High ionic strength formation of DOPA-melanin coating for loading and release of cationic antimicrobial compounds

Molecular Investigation of the Self-Assembly Mechanism Underlying Polydopamine Coatings: The Synergistic Effect of Typical Building Blocks Acting on Interfacial Adhesion

Polydopamine (PDA) is well known as a mussel-inspired adhesive material composed of oligomeric heteropolymers. However, the conventional eumelanin-like structural assumption of PDA seems deficient in explaining its interfacial adhesion. To determine the decisive mechanism of PDA coating formation, experiments and simulations were performed in this study. 5,6-Dihydroxyindole (DHI), the signature building block of eumelanin, was introduced as the control group. Various typical building blocks in PDA were quantified by physicochemical characterizations, and the polar-group-dominated interfacial interaction was evaluated by classic molecular dynamics and metadynamics methods. Aminoethyl has been proven to be the key functional group inducing the adsorption of PDA on the hydroxylated silica substrates, while DHI shows limited adhesion to the substrate due to the absence of aminoethyl as the catechol-indole structure of DHI exhibits poor affinity to the silica surface. Pyrrole carboxylic acid, as an oxidative product detected from PDA/DHI, is unfavorable for its adhesion to silica substrates. Overall, the coating formation and self-aggregating precipitation of PDA are two competitive aminoethyl-consuming paths; thus, the in situ oxidative coupling of dopamine is indispensable for the PDA coating preparation. The collected PDA precipitates can no longer present satisfactory coating forming behavior, resulting from a shortage of aminoethyl moieties.

2D Titanium carbide printed flexible ultrawideband monopole antenna for wireless communications

Flexible titanium carbide (Ti₃C₂) antenna offers a breakthrough in the penetration of information communications for the spread of Internet of Things (IoT) applications. Current configurations are constrained to multi-layer complicated designs due to the limited conformal integration of the dielectric substrate and additive-free Ti₃C₂ inks. Here, we report the flexible ultrawideband Ti₃C₂ monopole antenna by combining strategies of interfacial modification and advanced extrusion printing technology. The polydopamine, as molecular glue nano-binder, contributes the tight adhesion interactions between Ti₃C₂ film and commercial circuit boards for high spatial uniformity and mechanical flexibility. The bandwidth and center frequency of Ti₃C₂ antenna can be well maintained and the gain differences fluctuate within ±0.2 dBi at the low frequency range after the bent antenna returns to the flat state, which conquers the traditional inelastic Cu antenna. It also achieves the demo instance for the fluent and stable real-time wireless transmission in bending states.

Non-covalent small molecule partnership for redox-active films: Beyond polydopamine technology

HYPOTHESIS

The possibility to use hexamethylenediamine (HMDA) to impart film forming ability to natural polymers including eumelanins and plant polyphenols endowed with biological activity and functional properties has been recently explored with the aim to broaden the potential of polydopamine (PDA)-based films overcoming their inherent limitations. 5,6-dihydroxyindole-2-carboxylic acid, its methyl ester (MeDHICA) and eumelanins thereof were shown to exhibit potent reducing activity.

EXPERIMENTS

MeDHICA and HMDA were reacted in aqueous buffer, pH 9.0 in the presence of different substrates to assess the film forming ability. The effect of different reaction parameters (pH, diamine chain length) on film formation was investigated. Voltammetric and AFM /SEM methods were applied for analysis of the film redox activity and morphology. HPLC, MALDI-MS and ¹HNMR were used for chemical characterization. The film reducing activity was evaluated in comparison with PDA by chemical assays and using UV stressed human immortalized keratinocytes (HaCat) cells model.

FINDINGS

Regular and homogeneous yellowish films were obtained with moderately hydrophobic properties. Film deposition was optimal at pH 9, and specifically induced by HMDA. The film consisted of HMDA and monomeric MeDHICA accompanied by dimers/small oligomers, but no detectable MeDHICA/HMDA covalent conjugation products. Spontaneous assembly of self-organized networks held together mainly by electrostatic interactions of MeDHICA in the anion form and HMDA as the dication is proposed as film deposition mechanism. The film displayed potent reducing properties and exerted significant protective effects from oxidative stress on HaCaT.

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.

