Polydopamine nanoparticles kill cancer cells

Multifunctional Natural and Synthetic Melanin for Bioelectronic Applications: A Review

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

Enhancing Antimicrobial Performance of Gauze via Modification by Ag-Loaded Polydopamine Submicron Particles

Silver nanoparticles (AgNPs) are known for their antibacterial properties and their ability to promote wound healing. By incorporating silver nanoparticles into medical gauze, the resulting composite material shows promise as an advanced wound dressing. However, clinical applications are hindered by challenges related to the stability of silver nanoparticle loading on the gauze as nanoparticle leaching can compromise antibacterial efficacy. In this study, silver nanoparticles were immobilized onto polydopamine (PDA) submicron particles, which were then used to modify medical gauze. Energy dispersive spectroscopy (EDS) was employed to analyze the elemental distribution on the modified gauze, confirming successful surface modification. The antibacterial properties of the modified gauze were assessed using a laser scanning confocal microscope (CLSM). The results demonstrated a significant reduction in the adhesion rates of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) by 99.1% and 63%, respectively, on the PDA-Ag-modified gauze. Optical density (OD) measurements at 590 nm indicated that the modified gauze effectively inhibited biofilm formation, underscoring its potent antimicrobial capabilities. Further antibacterial efficacy was evaluated by diluting and plating co-cultured bacterial solutions with the modified dressing, followed by 24 h incubation and colony counting. The gauze exhibited an antibacterial efficiency of 99.99% against E. coli and 99.8% against S. aureus. Additionally, cell compatibility tests, involving the co-culture of PDA-Ag composites with human cells, demonstrated excellent biocompatibility. These findings suggest that PDA-Ag-modified medical gauze holds significant potential for the treatment of infected wounds, offering a promising solution to improve wound care through enhanced antimicrobial activity and biocompatibility.

Drug-Loaded Polydopamine Nanoparticles for Chemo/Photothermal Therapy against Colorectal Cancer Cells

Colorectal cancer (CRC) is a common and deadly malignancy, ranking second in terms of mortality and third in terms of incidence on a global scale. The survival rates for CRC patients are unsatisfactory primarily because of the absence of highly effective clinical strategies. The efficacy of existing CRC treatments, such as chemotherapy (CT), is constrained by issues such as drug resistance and damage to healthy tissues. Alternative approaches such as photothermal therapy (PTT), while offering advantages over traditional therapies, suffer instead from a low efficiency in killing tumor cells when used alone. In this context, nanostructures can efficiently contribute to a selective and targeted treatment. Here, we combined CT and PTT by developing a nanoplatform based on polydopamine nanoparticles (PDNPs), selected for their biocompatibility, drug-carrying capabilities, and ability to produce heat upon exposure to near-infrared (NIR) irradiation. As a chemotherapy drug, sorafenib has been selected, a multikinase inhibitor already approved for clinical use. By encapsulating sorafenib in polydopamine nanoparticles (Sor-PDNPs), we were able to successfully improve the drug stability in physiological media and the consequent uptake by CRC cells, thereby increasing its therapeutic effects. Upon NIR stimulus, Sor-PDNPs can induce a temperature increment of about 10 °C, encompassing both PTT and triggering a localized and massive drug release. Sor-PDNPs were tested on healthy colon cells, showing minimal adverse outcomes; conversely, they demonstrated excellent efficacy against CRC cells, with a strong capability to hinder cancer cell proliferation and induce apoptosis. Obtained findings pave the way to new synergistic chemo-photothermal approaches, maximizing the therapeutic outcomes against CRC while minimizing side effects on healthy cells.

Macrophage Reprogramming via the Modulation of Unfolded Protein Response with siRNA-Loaded Magnetic Nanoparticles in a TAM-like Experimental Model

