Adhesive, stretchable and antibacterial hydrogel with external/self-power for flexible sensitive sensor used as human motion detection
Graphical abstract
Introduction
In recent years, the demand for smart devices has increased, and the development of stretchable conductive elastomers with rich properties were play great importance to modern electronic products [[1], [2], [3], [4], [5]]. But most elastomers composed of semiconductors and metals would separate from each other under large strain, causing the conductive network to rupture, losing its conductivity stability and sensing performance [[6], [7], [8], [9]]. Therefore, many researchers use soft polymers as an alternative to new artificial skin. Hydrogel is a material with a large amount of water, which has a flexible 3D network structure [[10], [11], [12], [13], [14]]. High content of water can provide a transport path for conductive ions, and its mechanical properties are similar to human skin, so the hydrogel with good mechanical properties, biocompatibility and electrical conductivity were promising candidates for the manufacture of artificial skin [[15], [16], [17]]. At present, various hydrogel-based strain sensors have been manufactured. They play an important role in detecting human movements due to their high sensitivity, wearability and long-term usability [[18], [19], [20], [21], [22]].
However, many conductive hydrogels lack adhesion, resulting in high resistance and unstable electrical signals at the interface [23,24]. In fact, the skin strain sensor requires the hydrogel to have excellent adhesion properties. This ensures that the skin deformation can be converted into electrical signals to the greatest extent during the application process [25,26]. Interestingly, it has been noted that many plants exhibit adhesion spontaneously due to the presence of adhesion molecules in their extracellular matrix, such as aloe vera and maltose [27,28]. Inspired by this phenomenon, zwitterionic [2-(methacryloyloxy) ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide (SBMA) with both positive and negative charges on the polymer chain derived from natural polysaccharides has attracted people's attention [[29], [30], [31]]. Since the positive and negative charges in zwitterionic polymers can produce high dipole moments, hydrogels containing zwitterions can produce ideal adhesion to most surfaces through ion-dipole or dipole-dipole interactions force [[32], [33], [34]]. For example, Zhang and Fu et al. synthesized zwitterionic nanocomposite hydrogel by free radical polymerization of SBMA and HEMA, and the hydrogel had good mechanical properties, adhesion, self-healing and high conductivity sensitivity, and can be used to detect human movement [35]. Therefore, polyzwitterionic SBMA with good biocompatibility and inherent conductivity can make zwitterionic composite hydrogels have an excellent prospect in monitoring the complex dynamic movement of the human body surface [36,37].
In addition, most of the flexible electronic sensors prepared currently need external power supply to use [[38], [39], [40], [41]]. Once the external power supply meets problems, these sensors will not work, which greatly limits their applications [42,43]. Therefore, the development of a self-powered flexible strain sensor is of great significance in the manufacture of portable and wearable electronic skins, which can promote the further development of sensing devices [[44], [45], [46]]. Devices based on the galvanic battery structure are potential choices for self-powered sensing. For instance, Li et al. [47] used gelatin and tannic acid to prepare a hydrogel with rapid self-repair properties, which can be assembled into a self-powered strain sensor with the galvanic mechanism, and the self-powered sensor has good responsiveness and flexibility. Hydrogel with excellent ion transport capabilities is expected to an ideal electrolyte material for manufacturing “flexible batteries”.
Moreover, antibacterial properties are also essential for flexible bioelectronic skin. The antibacterial property can prevent allergic symptoms of the skin that was in direct contact with electronic skin devices, prolong the service life of the device and reduce the replaceable frequency of the device [[48], [49], [50], [51], [52]]. This is extremely important for flexible conductive sensors. Hu and Wang et al. synthesized polypyrrole or Zn-functionalized chitosan molecules and cross-linked with PVA to prepare a stretchable, conductive, self-repairing and antibacterial hydrogel, which can promote wound healing by electrical stimulation [53], but did not reflect the adhesiveness of the hydrogel and the characteristics of self-powered use, so it existed certain limitations on the high sensitivity and portability of the sensor.
