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Stretchable ionic skins are intriguing in mimicking the versatile sensations of natural skins. However, for their applications in advanced electronics, good elastic recovery, self-healing, and more importantly, skin-like nonlinear mechanoresponse (strain-stiffening) are essential but can be rarely met in one material. Here we demonstrate a robust proton-conductive ionic skin design via introducing an entropy-driven supramolecular zwitterionic reorganizable network to the hydrogen-bonded polycarboxylic acid network. The design allows two dynamic networks with distinct interacting strength to sequentially debond with stretch, and the conflict among elasticity, self-healing, and strain-stiffening can be thus defeated. The representative polyacrylic acid/betaine elastomer exhibits high stretchability (1600% elongation), immense strain-stiffening (24-fold modulus enhancement), ~100% self-healing, excellent elasticity (97.9 ± 1.1% recovery ratio, <14% hysteresis), high transparency (99.7 ± 0.1%), moisture-preserving, anti-freezing (elastic at −40 °C), water reprocessibility, as well as easy-to-peel adhesion. The combined advantages make the present ionic elastomer very promising in wearable iontronic sensors for human-machine interfacing. Ionic skins are of interest for a range of electronic, sensing and interfacing applications but often have trade-offs in properties. Here, the authors report on the creation of a dual network ionic skin using a supramolecular zwitterionic competing network to produce a strain-stiffening, self-healing adhesive sensor.

Zwitterionic hydrogels exhibit eminent nonfouling and hemocompatibility. Several key challenges hinder their application as coating materials for blood-contacting biomedical devices, including weak mechanical strength and low adhesion to the substrate. Here, we report a poly(carboxybetaine) microgel reinforced poly(sulfobetaine) (pCBM/pSB) pure zwitterionic hydrogel with excellent mechanical robustness and anti-swelling properties. The pCBM/pSB hydrogel coating was bonded to the PVC substrate via the entanglement network between the pSB and PVC chain. Moreover, the pCBM/pSB hydrogel coating can maintain favorable stability even after 21 d PBS shearing, 0.5 h strong water flushing, 1000 underwater bends, and 100 sandpaper abrasions. Notably, the pCBM/pSB hydrogel coated PVC tubing can not only mitigate the foreign body response but also prevent thrombus formation ex vivo in rats and rabbits blood circulation without anticoagulants. This work provides new insights to guide the design of pure zwitterionic hydrogel coatings for biomedical devices. Zwitterionic hydrogels are nonfouling and hemocompatibility but several key challenges such as weak mechanical strength and low adhesion hamper their application as coating materials for devices. Here, the authors report a microgel reinforced zwitterionic hydrogel with excellent mechanical robustness and anti-swelling properties.

Stimuli-responsive hydrogels have garnered significant attention as a versatile class of soft actuators. Introducing anisotropic properties, and shape-change programmability to responsive hydrogels promises a host of opportunities in the development of soft robots. Herein we report the synthesis of pH-responsive hydrogel nanocomposites with predetermined microstructural anisotropy, shape-transformation, and self-healing. Our hydrogel nanocomposites are largely composed of zwitterionic monomers and asymmetric cellulose nanocrystals. While the zwitterionic nature of the network imparts both self-healing and cytocompatibility to our hydrogel nanocomposites, the shear-induced alignment of cellulose nanocrystals renders their anisotropic swelling and mechanical properties. Thanks to the self-healing properties, we utilized a cut-and-paste approach to program reversible, and complex deformation into our hydrogels. As a proof-of-concept, we demonstrated the transport of light cargo using tethered and untethered soft robots made from our hydrogels. We believe the proposed material system introduce a powerful toolbox for the development of future generations of biomedical soft robots. Soft robots made of hydrogels with anisotropic and shape-change properties offer interesting design opportunities. Here, the authors report zwitterionic hydrogels and anisotropic cellulose nanocrystals composites in which the shear-induced alignment of cellulose nanocrystals allows for the development of shape-change programmable miniature robots.

