Effect of Carbon Spacer Length on Zwitterionic Carboxybetaines

Salt-Screened Transition toward Bulk-Like Water Dynamics near Polymeric Zwitterions

The superior antifouling performance of zwitterionic materials is commonly linked to their hydration structure, in which tight surface binding of water molecules inhibits solute adsorption. However, there is comparatively little direct experimental data on the hydration water structure and dynamics around zwitterionic moieties, including the longer-range behavior of the hydration shell that modulates the approach of solutes to the polymer surface. This work experimentally probes the dynamics of the diffusing hydration water molecules around a series of zwitterion chemistries using Overhauser dynamic nuclear polarization relaxometry. Surprisingly, water dynamics measured within ∼1 nm of the zwitterions were minimally inhibited compared to those near uncharged hydrophilic or cationic side chains. Specific dissolved ions further enhance the water diffusivity near the zwitterions, rendering the hydration shell bulk water-like. These results that the hydration of a zwitterion surface is nearly indistinguishable from bulk water suggest that these surfaces are "invisible" to biological constituents in a manner tunable by the ionic environment and the chemical design of the zwitterionic surface.

Diffusive delivery of plasmid DNA using zwitterionic carboxyalkyl poly(1-vinylimidazole) into skeletal muscle in vivo

Zwitterionic carboxyalkyl poly(1-vinylimidazole) (CA-PVIm) polymers with imidazolium cations and carboxylate anions have been synthesized as a carrier for the in vivo delivery of plasmid DNA (pDNA) to skeletal muscle. From differential scanning calorimetry measurements, resulting CA-PVIm had intermediate water in hydration water as a biocompatible polymer. Notably, when the pDNA and resulting CA-PVIm were mixed, slight retarded bands of the pDNA were observed in agarose gel electrophoresis, suggesting the polyion complex (PIC) formation between the pDNA and CA-PVIm despite zwitterionic polymers. Resulting PICs maintained the higher-order structure of the pDNA. Using resulting pDNA PICs, the highest pDNA expression by intramuscular injection was achieved in the PIC with 7 mol% carboxymethylated PVIm, that is, CA1(7)-PVIm, observed in a widespread area by in vivo imaging system. These results suggest that the CA1(7)-PVIm/pDNA PIC is effective for the diffusive delivery of the pDNA into skeletal muscle for the treatment of serious muscle diseases.

Effects of Carbon Spacer Length on Conformational Transitions and Protein Adsorption of Polyzwitterions

The properties of polyzwitterions are closely linked to their carbon spacer length (CSL) between oppositely charged groups. A thorough understanding of the effect of CSL on the properties of polyzwitterion-functionalized membranes is important for their fouling resistance and separation performances. In this work, polyzwitterion-functionalized membranes with different CSLs are prepared by coupling selective swelling-induced pore generation with zwitterionization, and the investigation is focused on comprehending the molecular mechanisms underlying protein resistance and conformational transitions within polyzwitterions under varying CSLs. The zwitterionized films show an enhancement in the surface negative potential with the increase of CSL, attributed to the negatively charged groups distanced from the positively charged groups. Quartz crystal microbalance with dissipation (QCM-D) demonstrates that zwitterionized films with different CSLs display distinct levels of resistance to protein adsorption. The trimethylamine N-oxide-derived polymer (PTMAO, CSL = 0) zwitterionized film shows the highest resistance compared to the poly(3-[dimethyl(2'-methacryloyloxyethyl] ammonio) ethanesulfonate (PMAES, CSL = 2) zwitterionized film and the poly(sulfobetaine methacrylate) (PSBMA, CSL = 3) zwitterionized film, owing to its electrical neutrality and pronounced hydrophilicity. Moreover, analysis of the anti-polyelectrolyte behaviors reveals that PTMAO does not undergo a significant conformation transition in deionized water and salt solutions, while the conformations of PMAES and PSBMA display to be more salt-dependent as the CSL increases, attributed to their increased polarization and dipole moment. As a result, the permeability of zwitterionized membranes exhibits enhanced salt responsiveness with the increase in CSL. The findings of this study are expected to facilitate the design of adsorption-resistant surfaces desired in diverse fields.

Protein adsorption on blood-contacting surfaces: A thermodynamic perspective to guide the design of antithrombogenic polymer coatings

Blood-contacting medical devices often succumb to thrombosis, limiting their durability and safety in clinical applications. Thrombosis is fundamentally initiated by the nonspecific adsorption of proteins to the material surface, which is strongly governed by thermodynamic factors established by the nature of the interaction between the material surface, surrounding water molecules, and the protein itself. Along these lines, different surface materials (such as polymeric, metallic, ceramic, or composite) induce different entropic and enthalpic changes at the surface-protein interface, with material wettability significantly impacting this behavior. Consequently, protein adsorption on medical devices can be modulated by altering their wettability and surface energy. A plethora of polymeric coating modifications have been utilized for this purpose; hydrophobic modifications may promote or inhibit protein adsorption determined by van der Waals forces, while hydrophilic materials achieve this by mainly relying on hydrogen bonding, or unbalanced/balanced electrostatic interactions. This review offers a cohesive understanding of the thermodynamics governing these phenomena, to specifically aid in the design and selection of hemocompatible polymeric coatings for biomedical applications. STATEMENT OF SIGNIFICANCE: Blood-contacting medical devices often succumb to thrombosis, limiting their durability and safety in clinical applications. A plethora of polymeric coating modifications have been utilized for addressing this issue. This review offers a cohesive understanding of the thermodynamics governing these phenomena, to specifically aid in the design and selection of hemocompatible polymeric coatings for biomedical applications.

