Dopamine-assisted deposition of dextran for nonfouling applications

Recent Advances in Dopamine-Based Membrane Surface Modification and Its Membrane Distillation Applications

Surface modification of membranes is essential for improving flux and resistance to contamination for membranes. This is of great significance for membrane distillation, which relies on the vapor pressure difference across the membrane as the driving force. In recent years, biomimetic mussel-inspired substances have become the research hotspots. Among them, dopamine serves as surface modifiers that would achieve highly desirable and effective membrane applications owing to their unique physicochemical properties, such as universal adhesion, enhanced hydrophilicity, tunable reducibility, and excellent thermal conductivity. The incorporation of a hydrophilic layer, along with the utilization of photothermal properties and post-functionalization capabilities in modified membranes, effectively addresses challenges such as low flux, contamination susceptibility, and temperature polarization during membrane distillation. However, to the best of our knowledge, there is still a lack of comprehensive and in-depth discussions. Therefore, this paper systematically compiles the modification method of dopamine on the membrane surface and summarizes its application and mechanism in membrane distillation for the first time. It is believed that this paper would provide a reference for dopamine-assisted membrane separation during production, and further promote its practical application.

Spatially Defined Cell-Secreted Protein Detection Using Granular Hydrogels: μGeLISA

Intercellular communication through secreted proteins is necessary in essential processes such as embryo and limb development, disease progression, and immune responses. There exist many techniques to study bulk solution protein concentrations, but there is a limited set of tools to study the concentrations of cell-secreted proteins in situ within diverse cell platforms while retaining spatial information. In this study, we have developed a microgel system that is able to quantitatively measure the cell-secreted protein concentration within defined three-dimensional culture configurations with single-cell spatial resolution, called μGeLISA (microgel-linked immunosorbent assay). This system, which is based on the surface modification of polyethylene glycol microgels, was able to detect interleukin 6 (IL-6) concentrations of 2.21-21.86 ng/mL. Microgels were also able to detect cell spheroid-secreted IL-6 and distinguish between low- and high-secreting single cells. The system was also adapted to measure the concentration of cell-secreted matrix metalloproteinase-2 (MMP-2). μGeLISA represents a highly versatile system with a straightforward fabrication process that can be adapted toward the detection of secreted proteins within a diverse range of cell culture configurations.

Dopamine-Assisted Layer-by-Layer Deposition Providing Coatings with Controlled Thickness, Roughness, and Functional Properties

In this study, dopamine-assisted deposition combined with layer-by-layer assembly was investigated as an efficient method for preparing coatings with tunable thickness, roughness, and functional properties. By this method, one can first benefit from the versatile chemistry of dopamine allowing the co-deposition of various functional materials, for example, polymers, ions, and nanoparticles, within the coating. Moreover, the layer-by-layer approach allows tuning the coating thickness and surface roughness, as well as varying the chemical composition of the coating in the vertical direction. Herein, we demonstrated the benefits of using this method in fabricating both single- and multi-component coatings.

Synthesis, characterization, and cytotoxicity evaluation of dextran-myristoyl-ECGKRK peptide conjugate

CGKRK is a well-known tumor homing peptide with significant specificity for many types of cancer tissues. Herein, we describe the synthesis of a novel drug delivery system based on dextran decorated with myristoyl-ECGKRK peptide. The myristoylated peptide was synthesized and conjugated to dextran via an ester bond followed by purification. FT-IR and NMR confirmed the success of the conjugation reaction, while the surface morphology examination revealed that the conjugate has a characteristic porous network-like structure. Dynamic-light scattering measurements indicated the ability of the conjugate to self-assemble into nanoparticles with an average size of 248 ± 6.33 nm, and zeta potential of 10.7 mV. The cytotoxicity profiles for the peptide, dextran (Dex0), and dextran-peptide conjugate (Dex1) were evaluated against triple-negative breast cancer cells (MDA-MB-231), breast cancer cells (MCF-7), and human embryonic normal kidney cells (HEK-293). The results revealed that myristoyl-ECGKRK was noncytotoxic on the two different breast cancer cell lines up to 50 μM, but the cell viability was minimally reduced to 85% at 50 μm in HEK-293 cells. Similarly, Dex0 showed a neglected cytotoxicity profile at all tested concentrations. The Dex1 was not toxic to the cells up to a concentration of 8.3 mg/mL.