New therapeutic strategies are required in cancer therapy. Considering the prominent role of tumor-associated macrophages (TAMs) in the development and progression of cancer, the re-education of TAMs in the tumor microenvironment (TME) could represent a potential approach for cancer immunotherapy. TAMs display an irregular unfolded protein response (UPR) in their endoplasmic reticulum (ER) to endure environmental stress and ensure anti-cancer immunity. Therefore, nanotechnology could be an attractive tool to modulate the UPR in TAMs, providing an alternative strategy for TAM-targeted repolarization therapy. Herein, we developed and tested polydopamine-coupled magnetite nanoparticles (PDA-MNPs) functionalized with small interfering RNAs (siRNA) to downregulate the protein kinase R (PKR)-like ER kinase (PERK) expression in TAM-like macrophages derived from murine peritoneal exudate (PEMs). After the evaluation of the cytocompatibility, the cellular uptake, and the gene silencing efficiency of PDA-MNPs/siPERK in PEMs, we analyzed their ability to re-polarize in vitro these macrophages from M2 to the M1 inflammatory anti-tumor phenotype. Our results indicate that PDA-MNPs, with their magnetic and immunomodulator features, are cytocompatible and able to re-educate TAMs toward the M1 phenotype by PERK inhibition, a UPR effector contributing to TAM metabolic adaptation. These findings can provide a novel strategy for the development of new tumor immunotherapies in vivo.

Functionalization of and through Melanin: Strategies and Bio-Applications

A unique feature of nanoparticles for bio-application is the ease of achieving multi-functionality through covalent and non-covalent functionalization. In this way, multiple therapeutic actions, including chemical, photothermal and photodynamic activity, can be combined with different bio-imaging modalities, such as magnetic resonance, photoacoustic, and fluorescence imaging, in a theragnostic approach. In this context, melanin-related nanomaterials possess unique features since they are intrinsically biocompatible and, due to their optical and electronic properties, are themselves very efficient photothermal agents, efficient antioxidants, and photoacoustic contrast agents. Moreover, these materials present a unique versatility of functionalization, which makes them ideal for the design of multifunctional platforms for nanomedicine integrating new functions such as drug delivery and controlled release, gene therapy, or contrast ability in magnetic resonance and fluorescence imaging. In this review, the most relevant and recent examples of melanin-based multi-functionalized nanosystems are discussed, highlighting the different methods of functionalization and, in particular, distinguishing pre-functionalization and post-functionalization. In the meantime, the properties of melanin coatings employable for the functionalization of a variety of material substrates are also briefly introduced, especially in order to explain the origin of the versatility of melanin functionalization. In the final part, the most relevant critical issues related to melanin functionalization that may arise during the design of multifunctional melanin-like nanoplatforms for nanomedicine and bio-application are listed and discussed.

In Vitro and In Vivo Evaluation of a Bio-Inspired Adhesive for Bone Fixation

Compared to metallic hardware, an effective bone adhesive can revolutionize the treatment of clinically challenging situations such as comminuted, articular, and pediatric fractures. The present study aims to develop such a bio-inspired bone adhesive, based upon a modified mineral-organic adhesive with tetracalcium phosphate (TTCP) and phosphoserine (OPS) by incorporating nanoparticles of polydopamine (nPDA). The optimal formulation, which was screened using in vitro instrumental tensile adhesion tests, was found to be 50%_molTTCP/50%_molOPS-2%_wtnPDA with a liquid-to-powder ratio of 0.21 mL/g. This adhesive has a substantially stronger adhesive strength (1.0-1.6 MPa) to bovine cortical bone than the adhesive without nPDA (0.5-0.6 MPa). To simulate a clinical scenario of autograft fixation under low mechanical load, we presented the first in vivo model: a rat fibula glued to the tibia, on which the TTCP/OPS-nPDA adhesive (n = 7) was shown to be effective in stabilizing the graft without displacement (a clinical success rate of 86% and 71% at 5 and 12 weeks, respectively) compared to a sham control (0%). Significant coverage of newly formed bone was particularly observed on the surface of the adhesive, thanks to the osteoinductive property of nPDA. To conclude, the TTCP/OPS-nPDA adhesive fulfilled many clinical requirements for the bone fixation, and potentially could be functionalized via nPDA to offer more biological activities, e.g., anti-infection after antibiotic loading.

