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

Real-Time In Situ Spectroscopic and Electrochemical Analysis of Ion-Water-Polymer Interactions at Functionalized PEDOT Interfaces

Understanding water dynamics at material interfaces is crucial for applications in biotechnology, electrochemistry, and energy systems. In this study, we employed in situ Fourier transform infrared spectroscopy and electrochemical quartz crystal microbalance with dissipation monitoring to investigate the hydration states and ion interactions of functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) films. By applying controlled potentials, we monitored ion absorption and desorption while using Gaussian fitting to analyze the O-H stretching bands. Our results revealed that sulfate ions (SO42-) compete with water molecules at PEDOT interfaces with hydroxyl groups, whereas perchlorate ions (ClO4-) exhibit minimal interference due to their weak water interactions. For PEDOT functionalized with zwitterionic phosphorylcholine groups, higher levels of intermediate water and nonfreezing water mitigated dehydration in saline environments. This work highlights the synergy between electrochemical and spectroscopic methods for real-time analysis of ion-water-polymer interactions, providing critical insights into interfacial phenomena regulated by applied potential.

Heterocyclic Group Functionalized Siloxane-Based Polymers for Interruption of pH-Dependent Marine Settlement

Marine biofouling is the natural accumulation of organisms on substrates that reside in rivers, lakes, and seas. To combat this issue, polymer-based coatings historically utilized tin or copper compounds, which, though effective, are also highly toxic. In this study, a series of functionalized toxicant-free PDMS-type polymers were designed with pH buffer and zwitterionic moieties for fouling inhibition. The water contact angles ranged from 41 to 98°, demonstrating significant differences in the wettability of the coated surfaces. XPS and SEM-EDS testing confirmed the surface presence of buffer and zwitterionic functional groups. Assays were carried out using both laboratory and field testing against an array of marine species to gain an understanding of how these buffered polymer coatings hold up in the environment and to measure their antifouling and fouling-release capabilities. The organisms used for testing were a diatom, Navicula incerta, and two types of tubeworms, spirorbid and nonspirorbid serpulids. Piperazine and piperazine zwitterionic-based coatings performed the best overall as antifouling and fouling-release materials. Preliminary biological assays suggest that hydrophobic zwitterion-functionalized siloxane-based polymers may have both preventative antibacterial and antifouling interactions with target species compared to previously studied hydrophobic materials.

Accurate evaluation of diffusion coefficient for electroactive analytes in human serum samples using nitrogen-terminated sputtered carbon film electrode

We have developed an N-terminated carbon film electrode that allows accurate determination of the diffusion coefficient of electroactive molecules dissolved in a highly concentrated serum protein solution. The carbon film electrode was formed by the unbalanced magnetron sputtering (UBM) method. Then, nitrogen functional groups were introduced by employing NH3 or H2O plasma treatment. Cyclic voltammetry measurements with ferricyanide ion ([Fe(CN)6]3-) showed that the N-terminated carbon film electrode exhibited great anti-fouling property against simulated serum proteins (50 mg/mL human serum albumin and 15 mg/mL γ-globulin dissolved in 1 M KCl solution). In contrast, glassy carbon, H2O plasma-treated, and especially untreated carbon film electrodes were subject to severe electrode fouling, making it difficult to electrochemically determine the diffusion coefficient of the [Fe(CN)6]3- ion. The control experiment using less adsorptive ethylene glycol as a viscosity modifier showed that the increase in viscosity is a main factor of the decrease in diffusion coefficient for nitrogen plasma treated electrode, which is not significantly affected by the possible interaction between [Fe(CN)6]3- ions and serum proteins. Finally, we applied the electrode for the electrochemical analysis of acetaminophen dissolved in phosphate buffer (0.1 M, pH = 7.0), which suggests that NH3 plasma-treated carbon film exhibits the lowest ΔE increase when we compare ΔE with and without proteins and also a more stable peak current in continuous voltametric measurements compared with other carbon electrodes.