Recent advances in dopamine-based materials constructed via one-pot co-assembly strategy

Dopamine-based materials have attracted widespread interest due to the outstanding physicochemical and biological properties. Since the first report on polydopamine (PDA) films, great efforts have been devoted to develop new fabrication strategies for obtaining novel nanostructures and desirable properties. Among them, one-pot co-assembly strategy offers a unique pathway for integrating multiple properties and functions into dopamine-based platform in a single simultaneous co-deposition step. This review focuses on the state of the art development of one-pot multicomponent self-assembly of dopamine-based materials and summarizes various single-step co-deposition approaches, including PDA-assisted adaptive encapsulation, co-assembly of dopamine with other molecules through non-covalent interactions or covalent interactions. Moreover, emerging applications of dopamine-based materials in the fields ranging from sensing, cancer therapy, catalysis, oil/water separation to antifouling are outlined. In addition, some critical remaining challenges and opportunities are discussed to pave the way towards the rational design and applications of dopamine-based materials.

Bioinspired Dopamine/Mucin Coatings Provide Lubricity, Wear Protection, and Cell-Repellent Properties for Medical Applications

Even though medical devices have improved a lot over the past decades, there are still issues regarding their anti-biofouling properties and tribological performance, and both aspects contribute to the short- and long-term failure of these devices. Coating these devices with a biocompatible layer that reduces friction, wear, and biofouling at the same time would be a promising strategy to address these issues. Inspired by the adhesion mechanism employed by mussels, here, dopamine is made use of to immobilize lubricious mucin macromolecules onto both manufactured commercial materials and real medical devices. It is shown that purified mucins successfully adsorb onto a dopamine pre-coated substrate, and that this double-layer is stable toward mechanical challenges and storage in aqueous solutions. Moreover, the results indicate that the dopamine/mucin double-layer decreases friction (especially in the boundary lubrication regime), reduces wear damage, and provides anti-biofouling properties. The results obtained in this study show that such dopamine/mucin double-layer coatings can be powerful candidates for improving the surface properties of medical devices such as catheters, stents, and blood vessel substitutes.

A scope at antifouling strategies to prevent catheter-associated infections

The use of invasive medical devices is becoming more common nowadays, with catheters representing one of the most used medical devices. However, there is a risk of infection associated with the use of these devices, since they are made of materials that are prone to bacterial adhesion with biofilm formation, often requiring catheter removal as the only therapeutic option. Catheter-related urinary tract infections (CAUTIs) and central line-associated bloodstream infections (CLABSIs) are among the most common causes of healthcare-associated infections (HAIs) worldwide while endotracheal intubation is responsible for ventilator-associated pneumonia (VAP). Therefore, to avoid the use of biocides due to the potential risk of bacterial resistance development, antifouling strategies aiming at the prevention of bacterial adherence and colonization of catheter surfaces represent important alternative measures. This review is focused on the main strategies that are able to modify the physical or chemical properties of biomaterials, leading to the creation of antiadhesive surfaces. The most promising approaches include coating the surfaces with hydrophilic polymers, such as poly(ethylene glycol) (PEG), poly(acrylamide) and poly(acrylates), betaine-based zwitterionic polymers and amphiphilic polymers or the use of bulk-modified poly(urethanes). Natural polysaccharides and its modifications with heparin, have also been used to improve hemocompatibility. Recently developed bioinspired techniques yielding very promising results in the prevention of bacterial adhesion and colonization of surfaces include slippery liquid-infused porous surfaces (SLIPS) based on the superhydrophilic rim of the pitcher plant and the Sharklet topography inspired by the shark skin, which are potential candidates as surface-modifying approaches for biomedical devices. Concerning the potential application of most of these strategies in catheters, more in vivo studies and clinical trials are needed to assure their efficacy and safety for possible future use.