Synthetic Melanin Acts as Efficient Peptide Carrier in Cancer Vaccine Strategy

We previously reported that a novel peptide vaccine platform, based on synthetic melanin nanoaggregates, triggers strong cytotoxic immune responses and significantly suppresses tumor growth in mice. However, the mechanisms underlying such an efficacy remained poorly described. Herein, we investigated the role of dendritic cells (DCs) in presenting the antigen embedded in the vaccine formulation, as well as the potential stimulatory effect of melanin upon these cells, in vitro by coculture experiments and ELISA/flow cytometry analysis. The vaccine efficiency was evaluated in FLT3-L^-/- mice constitutively deficient in DC1, DC2, and pDCs, in Zbtb46^DTR chimera mice deficient in DC1 and DC2, and in Langerin^DTR mice deficient in dermal DC1 and Langerhans cells. We concluded that DCs, and especially migratory conventional type 1 dendritic cells, seem crucial for mounting the immune response after melanin-based vaccination. We also assessed the protective effect of L-DOPA melanin on peptides from enzymatic digestion, as well as the biodistribution of melanin-peptide nanoaggregates, after subcutaneous injection using [¹⁸F]MEL050 PET imaging in mice. L-DOPA melanin proved to act as an efficient carrier for peptides by fully protecting them from enzymatic degradation. L-DOPA melanin did not display any direct stimulatory effects on dendritic cells in vitro. Using PET imaging, we detected melanin-peptide nanoaggregates up to three weeks after subcutaneous injections within the secondary lymphoid tissues, which could explain the sustained immune response observed (up to 4 months) with this vaccine technology.

Melanin and Melanin-Functionalized Nanoparticles as Promising Tools in Cancer Research-A Review

Cancer poses an ongoing global challenge, despite the substantial progress made in the prevention, diagnosis, and treatment of the disease. The existing therapeutic methods remain limited by undesirable outcomes such as systemic toxicity and lack of specificity or long-term efficacy, although innovative alternatives are being continuously investigated. By offering a means for the targeted delivery of therapeutics, nanotechnology (NT) has emerged as a state-of-the-art solution for augmenting the efficiency of currently available cancer therapies while combating their drawbacks. Melanin, a polymeric pigment of natural origin that is widely spread among many living organisms, became a promising candidate for NT-based cancer treatment owing to its unique physicochemical properties (e.g., high biocompatibility, redox behavior, light absorption, chelating ability) and innate antioxidant, photoprotective, anti-inflammatory, and antitumor effects. The latest research on melanin and melanin-like nanoparticles has extended considerably on many fronts, allowing not only efficient cancer treatments via both traditional and modern methods, but also early disease detection and diagnosis. The current paper provides an updated insight into the applicability of melanin in cancer therapy as antitumor agent, molecular target, and delivery nanoplatform.

Insight into the influence of the polymerization time of polydopamine nanoparticles on their size, surface properties and nanomedical applications

In the last decade, novel strategies to synthesize polydopamine nanoparticles (PDA NPs) have been continuously developed owing to useful applications of this synthetic melanin analog in nanotechnology.

Design and Synthesis of New PEGylated Polydopamine-Based Nanoconstructs Bearing ROS-Responsive Linkers and a Photosensitizer for Bimodal Photothermal and Photodynamic Therapies against Cancer

Polydopamine (PDA) nanoparticles (NPs) have recently acquired considerable attention for the development of nanoplatforms with multifunctional properties including photothermal (PTT) and photodynamic (PDT) activities. In addition to their high PTT performance, they can be easily conjugated to different types of photosensitizers (PSs) to acquire PDT activity. However, because of PDA free-radical scavenging properties, grafting the PSs directly to PDA surfaces may lead to an inefficient PDT outcome. Thus, the present work aims at synthesizing and characterizing a new PEGylated PDA-based nanoplatform with bifunctional PTT and PDT properties, which allows bimodal cancer therapy with the possibility to release the PS on demand in a spatiotemporal fashion. To do so, PDA NPs with a well-defined size and shape were prepared by the auto-oxidative self-polymerization process of dopamine hydrochloride in mild alkaline solution. The impact of the size on the PTT conversion efficiency was then determined. This allowed us to choose the optimal PDA NP size for PTT applications. Next, PDA NPs were decorated with SH-PEG polymers that bear at their extremity a thioketal reactive oxygen species-cleavable linker coupled to trisulfonated-tetraphenylporphyrin (TPPS₃) chosen as a hydrophilic PS. The grafting efficiency of PS-conjugated PEG on PDA was demonstrated in situ using a quartz crystal microbalance with dissipation monitoring. In addition, the photoinduced release of the PS was demonstrated by ¹H NMR. Finally, PTT/PDT bimodal therapy was assessed in vitro on human squamous esophageal cells by illuminating the PDA NPs at two different wavelengths, which showed the strong synergistic effect of combining PTT and PDT within this nanoplatform.