In this work, we constructed a new type of external/self-powered hydrogel flexible sensor with good ion conductivity, excellent comprehensive mechanical properties, adhesion and antibacterial properties, as shown in Fig. 1. In particular, the PVA/P(AM-co-SBMA) (PPS) hydrogel prepared by the one-pot method and UV rapid cross-linking technology can detect human movement through ion signals and imitate the sensitivity of human skin. And the PPS hydrogel can achieve high adhesion to a variety of substrates, and still had satisfactory adhesion under sweat conditions. At the same time, the hydrogel was assembled with zinc (Zn) and copper (Cu) sheets to form a self-powered strain sensor with a galvanic cell structure, which was installed directly on the human body as a motion monitoring device to convert subtle motion stimuli into voltage signals without external power supply. Therefore, the hydrogel not only be used for sensing by external power supply, but also can be used to realize self-powered to real-time monitor the human body. More importantly, the prepared PPS hydrogel also has high-efficiency antibacterial properties and low toxicity, which can meet the needs of bioelectronic sensors. This research provides a new idea for non-power flexible strain sensors as the next generation of wearable and portable electronic devices.
Section snippets
Materials
Polyvinyl alcohol (PVA, type 1799) was purchased from Adamas. Acrylamide (Am, 99.0%), [2-(Methacryloyloxy) ethyl] dimethyl-(3-sulfo-propyl) ammonium hydroxide (SBMA), 2-hydroxy-4’-(2-hydroxyethoxy)-2-methylpropiophenone (HHMP) and N, N′-methylene-bis-AM (MBA) were purchased from Sigma-Aldrich. ZnCl2(≥98.0%) was bought from Greagent. Escherichia coli (ATCC25922), Staphylococcus aureus (ATCC6538), LB broth and LB agar were bought from Qingdao Haibo Biotechnology Co., Ltd. The mouse breast cancer
Formation and structure of the hydrogels
PPS hydrogel with good mechanical properties, electrical conductivity, adhesion and antibacterial properties was prepared successfully through UV radiation and freeze-thaw cycles. PVA and PAM were used to construct the hydrogel network system. Due to its good biodegradability, biocompatibility and has a large number of hydroxyl group, PVA can form the hydrogel system easily. PAM is non-toxic and has good mechanical properties and the crosslinking network was formed through copolymerization with
Conclusion
In summary, a facile method was designed to prepare the PPS conductive hydrogel and self-powered sensor. Surprisingly, the PPS hydrogel prepared by UV radiation and freeze-thaw cycle has good mechanical properties, adhesion, electrical conductivity and antibacterial properties. And the self-powered strain sensor prepared by combining the hydrogel sensor and the galvanic cell structure has satisfactory sensitivity, it can convert external stimuli into electrical signals effectively for stable
Author statement
Zixuan Zhou-Methodology, Validation, Investigation, Writing-Original Draft, Zhirui He-Investigation, Shiwu Yin-Supervision, Project administration, Xiaoyun Xie-Supervision, Project administration, Weizhong Yuan-Conceptualization, Resources, Writing-Review and Editing, Supervision, Project administration.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was financially supported by the National Natural Science Foundation of China (81771942 and 82072024).
References (53)
- et al.
Biomass derived carbon as binder-free electrode materials for supercapacitors
Carbon
(2019) - et al.
Nanocomposite sponges of sodium alginate/graphene oxide/polyvinyl alcohol as potential wound dressing: in vitro and in vivo evaluation
Compos B Eng
(2019) - et al.
Synthesis of deformable hydrogel composites based on Janus bilayer multi-walled carbon nanotubes/host-guest complex structure
Compos B Eng
(2019) - et al.
A novel xanthan gum-based conductive hydrogel with excellent mechanical, biocompatible, and self-healing performances
Carbohydr Polym
(2020) - et al.
