Self-Polymerization of Dopamine in Acidic Environments without Oxygen

Novel microfluidic development of pH-responsive hybrid liposomes: In vitro and in vivo assessment for enhanced wound Healing

Wound healing is a complex biological process crucial for tissue repair, especially in chronic wounds where healing is impaired. Liposomes have emerged as promising vehicles for delivering therapeutics to facilitate wound repair. Liposomes have been explored as effective carriers for therapeutic agents. However, traditional methods of liposome preparation face significant challenges, particularly in achieving consistent stability and precise control over drug encapsulation and release. This study addresses these challenges by pioneering the development of Hybrid Liposomes (HLPs) using microfluidic technology, which provides more controlled characteristics through precisely managed formulation parameters. Notably, the formation of Polydopamine (PDA) polymer within HLPs facilitates pH-responsive drug release, making them well-suited for acidic wound environments. Furthermore, surface modification with Folic Acid (FA) enhances cellular interaction with the HLPs. In vitro and in vivo studies demonstrate the efficacy of HLPs loaded with Hyaluronic Acid (HA) or Phenytoin (PHT) in promoting wound healing. Microfluidics optimizes the stability of HLPs over 90 days, underscoring their potential as a potent, antibiotic-free drug delivery system. In conclusion, this research advances the understanding of microfluidic optimization for HLPs, offering cutting-edge drug delivery systems. The transformative potential of targeted HLPs through microfluidics holds promise for revolutionizing wound healing and inspires optimism for effective therapeutic interventions.

Mussel-Inspired, Self-Healing, Highly Effective Fully Polymeric Fire-Retardant Coatings Enabled by Group Synergy

Fire-retardant coatings represent a universal cost-effective approach to providing fire protection for various substrates without compromising substrates' bulk properties. However, it has been attractive yet highly challenging to create waterborne polymeric fire-retardant coatings combining high-efficiency, generally strong adhesion, and self-repairability due to a lack of rational design principles. Inspired by mussel's unique adhesive, self-healing, and char-forming mechanisms, herein, a "group synergy" design strategy is proposed to realize the combination of self-healing, strong adhesion, and high efficiency in a fully polymeric fire-retardant coating via multiple synergies between catechol, phosphonic, and hydroxyethyl groups. As-created fire-retardant coating exhibits a rapid room-temperature self-healing ability and strong adhesion to (non)polar substrates due to multiple dynamic non-covalent interactions enabled by these groups. Because these functional groups enable the formation of a robust structurally intact yet slightly expanded char layer upon exposure to flame, a 200 µm-thick such coating can make extremely flammable polystyrene foam very difficult to ignite and self-extinguishing, which far outperforms previous strategies. Moreover, this coating can provide universal exceptional fire protection for a variety of substrates from polymer foams, and timber, to fabric and steel. This work presents a promising material design principle to create next-generation sustainable high-performance fire-retardant coatings for general fire protection.

Preparation and characterization of mussel-inspired chitosan/polydopamine films and their feasibility for oral mucosa application

Oral mucosal lesions (OML), which represent a major public health issue worldwide, include any pathological changes in the oral mucosa, such as ulcers, pigmentation, and swelling. Due to its humid and dynamic complex environment, designing oral mucosal preparations poses significant challenges. Drawing inspiration from mussels, this study employed an eco-friendly one-pot strategy for the preparation of chitosan/polydopamine (CS/PDA) films. We demonstrated that CS-induced polymerization of dopamine monomers under acidic conditions, which might be attributed to the large number of hydrogen bonding sites of CS chains. PDA markedly enhances properties of the CS film and exhibits concentration dependence. At the concentration of 1 wt% PDA, the lap-shear strength and tensile strength of CS/PDA films reached 5.01 ± 0.24 kpa and 4.20 ± 0.78 kpa, respectively, indicating that the mucosal adhesion ability was significantly improved. In comparison with the single CS film, the swelling rate of CS/PDA film decreased by about 30 %. Rheological results also showed that the storage modulus returned to 93 % after cyclic large strain, while the single CS film only recovered to 73 %. Moreover, these films demonstrated good biocompatibility and enhanced oral ulcer healing in rats, providing a new and practical option for the local treatment of OML.

Multifunctional Natural and Synthetic Melanin for Bioelectronic Applications: A Review

Emerging material interest in bioelectronic applications has highlighted natural melanin and its derivatives as promising alternatives to conventional synthetic conductors. These materials, traditionally noted for their adhesive, antioxidant, biocompatible, and biodegradable properties, have barely been used as conductors due to their extremely low electrical activities. However, recent studies have demonstrated good conductive properties in melanin materials that promote electronic-ionic hybrid charge transfer, attributed to the formation of an extended conjugated backbone. This review examines the multifunctional properties of melanin materials, focusing on their chemical and electrochemical synthesis and their resulting structure-property-function relationship. The wide range of bioelectronic applications will also be presented to highlight their importance and potential to expand into new design concepts for high-performance electronic functional materials. The review concludes by addressing the current challenges in utilizing melanin for biodegradable bioelectronics, providing a perspective on future developments.

