Hofmeister Effect Research Articles

Hofmeister Effect Promoted the Introduction of Tunable Large Mesopores in MOFs at Low Temperature for Femtomolar ALP Detection.

In addressing the demand for hierarchically mesoporous metal-organic frameworks (HMMOFs) with adjustable large mesopores, a method based on the synergistic effects of low-temperature microemulsions and Hofmeister ions is developed. Low temperaturedramatically enhanced the solubility of hydrophobic solvent in the microemulsion core, enlarging the mesopores in HMMOFs replica. Meanwhile, Hofmeister salt-in ions continuously controlled mesopore expansion by modulating the permeability of swelling agent into the microemulsion core. The large mesopores up to 33nm provided sufficient space for the alkaline phosphatase (ALP) enrichment, and retained the remaining channel to facilitate the free mass diffusion. Leveraging these advantages, a colorimetric sensor is successfully developed using large-mesopore HMMOFs for femtomolar ALP detection based on the enrichment and cycling amplification principles. The sensor exhibited a linear detection range of 100 to 7500fm and a limit of detection of 42fm, presenting over 4000 times higher sensitivity than classic para-nitrophenyl phosphate colorimetric methods. Such high sensitivity highlights the importance of adjustable mesoporous structures of HMMOFs in advanced sensing applications, and prefigures their potential for detecting large biomolecules in diagnostics and biomedical research.

Beta-Barrel Channel Response to High Electric Fields: Functional Gating or Reversible Denaturation?

Ion channels exhibit gating behavior, fluctuating between open and closed states, with the transmembrane voltage serving as one of the essential regulators of this process. Voltage gating is a fundamental functional aspect underlying the regulation of ion-selective, mostly α-helical, channels primarily found in excitable cell membranes. In contrast, there exists another group of larger, and less selective, β-barrel channels of a different origin, which are not directly associated with cell excitability. Remarkably, these channels can also undergo closing, or “gating”, induced by sufficiently strong electric fields. Once the field is removed, the channels reopen, preserving a memory of the gating process. In this study, we explored the hypothesis that the voltage-induced closure of the β-barrel channels can be seen as a form of reversible protein denaturation by the high electric fields applied in model membranes experiments—typically exceeding twenty million volts per meter—rather than a manifestation of functional gating. Here, we focused on the bacterial outer membrane channel OmpF reconstituted into planar lipid bilayers and analyzed various characteristics of the closing-opening process that support this idea. Specifically, we considered the nearly symmetric response to voltages of both polarities, the presence of multiple closed states, the stabilization of the open conformation in channel clusters, the long-term gating memory, and the Hofmeister effects in closing kinetics. Furthermore, we contemplate the evolutionary aspect of the phenomenon, proposing that the field-induced denaturation of membrane proteins might have served as a starting point for their development into amazing molecular machines such as voltage-gated channels of nerve and muscle cells.

Chaotropic Salt‐Aided “Water‐In‐Organic” Electrolyte for Highly Reversible Zinc‐Ion Batteries Across a Wide Temperature Range

AbstractAqueous zinc‐ion batteries are promising alternatives to lithium‐ion batteries due to their cost‐effectiveness and improved safety. However, several challenges, including corrosion, dendrites, and water decomposition at the Zn anode, hinder their performance. Herein, an approach is proposed, that deviates from the conventional design by adding water into a propylene carbonate‐based organic electrolyte to prepare a non‐flammable “water‐in‐organic” electrolyte. The chaotropic salt Zn(ClO4)2 exploits the Hofmeister effect to promote the miscibility of immiscible liquid phases. Interactions between propylene carbonate and water restrict water activity and mitigate unfavorable reactions. This electrolyte facilitates preferential Zn (002) deposition and the formation of solid electrolyte interphase. Consequently, the “water‐in‐organic” electrolyte achieves a 99.5% Coulombic efficiency at 1 mA cm−2 over 1000 cycles in Zn/Cu cells, and constant cycling over 1000 h in Zn/Zn symmetric cells. A Na0.33V2O5/Zn battery exhibits impressive cycling stability with a capacity of 175 mAh g−1 for 800 cycles at 2 A g−1. Additionally, this electrolyte enables sustainable cycling across a wide temperature range from −20 to 50 °C. The design of a “water‐in‐organic” electrolyte employing a chaotropic salt presents a potential strategy for high‐performance electrolytes in zinc‐ion batteries with a large stability window and a wide temperature range.

