Direct Evidence for the Polymeric Nature of Polydopamine

Metal-chelated polydopamine nanomaterials: Nanoarchitectonics and applications in biomedicine, catalysis, and energy storage

Polydopamine (PDA)-based materials inspired by the adhesive proteins of mussels have attracted increasing attention owing to the universal adhesiveness, antioxidant activity, fluorescence quenching ability, excellent biocompatibility, and especially photothermal conversion capability. The high binding ability of PDA to a variety of metal ions offers a paradigm for the exploration of metal-chelated polydopamine nanomaterials with fantastic properties and functions. This review systematically summarizes the latest progress of metal-chelated polydopamine nanomaterials for the applications in biomedicine, catalysis, and energy storage. Different fabrication strategies for metal-chelated polydopamine nanomaterials with various composition, structure, size, and surface chemistry, such as the pre-functionalization method, the one-pot co-assembly method, and the post-modification method, are summarized. Furthermore, emerging applications of metal-chelated polydopamine nanomaterials in the fields ranging from cancer therapy, theranostics, antibacterial, catalysis to energy storage are highlighted. Additionally, the critical remaining challenges and future directions of this area are discussed to promote the further development and practical applications of PDA-based materials.

Uptake of Magnetite Nanoparticles on Polydopamine Films Deposited on Gold Surfaces: A Study by AFM and XPS

Polydopamine has the capacity to adhere to a large variety of materials and this property offers the possibility to bind nanoparticles to solid surfaces. In this work, magnetite nanoparticles were deposited on gold substrates coated with polydopamine films. The aim of this work was to investigate the effects of the composition and morphology of the PDA layers on the sticking of magnetite nanoparticles. The polydopamine coating of gold surfaces was achieved by the oxidation of alkaline solutions of dopamine with various reaction times. The length of the reaction time to form PDA was expected to influence the composition and surface roughness of the PDA films. Magnetite nanoparticles were deposited on these polydopamine films by immersing the samples in aqueous dispersions of nanoparticles. The morphology at the nanometric scale and the composition of the surfaces before and after the deposition of magnetite nanoparticles were investigated by means of AFM and XPS. We found that the amount of magnetite nanoparticles on the surface did not vary monotonically with the reaction time of PDA formation, but it was at the minimum after 20 min of reaction. This behavior may be attributed to changes in the chemical composition of the coating layer with reaction time.

Sequentially photocatalytic degradation of mussel-inspired polydopamine: From nanoscale disassembly to effective mineralization

Mussel-inspired polydopamine (PDA) coating has been utilized extensively as versatile deposition strategies that can functionalize surfaces of virtually all substrates. However, the strong adhesion, stability and intermolecular interaction of PDA make it inefficient in certain applications. Herein, a green and efficient photocatalytic method was reported to remove adhesion and degrade PDA by using TiO2-H2O2 as photocatalyst. The photodegradation process of the PDA spheres was first undergone nanoscale disassembly to form soluble PDA oligomers or well-dispersed nanoparticles. Most of the disassembled PDA can be photodegraded and finally mineralized to CO2 and H2O. Various PDA coated templates and PDA hollow structures can be photodegraded by this strategy. Such process provides a practical strategy for constructing the patterned and gradient surfaces by the "top-down" method under the control of light scope and intensity. This sequential degradation strategy is beneficial to achieve the decomposition of highly crosslinked polymers.

The synthesis of polydopamine nano- and microspheres in microdroplets

Here we developed a microdroplet-based strategy for the rapid synthesis of uniform polydopamine nano- and microspheres. Polydopamine spheres with controllable sizes were generated within hundreds of microseconds by simply spraying water solutions of dopamine into microdroplets. Mass spectrometry revealed that dopamine was primarily oxidized into aminochrome, acting as the major building block for polydopamine. We anticipate that microdroplet chemistry will be rich in opportunities for the synthesis of functional nano- and micromaterials.

Long-Term Prevention of Biofilm Formation by Polycatechol-Based Supramolecular Assemblies with Low Molecular Weight Polymers on Surfaces

Achievement of a stable surface coating with long-term resistance to biofilm formation remains a challenge. Catechol-based polymerization chemistry and surface deposition are used as tools for surface modification of diverse materials. However, the control of surface deposition of the coating, surface coverage, coating properties, and long-term protection against biofilm formation remain to be solved. We report a new approach based on supramolecular assembly to generate long-acting antibiofilm coating. Here, we utilized catechol chemistry in combination with low molecular weight amphiphilic polymers for the generation of such coatings. Screening studies with diverse low molecular weight (LMW) polymers and different catechols are utilized to identify lead compositions, which resulted in a thick coating with high surface coverage, smoothness, and antibiofilm activity. We have identified that small supramolecular assemblies (∼10 nm) formed from a combination of polydopamine and LMW poly(N-vinyl caprolactam) (PVCL) resulted in relatively thick coating (∼300 nm) with excellent surface coverage in comparison to other polymers and catechol combinations. The coating properties, such as thickness (10-300 nm) and surface hydrophilicity (with water contact angle: 20-60°), are readily controlled. The optimal coating composition showed excellent antibiofilm properties with long-term (>28 days) antibiofilm activity against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) strains. We further utilized the combination of optimal binary coating with silver to generate a coating with sustained release of silver ions, resulting in killing both adhered and planktonic bacteria and preventing long-term surface bacterial colonization. The new coating method utilizing LMW polymers opens a new avenue for the development of a novel class of thick, long-acting antibiofilm coatings.

Ion and Molecular Sieving With Ultrathin Polydopamine Nanomembranes

In contrast to biological cell membranes, it is still a major challenge for synthetic membranes to efficiently separate ions and small molecules due to their similar sizes in the sub-nanometer range. Inspired by biological ion channels with their unique channel wall chemistry that facilitates ion sieving by ion-channel interactions, the first free-standing, ultrathin (10-17 nm) nanomembranes composed entirely of polydopamine (PDA) are reported here as ion and molecular sieves. These nanomembranes are obtained via an easily scalable electropolymerization strategy and provide nanochannels with various amine and phenolic hydroxyl groups that offer a favorable chemical environment for ion-channel electrostatic and hydrogen bond interactions. They exhibit remarkable selectivity for monovalent ions over multivalent ions and larger species with K+/Mg2+ of ≈4.2, K+/[Fe(CN)6]3- of ≈10.3, and K+/Rhodamine B of ≈273.0 in a pressure-driven process, as well as cyclic reversible pH-responsive gating properties. Infrared spectra reveal hydrogen bond formation between hydrated multivalent ions and PDA, which prevents the transport of multivalent ions and facilitates high selectivity. Chemically rich, free-standing, and pH-responsive PDA nanomembranes with specific interaction sites are proposed as customizable high-performance sieves for a wide range of challenging separation requirements.