Nature-Inspired Nanoparticles as Paclitaxel Targeted Carrier for the Treatment of HER2-Positive Breast Cancer

Despite the advances made in the fight against HER2-positive breast cancer, the need for less toxic therapies and strategies that avoid the apparition of resistances is indisputable. For this reason, a targeted nanovehicle for paclitaxel and trastuzumab, used in the first-line treatment of this subtype of breast cancer, had already been developed in a previous study. It yielded good results in vitro but, with the aim of further reducing paclitaxel effective dose and its side effects, a novel drug delivery system was prepared in this work. Thus, polydopamine nanoparticles, which are gaining popularity in cancer nanomedicine, were novelty loaded with paclitaxel and trastuzumab. The effectiveness and selectivity of the nanoparticles obtained were validated in vitro with different HER2-overexpressing tumor and stromal cell lines. These nanoparticles showed more remarkable antitumor activity than the nanosystem previously designed and, in addition, to affect stromal cell viability rate less than the parent drug. Moreover, loaded polydopamine nanoparticles, which notably increased the number of apoptotic HER2-positive breast cancer cells after treatment, also maintained an efficient antineoplastic effect when validated in tumor spheroids. Thereby, these bioinspired nanoparticles charged with both trastuzumab and paclitaxel may represent an excellent approach to improve current HER2-positive breast cancer therapies.

Polydopamine and dopamine interfere with tetrazolium-based cytotoxicity assays and produce exaggerated cytocompatibility inferences

Tetrazolium-based assays such as the MTT assay have been commonly employed in evaluating biocompatibility. Here, we show that PDA (or its precursor dopamine (DA)) spontaneously reduces MTT and produces exaggerated cytocompatibility inferences. The extent of interference depends on the method of DA polymerization. We observed that the trypan blue exclusion assay allowed more accurate determination of cell viability in the presence of DA- and PDA-based nanomaterials.

Applications of Melanin and Melanin-Like Nanoparticles in Cancer Therapy: A Review of Recent Advances

Thanks to the growing knowledge about cancers and their interactions with the immune system, a huge number of therapeutic cancer vaccines have been developed in the past two decades. Despite encouraging results in pre-clinical models, cancer vaccines have not yet achieved significant clinical efficacy. Several factors may contribute to such poor results, including the difficulty of triggering a strong immune response and the immunosuppressive tumor microenvironment. Many strategies are currently being explored. Different types of adjuvants have been incorporated into vaccine formulations to improve their efficacy, as cancer antigens are usually poorly immunogenic. Nanoparticle systems are promising tools as they act as carriers for antigens and can be surface-modified so that they specifically target antigen-presenting cells in lymph nodes. Bioinspired nanomaterials are ideal candidates thanks to their biocompatibility. Recently, melanin-based nanoparticles were reported to efficiently localize into draining lymphoid tissues and trigger immune responses against loaded antigens. In addition, by virtue of their photochemical properties, melanin-based nanoparticles can also play an immunomodulatory role to promote anti-cancer responses in the context of photothermal therapy. In this review, we discuss the above-mentioned properties of melanin, and summarize the promising results of the melanin-based cancer vaccines recently reported in preclinical models.

Tailored-Made Polydopamine Nanoparticles to Induce Ferroptosis in Breast Cancer Cells in Combination with Chemotherapy

Ferroptosis is gaining followers as mechanism of selective killing cancer cells in a non-apoptotic manner, and novel nanosystems capable of inducing this iron-dependent death are being increasingly developed. Among them, polydopamine nanoparticles (PDA NPs) are arousing interest, since they have great capability of chelating iron. In this work, PDA NPs were loaded with Fe3+ at different pH values to assess the importance that the pH may have in determining their therapeutic activity and selectivity. In addition, doxorubicin was also loaded to the nanoparticles to achieve a synergist effect. The in vitro assays that were performed with the BT474 and HS5 cell lines showed that, when Fe3+ was adsorbed in PDA NPs at pH values close to which Fe(OH)3 begins to be formed, these nanoparticles had greater antitumor activity and selectivity despite having chelated a smaller amount of Fe3+. Otherwise, it was demonstrated that Fe3+ could be released in the late endo/lysosomes thanks to their acidic pH and their Ca2+ content, and that when Fe3+ was co-transported with doxorubicin, the therapeutic activity of PDA NPs was enhanced. Thus, reported PDA NPs loaded with both Fe3+ and doxorubicin may constitute a good approach to target breast tumors.