Nature-inspired adhesive systems

Many organisms in nature thrive in intricate habitats through their unique bio-adhesive surfaces, facilitating tasks such as capturing prey and reproduction. It's important to note that the remarkable adhesion properties found in these natural biological surfaces primarily arise from their distinct micro- and nanostructures and/or chemical compositions. To create artificial surfaces with superior adhesion capabilities, researchers delve deeper into the underlying mechanisms of these captivating adhesion phenomena to draw inspiration. This article provides a systematic overview of various biological surfaces with different adhesion mechanisms, focusing on surface micro- and nanostructures and/or chemistry, offering design principles for their artificial counterparts. Here, the basic interactions and adhesion models of natural biological surfaces are introduced first. This will be followed by an exploration of research advancements in natural and artificial adhesive surfaces including both dry adhesive surfaces and wet/underwater adhesive surfaces, along with relevant adhesion characterization techniques. Special attention is paid to stimulus-responsive smart artificial adhesive surfaces with tunable adhesive properties. The goal is to spotlight recent advancements, identify common themes, and explore fundamental distinctions to pinpoint the present challenges and prospects in this field.

Preparation and Characterization of Dopamine-Modified Carbon Fiber Paper Composites for Gas Diffusion Layers

Carbon fibers (CFs) cannot be directly used for the preparation of CF paper because of their chemically inert nature. Herein, the surface of CFs was modified using the spontaneous oxidative self-polymerization of dopamine. By taking full advantage of the spontaneous oxidation and self-polymerization properties of PD to maintain the maximum strength of CFs, a polydopamine-modified CF paper (PDA-CFP) with excellent performance was prepared using PD-modified CFs (PDA-CFs). This increased the proportion of hydrophilic functional groups on the surface of carbon fibers, increased the O/C ratio on the CF surface by 6 times, and improved the bond strength between the modified CF and the adhesive by making full use of the interaction force between polydopamine and PVA fibers. In this way, the primary properties of the CF paper were improved. Overall, the results showed that the dispersion of CF was considerably improved with dopamine modification. In addition, the primary physical properties of PDA-CFP were better than those of virgin CF paper (CFP-0). PDA-CFP exhibited a maximum tensile strength of 2.04 kN·m-1, a minimum resistivity of 0.06055 Ω·cm-1, and a minimum porosity of 72.4%. The tightness was increased by up to 12.1%.

Felix D, Yeh HH, Luo HD, Moskalev I, Wang Q, Wang R, Grecov D, Fazli L, Lange D, Kizhakkedathu JN. Robust Nanoparticle-Derived Lubricious Antibiofilm Coating for Difficult-to-Coat Medical Devices with Intricate Geometry

A major medical device-associated complication is the biofilm-related infection post-implantation. One promising approach to prevent this is to coat already commercialized medical devices with effective antibiofilm materials. However, developing a robust high-performance antibiofilm coating on devices with a nonflat geometry remains unmet. Here, we report the development of a facile scalable nanoparticle-based antibiofilm silver composite coating with long-term activity applicable to virtually any objects including difficult-to-coat commercially available medical devices utilizing a catecholic organic-aqueous mixture. Using a screening approach, we have identified a combination of the organic-aqueous buffer mixture which alters polycatecholamine synthesis, nanoparticle formation, and stabilization, resulting in controlled deposition of in situ formed composite silver nanoparticles in the presence of an ultra-high-molecular-weight hydrophilic polymer on diverse objects irrespective of its geometry and chemistry. Methanol-mediated synthesis of polymer-silver composite nanoparticles resulted in a biocompatible lubricious coating with high mechanical durability, long-term silver release (∼90 days), complete inhibition of bacterial adhesion, and excellent killing activity against a diverse range of bacteria over the long term. Coated catheters retained their excellent activity even after exposure to harsh mechanical challenges (rubbing, twisting, and stretching) and storage conditions (>3 months stirring in water). We confirmed its excellent bacteria-killing efficacy (>99.999%) against difficult-to-kill bacteria (Proteus mirabilis) and high biocompatibility using percutaneous catheter infection mice and subcutaneous implant rat models, respectively, in vivo. The developed coating approach opens a new avenue to transform clinically used medical devices (e.g., urinary catheters) to highly infection-resistant devices to prevent and treat implant/device-associated infections.

Mussel-Inspired Two-Dimensional Halide Perovskite Facilitated Dopamine Polymerization and Self-Adhesive Photoelectric Coating

Polydopamine (PDA) is a good adhesion agent for lots of gels inspired by the mussel, whereas hybrid organic-inorganic perovskites (HOIPs) usually exhibit extraordinary optoelectronic performance. Herein, mussel-inspired chemistry has been integrated with two-dimensional HOIPs first, leading to the preparation of new crystal (HDA)₂PbBr₄ (1) (DA = dopamine). The organic cation dopamine can be introduced into PDA resulting in a thin film of (HPDA)₂PbBr₄ (PDA-1). The dissolved inorganic components of layered perovskite in DMF solution together with H₂O₂ addition can facilitate DA polymerization greatly. More importantly, PDA-1 can inherit an excellent semiconductor property of HOIPs and robust adhesion of the PDA hydrogel resulting in a self-adhesive photoelectric coating on various interfaces.