Polydopamine Adhesion: Catechol, Amine, Dihydroxyindole, and Aggregation Dynamics

While polydopamine (PDA) possesses the surface-independent adhesion property of mussel-binding proteins, significant differences exist between them. Particularly, PDA's short and rigid backbone differs from the long and flexible protein sequence of mussel-binding proteins. Given that adhesion relies on achieving a conformal contact with large surface coverage, PDA has drawbacks as an adhesive. In our study, we investigated the roles of each building block of PDA to build a better understanding of their binding mechanisms. Initially, we anticipated that catecholamine oligomers form specific binding with substrates. However, our study showed that the universal adhesion of PDA is initiated by the solubility limit of growing oligomers by forming agglomerates, complemented by multiple binding modes of catechol. Notably, in the absence of amines, poly(catechol) either remained in solution or formed minor suspensions without any surface coating, underscoring the essential role of amines in the adhesion process by facilitating insoluble aggregate formation. To substantiate our findings, we induced poly(catechol) aggregation using quaternized poly(4-vinylpyridine) (qPVP), leading to subsequent surface adhesion upon agglomerate formation.

Activation of the PPARγ/NF-κB pathway by A-MPDA@Fe3O4@PVP via scavenging reactive oxygen species to alleviate hepatic ischemia-reperfusion injury

Hepatic ischemia-reperfusion injury (IRI) is a common pathological process during hepatectomy and liver transplantation and the two primary reasons for hepatic IRI are reactive oxygen species (ROS)-mediated oxidative stress and excessive inflammatory responses. Herein, a novel antioxidant nanodrug (A-MPDA@Fe3O4@PVP) is prepared by employing L-arginine-doped mesoporous polydopamine (A-MPDA) nanoparticles as the carrier for deposition of ultra-small ferric oxide (Fe3O4) nanoparticles and further surface modification with polyvinylpyrrolidone (PVP). A-MPDA@Fe3O4@PVP not only effectively reduces the aggregation of ultra-small Fe3O4, but also simultaneously replicates the catalytic activity of catalase (CAT) and superoxide dismutase (SOD). A-MPDA@Fe3O4@PVP with good antioxidant activity can rapidly remove various toxic reactive oxygen species (ROS) and effectively regulate macrophage polarization in vitro. In the treatment of hepatic IRI, A-MPDA@Fe3O4@PVP effectively alleviates ROS-induced oxidative stress, reduces the expression of inflammatory factors, and prevents apoptosis of hepatocytes through immune regulation. A-MPDA@Fe3O4@PVP can further protect liver tissue by activating the PPARγ/NF-κB pathway. This multiplex antioxidant enzyme therapy can provide new references for the treatment of IRI in organ transplantation and other ROS-related injuries such as fibrosis, cirrhosis, and bacterial and hepatic viral infection.

Construction of strain responsive Ti-containing carboxymethyl cellulose hydrogel with transitional coordination precursor

Due to marvelous sensitivity and flexibility, conductive hydrogels are popularly used as strain sensors in intelligent skin and wearable electronic devices fields. However, hydrogel tends to be destroyed after long-term use or in accident, leading to performance degradation. Herein, we developed an environmental-friendly Ti-containing conductive hydrogel. The hydrogel network was constructed via a simple two-step method with coordination reaction and amidation reaction based on a metal ion precursor from transitional coordination. The synergies of reversible metal coordination bonds and dynamic hydrogen bonds endowed the hydrogel with excellent self-healing properties (3 h, 93.66 %), tensile properties (136.46 kPa), compression properties (1.122 MPa), and anti-fatigue performance. At the same time, the hydrogel showed excellent self-adhesion, even underwater. Due to Ti4+, electrical conductivity of the hydrogel was visibly enhanced (σ = 25.64 mS·cm-1), which resulted in fast response (TS [time sensitivity] = 24.78 s-1) and short recovery time (153 ms). As a flexible strain sensor, the hydrogel with stable conductivity and high sensitivity could precisely detect and distinguish a series of human motions, even different letter pronunciations. These remarkable features make it a promising application in the fields of intelligent skin and wearable electronic devices.

A perylene diimide electrochemical probe with persulfate as a signal enhancer for dopamine sensing

Dopamine (DA) is an important biomarker related to parkinsonism, schizophrenia and renal disease. Traditional electrochemical sensors for DA were based on the direct electrochemical oxidation of DA. In this paper, we report a new sensing strategy using N,N'-di(trimethylaminoethyl)perylene diimide (TMPDI) as an electrochemical probe and K2S2O8 as a signal enhancer for DA detection between 0 and -0.7 V with the DPV technique. MoS2 nanoflowers prepared by the hydrothermal method were used as a nanocarrier to load TMPDI. The reduction current of TMPDI was found to show a stepwise and significant increase at -0.24 V with the increase of concentration of K2S2O8 due to the continuous cycle of TMPDI molecules' electrochemical reduction and chemical oxidation. The presence of DA caused a large decrease of the reduction current of TMPDI due to the synergistic interaction of the competitive consumption of DA for K2S2O8 and the blocking effect of polyDA adhering to the electrode surface. The decreased current exhibited a linear response for DA from 10 pM to 100 μM with a detection limit of 4.1 pM and the proposed sensor showed high selectivity and excellent feasibility in human urine/serum sample detection.

Surface Modification Progress for PLGA-Based Cell Scaffolds

Poly(lactic-glycolic acid) (PLGA) is a biocompatible bio-scaffold material, but its own hydrophobic and electrically neutral surface limits its application as a cell scaffold. Polymer materials, mimics ECM materials, and organic material have often been used as coating materials for PLGA cell scaffolds to improve the poor cell adhesion of PLGA and enhance tissue adaptation. These coating materials can be modified on the PLGA surface via simple physical or chemical methods, and coating multiple materials can simultaneously confer different functions to the PLGA scaffold; not only does this ensure stronger cell adhesion but it also modulates cell behavior and function. This approach to coating could facilitate the production of more PLGA-based cell scaffolds. This review focuses on the PLGA surface-modified materials, methods, and applications, and will provide guidance for PLGA surface modification.