Collagen-Sealed Polyester Vascular Prostheses Functionalized by Polycatecholamine Coatings

Collagen-sealed polyester (PET) prostheses are commonly used in reconstructive vascular surgery due to their self-sealing properties. To prevent post-surgical infection, different modification methods have been tested but so far none have showed long-term satisfactory efficiency. For this reason, in the present study, a commercial collagen-sealed PET prosthesis was coated by a highly adhesive poly (L-DOPA) layer maintaining the sealing protein without losing the original properties and functionality. This modified (as proven by SEM, FTIR, XPS and contact angle) graft exhibited comparable wettability and elasticity as pristine commercial graft, as well as reduced hemolysis-inducing effect, lowered toxicity against human endothelial cells and reduced toxicity in Danio rerio model. Poly (L-DOPA)-coated grafts were shown to bind six times more aminoglycoside antibiotic (gentamicin) than pristine graft. Poly (L-DOPA)-coated antibiotic-bound prostheses exhibited an improved antibacterial activity (bacterial growth inhibition and anti-adhesive capacity) in comparison with pristine antibiotic-bound graft. Overall, poly (L-DOPA)-coatings deposited on PET vascular grafts can effectively functionalize collagen-sealed prostheses without the loss of protein sealing layer and allow for antibiotics incorporation to provide higher safety in biomedical applications.

Polycatecholamine and gentamicin as modifiers for antibacterial and blood-biocompatible polyester vascular prostheses

Polyester (PET) prostheses are commonly used in reconstructive vascular surgery. The most serious complication after implantation is early or late infection of the graft. Therefore, there is high demand to protect prosthesis against bacterial adhesion and biofilm development. For this reason, in this work PET prostheses were first coated by highly adhesive polycatecholamine layer. The grafts were then coupled with gentamicin and studied in relation to morphological and structural properties, biological safety (contact with blood, reaction of vascular endothelial cells (HUVEC), Danio rerio fish), drug release and antibacterial activity. Among two tested catecholamine monomers, L-DOPA was found to be more effective precursor in this process than dopamine. For L-DOPA, assistance of Cu²⁺, Mg²⁺ and Na⁺ ions seems to increase the amount of further immobilized drug. Coated prostheses exhibited greater human endothelial cell proliferation increase and lower cytotoxic effect than uncoated. The modification reduced the hemolysis observed for pristine commercial graft and limited the rate of abnormalities in D. rerio larvae, confirming the safety of the proposed modification. The coating allowed to double the amount of immobilized antibiotic in comparison with uncoated graft which resulted in increased antibacterial activity and reduced bacterial adhesion against 4 bacterial strains prevalent in biomaterials infections. Overall, poly(L-DOPA)-coatings deposited on PET vascular grafts can effectively functionalize these prostheses for higher safety in biomedical applications.

Synthesis and characterisation of polynorepinephrine-shelled microcapsules via an oil-in-water emulsion templating route

In this article, we present a facile and robust method for the surfactant-free preparation of polynorepinephrine stabilised microcapsules templated from an oil-in-water emulsion. The resulting microcapsule structures are dependent on the concentration of Cu²⁺ used to catalyse norepinephrine polymerisation. When the concentration of Cu²⁺ increases, the diameter of the microcapsules and the thickness of the shell increase correspondingly. The mechanical and chemical stability provided by the polynorepinephrine shell are explored using surface pressure measurements and atomic force microscopy, demonstrating that a rigid and robust polynorepinephrine shell is formed. In order to demonstrate potential application of the microcapsules in sustained release, Nile red stained squalane was encapsulated, and pH responsive release was monitored. It was seen that by controlling pH, the release profile could be controlled, with highest release efficacy achieved in alkaline conditions, offering a new pathway for development of encapsulation systems for the delivery of water insoluble actives.

Poly(levodopa)-modified β-glucan as a candidate for wound dressings

Levodopa (biological precursor of dopamine) is sometimes used instead of dopamine for synthesis of highly adhesive polycatecholamine coatings on different materials. However, in comparison of polydopamine, little is known about biological safety of poly(levodopa) coatings and their efficacy in binding of therapeutically active substances. Therefore, thermally polymerized curdlan hydrogel was modified via two different modes using levodopa instead of commonly used dopamine and then coupled with gentamicin - aminoglycoside antibiotic. Physicochemical properties, biological safety and antibacterial potential of the hydrogels were evaluated. Poly(levodopa) deposited on curdlan exhibited high stability in wide pH range and blood or plasma, were nontoxic in zebrafish model and favored blood clot formation. Simultaneously, one of hydrogel modification modes allowed to observe high gentamicin binding capacity, antibacterial activity, relatively high nontoxicity for fibroblasts and was unfavorable for fibroblasts adhesion. Such modified poly(levodopa)-modified curdlan showed therefore high potential as wound dressing biomaterial.