Anti-swelling and adhesive γ-PGA/PVA/PEDOT:PSS/TA composite conductive hydrogels for underwater wearable sensors

Unnecessary swelling and lack of interfacial adhesion in underwater environments will lead to distortion of sensing signal based on the conductive hydrogel. However, achieving the anti-swelling and underwater adhesive capabilities of conductive hydrogels is still challenging. Based on the strategies of the Hofmeister effect and catechol chemistry, polyglutamic acid (γ-PGA) and polyvinyl alcohol (PVA) were used as the hydrogel matrix, and poly (3,4-ethylene dioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) and tannic acid (TA) were performed as a conductive filler and modifier, respectively. The γ-PGA/PVA/PEDOT:PSS/TA composite conductive hydrogel was successfully prepared by freezing-crystallization (FC γ-PGA/PVA/PEDOT:PSS/TA). The resultant composite hydrogel reveals high anti-swelling and underwater adhesive properties, the equilibrium water absorption rate is 13.0 ± 0.9 %, and the underwater adhesive strength to human skin is up to 11.2 kPa. In addition, the composite hydrogel shows high tensile mechanical strength (0.9 ± 0.1 MPa) at break and tensile breaking elongation (1495.5 ± 15.5 %), and its electrical conductivity is 0.94 ± 0.05 S·m−1. Most importantly, the FC γ-PGA/PVA/PEDOT:PSS/TA composite conductive hydrogel can maintain long-term underwater mechanical and sensing stability. Underwater strain sensors of the composite hydrogel can be employed for motion signal detection (breathing, drinking, finger bending) and underwater communication (Morse code). The research provides ideas for designing conductive hydrogel sensors with anti-swelling and underwater adhesion, which can be utilized for long-term underwater applications.

Live-Cell Imaging to Resolve Salt-Induced Liquid-Liquid Phase Separation of FUS Protein by Dye Self-Labeling.

The aggregation of fusion in sarcoma (FUS) in the cytoplasm and nucleus is a pathological feature of Amyotrophic lateral sclerosis (ALS) and Frontotemporal Dementia (FTD). Genetic mutations, abnormal protein synthesis, environmental stress, and aging have all been implicated as causative factors in this process. Salt ions are essential to many physiological processes in the body, and the imbalance of them is an important environmental stress factor in cells. However, their effect on liquid-liquid phase separation (LLPS) of FUS proteins in living cells is not well understood. Here, we map the various salt-induced LLPS of FUS in living cells by genetically coding and self-labeling FUS with organic dyes. The brightness and photostability of the dyes enable long-term imaging to track the mechanism of the assembly and disappearance of FUS phase separation. The FUS protein showed a better phase separation tendency under 0.3 M salt stimulation, and there was a large amount of FUS shuttling from the nucleus to the cytoplasm. At this concentration, various salt solutions displayed different effects on the phase separation of FUS protein, following the Hofmeister effects. We further observed that the assembly of FUS droplets underwent a process of rapid formation of small droplets, plateaus, and mutual fusion. Strikingly, The CsCl-stimulated FUS droplets were not completely reversible after washing, and some solid-like granules remained in the nucleus. Taken together, these results help broaden our understanding of the LLPS of FUS proteins in cellular stress responses.

Utilizing the Hofmeister Effect to Induce Hydrogelation of Nonionic Supramolecular Polymers into a Therapeutic Depot

AbstractNonionic hydrogels are of particular interest for long‐term therapeutic implantation due to their minimal immunogenicity relative to their charged counterparts. However, in situ formation of nonionic supramolecular hydrogels under physiological conditions has been a challenging task. In this context, we report on our discovery of salt‐triggered hydrogelation of nonionic supramolecular polymers (SPs) formed by self‐assembling prodrug hydrogelators (SAPHs) through the Hofmeister effect. The designed SAPHs consist of two SN‐38 units, which is an active metabolite of the anticancer drug irinotecan, and a short peptide grafted with two or four oligoethylene glycol (OEG) segments. Upon self‐assembly in water, the resultant nonionic SPs can be triggered to gel upon addition of phosphate salts. Our 1H NMR studies revealed that the added phosphates led to a change in the chemical shift of the methylene protons, suggestive of a disruption of the water‐ether hydrogen bonds and consequent reorganization of the hydration shell surrounding the SPs. This deshielding effect, commensurate with the amount of salt added, likely promoted associative interactions among the SAPH filaments to percolate into a 3D network. The formed hydrogels exhibited a sustained release profile of SN‐38 hydrogelator that acted potently against cancer cells.