A novel self-coated polydopamine nanoparticle for synergistic photothermal-chemotherapy

The combination of photothermal therapy (PTT) and chemotherapy is a promising strategy to overcome the shortcomings of monotherapy. For the first time, we designed a self-coated nanoparticle formed by mesoporous polydopamine (MPDA) core and polydopamine (PDA) shell, which was used to load docetaxel and modified with hyaluronic acid (HA). The obtained nanoparticle can achieve targeted drug delivery and further exert the synergistic effect of PTT and chemotherapy. The MPDA core has high drug loading due to mesopores, and the PDA shell can prevent the drug from releasing in the non-target-site because of the pH-sensitivity of the PDA. Compared with other PDA coated nanoparticle, self-coated nanoparticle has a simpler composition and can avoid the potential toxicity caused by the introduction of other materials. Experimental results showed that it had good photothermal conversion ability both in vivo and in vitro, and could be actively targeted into tumor cells through HA-mediated targeting. Under laser irradiation, it ablated the tumors. Simple ingredient and preparation, good compatibility and obvious therapeutic effect make it have a broad application prospect in tumor therapy.

Recent Advances in a Polydopamine-Mediated Antimicrobial Adhesion System

The drug resistance developed by bacteria during antibiotic treatment has been a call to action for researchers and scientists across the globe, as bacteria and fungi develop ever increasing resistance to current drugs. Innovative antimicrobial/antibacterial materials and coatings to combat such infections have become a priority, as many infections are caused by indwelling implants (e.g., catheters) as well as improving postsurgical function and outcomes. Pathogenic microorganisms that can exist either in planktonic form or as biofilms in water-carrying pipelines are one of the sources responsible for causing water-borne infections. To combat this, researchers have developed nanotextured surfaces with bactericidal properties mirroring the topographical features of some natural antibacterial materials. Protein-based adhesives, secreted by marine mussels, contain a catecholic amino acid, 3,4-dihydroxyphenylalanine (DOPA), which, in the presence of lysine amino acid, empowers with the ability to anchor them to various surfaces in both wet and saline habitats. Inspired by these features, a novel coating material derived from a catechol derivative, dopamine, known as polydopamine (PDA), has been designed and developed with the ability to adhere to almost all kinds of substrates. Looking at the immense potential of PDA, this review article offers an overview of the recent growth in the field of PDA and its derivatives, especially focusing the promising applications as antibacterial nanocoatings and discussing various antimicrobial mechanisms including reactive oxygen species-mediated antimicrobial properties.

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.

Antineoplastic behavior of polydopamine nanoparticles prepared in different water/alcohol media

Polydopamine nanoparticles (PD NPs) have been synthesized in the present work through the oxidative polymerization of dopamine in aqueous media containing five different types of alcohol in a constant solvent volume ratio. We have shown that the type of alcohol, along with the ammonium hydroxide concentration used in the synthesis process, conditions particle size. Additionally, it has been found that the type of alcohol employed influences the well-known capacity of polydopamine nanoparticles to adsorb iron. As a consequence, since a ferroptosis-like mechanism may account for the cytotoxicity of these nanoparticles, the type of alcohol could also have a determining role in their antineoplastic activity. Here, the existence of a correlation between the ability of polydopamine nanoparticles to load Fe³⁺ and their toxic effect on breast cancer cells has been proven. For instance, nanoparticles synthesized using 2-propanol adsorbed more Fe³⁺ and had the greatest capacity to reduce breast tumor cell viability. Moreover, none of the nanoparticle synthesized with the different alcohols significantly decreased normal cell survival. Cancer cells present greater iron-dependence than healthy cells and this fact may explain why polydopamine nanoparticles toxicity, in which Fenton chemistry could be implicated, seems tumor-specific.