Design, preparation, and characterization of lubricating polymer brushes for biomedical applications

The lubrication modification of biomedical devices significantly enhances the functionality of implanted interventional medical devices, thereby providing additional benefits for patients. Polymer brush coating provides a convenient and efficient method for surface modification while ensuring the preservation of the substrate's original properties. The current research has focused on a "trial and error" method to finding polymer brushes with superior lubricity qualities, which is time-consuming and expensive, as obtaining effective and long-lasting lubricity properties for polymer brushes is difficult. This review summarizes recent research advances in the biomedical field in the design, material selection, preparation, and characterization of lubricating and antifouling polymer brushes, which follow the polymer brush development process. This review begins by examining various approaches to polymer brush design, including molecular dynamics simulation and machine learning, from the fundamentals of polymer brush lubrication. Recent advancements in polymer brush design are then synthesized and potential avenues for future research are explored. Emphasis is placed on the burgeoning field of zwitterionic polymer brushes, and highlighting the broad prospects of supramolecular polymer brushes based on host-guest interactions in the field of self-repairing polymer brush applications. The review culminates by providing a summary of methodologies for characterizing the structural and functional attributes of polymer brushes. It is believed that a development approach for polymer brushes based on "design-material selection-preparation-characterization" can be created, easing the challenge of creating polymer brushes with high-performance lubricating qualities and enabling the on-demand creation of coatings. STATEMENT OF SIGNIFICANCE: Biomedical devices have severe lubrication modification needs, and surface lubrication modification by polymer brush coating is currently the most promising means. However, the design and preparation of polymer brushes often involves "iterative testing" to find polymer brushes with excellent lubrication properties, which is both time-consuming and expensive. This review proposes a polymer brush development process based on the "design-material selection-preparation-characterization" strategy and summarizes recent research advances and trends in the design, material selection, preparation, and characterization of polymer brushes. This review will help polymer brush researchers by alleviating the challenges of creating polymer brushes with high-performance lubricity and promises to enable the on-demand construction of polymer brush lubrication coatings.

Recent advances in zwitterionic nanoscale drug delivery systems to overcome biological barriers

Nanoscale drug delivery systems (nDDS) have been employed widely in enhancing the therapeutic efficacy of drugs against diseases with reduced side effects. Although several nDDS have been successfully approved for clinical use up to now, biological barriers between the administration site and the target site hinder the wider clinical adoption of nDDS in disease treatment. Polyethylene glycol (PEG)-modification (or PEGylation) has been regarded as the gold standard for stabilising nDDS in complex biological environment. However, the accelerated blood clearance (ABC) of PEGylated nDDS after repeated injections becomes great challenges for their clinical applications. Zwitterionic polymer, a novel family of anti-fouling materials, have evolved as an alternative to PEG due to their super-hydrophilicity and biocompatibility. Zwitterionic nDDS could avoid the generation of ABC phenomenon and exhibit longer blood circulation time than the PEGylated analogues. More impressively, zwitterionic nDDS have recently been shown to overcome multiple biological barriers such as nonspecific organ distribution, pressure gradients, impermeable cell membranes and lysosomal degradation without the need of any complex chemical modifications. The realization of overcoming multiple biological barriers by zwitterionic nDDS may simplify the current overly complex design of nDDS, which could facilitate their better clinical translation. Herein, we summarise the recent progress of zwitterionic nDDS at overcoming various biological barriers and analyse their underlying mechanisms. Finally, prospects and challenges are introduced to guide the rational design of zwitterionic nDDS for disease treatment.

Effect of Zwitterionic Additives on Solvation and Transport of Sodium and Potassium Cations in (Ethylene Oxide)10: A Molecular Dynamics Simulation Study

Sodium- (Na+) and potassium- (K+) ion batteries are cost-effective alternatives to lithium-ion (Li+) batteries due to the abundant sodium and potassium resources. Solid polymer electrolytes (SPEs) are essential for safer and more efficient Na+ and K+ batteries because they often exhibit low ionic conductivity at room temperature. While zwitterionic (ZW) materials enhance Li+ battery conductivity, their potential for Na+ and K+ transport in batteries remains unexplored. In this study, we investigated the effect of three ZW molecules (ChoPO4, i.e., 2-methacryloyloxyethyl phosphorylcholine, ImSO3, i.e., sulfobetaine ethylimidazole, and ImCO2, i.e., carboxybetaine ethylimidazole) on the dissociation of Na+ and K+ coordination with ethylene oxide (EO) chains in EO-based electrolytes through molecular dynamics simulations. Our results showed that ChoPO4 possessed the highest cation-EO10 dissociation ability, while ImSO3 exhibited the lowest. Such dissociation ability correlated with the cation-ZW molecule coordination strength: ChoPO4 and ImSO3 showed the strongest and the weakest coordination with cations. However, the cation-ZW molecule coordination could slow the cationic diffusion. The competition of these effects resulted in accelerating or decelerating cationic diffusion. Our simulated results showed that ImCO2 enhanced Na+ diffusion by 20%, while ChoPO4 and ImSO3 led to a 10% reduction. For K+, ChoPO4 reduced its diffusion by 40%, while ImCO2 and ImSO3 caused a similar decrease of 15%. These findings suggest that the ZW structure and the cationic size play an important role in the ionic dissociation effect of ZW materials.