Beyond Surfactants: Janus Particles for Functional Interfaces and Coatings

Janus particles (JPs), initially introduced as soft matter, have evolved into a distinctive class of materials that set them apart from traditional surfactants, dispersants, and block copolymers. This mini-review examines the similarities and differences between JPs and their molecular counterparts to elucidate the unique properties of JPs. Key studies on the assembly behavior of JPs in bulk phases and at interfaces are reviewed, highlighting their unique ability to form diverse, complex structures. The superior interfacial stability and tunable amphiphilicity of JPs make them highly effective emulsifiers and dispersants, particularly in emulsion polymerization systems. Beyond these applications, JPs demonstrate immense potential as coating materials, facilitating the development of eco-friendly, anti-icing, and antifouling coatings. A comparative discussion with zwitterionic polymers also highlights the distinctive advantages of each system. This review emphasizes that while JPs mimic some of the behaviors of small molecular surfactants, they also open doors to entirely new applications, making them indispensable as next-generation functional materials.

Mitigating Membrane Biofouling in Protein Production with Zwitterionic Peptides

Biofouling on polymeric membranes poses a significant challenge in protein production and separation processes. We report here on the use of zwitterionic peptides composed of alternating lysine (K) and glutamic acid (E) residues to reduce biomolecular fouling on gold substrates and polymeric membranes within a protein production-mimicking environment. Our findings demonstrate that both gold chips and polymeric membranes functionalized with longer sequence zwitterionic peptides, along with a hydrophilic linker, exhibit superior antifouling performance across various protein-rich environments. Furthermore, increasing the grafting density of these peptides on substrates enhances their antifouling properties. We believe that this work sheds light on the antifouling capabilities of zwitterionic peptides in cell culture environments, advancing our understanding and paving the way for the development of zwitterionic peptide-based antifouling materials for polymeric membranes.

Preparation of Zwitterionic Sulfobetaines and Study of Their Thermal Properties and Nanostructured Self-Assembling Features

Zwitterionic polymers have garnered significant attention for their distinctive properties, such as biocompatibility, antifouling capabilities, and resistance to protein adsorption, making them promising candidates for a wide range of applications, including drug delivery, oil production inhibitors, and water purification membranes. This study reports the synthesis and characterization of zwitterionic monomers and polymers through the modification of linear, vinyl, and aromatic heterocyclic functional groups via reaction with 1,3-propanesultone. Four zwitterionic polymers with varying molecular structures-ranging from linear to five and six membered ring systems-were synthesized: poly(sulfobetaine methacrylamide) (pSBMAm), poly(sulfobetaine-1-vinylimidazole) (pSB1VI), poly(sulfobetaine-2-vinylpyridine) (pSB2VP), and poly(sulfobetaine-4-vinylpyridine) (pSB4VP). Their molecular weights, thermal behavior, and self-assembly properties were analyzed using gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and zeta potential measurements. The glass transition temperatures (Tg) ranged from 276.52 °C for pSBMAm to 313.69 °C for pSB4VP, while decomposition temperatures exhibited a similar trend, with pSBMAm degrading at 301.03 °C and pSB4VP at 387.14 °C. The polymers' self-assembly behavior was strongly dependent on pH and their surface charge, particularly under varying pH conditions: spherical micelles were observed at neutral pH, while fractal aggregates formed at basic pH. These results demonstrate that precise modifications of the chemical structure, specifically in the linear, imidazole, and pyridine moieties, enable fine control over the thermal properties and self-assembly behavior of polyzwitterions. Such insights are essential for tailoring polymer properties for targeted applications in filtration membranes, drug delivery systems, and solid polymer electrolytes, where thermal stability and self-assembly play crucial roles.