Utilizing the Hofmeister Effect to Induce Hydrogelation of Nonionic Supramolecular Polymers into a Therapeutic Depot.

Nonionic hydrogels are of particular interest for long-term therapeutic implantation due to their minimal immunogenicity relative to their charged counterparts. However, in situ formation of nonionic supramolecular hydrogels under physiological conditions has been a challenging task. In this context, we report on our discovery of salt-triggered hydrogelation of nonionic supramolecular polymers (SPs) formed by self-assembling prodrug hydrogelators (SAPHs) through the Hofmeister effect. The designed SAPHs consist of two SN-38 units, which is an active metabolite of the anticancer drug irinotecan, and a short peptide grafted with two or four oligoethylene glycol (OEG) segments. Upon self-assembly in water, the resultant nonionic SPs can be triggered to gel upon addition of phosphate salts. Our 1 H NMR studies revealed that the added phosphates led to a change in the chemical shift of the methylene protons, suggestive of a disruption of the water-ether hydrogen bonds and consequent reorganization of the hydration shell surrounding the SPs. This deshielding effect, commensurate with the amount of salt added, likely promoted associative interactions among the SAPH filaments to percolate into a 3D network. The formed hydrogels exhibited a sustained release profile of SN-38 hydrogelator that acted potently against cancer cells.

Nanoscale iodophoric poly(vinyl amide) coatings for the complexation and release of iodine for antimicrobial surfaces

Wound infection exacerbated by multidrug-resistant (MDR) bacteria has necessitated the need for wound dressing materials with embedded antimicrobial property to prevent the development of chronic wounds. Iodine (I2), typically as a poly(vinyl pyrrolidone)-I2 (PVP–I) complex, is a widely used antiseptic agent in wound care owing to its efficacy, safety, and low probability to cause further resistance. Despite extensive research on PVP–I formulations, there is potentially a large selection of poly(vinyl amide)s that have remained largely unexplored as iodophoric materials, particularly as coatings for wound dressings and medical devices. Therefore, in this study we prepared a series of stable, cross-linked poly(vinyl amide) coatings via plasma polymerization and studied their structure–property relationships for the complexation and release of I2. Plasma polymerized poly(N-vinyl-2-pyrrolidone) (pPVP), poly(N-methyl-N-vinylacetamide) (pPMVA) and poly(N-vinylcaprolactam) (pPVCl) nanoscale coatings were prepared with uniform thicknesses of 330–340 nm and low surface roughness. Complexation of I2 as polyiodides resulted in a significant increase in the pPVCl coating thickness in phosphate buffered saline (PBS), consistent with the Hofmeister effect. Raman spectroscopy confirmed that the I2 was complexed exclusively as the triiodide ion (I3-) in all coatings, which was confirmed by synchrotron X-ray photoelectron spectroscopy (XPS) experiments. Nuclear magnetic resonance (NMR) spectroscopy of poly(vinyl amides) was employed to further prove that the complexing species was hydrogen triiodide (HI3). The loading of I2 species increased from pPVP < pPMVA < pPVCl, with percentage elemental compositions of 1.3, 1.8, and 2.9%, respectively, which correlated with the extent of nitrogen loss during polymerization and oxidation, and was also in agreement with determined negative zeta potential values. However, quantification of the released I2 species over 5 h showed that the greatest release was observed from pPMVA (121.3 µg.cm−2), with pPVP (77.4 µg.cm−2) and pPVCl (74.6 µg.cm−2) releasing a similar amount, highlighting that I2 release from poly(vinyl amide) coatings is a function of the loading and composition of the polymer, not just the I2 complexing amide motif. The I2 complexed pPMVA coated wound dressings were highly effective against Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus, the two major strains associated with wound infection, reducing bacterial viability by up to 4 and 7 (log10 reduction) orders of magnitude. Overall, the poly(vinyl amide) coatings are promising iodophors for the prevention and treatment of wound infections.

