Zwitterionic Biomaterials.

The term "zwitterionic polymers" refers to polymers that bear a pair of oppositely charged groups in their repeating units. When these oppositely charged groups are equally distributed at the molecular level, the molecules exhibit an overall neutral charge with a strong hydration effect via ionic solvation. The strong hydration effect constitutes the foundation of a series of exceptional properties of zwitterionic materials, including resistance to protein adsorption, lubrication at interfaces, promotion of protein stabilities, antifreezing in solutions, etc. As a result, zwitterionic materials have drawn great attention in biomedical and engineering applications in recent years. In this review, we give a comprehensive and panoramic overview of zwitterionic materials, covering the fundamentals of hydration and nonfouling behaviors, different types of zwitterionic surfaces and polymers, and their biomedical applications.

Environment-Resistant Organohydrogel-Based Sensor Enables Highly Sensitive Strain, Temperature, and Humidity Responses.

Conductive hydrogels have been extensively used in wearable skin sensors owing to their outstanding flexibility, tissuelike compliance, and biocompatibility. However, the dehydration and embrittlement of hydrogels can result in sensitivity loss or even invalidation, restraining their wearable applications in external environments, especially at low temperatures and in arid environments. Herein, an environment-resistant organohydrogel is developed for multifunctional sensors. A double-network organohydrogel based on hyaluronic acid and poly(acrylic acid-co-acrylamide) is developed, and glycerol is introduced into the organohydrogel network via a solvent displacement strategy. Owing to the water-locking effects of glycerol and tough polymeric backbone, the resultant organohydrogel not only exhibits stable tensibility but also maintains excellent flexibility and stable conductivity with the environment-resistant properties, including freezing resistance against -30 °C and moisture retention at 4% relative humidity in a high temperature of 60 °C. Moreover, a series of organohydrogel-based sensors and an array device are developed to achieve highly sensitive strain, temperature, and humidity responses and exhibit a high gauge factor of 10.79 in the strain-sensitive test. This work develops a universal ionic skin based on organohydrogels to be applied to wearable sensors for health monitoring.

A Degradable-Renewable Ionic Skin Based on Edible Glutinous Rice Gel.

Traditional wearable devices are commonly nonrecyclable and nondegradable, resulting in energy waste and environmental pollution. Here, a household degradable and renewable ionic skin based on edible glutinous rice gel is developed for a strain, temperature and salivary enzyme activity sensor. This gel depends on intermolecular and intramolecular H-bonds among amylopectin and amylose, and this presents excellent skin-like properties, including stretchability, self-healing property, and adhesion to various substrates. The glutinous rice gel-based skin sensor can be used to monitor vital signs and physiological parameters such as body temperature and heart rate. The sensor also achieves specific speech recognition and detects temperature and body micromovements, which provides the potential to reconstruct language or sensory/motor functions. More importantly, because of the excellent biocompatibility and degradability, the sensor can directly detect the activity of human salivary amylase, which is useful for diagnosing pancreas-, kidney-, and spleen-related diseases in the elderly. Finally, the raw material of ionic skin that originates from traditional grains is degradable and renewable as well as it can be used to prepare household wearable devices. Hence, this work not only extends the application of wearable electronics in daily life but also facilitates health monitoring in the elderly and improves their quality of life.

A Zwitterionic-Aromatic Motif-Based ionic skin for highly biocompatible and Glucose-Responsive sensor.

Electronic skins that can sense external stimuli have been of great significance in artificial intelligence and smart wearable devices in recent years. However, most of current skin materials are unable to achieve high biocompatibility and anti-bacterial activity, which are particularly critical to wearable sensors for neonatal/premature monitoring or tissue-interfaced biosensors (such as electronic wound dressing and smart contact lens). Herein, a zwitterionic-aromatic motif-based conductive hydrogel with electrostatic and π-π interactions is designed for the development of ionic skin sensors. The hydrogel possesses high biocompatibility, anti-bacterial activity, especially glucose-responsive property which has not been achieved by previous ionic skins. Due to its unique molecular design, the zwitterionic-aromatic skin sensor exhibits excellent mechanical properties (robust elasticity and large stretchability) and high-sensitive pressure detection (including a gentle finger touch, small water droplets, and vocal cord vibration). More importantly, aromatic motives in phenylboronic acid segments endow the skin with glucose-responsive property. This skin sensor not only shows great potential in wearable e-skins, but also possesses a promising property for the tissue-interfaced and implantable continuous-glucose-monitor biosensors such as smart wound dressing with a high demand of biocompatibility.

Universal Intraductal Surface Antifouling Coating Based on an Amphiphilic Copolymer.