Diffusely Charged Polymeric Zwitterions as Loosely Hydrated Marine Antifouling Coatings

Polymeric zwitterions exhibit exceptional fouling resistance through the formation of a strongly hydrated surface of immobilized water molecules. While being extensively tested for their performance in biomedical, membrane, and, to a lesser extent, marine environments, few studies have investigated how the molecular design of the zwitterion may enhance its performance. Furthermore, while theories of zwitterion antifouling mechanisms exist for molecular-scale foulant species (e.g., proteins and small molecules), it remains unclear how molecular-scale mechanisms influence the micro- and macroscopic interactions of relevance for marine applications. The present study addresses these gaps through the use of a modular zwitterion chemistry platform, which is characterized by a combination of surface-sensitive sum frequency generation (SFG) vibrational spectroscopy and marine assays. Zwitterions with increasingly delocalized cations demonstrate improved fouling resistance against the green alga Ulva linza. SFG spectra correlate well with the assay results, suggesting that the more diffuse charges exhibit greater surface hydration with more bound water molecules. Hence, the number of bound interfacial water molecules appears to be more influential in determining the marine antifouling activities of zwitterionic polymers than the binding strength of individual water molecules at the interface.

Boosting Phosphoric Acid Retention in Polymer Electrolyte Membranes by Zwitterions: Insights from DFT Calculations and MD Simulations

Effective retention of phosphoric acid (PA) is crucial for the efficient operation of fuel cells based on PA-doped polymeric membranes, which is highly challenging due to the moisture-induced loss of PA. Therefore, a comprehensive understanding of the interplay among PA, functional groups, and water is essential for designing membrane materials. Using density functional theory (DFT) calculations and molecular dynamics (MD) simulations, we unveil the remarkable capability of zwitterions to effectively sequester PA, thereby unlocking the potential for fuel cell optimization. Our DFT calculations show that zwitterions, termed "charged proton-accepting bases", exhibit stronger interactions with PA compared to the traditional neutral proton-accepting bases. Furthermore, the presence of water amplifies such a discrepancy, with the zwitterion-PA interactions playing a dominant role in the zwitterion-PA-water cluster due to the strongest affinity of zwitterions to PA. Conversely, the ability of neutral bases to retain PA is significantly attenuated by moisture as the interactions between water and PA surpass those between neutral bases and PA. The strong zwitterion-PA associations arise primarily from the formation of multiple hydrogen bonds. Furthermore, MD simulations reveal the uniform distribution of zwitterions in aqueous environments and their pronounced affinities for both PA and water. In contrast, neutral bases tend to aggregate, interacting limitedly with PA. These findings underscore the effectiveness of zwitterions in boosting PA retention in fuel cells.

Harnessing biomaterial architecture to drive anticancer innate immunity

Immunomodulation is a powerful therapeutic approach that harnesses the body's own immune system and reprograms it to treat diseases, such as cancer. Innate immunity is key in mobilizing the rest of the immune system to respond to disease and is thus an attractive target for immunomodulation. Biomaterials have widely been employed as vehicles to deliver immunomodulatory therapeutic cargo to immune cells and raise robust antitumor immunity. However, it is key to consider the design of biomaterial chemical and physical structure, as it has direct impacts on innate immune activation and antigen presentation to stimulate downstream adaptive immunity. Herein, we highlight the widespread importance of structure-driven biomaterial design for the delivery of immunomodulatory cargo to innate immune cells. The incorporation of precise structural elements can be harnessed to improve delivery kinetics, uptake, and the targeting of biomaterials into innate immune cells, and enhance immune activation against cancer through temporal and spatial processing of cargo to overcome the immunosuppressive tumor microenvironment. Structural design of immunomodulatory biomaterials will profoundly improve the efficacy of current cancer immunotherapies by maximizing the impact of the innate immune system and thus has far-reaching translational potential against other diseases.

Zwitterionic Polymeric Sulfur Ylides with Minimal Charge Separation Open a New Generation of Antifouling and Bactericidal Materials

Zwitterionic polymers are widely employed hydrophilic building blocks for antifouling coatings with numerous applications across a wide range of fields, including but not limited to biomedical science, drug delivery and nanotechnology. Zwitterionic polymers are considered as an attractive alternative to polyethylene glycol because of their biocompatibility and effectiveness to prevent formation of biofilms. To this end, zwitterionic polymers are classified in two categories, namely polybetaines and polyampholytes. Yet, despite a fundamental interest to drive the development of new antifouling materials, the chemical composition of zwitterionic polymer remains severely limited. Here, we show that poly(sulfur ylides) that belong to the largely overlooked class of poly(ylides), effectively prevent the formation of biofilms from pathogenic bacteria. While surface energy analysis reveals strong hydrogen-bond acceptor capabilities of poly(sulfur ylide), membrane damage of pathogenic bacteria induced by poly(sulfur ylides) indicates toxicity towards bacteria while not affecting eucaryotic cells. Such synergistic effect of poly(sulfur ylides) offers distinct advantages over polyethylene glycol when designing new antifouling materials. We expect that our findings will pave the way for the development of a range of ylide-based materials with antifouling properties that have yet to be explored, opening up new directions at the interface of chemistry, biology, and material science.

Supramolecular Self-Healing Antifouling Coating for Dental Materials

In orthodontic treatment, orthodontic appliances are prone to bacterial infections, which pose a risk to oral health. Surface modification of orthodontic appliances has been explored to improve their antifouling properties and impart antibacterial capabilities, inhibiting initial bacterial adhesion and biofilm formation. However, coatings are susceptible to damage in the complex oral environment, leading to a loss of functionality. Here, we have prepared an antifouling self-healing coating based on supramolecular bonding by employing a simple spin coating method. The presence of the hydrophilic zwitterionic trimethylamine N-oxide (TMAO) and the hydrophobic antimicrobial moieties triclosan acrylate (TCSA) imparts to the polymers an amphiphilic structure and enhances the interaction with bacteria, resulting in excellent antimicrobial activity and surface antifouling properties. The multiple hydrogen bonds of ureido-pyrimidinone methacrylate (UPyMA) and ionic interactions contained in the polymers not only increased the adhesion of the coating to the material substrate (approximately 3 times) but also endowed the coating with the intrinsic self-healing ability to restore the antibiofouling properties at oral temperature and humidity. Finally, the polymer coating is biologically safe both in vitro and in vivo, showing no cytotoxic effects on cells and tissues. This research offers a promising avenue for improving the performance of orthodontic appliances and contributes to the maintenance and treatment of oral health.