Multiscale Structural Nanocellulosic Triboelectric Aerogels Induced by Hofmeister Effect

AbstractThe advent of self‐powered wearable electronics will revolutionize the fields of smart healthcare and sports monitoring. This technological advancement necessitates more stringent design requirements for triboelectric materials. The triboelectric aerogels must enhance their mechanical properties to address the issue of structural collapse in real‐world applications. This study fabricates stiff nanocellulosic triboelectric aerogels with multiscale structures induced by the Hofmeister effect. The aggregation and crystallization of polymer molecular chains are enhanced by the Hofmeister effect, while ice crystal growth imparts a porous structure to the aerogel at the micron scale. Therefore, the triboelectric aerogel exhibits exceptional stiffness, boasting a Young's modulus of up to 142.9 MPa and a specific modulus of up to 340.6 kN m kg–1, while remaining undeformed even after supporting 6600 times its weight. Even after withstanding an impact of 343 kPa, highly robust wearable self‐powered sensors fabricated with triboelectric aerogels remain operational. Additionally, the self‐powered sensor is capable of accurately detecting human movements, particularly in abnormal fall postures detection. This study provides considerable research and practical value for promoting material design and broadening application scenarios for self‐powered wearable electronics.

A facile method to fabricate multifunctional polyvinyl alcohol mineralized hydrogels with high strength and adaptable shape

AbstractHydrogel‐based materials are widely used in many fields, but most of them compared to tendons with the same water content do not exhibit high toughness, strength or fatigue resistance, which limits their application. The Hofmeister effect can adjust the mechanical properties of hydrogels by ions affecting the aggregation of polymer chains. Herein, we prepared a bioactivated hydrogel through simply mixing polyvinyl alcohol (PVA) and Na2CO3 aqueous solutions. PVA chains are aggregated by strong hydrogen bonds between CO32− and OH, at which stage the hydrogel is soft and easy to shape. Further salting out promotes the formation of crystal microphase of PVA chain, resulting in high mechanical strength and excellent toughness. The existence of Na2CO3 endow the hydrogel with conductivity, exhibits high and stable sensitivity in strain sensing, and could be used to monitor human actions. On the basis of this method, Ca2+ was added to prepare mineralized PVA hydrogels, which had high stability and long‐term swelling resistance in different ionic solutions. In vitro cell experiment, hydrogel had obvious effect of promoting bone cell proliferation and calcium deposition. This work provides a facile and feasible method for preparing bionic hydrogels with high strength, toughness, and adaptable shape.

“Salting out” in Hofmeister Effect Enhancing Mechanical and Electrochemical Performance of Amide‐based Hydrogel Electrolytes for Flexible Zinc‐Ion Battery (Small 30/2023)

“Salting out” in Hofmeister Effect Enhancing Mechanical and Electrochemical Performance of Amide‐based Hydrogel Electrolytes for Flexible Zinc‐Ion Battery (Small 30/2023)

Hofmeister effect induced advancement of the hydrogels by 3D printing

This study explores the cooperative effect of the Hofmeister phenomenon and three-dimensional (3D) printing in synthesizing high-strength hydrogels. We discovered that, when the printed hydrogels were exposed to a high salt concentration solution, the Hofmeister effect instigated robust and more compact interface interactions between the PHEMA/PVP covalent matrix and the gelatin. This significantly improved the mechanical attributes of the hydrogels. Upon comparison with the newly formed hydrogels, the tensile strength, fracture elongation, toughness, and modulus of the hydrogels subjected to the salting-out effect were amplified by factors of 20, 4, 110, and 70 respectively, thus demonstrating their exceptional mechanical performance. The study further reveals that the Hofmeister effect can augment the mechanical anisotropy of the printed hydrogels. In particular, Hofmeister ions trigger a reversible entanglement in the polymer chain. In this condition, adjacent filaments in a single printed layer of hydrogel display more densely entangled chains than the interior of the filaments, resulting in enhanced toughness in different orientations of the hydrogel. The approach described herein is not only applicable to current hydrogel materials but also can be extended to other printable hydrogel materials. By integrating 3D printing and the Hofmeister effect, we can customize the properties of hydrogels to satisfy specific requirements, facilitating the creation of advanced biomedical devices and applications.

Alleviating Side Reactions on Zn Anodes for Aqueous Batteries by a Cell Membrane Derived Phosphorylcholine Zwitterionic Protective Layer.