Enhanced Electrochemiluminescence Detection of Dopamine Using Antifouling PEDOT-Modified SPEs for Complex Biological Samples

Detecting medically important biomarkers in complex biological samples without prior treatment or extraction poses a major challenge in biomedical analysis. Electrochemical methods, specifically electrochemiluminescence (ECL), show potential due to their high sensitivity, minimal background noise, and straightforward operation. This study investigates the ECL performance of screen-printed electrodes (SPEs) modified with the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and its derivatives for dopamine (DA) detection. PEDOT modification significantly enhances ECL intensity, improves sensitivity, and expands the linear range for DA detection. Functionalizing PEDOT with ethylene glycol (EG) further enhances stability, specificity, and resistance to interferences for DA detection. These modified SPEs demonstrate the linear range of 1-200 μM and a detection limit as low as 0.887 nM (S/N = 3), surpassing many previous studies using SPEs. Moreover, the PEDOT-EG4-OMe-modified SPEs can reliably detect DA in solutions with high protein concentrations or artificial cerebrospinal fluid. These results suggest that the PEDOT derivative-modified SPE can serve as reusable and sensitive DA sensors in complex biological environments, highlighting the potential of the ECL system for a range of challenging applications.

Quantitatively Elucidating the Trade-Off between Zwitterionic Antifouling Surfaces and Bioconjugation Performance

Zwitterionic materials, known for their high hydrophilicity, are widely used to minimize the nonspecific adsorption of biomolecules in complex biological solutions. However, these materials can also reduce the capture efficiency between targets and peptide probes. To demonstrate how antifouling surfaces affect capture efficiency, we utilize a poly(3,4-ethylenedioxythiophene) (PEDOT)-based surface incorporating varying ratios of phosphorylcholine (PEDOT-PC) and maleimide functional groups to achieve both antifouling properties and peptide-protein binding. As a model system, the peptide YWDKIKDFIGGSSSSC, attached via maleimide groups, is used to capture the target protein, calmodulin (CaM). By systematically monitoring protein binding on both antifouling and peptide-immobilized PEDOT surfaces using a quartz crystal microbalance with dissipation, the results reveal that PEDOT-PC reduces both the specific binding between peptides and target proteins as well as the rate of protein fouling on the electrode surface. From these findings, we propose an equation for quantitative analysis. Furthermore, electrochemical impedance spectroscopy and differential pulse voltammetry are performed to measure the changes in the impedance in CaM solutions. The data indicate that impedance increases with protein adsorption, confirming the practical utility of the designed electrode surface.

Zwitterionic Polymers for Biomedical Applications: Antimicrobial and Antifouling Strategies toward Implantable Medical Devices and Drug Delivery

Poly(ethylene glycol) (PEG) is extensively utilized in biomedical applications due to its biocompatibility; however, its thermal instability and susceptibility to oxidative degradation significantly constrain its long-term effectiveness. Zwitterionic polymers, characterized by their distinctive structure, enhanced stability, and superior biocompatibility, offer a more advantageous alternative. These polymers exhibit super hydrophilicity, resist nonspecific protein adsorption, and maintain stability in biological environments due to their charge-neutral ionic nature. Zwitterionic polymers enhance anticancer drug delivery by precisely targeting tumor cells and facilitating an efficient drug release. Their inherent antifouling properties and prolonged circulation within the bloodstream render them highly suitable for redox-sensitive drug carriers, thereby augmenting the antitumor efficacy. Moreover, zwitterionic polymers markedly mitigate biofouling in implants, biosensors, and wound dressings, thereby improving both their functionality and their therapeutic outcomes. These advantages arise from the formation of robust hydration layers, which significantly enhance the hemocompatibility and inhibit the adhesion of proteins, platelets, and bacteria. Zwitterionic polymers, including sulfobetaine (SB), phosphorylcholine (PC), and carboxybetaine (CB), are increasingly employed in blood-contacting devices and as effective coating materials for implantable devices. This mini-review paper aims to explore the recent diverse biomedical applications of zwitterionic polymers and highlight their advantageous properties compared with unmodified polymers. We will cover their use in drug delivery systems, tumor targeting nanocarriers, antibiofouling and antibacterial activities in implantable devices, tissue engineering, and diagnostic devices, demonstrating how their unique properties can translate into different applications. Through this exploration, this Perspective will display the potential of zwitterionic polymers as innovative polymer materials in the field of biomedical engineering and beyond.

