Conductive Organohydrogel Research Articles

Skin-like dual-network gelatin/chitosan/emodin organohydrogel sensors mediated by Hofmeister effect and Schiff base reaction

Conductive gels have been extensively explored in the field of wearable electronics due to their excellent flexibility and deformability. Traditional gels constructed from synthetic networks pose risks to biosecurity due to residual monomers like acrylamide, while pure biological hydrogels are plagued by inadequate mechanical performance. This study explores an innovative strategy, employing a dual-network (DN) system with purely biological components, as a superior alternative to conventional synthetic networks. By integrating gelatin and chitosan, two natural polymers with inherent biocompatibility and advantageous biomedical properties, this approach successfully avoids the toxic risk of synthetic polymers. By utilizing emodin, a natural extract from Rheum officinale, as a cross-linking agent for chitosan by Schiff base reactions, and Hofmeister effect of gelatin induced by sodium carbonate, the DN gelatin/chitosan/emodin organohydrogels achieve ultrahigh tensile strength (up to 9.45 MPa), tunable moduli (ranging from 0.07 to 3.42 MPa), excellent toughness (~9.64 MJ/m3), and high ionic conductivity (7.63 mS/cm). Remarkably, these conductive organohydrogels also exhibit high sensitivity (gauge factor up to 1.5) and ultrahigh linearity (R2 up to 0.9995), making them promising candidates for soft human-motion sensors capable of accurately detecting and monitoring human movements in real time with high sensitivity and durability.

Lignin sulfonate induced ultrafast fabrication of polypyrrole-based conductive organohydrogel for high performance flexible strain and temperature sensor

The ultrafast preparation of electrically conductive hydrogels to endow high sensing performance and temperature tolerance remains a critical challenge. Herein, lignosulfonate sodium-templated polypyrrole (LS-PPy) nanofillers were rapidly introduced into polyacrylic acid (PAA) hydrogel through ultrafast free radical polymerization in a glycerol/water binary solvent system. The resultant LS-PPy/PAA electrically conductive organohydrogel possesses satisfactory mechanical performance (strength of 56 kPa at a tensile strain of 800 %), strong adhesion, and a desirable low freezing point (−35 °C). Furthermore, this organohydrogel exhibits high strain sensitivity (gauge factor = 2.65), fast response time (~160 ms), low signal hysteresis, and excellent cyclic stability (over 1200 cycles). And the wearable LS-PPy/PAA organohydrogel sensor could accurately and real-time monitor various intense or subtle human movements, such as joint bending, facial expression and hand writing. Besides, the developed LS-PPy/PAA temperature sensor can respond to environmental temperature variations over a wide range of −20–100 °C. High resolution of 0.5 °C with remarkable sensitivity (−0.80 %/°C and linearity of R2 = 0.99) and repeatability were achieved within 36.5–40 °C, which makes it suitable for human body temperature monitoring. All these results demonstrate the substantial prospective value of the LS-PPy/PAA hydrogel in wearable sensors and other associated fields.

Multifunctional conductive organohydrogel with environmental tolerance for flexible wearable devices

Multifunctional conductive organohydrogel with environmental tolerance for flexible wearable devices

The development of anti-freezing and anti-evaporating conductive organohydrogel for flexible strain-sensing electronic devices.

The hydrogels got hot attention from the researchers due to their excellent flexibility, mechanical properties, conductivity, and response to external stimuli, however, their applications are hampered due to a lack of water retention properties and anti-freezing ability. In this study, the organohydrogel was designed from the two solvents system (DMSO and water) in which acrylamide (Amm) and acrylic acid (AA) work as monomers and Arabic gum (AG) works as biopolymers. The functional groups, surface morphology, mechanical properties, rheological properties, anti-freezing properties, and strain-sensing properties of the fabricated organohydrogel were studied. The DMGA6 organohydrogel showed good mechanical properties with fracture stress of 197 kPa, fracture strain of 593%, cyclic stability to five cycles at 400% strain without relaxation time, excellent rheological performance (elastic behavior), anti-freezing properties (-54.6 °C), the response time of 65 ms with a gauge factor of 8.86 at 500% strain. The organohydrogel can detect different human motions like bending of the finger, elbow, neck, and wrist at normal and harsh temperatures. Additionally, the organohydrogel can also detect the mood of humans, etc. The designed organohydrogels can be used in strain-sensing smart electronic devices for writing, drawing, etc. as an electronic pen.