Recent developments in mussel-inspired materials for biomedical applications

Over the decades, researchers have strived to synthesize and modify nature-inspired biomaterials, with the primary aim to address the challenges of designing functional biomaterials for regenerative medicine and tissue engineering. Among these challenges, biocompatibility and cellular interactions have been extensively investigated. Some of the most desirable characteristics for biomaterials in these applications are the loading of bioactive molecules, strong adhesion to moist areas, improvement of cellular adhesion, and self-healing properties. Mussel-inspired biomaterials have received growing interest mainly due to the changes in mechanical and biological functions of the scaffold due to catechol modification. Here, we summarize the chemical and biological principles and the latest advancements in production, as well as the use of mussel-inspired biomaterials. Our main focus is the polydopamine coating, the conjugation of catechol with other polymers, and the biomedical applications that polydopamine moieties are used for, such as matrices for drug delivery, tissue regeneration, and hemostatic control. We also present a critical conclusion and an inspired view on the prospects for the development and application of mussel-inspired materials.

Colored Surfaces Made of Synthetic Eumelanin

The polymerization of 3,4-dihydroxy-L-phenylalanine leads to a carboxylic acid-rich synthetic melanin-like material (poly-L-DOPA). Synthetic melanin most resembles natural eumelanin in chemical structure. However, its deposition on surfaces leading to colored surfaces by interference is not as easy to accomplish as in the case of the preparation of colored surfaces by dopamine hydrochloride polymerization. This study deals with the preparation of new colored surfaces made from poly-L-DOPA displaying vivid colors by interference. These surfaces were obtained by depositing thin films of poly-L-DOPA on a reflective silicon nitride substrate. A high ionic strength in the polymerization medium was essential to accomplish the coating. The effect of ionic strength on the resulting surfaces was studied via reflectance, Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The refractive index was determined by ellipsometry, and was nearly constant to 1.8 when λ > 650 nm. In the visible spectral region, the imaginary part of the refractive index becomes relevant. The refractive index in the visible wavelength range (400–600 nm) was in the range 1.7–1.80.

Hybrid Metal-Phenol Nanoparticles with Polydopamine-like Coating for PET/SPECT/CT Imaging

The validation of metal-phenolic nanoparticles (MPNs) in preclinical imaging studies represents a growing field of interest due to their versatility in forming predesigned structures with unique properties. Before MPNs can be used in medicine, their pharmacokinetics must be optimized so that accumulation in nontargeted organs is prevented and toxicity is minimized. Here, we report the fabrication of MPNs made of a coordination polymer core that combines In(III), Cu(II), and a mixture of the imidazole 1,4-bis(imidazole-1-ylmethyl)-benzene and the catechol 3,4-dihydroxycinnamic acid ligands. Furthermore, a phenolic-based coating was used as an anchoring platform to attach poly(ethylene glycol) (PEG). The resulting MPNs, with effective hydrodynamic diameters of around 120 nm, could be further derivatized with surface-embedded molecules, such as folic acid, to facilitate in vivo targeting and multifunctionality. The prepared MPNs were evaluated for in vitro plasma stability, cytotoxicity, and cell internalization and found to be biocompatible under physiological conditions. First, biomedical evaluations were then performed by intrinsically incorporating trace amounts of the radioactive metals 111In or 64Cu during the MPN synthesis directly into their polymeric matrix. The resulting particles, which had identical physicochemical properties to their nonradioactive counterparts, were used to perform in vivo single-photon emission computed tomography (SPECT) and positron emission tomography (PET) in tumor-bearing mice. The ability to incorporate multiple metals and radiometals into MPNs illustrates the diverse range of functional nanoparticles that can be prepared with this approach and broadens the scope of these nanoconstructs as multimodal preclinical imaging agents.

Fluorescence copolymer-based dual-signal monitoring tyrosinase activity and its inhibitor screening via blue-green emission transformation

Tyrosinase (TYR) is a crucial enzyme in melanin metabolism and catecholamine production, its abnormal overexpression is closely associated with many human diseases involving melanoma cancer, vitiligo, Parkinson's disease and so on. Herein, a dual-signal fluorescence sensing system for monitoring TYR activity is constructed depending on the transformation of blue-green fluorescence emission of copolymer. The developed sensing system is based on TYR catalyzing the hydroxylation of mono-phenol to o-diphenol and the conversion of fluorescence copolymer (FCP) blue emission (430 nm) and green emission (535 nm) in the presence of PEI. In the system, both blue and green emission exhibit a high selectivity and sensitivity (S/B up to 300 and 30 for blue and green emission, respectively) toward TYR in the range from 0.5 to 2.5 U/mL with the detection limit of 0.002 U/mL and 0.06 U/mL, respectively. Additionally, this assay is used to detect TYR in human serum with excellent recovery even at 30% human serum concentrations. Furthermore, it still has been successfully applied to TYR inhibitor screening by taking kojic acid as a model. We believe that our developed sensor has great potential application in TYR-associated disease diagnosis and treatment and drug discovery.