Zwitterionic Peptides: From Mechanism, Design Strategies to Applications

Zwitterionic peptides, as a type of peptide composed of charged residues, are electrically neutral, which combine the advantages of zwitterionic materials and biological peptides, exhibiting hydrophilicity and programmable properties. As attractive candidates for resisting nonspecific adsorption of biomacromolecules and microorganisms, zwitterionic peptides have been applied in materials science, biomedicine, and biochemistry over the past decade. In this review, the development of zwitterionic peptides has been systematically outlined and analyzed, including their mechanisms, structure-function relationships, and design strategies. Furthermore, this review emphasizes and discusses their recent applications for developing functional coatings, biosensors, drug delivery systems, and engineering proteins. Finally, future research perspectives and challenges of zwitterionic peptides are also prospected and discussed. This review is intended to provide clarity and insight into the design and applications of zwitterionic peptides.

Chelation-Induced Zwitterion-like Antifouling Behavior on Anionic Poly(3,4-ethylenedioxythiophene) Surfaces

Antifouling properties are crucial for enhancing the longevity and functionality of biomedical implants, drug delivery systems, and biosensors. Zwitterionic polymers are renowned for their exceptional surface hydration and charge neutrality, which effectively resist biomolecular adsorption and protein attachment. We propose an innovative approach to develop zwitterion-like antifouling surfaces by chelating divalent cations with anionic poly(3,4-ethylenedioxythiophene) (PEDOT) films, specifically PEDOT-PO4 and PEDOT-COOH. The chelation behavior of these films was systematically evaluated using Na+, Mg2+, and Ca2+ ions. Divalent ions, particularly Ca2+ and Mg2+, exhibit a strong affinity for the anionic groups, leading to significant antifouling properties. These modified surfaces effectively repelled both negatively charged bovine serum albumin (BSA) and positively charged lysozyme (LYZ) proteins across various pH environments. This study offers valuable insights into the antifouling characteristics of charged surfaces, enhancing our understanding of how ion-mediated surface modifications influence protein adsorption and interactions.

Recent Progress in Artificial Neurons for Neuromodulation

Driven by the rapid advancement and practical implementation of biomaterials, fabrication technologies, and artificial intelligence, artificial neuron devices and systems have emerged as a promising technology for interpreting and transmitting neurological signals. These systems are equipped with multi-modal bio-integrable sensing capabilities, and can facilitate the benefits of neurological monitoring and modulation through accurate physiological recognition. In this article, we provide an overview of recent progress in artificial neuron technology, with a particular focus on the high-tech applications made possible by innovations in material engineering, new designs and technologies, and potential application areas. As a rapidly expanding field, these advancements have a promising potential to revolutionize personalized healthcare, human enhancement, and a wide range of other applications, making artificial neuron devices the future of brain-machine interfaces.

In Situ Growth of Columnar PEG on PEDOT and Its Antifouling Properties

The antifouling properties of conductive polymers have received extensive attention for biosensor and bioelectronic applications. Polyethylene glycol (PEG) is a well-known antifouling material, but the controlled regulation of the surface topography of PEG without a template remains a challenge. Here, we show a columnar structure antifouling conductive polymer brush with enhanced antifouling properties and considerable conductivity. The method involves synthesizing the 3,4-ethylenedioxythiophene monomer modified with azide (EDOT-N3), the electropolymerization of PEDOT-N3, and the in situ growth of PEG polymer brushes on PEDOT through double-click reactions. The resultant columnar structure polymer brush exhibits high electrical conductivity (3.5 Ω·cm2), ultrahigh antifouling property, electrochemical stability (capacitance retention was 93.8% after 2000 cycles of CV scans in serum), and biocompatibility.

