A sweet polydopamine nanoplatform for synergistic combination of targeted chemo-photothermal therapy

Near-Infrared Absorbing Para-Azaquinodimethane Conjugated Polymers Synthesized via the Transition-Metal-Free Route toward Efficient Photothermal Conversion

Conjugated polymers with strong absorption in the second near-infrared (NIR-II) window have multiple applications. However, the development of new type of NIR-II conjugated polymers via facile and green methods remains challenging. Herein, this work reports a mild and convenient transition-metal-free method to synthesize near-infrared absorbing quinoidal conjugated polymers containing para-azaquinodimethane (AQM) moieties. The AQM quinoidal conjugated polymers with unique molecular structures and tunable optoelectronic properties can be synthesized by combining the Knoevenagel polycondensation of aromatic dialdehyde monomers with commercially available 1,4-diacetyl-2,5-piperazinedione and the following alkylation reaction. The resultant polymer PQ-DPP shows remarkable NIR-II absorption with a narrow band gap of about 1.08 eV. PQ-DPP nanoparticles exhibit high photothermal conversion efficiency of up to 48% under 1064 nm laser irradiation (1 W cm-2) endowing this polymer with potential in bio-related applications.

Polydopamine-containing nano-systems for cancer multi-mode diagnoses and therapies: A review

Polydopamine (PDA) has fascinating properties such as inherent biocompatibility, simple preparation, strong near-infrared absorption, high photothermal conversion efficiency, and strong metal ion chelation, which have catalyzed extensive research in PDA-containing multifunctional nano-systems particularly for biomedical applications. Thus, it is imperative to overview synthetic strategies of various PDA-containing nanoparticles (NPs) for state-of-the-art cancer multi-mode diagnoses and therapies applications, and offer a timely and comprehensive summary. In this review, we will focus on the synthetic approaches of PDA NPs, and summarize the construction strategies of PDA-containing NPs with different structure forms. Additionally, the application of PDA-containing NPs in bioimaging such as photoacoustic imaging, fluorescence imaging, magnetic resonance imaging and other imaging modalities will be reviewed. We will especially offer an overview of their therapeutic applications in tumor chemotherapy, photothermal therapy, photodynamic therapy, photocatalytic therapy, sonodynamic therapy, radionuclide therapy, gene therapy, immunotherapy and combination therapy. At the end, the current trends, limitations and future prospects of PDA-containing nano-systems will be discussed. This review aims to provide guidelines for new scientists in the field of how to design PDA-containing NPs and what has been achieved in this area, while offering comprehensive insights into the potential of PDA-containing nano-systems used in cancer diagnosis and treatment.

Photocatalytic and Photothermal Antimicrobial Mussel-Inspired Nanocomposites for Biomedical Applications

Bacterial infection has traditionally been treated with antibiotics, but their overuse is leading to the development of antibiotic resistance. This may be mitigated by alternative approaches to prevent or treat bacterial infections without utilization of antibiotics. Among the alternatives is the use of photo-responsive antimicrobial nanoparticles and/or nanocomposites, which present unique properties activated by light. In this study, we explored the combined use of titanium oxide and polydopamine to create nanoparticles with photocatalytic and photothermal antibacterial properties triggered by visible or near-infrared light. Furthermore, as a proof-of-concept, these photo-responsive nanoparticles were combined with mussel-inspired catechol-modified hyaluronic acid hydrogels to form novel light-driven antibacterial nanocomposites. The materials were challenged with models of Gram-negative and Gram-positive bacteria. For visible light, the average percentage killed (PK) was 94.6 for E. coli and 92.3 for S. aureus. For near-infrared light, PK for E. coli reported 52.8 and 99.2 for S. aureus. These results confirm the exciting potential of these nanocomposites to prevent the development of antibiotic resistance and also to open the door for further studies to optimize their composition in order to increase their bactericidal efficacy for biomedical applications.