Strong, tough and environment-tolerant organohydrogels for flaw-insensitive strain sensing.

Conductive organohydrogels are promising for strain sensing, while their weak mechanical properties, poor crack propagation resistance and unstable sensing signals during long-term use have seriously limited their applications as high-performance strain sensors. Here, we propose a facile method, i.e., solvent exchange assisted hot-pressing, to prepare strong yet tough, transparent and anti-fatigue ionically conductive organohydrogels (ICOHs). The densified polymeric network and improved crystallinity endow ICOHs with excellent mechanical properties. The tensile strength, toughness, fracture energy and fatigue threshold of ICOHs can reach 36.12 ± 4.15 MPa, 54.57 ± 2.89 MJ m-3, 43.44 ± 8.54 kJ m-2 and 1212.86 ± 57.20 J m-2, respectively, with a satisfactory fracture strain of 266 ± 33%. In addition, ICOH strain sensors with freezing and drying resistance exhibit excellent cycling stability (10 000 cycles). More importantly, the fatigue resistance allows the notched strain sensor to work normally with no crack propagation and output stable and reliable sensing signals. Overall, the unique flaw-insensitive strain sensing makes ICOHs promising in the field of wearable and durable electronics.

Ultra-Flexible, Anti-Freezing, and Adhesive Collagen Fiber-Derived Conductive Organohydrogel E-Skin for Strain, Humidity, Temperature, and Bioelectric Sensing Applications

Ultra-Flexible, Anti-Freezing, and Adhesive Collagen Fiber-Derived Conductive Organohydrogel E-Skin for Strain, Humidity, Temperature, and Bioelectric Sensing Applications

Antifreeze Polyvinyl Alcohol Organohydrogel Sensors Containing Polypyrrole Nanowires Self‐Assembled onto Graphene Oxide Nanoplatelets with High Electrical Conductivity and Improved Mechanical Properties

AbstractConductive hydrogels exhibit significant potential for flexible electronics owing to their exceptional flexibility, resistance to deformation, and high conductivity. However, there is a critical need to develop hydrogels that can withstand extremely low temperatures while exhibiting good mechanical properties. In this study, carboxyl‐modified polyvinyl alcohol (PVA) as the gel matrix, dimethylsulfoxide and water as a mixed solvent solution, and graphene oxide (GO) assembled polypyrrole (PPy) nanowires are used to prepare a new type of antifreeze conductive organohydrogel (PGOPPy). The PGOPPy organohydrogel demonstrates outstanding antifreeze properties, retaining its flexibility at temperatures as low as −75 °C. It exhibits a fracture strength of 0.80 MPa and an elongation at break of 436% at room temperature. Remarkably, after being stored at room temperature for 15 days, the diameter of the PGOPPy organohydrogel changes only by 4%. Moreover, PGOPPy shows high electrical conductivity, up to 1.07 S m−1, and exhibits variable conductivity in response to mechanical deformation, with a stable response over cyclic deformations, allowing its use as a sensor to monitor body movements. Results demonstrate that the developed material is very promising as an effective sensor technology for use in extremely cold environments. Moreover, this work provides a general method for preparing antifreeze organhydrogels using water and dimethylsulfoxide as mixed solvents.

Environmentally tolerant conductive organohydrogel toward superior electromagnetic interference shielding and human motion detection

Environmentally tolerant conductive organohydrogel toward superior electromagnetic interference shielding and human motion detection

Environment-tolerant gelatin based ionic conductive organohydrogel for flexible sensor

Flexible wearable devices based on hydrogels have attracted more and more attention, however, the preparation of hydrogels with high toughness, conductivity and anti-freezing and anti-drying is still a challenge. In this study, a chemical-physical cross-linked double network conductive organohydrogel was designed by incorporating gelatin and Lithium chloride (LiCl) into polyacrylamide (AM) network with water-glycerol binary solvent. The results displayed that the organohydrogel exhibited high toughness, high stretchability, anti-freezing and anti-drying capability. With the addition of glycerol and LiCl, the organohydrogel has shown good conductivity in wide ranges of temperature. Moreover, the organohydrogel could be used as a strain sensor for the detection of various human body motions. Meanwhile, it was found that the introduction of LiCl enhanced the strain sensing performance, the stability and working temperature range. The sensors exhibited a high thermal sensitivity (5.72 % /℃), broad temperature detection range (0–65℃). These outstanding advantages indicated that the organohydrogels have potential application as strain and temperature sensors.