The dual nature of biomimetic melanin

Melanin-inspired nanomaterials offer unique photophysical, electronic and radical scavenging properties that are widely explored for health and environmental preservation, or energy conversion and storage. The incorporation of functional melanin building blocks in more complex nanostructures or surfaces is typically achieved via a bottom-up approach starting from a molecular precursor, in most cases dopamine. Here we demonstrate that indeed, the oxidative polymerization of dopamine, for the synthesis of melanin-like polydopamine (PDA), leads to the simultaneous formation of more than one nanosized species with different compositions, morphologies and properties. In particular, a low-density polymeric structure and dense nanoparticles (NP) are simultaneously formed. The two populations could be separated and analyzed in real time using a chromatographic technique free of any stationary phase (flow field fractionation, FFF). The results following the synthesis of melanin-like PDA showed that the NP are formed only during the first 6 hours as a result of a supramolecular self-assembly-driven polymerization, while the formation of the polymer continues for about 36 hours. The two populations were also separated and characterized using TEM, UV-vis absorption spectroscopy, fluorescence and light scattering spectroscopy, DLS, FTIR, ζ-potential measurements, gel electrophoresis and pH titrations. Interestingly, very different properties between the two populations were observed: in particular the polymer contains a higher number of catechol units (8 mmol g-1 -OH) with respect to the NP (1 mmol g-1 -OH) and presents a much higher antioxidant activity. The attenuation of light by NP is more efficient than that by the polymer especially in the Vis-NIR region. Moreover, while the NP scatter light with an efficiency up to 27% they are not fluorescent, and the polymer does not scatter light but shows an excitation wavelength-dependent fluorescence typical of multi-fluorophoric uncoupled systems.

Polyelectrolyte chain conformation matters in macroscopic supramolecular self-assembly

We demonstrate molecular-conformation-dependent macroscopic supramolecular self-assembly (MSA) driven by electrostatic interactions. Evidence from single molecular force spectroscopy reveals that polyelectrolytes modified on MSA component surfaces make MSA possible with a loop conformation, while those with a flat conformation lead to no assembly, which is attributed to distinct molecular mobility. We believe that this finding is also applicable in fundamental phenomena such as surface adsorption and adhesion regarding polymers.

In Vitro/In Vivo Preparation and Evaluation of cRGDyK Peptide-Modified Polydopamine-Bridged Paclitaxel-Loaded Nanoparticles

Cancer remains a disease with one of the highest mortality rates worldwide. The poor water solubility and tissue selectivity of commonly used chemotherapeutic agents contribute to their poor efficacy and serious adverse effects. This study proposes an alternative to the traditional physicochemically combined modifications used to develop targeted drug delivery systems, involving a simpler surface modification strategy. cRGDyK peptide (RGD)-modified PLGA nanoparticles (NPs) loaded with paclitaxel were constructed by coating the NP surfaces with polydopamine (PD). The average particle size of the produced NPs was 137.6 ± 2.9 nm, with an encapsulation rate of over 80%. In vitro release tests showed that the NPs had pH-responsive drug release properties. Cellular uptake experiments showed that the uptake of modified NPs by tumor cells was significantly better than that of unmodified NPs. A tumor cytotoxicity assay demonstrated that the modified NPs had a lower IC50 and greater cytotoxicity than those of unmodified NPs and commercially available paclitaxel formulations. An in vitro cytotoxicity study indicated good biosafety. A tumor model in female BALB/c rats was established using murine-derived breast cancer 4T1 cells. RGD-modified NPs had the highest tumor-weight suppression rate, which was higher than that of the commercially available formulation. PTX-PD-RGD-NPs can overcome the limitations of antitumor drugs, reduce drug toxicity, and increase efficacy, showing promising potential in cancer therapy.

Experimental Methods to Get Polydopamine Films: A Comparative Review on the Synthesis Methods, the Films' Composition and Properties

In 2007, polydopamine (PDA) films were shown to be formed spontaneously on the surface of all known classes of materials by simply dipping those substrates in an aerated dopamine solution at pH = 8.5 in the presence of Tris(hydroxymethyl) amino methane buffer. This universal deposition method has raised a burst of interest in surface science, owing not only to the universality of this water based one pot deposition method but also to the ease of secondary modifications. Since then, PDA films and particles are shown to have applications in energy conversion, water remediation systems, and last but not least in bioscience. The deposition of PDA films from aerated dopamine solutions is however a slow and inefficient process at ambient temperature with most of the formed material being lost as a precipitate. This incited to explore the possibility to get PDA and related films based on other catecholamines, using other oxidants than dissolved oxygen and other deposition methods. Those alternatives to get PDA and related films are reviewed and compared in this paper. It will appear that many more investigations are required to get better insights in the relationships between the preparation method of PDA and the properties of the obtained coatings.

D-A Structured High-Performance Photothermal/Photodynamic Thionin-Synthetic Melanin Nanoparticles for Rapid Bactericidal and Wound Healing Effects

Synthesized melanin nanoparticles (SMNPs) are used as advanced photothermal materials. However, their internal structures are complex and disordered, and tuning the photothermal performance of nanoparticles is still a hot spot of concern. This article presents thionin (Th)-doped SMNPs, namely Th-SMNPs, which are the first SMNPs formed using the one-pot polymerization of Th with Levodopa. Th can undergo Michael addition and Schiff base reaction between indole dihydroxy/indolequinone and their oligomers to form donor-acceptor pairs in the structure to modulate the photothermal performance of SMNPs. Structural and spectroscopic analyses and density functional theory simulations further confirm the existence of the donor-acceptor structure. Th-SMNPs exhibit excellent total photothermal efficiency (34.49%) in the near-infrared region (808 nm), which is a 60% improvement compared to SMNPs. This allows Th-SMNPs to exhibit excellent photothermal performance at low power 808 nm laser irradiation. Meanwhile, Th not only enhances the photothermal properties of SMNPs, but also imparts photodynamic effects to SMNPs. Th-SMNPs can produce 1 O2 under 660 nm laser irradiation. A dual-function photothermal and photodynamic textile named Th-SMNPs@cotton is constructed based on Th-SMNPs, which can act as a rapid photothermal/photodynamic sterilization and is promising for wound healing treatment of bacterial infections under low-power dual laser irradiation.