New insight into melanin for food packaging and biotechnology applications

Melanin is a dark brown to black biomacromolecule with biologically active multifunctional properties that do not have a precise chemical structure, but its structure mainly depends on the polymerization conditions during the synthesis process. Natural melanin can be isolated from various animal, plant, and microbial sources, while synthetic melanin-like compounds can be synthesized by simple polymerization of dopamine. Melanin is widely used in various areas due to its functional properties such as photosensitivity, light barrier property, free radical scavenging ability, antioxidant activity, etc. It also has an excellent ability to act as a reducing agent and capping agent to synthesize various metal nanoparticles. Melanin nanoparticles (MNP) or melanin-like nanoparticles (MLNP) have the unique potential to act as functional materials to improve nanocomposite films' physical and functional properties. Various food packaging and biomedical applications have been made alone or by mixing melanin or MLNP. In this review, the general aspects of melanin that highlight biological activity, along with a description of MNP and the use as nanofillers in packaging films as well as reducing and capping agents and biomedical applications, were comprehensively reviewed.

Poly-dopamine, poly-levodopa, and poly-norepinephrine coatings: Comparison of physico-chemical and biological properties with focus on the application for blood-contacting devices

Thanks to its simplicity, versatility, and secondary reactivity, dopamine self-polymerized coatings (pDA) have been widely used in surface modification of biomaterials, but the limitation in secondary molecular grafting and the high roughness restrain their application in some special scenarios. Therefore, some other catecholamine coatings analog to pDA have attracted more and more attention, including the smoother poly-norepinephrine coating (pNE), and the poly-levodopa coating (pLD) containing additional carboxyl groups. However, the lack of a systematic comparison of the properties, especially the biological properties of the above three catecholamine coatings, makes it difficult to give a guiding opinion on the application scenarios of different coatings. Herein, we systematically studied the physical, chemical, and biological properties of the three catecholamine coatings, and explored the feasibility of their application for the modification of biomaterials, especially cardiovascular materials. Among them, the pDA coating was the roughest, with the largest amount of amino and phenolic hydroxyl groups for molecule grafting, and induced the strongest platelet adhesion and activation. The pLD coating was the thinnest and most hydrophilic but triggered the strongest inflammatory response. The pNE coating was the smoothest, with the best hemocompatibility and histocompatibility, and with the strongest cell selectivity of promoting the proliferation of endothelial cells while inhibiting the proliferation of smooth muscle cells. To sum up, the pNE coating may be a better choice for the surface modification of cardiovascular materials, especially those for vascular stents and grafts, but it is still not widely recognized.

Codeposition of Levodopa and Polyethyleneimine: Reaction Mechanism and Coating Construction

Mussel-inspired poly(catecholamine) coatings from polydopamine (PDA) have been widely studied to design functional coatings for various materials. The chemical precursor of dopamine (DA), levodopa (l-DOPA, 3,4-dihydroxyphenyl-l-alanine), is known as the main element of mussel adhesive foot protein, but it is relatively hard to be constructed into a desirable coating on a given material surface under the same conditions as those for DA. Herein, we report a codeposition strategy to achieve the rapid fabrication of mussel-inspired coatings by l-DOPAwith polyethyleneimine (PEI) and to deeply understand the formation mechanism of those aggregates and coatings from l-DOPA/PEI. DFT calculations, fluorescence spectra, nuclear magnetic resonance analysis, and liquid chromatography-tandem mass spectrometry identification demonstrate that the formation of l-DOPA/PEI aggregates is effectively accelerated by PEI crosslinking with those intermediates of oxidized l-DOPA, including l-DOPAquinone and 5,6-dihydroxyindole-2-carboxylic acid as well as 5,6-dihydroxyindole, through Michael-addition and Schiff-base reactions. Therefore, we can facilely control the growth rate and the particle size of the l-DOPA/PEI aggregates in the deposition solution by adjusting the concentration of PEI. The coating formation rate of l-DOPA/PEI is four times faster than that of PDA and DA/PEI within 12 h. These l-DOPA/PEI coatings are demonstrated to display potential as structure colors, superhydrophilic surfaces, and antibacterial materials.

Electrochemically assisted synthesis of poly(3,4-dihydroxyphenylalanine) fluorescent organic nanoparticles for sensing applications

Facile preparation of polyDOPA-FONs is achieved via the electrochemical oxidation method.

