Electrically Reversible Redox-Switchable Polydopamine Films for Regulating Cell Behavior

A novel modified polydopamine based on melanin-like materials for antibacterial, hydrophobic, and ultraviolet protective of textiles

The development of environmentally friendly multifunctional auxiliaries for textile modification is the focus of attention in textile industry in recent years. Polydopamine is an important biological macromolecule and widely used in biomedicine, nanomaterials, material surface modification and other fields. In this study, the novel multifunctional melanin-like nanoparticles (Nha-PDA NPs) were prepared and used for antibacterial, hydrophobic, and UV protective of textiles. Nha-PDA NPs were prepared with dopamine (DA) and n-hexylamine (Nha) by simple autoxidation copolymerization. Nha-PDA NPs were bound to the fabric surface through the PDA structure in Nha-PDA NPs that has been widely confirmed to have strong adhesion on the surface of many materials. The modified fabrics, Nha-PDA NPs@Cotton, had good hydrophobic, antibacterial and UV protective properties. The static water contact angles of the modified fabrics could reach 120°. The antibacterial rates of Nha-PDA NPs@Cotton against E. coli and S. aureus were above 85 %. The maximum UPF value of the modified cotton was 362, indicating that the ultraviolet protection performance was excellent. The fabric modified with multifunctional melanin-like nanoparticle provides a green way for the multifunctional modification of textiles.

Applications of Polydopamine in Implant Surface Modification

There is great clinical demand for orthopedic and dental implant surface modification methods to prevent osseointegration failure and improve implant biological functions. Notably, dopamine (DA) can be polymerized to form polydopamine (PDA), which is similar to the adhesive proteins secreted by mussels, to form a stable bond between the bone surface and implants. Therefore, PDA has the potential to be used as an implant surface modification material with good hydrophilicity, roughness, morphology, mechanical strength, biocompatibility, antibacterial activity, cellular adhesion, and osteogenesis. In addition, PDA degradation releases DA into the surrounding microenvironment, which is found to play an important role in regulating DA receptors on both osteoblasts and osteoclasts during the bone remodeling process. Furthermore, the adhesion properties of PDA suggest its use as an intermediate layer in assisting other functional bone remodeling materials, such as nanoparticles, growth factors, peptides, and hydrogels, to form "dual modifications." The purpose of this review is to summarize the recent progress in research on PDA and its derivatives as orthopedic and dental implant surface modification materials and to analyze the multiple functions of PDA.

Advanced surface engineering of titanium materials for biomedical applications: From static modification to dynamic responsive regulation

Titanium (Ti) and its alloys have been widely used as orthopedic implants, because of their favorable mechanical properties, corrosion resistance and biocompatibility. Despite their significant success in various clinical applications, the probability of failure, degradation and revision is undesirably high, especially for the patients with low bone density, insufficient quantity of bone or osteoporosis, which renders the studies on surface modification of Ti still active to further improve clinical results. It is discerned that surface physicochemical properties directly influence and even control the dynamic interaction that subsequently determines the success or rejection of orthopedic implants. Therefore, it is crucial to endow bulk materials with specific surface properties of high bioactivity that can be performed by surface modification to realize the osseointegration. This article first reviews surface characteristics of Ti materials and various conventional surface modification techniques involving mechanical, physical and chemical treatments based on the formation mechanism of the modified coatings. Such conventional methods are able to improve bioactivity of Ti implants, but the surfaces with static state cannot respond to the dynamic biological cascades from the living cells and tissues. Hence, beyond traditional static design, dynamic responsive avenues are then emerging. The dynamic stimuli sources for surface functionalization can originate from environmental triggers or physiological triggers. In short, this review surveys recent developments in the surface engineering of Ti materials, with a specific emphasis on advances in static to dynamic functionality, which provides perspectives for improving bioactivity and biocompatibility of Ti implants.

A versatile and tunable bio-patterning platform for the construction of various cell array biochips

In this work, we report a versatile and tunable platform for the construction of various cell array biochips using a simple soft lithographic approach to pattern polydopamine (PDA) arrays via microcontact printing (μCP). Instead of direct polymerization of PDA on the polydimethylsiloxane (PDMS) tips, dopamine monomers were first printed on the substrate followed by a self-oxidative polymerization step facilitated by ammonia vapor to grow PDA in situ, which greatly reduced the reaction time and prevented the PDMS tips from damaging. The improved robustness and utility of the PDMS tips allows the formation of tunable PDA array chips with controllable PDA feature size and shape. As a result, single cell, multi-cells and cell line arrays can be constructed. The obtained cell array chips showed high single cell capture efficiency, providing a standardized single cell array analysis platform. Meanwhile, the adhered cells can maintain excellent viability and proliferation ability on the PDA chips. Moreover, a cytotoxicity sensor with single cell resolution was enabled on the single cell array chip. This work provides a promising cell array biochip platform for high-throughput cellular analysis and cell screening.