Surface modification on the inner wall of medical or industrial polymeric catheters with a high length/diameter ratio is highly desired. Herein, a universal and facile method based on an amphiphilic copolymer was developed to immobilize an intraductal surface antifouling coating for a variety of polymeric catheters. A fouling-repelled thin layer was formed by swelling-driven adsorption via directly perfusing an amphiphilic copolymer [polyvinylpyrrolidone-polydimethylsiloxane-polyvinylpyrrolidone (PVP-PDMS-PVP)] solution into catheters. In this copolymer, hydrophobic PDMS was embedded into a shrinking cross-linked network of catheters; also, PVP segments migrated to the surface under driving water to form a hydrophilic antifouling coating. Moreover, because of the coordination between I2 and pyrrolidone of PVP, the copolymer-modified intraductal surface was then infused with aqueous I2 to form the PVP-I2 complex, endowing this coating with bactericidal activity. Notably, diverse catheters with arbitrary shapes (circular, rectangular, triangular, and hexagonal) and different components (silicone, polyurethane, and polyethylene) were also verified to work using this interfacial interpenetration strategy. The findings in this work provide a new avenue toward facile and universal fabrication of intraductal surface antifouling catheters, creating a superior option for decreasing the consumable costs in industrial production and alleviating the pain of replacing catheters for patients.

Amphiphilic Marine Antifouling Coatings Based on a Hydrophilic Polyvinylpyrrolidone and Hydrophobic Fluorine-Silicon-Containing Block Copolymer.

The development of environmentally friendly and highly efficient antifouling coatings is vastly desirable in the marine industry. Herein, we prepared a novel amphiphilic block copolymer that combined hydrophilic polyvinylpyrrolidone (PVP) with hydrophobic poly(1-(1H,1H,2H,2H-perfluorodecyloxy)-3-(3,6,9-trioxadecyloxy)-propan-2-yl acrylate) (PFA) and polydimethylsiloxane (PDMS). The amphiphilic copolymer (PVP-PFA-PDMS) was blended into a cross-linked PDMS matrix to form a set of controlled surface composition and surface-renewal coatings with efficient antifouling and fouling-release properties. These coatings incorporated the biofouling settlement resistance ability attributed to the hydrophilic PVP segments and the reduced adhesion strength attributed to the low surface energy of fluorine-silicon-containing segments. As expected, the coatings showed an excellent antifouling performance against bacteria and marine unicellular Navicula parva diatoms (98.1 and 98.5% of reduction, respectively) and fouling-release performance against pseudobarnacle adhesion (84.3% of reduction) compared to the pristine PDMS coating. Moreover, a higher-content PVP-based coatings presented higher ability to resist biofouling adhesion. The nontoxic antifouling coating developed in this paper hold the potential to be applied in a variety of marine industrial facilities.

A zwitterionic hydrogel coated titanium surface with high-efficiency endothelial cell selectivity for rapid re-endothelialization.

Coronary stent implantation is an effective procedure for percutaneous coronary intervention treatment. However, its long-term safety and efficacy are still hindered by the in-stent restenosis and late thrombus formation. Herein, an anti-biofouling and endothelial cell selective zwitterionic hydrogel coating was developed to simultaneously enhance the nonspecific resistance and rapid re-endothelialization of the titanium surface. An endothelial cell selective peptide, REDV, could be simply conjugated on the zwitterionic carboxybetaine (CB) hydrogel to prepare the REDV/CB coating. It was found that the REDV/CB hydrogel layer maintained antifouling properties, which could inhibit the protein adsorption, bacterial adhesion, platelet activation and aggregation, and smooth muscle cell proliferation. More importantly, the co-culture study confirmed that the conjugated REVD peptide could specifically capture endothelial cells and promote their migration and proliferation, and simultaneously decrease the adhesion and proliferation of smooth muscle cells. Therefore, the antifouling and endothelial cell selective coating proposed in this work provides a promising strategy to develop an intravascular stent for promoted re-endothelialization and inhibited neointimal hyperplasia in clinical applications.

Mussel-inspired triblock functional protein coating with endothelial cell selectivity for endothelialization.

Surface modification of biomaterials for rapid endothelialization is a promising approach for improving long-term patency of artificial vascular grafts (e.g. polytetrafluoroethylene, PTFE) with small-caliber vascular (<6 mm). However, surfaces modified with traditional strategies using hydrophilic polymers may be excessively hydrophilic to limit endothelial cell adhesion and formation of confluent endothelial lining. In this study, a triblock functional protein cofp-MZY/R was fabricated with cell selectivity of endothelial cells (ECs) over smooth muscle cells (SMCs) for endothelialization on PTFE. This rational designed triblock protein consisted of mussel-inspired domain, zwitterionic polypeptide and bioactive peptides (YIGSR and REDV), in which Dopa was efficiently obtained with residue-specificity in vivo. The triblock protein could facilely form coating on PTFE surface and the resulting protein coating exhibited moderate nonspecific resistance of protein and platelets. Together with bioactive peptides tail, it was available for cell attachment on surfaces. As protein material, this coating displayed remarkable biocompatibility through cytotoxicity and hemolysis measurements. Moreover, cellular behavior assay demonstrated that triblock protein coating could selectively promote adhesion, proliferation and migration of ECs rather than SMCs. This mussel-inspired triblock functional protein coating indicated a promising strategy for endothelialization of artificial vascular grafts.