Tris(hydroxymethyl)aminomethane-grafted polyamine nanofiltration membrane: enhanced antifouling and pH resistant properties

In this study, to fabricate a pH resistant membrane with antifouling properties, a Tris-grafted polyamine thin film composite (TFC) membrane has been synthesized.

Accelerating the peroxidase-like activity of MoSe2 nanosheets at physiological pH by dextran modification

One-pot synthesis of dextran-modified MoSe₂ nanosheets with peroxidase-like activity at physiological pH for bio-sensing.

Design of comb-like poly(2-methyl-2-oxazoline) and its rapid co-deposition with dopamine for the study of antifouling properties

In this work, the comb-like poly(2-methyl-2-oxazoline) copolymer, poly(2-aminoethyl methacrylate-random-poly(2-methyl-2-oxazoline) (PMOXA-r-AEMA, PMA) is synthesized, and the CuSO₄/H₂O₂-triggered dopamine/PMA co-deposition process is investigated. Ellipsometry, water contact angle (WCA), and X-ray photoelectron spectroscopy (XPS) are used to characterize the thickness, hydrophilicity, and surface composition of PMA-based coatings. PMA is facilely anchored to substrates within 60 min with the assistance of dopamine/polydopamine triggered by CuSO₄/H₂O₂, and the coating thickness can achieve about 13 nm. Anti-protein adsorption and anti-blood platelet adhesion measurements are also studied to verify their antifouling properties. The adsorption capacity of FITC-BSA can be reduced to 5% of the original surface, and PMA-based coatings present excellent protein-resistant properties (∼95% reduction relative to gold surface) according to surface plasmon resonance (SPR) measurement, and it can resist adhesion of almost all blood platelets. Moreover, it is applied to a capillary inner wall for surface modification. An alkaline protein mixture and egg white proteins are successfully separated, and present excellent stability. The relative standard deviation (RSD) of migration time is lower than 0.71%. The practicability of this promising PMA-based coatings with this preparation strategy can be used for further proteomics analysis.

Co-deposition Kinetics of Polydopamine/Polyethyleneimine Coatings: Effects of Solution Composition and Substrate Surface

Polydopamine-based chemistry has been employed for various surface modifications attributed to the advantages of universality, versatility, and simplicity. Co-deposition of polydopamine (PDA) with polyethyleneimine (PEI) has then been proposed to realize one-step fabrication of functional coatings with improved morphology uniformity, surface hydrophilicity, and chemical stability. Herein, we report the co-deposition kinetics related to the solution composition with different dopamine/PEI ratios, PEI molecular weights, dopamine/PEI concentrations, and the substrate surface with varying chemistry and wettability. The addition of PEI to dopamine solution suppresses the precipitation of PDA aggregates, resulting in an expanded time window of steady co-deposition compared with that of PDA deposition. Low-molecular-weight PEI at low concentration accelerates the co-deposition process, while high-molecular-weight PEI and high concentration of either PEI or dopamine/PEI are detrimental to the co-deposition efficiency. Meanwhile, the surface morphology and chemical composition of the co-deposition coatings can be regulated by the solution conditions during co-deposition. Moreover, obvious deviations in the co-deposition rate and the amount of substrates bearing various functional groups, such as alkyl, phenyl, hydroxyl, and carboxyl, are revealed, which are quite different from PDA deposition. The initial adsorption rates further reflect the change in interactions between the aggregates and these substrates caused by PEI, which follows the sequence of carboxyl > hydroxyl > alkyl > phenyl. These results provide deep insights into the PDA/PEI co-deposition process on various substrates.

Dopamine-assisted co-deposition: An emerging and promising strategy for surface modification

Mussel-inspired chemistry based on polydopamine (PDA) deposition has been developed as a facile and universal method for the surface modification of various materials. However, the inherent shortcomings of PDA coatings still impede their practical applications in the development of functional materials. In this review, we introduce the recent progress in the emerging dopamine-assisted co-deposition as a one-step strategy for functionalizing PDA-based coatings, and improving them in the aspects of deposition rate, morphology uniformity, surface wettability and chemical stability. The co-deposition mechanisms are categorized and discussed according to the interactions of dopamine or PDA with the introduced co-component. We also emphasize the influence of these interactions on the properties of the resultant PDA-based coatings. Meanwhile, we conclude the representative potential applications of those dopamine-assisted co-deposited coatings in material science, especially including separation membranes and biomaterials. Finally, some important issues and perspectives for theoretical study and applications are briefly discussed.