Chemically revised conducting polymers with inflammation resistance for intimate bioelectronic electrocoupling

Conducting polymers offer attractive mixed ionic-electronic conductivity, tunable interfacial barrier with metal, tissue matchable softness, and versatile chemical functionalization, making them robust to bridge the gap between brain tissue and electronic circuits. This review focuses on chemically revised conducting polymers, combined with their superior and controllable electrochemical performance, to fabricate long-term bioelectronic implants, addressing chronic immune responses, weak neuron attraction, and long-term electrocommunication instability challenges. Moreover, the promising progress of zwitterionic conducting polymers in bioelectronic implants (≥4 weeks stable implantation) is highlighted, followed by a comment on their current evolution toward selective neural coupling and reimplantable function. Finally, a critical forward look at the future of zwitterionic conducting polymers for in vivo bioelectronic devices is provided.

Hydration behaviors of nonfouling zwitterionic materials

Zwitterionic materials have emerged as highly effective ultralow fouling materials for many applications, however the underlying mechanism of fouling resistance remains unclear. Using ab initio molecular dynamics simulations and surface-sensitive sum frequency generation vibrational spectroscopy, we studied the hydration behaviors of zwitterionic materials, including trimethylamine-N-oxide (TMAO) and carboxybetaines of different charge-separation distances, to understand their fouling-resistant mechanism and provide a design principle for improved performance. Our study reveals that the interplay among hydrogen bonding, net charge, and dipole moment is crucial to the fouling-resistant capabilities of zwitterionic materials. Shortening of the zwitterionic spacing strengthens hydrogen bonding with water against biomolecule attachment due to the increased electrostatic and induction interactions, charge transfer, and improved structural stability. Moreover, the shortened charge separation reduces the dipole moment of zwitterionic materials with an intrinsic near-neutral net charge, decreasing their electrostatic and dipole-dipole interactions with biofoulers, and increasing their resistance to fouling. Compared to carboxybetaine compounds, TMAO has the shortest zwitterionic spacing and exhibits the strongest hydrogen bonding, the smallest net charge, and the minimum dipole moment, making it an excellent nonfouling material.

Bioinspired N-Oxide-Based Zwitterionic Polymer Brushes for Robust Fouling-Resistant Surfaces

Fouling-resistant surfaces are needed for various environmental applications. Inspired by superhydrophilic N-oxide-based osmolytes in saltwater fish, we demonstrate the use of a trimethylamine N-oxide (TMAO) analogue for constructing fouling-resistant surfaces. The readily synthesized N-oxide monomer of methacrylamide is grafted to filtration membrane surfaces by surface-initiated atom transfer radical polymerization (SI-ATRP). Successful grafting of the amine N-oxide brush layer as confirmed by material characterization endows the surface with increased hydrophilicity, reduced charge, and decreased roughness. Notably, the introduction of the N-oxide layer does not compromise transport properties, i.e., water permeability and water-salt selectivity. Moreover, the modified membrane exhibits improved antifouling properties with a lower flux decline (32.1%) and greater fouling reversibility (18.55%) than the control sample (45.4% flux decline and 3.26% fouling reversibility). We further evaluate foulant-membrane interaction using surface plasmon resonance (SPR) to relate the reduced fouling tendency to the synergic effects of surface characteristic changes after amine N-oxide modification. Our results demonstrate the promise and potential of the N-oxide-based polymer brushes for the design of fouling resistance surfaces for a variety of emerging environmental applications.

Prediction of zwitterion hydration and ion association properties using machine learning

Molecular dynamics simulations were performed to study the hydration and ion association properties of a library of zwitterionic molecules with varying charged moieties and spacer chemistries in pure water and with Na⁺ and Cl^- ions. The structure and dynamics of associations were calculated using the radial distribution and residence time correlation function. Resulting association properties are used as target variables for a machine learning model, with cheminformatic descriptors of the molecule subunits used as descriptors. Prediction of hydration properties revealed that steric and hydrogen bonding descriptors were of greatest importance and there was influence from the cationic moiety on the anionic moiety hydration properties. Ion association properties prediction performed poorly, which is attributed to the role of hydration layers in ion association dynamics. This study is the first to quantitatively describe the influence of subunit chemistry on hydration and ion association properties of zwitterions. These quantitative descriptions supplement prior studies of zwitterion association and previously described design principles.