Doxorubicin-Loaded Fungal-Carboxymethyl Chitosan Functionalized Polydopamine Nanoparticles for Photothermal Cancer Therapy

In this work, we synthesized doxorubicin-loaded fungal-carboxymethyl chitosan (FC) functionalized polydopamine (Dox@FCPDA) nanoparticles for improved anticancer activity via photothermal drug release. The photothermal properties revealed that the FCPDA nanoparticles with a concentration of 400 µg/mL produced a temperature of about 61.1 °C at 2 W/cm² laser illumination, which is more beneficial for cancer cells. Due to the hydrophilic FC biopolymer, the Dox was successfully encapsulated into FCPDA nanoparticles via electrostatic interactions and pi-pi stacking. The maximum drug loading and encapsulation efficiency were calculated to be 19.3% and 80.2%, respectively. The Dox@FCPDA nanoparticles exhibited improved anticancer activity on HePG2 cancer cells when exposed to an NIR laser (800 nm, 2 W/cm²). Furthermore, the Dox@FCPDA nanoparticles also improved cellular uptake with HepG2 cells. Therefore, functionalizing FC biopolymer with PDA nanoparticles is more beneficial for drug and photothermal dual therapeutic properties for cancer therapy.

Fabricating a PDA-Liposome Dual-Film Coated Hollow Mesoporous Silica Nanoplatform for Chemo-Photothermal Synergistic Antitumor Therapy

In this study, we synthesized hollow mesoporous silica nanoparticles (HMSNs) coated with polydopamine (PDA) and a D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS)-modified hybrid lipid membrane (denoted as HMSNs-PDA@liposome-TPGS) to load doxorubicin (DOX), which achieved the integration of chemotherapy and photothermal therapy (PTT). Dynamic light scattering (DLS), transmission electron microscopy (TEM), N₂ adsorption/desorption, Fourier transform infrared spectrometry (FT-IR), and small-angle X-ray scattering (SAXS) were used to show the successful fabrication of the nanocarrier. Simultaneously, in vitro drug release experiments showed the pH/NIR-laser-triggered DOX release profiles, which could enhance the synergistic therapeutic anticancer effect. Hemolysis tests, non-specific protein adsorption tests, and in vivo pharmacokinetics studies exhibited that the HMSNs-PDA@liposome-TPGS had a prolonged blood circulation time and greater hemocompatibility compared with HMSNs-PDA. Cellular uptake experiments demonstrated that HMSNs-PDA@liposome-TPGS had a high cellular uptake efficiency. In vitro and in vivo antitumor efficiency evaluations showed that the HMSNs-PDA@liposome-TPGS + NIR group had a desirable inhibitory activity on tumor growth. In conclusion, HMSNs-PDA@liposome-TPGS successfully achieved the synergistic combination of chemotherapy and photothermal therapy, and is expected to become one of the candidates for the combination of photothermal therapy and chemotherapy antitumor strategies.

Inhibition of melanoma using a nanoceria-based prolonged oxygen-generating phototherapy hydrogel

Tumor hypoxic environment is an inevitable obstacle for photodynamic therapy (PDT) of melanoma. Herein, a multifunctional oxygen-generating hydrogel loaded with hyaluronic acid-chlorin e6 modified nanoceria and calcium peroxide (Gel-HCeC-CaO2) was developed for the phototherapy of melanoma. The thermo-sensitive hydrogel could act as a sustained drug delivery system to accumulate photosensitizers (chlorin e6, Ce6) around the tumor, followed by cellular uptake mediated by nanocarrier and hyaluronic acid (HA) targeting. The moderate sustained oxygen generation in the hydrogel was produced by the reaction of calcium peroxide (CaO2) with infiltrated H2O in the presence of catalase mimetic nanoceria. The developed Gel-HCeC-CaO2 could efficiently alleviate the hypoxia microenvironment of tumors as indicated by the expression of hypoxia-inducible factor -1α (HIF-1α), meeting the “once injection, repeat irradiation” strategy and enhanced PDT efficacy. The prolonged oxygen-generating phototherapy hydrogel system provided a new strategy for tumor hypoxia alleviation and PDT.

Self-Healing Polymeric Soft Actuators

Natural evolution has provided multicellular organisms with sophisticated functionalities and repair mechanisms for surviving and preserve their functions after an injury and/or infection. In this context, biological systems have inspired material scientists over decades to design and fabricate both self-healing polymeric materials and soft actuators with remarkable performance. The latter are capable of modifying their shape in response to environmental changes, such as temperature, pH, light, electrical/magnetic field, chemical additives, etc. In this review, we focus on the fusion of both types of materials, affording new systems with the potential to revolutionize almost every aspect of our modern life, from healthcare to environmental remediation and energy. The integration of stimuli-triggered self-healing properties into polymeric soft actuators endow environmental friendliness, cost-saving, enhanced safety, and lifespan of functional materials. We discuss the details of the most remarkable examples of self-healing soft actuators that display a macroscopic movement under specific stimuli. The discussion includes key experimental data, potential limitations, and mechanistic insights. Finally, we include a general table providing at first glance information about the nature of the external stimuli, conditions for self-healing and actuation, key information about the driving forces behind both phenomena, and the most important features of the achieved movement.