Design, synthesis, and characterization of a novel dual cross-linked gelatin-based bioadhesive for hard and soft tissues adhesion capability

Many surgical treatments require a suitable tissue adhesive that maintains its performance in wet conditions and can be applied simultaneously for hard and soft tissues. In the present study, a dual cross-linked tissue adhesive was synthesized by mixing the gelatin methacryloyl (Gel-MA) and gelatin-dopamine conjugate (Gel-Dopa). The setting reaction was based on a photopolymerization process in the presence of a combination of riboflavin and triethanolamine and a chemical cross-linking process attributed to the genipin as a natural cross-linker. Modified gelatin macromolecules were characterized and the best wavelength for free radical generation in the presence of riboflavin was obtained. Tissue adhesives were prepared with 30% hydrogels of Gel-MA and Gel-Dopa with different ratios in distilled water. The gelation occurred in a short time after light irradiation. The chemical, mechanical, physical, and cytotoxicity properties of the tissue adhesives were evaluated. The results showed that despite photopolymerization, chemical crosslinking with genipin played a more critical role in the setting process. Water uptake, degradation behavior, cytotoxicity, and adhesion properties of the adhesives were correlated with the ratio of the components. The SEM images showed a porous structure that could ensure the entry of cells and nutrients into the surgical area. While acceptable properties in most experiments were observed, all features were improved as the Gel-Dopa ratio increased. Also, the obtained hydrogels revealed excellent adhesive properties, particularly with bone even after wet incubation, and it was attributed to the amount of gelatin-dopamine conjugate. From the obtained results, it was concluded that a dual adhesive hydrogel based on gelatin macromolecules could be a good candidate as a tissue adhesive in wet condition.

Mussel-inspired biomaterials: From chemistry to clinic

After several billions of years, nature still makes decisions on its own to identify, develop, and direct the most effective material for phenomena/challenges faced. Likewise, and inspired by the nature, we learned how to take steps in developing new technologies and materials innovations. Wet and strong adhesion by Mytilidae mussels (among which Mytilus edulis-blue mussel and Mytilus californianus-California mussel are the most well-known species) has been an inspiration in developing advanced adhesives for the moist condition. The wet adhesion phenomenon is significant in designing tissue adhesives and surgical sealants. However, a deep understanding of engaged chemical moieties, microenvironmental conditions of secreted proteins, and other contributing mechanisms for outstanding wet adhesion mussels are essential for the optimal design of wet glues. In this review, all aspects of wet adhesion of Mytilidae mussels, as well as different strategies needed for designing and fabricating wet adhesives are discussed from a chemistry point of view. Developed muscle-inspired chemistry is a versatile technique when designing not only wet adhesive, but also, in several more applications, especially in the bioengineering area. The applications of muscle-inspired biomaterials in various medical applications are summarized for future developments in the field.

Anticancer efficacy of endo- and exogenous potent ligands acting at dopaminergic receptor-expressing cancer cells

Cancer is one of the most common and dreaded diseases affecting the vastness of society. Unfortunately, still some people die especially when cancer is not diagnosed and thus caught early enough. On the other hand, using available chemo- or radiotherapy may result in serious side effects. Therefore, cancer-specific medications seem to be the most desired and safe therapy. Knowing that some cancers are characterized by overexpression of specific receptors on the cell surface, target-mediated drugs could serve as a unique and effective form of therapy. In line with this, recently dopaminergic receptors were presented important in cancer therapy as several dopaminergic ligands revealed their efficacy in tumor growth reduction as well as in apoptosis mediation. Unfortunately, the indication of whether DA receptor agonists or antagonists are the best choices in cancer treatment is quite difficult, since both of them may exert either pro- or anticancer effects. In this review, we analyze the therapeutic efficacy of compounds, both of exogenous and endogenous origin, targeting dopaminergic receptor-expressing cancers.

Combining heteronuclear correlation NMR with spin-diffusion to detect relayed Cl-H-H and N-H-H proximities in molecular solids

Analysis of short-to-intermediate range intermolecular interactions offers a great way of characterizing the solid-state organization of small molecules and materials. This can be achieved by two-dimensional (2D) homo- and heteronuclear correlation NMR spectroscopy, for example, by carrying out experiments at high magnetic fields in conjunction with fast magic-angle spinning (MAS) techniques. But, detecting 2D peaks for heteronuclear dipolar coupled spin pairs separated by greater than 3 Å is not always straightforward, particularly when low-gamma quadrupolar nuclei are involved. Here, we present a 2D correlation NMR experiment that combines the advantages of heteronuclear-multiple quantum coherence (HMQC) and proton-based spin-diffusion (SD) pulse sequences using radio-frequency-driven-recouping (RFDR) to probe inter and intramolecular ¹H-X (X = ¹⁴N, ³⁵Cl) interactions. This experiment can be used to acquire 2D ¹H{X}-HMQC filtered ¹H-¹H correlation as well as 2D ¹H-X HMQC spectra. Powder forms of dopamine·HCl and l-histidine·HCl·H₂O are characterized at high fields (21.1 T and 18.8 T) with fast MAS (60 kHz) using the 2D HMQC-SD-RFDR approach. Solid-state NMR results are complemented with NMR crystallography analyses using the gauge-including projector augmented wave (GIPAW) approach. For histidine·HCl·H₂O, 2D peaks associated with ¹⁴N-¹H-¹H and ³⁵Cl-¹H-¹H distances of up to 4.4 and 3.9 Å have been detected. This is further corroborated by the observation of 2D peaks corresponding to ¹⁴N-¹H-¹H and ³⁵Cl-¹H-¹H distances of up to 4.2 and 3.7 Å in dopamine·HCl, indicating the suitability of the HMQC-SD-RFDR experiments for detecting medium-range proximities in molecular solids.