Wireless Sensor System Based on Organohydrogel Ionic Skin for Physiological Activity Monitoring.

Supermolecular hydrogel ionic skin (i-skin) linked with smartphones has attracted widespread attention in physiological activity detection due to its good stability in complex scenarios. However, the low ionic conductivity, inferior mechanical properties, poor contact adhesion, and insufficient freeze resistance of most used hydrogels limit their practical application in flexible electronics. Herein, a novel multifunctional poly(vinyl alcohol)-based conductive organohydrogel (PCEL5.0%) with a supermolecular structure was constructed by innovatively employing sodium carboxymethyl cellulose (CMC-Na) as reinforcement material, ethylene glycol as antifreeze, and lithium chloride as a water retaining agent. Thanks to the synergistic effect of these components, the PCEL5.0% organohydrogel shows excellent performance in terms of ionic conductivity (1.61 S m-1), mechanical properties (tensile strength of 70.38 kPa and elongation at break of 537.84%), interfacial adhesion (1.06 kPa to pig skin), frost resistance (-50.4 °C), water retention (67.1% at 22% relative humidity), and remoldability. The resultant PCEL5.0%-based i-skin delivers satisfactory sensitivity (GF = 1.38) with fast response (348 ms) and high precision under different deformations and low temperature (-25 °C). Significantly, the wireless sensor system based on the PCEL5.0% organohydrogel i-skin can transmit signals from physiological activities and sign language to a smartphone by Bluetooth technology and dynamically displays the status of these movements. The organohydrogel i-skin shows great potential in diverse fields of physiological activity detection, human-computer interaction, and rehabilitation medicine.

CQDs-Cross-Linked Conductive Collagen/PAA-Based Nanocomposite Organohydrogel Coupling Flexibility with Multifunctionality for Dual-Modal Sensing of Human Motions.

Conductive hydrogels are ideal materials for intelligent medical devices, human-machine interfaces, and flexible bioelectrodes due to their adjustable mechanical properties and electrical responsiveness, whereas it is still a great challenge to achieve the integration of excellent flexibility and biocompatibility into one hydrogel sensor while also incorporating self-healing, self-adhesion, environmental tolerance, and antimicrobial properties. Here, a nanocomposite conductive organohydrogel was constructed by using collagen (Col), alginate-derived carbon quantum dots (OSA-CQDs), poly(acrylic acid) (PAA), ethylene glycol reduced AgNPs, and Fe3+ ions. Depending on OSA-CQDs with multiple chemical binding sites and high specific surface area as cross-linkers, while coupling highly biologically active Col chains and PAA chains are serving as an energy dissipation module, the resulting organohydrogel exhibited excellent flexibility (795% of strain, 193 kPa of strength), high cell compatibility (>95% survival rate), self-healing efficiency (HE = 79.5%), antifreezing (-20 °C), moisturizing (>120 h), repeatable adhesion (strength >20 kPa, times >10), inhibitory activity against Escherichia coli and Staphylococcus aureus (9 and 21.5 cm2), conductivity, and strain sensitivity (σ = 1.34 S/m, gauge factor (GF) = 11.63). Based on the all-in-one integration of multifunction, the organohydrogel can collaboratively adapt to the multimode of strain sensing and electrophysiological sensing to realize wireless real-time monitoring of human activities and physiological health. Therefore, this work provides a new and common platform for the design and sensing of next-generation hydrogel-based smart wearable sensors.