Recent Development of Polydopamine Anti-Bacterial Nanomaterials

Polydopamine (PDA), as a mussel-inspired material, exhibits numerous favorable performance characteristics, such as a simple preparation process, prominent photothermal transfer efficiency, excellent biocompatibility, outstanding drug binding ability, and strong adhesive properties, showing great potential in the biomedical field. The rapid development of this field in the past few years has engendered substantial progress in PDA antibacterial materials. This review presents recent advances in PDA-based antimicrobial materials, including the preparation methods and antibacterial mechanisms of free-standing PDA materials and PDA-based composite materials. Furthermore, the urgent challenges and future research opportunities for PDA antibacterial materials are discussed.

A triple-stimulus responsive melanin-based nanoplatform with an aggregation-induced emission-active photosensitiser for imaging-guided targeted synergistic phototherapy/hypoxia-activated chemotherapy

Multimodal synergistic therapy has gained increasing attention in cancer treatment to overcome the limitations of monotherapy and achieve high anticancer efficacy. In this study, a synergistic phototherapy and hypoxia-activated chemotherapy nanoplatform based on natural melanin nanoparticles (MPs) loaded with the bioreduction prodrug tirapazamine (TPZ) and decorated with hyaluronic acid (HA) was developed. A self-reporting aggregation-induced emission (AIE)-active photosensitizer (PS) (BATTMN) was linked to the prepared nanoparticles by boronate ester bonds. The MPs and BATTMN-HA played roles as quenchers for PS and cancer targeting/photodynamic moieties, respectively. As a pH sensitive bond, the borate ester bonds between HA and BATTMN are hydrolysed in the acidic cancer environment, thereby separating BATTMN from the nanoparticles and leading to the induction of fluorescence for imaging-guided synergistic phototherapy/hypoxia-activated chemotherapy under dual irradiation. TPZ can be released upon activation by pH, near-infrared (NIR) and hyaluronidase (Hyal). Particularly, the hypoxia-dependent cytotoxicity of TPZ was amplified by oxygen consumption in the tumor intracellular environment induced by the AIE-active PS in photodynamic therapy (PDT). The nanoparticles developed in our research showed favorable photothermal conversion efficiency (η = 37%), desired cytocompatibility, and excellent synergistic therapeutic efficacy. The proposed nanoplatform not only extends the application scope of melanin materials with AIE-active PSs, but also offers useful insights into developing multistimulus as well as multimodal synergistic tumor treatment.

2D materials for bone therapy

Due to their prominent physicochemical properties, 2D materials are broadly applied in biomedicine. Currently, 2D materials have achieved great success in treating many diseases such as cancer and tissue engineering as well as bone therapy. Based on their different characteristics, 2D materials could function in various ways in different bone diseases. Herein, the application of 2D materials in bone tissue engineering, joint lubrication, infection of orthopedic implants, bone tumors, and osteoarthritis are firstly reviewed comprehensively together. Meanwhile, different mechanisms by which 2D materials function in each disease reviewed below are also reviewed in detail, which in turn reveals the versatile functions and application of 2D materials. At last, the outlook on how to further broaden applications of 2D materials in bone therapies based on their excellent properties is also discussed.

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.

Polymeric photothermal agents for cancer therapy: recent progress and clinical potential

Over the past decades, near infrared light (NIR)-sensitive photothermal agents (PTAs) that can efficiently absorb light and generate heat have been investigated worldwide for cancer photothermal therapy (PTT) and the combination treatments, which have some peculiar advantages including spatiotemporal targeting, the ability-to-reverse multidrug resistance, the immunity-stimulating function, and the synergistic effect in combination treatments. In this review, we first focus on emerging melanin-like polymers and coordination polyphenol polymer-based PTAs that hold transition potential because of their facile synthesis and good biocompatibility/biodegradability. We briefly introduce polymeric PTAs for emerging NIR-II (1000-1700 nm) PTT in deep tumors to overcome shallow penetration depth and threshold irradiation intensity of NIR-I (700-900 nm). Then we discuss polymeric PTAs for combination PTT treatments with photodynamic therapy (PDT), ferroptosis therapy (ferrotherapy), and immunotherapy, which are intensively studied for achieving anticancer synergistic effects. Finally, we discuss those polymeric PTAs for reversing cancer multidrug resistance and for mild/low-temperature PTT (43 °C ≤ T < 50 °C) in contrast to conventional high-temperature PTT (>50 °C). The polymeric PTA-based PTT and the combination treatments are still being developed in the early stage and need much more effort before potential clinical transitions and applications.