Polydopamine Coating of Glucan Particles Increases Uptake into Peyer's Patches

Glucan particles (GPs) are hollow, porous 3-4 μm microspheres derived from the cell walls of Baker's yeast (Saccharomyces cerevisiae). The β-1,3-D glucan outer shell of GPs provides for receptor-mediated uptake by phagocytic cells expressing β-glucan receptors. GPs have been used for efficient encapsulation of different types of payloads (DNA, siRNA, proteins, antigens, small molecules), and these payloads have been delivered in vivo by a variety of routes including oral delivery. It is known that GPs are transported across the intestinal epithelium by Peyer's patch M-cells and accumulate in a subset of CD11c+Langerin-positive dendritic cells (DC) in the subepithelial dome (SED). An increase in GP uptake in the intestinal epithelium is needed to improve our efforts to develop GPs for oral delivery of therapeutics and vaccines. In this Article, we report that polydopamine coating of GPs (PDA-GPs) increases transepithelial uptake. Synthesis of PDA-GPs was optimized to allow for encapsulation of payloads inside the hollow cavity of GPs. PDA-GPs and GP controls were orally administered to mice, and PDA-GPs showed a 42% increased uptake in SED phagocytes. PDA-GP uptake by SED phagocytes in control and M-cell-depleted mice demonstrated both M-cell-dependent and -independent mechanisms. In future studies, we will evaluate PDA-GPs for oral vaccine delivery and the use of PDA-functional groups for secondary surface derivatization to generate particles with ligands targeting other intestinal epithelium cell-surface receptors.

Modular, tissue-specific, and biodegradable hydrogel cross-linkers for tissue engineering

Synthetic hydrogels are investigated extensively in tissue engineering for their tunable physicochemical properties but are bioinert and lack the tissue-specific cues to produce appropriate biological responses. To introduce tissue-specific biochemical cues to these hydrogels, we have developed a modular hydrogel cross-linker, poly(glycolic acid)-poly(ethylene glycol)-poly(glycolic acid)-di(but-2-yne-1,4-dithiol) (PdBT), that can be functionalized with small peptide-based cues and large macromolecular cues simply by mixing PdBT in water with the appropriate biomolecules at room temperature. Cartilage- and bone-specific PdBT macromers were generated by functionalization with a cartilage-associated hydrophobic N-cadherin peptide, a hydrophilic bone morphogenetic protein peptide, and a cartilage-derived glycosaminoglycan, chondroitin sulfate. These biofunctionalized PdBT macromers can spontaneously cross-link polymers such as poly(N-isopropylacrylamide) to produce rapidly cross-linking, highly swollen, cytocompatible, and hydrolytically degradable hydrogels suitable for mesenchymal stem cell encapsulation. These favorable properties, combined with PdBT's modular design and ease of functionalization, establish strong potential for its usage in tissue engineering applications.

Oxidation-Mediated, Zwitterionic Polydopamine Coatings for Marine Antifouling Applications

We synthesized a zwitterionic dopamine derivative ( ZW-DOPA) containing both catechol and amine groups, and we demonstrated an excellent marine antifouling surface by controlling the oxidation of ZW-DOPA. The oxidation was mediated by the deprotonation of catechol or the addition of an oxidant (ammonium persulfate (AP) or sodium periodate (NaIO₄)). The oxidation and subsequent molecular transformation of ZW-DOPA was investigated over time by UV-vis spectroscopy. Among the different oxidation conditions tested, NaIO₄-induced ZW-DOPA coating was the most efficient and successfully formed on various substrates, such as titanium dioxide, stainless steel, and nylon. Compared with uncoated substrates, ZW-DOPA-coated substrates showed high resistance to marine diatom adhesion. Considering the ease of use and substrate independence of the ZW-DOPA coating, this method shows promise as a basis for inhibiting marine fouling on a variety of substrates used in the marine industry and aquatic environments.

Salt-Induced, Continuous Deposition of Supramolecular Iron(III)-Tannic Acid Complex

One-step assembly of iron(III)-tannic acid (Fe³⁺-TA) complex forms nanothin (∼10 nm) films on various substrates within minutes. In this deposition scheme, however, the film does not grow continuously over time even though Fe³⁺-TA complex is still abundant in the coating solution. In this paper, we report that the salt addition dramatically changes the one-off coating characteristic to continuous one, and each salt has its optimum concentration ( C_MFT) that produces maximum film thickness. For detailed investigation of the salt effects, we employed various salts, including LiCl, NaCl, KCl, CaCl₂, SrCl₂, BaCl₂, NaBr, and NaNO₃, and found that only cations played an important role in the continuous deposition of the Fe³⁺-TA complex, with smaller C_MFT values for the cations of higher valency and larger size. On the basis of the results, we suggested that the positively charged cations screened the negative surface charges of Fe³⁺-TA complex particles, leading to coagulation and continuous deposition, further supported by the ζ-potential measurement and time-resolved dynamic light-scattering analysis.