Dopamine-assisted fixation of drug-loaded polymeric multilayers to osteoarticular implants for tuberculosis therapy

Currently, the major issues in the treatment of osteoarticular tuberculosis (TB) after implant placement are low drug concentration at the infected focus and drug resistance resulting from the long-term chemotherapy. The application of drug-loaded polymeric multilayers on implantable devices offers a promising solution to the problems. Herein, a poly(ethylene glycol)-based hydrogel film embedded with isoniazid (INH)-loaded alginate microparticles was fixed to Ti implants via adhesive polydopamine, subsequently capped by poly(lactic-co-glycolic acid) membranes for the sustained and localized delivery of the anti-TB drug. The antibacterial efficacy of the released INH was confirmed by a 4.5 ± 0.8 cm inhibition zone formed in the fourth week after inoculation of Mycobacterium tuberculosis. The INH-loaded Ti implants showed no toxicity to the osteoblast cell and provided a consistent drug release for nearly one week in vitro. The release profile in vivo showed a high local concentration and low systemic exposure. The local INH concentration could be kept higher than its minimum inhibitory concentration over a period of 8 weeks, which proves that it is a promising strategy to improve the severe osteoarticular TB treatment.

Antifouling membranes for sustainable water purification: strategies and mechanisms

One of the greatest challenges to the sustainability of modern society is an inadequate supply of clean water. Due to its energy-saving and cost-effective features, membrane technology has become an indispensable platform technology for water purification, including seawater and brackish water desalination as well as municipal or industrial wastewater treatment. However, membrane fouling, which arises from the nonspecific interaction between membrane surface and foulants, significantly impedes the efficient application of membrane technology. Preparing antifouling membranes is a fundamental strategy to deal with pervasive fouling problems from a variety of foulants. In recent years, major advancements have been made in membrane preparation techniques and in elucidating the antifouling mechanisms of membrane processes, including ultrafiltration, nanofiltration, reverse osmosis and forward osmosis. This review will first introduce the major foulants and the principal mechanisms of membrane fouling, and then highlight the development, current status and future prospects of antifouling membranes, including antifouling strategies, preparation techniques and practical applications. In particular, the strategies and mechanisms for antifouling membranes, including passive fouling resistance and fouling release, active off-surface and on-surface strategies, will be proposed and discussed extensively.

Effect of Catechol Content in Catechol-Conjugated Dextrans on Antiplatelet Performance

The surface coating of solid substrates using dextrans has gained a great deal of attention, because dextran-coated surfaces show excellent anti-fouling property as well as biocompatibility behavior. Much effort has been made to develop efficient methods for grafting dextrans on solid surfaces. This led to the development of catechol-conjugated dextrans (Dex-C) which can adhere to a number of solid surfaces, inspired by the underwater adhesion behavior of marine mussels. The present study is a systematic investigation of the characteristics of surface coatings developed with Dex-C. Various Dex-C with different catechol contents were synthesized and used as a surface coating material. The effect of catechol content on surface coating and antiplatelet performance was investigated.

Oxidant-Induced High-Efficient Mussel-Inspired Modification on PVDF Membrane with Superhydrophilicity and Underwater Superoleophobicity Characteristics for Oil/Water Separation

In this work, a facile one-step approach was developed to modify hydrophobic polyvinylidene fluoride (PVDF) microfiltration membrane with superhydrophilicity and underwater superoleophobicity properties via a high-efficient deposition of polydopamine (PDA) coating oxidized by sodium periodate in a slightly acidic environment (pH = 5.0). In contrast to the traditional PDA coating on hydrophobic membranes autoxidized by O₂ in a weak basic buffer solution, the superhydrophilicity and ultrahigh pure water permeability (about 11 934 L m^-2 h^-1 under 0.038 MPa) of the PDA-decorated PVDF membrane are derived from optimized chemical oxidation without postmodifications or additional reactants. The as-prepared membrane exhibits excellent oil/water separation ability evaluated by water fluxes and oil rejection ratios of various oil/water mixtures and oil-in-water emulsions. Moreover, the outstanding antifouling performance and reusability of the PDA-modified PVDF membrane provide a long-term durability for many potential applications. The modified membrane also exhibits excellent chemical stability in harsh pH environments and mechanical stability for practical applications.