Melanin-Like Nanomedicine in Photothermal Therapy Applications

Photothermal therapy (PTT) mediated by nanomaterial has become an attractive tumor treatment method due to its obvious advantages. Among various nanomaterials, melanin-like nanoparticles with nature biocompatibility and photothermal conversion properties have attracted more and more attention. Melanin is a natural biological macromolecule widely distributed in the body and displays many fascinating physicochemical properties such as excellent biocompatibility and prominent photothermal conversion ability. Due to the similar properties, Melanin-like nanoparticles have been extensively studied and become promising candidates for clinical application. In this review, we give a comprehensive introduction to the recent advancements of melanin-like nanoparticles in the field of photothermal therapy in the past decade. In this review, the synthesis pathway, internal mechanism and basic physical and chemical properties of melanin-like nanomaterials are systematically classified and evaluated. It also summarizes the application of melanin-like nanoparticles in bioimaging and tumor photothermal therapy (PTT)in detail and discussed the challenges they faced in clinical translation rationally. Overall, melanin-like nanoparticles still have significant room for development in the field of biomedicine and are expected to applied in clinical PTT in the future.

Emerging photothermal-derived multimodal synergistic therapy in combating bacterial infections

Due to the emerging bacterial resistance and the protection of tenacious biofilms, it is hard for the single antibacterial modality to achieve satisfactory therapeutic effects nowadays. In recent years, photothermal therapy (PTT)-derived multimodal synergistic treatments have received wide attention and exhibited cooperatively enhanced bactericidal activity. PTT features spatiotemporally controllable generation of hyperthermia that could eradicate bacteria without inducing resistance. The synergy of it with other treatments, such as chemotherapy, photo-dynamic/catalytic therapy (PDT/PCT), immunotherapy, and sonodynamic therapy (SDT), could lower the introduced laser density in PTT and avoid undesired overheating injury of normal tissues. Simultaneously, by heat-induced improvement of the bacterial membrane permeability, PTT is conducive for accelerated intracellular permeation of chemotherapeutic drugs as well as reactive oxygen species (ROS) generated by photosensitizers/sonosensitizers, and could promote infiltration of immune cells. Thereby, it could solve the currently existing sterilization deficiencies of other combined therapeutic modes, for example, bacterial resistance for chemotherapy, low drug permeability for PDT/PCT/SDT, adverse immunoreactions for immunotherapy, etc. Admittedly, PTT-derived synergistic treatments are becoming essential in fighting bacterial infection, especially those caused by antibiotic-resistant strains. This review firstly presents the classical and newly reported photothermal agents (PTAs) in brief. Profoundly, through the introduction of delicately designed nanocomposite platforms, we systematically discuss the versatile photothermal-derived multimodal synergistic therapy with the purpose of sterilization application. At the end, challenges to PTT-derived combinational therapy are presented and promising synergistic bactericidal prospects are anticipated.

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.

Polydopamine-based nanomaterials and their potentials in advanced drug delivery and therapy

Polydopamine (PDA) has shown great potentials in biomedical fields due largely to its unique physicochemical properties, including high photothermal transfer efficiency, excellent drug binding capacity, versatile adhesion ability, sensitive pH responsibility and great biocompatibility and biodegradability. These properties confer PDA-based nanoparticles the potentials either as the drug carriers for advanced drug delivery or as the bioactive agents for photothermal therapy, imaging and biosensing. This review aims to provide a comprehensive understanding of PDA, its polymerization mechanisms and the potentials of PDA-based nano-systems in treating various diseases, including cancer, diabetes, inflammation, bacterial infection and Parkinson's disease. In addition, the concerns of PDA in biomedical use are also discussed.