Highly transparent, stretchable, and rapid self-healing polyvinyl alcohol/cellulose nanofibril hydrogel sensors for sensitive pressure sensing and human motion detection
Sens Actuators, B
(2019) - et al.
An antibacterial hydrogel with desirable mechanical, self-healing and recyclable properties based on triple-physical crosslinking
Chem Eng J
(2019) - et al.
High strength zwitterionic nano-micelle hydrogels with superior self-healing, adhesive and ion conductive properties
Eur Polym J
(2020) - et al.
Highly transparent, self-healing, injectable and self-adhesive chitosan/polyzwitterion-based double network hydrogel for potential 3D printing wearable strain sensor
Mater Sci Eng C Mater Biol Appl
(2020) - et al.
Environment-resisted flexible high performance triboelectric nanogenerators based on ultrafast self-healing non-drying conductive organohydrogel
Nano Energy
(2021) - et al.
Anti-freezing and antibacterial conductive organohydrogel co-reinforced by 1D silk nanofibers and 2D graphitic carbon nitride nanosheets as flexible sensor
Chem Eng J
(2021)
A high performance wearable strain sensor with advanced thermal management for motion monitoring
Nat Commun
Polymerizable deep eutectic solvent-based mechanically strong and ultra-stretchable conductive elastomers for detecting human motions
J Mater Chem A
Multifunctional and high-sensitive sensor capable of detecting humidity, temperature, and flow stimuli using an integrated microheater
ACS Appl Mater Interfaces
Ionoskins: nonvolatile, highly transparent, ultrastretchable ionic sensory platforms for wearable electronics
Adv Funct Mater
Development of an ultrastretchable double-network hydrogel for flexible strain sensors
ACS Appl Mater Interfaces
Ultra-stretchable hydrogels with reactive liquid metals as asymmetric force-sensors
Mater Horiz
Elastic, conductive, and mechanically strong hydrogels from dual-cross-linked aramid nanofiber composites
ACS Appl Mater Interfaces
Plant-inspired adhesive and tough hydrogel based on Ag-Lignin nanoparticles-triggered dynamic redox catechol chemistry
Nat Commun
Conductive hydrogels as smart materials for flexible electronic devices
Chem.-A Eur. J.
Role of a high calcium ion content in extending the properties of alginate dual-crosslinked hydrogels
J Mater Chem A
Cartilage-inspired hydrogel strain sensors with ultrahigh toughness, good self-recovery and stable anti-swelling properties
J Mater Chem A
Wearable, antifreezing, and healable epidermal sensor assembled from long-lasting moist conductive nanocomposite organohydrogel
ACS Appl Mater Interfaces
Highly stretchable and self-healing strain sensors based on nanocellulose-supported graphene dispersed in electro-conductive hydrogels
Nanomaterials
Polyelectrolyte complex-based self-healing, fatigue-resistant and anti-freezing hydrogels as highly sensitive ionic skins
J Mater Chem A
Highly stretchable and transparent thermistor based on self-healing double network hydrogel
ACS Appl Mater Interfaces
Skin-Inspired gels with toughness, antifreezing, conductivity, and remoldability
ACS Appl Mater Interfaces
Cited by (77)
Self-healing, ultra-stretchable, and highly sensitive conductive hydrogel reinforced by sulfate polysaccharide from Enteromorpha prolifera for human motion sensing
2023, International Journal of Biological MacromoleculesPortable, antibacterial and adhesive double-network instant hydrogel senor with self-power and reutilization for human motion/health detection and wild-field signal transmission
2023, Composites Part A: Applied Science and ManufacturingAnti-freezing conductive zwitterionic composite hydrogels for stable multifunctional sensors
2023, European Polymer JournalHigh performance zwitterionic hydrogels for ECG/EMG signals monitoring
2023, Colloids and Surfaces A: Physicochemical and Engineering Aspects