A multifunctional conductive organohydrogel as a flexible sensor for synchronous real-time monitoring of traumatic wounds and pro-healing process

Ion-conductive hydrogels (ICHs) offer promising applications in the realm of flexible bioelectronics due to their attributes, such as transparency, flexibility, tissue adhesion, and self-healing. However, it remains a challenge to integrate excellent material properties and bio-properties into ICHs-based smart wearables for intricate biomedical applications. Herein, a multifunctional conductive C-CST/PMC organohydrogel with stretchability, anti-freezing, self-healing, antibacterial, antioxidant, and biocompatibility was synthesized by catechol-conjugated chitosan (C-CS), silk nanofibrils (SNFs), tannic acid (TA), MgCl2/CaCl2, and polyvinyl alcohol (PVA), with a binary solvent system composed of ethylene glycol (EG) and H2O. The C-CST/PMC exhibited excellent mechanical properties (175 kPa stress and 330 % strain), anti-freezing capacity, moisture retention, self-healing performance, and high conductivity (1.76 mS/cm at 25 °C and 1.43 mS/cm at –18 °C). Moreover, we have employed this organohydrogel as a flexible strain sensor for monitoring human movements, achieving a high sensitivity (gauge factor (GF) = 1.20 at 100 % strain) and glorious fatigue resistance (>1000 cycles). Furthermore, the C-CST/PMC displayed good antibacterial, antioxidant, hemo-, and cytocompatibility. In vivo tests on diabetic rats have demonstrated that the C-CST/PMC organohydrogel effectively reduces inflammatory responses and promotes angiogenesis, consequently expediting wound healing. Notably, trials involving the use of this flexible sensor in a medical silicone bionic shoulder have indicated its potential as a wearable electronic device for real-time monitoring of human wound healing progress. Overall, this research contributes novel insights to the design and fabrication of multifunctional flexible sensors that synchronous pro-healing and real-time monitoring of traumatic skin.

Coordination/salting-out synergistic construction of multifunctional PVA/chitosan conductive organohydrogel as strain and bioelectrical sensors

The salting-out action and the cation-induced-crosslinking reaction have been reported separately for the preparation of conductive hydrogels, but there are few studies on the synergistic effect of these two interactions. Also, how to construct flexible strain sensors with more functions is rarely reported by introducing multiple ions through the simple immersion method based on the synergistic action of two kinds of ions. Herein, a polyvinyl alcohol (PVA)/O-carboxymethyl chitosan (O-CMCS)-based composite conductive organohydrogel POAPZ was designed and fabricated by replacing pure water solvent with nano-silver particles (AgNPs) solution, followed by the immersion treatment in the PDO (1, 3-propylene glycol)-ZnSO4 (zinc sulfate) blended solution. Due to the synergistic effect of crosslinking coordination, salting out and hydrogen bonding, the electromechanical properties and sensing behavior of the resulting organohydrogel POAPZ were almost unchanged at room temperature and long-term storage conditions. The flexible electronic device, constructed by this organohydrogel, exhibited considerable anti-freezing, moisturizing, antibacterial, conductive (1.4 S/m) and mechanical properties (fracture stress of 2.2 MPa), and could be used as strain sensor to monitor human movement at room or low temperatures, including large-scale and subtle body movements and bioelectrical signals, which is a long-term wearable sports health monitoring system. In summary, this work successfully constructed an organic flexible electronic device POAPZ with the advantage of remaining good mechanical durability and applicability under harsh environmental conditions, and the fabrication strategy used provides a new idea for the construction of conductive hydrogel via ion immersion procedure.

Tough and Strain-Sensitive Organohydrogels Based on MXene and PEDOT/PSS and Their Effects on Mechanical Properties and Strain-Sensing Performance.

Conductive hydrogels have shown promising application prospects in the field of flexible sensors, but they often suffer from poor mechanical properties, low sensitivity, and lack of frost resistance. Herein, we report a tough, highly sensitive, and antifreeze strain sensor assembled from a conductive organohydrogel composed of a dual-cross-linked polyacrylamide and poly(vinyl alcohol) (PVA) network, as well as MXene nanosheets as nanofillers and poly(3,4-ethylenedioxythiophene)-doped poly(styrenesulfonate) (PEDOT/PSS) as the main conducting component (PPMP-OH organohydrogel). The tensile strength and toughness of PPMP-OH had been greatly enhanced by MXene nanosheets due to the mechanical reinforcement of MXene nanosheets, as well as various strong noncovalent interactions formed in the organohydrogels. The PPM1P-OH organohydrogels showed a tensile strength of 1.48 MPa at 772% and a toughness of 5.59 MJ/m3. Moreover, the conductivity and strain-sensing performance of PPMP-OH were significantly improved by PEDOT/PSS, which can form hydrogen bonds with PVA and electrostatic interactions with MXene. This was greatly beneficial for constructing a uniformly distributed and stable 3D conductive network and helped to obtain strain-dependent resistance of PPMP-OH. The strain sensors assembled from PPMP1-OH exhibited a high sensitivity of 5.16, a wide range of detectable strains up to 500%, and a short response time of 122 ms, which can effectively detect various physiological activities of the human body with high stability. In addition, the corresponding pressure sensor array also showed high sensitivity in identifying pressure magnitude and position.