Injectable zwitterionic thermosensitive hydrogels with low-protein adsorption and combined effect of photothermal-chemotherapy

Injectable hydrogels have been developed as biomedical materials in various fields but the biofouling on their surface limits applications in vivo. In this work, a zwitterionic structure was introduced into an injectable hydrogel based on thermosensitive nanogels to overcome the foreign body reaction. The hydrodynamic diameter of the resultant poly(N-isopropylacrylamide-co-sulfobetaine methacrylate) (PNS) nanogels was ca. 105 nm. The aqueous dispersion with a high content of PNS nanogels showed a flowable sol state at room temperature, and turned into a hydrogel in situ at ∼36 °C due to the thermosensitivity of the PNS nanogels. In particular, the resulting hydrogel exhibited lower biofouling both in vitro and in vivo in comparison with similar hydrogels without a zwitterionic structure. Polydopamine nanoparticles (PDA NPs) as a photothermal agent and an anti-tumour drug could be easily co-loaded in the injectable hydrogel. Under near-infrared (NIR) irradiation for 10 min, the temperature of the PNS system containing PDA NPs could reach ca. 38 °C. The drug release from the in situ-forming hydrogel could be accelerated by NIR laser irradiation, and showed a sustainable release behavior and adjustability. The results of intratumoral injection of the as-prepared injectable hydrogel containing PDA NPs and an anti-tumour drug showed significant anticancer effects combining photothermal therapy and local chemotherapy. This constructed injectable zwitterionic thermosensitive hydrogel is easy to use with the advantage of low-fouling and may become a promising platform for various biomedical applications.

Polydopamine-Incorporated Nanoformulations for Biomedical Applications

Polydopamine (PDA), a pigment in natural melanin, has attracted considerable attention because of its excellent optical properties, extraordinary adhesion, and good biocompatibility, which make it a promising material for application in energy, environmental, and biomedical fields. In this review, PDA-incorporated nanoformulations are focused for biomedical applications such as drug delivery, bioimaging, and tumor therapy. First, the recent advances in PDA-incorporated nanoformulations for drug delivery are discussed. Further, their application in boimaging, such as fluorescence imaging, photothermal imaging, and photoacoustic imaging, is reviewed. Next, their therapeutic applications, including chemotherapy, photodynamic therapy, photothermal therapy, and synergistic therapy are discussed. Finally, other biomedical applications of PDA-incorporated nanoformulations such as biosensing and clinical diagnosis are briefly presented. Finally, the biomedical applications of PDA-incorporated nanoformulations along with their prospects are summarized.

Bowl-Shaped Polydopamine Nanocapsules: Control of Morphology via Template-Free Synthesis

Synthesis of hollow polydopamine bowl-shaped nanoparticles (nanobowls), as small as 80 nm in diameter, via a one-pot template-free rapid method is reported. Addition of dopamine to a solution of 0.606 mg/mL tris(hydroxymethyl)aminomethane in an ethanol/water mixed solvent resulted in the formation of hollow spherical nanocapsules within 2 h. At longer reaction times, the formation of conventional solid nanospheres dominated the reaction. The wall thickness of the nanocapsules increased with increasing dopamine concentration in the reaction medium. Wall thickness was also influenced by oxygen availability during the reaction. Nanocapsules with thin walls were prone to collapse. When dried, over 90% of the nanocapsules with wall thickness on the order of 11 nm collapsed. Also, the degree of collapse of individual nanoparticles changed from complete to partial to no collapse as the wall thickness was increased. Varying the ethanol content affected the cavity size and overall dimension of the nanocapsules produced but did not result in a significant change to the wall thickness. A mechanism describing the formation of the nanocapsules and their subsequent collapse into nanobowls is presented. The shape-tunable nanobowls prepared through this green, rapid, and affordable method are expected to have applications in the biomedical, electrochemical, and catalytic fields.

Melanin-based nanomaterials: The promising nanoplatforms for cancer diagnosis and therapy

Melanin-based nanoplatforms are biocompatible nanomaterials with a variety of unique physicochemical properties such as strong photothermal conversion ability, excellent drug binding capacity, strong metal chelation capacity, high chemical reactivity and versatile adhesion ability. These innate talents not only make melanin-based nanoplatforms be an inborn theranostic nanoagent for photoacoustic imaging-guided photothermal therapy of cancers, but also enable them to be conveniently transferred into cancer-targeting drug delivery systems and multimodality imaging nanoprobes. Due to the intriguing properties, melanin-based nanoplatforms have attracted much attention in investigations of cancer diagnosis and therapy. This review provides an overview of recent research advances in applications of melanin-based nanoplatforms in the fields of cancer diagnosis and therapy including cancer photothermal therapy, anticancer drug delivery, cancer-specific multimodal imaging and theranostics, etc. The remaining challenges and prospects of melanin-based nanoplatforms in biomedical applications are discussed at the end of this review.