Influence of divalent cations on the biofouling behaviors of alginate hydrogels.

Alginate is one of the most favorable materials in many biomedical applications. The mechanical properties of alginate hydrogels can be easily tailored by adding different concentrations of divalent cations. In this work, we demonstrate that the method can also notably influence the biofouling behaviors of alginate hydrogels. A series of alginate hydrogels was prepared by tuning the concentrations of two types of divalent cation (Ca2+ or Ba2+). It was found that the biofouling behaviors of the hydrogels exhibited a 'U' curve tendency with the cation concentrations. Interestingly, we found that in optimal conditions ([Ca2+] = 0.9 mM or [Ba2+] = 0.54 mM), the resultant Ca0.9- and Ba0.54-alginate hydrogels were able to achieve negligible adhesion of the proteins and bacteria. Moreover, these two formulations were also able to prevent inflammatory responses at least 4 weeks after subcutaneous implantation in a mouse model. The findings in this work provide more insights into the design and development of appropriate alginate hydrogels for different applications.

Dimethyl Sulfoxide-Free Cryopreservation of Chondrocytes Based on Zwitterionic Molecule and Polymers.

Cartilage tissue engineering highly relies on the ability to store and transport chondrocytes in order to be clinically successful. Cryopreservation is a most reliable technology for chondrocyte storage, but it suffers from the intrinsic toxicity of current state-of-the-art cryoprotectant, dimethyl sulfoxide (DMSO). In this work, we used the first fully zwitterionic compound-based approach for effective chondrocyte cryopreservation. A zwitterionic molecule combined with zwitterionic polymers could balance intra/extracellular osmotic stress and prevent ice formation, which were the keys of successful cryopreservation. Moreover, this zwitterionic combination showed noncytotoxicity due to its high biocompatibility, superior to cytotoxic DMSO. On the basis of these performances, chondrocytes could be well cryopreserved (∼90% post-thaw survival efficiency) for a long time without any addition of DMSO, and the recovered cells could maintain their normal functionalities. In view of the association between polymer molecular weight and cryopreservation efficacy, further mechanism of cryoprotection provided by zwitterionic molecule/polymer was proposed. This work opens a new window of opportunity for DMSO-free cryopreservation using biocompatible zwitterionic materials.

Beetle-Inspired Hierarchical Antibacterial Interface for Reliable Fog Harvesting.

The microdroplets in fog flow have been considered as an important resource for supplying fresh drinking water. Most of the reported works of fog collection focus on the water-collecting ability rather than the environmental reliability of selected materials. In this work, a beetle-inspired hierarchical fog-collecting interface based on the antibacterial needle-array (ABN) and hydrophilic/hydrophobic cooperative structure is displayed. The hydrophilic ABN is coated with zwitterionic carboxybetaine (CB) brushes that endow the fog collector with a long-term cleaning in harsh environment. Due to its strong affinity to water molecules, the tilted needles with a CB coating can facilitate the capture of fog and the rapid delivery of condensed water driven by gravity. After being transported to the connected hydrophobic sheet, the collected droplets can be rapidly detached and stored in the container, achieving a high fog-harvesting rate. Furthermore, CB-patterned channels are integrated on the hydrophobic sheet for the pathway-controlled water delivery. The CB coating is able to efficiently resist bacterial adhesion and contamination during fog harvesting, protecting the device from microbiological corrosion. The current design provides a promising method to incorporate antibacterial ability into fog collectors, which offer great opportunity to develop water harvesters for real-world applications.

A Robust Cotton Textile-Based Material for High-Flux Oil-Water Separation.

PDMS-based materials have been extensively studied in oil-water separation. However, their successful application is commonly limited by low efficiency, vulnerability to acid/alkali, complex processing procedures, incapability for emulsion separation, etc. Here, a highly durable and robust separation material is developed by coating PDMS-based copolymers on cotton textiles with a facile sol-gel approach. Solely driven by gravity, this new material not only can enable effective separation of oil-water mixture with a flux as high as ∼7500 L m-2 h-1 but also can separate surfactant-stabilized water-in-oil emulsion. Moreover, it remains fully functional even in the environments with high concentrations of acid, alkali, or salt. This novel and versatile strategy holds great promise to be widely used in practical applications of oil-water separation, including oil/chemical spill accidents and industrial sewage emission.