Bioinspired, Ultra-fast Polymerization of Dopamine Under Mild Conditions

Spontaneous oxidative polymerization of dopamine (DA) has been widely exploited as a facile and versatile method for surface modification. However, the reaction is very slow and only occurs in alkaline solutions, which severely limit its applications. Herein we report that the reaction can be dramatically accelerated by using Fe²⁺ as catalyst. While it takes hours and days using conventional method, the Fe²⁺ -catalyzed reaction finishes almost immediately at pH 7.0. In addition, under the catalysis of Fe²⁺ , the reaction can occur at a pH down to 4.0. The fast Fe²⁺ -catalyzed polymerization of DA leads to fast deposition of polydopamine (PDA) coating, thus allowing fast surface modification and textile dyeing. The Fe²⁺ -catalyzed reaction also allows spatial control over the PDA deposition. The fast, simple and mild surface modification method developed here will find applications in numerous fields. This article is protected by copyright. All rights reserved.

Transformation of L-DOPA and Dopamine on the Surface of Gold Nanoparticles: An NMR and Computational Study

Gold nanoparticles (AuNPs) have found applications in biomedicine as diagnostic tools, but extensive research efforts have been also directed toward their development as more efficient drug delivery agents. The high specific surface area of AuNPs may provide dense loading of molecules like catechols (L-DOPA and dopamine) on nanosurfaces, enabling functionalization strategies for advancing conventional therapy and diagnostic approaches of neurodegenerative diseases. Despite numerous well-described procedures in the literature for preparation of different AuNPs, possible transformation and structural changes of surface functionalization agents have not been considered thoroughly. As a case in point, the catechols L-DOPA and dopamine were selected because of their susceptibility to oxidation, cyclization, and polymerization. To assess the fate of coating and functionalization agents during the preparation of AuNPs or interaction at the nano-bio interface, a combination of spectroscopy, light scattering, and microscopy techniques was used while structural information and reaction mechanism were obtained by NMR in combination with computational tools. The results revealed that the final form of catechol on the AuNP nanosurface depends on the molar ratio of Au used for AuNP preparation. A large molar excess of L-DOPA or dopamine is needed to prepare AuNPs funtionalized with fully reduced catechols. In the case of molar excess of Au, the oxidation of catechols to dopamine quinone and dopaquinone was promoted, and dopaquinone underwent intramolecular cyclization in which additional oxidation products, leukodopachrome, dopachrome, or its tautomer, were formed because of the larger intrinsic acidity of the more nucleophilic amino group in dopaquinone. MD simulations showed that, of the oxidation products, dopachrome had the highest affinity for binding to the AuNPs surface. The results highlight how a more versatile methodological approach, combining experimental and in silico techniques, allows more reliable characterization of binding events at the surface of AuNPs for possible applications in biomedicine.

Detection of pesticides in food products using paper-based devices by UV-induced fluorescence spectroscopy combined with molecularly imprinted polymers

In this proof-of-concept study, we explore the detection of pesticides in food using a combined power of sensitive UV-induced fingerprint spectroscopy with selective capture by molecularly imprinted polymers (MIPs) and portable cost-effective paper-based analytical devices (PADs). The specific pesticides used herein as model compounds (both pure substances and their application products for spraying), were: strobilurins (i.e. trifloxystrobin), urea pesticides (rimsulfuron), pyrethroids (cypermethrine) and aryloxyphenoxyproponic acid herbicides (Haloxyfop-methyl). Commercially available spraying formulations containing the selected pesticides were positively identified by MIP-PADs swabs of sprayed apple and tomato. The key properties of MIP layer - imprinting factor (IF) and selectivity factor (α) were characterized using trifloxystrobin (IF-3.5, α-4.4) was demonstrated as a potential option for in-field application. The presented method may provide effective help with in-field testing of food and reveal problems such as false product labelling.

Polydopamine Biomaterials for Skin Regeneration

Designing biomaterials capable of biomimicking wound healing and skin regeneration has been receiving increasing attention recently. Some biopolymers behave similarly to the extracellular matrix (ECM), supporting biointerfacial adhesion and intrinsic cellular interactions. Polydopamine (PDA) is a natural bioadhesive and bioactive polymer that endows high chemical versatility, making it an exciting candidate for a wide range of biomedical applications. Moreover, biomaterials based on PDA and its derivatives have near-infrared (NIR) absorption, excellent biocompatibility, intrinsic antioxidative activity, antibacterial activity, and cell affinity. PDA can regulate cell behavior by controlling signal transduction pathways. It governs the focal adhesion behavior of cells at the biomaterials interface. These features make melanin-like PDA a fascinating biomaterial for wound healing and skin regeneration. This paper overviews PDA-based biomaterials' synthesis, properties, and interactions with biological entities. Furthermore, the utilization of PDA nano- and microstructures as a constituent of wound-dressing formulations is highlighted.