Efficient removal of Cr from aqueous solution by catechol/m-phenylenediamine nanospheres combined with Fe(II)

The discharge of chromium-containing wastewater in industrial production causes resource loss and damage to the ecological environment. Currently, various phenolamine materials have been used to remove chromium, but their harsh adsorption conditions bring many difficulties. For example, ideal chromium removal is only achieved at low pH. In this study, we synthesized catechol/m-phenylenediamine nanospheres (CMN) and combined CMN with Fe(II) for Cr removal from aqueous solutions, and Fe(II) comes from FeSO4·7H2O. CMN was characterized and analyzed by field-emission scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscopy (TEM), Fourier transformed infrared (FTIR), X-ray diffraction (XRD), X-ray photoelectron (XPS). The adsorption performance was studied through a series of adsorption experiments. When C0 = 900 mg/L and pH = 6, the maximum adsorption capacity obtained in the experiment was 977.1 mg/g. It maintains excellent adsorption properties in acidic, neutral and alkaline environments. The results of the adsorption mechanism showed that the ultra-high adsorption capacity of CMN and Fe(II) for Cr was the result of the synergistic effect of adsorption and reduction, including electrostatic attraction, reduction and coprecipitation. CMN is expected to be an ideal adsorbent for Cr removal in aqueous solution due to its low cost, high biocompatibility and high efficiency in Cr removal.

Recent progress and future perspectives of polydopamine nanofilms toward functional electrochemical sensors

Since its discovery in 2007, polydopamine nanofilms have been widely used in many areas for surface functionalization. The simple and low-cost preparation method of the nanofilms with tunable thickness can incorporate amine and oxygen-rich chemical groups in virtually any interface. The remarkable advantages of this route have been successfully used in the field of electrochemical sensors. The self-adhesive properties of polydopamine are used to attach nanomaterials onto the electrode's surface and add chemical groups that can be explored to immobilize recognizing species for the development of biosensors. Thus, the combination of 2D materials, nanoparticles, and other materials with polydopamine has been successfully demonstrated to improve the selectivity and sensitivity of electrochemical sensors. In this review, we highlight some interesting properties of polydopamine and some applications where polydopamine plays an important role in the field of electrochemical sensors.

A biomimetic beetle-like membrane with superoleophilic SiO2-induced oil coalescence on superhydrophilic CuC2O4 nanosheet arrays for effective O/W emulsion separation

It is highly attractive to develop highly efficient oil-in-water (O/W) emulsion separation technologies for promoting the oily wastewater treatment. Herein, a novel inversely Stenocara beetle-like hierarchical structure of superhydrophobic SiO₂ nanoparticle-decorated CuC₂O₄ nanosheet arrays were prepared on copper mesh membrane by bridging polydopamine (PDA) to make a SiO₂/PDA@CuC₂O₄ membrane for substantially enhanced separation of O/W emulsions. The superhydrophobic SiO₂ particles on the as-prepared SiO₂/PDA@CuC₂O₄ membranes were served as localized active sites to induce coalescence of small-size oil droplets in oil-in-water (O/W) emulsions. Such innovated membrane delivered outstanding demulsification ability of O/W emulsion with a high separation flux of 2.5 kL⋅m^-2⋅h^-1 and its filtrate's chemical oxygen demand (COD) being 30 and 100 mg⋅L^-1 for surfactant-free emulsion (SFE) and surfactant-stabilized emulsion (SSE), respectively, and also exhibited a good anti-fouling performance in cycling tests. The innovative design strategy developed in this work broadens the application of superwetting materials for oil-water separation and presents a promising prospect in practical oily wastewater treatment applications.

In Situ Polymerization-Mediated Antigen Presentation

Activating antigen-presenting cells is essential to generate adaptive immunity, while the efficacy of conventional activation strategies remains unsatisfactory due to suboptimal antigen-specific priming. Here, in situ polymerization-mediated antigen presentation (IPAP) is described, in which antigen-loaded nanovaccines are spontaneously formed and efficiently anchored onto the surface of dendritic cells in vivo through co-deposition with dopamine. The resulting chemically bound nanovaccines can promote antigen presentation by elevating macropinocytosis-based cell uptake and reducing lysosome-related antigen degradation. IPAP is able to prolong the duration of antigen reservation in the injection site and enhance subsequent accumulation in the draining lymph nodes, thereby eliciting robust antigen-specific cellular and humoral immune responses. IPAP is also applicable for different antigens and capable of circumventing the disadvantages of complicated preparation and purification. By implementation with ovalbumin, IPAP induces a significant protective immunity against ovalbumin-overexpressing tumor cell challenge in a prophylactic murine model. The use of the SARS-CoV-2 Spike protein S1 subunit also remarkably increases the production of S1-specific immunoglobulin G in mice. IPAP offers a unique strategy for stimulating antigen-presenting cells to boost antigen-specific adaptive responses and proposes a facile yet versatile method for immunization against various diseases.

A novel antibacterial and fluorescent coating composed of polydopamine and carbon dots on the surface of orthodontic brackets

Many kinds of antibacterial coatings have been designed to prevent the adherence of bacteria onto the surface of a fixed orthodontic device of brackets. However, the problems such as weak binding force, undetectable, drug resistance, cytotoxicity and short duration needed to be solved. Thus, it has great value in developing novel coating methods with long-term antibacterial and fluorescence properties according to the clinical application of brackets. In this study, we synthesized blue fluorescent carbon dots (HCDs) using the traditional Chinese medicinal honokiol, which could cause irreversible killing effects on both gram-positive and gram-negative bacteria through positive charges on the surface and inducing reactive oxygen species (ROS) production. Based on this, the surface of brackets was serially modified with polydopamine and HCDs, taking advantage of the strong adhesive properties as well as the negative surface charge of polydopamine particles. It is found that this coating exhibits stable antibacterial properties in 14 days with good biocompatibility, which can provide a new solution and strategy to solve the series of hazards caused by bacterial adhesion on the surface of orthodontic brackets.

Structural elucidation of polydopamine facilitated by ionic liquid solvation

Minimal understanding of the formation mechanism and structure of polydopamine (pDA) and its natural analogue, eumelanin, impedes the practical application of these versatile polymers and limits our knowledge of the origin of melanoma. The lack of conclusive structural evidence stems from the insolubility of these materials, which has spawned significantly diverse suggestions of pDA's structure in the literature. We discovered that pDA is soluble in certain ionic liquids. Using these ionic liquids (ILs) as solvents, we present an experimental methodology to solvate pDA, enabling us to identify pDA's chemical structure. The resolved pDA structure consists of self-assembled supramolecular aggregates that contribute to the increasing complexity of the polymer. The underlying molecular energetics of pDA solvation and a macroscopic picture of the disruption of the aggregates using IL solvents have been investigated, along with studies of the aggregation mechanism in water.