Design and mechanisms of antifouling materials for surface plasmon resonance sensors

Surface plasmon resonance (SPR) biosensors have many possible applications, but are limited by sensor chip surface fouling, which blocks immobilization and specific binding by the recognizer elements. Therefore, there is a pressing need for the development of antifouling surfaces. In this paper, the mechanisms of antifouling materials were firstly discussed, including both theories (hydration and steric hindrance) and factors influencing antifouling effects (molecular structures and self-assembled monolayer (SAM) architectures, surface charges, molecular hydrophilicity, and grafting thickness and density). Then, the most recent advances in antifouling materials applied on SPR biosensors were systematically reviewed, together with the grafting strategies, antifouling capacity, as well as their merits and demerits. These materials included, but not limited to, zwitterionic compounds, polyethylene glycol-based, and polysaccharide-based materials. Finally, the prospective research directions in the development of SPR antifouling materials were discussed.

STATEMENT OF SIGNIFICANCE

Surface plasmon resonance (SPR) is a powerful tool in monitoring biomolecular interactions. The principle of SPR biosensors is the conversion of refractive index change caused by molecular binding into resonant spectral shifts. However, the fouling on the surface of SPR gold chips is ubiquitous and troublesome. It limits the application of SPR biosensors by blocking recognition element immobilization and specific binding. Hence, we write this paper to review the antifouling mechanisms and the recent advances of the design of antifouling materials that can improve the accuracy and sensitivity of SPR biosensors. To our knowledge, this is the first review focusing on the antifouling materials that were applied or had potential to be applied on SPR biosensors.

Conjugation of Hyaluronic Acid onto Surfaces via the Interfacial Polymerization of Dopamine to Prevent Protein Adsorption

A versatile, convenient, and cost-effective method that can be used for grafting antifouling materials onto different surfaces is highly desirable in many applications. Here, we report the one-step fabrication of antifouling surfaces via the polymerization of dopamine and the simultaneous deposition of anionic hyaluronic acid (HA) on Au substrates. The water contact angle of the Au surfaces decreased from 84.9° to 24.8° after the attachment of a highly uniform polydopamine (PDA)/HA hybrid film. The results of surface plasmon resonance analysis showed that the Au-PDA/HA surfaces adsorbed proteins from solutions of bovine serum albumin, lysozyme, β-lactoglobulin, fibrinogen, and soybean milk in ultralow or low amounts (4.8-31.7 ng/cm(2)). The hydrophilicity and good antifouling performance of the PDA/HA surfaces is attributable to the HA chains that probably attached onto their upper surface via hydrogen bonding between PDA and HA. At the same time, the electrostatic repulsion between PDA and HA probably prevents the aggregation of PDA, resulting in the formation of a highly uniform PDA/HA hybrid film with the HA chains (with a stretched structure) on the upper surface. We also developed a simple method for removing this PDA/HA film and recycling the Au substrates by using an aqueous solution of NaOH as the hydrolyzing agent. The Au surface remained undamaged, and a PDA/HA film could be redeposited on the surface, with the surface exhibiting good antifouling performance even after 10 such cycles. Finally, it was found that this grafting method is applicable to other substrates, including epoxy resins, polystyrene, glass, and steel, owing to the strong adhesion of PDA with these substrates.