Investigation of a chondroitin sulfate-based bioactive coating for neural interface applications

Invasive neural implants allow for high-resolution bidirectional communication with the nervous tissue and have demonstrated the ability to record neural activity, stimulate neurons, and sense neurochemical species with high spatial selectivity and resolution. However, upon implantation, they are exposed to a foreign body response which can disrupt the seamless integration of the device with the native tissue and lead to deterioration in device functionality for chronic implantation. Modifying the device surface by incorporating bioactive coatings has been a promising approach to camouflage the device and improve integration while maintaining device performance. In this work, we explored the novel application of a chondroitin sulfate (CS) based hydrophilic coating, with anti-fouling and neurite-growth promoting properties for neural recording electrodes. CS-coated samples exhibited significantly reduced protein-fouling in vitro which was maintained for up to 4-weeks. Cell culture studies revealed a significant increase in neurite attachment and outgrowth and a significant decrease in microglia attachment and activation for the CS group as compared to the control. After 1-week of in vivo implantation in the mouse cortex, the coated probes demonstrated significantly lower biofouling as compared to uncoated controls. Like the in vitro results, increased neuronal population (neuronal nuclei and neurofilament) and decreased microglial activation were observed. To assess the coating's effect on the recording performance of silicon microelectrodes, we implanted coated and uncoated electrodes in the mouse striatum for 1 week and performed impedance and recording measurements. We observed significantly lower impedance in the coated group, likely due to the increased wettability of the coated surface. The peak-to-peak amplitude and the noise floor levels were both lower in the CS group compared to the controls, which led to a comparable signal-to-noise ratio between the two groups. The overall single unit yield (% channels recording a single unit) was 74% for the CS and 67% for the control group on day 1. Taken together, this study demonstrates the effectiveness of the polysaccharide-based coating in reducing biofouling and improving biocompatibility for neural electrode devices.

Organic Mixed Ionic-Electronic Conductors Based on Tunable and Functional Poly(3,4-ethylenedioxythiophene) Copolymers

Organic mixed ionic-electronic conductors (OMIECs) are being explored in applications such as bioelectronics, biosensors, energy conversion and storage, and optoelectronics. OMIECs are largely composed of conjugated polymers that couple ionic and electronic transport in their structure as well as synthetic flexibility. Despite extensive research, previous studies have mainly focused on either enhancing ion conduction or enabling synthetic modification. This limited the number of OMIECs that excel in both domains. Here, a series of OMIECs based on functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) copolymers that combine efficient ion/electron transport with the versatility of post-functionalization were developed. EDOT monomers bearing sulfonic (EDOTS) and carboxylic acid (EDOTCOOH) groups were electrochemically copolymerized in different ratios on oxygen plasma-treated conductive substrates. The plasma treatment enabled the synthesis of copolymers containing high ratios of EDOTS (up to 68%), otherwise not possible with untreated substrates. This flexibility in synthesis resulted in the fabrication of copolymers with tunable properties in terms of conductivity (2-0.0019 S/cm) and ion/electron transport, for example, as revealed by their volumetric capacitances (122-11 F/cm3). The importance of the organic nature of the OMIECs that are amenable to synthetic modification was also demonstrated. EDOTCOOH was successfully post-functionalized without influencing the ionic and electronic transport of the copolymers. This opens a new way to tailor the properties of the OMIECs to specific applications, especially in the field of bioelectronics.

Electrified Interactions of Polyzwitterions with Charged Surfaces: Role of Dipole Orientation and Surface Potentials

The zwitterionic groups possess strong dipole moments, leading to inter- or intrachain interactions among zwitterionic polymers. This study aims to demonstrate the interaction of polyzwitterions poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), and poly(carboxybetaine methacrylate) (PCBMA) with electrified surfaces, despite their electrically neutral nature. We studied the adsorption of polyzwitterions and their monomers on electrified surfaces by using an electrochemical quartz crystal microbalance with dissipation (EQCM-D). The interaction between zwitterionic molecules and charged surfaces is explored by adjusting the surface potentials. Interestingly, the adsorption of polyzwitterions can be influenced by external potential, primarily due to the formation of polyzwitterions restricting the mobility of zwitterionic groups, affecting the adsorption behavior of polyzwitterions based on the surface potential. The impact is determined by the arrangement of positive and negative ions within the zwitterionic groups, which are the dipole orientation. Additionally, surface potentials determine the adsorption rate, amount, and chain conformation of the adsorbed thin polyzwitterion layers. The effect of ionic strength was investigated by introducing electrolytes into the aqueous solutions to assess the range of influenced surface potentials.