Distinct effects of zwitterionic molecules on ionic solvation in (ethylene oxide)10: a molecular dynamics simulation study

Ion-containing polymers play a critical role in various energy and sensing applications. Adjusting ionic solvation is one approach to tune the performance of ion-containing polymers. Small zwitterionic molecule additives have presented their ability to regulate ionic solvation because they possess two charged groups covalently connected together. One remaining question is how the effect of zwitterionic molecules on ionic solvation depends on their own chemical structures, especially the anionic groups. To shed light on this question, we investigate the ionic solvation structure and dynamics in LiTFSI/(ethylene oxide)₁₀ (EO₁₀) with the presence of three distinct zwitterionic molecules (MPC, SB, and CB) using molecular dynamics simulations (MPC: 2-methacryloyloxyethyl phosphorylcholine, SB: sulfobetaine ethylimidazole, CB: carboxybetaine ethylimidazole, and LiTFSI: lithium bis(trifluoromethylsulfonyl)-imide). The simulation systems include two Li⁺ : O(EO₁₀) molar ratios: 1 : 6 and 1 : 18. The simulation results show that all three zwitterionic molecules reduce the Li⁺-EO₁₀ coordination number in the order of MPC > CB > SB. In addition, nearly 10% of Li⁺ exclusively coordinates with MPC molecules, only 2-4% of Li⁺ exclusively cooridinates with CB molecules, while no Li⁺ exclusively coordinates with SB molecules. MPC molecules also present the most stable Li⁺ coordination among the three zwitterionic molecules. Our simulations indicate that zwitterionic molecule additives may benefit a high Li⁺ concentration environment. At a low Li⁺ concentration, all three zwitterionic molecules reduce the diffusion coefficient of Li⁺. However, at a high Li⁺ concentration, only SB molecules reduce the diffusion coefficient of Li⁺.

Polyzwitterionic Coating of Porous Adsorbents for Therapeutic Apheresis

Adsorbents for whole blood apheresis need to be highly blood compatible to minimize the activation of blood cells on the biomaterial surface. Here, we developed blood-compatible matrices by surface modification with polyzwitterionic polysulfobetainic and polycarboxybetainic coatings. Photoreactive zwitterionic terpolymers were synthesized by free-radical polymerization of zwitterionic, photoreactive, and fluorescent monomers. Upon UV irradiation, the terpolymers were photodeposited and mutually crosslinked on the surface of hydrophobic polystyrene-co-divinylbenzene and hydrophilic polyacrylamide-co-polyacrylate (DALI) beads. Fluorescent microscopy revealed coatings with an average thickness of 5 µm, which were limited to the bead surface. Blood compatibility was assessed based on polymer-induced hemolysis, coagulation parameters, and in vitro tests. The maintenance of the adsorption capacity after coating was studied in human whole blood with cytokines for polystyrene beads (remained capacity 25-67%) and with low-density lipoprotein (remained capacity 80%) for polyacrylate beads. Coating enhanced the blood compatibility of hydrophobic, but not of hydrophilic adsorbents. The most prominent effect was observed on coagulation parameters (e.g., PT, aPTT, TT, and protein C) and neutrophil count. Polycarboxybetaine with a charge spacer of five carbons was the most promising polyzwitterion for the coating of adsorbents for whole blood apheresis.

Modeling Polyzwitterion-Based Drug Delivery Platforms: A Perspective of the Current State-of-the-Art and Beyond

Drug delivery platforms are anticipated to have biocompatible and bioinert surfaces. PEGylation of drug carriers is the most approved method since it improves water solubility and colloid stability and decreases the drug vehicles’ interactions with blood components. Although this approach extends their biocompatibility, biorecognition mechanisms prevent them from biodistribution and thus efficient drug transfer. Recent studies have shown (poly)zwitterions to be alternatives for PEG with superior biocompatibility. (Poly)zwitterions are super hydrophilic, mainly stimuli-responsive, easy to functionalize and they display an extremely low protein adsorption and long biodistribution time. These unique characteristics make them already promising candidates as drug delivery carriers. Furthermore, since they have highly dense charged groups with opposite signs, (poly)zwitterions are intensely hydrated under physiological conditions. This exceptional hydration potential makes them ideal for the design of therapeutic vehicles with antifouling capability, i.e., preventing undesired sorption of biologics from the human body in the drug delivery vehicle. Therefore, (poly)zwitterionic materials have been broadly applied in stimuli-responsive “intelligent” drug delivery systems as well as tumor-targeting carriers because of their excellent biocompatibility, low cytotoxicity, insignificant immunogenicity, high stability, and long circulation time. To tailor (poly)zwitterionic drug vehicles, an interpretation of the structural and stimuli-responsive behavior of this type of polymer is essential. To this end, a direct study of molecular-level interactions, orientations, configurations, and physicochemical properties of (poly)zwitterions is required, which can be achieved via molecular modeling, which has become an influential tool for discovering new materials and understanding diverse material phenomena. As the essential bridge between science and engineering, molecular simulations enable the fundamental understanding of the encapsulation and release behavior of intelligent drug-loaded (poly)zwitterion nanoparticles and can help us to systematically design their next generations. When combined with experiments, modeling can make quantitative predictions. This perspective article aims to illustrate key recent developments in (poly)zwitterion-based drug delivery systems. We summarize how to use predictive multiscale molecular modeling techniques to successfully boost the development of intelligent multifunctional (poly)zwitterions-based systems.

Prediction of Serum Adsorption onto Polymer Brush Films by Machine Learning

Using machine learning based on a random forest (RF) regression algorithm, we attempted to predict the amount of adsorbed serum protein on polymer brush films from the films' physicochemical information and the monomers' chemical structures constituting the films using a RF model. After the training of the RF model using the data of polymer brush films synthesized from five different types of monomers, the model became capable of predicting the amount of adsorbed protein from the chemical structure, physicochemical properties of monomer molecules, and structural parameters (density and thickness of the films). The analysis of the trained RF quantitatively provided the importance of each structural parameter and physicochemical properties of monomers toward serum protein adsorption (SPA). The ranking for the significance of the parameters agrees with our general understanding and perception. Based on the results, we discuss the correlation between brush film's physical properties (such as thickness and density) and SPA and attempt to provide a guideline for the design of antibiofouling polymer brush films.