Kinetic study of polydopamine sphere synthesis using TRIS: relationship between synthesis conditions and final properties

The synthesis and characterization of polydopamine (PDA) using dopamine (DA) as the monomer and (hydroxymethyl)aminomethane (TRIS) as the oxidant is studied. The effect of temperature and TRIS concentration on the kinetics of dopamine polymerization is evaluated, and the kinetic parameters are also calculated. Three TRIS concentrations are used to assess their effect on DA polymerization kinetics. The reaction at 1.5 mmol of TRIS shows a sustained increase of the rate constant with temperature from 2.38 × 10^-4 to 5.10 × 10^-4 when the temperature is increased from 25 to 55 °C; however, not all reactions follow an Arrhenius law. In addition, the correlation between the synthesis parameters and morphological, structural, and thermal properties of polydopamine is established. The morphology of the PDA particles is evaluated by Scanning Electron Microscopy (SEM), the relationships between the diameter, distribution size, and the rate constant. Thermal characterization by Differential Scanning Calorimetry (DSC) shows an endothermic transition around 130 °C associated with the melting of PDA's regular structure. It is supported by structural studies, such as infrared and Raman spectroscopy and X-ray Diffraction (XRD), by observing a broad peak at 23.1° (2θ) that fits with a graphitic-like structure of PDA.

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.

Structure and properties of flexible starch-based double network composite films induced by dopamine self-polymerization

Starch-based packaging materials are being developed to alleviate environmental pollution and greenhouse gas emissions associated with plastic-based ones. However, the high hydrophilicity and poor mechanical properties of pure-starch films limit their widespread application. In this study, dopamine self-polymerization was used as a strategy to improve the performance of starch-based films. Spectroscopy analysis showed that strong hydrogen bonding occurred between polydopamine (PDA) and starch molecules within the composite films, which significantly altered their internal and surface microstructures. The composite films had a greater water contact angle (> 90°), which indicated that the incorporation of PDA reduced their hydrophilicity. Additionally, the elongation at break of the composite films was 11-fold higher than pure-starch films, indicating that PDA improved film flexibility, while the tensile strength decreased to some extent. The composite films also exhibited excellent UV-shielding performance. These high-performance films may have practical applications in food and other industries as biodegradable packaging materials.

Atomic force and infrared spectroscopic studies on the role of surface charge for the anti-biofouling properties of polydopamine films

Antibacterial polymer materials have gained interest due to their capability to inhibit or eradicate biofilms with greater efficiency in comparison with their monomeric counterparts. Among the antimicrobial and anti-biofouling polymers, catecholamine-based polymers - and in particular polydopamine - have been studied due to their favorable adhesion properties, which can be tuned by controlling the pH value. In this study, we used atomic force microscopy (AFM)-based spectroscopy to investigate the relation between the adhesion properties and surface charge density and the pH of electrochemically deposited polydopamine films presenting a dissociation constant of polydopamine of 6.3 ± 0.2 and a point of zero charge of 5.37 ± 0.06. Furthermore, using AFM and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), the influence of the surface charge density of polydopamine on bacterial adhesion and biofilm formation was investigated. It was shown that the adhesion of Escherichia coli at positively charged polydopamine is three times higher compared to a negatively charged polymer, and that the formation of biofilms is favored at positively charged polymers.

Reversible Supramolecular Noncovalent Self-Assembly Determines the Optical Properties and the Formation of Melanin-like Nanoparticles

The role of noncovalent supramolecular self-assembly in the formation of melanin-like NP, as well as the nature of the electronic transition at the basis of their unique optical properties, is strongly debated. Here we demonstrate that, during the first stage of formation of synthetic melanin, polydopamine (PDA), a small fraction of the molecular precursor dopamine (DA) is oxidized to quinone (Q) and a simple supramolecular charge-transfer (CT) adduct is formed thanks to the electron donor and electron acceptor properties of DA and Q, respectively. This adduct, also detectable by HPLC-MS, presents the broad absorption band in the red-NIR region typical of melanin-like materials. Importantly, its disaggregation upon dilution can be easily detected since it leads to the disappearance of the CT band, indicating the reversibility of the process. Moreover, the stability constant K of the CT adduct could be obtained using a simple association model.

Design of Cefotaxime Sodium-Loaded Polydopamine Coatings with Controlled Surface Roughness for Titanium Implants

The success rate of dental implants is limited by peri-implant infection and insufficient osseointegration. Therefore, reducing the occurrence of peri-implantitis and promoting osseointegration are in demand. A roughened surface has commonly been applied to improve the osseointegration of implants, but it will accelerate the attachment of bacteria. We have developed novel antibiotic-decorated titanium (Ti) surfaces by the immobilization of dopamine and cefotaxime sodium (CS) simultaneously. Moreover, the surface roughness of the polydopamine (PDA)/CS coating was controlled by the changes in polymerization times as determined by atomic force microscopy. Then, all antibiotic-grafted Ti surfaces could effectively prevent the adhesion and proliferation of both Escherichia coli and Streptococcus mutans in comparison to the pristine control. For the culture and osteogenic differentiation of human umbilical mesenchymal stem cells (hUMSCs) on the substrate surface, PDA/CS coating with polymerization times less than 30 min showed acceptable biocompatibility, but the upregulation of marker genes and proteins was detected when the polymerization time was more than 30 min. Moreover, the best calcium deposition results were found in the 30 min PDA/CS group with or without the addition of osteogenic factors. Therefore, our PDA/CS coating with a polymerization time of 30 min holds great potential to design dental implants with dual bacteriostatic and osteogenic properties.