Synthesis of soluble melanin nanoparticles under acidic conditions using Burkholderia cepacia tyrosinase and their characterization

Melanin nanoparticles (MNPs) used for biomedical applications are often synthesized via the chemical auto-oxidation of catecholic monomers such as dopamine and 3,4-dihydroxyphenylalanine (DOPA) under alkaline conditions. However, the synthetic method for the chemical synthesis of MNP (cMNP) is relatively straightforward and more robust to control their homogenous particle size and morphology than the corresponding enzymatic synthetic methods. In this study, we demonstrated that the simple enzymatic synthesis of MNPs (eMNPs) with homogenous and soluble (<20 nm diameter) properties is possible using dopamine and Burkholderia cepacia tyrosinase (BcTy) under acidic conditions (i.e., pH 3.0). BcTy was highly reactive under pH 5.0, where the natural and chemical oxidation of catechol is complex, and thus melanin was synthesized via the hydroxylation of phenolic substrates. The detailed chemical analysis and characterization of the physical properties of the eMNPs confirmed the higher preservation of the catechol and primary amine moieties in the monomer substrate such as dopamine under acidic conditions. The eMNPs showed enhanced antioxidant activity and conferred stickiness to the formed hydrogel compared to the chemical auto-oxidation method owing to the large number of hydroxyl groups remaining such as catechol and quinone moieties. Because of these advantages and characteristics, the synthesis of MNPs using BcTy under acidic conditions can open a new path for their biomedical applications.

Melanin nanoparticles (MNPs) used for biomedical applications are often synthesized via the chemical auto-oxidation of catecholic monomers such as dopamine and 3,4-dihydroxyphenylalanine (DOPA) under alkaline conditions.

Rational design of two-dimensional flaky Fe/void/C composites for enhanced microwave absorption properties

Owing to their unique electromagnetic properties and structure anisotropy, two-dimensional (2D) magnetic metal flakes are attracting special attention for applications as microwave absorption materials. However, the conductive network formed by the connected metal flakes may lead to impedance mismatching and reduced performance. In this study, a facile and rational strategy was developed to fabricate yolk-shell-structured 2D flaky Fe/void/C composites by using α-Fe₂O₃ hexagonal flakes as the template, followed by the coating of polydopamine (PDA) on the composite surface and calcination under H₂/Ar. The volume shrinkage from Fe₂O₃ to Fe and PDA to carbon led to the formation of several irregular holes in Fe flakes and void space between the Fe cores and carbon cages. The thickness of carbon cages of the composites can be tailored by the simple modulation of the synthetic parameters. As a result of the synergistic effects of multiple chemical components, the shape anisotropy of iron flakes, and unique yolk-shell structures, the optimized sample exhibited excellent microwave absorption properties. With a matching thickness of only 1.6 mm, the strongest reflection loss (RL) was up to -27.80 dB at 14.72 GHz, and the effective absorption bandwidth (EAB, RL < -10 dB) reached 6.40 GHz (11.60-18.00 GHz), which can cover the whole Ku-band. This study provides a novel approach to adjust and balance the permeability and permittivity of 2D magnetic metal flakes, which may promote the practical applications of flaky magnetic metal materials in microwave absorption.

High-Precision Micropatterning of Polydopamine by Multiphoton Lithography

Mussel-inspired polydopamine (PDA) initiates a multifunctional modification route that leads to the generation of novel advanced materials and their applications. However, existing PDA deposition techniques still exhibit poor spatial control, have a very limited capability of micropatterning, and do not allow local tuning of the PDA topography. Herein, PDA deposition based on multiphoton lithography (MPL) is demonstrated, which enables full spatial and temporal control with nearly total freedom of patterning design. Using MPL, 2D microstructures of complex design are achieved with pattern precision of 0.8 µm without the need of a photomask or stamp. Moreover, this approach permits adjusting the morphology and thickness of the fabricated microstructure within one deposition step, resulting in a unique tunability of material properties. The chemical composition of PDA is confirmed and its ability for protein enzyme immobilization is demonstrated. This work presents a new methodology for high-precision and complete control of PDA deposition, enabling PDA incorporation in applications where fine and precise local surface functionalization is required. Possible applications include multicomponent functional elements and devices in microfluidics or lab-on-a-chip systems.

Recent Advances in Intrinsically Fluorescent Polydopamine Materials

Fluorescence nanoparticles have gained much attention due to their unique properties in the sensing and imaging fields. Among the very successful candidates are fluorescent polydopamine (FPDA) nanoparticles, attributed to their simplicity in tracing and excellent biocompatibility. This article aims to highlight the recent achievements in FPDA materials, especially on the part of luminescence mechanisms. We focus on the intrinsic fluorescence of PDA and will not discuss fluorescent reaction with a fluorometric reagent or coupling reaction with a fluorophore, which may cause more in vivo interferences. We believe that intrinsic FPDA presents great potential in bioapplications.

Tunable Properties of Polydopamine Nanoparticles and Coated Surfaces

Polydopamine (PDA) nanoparticles and PDA-coated surfaces have wide applications due to PDA's unique reactivity and efficient coating ability on nearly any surface. However, challenges in manipulating and controlling dopamine polymerization and thus the PDA nanoparticle formations and surface coatings still exist. Here, dopamine with a tetraborate (borax)-protected catechol group was utilized to tune the properties of PDA nanoparticles and PDA coatings. This method allows us to (1) synthesize PDA nanoparticles with a narrow size distribution and low aggregation and (2) create surface coating with the desired PDA layer thickness and varying water contact angles. PDA nanoparticles and PDA-coated surfaces of varying but tunable chemical and physical properties will find wide applications. For example, such PDA-coated surfaces were successfully used to construct Ag nanoparticle patterned surfaces with varying Ag particle sizes and densities.