Free-standing polydopamine films generated in the presence of different metallic ions: the comparison of reaction process and film properties

Polydopamine is widely used in surface modification, nanofiltration, photonic devices and drug delivery. The formation mechanism and properties of polydopamine are modified by the experimental conditions. Herein we demonstrated a comparison study of free-standing polydopamine films generated at the air-solution interface and their corresponding nanoparticles in solutions, in the presence of various metallic cations, Na+, Ca2+, Mg2+ and Co2+. Adding metallic ions influenced the intermediates in dopamine polymerization, and in turn the morphology and properties of the produced free-standing polydopamine films. Moreover, we observed that the polymerization process accompanying the stratification determines the formation of free-standing films at the air-solution interface: the fast polymerization of dopamine in a Co2+ environment leads to a rugged film surface and porous film body, whereas the comparatively slow polymerization of dopamine under conditions of other metallic ions results in a smooth and solid film. In addition, the water contact angles of the upper and lower surface of the polydopamine films were different. This investigation enriches our knowledge of dopamine polymerization in different environments, which is particularly useful for further application of free-standing polydopamine films.

New Poly(lactic acid) Active Packaging Composite Films Incorporated with Fungal Melanin

In this work, fungal melanin was used for the first time to prepare poly(lactic acid)-based composites. The films of various melanin concentrations (0.025%, 0.05% and 0.2% w/w) were prepared using an extrusion method. The mechanical, antioxidant, antimicrobial, water vapor and UV-Vis barrier properties, as well as available polyphenolics on the surface, were studied. FT-IR and Raman spectroscopy studies were carried out to analyze the chemical composition of the resulting films. The hydrophobicity, color response, thermal, optical properties, and opacity values were also determined. The results of this study show that the addition of fungal melanin to poly(lactic acid) (PLA) as a modifier influenced mechanical and water vapor barrier properties depending on melanin concentration. In low concentration, melanin enhanced the mechanical and barrier properties of the modified films, but in larger amounts, the properties were decreased. The UV-Vis barrier properties of PLA/melanin composites were marginally improved. Differential Scanning Calorimetry (DSC) analysis indicated that crystallinity of PLA increased by the addition of melanin, but this did not affect the thermal stability of the films. Modified PLA/melanin films showed good antioxidant activity and were active against Enterococcus faecalis, Pseudomonas aeruginosa and Pseudomonas putida. The addition of melanin caused changes in color values, decreasing lightness and increasing the redness and yellowness of films. Based on the results of this study, fungal melanin has good potential to be exploited as a value-added modifier that can improve the overall properties of PLA.

Polydopamine Surface Chemistry: A Decade of Discovery

Polydopamine is one of the simplest and most versatile approaches to functionalizing material surfaces, having been inspired by the adhesive nature of catechols and amines in mussel adhesive proteins. Since its first report in 2007, a decade of studies on polydopamine molecular structure, deposition conditions, and physicochemical properties have ensued. During this time, potential uses of polydopamine coatings have expanded in many unforeseen directions, seemingly only limited by the creativity of researchers seeking simple solutions to manipulating surface chemistry. In this review, we describe the current state of the art in polydopamine coating methods, describe efforts underway to uncover and tailor the complex structure and chemical properties of polydopamine, and identify emerging trends and needs in polydopamine research, including the use of dopamine analogs, nitrogen-free polyphenolic precursors, and improvement of coating mechanical properties.

Biomimetic Oxygen-Evolving Photobacteria Based on Amino Acid and Porphyrin Hierarchical Self-Organization

Biomimetic organization provides a promising strategy to develop functional materials and understand biological processes. However, how to mimic complex biological systems using simple biomolecular units remains a great challenge. Herein, we design and fabricate a biomimetic cyanobacteria model based on self-integration of small bioinspired molecules, including amphiphilic amino acid, 3,4-dihydroxyphenylalanine (DOPA), and metalloporphyrin and cobalt oxide nanoparticles (Co₃O₄ NPs), with the assistance of chemical conjugation and molecular self-assembly. The assembled amino acid fiber can be modified by DOPA to form covalently bound DOPA melanin containing hydroxyl and quinone species via Schiff base reaction. The adhering template can further tune the self-assembly of metalloporphyrin and Co₃O₄ NPs into J-aggregation and dispersive distribution, respectively, mainly via coordination binding. Metalloporphyrin molecules in the resulting hybrid fibers capture light; quinone species accept the excited electrons, and Co₃O₄ NPs catalyze water oxidation. Thus, the essential components of the photosystem-II protein complex in cyanobacteria are simplified and engineered into a simple framework, still retaining a similar photosynthetic mechanism. In addition, this architecture leads to efficient coupling of antenna, quinone-type reaction center, and photocatalyst, which increases the flux of light energy from antenna to reaction center for charge separation, resulting in enhanced oxygen evolution rate with excellent sustainability.