Multi-functional plant flavonoids regulate pathological microenvironments for vascular stent surface engineering

In-stent restenosis (ISR) and late thrombosis, usually caused by excessive smooth muscle cell (SMC) proliferation and delayed endothelial layer repair, respectively, are the main risks for the failure of vascular stent implantation. For years, modification of stents with biomolecules that could selectively inhibit SMC proliferation and support endothelial cell (EC) growth had drawn extensive attention. However, the modulatory effect of these biomolecules faces the impact of oxidative stress, inflammation, and hyperlipidemia of the pathological vascular microenvironment, which is caused by the stent implantation injury and atherosclerosis lesions. Here, we modified stents with a natural and multi-functional flavonoid, baicalin (BCL), using poly-dopamine (PDA) coating technology to combat the harmful impact of the pathological microenvironment. Stent with an appropriate BCL immobilization density (approximately 2.03 μg/cm2) successfully supported ECs growth while inhibited SMC proliferation. Furthermore, baicalin-modified surfaces regulated the oxidative stress, inflammation, and high-lipid of the pathological microenvironment to inhibit endothelial dysfunction and the oxidized low-density lipoprotein (ox-LDL)-induced macrophage foam cells formation. In vivo results showed that baicalin-modified stents exhibited significant anti-ISR, anti-inflammatory, and endothelialization-promoting functions. Our study suggests that the multi-functional baicalin with pathological microenvironment-regulation (PMR) effect has potential use in the surface engineering of cardiovascular devices. STATEMENT OF SIGNIFICANCE: Empowering vascular stents with selective modulation of smooth muscle cells and endothelial cells by surface technology has become an important research direction for stent surface engineering. However, stent coatings that can furthermodulate the pathological microenvironment of blood vessels have been rarely reported. In this study, we constructed a multifunctional coating based on a flavonoid, baicalin, which can selectively modulate vascular wall cells and improve the pathological microenvironment. This study may provide a reference for developing advanced vascular stents.

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.

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.

The comparison of biological effects of bacterial and synthetic melanins in neuroblastoma cells

Melanins belong to a group of pigments of different structure and origin. They can be produced synthetically or isolated from living organisms. A number of studies have reported testing of various melanins in neurological studies providing different outcomes. Because the structure of melanins can have an effect on obtained results in cell toxicity studies, we present here our original study which aimed to compare the biological effects of bacterial melanin (biotechnologically obtained from B. thuringiensis) with that of synthetic melanin in neuroblastoma cells. Both melanins were structurally characterized in detail. After melanin treatment (0-200 μg/mL), cell viability, glutathione levels, cell morphology and respiration were assessed in SH-SY5Y cells. The structural analysis showed that bacterial melanin is more hydrophilic according to the presence of larger number of -OH moieties. After melanin treatment, we found that synthetic melanin at similar dosage caused always larger cell impairment compared to bacterial melanin. In addition, more severe toxic effect of synthetic melanin was found in mitochondria. In general, we conclude that more hydrophilic, bacterial melanin induced lower toxicity in neuroblastoma cells in comparison to synthetic melanin. Our findings can be useable for neuroscientific studies estimating the potential use for study of neuroprotection, neuromodulation or neurotoxicity.

A novel polydopamine-modified metal organic frameworks catalyst with enhanced catalytic performance for efficient degradation of sulfamethoxazole in wastewater

In this study, a novel polydopamine (PDA)-modified metal organic frameworks (MOFs) catalyst (MIL/PDA) was successfully fabricated to activate persulfate (PS) for the degradation of sulfamethoxazole (SMX) in wastewater. The experimental results indicated that PDA-modified catalyst exhibited superior catalytic performance and enhanced the degradation of SMX (91.5%) compared to pure MOFs. The physical-chemical properties of the MIL/PDA catalyst were comprehensively characterized, and the applications in the catalytic degradation of SMX were evaluated. It was found that the modification of PDA enhanced the electron transfer, while promoting the redox cycle of Fe(III)/Fe(II), which in turn boosted the production of active oxygen species. Furthermore, MIL/PDA showed high stability and reusable performance over multiple cycles. Both radical and non-radical pathways were jointly involved in the activation process of PS were confirmed by quenching experiments combined with electron paramagnetic resonance (EPR). Based on this, the possible mechanism of the catalytic reaction was investigated. Finally, five degradation pathways of SMX degradation were proposed according to the results of liquid chromatography-mass spectrometry (LC-MS). This work provided a new insight into the design of novel and efficient heterogeneous catalysts for advanced wastewater treatment.