Zwitterionic Conducting Polymers: From Molecular Design, Surface Modification, and Interfacial Phenomenon to Biomedical Applications

Conducting polymers (CPs) have gained attention as electrode materials in bioengineering mainly because of their mechanical softness compared to conventional inorganic materials. To achieve better performance and broaden bioelectronics applications, the surface modification of soft zwitterionic polymers with antifouling properties represents a facile approach to preventing unwanted nonspecific protein adsorption and improving biocompatibility. This feature article emphasizes the antifouling properties of zwitterionic CPs, accompanied by their molecular synthesis and surface modification methods and an analysis of the interfacial phenomenon. Herein, commonly used methods for zwitterionic functionalization on CPs are introduced, including the synthesis of zwitterionic moieties on CP molecules and postsurface modification, such as the grafting of zwitterionic polymer brushes. To analyze the chain conformation, the structure of bound water in the vicinity of zwitterionic CPs and biomolecule behavior, such as protein adsorption or cell adhesion, provide critical insights into the antifouling properties. Integrating these characterization techniques offers general guidelines and paves the way for designing new zwitterionic CPs for advanced biomedical applications. Recent advances in newly designed zwitterionic CP-based electrodes have demonstrated outstanding potential in modern biomedical applications.

Materials Selection for Antifouling Systems in Marine Structures

Fouling is the accumulation of unwanted substances, such as proteins, organisms, and inorganic molecules, on marine infrastructure such as pylons, boats, or pipes due to exposure to their environment. As fouling accumulates, it can have many adverse effects, including increasing drag, reducing the maximum speed of a ship and increasing fuel consumption, weakening supports on oil rigs and reducing the functionality of many sensors. In this review, the history and recent progress of techniques and strategies that are employed to inhibit fouling are highlighted, including traditional biocide antifouling systems, biomimicry, micro-texture and natural components systems, superhydrophobic, hydrophilic or amphiphilic systems, hybrid systems and active cleaning systems. This review highlights important considerations, such as accounting for the effects that antifouling strategies have on the sensing mechanism employed by the sensors. Additionally, due to the specialised requirements of many sensors, often a bespoke and tailored solution is preferential to general coatings or paints. A description of how both fouling and antifouling techniques affect maritime sensors, specifically acoustic sensors, is given.

Structure and pH-Induced Swelling of Polymer Films Prepared from Sequentially Grafted Polyelectrolytes

We have prepared a series of ampholytic polymer films, using a self-initiated photografting and photopolymerization (SI-PGP) method to sequentially polymerize first anionic (deuterated methacrylic acid (dMAA)) and thereafter cationic (2-aminoethyl methacrylate (AEMA)) monomers to investigate the SI-PGP grafting process. Dry films were investigated by ellipsometry, X-ray, and neutron reflectometry, and their swelling was followed over a pH range from 4.5 to 10.5 with spectroscopic ellipsometry. The deuterated monomer allows us to separate the distributions of the two components by neutron reflectometry. Growth of both polymers proceeds via grafting of solution-polymerized fragments to the surface, and also the second layer is primarily grafted to the substrate and not as a continuation of the existing chains. The polymer films are stratified, with one layer of near 1:1 composition and the other layer enriched in one component and located either above or below the former layer. The ellipsometry results show swelling transitions at low and high pH but with no systematic variation in the pH values where these transitions occur. The results suggest that grafting density in SI-PGP-prepared homopolymers could be increased via repeated polymerization steps, but that this process does not necessarily increase the average chain length.

Motif-based zwitterionic peptides impact their structure and immunogenicity

The linkage of zwitterionic peptides containing alternating glutamic acid (E) and lysine (K) amino acids exhibits protective effects on protein drugs due to their high hydration capacity. Previously, short EK peptides covering the surface of a protein drug showed significant protective effects and low immunogenicity. However, for high-molecular-weight single-chain (HMWSC) zwitterionic peptides, the incorporation of structure-disrupting amino acids such as proline (P), serine (S), and glycine (G) is necessary to improve their protective ability. Herein, we first probe the immunogenicity of eight EK-containing motif-based peptides, six of which incorporate structure-disrupting amino acids P, S, and G, linked to keyhole limpet hemocyanin (KLH). These studies uncover two sequence motifs, EKS and EKG, which show uniquely higher immunogenicity, while the other motifs, especially those containing P, exhibit lower immunogenicity. Additionally, the structure and dynamics of these sequence motifs are computationally modeled by Rosetta protein predictions and molecular dynamics (MD) simulations to predict properties of higher and lower immunogenicity peptides. These simulations revealed peptides with higher immunogenicity, namely EKS and EKG, exhibit regions of charge imbalance. Then, HMWSC zwitterionic sequences were linked to a typical protein drug, interferon-alpha 2a (IFN), which showed consistent immunogenic behaviors. Finally, epitope mapping and alanine scanning experiments using the serum collected from mice injected with HMWSC sequences also implicated a link between charge imbalance and peptide immunogenicity.

Structure breaking amino acids, P, S, and G, are incorporated into low immunogenic unstructured zwitterionic peptide fusion proteins. We find unique sequence motifs that exhibit charge balanced conformations and low immunogenicity.

