Achieving Swollen yet Strengthened Hydrogels by Reorganizing Multiphase Network Structure

Abstract

Many living tissues, such as muscle, become mechanically stronger with growth. Yet, synthetic hydrogels usually exhibit an opposite size‐mechanical property relation, that is, swelling‐weakening behavior. Herein, a series of swollen yet strengthened polyampholyte (PA) hydrogels are developed via a simple metal‐ion solution soaking strategy. In this strategy, a dynamic PA hydrogel (with ionic bonds) is dialyzed in ZrOCl2 solutions (Step‐I) and deionized water (Step‐II) successively to obtain equilibrated hydrogels. Due to the specific Zr4+ ions and PA network structure, Step‐I takes several months with sample size and mechanical performance increasing continuously, while Step‐II only needs several days. Through this strategy, the resultant hydrogel networks are reorganized and eventually constructed by ionic and metalligand bonds, enabling the swelling yet strengthening behavior. A systematic study confirms that dialysis time in Step‐I and corresponding ZrOCl2 concentration can significantly affect the multiphase microstructures of the hydrogels, resulting in different mechanical enhancements. The optimized hydrogel possesses 39.2 MPa of Young's modulus and 3.7 MPa of tensile strength, which are 302 and 5.5 times these of the original PA gel, respectively. Despite distinct swelling, these hydrogels still mechanically surpass many existing high‐performance hydrogels. This study opens a novel pathway for fabricating swollen yet strengthened hydrogels.

Tough Ion-Conductive Hydrogel with Anti-Dehydration as a Stretchable Strain Sensor for Gesture Recognition

“…After dialyzed in FeCl 3 solution, these peaks become weaker gradually in ASP-PA-Fe 3+ gels, mainly because more and more charged −(CH 3 ) 3 N + groups become free when nearly all ionic bonds are disrupted. The 1493 cm –1 peak becomes stronger after drying out, indicating the reconstruction of ionic bonds in DRY-PA-Fe 3+ gel . The FTIR results are in agreement with the Q v data (Figure c) and provide further evidence in support of our hypothesis.…”

“…The 1493 cm −1 peak becomes stronger after drying out, indicating the reconstruction of ionic bonds in DRY-PA-Fe 3+ gel. 25 The FTIR results are in agreement with the Q v data (Figure 2c) and provide further evidence in support of our hypothesis. Furthermore, the effect of Fe 3+ on Q v and chemical structures of the DRY-PA-Fe 3+ gels could also impact their mechanical properties.…”

“…Based on the tensile data, we first discuss the strain softening and hardening behaviors of DRY-PA-M n+ hydrogels according to the phenomenological Mooney–Rivlin equation, − which is expressed as follows: σ red = σ λ − λ − 2 = 2 C 1 + 2 C 2 1 λ where σ red is the reduced stress, λ is the stretch ratio, and C 1 and C 2 are the material constants. C 1 is equal to the shear modulus (≈ E /3), and C 2 is related to strain hardening ( C 2 < 0) and/or softening ( C 2 > 0).…”

Ionically Conductive and Self-Healing Polyampholyte Hydrogels for Wearable Resistive Strain Sensors and Capacitive Pressure Sensors

“…Polyampholyte hydrogels are a typical kind of self-healing hydrogels containing both anions and cations in polymer networks. − The anions and cations endow hydrogels not only intrinsic ion conductivity but also self-healing ability based on ionic interactions. Generally, polyampholyte hydrogels can be prepared using charged monomers, such as (acryloyloxyethyl)­trimethylammonium chloride, sodium p -styrenesulfonate (NaSS), [3-(methacryloylamino)­propyl]­trimethylammonium chloride, and others. − The unique properties of polyampholyte hydrogels have made them promising materials in diverse fields. For example, Luo and co-workers reported physically cross-linked double-network hydrogels, which exhibit high strength and toughness.…”

Tough, Ion-Conductive Poly(vinyl alcohol)/Polyelectrolyte Hydrogels Based on a Double Network for Use as Strain Sensors

“…In addition, the double-network structure can effectively enhance the elastic retraction force of the polymer chain, making it a means of antiswelling . Huang et al made polyampholyte hydrogel with multiple network structures that retain high mechanical strength after swelling by ionic and metal–ligand bonding . Despite the extensive and impressive research into antiswelling hydrogels, they still have some problems, such as a very tedious and time-consuming preparation process.…”