Nafion Composite Membranes Impregnated with Polydopamine and Poly(Sulfonated Dopamine) for High-Performance Proton Exchange Membranes

We prepared Nafion composite membranes by impregnating Nafion-212 with polydopamine, poly(sulfonated dopamine), and poly(dopamine-co-sulfonated dopamine) using the swelling-filling method to generate nanopores in the Nafion framework that were filled with these polymers. Compared to the pristine Nafion-212 membrane, these composite membranes showed improved thermal and mechanical stabilities due to the strong interactions between the catecholamine of the polydopamine derivatives and the Nafion matrix. For the composite membrane filled with poly(sulfonated dopamine) (N-PSDA), further interactions were induced between the Nafion and the sulfonic acid side chain, resulting in enhanced water uptake and ion conductivity. In addition, filling the nanopores in the Nafion matrix with polymer fillers containing aromatic hydrocarbon-based dopamine units led to an increase in the degree of crystallinity and resulted in a significant decrease in the hydrogen permeability of the composite membranes compared to Nafion-212. Hydrogen crossovers 26.8% lower than Nafion-212 at 95% relative humidity (RH) (fuel cell operating conditions) and 27.3% lower at 100% RH (water electrolysis operating conditions) were obtained. When applied to proton exchange membrane-based fuel cells, N-PSDA exhibited a peak power density of 966 mW cm^-2, whereas N-PSDA showed a current density of 4785 mA cm^-2, which is 12.4% higher than Nafion-212 at 2.0 V and 80 °C.

Optimization and Antibacterial Response of N-Halamine Coatings Based on Polydopamine

Due to the ability of microorganisms to first adhere to a material surface and then to lead to the formation of a biofilm, it is essential to develop surfaces that have antimicrobial properties. It is well known that N-halamine coatings allow us to prevent or minimize such phenomena. In the present work, various polydopamine (PDA) coatings containing chloramine functions were studied. In fact, three PDA-based films were formed by the simple immersion of a gold substrate in a dopamine solution, either at pH 8 in the presence or not of polyethyleneimine (PEI), or at pH 5 in the presence of periodate as an oxidant. These films were characterized by polarization modulation reflection absorption infrared spectroscopy and X-ray photoelectron spectroscopy analyses, and by scanning electron microscopy observations. The chlorination of these PDA films was performed by their immersion in a sodium hypochlorite aqueous solution, in order to immobilize Cl(+I) into the (co)polymers (PDA or PDA–PEI). Finally, antibacterial assays towards the Gram-negative bacteria Escherichia coli (E. coli) and the Gram-positive bacteria Staphylococcus epidermidis (S. epidermidis) were conducted to compare the bactericidal properties of these three N-halamine coatings. Regardless of the bacteria tested, the PDA coating with the best antibacterial properties is the coating obtained using periodate.

Dopamine-Initiated Photopolymerization for a Versatile Catechol-Functionalized Hydrogel

Biomimetic catechol-functionalized hydrogels have attracted substantial attention due to their potential in a variety of biomedical applications, such as tissue repair and regeneration, drug delivery, and antimicrobial and antifouling applications. In this study, a one-pot strategy for fabrication of functional catecholic hydrogels using dopamine as a photoinitiator was developed. Under UV irradiation in an acidic solution, dopamine generates free radicals, likely semiquinone radicals, to trigger the addition polymerization, following pseudo-first-order kinetics. The dopamine-initiated photopolymerization provides a straightforward and facile approach and, in addition, prevents the undesirable oxidation to catecholic groups. Superhydrophilic sulfobetaine methacrylate (SBMA) was applied for developing biocompatible hydrogels. ¹H nuclear magnetic resonance, UV-vis spectroscopy, gel permeation chromatography, and rheological studies were conducted to explore the polymerization mechanism and optimal experimental conditions in terms of pH, UV doses, and the concentration of dopamine. The unique properties of the resultant catechol-functionalized pSBMA hydrogels were demonstrated by enhanced mechanical properties through metal-catechol complexation, self-healing and injectable capability, high adhesiveness, and fouling resistance. Consequently, the synthetic strategy to design catecholic hydrogels can leverage the use of dopamine in a variety of applications.

Recent Advances in Antioxidant Polymers: From Sustainable and Natural Monomers to Synthesis and Applications

Advances in technology have led to the production of sustainable antioxidants and natural monomers for food packaging and targeted drug delivery applications. Of particular importance is the synthesis of lignin polymers, and graft polymers, dopamine, and polydopamine, inulin, quercetin, limonene, and vitamins, due to their free radical scavenging ability, chemical potency, ideal functional groups for polymerization, abundance in the natural environment, ease of production, and activation of biological mechanisms such as the inhibition of the cellular activation of various signaling pathways, including NF-κB and MAPK. The radical oxygen species are responsible for oxidative damage and increased susceptibility to cancer, cardiovascular, degenerative musculoskeletal, and neurodegenerative conditions and diabetes; such biological mechanisms are inhibited by both synthetic and naturally occurring antioxidants. The orientation of macromolecules in the presence of the plasticizing agent increases the suitability of quercetin in food packaging, while the commercial viability of terpenes in the replacement of existing non-renewable polymers is reinforced by the recyclability of the precursors (thyme, cannabis, and lemon, orange, mandarin) and marginal ecological effect and antioxidant properties. Emerging antioxidant nanoparticle polymers have a broad range of applications in tumor-targeted drug delivery, food fortification, biodegradation of synthetic polymers, and antimicrobial treatment and corrosion inhibition. The aim of the review is to present state-of-the-art polymers with intrinsic antioxidant properties, including synthesis scavenging activity, potential applications, and future directions. This review is distinct from other works given that it integrates different advances in antioxidant polymer synthesis and applications such as inulin, quercetin polymers, their conjugates, antioxidant-graft-polysaccharides, and polymerization vitamins and essential oils. One of the most comprehensive reviews of antioxidant polymers was published by Cirillo and Iemma in 2012. Since then, significant progress has been made in improving the synthesis, techniques, properties, and applications. The review builds upon existing research by presenting new findings that were excluded from previous reviews.