Bio-Applications of Multifunctional Melanin Nanoparticles: From Nanomedicine to Nanocosmetics

Bioinspired nanomaterials are ideal components for nanomedicine, by virtue of their expected biocompatibility or even complete lack of toxicity. Natural and artificial melanin-based nanoparticles (MNP), including polydopamine nanoparticles (PDA NP), excel for their extraordinary combination of additional optical, electronic, chemical, photophysical, and photochemical properties. Thanks to these features, melanin plays an important multifunctional role in the design of new platforms for nanomedicine where this material works not only as a mechanical support or scaffold, but as an active component for imaging, even multimodal, and simple or synergistic therapy. The number of examples of bio-applications of MNP increased dramatically in the last decade. Here, we review the most recent ones, focusing on the multiplicity of functions that melanin performs in theranostics platforms with increasing complexity. For the sake of clarity, we start analyzing briefly the main properties of melanin and its derivative as well as main natural sources and synthetic methods, moving to imaging application from mono-modal (fluorescence, photoacoustic, and magnetic resonance) to multi-modal, and then to mono-therapy (drug delivery, anti-oxidant, photothermal, and photodynamic), and finally to theranostics and synergistic therapies, including gene- and immuno- in combination to photothermal and photodynamic. Nanomedicine aims not only at the treatment of diseases, but also to their prevention, and melanin in nature performs a protective action, in the form of nanopigment, against UV-Vis radiations and oxidants. With these functions being at the border between nanomedicine and cosmetics nanotechnology, recently examples of applications of artificial MNP in cosmetics are increasing, paving the road to the birth of the new science of nanocosmetics. In the last part of this review, we summarize and discuss these important recent results that establish evidence of the interconnection between nanomedicine and cosmetics nanotechnology.

Polydopamine nanoparticles-assisted impedimetric sensor towards label-free lung cancer cell detection

Polydopamine nanoparticles (PDA NPs), among nature-inspired building materials, show special functions for biomedical systems and exploring PDA derived nanostructures for future developments is a fast growing field. Herein, we demonstrated the first evaluation of the PDA NPs for the electrochemical determination of lung cancer cells. In the presented study, PDA NPs were synthesized in a mild and cost-effective fashion by self-polymerization of dopamine in an alkaline environment. The structural and chemical characterizations clearly demonstrated the formation of PDA NPs with controllable size (130 nm), hence applied as a suitable material to functionalize the pencil graphite electrode (PGE) surface to construct a cytosensing nanoprobe. The ability of the developed sensor (PDA NPs/PGE) for label-free electrochemical A-549 lung cancer cells detection was investigated. The designed PDA NPs based cytosensor exhibited good biocompatibility and sensitivity for impedimetric diagnosis of A-549 cells in a wide linear range (1.0 × 10²-1.0 × 10⁵ cells mL^-1) with low detection limit (25 cells mL^-1). Furthermore, the developed bioassay has great potential as liquid biopsy for early cancer detection.

Optimization of Polydopamine Coatings onto Poly-ε-Caprolactone Electrospun Fibers for the Fabrication of Bio-Electroconductive Interfaces

In recent years, mussel adhesive proteins have attracted much attention because they can form strong adhesive interface interactions with various substrates in a wet environment. Inspired by their catechol- and amine-based molecular structure, polydopamine (PDA), a dopamine derived synthetic eumelanin polymer, was recognized as a suitable bio-interface coating. PDA was successfully used to improve adhesion due to the availability of copious functional groups for covalently immobilizing biomolecules and anchoring reactive species and ions. Recently, it has been demonstrated that PDA and its derivatives can be successfully used for the surface modification of implants interfaces to modulate in vitro cellular responses in order to enhance the in vivo functionality of biomedical implants (i.e., prosthesis). Herein, we propose the development of multifunctional scaffolds based on polyε-caprolactone (PCL) electrospun fibers coated with PDA via electro fluid dynamic methods, by optimizing polymerization/oxidation reactions capable of driving PDA self-assembly, and, ultimately, investigating the effects on cell response. Morphological analyses have confirmed the possibility to obtain different surface topographies as a function of the coating process while in vitro studies proved the ability of PDA coating to interact with cells no compromising in vitro viability. In perspective, in vitro conductive properties of fibers will be further investigated in order to validate their promising use as bioconductive interfaces for tissue engineering applications.