Versatile polyphenolic platforms in regulating cell biology

Polyphenolic materials are a class of fascinating and versatile bioinspired materials for biointerfacial engineering. In particular, due to the presence of active chemical groups, a series of unique physicochemical properties become accessible and tunable of the as-prepared polyphenolic platforms, which could delicately regulate the cell activities via cell-material contact-dependent interactions. More interestingly, polyphenols could also affect the cell behaviors via cell-material contact-independent manner, which arise due to their intrinsically functional characteristics (e.g., antioxidant and photothermal behaviors). As such, a comprehensive understanding on the relationship between material properties and desired biomedical applications, as well as the underlying mechanism at the cellular and molecular level would provide material design principles and accelerate the lab-to-clinic translation of polyphenolic platforms. In this review, we firstly give a brief overview of cell hallmarks governed by surrounding cues, followed by the introduction of polyphenolic material engineering strategies. Subsequently, a detailed discussion on cell-polyphenols contact-dependent interfacial interaction and contact-independent interaction was also carefully provided. Lastly, their biomedical applications were elaborated. We believe that this review could provide guidances for the rational material design of multifunctional polyphenols and extend their application window.

Physicochemical and Electrochemical Characterization of Electropolymerized Polydopamine Films: Influence of the Deposition Process

Polydopamine (PDA) is a synthetic eumelanin polymer which is, to date, mostly obtained by dip coating processes. In this contribution, we evaluate the physical and electrochemical properties of electrochemically deposited PDA films obtained by cyclic voltammetry or pulsed deposition. The obtained PDA thin films are investigated with respect to their electrochemical properties, i.e., electron transfer (ET) kinetics and charge transfer resistance using scanning electrochemical microscopy and electrochemical impedance spectroscopy, and their nanomechanical properties, i.e., Young’s modulus and adhesion forces at varying experimental conditions, such as applied potential or pH value of the medium using atomic force microscopy. In particular, the ET behavior at different pH values has not to date been investigated in detail for electrodeposited PDA thin films, which is of particular interest for a multitude of applications. Adhesion forces strongly depend on applied potential and surrounding pH value. Moreover, force spectroscopic measurements reveal a significantly higher percentage of polymeric character compared to films obtained by dip coating. Additionally, distinct differences between the two depositions methods are observed, which indicate that the pulse deposition process leads to denser, more cross-linked films.

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

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

Stimuli-responsive polydopamine-based smart materials

This review provides in-depth insight into the structural engineering of PDA-based materials to enhance their responsive feature and the use of them in construction of PDA-based stimuli-responsive smart materials.

Redox Switchable Polydopamine-Modified AFM-SECM Probes: A Probe for Electrochemical Force Spectroscopy

Polydopamine (PDA) has high potential in biorelevant applications as a versatile thin film material, e.g., as adhesive coating for cell immobilization or for sensing applications due to the plethora of functional groups. In this study we present the modification of conductive colloidal atomic force-scanning electrochemical microscopy (AFM-SECM) probes with electrochemically deposited PDA resulting in functional probes for quantitative electrochemical adhesion studies. Surface functionality of PDA can be altered by oxidation or reduction of functional groups applying an appropriate potential to the PDA-modified AFM-SECM probe, thereby enabling adhesion measurements under potential control. This facilitates probing specific interactions of surface groups present in PDA with various surfaces of different wettabilities. The versatility of such switchable AFM-SECM probes is demonstrated for electrochemical force spectroscopic studies at model samples such as plasma-treated gold substrates, hydrophobic or hydrophilic self-assembled monolayers, and for adhesion measurements of bacteria in dependence of altered surface charges of the colloidal probe. The maximum obtained adhesion force of a positively polarized PDA-modified AFM-SECM probe was 6.2 ± 2.2 nN, and it was about 50% less (i.e., 2.6 ± 1.1 nN) for a negatively polarized probe at a hydrophilic OH-terminated gold surface. In situ control of the active surface groups enabled investigations on the influence of surface charges on adhesion. Furthermore, plateaus of constant force were observed, which are a characteristic of polymer structures. Finally, electrochemical force measurements with switchable probes were used for the first time during adhesion studies of bacterial cells (i.e., Pseudomonas fluorescens). Positively biased PDA-coated colloidal probes revealed adhesion forces of 6.0 ± 1.1 nN, whereas significantly reduced adhesion forces 1.1 ± 0.7 nN were observed for negatively biased PDA-modified colloidal probes.