Preparation of β-cyclodextrin/dopamine hydrochloride-graphene oxide and its adsorption properties for sulfonamide antibiotics

To develop high-efficiency antibiotic adsorbents, β-cyclodextrin and dopamine hydrochloride were used to modify graphene oxide to prepare a new type of ternary composite material (β-cyclodextrin/dopamine hydrochloride-graphene oxide, CD-DGO). The material was characterized using scanning electron microscopy, Fourier infrared spectrometry, transmission electron microscopy, and specific surface area optical analysis. Two typical sulfonamides antibiotics (sulfamethoxazole, sulfadiazine) adsorption capacity were evaluated in terms of the dosage of composite materials, the ratio of each component, and the pH of the solution. We analyzed the adsorption characteristics via adsorption kinetics and adsorption isotherms, and then investigated the stability of the adsorbent through desorption and regeneration of the adsorbent. The results show that the adsorption effect of sulfonamides antibiotics is best at pH = 2; the adsorption kinetics conform to the pseudo-second-order kinetic model, and the adsorption equilibrium follows the Langmuir adsorption isotherm; the maximum adsorption capacity of CD-DGO for sulfamethoxazole and sulfadiazine is 144 mg·g^-1 and 152 mg·g^-1, respectively. The material has good reusability, and the dominant force in the adsorption process is the π-π electron conjugation effect with hydrogen bonding. This offers a theoretical basis for the treatment of sulfonamides antibiotics water pollution.

Polydopamine-doped supramolecular chiral hydrogels for postoperative tumor recurrence inhibition and simultaneously enhanced wound repair

Cancer recurrence remains a major challenge after primary tumor excision, and the inflammation of tumor-caused wounds can hinder wound healing and potentially promote tumor growth. Herein, a chiral L-phenylalanine-based (LPFEG) supramolecular hydrogel system encapsulated with polydopamine nanoparticles (PDA-NPs) has been developed in order to prevent tumor relapse after surgery and promote wound repair. PDA-NPs allow for near-infrared (NIR) light-triggered photothermal therapy, especially, it can scavenge free radicals in the surgical wound. LPFEG can mimic native extracellular matrix (ECM) structure to create a chiral microenvironment that enhances fibroblast adhesion, proliferation, and new tissue regeneration. With anticancer drug doxorubicin (DOX) loaded into the composite hydrogel, the antitumor effect is significantly enhanced by the integration of chemo-photothermal therapy both in vitro and in vivo. The PDA-based chiral supramolecular composite hydrogel as an effective postoperative adjuvant possesses promising applicable prospects in inhibiting tumor recurrence and accelerating wound healing after operation. STATEMENT OF SIGNIFICANCE: After primary tumor excision, cancer recurrence remains a severe concern, and the inflammation induced by tumor-related wounds can delay wound healing. Herein, we designed a chiral L-phenylalanine-based (LPFEG) supramolecular hydrogel platform that was co-assembled with polydopamine nanoparticles (PDA-NPs). Among them, PDA-NPs can offer photothermal therapy and scavenge free radicals in surgical wounds. LPFEG can create a chiral microenvironment that promotes fibroblast adhesion, proliferation, and new tissue regeneration. Furthermore, with anticancer drug doxorubicin (DOX) loaded into the composite hydrogel, the antitumor effect is considerably boosted. Therefore, the PDA-based chiral supramolecular hydrogel shows high application potential as a postoperative adjuvant in preventing tumor relapse as well as accelerating wound healing after surgery.

Interfacially responsive electron transfer and matter conversion by polydopamine-mediated nanoplatforms for advancing disease theranostics

Polydopamine (PDA) is an artificial melanin polymer that has been spotlighted due to its extraordinary optoelectronic characteristics and advance theranosctic applications in biomaterial fields. Moreover, interactions on the nano-bio interface interplay whereby substances exchange in response to endogenous or exogenous stimuli, and electron transfer driven by light, energy-level transitions, or electric field greatly affect the functional performance of PDA-modified nanoparticles. The full utilization of potential in PDA's interfacial activities, optoelectrical properties and related responsiveness is therefore an attractive means to construct advanced nanostructures for regulating biological processes and metabolic pathways. Herein, we strive to summarize recent advances in the construction of functional PDA-based nanomaterials with state-of-the-art architectures prepared for modulation of photoelectric sensing and redox reversibility, as well as manipulation of photo-activated therapeutics. Meanwhile, contributions of interfacial electron transfer and matter conversion are highlighted by discussing the structure-property-function relationships and the biological effects in their featured applications including disease theranostics, antibacterial activities, tissue repair, and combined therapy. Finally, the current challenges and future perspectives in this emerging research field will also be outlined. Recent advances on polydopamine-based nanotherapeutics with an emphasis on their interfacial activities, optoelectrical properties and related responsiveness are reviewed for providing insightful guidance to the rational design of integrated theranostic nanoplatforms with high performance in the biomedical fields. This article is categorized under: Diagnostic Tools > Diagnostic Nanodevices Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Engineering Bio-Adhesives Based on Protein-Polysaccharide Phase Separation

Glue-type bio-adhesives are in high demand for many applications, including hemostasis, wound closure, and integration of bioelectronic devices, due to their injectable ability and in situ adhesion. However, most glue-type bio-adhesives cannot be used for short-term tissue adhesion due to their weak instant cohesion. Here, we show a novel glue-type bio-adhesive based on the phase separation of proteins and polysaccharides by functionalizing polysaccharides with dopa. The bio-adhesive exhibits increased adhesion performance and enhanced phase separation behaviors. Because of the cohesion from phase separation and adhesion from dopa, the bio-adhesive shows excellent instant and long-term adhesion performance for both organic and inorganic substrates. The long-term adhesion strength of the bio-glue on wet tissues reached 1.48 MPa (shear strength), while the interfacial toughness reached ~880 J m-2. Due to the unique phase separation behaviors, the bio-glue can even work normally in aqueous environments. At last, the feasibility of this glue-type bio-adhesive in the adhesion of various visceral tissues in vitro was demonstrated to have excellent biocompatibility. Given the convenience of application, biocompatibility, and robust bio-adhesion, we anticipate the bio-glue may find broad biomedical and clinical applications.

Hydrophilic Polymer-Guided Polycatecholamine Assembly and Surface Deposition

Mussel-inspired surface chemistry based on polycatecholamines and polyphenols has been widely applied as a facile and universal method for modifying surfaces. Specifically, the catecholamine-assisted codeposition as a one-step strategy is a versatile strategy used to impart surface functionalities. Despite successful incorporation of numerous functional agents, very little understanding has emerged over the years regarding the mechanism behind their coassembly and codeposition. Here, we employed six different ultrahigh molecular weight hydrophilic polymers of diverse chemistry and architecture and three catecholamines and a polyphenol for investigating the coassembly and codeposition process. The chemistry of the polymers is found to influence the strength of the interaction between the polycatecholamine and the hydrophilic polymers, thus playing an important role in the aqueous self-assembly in solution to nanoaggregates, its formation kinetics, steric stabilization, and surface deposition. Additionally, the codeposition method was used as a platform for developing antifouling and antibiofilm coatings and evaluating their efficiency. Both the chemistry of hydrophilic polymers and the type of the catecholamine influence the antibiofilm properties of the coating. Our studies demonstrated that significant opportunities exist to further define the surface coating process and polycatecholamine self-assembly process by altering the polycatecholamine-hydrophilic polymer interactions.

