material for the development of flexible devices in the future [10,41]. Eutectogels are an exciting area of study for researchers because of the continuous advances in materials science and their potential to transform industries and enhance people's quality of life [47]. A wide variety of environmental sensing applications is being advanced by the development of functional nanoscale electrode materials [48]. Eutectogels have demonstrated potential in robotics applications, in addition to their potential in environmental sensing applications [49,50]. By closely mimicking the mechanical properties of natural tissues, these materials' flexibility and conductivity open up new possibilities for manufacturing wearable sensors, prosthetic limbs, and soft robotics that can enhance human-machine interactions [51]. In this review, we first provide an overview of the several common design strategies used to synthesize multifunctional eutectogels classified by composition, optimization strategies, and cross-linking methods, including chemical cross-linking, physical cross-linking, and physico-chemical cross-linking. Next, we explore the latest developments in eutectogel technology, highlighting how they are used in wearable health monitors. We also go over the cutting-edge methods for enhancing the mechanical, electrical, and thermal characteristics, self-healing capacity, and biocompatibility, this review also emphasizes how revolutionary they are in wearable health monitoring applications (Fig. 1). We also give an overview of the most recent advancements in multifunctional eutectogel-based flexible devices and how they might be used in energy storage systems, sensors, and actuators. The final part of this review concludes by integrating eutectogel into next-generation flexible technologies and offers a comprehensive summary of the current developments in multifunctional eutectogel research.