A one step method for the functional and property modification of DOPA based nanocoatings

Biomimetic poly(catecholamine) coatings have gained much attention in recent years due to their versatility as functional materials. Despite this, only limited methods are available to modify the function and property of poly(catecholamine) coatings, primarily through post-modification methods. Our approach reported herein provides a simple approach to the fabrication of novel functionalized poly(catecholamine) coatings. The strategy employs the copolymerization of N-Ac-3,4-dihydroxyphenylalanine methyl ester (NADOPAMe) with nucleophilic additives, giving rise to nano-coatings on various surfaces including plastic, metal, glass and polymers. With the appropriate choice of nucleophilic additives, coatings with desired properties can be achieved. This is demonstrated through the fabrication of a redox responsive coating based on NADOPAMe with cysteamine as additive, which shows a concentration-dependent glutathione (GSH) responsive behavior. The ability to utilize this as a controlled release system is also demonstrated.

Well-defined protein immobilization on photo-responsive phosphorylcholine polymer surfaces

In this study, we propose a new polymer substrate that is able to covalently couple intended proteins and reduce nonspecific protein fouling. Poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-ran-N-methacryloyl-(L)-tyrosinemethylester (MAT)] [P(MPC/MAT)] was synthesized by free-radical polymerization. The photooxidation of the MAT unit in the copolymer was observed under ultraviolet (UV) light at 254 nm. P(MPC/MAT) was spin-coated on silicon (Si) and gold substrates. Without UV irradiation of the polymer-coated surface, P(MPC/MAT) physisorbed on the substrates, and the thickness of the polymer layer was less than 10 nm, regardless of the polymer concentration in the coating solution. In contrast, when the polymer-coated surface was irradiated with UV light, the thickness of the polymer layer could be controlled by changing the polymer concentration of the coating solution. Competitive protein adsorption on P(MPC/MAT) was studied. Bovine serum albumin was first contacted with the surface and later challenged with bovine fibrinogen. On bare gold and Si substrates, a large amount of albumin was adsorbed, and the competitive adsorption of albumin and fibronectin was observed. In contrast, the non-UV-irradiated P(MPC/MAT) surface effectively reduced protein adsorption. Interestingly, on the UV-irradiated P(MPC/MAT) surface, the primary protein preferably bonded, and significantly less secondary protein was adsorbed compared to primary protein. Cell adhesion was also tested on the substrate to clarify the effects of proteins existing on the substrates. On the bare Si surface, many adherent cells were observed, regardless of the protein pretreatment. On the non-UV-irradiated P(MPC/MAT) surface, cell adhesion was effectively reduced along with protein adsorption. Cell adhesion on the UV-irradiated P(MPC/MAT) surface depended strongly on the type of protein that was initially in contact with the surface. We concluded that the desired proteins could be immobilized on the photo-activated P(MPC/MAT) surface while preserving their function. Moreover, competitive protein exchange and multilayer adsorption hardly occurred on the surface.

Evidence of Porphyrin-Like Structures in Natural Melanin Pigments Using Electrochemical Fingerprinting

Eumelanins are extended heterogeneous biopolymers composed of molecular subunits with ambiguous macromolecular topology. Here, an electrochemical fingerprinting technique is described, which suggests that natural eumelanin pigments contain indole-based tetramers that are arranged into porphyrin-like domains. Spectroscopy and density functional theory calculations suggest that sodium ions undergo occupancy-dependent stepwise insertion into the core of porphyrin-like tetramers in natural eumelanins at discrete potentials.

Multifunctional Polyphenols- and Catecholamines-Based Self-Defensive Films for Health Care Applications

In an era of relentless evolution of antimicrobial resistance, there is an increasing demand for the development of efficient antimicrobial coatings or surfaces for food, biomedical, and industrial applications. This study reports the laccase-catalyzed room-temperature synthesis of mechanically robust, thermally stable, broad spectrum antimicrobial films employing interfacial interactions between poly(vinyl alcohol), PVA, and 14 naturally occurring catecholamines and polyphenols. The oxidative products of catecholamines and polyphenols reinforce the PVA films and also alter their surface and bulk properties. Among the catecholamines-reinforced films, optimum surface and bulk properties can be achieved by the oxidative products of epinephrine. For polyphenols, structure-property correlation reveals an increase in surface roughness and elasticity of PVA films with increasing number of phenolic groups in the precursors. Interestingly, PVA films reinforced with oxidized/polymerized products of pyrogallol (PG) and epinephrine (EP) display potent antimicrobial activity against pathogenic Gram-positive and Gram-negative strains, whereas hydroquinone (HQ)-reinforced PVA films display excellent antimicrobial properties against Gram-positive bacteria only. We further demonstrate that HQ and PG films retain their antimicrobial efficacy after steam sterilization. With an increasing trend of giving value to natural and renewable resources, our results have the potential as durable self-defensive antimicrobial surfaces/films for advanced healthcare and industrial applications.