A Freeze‐Resistant, Highly Stretchable and Biocompatible Organohydrogel for Non‐Delayed Wearable Sensing at Ultralow‐Temperatures

AbstractWearable electronics based on conductive hydrogels (CHs) easily suffer from prolonged response times, reduced wearing comfort, shortened service lives, and impaired signal accuracy in cold environments, because conventional CHs tend to freeze at subzero temperatures and lose their flexibility, adhesion, transparency, and conductivity, which will limit their applications in extreme environments. Inspired by the way psychrotolerant creatures and superabsorbent materials interfere with the hydrogen bonding networks of water, a freeze‐resistant conductive organohydrogel (COH) is facilely fabricated. The synergy effect between charged polar terminal groups and a binary solvent system of water–ethylene glycol weakens the hydrogen bonding between water molecules and endows the COH with remarkable freezing tolerance (−78 °C). Additionally, the obtained COH is ultra‐stretchable (≈6185%), tough (9.2 MJ m−3), highly transparent (≈99%), self‐adhesive (10.2–27.8 kPa), and biocompatible. This versatile COH is assembled into a strain sensor and a well‐designed bracelet electrocardiogram sensor. Benefiting from the exceptional low‐temperature tolerance of the prepared COH, these devices exhibit fast response with delay‐free signals even at −40 °C. Overall, this work proposes a strategy to develop multifunctional COHs for supporting human health in cold environments.

Water vapor assisted aramid nanofiber reinforcement for strong, tough and ionically conductive organohydrogels as high-performance strain sensors.

Conductive organohydrogels have gained increasing attention in wearable sensors, flexible batteries, and soft robots due to their exceptional environment adaptability and controllable conductivity. However, it is still difficult for conductive organohydrogels to achieve simultaneous improvement in mechanical and electrical properties. Here, we propose a novel "water vapor assisted aramid nanofiber (ANF) reinforcement" strategy to prepare robust and ionically conductive organohydrogels. Water vapor diffusion can induce the pre-gelation of the polymer solution and ensure the uniform dispersion of ANFs in organohydrogels. ANF reinforced organohydrogels have remarkable mechanical properties with a tensile strength, stretchability and toughness of up to 1.88 ± 0.04 MPa, 633 ± 30%, and 6.75 ± 0.38 MJ m-3, respectively. Furthermore, the organohydrogels exhibit great crack propagation resistance with the fracture energy and fatigue threshold as high as 3793 ± 167 J m-2 and ∼328 J m-2, respectively. As strain sensors, the conductive organohydrogel demonstrates a short response time of 112 ms, a large working strain and superior cycling stability (1200 cycles at 40% strain), enabling effective monitoring of a wide range of complex human motions. This study provides a new yet effective design strategy for high performance and multi-functional nanofiller reinforced organohydrogels.

Collagen fiber-reinforced, tough and adaptive conductive organohydrogel e-skin for multimodal sensing applications.

Conductive hydrogels (CHs) with high sensitivity and multifunctional property are considered as excellent materials for wearable devices and flexible electronics. Surface synapses and internal multilayered structures are key factors for highly sensitive pressure sensors. Nevertheless, current CHs lack environmental adaptability, multifunctional perception, and instrument portability, which seriously hinders their application as sensors. Here, waste collagen fibers (buffing dust of leather), polyvinyl alcohol (PVA) and gelatin (Gel) were used as the basic framework of the hydrogel, loaded with a conductive material (silver nanoparticles (BD-CQDs@AgNPs)) and an anti-freezing moisturizer (glycerol (Gly)), resulting in a multifunctional conductive organohydrogel (BPGC-Gly). As a temperature and humidity sensor, it demonstrated an excellent temperature response range (-20-60 °C) and was capable of rapid response (2.4 s) and recovery (1.6 s) to human breathing. As a strain/pressure sensor, it allowed real-time monitoring of human movement and had a high low-pressure sensitivity (S = 4.26 kPa-1, 0-12.5 kPa). Interestingly, BPGC-Gly could also be used as a portable bioelectrode or the acquisition, monitoring and analysis of EMG/ECG signals. In this work, BPGC-Gly was assembled with wireless transmission to achieve multimodal heath detection, which opens new avenues for multi-responsive CHs, comprehensive human health monitoring and next-generation wearable electronic skin (e-skin).