Facile surface functionalization of triboelectric layers via electrostatically self-assembled zwitterionic molecules for achieving efficient and stable antibacterial flexible triboelectric nanogenerators

Manipulation of the surface properties of the triboelectric layer has been proven to be one of the key parameters to achieve high-performance and stable triboelectric nanogenerators (TENG). Herein, a pragmatic surface engineering strategy that can substantially boost the performance and stability of flexible TENG is elaborated by incorporating the zwitterionic molecule dimethylethylammoniumpropane sulfonate (NDSB) as the surface modification layer. Given that zwitterionic molecules tend to form aggregated structures, realizing ordered arrangement on the substrate surface remains challenging to date. To address this issue, in this work, a combination of multiple surface treatments and molecular manipulation strategy is proposed. Our results prove that NDSB is effective in modifying the surface properties of the dielectric layer and electrode layer, leading to a remarkable power density and specific power of 2.86 W m-2 and 20.73 mW g-1 for flexible TENG, respectively. In addition, due to the strong interaction between the NDSB/dielectric and NDSB/electrode, a water-resistant long-term stable flexible TENG is realized. More encouragingly, our strategy is compatible with a cost-effective dip-coating technique, and an unprecedented demonstration of batch fabrication of TENG using NDSB to functionalize the surface of the dielectric layer and electrode layer synchronously can be realized, which is advantageous for rapid and up-scalable manufacturing of TENG. We also prove that the TENG based on zwitterionic materials reveals exceptional antibacterial properties against Escherichia coli. This study represents an important step towards the development of long-term stable flexible TENG that possesses a high output performance and excellent antibacterial activity based on a facile and economical strategy, enabling TENG technology to show bright prospects in a wide variety of application domains.

PEGylated curcumin-loaded poly(vinyl alcohol)/Zwitterionic poly(sulfobetaine vinylimidazole)-grafted chitosan nanofiber as a second-degree burn wound dressing

Burn injuries damage skin function and increased the risk of infection. Using natural-inspired antibiotic-free nanofibrous in wound healing has attracted increasing attention. Here, mPEG-Curcumin (mPEG-CUR) was synthesized through a novel, cheap, and high-efficiency method, and incorporated onto poly(vinyl alcohol) (PVA)/zwitterionic poly(sulfobetaine vinylimidazole)-grafted chitosan (CS-g-PNVIS) nanofiber. Due to the lack of electrospinning capability of CS-g-PNVIS and its brittleness, to obtain nanofibers with uniform and bead-free morphology, PVA was used as an electrospinning aid polymer, so that the prepared nanofibers have suitable mechanical properties with an average diameter between 115 ± 18-157 ± 39 nm. The heat-treated nanofibers have adequate swelling and dimensional stability. Time-killing assay proved the antibacterial activity of the mPEG-CUR-loaded nanofibers towards Gram-positive and Gram-negative bacterium. The MTT investigation illustrated the non-cytotoxicity and biocompatibility of the nanofibers. In vivo studies exhibited significant improvement in the mean wound area closure by applying mPEG-CUR nanofibers. The mPEG-CUR-loaded nanofibers showed the highest antioxidant (86 %) power after 40 min. Moreover, nanofibers possess a desirable WVT rate (3.4 ± 0.24-5.5 ± 0.3 kg/m2.d) and good breathability and had the potential to supply a suitable moist environment in the wounded area. This approach can be the beginning of a new path in designing a new generation of nanofiber mats for wound healing applications.