Ultrasound expands the versatility of polydopamine coatings

Polydopamine (PDA) coating of surfaces is a versatile strategy to fabricate functional films on various substrates, which typically requires oxygen and alkaline pH. Overcoming such limitations may enhance the versatility of this technique. Herein, we develop a simple and green sonochemical process for PDA coatings, which overcomes the limitations of traditional coating technique and expands the versatility of PDA chemistry. The oxidizing radicals generated by high frequency ultrasound (412 kHz) are utilized to initiate and accelerate the polymerization of dopamine. The sonochemical rate of film deposition is found to be about twice faster than that of the traditional method in the presence of oxygen. Importantly, the PDA coatings can be obtained in neutral or acidic aqueous solutions and even in the absence of oxygen. The PDA coatings can be moderated by turning on or off high frequency ultrasound. This study provides an environmentally friendly and economic method for the engineering of PDA coatings independent of the solution pH and nature of dissolved gas.

Detection of microbial contamination based on uracil-selective synthetic receptors

The here presented work is focused on the development of a method for detection of microbial contamination of food based on uracil-selective synthetic receptors. Because uracil may serve as an indicator of bacterial contamination, its selective and on-site detection may prevent spreading of foodborne diseases. The synthetic receptors were created by molecular imprinting. Molecularly imprinted polymers for selective uracil isolation were prepared by a non-covalent imprinting method using dopamine as a functional monomer. Detection of isolated uracil was performed by capillary electrophoresis with absorption detection (λ - 260 nm). The conditions of preparation of molecularly imprinted polymers, their binding properties, adsorption kinetics and selectivity were investigated in detail. Furthermore, the prepared polymer materials were used for selective isolation and detection of uracil from complex samples as tomato products by miniaturized electrophoretic system suggesting the potential of in situ analysis of real samples.

Synthesis of mussel-inspired polydopamine-gallium nanoparticles for biomedical applications

Aim: To established a simple, controlled and reproducible method to synthesize gallium (Ga)-coated polydopamine (PDA) nanoparticles (NPs). Materials & methods: PDA NPs were synthesized in alkali medium with posterior Ga shell formation due to ion chelation on the NP surface. Results: The obtained results with energy-dispersive x-ray spectroscopy confirmed the incorporation of Ga on the PDA NP surface. The cytotoxicity of Ga-coated PDA NPs was evaluated in vitro at different concentrations in contact with human adipose-derived stem cells. Further cell analysis also demonstrated the benefit of Ga-coated PDA NPs, which increased the cell proliferation rate compared with noncoated PDA NPs. Conclusion: This study indicated that Ga could work as an appropriate shell for PDA NPs, inducing cell proliferation at the analyzed concentrations.

Facile and recyclable dopamine sensing by a label-free terbium(III) metal-organic framework

Herein, we present a facile strategy for dopamine (DA) sensing by a water-stable MOF of {[Tb(Cmdcp)(H₂O)₃]₂(NO₃)₂·5H₂O}_n (1, H₃CmdcpBr = N-carboxymethyl-(3,5-dicarboxyl)pyridinium bromide). Without any post-modification, MOF 1 functions as an effective fluorescent sensor for the label-free detection of DA with the detection limit of 0.41 μM (S/N = 3). Under the optimum condition of 80 °C, pH 9 for 80 min in Tris-HCl with natural ambient oxygen, DA polymerizes to give polydopamine (pDA), which adheres to the surface of MOF 1 and quenched its green luminescence thoroughly. The sensing process is visible to naked eyes under 365 nm UV light irradiation due to the partial overlap of its excitation spectrum with the absorption spectrum of pDA. The sensing process is not interfered by coexisting of bio-related organic substances, such as glucose (Glu), 5-hydroxytryptamine (5-HT), homocysteine (Hcy), ascorbic acid (AA), uric acid (UA), cysteine (Cys), glutathione (GSH), as well as the presence of metal ions, including Zn²⁺, Ca²⁺, Mg²⁺, Ni²⁺ and Co²⁺. The sensing process is also adaptable in biological fluids of serum and urine with satisfactory recoveries ranging from 96.14% to 104.32%.

Morphological Changes in Astrocytes by Self-Oxidation of Dopamine to Polydopamine and Quantification of Dopamine through Multivariate Regression Analysis of Polydopamine Images

Astrocytes, also known as astroglia, are important cells for the structural support of neurons as well as for biochemical balance in the central nervous system (CNS). In this study, the polymerization of dopamine (DA) to polydopamine (PDA) and its effect on astrocytes was investigated. The polymerization of DA, being directly proportional to the DA concentration, raises the prospect of detecting DA concentration from PDA optically using image-processing techniques. It was found here that DA, a naturally occurring neurotransmitter, significantly altered astrocyte cell number, morphology, and metabolism, compared to astrocytes in the absence of DA. Along with these effects on astrocytes, the polymerization of DA to PDA was tracked optically in the same cell culture wells. This polymerization process led to a unique methodology based on multivariate regression analysis that quantified the concentration of DA from optical images of astrocyte cell culture media. Therefore, this developed methodology, combined with conventional imaging equipment, could be used in place of high-end and expensive analytical chemistry instruments, such as spectrophotometry, mass spectrometry, and fluorescence techniques, for quantification of the concentration of DA after polymerization to PDA under in vitro and potentially in vivo conditions.