Multifunctional organohydrogel via the synergy of dialdehyde starch and glycerol for motion monitoring and sign language recognition

Conductive hydrogel which belongs to a type of soft materials has recently become promising candidate for flexible electronics application. However, it remains difficult for conductive hydrogel-based strain sensors to achieve the organic unity of large stretchability, high conductivity, self-healing, anti-freezing, anti-drying and transparency. Herein, a multifunctional conductive organohydrogel with all of the above superiorities is prepared by crosslinking polyacrylamide (PAM) with dialdehyde starch (DAS) in glycerol-water binary solvent. Attributing to the synergy of abundant hydrogen bonding and Schiff base interactions caused by introducing glycerol and dialdehyde starch, respectively, the organohydrogel achieved balanced mechanical and electrical properties. Besides, the addition of glycerol promoted the water-locking effects, making the organohydrogel retain the superior mechanical properties and conductivity even at extreme conditions. The resultant organohydrogel strain sensor exhibits desirable sensing performance with high sensitivity (GF = 6.07) over a wide strain range (0–697 %), enabling the accurate monitoring of subtle body motions even at −30 °C. On the basis, a hand gesture monitor system based on the organohydrogel sensors arrays is constructed using machine learning method, achieving a considerable sign language recognition rate of 100 %, and thus providing convenience for communications between the hearing or speaking-impaired and general person.

Tough Conductive Organohydrogel for Wearable Sensing in Extreme Environmental Conditions

AbstractConductive hydrogels, despite their significant potential, have faced historical limitations including vulnerability to dehydration, degradation of performance at extreme temperatures, and susceptibility to freezing in subzero conditions. Furthermore, the development of hydrogels that are both tough and stretchable, capable of maintaining performance under extreme environmental conditions, has remained a challenging task. Herein, an innovative conductive organohydrogel, distinguished by its superior toughness, stretchability, stability in regular ambient conditions, vacuum adaptability, and resistance to extreme temperatures is presented. By implementing a unique dry annealing process during synthesis, the mechanical strength of the organohydrogel has been substantially enhanced, dehydration concerns have been alleviated, and the structural integrity has been reinforced. In addition, the composition of the organohydrogel is specifically engineered to achieve both lasting endurance and sustainable longevity. This study signifies a crucial leap forward in creating high‐performing organohydrogels capable of functioning in a wide range of environments and conditions, thereby unlocking an array of adaptable applications.

Highly Robust Conductive Organo-Hydrogels with Powerful Sensing Capabilities Under Large Mechanical Stress.

The low mechanical strength of conductive hydrogels (<1MPa) has been a significant hurdle in their practical application, as they are prone to fracturing under complex conditions, limiting their effectiveness. Here, this work fabricates a strong and tough conductive hierarchical poly(vinyl alcohol) (PEDOT:PSS/PVA) organo-hydrogel (PPS organo-hydrogel) via a facile combining strategy of self-assembly and stretch training. With PVA/PEDOT:PSS microlayers and aligned PVA/PEDOT:PSS nanofibers, PVA and PEDOT:PSS nanocrystalline domains, and semi-interpenetrating polymer networks, PPS organo-hydrogels display outstanding mechanical performances (strength: 54.8MPa, toughness: 153.97MJ m-3 ). Additionally, PPS organo-hydrogels also exhibit powerful sensing capabilities (gauge factor (GF): 983) due to the aligned hierarchical structures and organic liquid phase of DMSO. Notably, with the synergy of such mechanical and sensing properties, organo-hydrogels can even detect objects as light as 1 gram, despite bearing a tensile strength of ≈23MPa. By incorporating these materials into human-machine interfaces, such as controlling artificial arms for grabbing objects and monitoring sport behaviors in soccer training, this work has unlocked a new realm of possibilities for these high-performance hierarchical organo-hydrogels. This approach to designing hierarchical structures has the potential to lead to even more high-performance hydrogels in the future.