Lactoferrin network with MC3T3-E1 cell proliferation, auxiliary mineralization, antibacterial functions: A multifunctional coating for biofunctionalization of implant surfaces

Developing biocompatible, low-immunoreactive, and antibacterial implants are challenging yet fundamental to osteosynthesis. In this study, mineralization-stimulative and antibacterial networking nanostructures are assembled via amyloid-like aggregation of lactoferrin (LF) triggered by reducing the intramolecular disulfide bonds. Due to the adhesive property of their rich β-sheet architecture, the LF networks are amenable to the deposition upon the surface of various implant materials, functionalizing the implants with cell-proliferative, mineralization-stimulative, and antibacterial properties. Specifically, the abundant functional groups and amino acids exposed on the surface of LF networks provide abundant functional microdomains for subsequent mineralization of different forms of calcium ions and promote the formation of hydroxyapatite (HAp) crystals in simulated body fluids. We further demonstrate that the LF network inherits the innate antibacterial properties of LF and exerts a synergistic antibacterial ability with surface-enriched positively charged and hydrophobic amino acid residues, disrupting bacterial biofilm formation, enhancing microbial cell wall perturbation, and ultimately leading to microbial death. The results underscore the feasibility of the LF network as a multifunctional coating on bioscaffold surfaces, which may provide insight into its future applications in next-generation artificial bone implants with bacterial/biofilm clearance and bone tissue remodeling capabilities.

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.

A biomimetic enzyme-linked immunosorbent assay (BELISA) for the analysis of gonadorelin by using molecularly imprinted polymer-coated microplates

An original biomimetic enzyme-linked immunoassay (BELISA) to target the small peptide hormone gonadorelin is presented. This peptide has been recently listed among the substances banned in sports by the World Antidoping Agency (WADA) since its misuse by male athletes triggers testosterone increase. Hence, in response to this emerging issue in anti-doping controls, we proposed BELISA which involves the growth of a polynorepinephrine (PNE)-based molecularly imprinted polymer (MIP) directly on microwells. PNE, a polydopamine (PDA) analog, has recently displayed impressive performances when it was exploited for MIP preparation, giving even better results than PDA. Gonadorelin quantification was accomplished via a colorimetric indirect competitive bioassay involving the competition between biotinylated gonadorelin linked to the signal reporter and the unlabeled analyte. These compete for the same MIP binding sites resulting in an inverse correlation between gonadorelin concentration and the output color signal (λ = 450 nm). A detection limit of 277 pmol L-1 was achieved with very good reproducibility in standard solutions (avCV% = 4.07%) and in urine samples (avCV% = 5.24%). The selectivity of the assay resulted adequate for biological specimens and non-specific control peptides. In addition, the analytical figures of merit were successfully validated by mass spectrometry, the reference anti-doping benchtop platform for the analyte. BELISA was aimed to open real perspectives for PNE-based MIPs as alternatives to antibodies, especially when the target analyte is a poorly or non-immunogenic small molecule, such as gonadorelin. Biomimetic enzyme-linked immunosorbent assay (BELISA).

Multi-responsive mesoporous polydopamine composite nanorods cooperate with nano-enzyme and photosensitizer for intensive immunotherapy of bladder cancer

Bladder cancer is a common malignancy in the urinary system. Defects of drug molecules in bladder during treatment, such as passive diffusion, rapid clearance of periodic urination, poor adhesion and permeation abilities, lead to low delivery efficiency of conventional drugs and high recurrence rate of disease. In this study, we designed multi-responsive mesoporous polydopamine (PDA) composite nanorods cooperating with nano-enzyme and photosensitizer for intensive immunotherapy of bladder cancer. The strongly adhesive mesoporous PDA with wheat germ agglutinin on nanoparticles could specifically adhere to epithelial glycocalyx and made the nanoparticles aggregate in urinary pathways. Meanwhile, 2,3-dimethylmaleic anhydride could be hydrolyzed in acidic conditions of tumor microenvironment, giving it a positive charge (charge reversal), which is more amenable to enter cancer cells. Afterwards, manganese dioxide nanorods could catalyze the reaction of excess H₂ O₂ in tumor microenvironment to generate active oxygen, so as to change the hypoxic environment in tumor, and achieve a pH-responsive for slow release of PD-L1. After the ICG was irradiated by infrared light, a large amount of singlet oxygen was generated, thereby enhancing the therapeutic effect and reducing toxicity in vivo. Besides, mesoporous PDA with indocyanine green photothermal agent could have a local heat up quickly under the near-infrared light to kill cancer cells, thereby enhancing therapeutic efficacy. Accordingly, this mesoporous PDA composite nanorods shed a light on bladder tumor treatment.

Polyserotonin as a versatile coating with pH-responsive degradation for anti-tumor therapy

Through self-polymerization of serotonin monomer, polyserotonin (PST) can coat on arbitrary surfaces with pH-responsive degradation, which was employed for nanoparticle coating and controlled drug release, achieving a robust anti-tumor effect when combined with its intrinsic photothermal effect.

TiO2 with Confined Water Boosts Ultrahigh Selective Enrichment of Phosphorylated Proteins

In the selective enrichment of phosphorylated proteins (PPs) from biological samples, the non-phosphorylated proteins (NPPs) adhered onto enrichment adsorbents due to the hydrophobic interaction, resulting in poor selectivity and low recovery of target PPs. Herein, superhydrophilic TiO₂-coated porous SiO₂ microspheres are prepared and boost remarkable selectivity toward standard PP spiked with 2000 mass-fold NPP interference. The outstanding performance of the superhydrophilic microspheres is attributed to the coordination interaction between TiO₂ and PPs, and the confined water layer generated from superhydrophilicity avoids the irreversible adsorption of NPPs by keeping NPP inner hydrophobic regions in a compact structure, which is verified by single molecule force spectroscopy, circular dichroism, and quartz crystal microbalance. This strategy for enrichment is expected to solve the challenge in proteomics and sheds light on the interactions between biomolecules and superwettability.