Role of polydopamine's redox-activity on its pro-oxidant, radical-scavenging, and antimicrobial activities

Polydopamine (PDA) is a bioinspired material and coating that offers diverse functional activities (e.g., photothermal, antioxidant, and antimicrobial) for a broad range of applications. Although PDA is reported to be redox active, the association between PDA's redox state and its functional performance has been difficult to discern because of PDA's complex structure and limitations in methods to characterize redox-based functions. Here, we use an electrochemical reverse engineering approach to confirm that PDA is redox-active and can repeatedly accept and donate electrons. We observed that the electron-donating ability of PDA offers the detrimental pro-oxidant effect of donating electrons to O₂ to generate reactive oxygen species (ROS) or, alternatively, the beneficial antioxidant effect of quenching oxidative free radicals. Importantly, PDA's electron-donating ability depends on its redox state and is strongly influenced by external factors including metal ion binding as well as near-infrared (NIR) irradiation. Furthermore, we demonstrated that PDA possesses redox state-dependent antimicrobial properties in vitro and in vivo. We envision that clarification of PDA's redox activity will enable better understanding of PDA's context-dependent properties (e.g., antioxidant and pro-oxidant) and provide new insights for further applications of PDA. STATEMENT OF SIGNIFICANCE: We believe this is the first report to characterize the redox activities of polydopamine (PDA) and to relate these redox activities to functional properties important for various proposed applications of PDA. We observed that polydopamine nanoparticles 1) are redox-active; 2) can repeatedly donate and accept electrons; 3) can accept electrons from reducing agents (e.g., ascorbate), donate electrons to O₂ to generate ROS, and donate electrons to free radicals to quench them; 4) have redox state-dependent electron-donating abilities that are strongly influenced by metal ion binding as well as NIR irradiation; and 5) have redox state-dependent antimicrobial activities.

Redox State of PDA Directs Cellular Responses through Preadsorbed Protein

Polydopamine (PDA) is capable of adhering on nearly all kinds of surfaces and shows good biocompatibility. Moreover, its surface state could be switched between oxidation and reduction states under different electrical stimulation. In this work, the effects of PDA redox states on protein adsorption, as well as the subsequent effects on cellular responses were characterized and evaluated. It was found that the electrical treatment changed the redox states of PDA, which in turn changed the state of preadsorbed protein molecules and eventually affected the cellular responses. BSA preadsorbed PDA film was found to be beneficial for cell proliferation when PDA was changed into reduction state (RPDA), while BMP-2 preadsorbed PDA film showed promotion on cell differentiation when PDA was changed into oxidation state (OPDA). It was found that the transitions of PDA to RPDA and OPDA greatly changed the secondary structure of protein preadsorbed on it. This work provides a deeper insight on changes of protein molecules between cells and PDA surfaces with different redox states, which is important for both optimization of cell-material interactions and application of PDA as a functional coating for biomedical engineering.

Nitrodopamine vs dopamine as an intermediate layer for bone regeneration applications

The aim of this paper was to present a parallel investigation of the poly(dopamine) (DP) and nitrodopamine (NDP) structures deposited on titanium surface (Ti) and titanium oxide nanotubes (NT-TiO₂/Ti) and to highlight their advantages and drawbacks to serve as an intermediary layer for bone regeneration applications. This study outlines some hypotheses regarding the manner in which these compounds are able to form a stable film that could serve as bioadhesive. The paper is also a study of structuring and evolution of film architecture for two coatings, polydopamine and nitrodopamine in terms of surface structure, stability, wettability, morphology, adhesion and ability to protect the titanium surface. All investigations are based on the data provided by surface characterization techniques: SEM, RAMAN, XRD, XPS, wettability and flexural strength. The impact of polydopamine and nitrodopamine coatings on the biocompatibility of titanium nanotubes was investigated in vitro. Cell morphology, viability, proliferation and pre-osteoblast differentiation were examined in detail. It was highlighted that both DP and NDP functionalized TiO₂ nanotubes display good cell response in terms of cell spreading, formation of focal adhesions, cell viability and proliferation, suggesting their suitability for applications in bone regeneration field. However, NDP coated TiO₂ nanotubes demonstrated an enhanced osteogenic potential compared to DP coated substrates.