Biomedical and Clinical Importance of Mussel-Inspired Polymers and Materials

The substance secreted by mussels, also known as nature's glue, is a type of liquid protein that hardens rapidly into a solid water-resistant adhesive material. While in seawater or saline conditions, mussels can adhere to all types of surfaces, sustaining its bonds via mussel adhesive proteins (MAPs), a group of proteins containing 3,4-dihydroxyphenylalanine (DOPA) and catecholic amino acid. Several aspects of this adhesion process have inspired the development of various types of synthetic materials for biomedical applications. Further, there is an urgent need to utilize biologically inspired strategies to develop new biocompatible materials for medical applications. Consequently, many researchers have recently reported bio-inspired techniques and materials that show results similar to or better than those shown by MAPs for a range of medical applications. However, the susceptibility to oxidation of 3,4-dihydroxyphenylalanine poses major challenges with regard to the practical translation of mussel adhesion. In this review, various strategies are discussed to provide an option for DOPA/metal ion chelation and to compensate for the limitations imposed by facile 3,4-dihydroxyphenylalanine autoxidation. We discuss the anti-proliferative, anti-inflammatory, anti-microbial activity, and adhesive behaviors of mussel bio-products and mussel-inspired materials (MIMs) that make them attractive for synthetic adaptation. The development of biologically inspired adhesive interfaces, bioactive mussel products, MIMs, and arising areas of research leading to biomedical applications are considered in this review.

Mussel-adhesive-inspired fabrication of multifunctional silver nanoparticle assemblies

The assembly of metal nanoparticles (NPs) has attracted a great deal of attention recently because of their collective properties that could not be exhibited by individual NPs. Here a one-step approach was reported for the fabrication of spherical silver NP assemblies (AgNAs). The formation of AgNAs simply included the stirring of silver ammonia and 3,4-dihydroxy-l-phenylalanine (DOPA) in aqueous solution at room temperature, in which DOPA acted as a reductant for AgNPs first because of its reducing ability and then directed the assembly of AgNPs into AgNAs. The AgNAs exhibited hierarchical structure with controllable sizes ranging from 180 to 610 nm by adjusting the concentrations of reagents. The two individual components, AgNPs and polyDOPA, also allowed AgNAs with multiple functions as demonstrated in this study of durable catalytic activity, high SERS sensitivity, and good antioxidant properties. The thin polyDOPA layer coated on AgNAs further offered the opportunity to modify the surface of AgNAs. The results presented here may provide a green and facile approach to designing multifunctional NP assemblies.

Polydopamine and eumelanin: from structure-property relationships to a unified tailoring strategy

CONSPECTUS: Polydopamine (PDA), a black insoluble biopolymer produced by autoxidation of the catecholamine neurotransmitter dopamine (DA), and synthetic eumelanin polymers modeled to the black functional pigments of human skin, hair, and eyes have burst into the scene of materials science as versatile bioinspired functional systems for a very broad range of applications. PDA is characterized by extraordinary adhesion properties providing efficient and universal surface coating for diverse settings that include drug delivery, microfluidic systems, and water-treatment devices. Synthetic eumelanins from dopa or 5,6-dihydroxyindoles are the focus of increasing interest as UV-absorbing agents, antioxidants, free radical scavengers, and water-dependent hybrid electronic-ionic semiconductors. Because of their peculiar physicochemical properties, eumelanins and PDA hold considerable promise in nanomedicine and bioelectronics, as they are biocompatible, biodegradable, and exhibit suitable mechanical properties for integration with biological tissues. Despite considerable similarities, very few attempts have so far been made to provide an integrated unifying perspective of these two fields of technology-oriented chemical research, and progress toward application has been based more on empirical approaches than on a solid conceptual framework of structure-property relationships. The present Account is an attempt to fill this gap. Following a vis-à-vis of PDA and eumelanin chemistries, it provides an overall view of the various levels of chemical disorder in both systems and draws simple correlations with physicochemical properties based on experimental and computational approaches. The potential of large-scale simulations to capture the macroproperties of eumelanin-like materials and their hierarchical structures, to predict the physicochemical properties of new melanin-inspired materials, to understand the structure-property-function relationships of these materials from the bottom up, and to design and optimize materials to achieve desired properties is illustrated. The impact of synthetic conditions on melanin structure and physicochemical properties is systematically discussed for the first time. Rational tailoring strategies directed to critical control points of the synthetic pathways, such as dopaquinone, DAquinone, and dopachrome, are then proposed, with a view to translating basic chemical knowledge into practical guidelines for material manipulation and tailoring. This key concept is exemplified by the recent demonstration that varying DA concentration, or using Tris instead of phosphate as the buffer, results in PDA materials with quite different structural properties. Realizing that PDA and synthetic eumelanins belong to the same family of functional materials may foster unprecedented synergisms between research fields that have so far been apart in the pursuit of tailorable and marketable materials for energy, biomedical, and environmental applications.