Molecular binding to receptors on the surface of field-effect transistors (FETs) can be sensed through changes in transconductance. However, the saline solutions typically used with biomolecules create an electrical double layer that masks any events that occur within about 1 nanometer from the surface. Nakatsuka et al. overcame this limitation by using binding to large, negatively charged DNA stem loop structures that, upon ligand binding, cause conformational changes that can be sensed with an FET, even in solutions with high ionic strength. The authors demonstrate the sensing of charged molecules such as dopamine in artificial cerebrospinal fluid as well as neutral molecules such as glucose and zwitterion molecules like sphingosine-1-phosphate. Science , this issue p. 319 Large conformational changes induced in charged DNA stem-loop receptors can be sensed in high–ionic strength solutions. Detection of analytes by means of field-effect transistors bearing ligand-specific receptors is fundamentally limited by the shielding created by the electrical double layer (the “Debye length” limitation). We detected small molecules under physiological high–ionic strength conditions by modifying printed ultrathin metal-oxide field-effect transistor arrays with deoxyribonucleotide aptamers selected to bind their targets adaptively. Target-induced conformational changes of negatively charged aptamer phosphodiester backbones in close proximity to semiconductor channels gated conductance in physiological buffers, resulting in highly sensitive detection. Sensing of charged and electroneutral targets (serotonin, dopamine, glucose, and sphingosine-1-phosphate) was enabled by specifically isolated aptameric stem-loop receptors.

Human-sensitive mechanosensation depends on ionic currents controlled by skin mechanoreceptors. Inspired by the sensory behavior of skin, we investigate zwitterionic hydrogels that generate ions under an applied force in a mobile-ion-free system. Within this system, water dissociates as the distance between zwitterions reduces under an applied pressure. Meanwhile, zwitterionic segments can provide migration channels for the generated ions, significantly facilitating ion transport. These combined effects endow a mobile-ion-free zwitterionic skin sensor with sensitive transduction of pressure into ionic currents, achieving a sensitivity up to five times that of nonionic hydrogels. The signal response time, which relies on the crosslinking degree of the zwitterionic hydrogel, was ~38 ms, comparable to that of natural skin. The skin sensor was incorporated into a universal throat-worn silent-speech recognition system that transforms the tiny signals of laryngeal mechanical vibrations into silent speech. The development of sensitive hydrogel sensor without additional mobile ionic species is challenging. Here, the authors demonstrate force-induced ion generation in a skin sensor based on zwitterionic hydrogel, and build a throat-worn silent-speech recognition system with high recognition accuracy.

The investigation of shear resistance of ionic liquids (ILs) on solid surfaces represents a significant scientific challenge in the advancement of slippery liquid infused porous surfaces (SLIPS). This study systematically examines the shear resistance and underlying mechanisms at the interface between the ILs and zwitterionic surface under shear load, employing a combination of molecular dynamics (MD) simulations and experimental methodologies. Shear resistance assessments were performed utilizing a spin coater at varying rotational velocities, and an MD model comprising over 6000 atoms was developed to explore the bonding force of ILs and solids. Experimental findings reveal that the shear resistance of the IL samples at the interface markedly exceeds that of conventional SLIPS. The MD results reveal that the electrostatic force, estimated at around -600 kcal·mol −1 , between the zwitterionic surface and the ILs plays a crucial role in enhancing the adhesion of the ILs to the substrate.

Endosomal escape remains a fundamental barrier hindering the advancement of nucleic acid therapeutics. Taking inspiration from natural phospholipids that comprise biological membranes, we report the combinatorial synthesis of multi-tailed ionizable phospholipids (iPhos) capable of delivering messenger RNA or mRNA/single-guide RNA for gene editing in vivo. Optimized iPhos lipids are composed of one pH-switchable zwitterion and three hydrophobic tails, which adopt a cone shape in endosomal acidic environments to facilitate membrane hexagonal transformation and subsequent cargo release from endosomes. Structure–activity relationships reveal that iPhos chemical structure can control in vivo efficacy and organ selectivity. iPhos lipids synergistically function with various helper lipids to formulate multi-component lipid nanoparticles (called iPLNPs) for selective organ targeting. Zwitterionic, ionizable cationic and permanently cationic helper lipids enable tissue-selective mRNA delivery and CRISPR–Cas9 gene editing in spleen, liver and lungs (respectively) following intravenous administration. This rational design of functional phospholipids demonstrates substantial value for gene editing research and therapeutic applications. Ionizable phospholipid nanoparticles have been designed to efficiently destabilize endosomal membranes and mediate organ-selective mRNA delivery and CRISPR–Cas9 gene editing.