Mussel-inspired injectable hydrogel and its counterpart for actuating proliferation and neuronal differentiation of retinal progenitor cells

Biomaterials-mediated retinal progenitor cell (RPC)-based transplantation therapy has shown substantial potential for retinal degeneration (RD), but it is limited by the poor RPC survival, proliferation and differentiation. Herein, the gelatin-hyaluronic acid (Gel-HA)-based hydrogels formed via moderate Michael-type addition reaction with or without the introduction of mussel-inspired polydopamine (PDA), i.e. Gel-HA-PDA and its counterpart Gel-HA hydrogels are developed, and their effects on the biological behaviour of RPCs, including adhesion, survival, proliferation, differentiation, delivery and migration are investigated. The hybrid hydrogels can adopt the intricate structure of the retina with suitable mechanical strength, degradation rate and biological activity to support cellular adhesion, survival and delivery. Meanwhile, Gel-HA hydrogel can remarkably promote RPC proliferation with much larger cell clusters, while Gel-HA-PDA hydrogel significantly enhances RPC adhesion and migration, and directs RPCs to preferentially differentiate toward retinal neurons such as photoreceptors (the most crucial cell-type for RD treatment), which is mainly induced by the activation of integrin α5β1-phosphatidylinositol-3-kinase (PI3K) pathway. This study demonstrates that Gel-HA hydrogel possesses great potential for RPC proliferation, while mussel-inspired PDA-modified Gel-HA hydrogel with superior biocompatibility can significantly promote RPC neuronal differentiation, providing new insights for developing biomedical materials applied for RPC-based transplantation therapy.

Genome-Scale Metabolic Model of Actinosynnema pretiosum ATCC 31280 and Its Application for Ansamitocin P-3 Production Improvement

Actinosynnema pretiosum ATCC 31280 is the producer of antitumor agent ansamitocin P-3 (AP-3). Understanding of the AP-3 biosynthetic pathway and the whole metabolic network in A. pretiosum is important for the improvement of AP-3 titer. In this study, we reconstructed the first complete Genome-Scale Metabolic Model (GSMM) Aspm1282 for A. pretiosum ATCC 31280 based on the newly sequenced genome, with 87% reactions having definite functional annotation. The model has been validated by effectively predicting growth and the key genes for AP-3 biosynthesis. Then we built condition-specific models for an AP-3 high-yield mutant NXJ-24 by integrating Aspm1282 model with time-course transcriptome data. The changes of flux distribution reflect the metabolic shift from growth-related pathway to secondary metabolism pathway since the second day of cultivation. The AP-3 and methionine metabolisms were both enriched in active flux for the last two days, which uncovered the relationships among cell growth, activation of methionine metabolism, and the biosynthesis of AP-3. Furthermore, we identified four combinatorial gene modifications for overproducing AP-3 by in silico strain design, which improved the theoretical flux of AP-3 biosynthesis from 0.201 to 0.372 mmol/gDW/h. Upregulation of methionine metabolic pathway is a potential strategy to improve the production of AP-3.

Melanin and Melanin-Related Polymers as Materials with Biomedical and Biotechnological Applications-Cuttlefish Ink and Mussel Foot Proteins as Inspired Biomolecules

The huge development of bioengineering during the last years has boosted the search for new bioinspired materials, with tunable chemical, mechanical, and optoelectronic properties for the design of semiconductors, batteries, biosensors, imaging and therapy probes, adhesive hydrogels, tissue restoration, photoprotectors, etc. These new materials should complement or replace metallic or organic polymers that cause cytotoxicity and some adverse health effects. One of the most interesting biomaterials is melanin and synthetic melanin-related molecules. Melanin has a controversial molecular structure, dependent on the conditions of polymerization, and therefore tunable. It is found in animal hair and skin, although one of the common sources is cuttlefish (Sepia officinalis) ink. On the other hand, mussels synthesize adhesive proteins to anchor these marine animals to wet surfaces. Both melanin and mussel foot proteins contain a high number of catecholic residues, and their properties are related to these groups. Dopamine (DA) can easily polymerize to get polydopamine melanin (PDAM), that somehow shares properties with melanin and mussel proteins. Furthermore, PDAM can easily be conjugated with other components. This review accounts for the main aspects of melanin, as well as DA-based melanin-like materials, related to their biomedical and biotechnological applications.