Development of Universal and Clickable Film by Mimicking Melanogenesis: On-Demand Oxidation of Tyrosine-Based Azido Derivative by Tyrosinase

In this study, we synthesized a tyrosine-based azido derivative (TBAD) that permits both substrate-independent surface coating and clickable film functionalization by mimicking natural melanogenesis. In contrast to catechol derivatives, which are generally susceptible to oxidation by air under ambient conditions, the monophenol-based TBAD remains stable under alkaline and neutral conditions, and is activated to oxidized quinone in situ by tyrosinase to initiate melanin-like polymerization. The resulting poly(TBAD) film can be formed on various substrates including noble metals, metal oxides, and synthetic polymers, which can undergo click reaction with terminal alkyne moieties on the entire surface or a specific region through Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The enzyme-mediated coating can rapidly form thin films (∼10 nm) and produce a uniform film morphology, which are important aspects in surface chemistry. This on-demand, clickable coating may become a significant tool for bioconjugation, soft lithography, and labeling techniques. This article is protected by copyright. All rights reserved.

Fe3O4@PDA@PEI Core-Shell Microspheres as a Novel Magnetic Sorbent for the Rapid and Broad-Spectrum Separation of Bacteria in Liquid Phase

Bacterial infection is a significant cause of morbidity and mortality to humans worldwide. Thus, a method for nonspecific, sensitive, and rapid enrichment of such bacteria is essential for bacteria detection and treatment. This study demonstrates a self-made core-shell Fe3O4@Polydopamine@Polyethyleneimine magnetic beads (Fe3O4@PDA@PEI MBs) with a high density positive charge-based magnetic separation scheme for the broad-spectrum rapid enrichment of microorganisms in the liquid phase. MBs with a high-density positive charge have a strong electrostatic attraction to most microorganisms in nature. Our scheme is as follows: (1) wrapping dopamine (DA) on the iron oxide through self-polymerization and wrapping PEI on the outermost shell layer in a mode of crosslinking with the PDA; (2) subsequently, the Fe3O4@PDA@PEI MBs were used to concentrate microorganisms from the sample solution; (3) performing magnetic separation and calculating the adsorption efficiency. The as-prepared Fe3O4@PDA@PEI MBs composite was carefully characterized by zeta potential analysis, Value stream-mapping (VSM), transmission electron microscopy (TEM), and Fourier transforms infrared spectrometry (FT-IR). In this study, both gram-positive and gram-negative bacteria could be captured in three minutes through electrostatic interaction. Furthermore, the adsorption efficiency on gram-negative (>98%) is higher than that on gram-positive (>95%), allowing for a simple, rapid assay to enrich organisms in resource-limited settings.

Revisiting the adhesion mechanism of mussel-inspired chemistry

Mussel-inspired chemistry has become an ideal platform to engineer a myriad of functional materials, but fully understanding the underlying adhesion mechanism is still missing. Particularly, one of the most pivotal questions is whether catechol still plays a dominant role in molecular-scale adhesion like that in mussel adhesive proteins. Herein, for the first time, we reveal an unexplored adhesion mechanism of mussel-inspired chemistry that is strongly dictated by 5,6-dihydroxyindole (DHI) moieties, amending the conventional viewpoint of catechol-dominated adhesion. We demonstrate that polydopamine (PDA) delivers an unprecedented adhesion of 71.62 mN m-1, which surpasses that of many mussel-inspired derivatives and is even 121-fold higher than that of polycatechol. Such a robust adhesion mainly stems from a high yield of DHI moieties through a delicate synergy of leading oxidation and subsidiary cyclization within self-polymerization, allowing for governing mussel-inspired adhesion by the substituent chemistry and self-polymerization manner. The adhesion mechanisms revealed in this work offer a useful paradigm for the exploitation of functional mussel-inspired materials.

Enhanced Photoacoustic Detection of Heparin in Whole Blood via Melanin Nanocapsules Carrying Molecular Agents

Photoacoustic (PA) imaging has proved versatile for many biomedical applications from drug delivery tracking to disease diagnostics and postoperative surveillance. It recently emerged as a tool for accurate and real-time heparin monitoring to avoid bleeding complications associated with anticoagulant therapy. However, molecular-dye-based application is limited by high concentration requirements, photostability, and a strong background hemoglobin signal. We developed polydopamine nanocapsules (PNCs) via supramolecular templates and loaded them with molecular dyes for enhanced PA-mediated heparin detection. Depending on surface charge, the dye-loaded PNCs undergo disassembly or aggregation upon heparin recognition: both experiments and simulation have revealed that the increased PA signal mainly results from dye-loaded PNC-heparin aggregation. Importantly, Nile blue (NB)-loaded PNCs generated a 10-fold higher PA signal than free NB dye, and such PNC enabled the direct detection of heparin in a clinically relevant therapeutic window (0-4 U/mL) in whole human blood (R² = 0.91). Furthermore, the PA signal of PNC@NB obtained from 17 patients linearly correlated with ACT values (R² = 0.73) and cumulative heparin (R² = 0.83). This PNC-based strategy for functional nanocapsules offers a versatile engineering platform for robust biomedical contrast agents and nanocarriers.

Hydrogel tapes for fault-tolerant strong wet adhesion

Fast and strong bio-adhesives are in high demand for many biomedical applications, including closing wounds in surgeries, fixing implantable devices, and haemostasis. However, most strong bio-adhesives rely on the instant formation of irreversible covalent crosslinks to provide strong surface binding. Repositioning misplaced adhesives during surgical operations may cause severe secondary damage to tissues. Here, we report hydrogel tapes that can form strong physical interactions with tissues in seconds and gradually form covalent bonds in hours. This timescale-dependent adhesion mechanism allows instant and robust wet adhesion to be combined with fault-tolerant convenient surgical operations. Specifically, inspired by the catechol chemistry discovered in mussel foot proteins, we develop an electrical oxidation approach to controllably oxidize catechol to catecholquinone, which reacts slowly with amino groups on the tissue surface. We demonstrate that the tapes show fast and reversible adhesion at the initial stage and ultrastrong adhesion after the formation of covalent linkages over hours for various tissues and electronic devices. Given that the hydrogel tapes are biocompatible, easy to use, and robust for bio-adhesion, we anticipate that they may find broad biomedical and clinical applications.