A hemocompatible cryoprotectant inspired by freezing-tolerant plants.

Cryopreservation can extend the storage time of red blood cells (RBCs) for even decades, offering a promising solution to blood waste and shortage caused by routinely used hypothermic preservation method (˜42 days). Currently, organic solvents such as glycerol or dimethyl sulfoxide are the state-of-the-art cryoprotectants (CPAs). However, severe RBC hemolysis induced by solvent CPA removal has raised serious concerns, which has been the bottleneck problem for RBC cryopreservation. Here, inspired by freezing-tolerant plants, we reported a natural zwitterionic betaine-based approach for effective RBC cryopreservation without the need of any organic solvent. Using a time-saving ultrarapid freezing protocol, about 80% of post-thaw RBC integrity rate could be achieved. Most importantly, RBC integrity was not affected during betaine removal, indicating its hemocompatibility. Mechanistically, we presented that betaine could inhibit ice formation and recrystallization during freeze-thaw cycle to protect cells from ice injury; moreover, betaine probably could be promptly taken up and released by cells to prevent them from osmotic injury. This approach provides an attractive solution for long-distance/long-term RBC transport/storage, and may benefit current cryopreservation technologies to support the lifesaving RBC transfusion.

Encapsulation of AgNPs within Zwitterionic Hydrogels for Highly Efficient and Antifouling Catalysis in Biological Environments.

Silver nanoparticles (AgNPs) have been widely used as catalysts in a variety of chemical reactions owing to their unique surface and electronic properties, but their practical applications have been hindered by severe aggregation. The immobilization of AgNPs is crucial to preventing their aggregation or precipitation as well as to improving their reusability. Herein, we developed a facile route for the reductant-free in situ synthesis of AgNPs in zwitterionic hydrogels. Via this method, the embedded AgNPs had a uniform distribution, high activity, and antibiofouling capability. The catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using polycarboxybetaine-AgNPs (PCB-AgNPs) could achieve >95% conversion efficiency within 5 min. Meanwhile, the normalized rate constant knor (10.617 s-1mmol-1) was higher than that of most of the reported immobilized nanocatalysts. More importantly, in a biofouling environment, PCB-AgNPs could still exhibit >97% initial catalytic activity while AgNPs in the PSB or PHEMA hydrogel lost ∼60% activity. This strategy holds great potential for the immobilization of nanoparticle catalysts, especially for applications in biological environments.

Betaine Combined with Membrane Stabilizers Enables Solvent-Free Whole Blood Cryopreservation and One-Step Cryoprotectant Removal.

Cryopreservation of red blood cells (RBCs) is fundamentally important to modern transfusion medicine. Currently, organic solvent glycerol is utilized as the state-of-the-art cryoprotectant (CPA) for RBC cryopreservation. However, glycerol must be removed before RBC transfusion to avoid intravascular hemolysis via a time-consuming deglycerolization process with specialized equipment (e.g., ACP 215), thus limiting the clinical use of frozen RBCs. Herein, we report novel biocompatible CPA formulations combining betaine with membrane stabilizers (disaccharides or amino acids), which can achieve outstanding efficiency for RBC cryopreservation directly using whole blood without any separation process. Most importantly, because of the osmotic regulation capacity of betaine, a simple and fast one-step method can be used for CPA removal, which is significantly superior to the current multistep deglycerolization process. This work offers a promising solution for highly efficient and solvent-free RBC cryopreservation and holds great potential for improving the long-term storage and long-distance distribution of RBCs.

Exploring the Potential of Biocompatible Osmoprotectants as Highly Efficient Cryoprotectants.

Cryoprotectants (CPAs) are critical to successful cryopreservation because they can protect cells from cryoinjuries. Because of the limitations of current CPAs, especially the toxicity, the search for new effective CPAs is attracting increasing attention. In this work, we reported that natural biocompatible osmoprotectants, which could protect cells from osmotic injury in various biological systems, might also be ideal candidates for CPAs. Three representative biocompatible osmoprotectants (proline, glycine, and taurine) were tested and compared. It was found that, aside from presenting a different ability to prevent osmotic injury, these biocompatible osmoprotectants also possessed a different ability to inhibit ice formation and thus mitigate intra-/extracellular ice injury. Because of the strongest ability to prevent the two types of injuries, we found that proline performed the best in cryopreserving five different types of cells. Moreover, the natural osmoprotectants are intrinsically biocompatible with the cells, superior to the current state-of-the-art CPA, dimethyl sulfoxide (DMSO), which is a toxic organic solvent. This work opens a new window of opportunity for DMSO-free cryopreservation, and sheds light on the applications of osmoprotectants in cryoprotection, which may revolutionize the current cryopreservation technologies.