Solar-driven desalination holds great promise for addressing the scarcity of global freshwater. However, salt accumulation remains a significant challenge, particularly for two-dimensional membrane materials. Inspired by aquaporins, we design a porous zwitterionic fibrous membrane that selectively transports water while rejecting Na + and Cl − , achieving efficient evaporation and salt resistance. The incorporation of porphyrin-based conjugated microporous polymers enhances photothermal conversion and antibacterial properties, while zwitterionic groups and porous structure disrupt high-salinity gradients, effectively preventing salt deposition. The membrane achieves an evaporation rate of 2.64 kg m −2 h −1 and a photothermal efficiency of 97.6% under 1 kW m −2 solar irradiation. Furthermore, the coupling of photothermal evaporator and thermoelectric module achieves a stable electric output (power density: 1.5 W m −2 ). This work presents a synergistic strategy for salt resistance, water purification and energy generation, advancing the design of solar-thermal-electric integrated systems. Solar-driven desalination can address global freshwater scarcity, though salt accumulation remains challenging in membrane design. Here the authors design a zwitterionic fibrous membrane which simultaneously desalinates water and generate energy.

Oral delivery of protein drugs is considered a life-changing solution for patients who require regular needle injections. However, clinical translation of oral protein formulations has been hampered by inefficient penetration of drugs through the intestinal mucus and epithelial cell layer, leading to low absorption and bioavailability, and safety concerns owing to tight junction openings. Here we report a zwitterionic micelle platform featuring a virus-mimetic zwitterionic surface, a betaine side chain and an ultralow critical micelle concentration, enabling drug penetration through the mucus and efficient transporter-mediated epithelial absorption without the need for tight junction opening. This micelle platform was used to fabricate a prototype oral insulin formulation by encapsulating a freeze-dried powder of zwitterionic micelle insulin into an enteric-coated capsule. The biocompatible oral insulin formulation shows a high oral bioavailability of >40%, offers the possibility to fine tune insulin acting profiles and provides long-term safety, enabling the oral delivery of protein drugs.A zwitterionic micelle platform enables the oral delivery and high bioavailability of insulin by transporting the protein across mucus and epithelial barriers in the gut without opening tight junctions.

Live-cell fluorescence nanoscopy is a powerful tool to study cellular biology on a molecular scale, yet its use is held back by the paucity of suitable fluorescent probes. Fluorescent probes based on regular fluorophores usually suffer from a low cell permeability and an unspecific background signal. Here we report a general strategy to transform regular fluorophores into fluorogenic probes with an excellent cell permeability and a low unspecific background signal. Conversion of a carboxyl group found in rhodamines and related fluorophores into an electron-deficient amide does not affect the spectroscopic properties of the fluorophore, but allows us to rationally tune the dynamic equilibrium between two different forms: a fluorescent zwitterion and a non-fluorescent, cell-permeable spirolactam. Furthermore, the equilibrium generally shifts towards the fluorescent form when the probe binds to its cellular targets. The resulting increase in fluorescence can be up to 1,000-fold. Using this simple design principle, we created fluorogenic probes in various colours for different cellular targets for wash-free, multicolour, live-cell nanoscopy.It is difficult to develop suitable fluorescent probes for live-cell nanoscopy, but a general strategy is now reported that can transform regular fluorophores into fluorogenic probes with excellent cell permeability and low unspecific background signals. Using this approach, probes in a variety of colours were developed for different cellular targets and used for wash-free, multicolour, live-cell confocal and STED microscopy.