Recent advances in melanin-like nanomaterials in biomedical applications: a mini review

BACKGROUND

Melanins are a group of biopigments in microorganisms that generate a wide range of colorants. Due to their multifunctionality, including ultraviolet protection, radical scavenging, and photothermal conversion, in addition to their intrinsic biocompatibility, natural melanins and synthetic melanin-like nanomaterials have been suggested as novel nano-bio platforms in biomedical applications.

MAIN BODY

Recent approaches in the synthesis of melanin-like nanomaterials and their biomedical applications have briefly been reviewed. Melanin-like nanomaterials have been suggested as endogenous chromophores for photoacoustic imaging and radical scavengers for the treatment of inflammatory diseases. The photothermal conversion ability of these materials under near-infrared irradiation allows hyperthermia-mediated cancer treatments, and their intrinsic fluorescence can be an indicator in biosensing applications. Furthermore, catechol-rich melanin and melanin-like nanomaterials possess a versatile affinity for various functional organic and inorganic additives, allowing the design of multifunctional hybrid nanomaterials that expand their range of applications in bioimaging, therapy, theranostics, and biosensing.

CONCLUSION

Melanin-like natural and synthetic nanomaterials have emerged; however, the under-elucidated chemical structures of these materials are still a major obstacle to the construction of novel nanomaterials through bottom-up approaches and tuning the material properties at the molecular level. Further advancements in melanin-based medical applications can be achieved with the incorporation of next-generation chemical and molecular analytical tools.

Size Matters in the Cytotoxicity of Polydopamine Nanoparticles in Different Types of Tumors

Polydopamine has acquired great relevance in the field of nanomedicine due to its physicochemical properties. Previously, it has been reported that nanoparticles synthetized from this polymer are able to decrease the viability of breast and colon tumor cells. In addition, it is well known that the size of therapeutic particles plays an essential role in their effect. As a consequence, the influence of this parameter on the cytotoxicity of polydopamine nanoparticles was studied in this work. For this purpose, polydopamine nanoparticles with three different diameters (115, 200 and 420 nm) were synthetized and characterized. Their effect on the viability of distinct sorts of human carcinomas (breast, colon, liver and lung) and stromal cells was investigated, as well as the possible mechanisms that could be responsible for such cytotoxicity. Moreover, polydopamine nanoparticles were also loaded with doxorubicin and the therapeutic action of the resulting nanosystem was analyzed. As a result, it was demonstrated that a smaller nanoparticle size is related to a more enhanced antiproliferative activity, which may be a consequence of polydopamine's affinity for iron ions. Smaller nanoparticles would be able to adsorb more lysosomal Fe3+ and, when they are loaded with doxorubicin, a synergistic effect can be achieved.

Comparison of Polydopamine-Coated Mesoporous Silica Nanorods and Spheres for the Delivery of Hydrophilic and Hydrophobic Anticancer Drugs

Mesoporous silica nanoparticles (MSNs) have been widely studied as drug delivery systems in nanomedicine. Surface coating of MSNs have enabled them to perform efficiently in terms of bioavailability, biocompatibility, therapeutic efficacy and targeting capability. Recent studies have suggested the use of polydopamine (PDA) as a facilitative coating for MSNs that provides sustained and pH-responsive drug release, owing to the adhesive "molecular-glue" function of PDA. This further endows these hybrid MSN@PDA particles with the ability to carry large amounts of hydrophilic drugs. In this study, we expand the feasibility of this platform in terms of exploring its ability to also deliver hydrophobic drugs, as well as investigate the effect of particle shape on intracellular delivery of both a hydrophilic and hydrophobic anticancer drug. MSN@PDA loaded with doxorubicin (hydrophilic) and fingolimod (hydrophobic) was studied via a systematic in vitro approach (cellular internalization, intracellular drug distribution and cytotoxicity). To promote the cellular uptake of the MSN@PDA particles, they were further coated with a polyethylene imine (PEI)-polyethylene glycol (PEG) copolymer. Drug-loaded, copolymer-coated MSN@PDA showed effective cellular uptake, intracellular release and an amplified cytotoxic effect with both doxorubicin and fingolimod. Additionally, rods exhibited delayed intracellular drug release and superior intracellular uptake compared to spheres. Hence, the study provides an example of how the choice and design of drug delivery systems can be tuned by the need for performance, and confirms the PDA coating of MSNs as a useful drug delivery platform beyond hydrophilic drugs.