Aqueous zinc (Zn) ion batteries are attractive for next generation batteries with high safety, yet their applications are still hindered by the uncontrollable dendrite formation and side reactions on Zn anode. Here, a polyzwitterion protective layer (PZIL) was engineered by polymerizing 2-methacryloyloxyethyl phosphorylcholine (MPC) in carboxymethyl chitosan (CMCS), which renders the following merits: the choline groups of MPC can preferentially adsorb onto Zn metal to avoid side reactions; the charged phosphate groups chelate with Zn2+ to regulate the solvation structure, further improving side reaction inhibition; the Hofmeister effect between ZnSO4 and CMCS can enhance the interfacial contact during electrochemical characterization. Consequently, the symmetrical Zn battery with PZIL can keep stable for more than 1000 hours under the ultra-high current density of 40 mA cm-2. The PZIL confers the Zn/MnO2 full battery and Zn/active carbon (AC) capacitor with stable cycling performance under high current density.

Alleviating Side Reactions on Zn Anodes for Aqueous Batteries by a Cell Membrane Derived Phosphorylcholine Zwitterionic Protective Layer

AbstractAqueous zinc (Zn) ion batteries are attractive for next generation batteries with high safety, yet their applications are still hindered by the uncontrollable dendrite formation and side reactions on Zn anode. Here, a polyzwitterion protective layer (PZIL) was engineered by polymerizing 2‐methacryloyloxyethyl phosphorylcholine (MPC) in carboxymethyl chitosan (CMCS), which renders the following merits: the choline groups of MPC can preferentially adsorb onto Zn metal to avoid side reactions; the charged phosphate groups chelate with Zn2+ to regulate the solvation structure, further improving side reaction inhibition; the Hofmeister effect between ZnSO4 and CMCS can enhance the interfacial contact during electrochemical characterization. Consequently, the symmetrical Zn battery with PZIL can keep stable for more than 1000 hours under the ultra‐high current density of 40 mA cm−2. The PZIL confers the Zn/MnO2 full battery and Zn/active carbon (AC) capacitor with stable cycling performance under high current density.

Divalent Anion-Induced Biohydrogels with High Strength, Anti-swelling, and Bioactive Capability for Enhanced Skull Bone Regeneration.

Increased intracranial pressure after traumatic brain injury (TBI) is an urgent problem in clinical practice. A pliable hydrogel is preferred for cranioplasty applications after TBI since it can protect brain tissue and promote bone healing. Nevertheless, biohydrogels for cranial bone regeneration still face challenges of poor mechanical properties, large swelling ratios, and low osteogenesis activity. Herein, inspired by Hofmeister effects, biopolymer hydrogels composed of protein and polysaccharides were treated with a Hofmeister series including a series of monovalent and divalent anions. Our results reveal that the divalent anion-cross-linked biohydrogels exhibit stronger mechanical properties and lower swelling ratios compared with monovalent-anion treated gels. Intriguingly, the divalent HPO42- anion induced biohybrid hydrogels with excellent mechanical behaviors (3.7 ± 0.58 MPa, 484 ± 76.7 kPa, and 148.3 ± 6.85 kJ/m3), anti-swelling capability (16.7%), and gradual degradation ability, significantly stimulating osteogenic differentiation and in vivo cranial bone regeneration. Overall, this study may provide new insights into the design of biomimetic hydrogels for treating cranial bone defects after TBI.

Improving physical properties of poly(vinyl alcohol)/montmorillonite nanocomposite hydrogels via the Hofmeister effect

Hydrogel is a kind of three-dimensional crosslinked polymer material with high moisture content. However, due to the network defects of polymer gels, traditional hydrogels are usually brittle and fragile, which limits their practical applications. Herein, we present a Hofmeister effect-aided facile strategy to prepare high-performance poly(vinyl alcohol)/montmorillonite nanocomposite hydrogels. Layered montmorillonite nanosheets can not only serve as crosslinking agents to enhance the mechanical properties of the hydrogel but also promote the ion conduction. More importantly, based on the Hofmeister effect, the presence of (NH4)2SO4 can endow nanocomposite hydrogels with excellent mechanical properties by affecting PVA chains' aggregation state and crystallinity. As a result, the as-prepared nanocomposite hydrogels possess unique physical properties, including robust mechanical and electrical properties. The as-prepared hydrogels can be further assembled into a high-performance flexible sensor, which can sensitively detect large-scale and small-scale human activities. The simple design concept of this work is believed to provide a new prospect for developing robust nanocomposite hydrogels and flexible devices in the future.