Convergent charge interval spacing of zwitterionic 4-vinylpyridine carboxybetaine structures for superior blood-inert regulation in amphiphilic phases

Antifouling materials are indispensable in the biomedical field, but their high hydrophilicity and surface free energy provoke contamination on surfaces under atmospheric conditions, thus limiting their applicability in medical devices. This study proposes a new zwitterionic structure, 4-vinylpyridine carboxybetaine (4VPCB), that results in lower surface free energy and increases biological inertness. In the design of 4VPCB, one to three carbon atoms are inserted between the positive charge and negative charge (carbon space length, CSL) of the pyridyl-containing side chain to adjust hydration with water molecules. The pyridine in the 4VPCB structure provides the hydrophobicity of the zwitterionic functional group, and thus it can have a lower free energy in the gas phase but maintain higher hydrophilicity in the liquid phase environment. Surface plasmon resonance and confocal microscopy were used to analyze the antiprotein adsorption and anti-blood cell adhesion properties of the P4VPCB brush surface. The results showed that the CSL in the P4VPCB structure affected the biological inertness of the surface. The protein adsorption on the surface of P4VPCB2 (CSL= 2) is lower than that on the surfaces of P4VPCB1 (CSL = 1) and P4VPCB3 (CSL = 3), and the optimal resistance to protein adsorption can be reduced to 7.5 ng cm^-2. The surface of P4VPCB2 can also exhibit excellent blood-inert function in the adhesion test with various human blood cells, offering a potential possibility for the future design of a new generation of blood-inert medical materials.

Liquid-to-Solid Phase Transitions of Imidazolium-Based Zwitterionic Polymers Induced by Hofmeister Anions

In this study, we compared the responses of two different types of zwitterionic polymers (ZPs), polyvinylimidzole sulfobetaine (poly(SBVI)) and polymethacrylate sulfobetaine (poly(SBMA)) to Hofmeister anions. Although the anions of the two ZPs were the same as the sulfonate anions and only the types of their cations were different from each other, the aggregation behavior of each in the salt aqueous solution was remarkably different. Consequently, poly(SBVI) exhibited both salting-in and salting-out effects depending on the type and concentration of salt, while poly(SBMA) only exhibited the anti-polyelectrolyte effect. The results of this study provide a deeper understanding of the behavior of zwitterionic polymers in salt solutions and will greatly expand their applications.

Integrating Emerging Polymer Chemistries for the Advancement of Recyclable, Biodegradable, and Biocompatible Electronics

Through advances in molecular design, understanding of processing parameters, and development of non-traditional device fabrication techniques, the field of wearable and implantable skin-inspired devices is rapidly growing interest in the consumer market. Like previous technological advances, economic growth and efficiency is anticipated, as these devices will enable an augmented level of interaction between humans and the environment. However, the parallel growing electronic waste that is yet to be addressed has already left an adverse impact on the environment and human health. Looking forward, it is imperative to develop both human- and environmentally-friendly electronics, which are contingent on emerging recyclable, biodegradable, and biocompatible polymer technologies. This review provides definitions for recyclable, biodegradable, and biocompatible polymers based on reported literature, an overview of the analytical techniques used to characterize mechanical and chemical property changes, and standard policies for real-life applications. Then, various strategies in designing the next-generation of polymers to be recyclable, biodegradable, or biocompatible with enhanced functionalities relative to traditional or commercial polymers are discussed. Finally, electronics that exhibit an element of recyclability, biodegradability, or biocompatibility with new molecular design are highlighted with the anticipation of integrating emerging polymer chemistries into future electronic devices.

Hydration of the Zwitterionic and Protonated Forms of Glycine Betaine Probed by Soft X-ray Emission Spectroscopy Coupled with Chemometrics

Soft X-ray absorption and emission spectra of glycine betaine (GB) have been measured at the O K-edge in neutral and strongly acidic solutions. The absorption spectra of the neutral solutions have a resonance peak at 532.6 eV, assigned to the transition to the π* orbital, whereas in the acidic solutions, the peak is shifted by -0.3 eV. The emission spectra taken as a function of the GB concentration have been analyzed by means of a modified classical least-squares regression method to obtain the hydration number of the solute. The analysis is successful when the emission spectra have been acquired at the energy of a slightly detuned resonance, giving 28 and 24 as the minimum values for the zwitterionic and protonated GB, respectively. The number of 28 accords with the reported values for the number of water molecules in the first hydration layer of the zwitterion and is greater than that obtained by other experimental techniques. The obtained numbers are used to discuss the hydration structure of GB with the aid of ab initio molecular orbital calculations. The hydration structure of the protonated form of GB is explored for the first time.

Enhancing Polyvalent Cation Rejection Using Perfluorophenylazide-Grafted-Copolymer Membrane Coatings

Surface modification offers a straightforward means to alter and enhance the properties and performance of materials, such as nanofiltration membranes for water softening. Herein, we demonstrate how a membrane's surface charge can be altered by grafting different electrostatically varying copolymers onto commercial membrane surfaces using perfluorophenylazide (PFPA) photochemistry for enhanced ion separation performance. The native membrane's performance-i.e., in terms of divalent cation separation-with copolymer coatings containing a positively charged quaternary ammonium (-N(Me)₃⁺), a negatively charged sulfonate (-SO₃^-), and an essentially neutral zwitterion (sulfobetaine, -N(Me)₂R₂⁺, and -SO₃^-), respectively, indicates that: (a) the sulfonated polymer induces robust Coulombic exclusion of divalent anions as compared to the negatively charged native membrane surface on account of its higher negative charge; (b) the positively charged ammonium coating induces exclusion of cations more effectively than the native membrane; and significantly, (c) the zwitterion polymer coating, which reduces the surface roughness and improves wettability, in spite of its near-neutral charge enhances exclusion of both divalent cations and anions on account of aperture sieving by the compact zwitterion polymer that arises from its ability to limit the size of ions that transport through the polymer along with dielectric exclusion. The outcomes thereby inform new pathways to achieve size- and charge-based exclusion of ionic, molecular, and other species contained in liquid streams.

