Electroluminescent devices have been sufficiently studied and realized using various materials, such as the light-emitting element. However, the durability of electroluminescent devices remains a challenge as abrasion and mechanical stress lead to the deterioration of the light-emitting element ^[1][43]. This paper presents various hydrogels with self-healing properties that can withstand mechanical stresses during operation and use. Nature plays an important role in the development of functional materials. Many new discoveries of today’s functional materials were inspired by nature ^[2][44]. For example, inspired by the luminosity of insects, the properties of bioluminescence were discovered as reported in ^[3][45]. Such inspirations help people to develop today’s electroluminescence technology by integrating model concepts into the design. Qian, X. et al. ^[4][46] developed self-healing flexible perovskite light-emitting diodes (PeLEDs) from a biologically inspired pangolin design. Developed PeLEDs have shown better bending strength. Because most wearable LEDs are subject to bending and twisting during wear, these resistance properties can be restored.

Other nature-inspired materials for the applications of self-healing light-emitting diodes include human-skin-inspired electrospun electronic skins ^[5][47] and natural nano-clay-based ^[6][48] and cytoskeleton-inspired hydrogels ^[7][49]. At the rear end, when such kinds of resistance are not garneted, cracks can occur, which reduces the electrical characteristics of the materials that are the main components of LEDs. It is common practice to measure efficiency against bending and twisting for several cycles to check the durability of such materials. The first electroluminescence device was exposed to loss of its properties due to mechanical pressures. Scientists have tried to eliminate these kinds of challenges, again by nature inspiration, with self-healing properties, i.e., the process of recovery in which the device can repair oneself itself. This phenomena is based on natural biological systems where researchers used this concept and adapted it to create self-healable functional materials ^[8][50]. Therefore, self-healing means the materials can restore their physical and mechanical, as well as structural, properties after being deformed by external stimuli, such as strain ^[9][51]. This phenomenon is typically very important for electroluminescence devices as it can be subjected to several external stimuli, such as light, electric, bending, stress and so on ^[10][52]. Moreover, nature-inspired hydrogel materials and their designs have also been explored to produce sustainable and low-cost electroluminescence devices.

Self-healable gels are most often fitted in wearable textiles ^[11][53]. Most electroluminescence devices can be integrated into wearable textiles, which are subjected to several instances of bending, abrasion, load, and tightening during wear ^[10][52]. Another important parameter for wearable electronics is their stretchability, which plays a crucial role in developing flexible electroluminescence devices. In this aspect, several methods have been employed to enhance the stretchability of electroluminescence electrodes. Among them, are self-healing and self-bonding, and with them a high-strength polyurethane-based electroluminescence (EL) device has been fabricated ^[12][54]. EL devices showed excellent performance against stretchability. Polyurethane (PU) is a highly stretchable material ^[13][55]. In addition, PU exhibited the enhancement of stretchability in EL devices, which is very useful for wearable devices. More importantly, the EL device is feasible in terms of applied load, water and other external forces due to dynamic bonding and the stretchability of PU. Tiwari and Mathews ^[14][56] reported the PU derivative based on the Diels–Alder (DA) chemistry (PU-DA) self-healable polymeric composite for EL applications. At a rapid low-temperature range, the PU-DA composite unveiled extremely attractive dielectric properties, and the dielectric constant improved from 2.7 to 12.9. This was due to the highly flexible and stretchable nature of polyurethane materials. This proved it to be a self-healable and highly flexible material that is feasible for the fabrication of EL devices with improved physicomechanical properties. Cho, S.H. et al. ^[15][57] demonstrated another very important finding with regard to deformable EL devices. Shape-ductile and self-healing EL displays have been offered in the last few decades. EL devices bear more than 100 cycles of failure–recovery actions. This helps to sustain the lifespan of the EL device, which further promotes sustainability and low-cost production. Outstanding stretchability (2500%) and high self-healing efficiency (96%) were attained by introducing reversible imine bonds ^[16][58]. This is the highest stretchable EL device with improved self-healing properties. The thermal properties of hydrogels are equally important for long-term stability ^[17][59].

In addition to this, a various number of self-healing polymeric materials have been reported for EL device fabrication, confirming the importance of being self-healable, stretchable, flexible, and having other unique properties for specified applications. Gao, L. et al. ^[18][60] described self-healing polymers that are able to completely restore dielectric properties against electrical treeing. The microcapsule approach helped to mend electrical failures against unfavorable conditions using polymer processing, which improved the lifetime of dielectric materials. Furthermore, a reversible cross-linkable PU has been demonstrated elsewhere ^[19][61].

Self-healing electroluminescence devices have diverse applications, such as in artificial skin, soft robotics, flexible electronics, wearable electronics, fashion clothing, actuators, different digital displays, and sensors. Electroluminescence devices have been combined into functional and flexible electronics as a light-emitting part. However, a long service life was not possible due damage occurred by mechanical strain. With self-healable hydrogels, such problems have been eliminated. Self-healable hydrogels are stretchable, stable for many cycles and can return to their original position after stretching.

Self-healing hydrogels are next-generation materials for various applications. They can be synthesized using different methods depending on the compatibility and properties of the starting materials. Liu, Y. and S.h. Hsu ^[20][62] described the synthesis of self-healing hydrogels by incorporating nanomaterials into a dual -network hydrogel. They also mentioned that non-covalent interactions, hydrogen bonding, covalent interactions and dual networks play an important role in restoring the properties of self-healing hydrogels. Hierarchical dynamic cross-links with multiple hydrogen bonds have been developed to impart remarkable mechanical properties to hydrogels, which are characterized by extreme ductility, toughness under high real load and good fatigue resistance ^[21][63]. Simple mixing of polymers under certain conditions could also contribute to synthesized hydrogels ^[22][64]. An effective and stable inorganic optoelectronic film with a rigid epitaxial substrate could be mixed to a foreign flexible/soft substrate to compensate for mechanical properties such as stretchability and self-healing ability. The most common synthesis method of hydrogels for EL applications is cross-linking with various nanocomposite materials ^[23][65]. An alternative synthesis method is photopolymerization of aqueous solutions using visible lights ^[24][66]. The fundamental question in the synthesis of hydrogel materials is whether the hydrogel is fully functional in terms of flexibility, stretchability, mechanical strength, and durability or not. The composite materials should be compatible and must fulfil the above properties to blend together. In general, there is no set way to synthesis hydrogels that has been reported, but depending on the final application, each researcher can develop their own mechanisms, as long as the required properties are achieved.