Hofmeister effect-based soaking strategy for gelatin hydrogels with adjustable gelation temperature, mechanical properties, and ionic conductivity

As a natural polymer with good biocompatibility, gelatin hydrogel has been widely used in the field of biomedical science for a long time. However, the lack of suitable gelation temperature and mechanical properties often limit the clinical applicability in diverse and complex environments. Here, we proposed a strategy based on the Hofmeister effect that gelatin hydrogels were soaked in the appropriate concentration of sodium sulfate solution, and the change in molecular chain interactions mainly guided by kosmotropic ions resulted in a comprehensive adjustment of multiple properties. A series of gelatin hydrogels treated with different concentrations of the salt solution gave rise to microstructural changes, which brought a decrease in the number and size of pores, a wide range of gelation temperature from 32 °C to 46 °C, a stress enhancement of about 40 times stronger to 0.8345 MPa, a strain increase of about 7 times higher to 238.05 %, and a certain degree of electrical conductivity to be utilized for versatile applications. In this regard, for example, we prepared microneedles and obtained a remarkable compression (punctuation) strength of 0.661 N/needle, which was 55 times greater than those of untreated ones. Overall, by integrating various characterizations and suggesting the corresponding mechanism behind the phenomenon, this method provides a simpler and more convenient performance control procedure. This allowed us to easily modulate the properties of the hydrogel as per the intended purpose, revealing its vast potential applications such as smart sensors, electronic skin, and drug delivery.

Caging the Hofmeister Effect by a Biomimetic Supramolecular Receptor.

The effect of anions on the solubility and function of proteins was recognized in 1888 and is now termed the Hofmeister effect. Numerous synthetic receptors are known that overcome the associated anion recognition bias. However, we are unaware of a synthetic host being used to overcome Hofmeister effect perturbations to natural proteins. Here, we report a protonated small molecule cage complex that acts as an exo-receptor and displays non-Hofmeister solubility behavior, with only the chloride complex remaining soluble in aqueous media. This cage allows for the activity of lysozyme to be retained under conditions where anion-induced precipitation would otherwise cause it to be lost. To our knowledge, this is the first time a synthetic anion receptor is used to overcome the Hofmeister effect in a biological system.

Anti-swelling P(DAC-co-NaSS-co-VDT) polyampholyte hydrogel with solvent displacement and salinity enhanced wet strength and adhesion

Polyampholyte (PA) hydrogels in general possess excellent mechanical properties, but their underwater applications are largely limited due to swelling induced dramatically reduced strength and poor wet adhesion, especially in high salinity environments. Here, we report our approach to fabricating an anti-swelling poly(acryloyloxyethyltrimethyl ammonium chloride (DAC)-co-sodium p-styrenesulfonate (NaSS)-co-2-Vinyl-4,6-diamino-1,3,5-triazine (VDT), or P(DAC-co-NaSS-co-VDT), PA hydrogel by introducing multi-hydrogen bonding capable functional VDT moieties into the DAC/NaSS coexisting and cation/anion ratio easily tunable PA network. The mechanical properties of the P(DAC-co-NaSS-co-VDT) hydrogel in bulk and at interface were controllable with dimethyl sulfoxide (DMSO)/H2O solvent displacement and Hofmeister effect in a wide salinity range, exhibiting maximum tensile strength, Young's modulus, and wet adhesion toughness of 7.6 MPa, 200 MPa, and 350 J m−2, respectively. The anti-swelling and strong P(DAC-co-NaSS-co-VDT) PA hydrogel developed in this work may find great potential in underwater sensing and sewage treatment as well as for many biomedical applications.

Hofmeister effect-inspired Ti3C2Tx MXene-based robust, multifunctional hydrogels

Developing multifunctional hydrogels with high strength, toughness, and conductivity is critical for various applications in soft robots, wearable devices, and human–computer interfaces. Inspired by the Hofmeister effect, a type of composite hydrogels was prepared using a freezing and salting-out approach, which combines transition metal carbide/nitride (MXene) and polyvinyl alcohol (PVA). The hydrogels exhibited great mechanical strength and toughness, and high conductivity, conferring its application as a multifunctional strain sensor. In addition, the synergy of highly conductive MXene, water-enriched porous structure, and sufficient MXene-PVA interfaces contributes to the controllable and high electromagnetic interference shielding effectiveness of 43–93 dB at thickness of 1.5–8.5 mm. Combined with the facile and scalable preparation approach for rational design of the MXene, PVA, water, and porous structure in the hydrogels, this work thus demonstrates the robust, ultra-flexible and electrically conductive multifunctional hydrogels for applications in Internet of Things, next-generation wearable electronics, electromagnetic protection, and smart devices.