Blood retention and antigenicity of polycarboxybetaine-modified liposomes

Zwitterionic polycarboxybetaines (PCBs) have gained attention as alternative stealth polymers whose liposomal formulation and protein conjugates were reported not to elicit anti-polymer antibodies. Here, we studied the blood retention and antigenicity of liposomes modified with PCBs focusing on their chemical structures and doses. We compared PCBs with either 1 or 3 (PCB1 or PCB3) spacer carbons between the carboxylate and ammonium groups. PCB3-modified liposomes had a short blood retention, whereas PCB1-modified liposomes demonstrated extended blood retention that was somewhat superior to PEGylated liposome. This confirmed the excellent non-fouling nature of PCB1 reported previously. Interestingly, PCB1-liposome as well as PCB3-liposome elicited specific IgMs toward each PCB. The dose-dependent production of specific IgMs to PCB-liposomes was similar to that of PEGylated liposome, i.e., high doses of PCB-liposomes reduced the production of specific IgMs, termed immunological tolerance. These results indicate the importance of investigating the effect of dose to clarify the existence of antigenicity of stealth polymers.

Hydration State Variation of Polyzwitterion Brushes through Interplay with Ions

Polyzwitterions have emerged as a new class of antifouling materials alternating poly(ethylene glycol). The exemplary biopassivation and lubrication behaviors are often attributed to the particular chemical structure of zwitterions, which involve a large dipole moment of the charged groups and a neutral net charge, while the hydration state and dynamics also associate with these characteristics. Polymer brushes composed of surface-tethered polyzwitterion chains produced by surface-initiated controlled radical polymerization have been developed as thin films which exhibit excellent antifouling and lubrication properties. In past decades, numerous studies have been devoted to examining the structure and dynamics of polyzwitterion brush chains in aqueous solutions. This feature article provides an overview of recent studies exploring the hydration state of polyzwitterion brushes with specular neutron reflectivity, highlights some newly published work on the nonuniform equilibrium structure, ion concentration dependence, ion specificity, and the effects of charge spacer length in the zwitterions, and discusses future perspective in this field.

Hydration of sulfobetaine dizwitterions as a function of alkyl spacer length

The solvation and structure of bolaform dizwitterions containing two sulfobetaine moieties in concentrated aqueous solution were determined using neutron diffraction with isotopic substitution (NDIS) combined with modelling of the measured structure factors using Empirical Potential Structure Refinement (EPSR). Strongly directional local hydration was observed in the polar regimes of the dizwitterions with 48-52 water molecules shared between dizwitterion molecules in a first shell water network around each zwitterion pair. Overall, the double zwitterions were highly hydrated, providing experimental evidence in support of the potential formation of protein-resistant hydration layers at zwitterion-water interfaces.

Molecular Understanding of Ion Effect on Polyzwitterion Conformation in an Aqueous Environment

Polyzwitterions (PZs) are promising materials for the antifouling in reverse osmosis and nanofiltration membrane technology for water treatment. Fundamental understanding of the structure and molecular interactions involving zwitterions is crucial to the optimal design of antifouling in membrane separation. Here we employ the umbrella sampling and molecular dynamics simulations to investigate molecular interactions between sulfobetaine/carboxybetaine zwitterions and different metal ions (Na⁺, K⁺, and Ca²⁺) in an aqueous solution. The simulation results show that these ions can form stable or metastable contact ionic/solvent-shared-ionic pairs with zwitterions. Simulations at different grafting densities of PZ brush arrays reveal complex competitive association mechanisms, which are attributed to nonbonded electrostatic and van der Waals interactions among zwitterions, water molecules, and different metal ions in an aqueous environment. While the high-grafting density of the PZ brush array leads to a strong branch association between different zwitterions in water, this association is decreased at intermediate- and low-grafting densities due to strong zwitterion-water interactions. More importantly, adding ions into water at intermediate- and low-grafting densities further breaks down the zwitterion branch association, resulting in a randomly oriented and dispersed branch configuration with significant swelling of the polymers. The degree of swelling depends on the type of ions, which further changes the surface electrostatic potential of PZ coatings.

Modified silica nanoparticle coatings: Dual antifouling effects of self-assembled quaternary ammonium and zwitterionic silanes

This work examines the antifouling effect of quaternary ammonium silane (QAS) grafted from coatings of silica nanoparticles (SiNPs), independently and in combination with a zwitterionic sulfobetaine (SB) silane. The binding of QAS to the SiNP coatings was monitored using quartz crystal microgravimetry with dissipation monitoring (QCM-D) under varied pH and solution concentrations. Adsorption of bovine serum albumin protein was reduced on QAS modified SiNP coatings prepared under alkaline conditions due to the proposed generation of a pseudozwitterionic interface, where the underlying SiNP surface presents an anionic charge at high pH. Significant reductions in protein binding were achieved at low functionalization concentrations and short modification times. Additionally, SiNP coatings modified with a combination of QAS and SB chemistries were investigated. Surface modifications were performed sequentially, varying silane concentration and order of addition, and monitored using QCM-D. Dual-functionalized surfaces presented enhanced resistance to protein adsorption compared to QAS or SB modified surfaces alone, even at low functionalization concentrations. The antiadhesive and antibacterial properties of functionalized surfaces were investigated by challenging the surfaces against the bacterium Escherichia coli. All dual-functionalized coatings showed equal or reduced bacterial adhesion compared to QAS and SB functionalizations alone, while coatings functionalized with high concentrations of combined chemistries reduced the adhesion of bacteria by up to 95% compared to control SiNP surfaces.