Hierarchically Porous Carbon Materials from Self-Assembled Block Copolymer/Dopamine Mixtures

Hierarchically porous carbon materials with interconnected frameworks of macro- and mesopores are desirable for electrochemical applications in biosensors, electrocatalysis, and supercapacitors. In this study, we report a facile synthetic route to fabricate hierarchically porous carbon materials by controlled macro- and mesophase separation of a mixture of polystyrene-block-poly(ethylene) and dopamine. The morphology of mesopores is tailored by controlling the coassembly of PS-b-PEO and dopamine in the acidic tetrahydrofuran-water cosolvent. HCl addition plays a critical role via enhancing the charge-dipole interactions between PEO and dopamine and suppressing the clustering and chemical reactions of dopamine in solution. As a result, subsequent drying can produce interpenetrated PS-b-PEO/DA mixtures without forming dopamine microsized crystallites. Dopamine oxidative polymerization induced by solvent annealing in NH₄OH vapor enables the formation of percolating macropores. Subsequent pyrolysis to selectively remove the PS-b-PEO template from the complex can produce hierarchically porous carbon materials with interconnected frameworks of macro- and mesopores when pyrolysis is implemented at a low temperature or when DA is a minor component.

A New Antibacterial N-Halamine Coating Based on Polydopamine

To prevent the formation of biofilms on material surfaces, the latter must have antibacterial properties. The aim of this study is to investigate the synthesis and the antibacterial effect of a new N-halamine coating based on polydopamine (PDA). The benefits of this coating are multiple, notably the green process used to prepare it and the wide variety of organic or inorganic materials that can be functionalized. First, the formation of the PDA coating by oxidative polymerization of dopamine in weak alkaline aqueous solution was studied and characterized. Then, these PDA films were exposed to a NaOCl solution in order to form chloramine functions into the coating, i.e., to immobilize oxidative chlorine on and into the coating. The PDA film chlorination was notably followed in situ by a quartz crystal microbalance (QCM). The influence of the NaOCl solution pH and concentration on chlorination kinetics and on PDA film degradation was evidenced. Finally, the antibacterial properties of the modified PDA coatings were highlighted by testing their antiadhesion and bactericidal properties toward the Escherichia coli bacterial strain.

Polydopamine-on-liposomes: stable nanoformulations, uniform coatings and superior antifouling performance

Polydopamine (PDA), a mussel-inspired synthetic polymer, affords biocompatible and antifouling coatings on a variety of surfaces. However, the traditional protocol of preparing PDA by polymerizing dopamine (DA) under basic conditions yields physically-unstable and non-uniform coatings that are prone to delamination and exhibit compromised antifouling performance in vivo. Here, we show that the high local pH in the vicinity of vesicular self-assemblies formed by a series of acetal-based cationic amphiphiles can be exploited to conveniently polymerise DA under physiological conditions in a gradual manner without requiring any external oxidant. Two of the four PDA-liposome nanoformulations viz. PDA-L1 and PDA-L2 turned out to be highly stable physically and resisted precipitation for more than a month while the other two formulations (PDA-L3 and PDA-L4) were less stable and formed visible precipitates with time. Further, the PDA-liposome formulations had significantly improved haemocompatibility compared to that of pristine liposomes. PDA-L1 formed highly uniform, nanostructured coatings on implants like catheter, cotton and bandages that did not delaminate even after a week of continuous incubation in simulated body fluid, or on exposure to pH change and presence of proteolytic enzymes. The PDA-L1 coated catheter implants resisted biofouling by both Gram-positive and Gram-negative bacteria in vitro and also had superior in vivo performance in mice vis-à-vis the implants coated with traditional base-polymerised PDA formulation (BP-PDA). Thus, these novel liposomal PDA nanoformulations significantly improve the practical utility of PDA-based coatings for antimicrobial applications.

Highly fluorescent oligodopamine (F-ODA) for accurate and sensitive detection of the neurotransmitter dopamine

Dopamine (DA) is an important neurotransmitter for regulating the central nervous system, hormones, and cardiovascular system. Fluorescence technique is usually applied for the rapid detection of DA neurotransmitter because DA is easily converted to fluorescent products under alkaline condition. However, it is difficult to accurately quantify low levels of DA (<10 nM) because the final product of DA conversion, so-called polydopamine (PDA), usually have low fluorescence efficiency. In this study, DA dissolved in Tris-EDTA buffer (pH 8.5) was oxidized and polymerized by adding NaOH as an oxidizing agent. After obtaining products with various degrees of polymerization, the fluorescent oligodopamine (F-ODA) (i.e., indole-5,6-quinone-rich compounds) was separated from non-fluorescent polydopamine (PDA) products. After removing non-fluorescent PDA by centrifugation, the F-ODA in the supernatant exhibited high FL intensity at 470 nm under excitation at 360 nm. At the optimal reaction conditions, the standard curve of the F-ODA exhibited a good linearity over wide range of DA concentration from 1 μM to 1 nM (limit of detection = ~0.1 nM), suggesting a very useful analytical tool for the accurate and sensitive detection of the neurotransmitter DA in bio-fluid.