Recent developments in poly(dopamine)-based coatings for biomedical applications

The success of polymer coatings for biomedical applications is undeniable. Among the very successful examples are poly(dopamine) (PDA) films due to their simplicity in deposition and beneficial interaction with biomolecules and cells. The aim of this review is to highlight the findings and achievement of PDA in nanomedicine since 2011. We discuss the progress that has been made to elucidate the structure of PDA and novel aspects considering the assembly of PDA-based films on diverse substrates. We highlight the newest results considering the biological evaluation PDA-based coatings to control cell behavior and the use of PDA in biosensing. The popularity of PDA remains unchanged, but the research efforts start to be consolidated toward more specific aims and clinical applications.

Mussel-Inspired Hybrid Coatings that Transform Membrane Hydrophobicity into High Hydrophilicity and Underwater Superoleophobicity for Oil-in-Water Emulsion Separation

We first report here mussel-inspired, hybrid coatings formed in a facile manner via simultaneous polymerization of mussel-inspired dopamine and hydrolysis of commercial tetraethoxysilane in a single-step process. The hybrid coatings can firmly adhered on hydrophobic polyvinylidene fluoride (PVDF) substrate, and the hydrophilicity of the coating can be tuned by adjusting silane concentration. The reason for the changed hydrophilicity of the coating is disclosed by a series of characterization, and was applied to rationally design optimized hybrid coatings that transform commercial PVDF microfiltration (MF) membrane hydrophobicity into high hydrophilicity with excellent water permeability and underwater superoleophobicity for oil-in-water emulsion separation. The PVDF MF membrane decorated with optimized coatings has ultrahigh water flux (8606 L m(-2) h(-1) only under 0.9 bar, which is 34 times higher than that of pristine membrane), highly efficient oil-in-water emulsion separation ability at atmospheric pressure (filtrate flux of 140 L m(-2) h(-1)) and excellent antifouling performance. More importantly, these membranes are extremely stable as underwater superoleophobicity are maintained, even after rigorous washings or cryogenic bending, disclosing outstanding stability. The simplicity and versatility of this novel mussel-inspired one-step strategy may bridge the material-induced technology gap between academia and industry, which makes it promising for eco-friendly applications.

Improving osteointegration and osteogenesis of three-dimensional porous Ti6Al4V scaffolds by polydopamine-assisted biomimetic hydroxyapatite coating

Titanium alloys with various porous structures can be fabricated by advanced additive manufacturing techniques, which are attractive for use as scaffolds for bone defect repair. However, modification of the scaffold surfaces, particularly inner surfaces, is critical to improve the osteointegration of these scaffolds. In this study, a biomimetic approach was employed to construct polydopamine-assisted hydroxyapatite coating (HA/pDA) onto porous Ti6Al4V scaffolds fabricated by the electron beam melting method. The surface modification was characterized with the field emission scanning electron microscopy, energy dispersive spectroscopy, water contact angle measurement, and confocal laser scanning microscopy. Attachment and proliferation of MC3T3-E1 cells on the scaffold surface were significantly enhanced by the HA/pDA coating compared to the unmodified surfaces. Additionally, MC3T3-E1 cells grown on the HA/pDA-coated Ti6Al4V scaffolds displayed significantly higher expression of runt-related transcription factor-2, alkaline phosphatase, osteocalcin, osteopontin, and collagen type-1 compared with bare Ti6Al4V scaffolds after culture for 14 days. Moreover, microcomputed tomography analysis and Van-Gieson staining of histological sections showed that HA/pDA coating on surfaces of porous Ti6Al4V scaffolds enhanced osteointegration and significantly promoted bone regeneration after implantation in rabbit femoral condylar defects for 4 and 12 weeks. Therefore, this study provides an alternative to biofunctionalized porous Ti6Al4V scaffolds with improved osteointegration and osteogenesis functions for orthopedic applications.

Polydopamine-assisted deposition of heparin for selective adsorption of low-density lipoprotein

Low-density lipoprotein (LDL) is the main carrier of blood cholesterol, with elevated levels of LDL increasing the risk of atherosclerosis.

Star-shaped poly(2-methyl-2-oxazoline)-based films: rapid preparation and effects of polymer architecture on antifouling properties

Star-shaped poly(2-methyl-2-oxazoline)-based films prepared through polydopamine-assistance provided enhanced antifouling properties than the linear ones, and showed superior stability than PEG films.