Nanoparticles modified by polydopamine: Working as "drug" carriers

Inspired by the mechanism of mussel adhesion, polydopamine (PDA), a versatile polymer for surface modification has been discovered. Owing to its unique properties like extraordinary adhesiveness, excellent biocompatibility, mild synthesis requirements, as well as distinctive drug loading approach, strong photothermal conversion capacity and reactive oxygen species (ROS) scavenging facility, various PDA-modified nanoparticles have been desired as drug carriers. These nanoparticles with diverse nanostructures are exploited in multifunctions, consisting of targeting, imaging, chemical treatment (CT), photodynamic therapy (PDT), photothermal therapy (PTT), tissue regeneration ability, therefore have attracted great attentions in plenty biomedical applications. Herein, recent progress of PDA-modified nanoparticle drug carriers in cancer therapy, antibiosis, prevention of inflammation, theranostics, vaccine delivery and adjuvant, tissue repair and implant materials are reviewed, including preparation of PDA-modified nanoparticle drug carriers with various nanostructures and their drug loading strategies, basic roles of PDA surface modification, etc. The advantages of PDA modification in overcoming the existing limitations of cancer therapy, antibiosis, tissue repair and the developing trends in the future of PDA-modified nanoparticle drug carriers are also discussed.

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Multifunctional PDA-modified drug systems are introduced in terms of classification, synthesis and drug loading strategies.

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Basic roles of PDA surface modification in the drug systems are discussed.

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Biomedical applications and unique advantages of the PDA-modified nanoparticle working as drug carriers are illustrated.

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Challenges and perspectives for future development are proposed.

From Bioinspired Glue to Medicine: Polydopamine as a Biomedical Material

Biological structures have emerged through millennia of evolution, and nature has fine-tuned the material properties in order to optimise the structure-function relationship. Following this paradigm, polydopamine (PDA), which was found to be crucial for the adhesion of mussels to wet surfaces, was hence initially introduced as a coating substance to increase the chemical reactivity and surface adhesion properties. Structurally, polydopamine is very similar to melanin, which is a pigment of human skin responsible for the protection of underlying skin layers by efficiently absorbing light with potentially harmful wavelengths. Recent findings have shown the subsequent release of the energy (in the form of heat) upon light excitation, presenting it as an ideal candidate for photothermal applications. Thus, polydopamine can both be used to (i) coat nanoparticle surfaces and to (ii) form capsules and ultra-small (nano)particles/nanocomposites while retaining bulk characteristics (i.e., biocompatibility, stability under UV irradiation, heat conversion, and activity during photoacoustic imaging). Due to the aforementioned properties, polydopamine-based materials have since been tested in adhesive and in energy-related as well as in a range of medical applications such as for tumour ablation, imaging, and drug delivery. In this review, we focus upon how different forms of the material can be synthesised and the use of polydopamine in biological and biomedical applications.

Melanin-Like Nanomaterials for Advanced Biomedical Applications: A Versatile Platform with Extraordinary Promise

Developing efficient, sustainable, and biocompatible high-tech nanoplatforms derived from naturally existing components in living organisms is highly beneficial for diverse advanced biomedical applications. Melanins are nontoxic natural biopolymers owning widespread distribution in various biosystems, possessing fascinating physicochemical properties and playing significant physiological roles. The multifunctionality together with intrinsic biocompatibility renders bioinspired melanin-like nanomaterials considerably promising as a versatile and powerful nanoplatform with broad bioapplication prospects. This panoramic Review starts with an overview of the fundamental physicochemical properties, preparation methods, and polymerization mechanisms of melanins. A systematical and well-bedded description of recent advancements of melanin-like nanomaterials regarding diverse biomedical applications is then given, mainly focusing on biological imaging, photothermal therapy, drug delivery for tumor treatment, and other emerging biomedicine-related implementations. Finally, current challenges toward clinical translation with an emphasis on innovative design strategies and future striving directions are rationally discussed. This comprehensive and detailed Review provides a deep understanding of the current research status of melanin-like nanomaterials and is expected to motivate further optimization of the design of novel tailorable and marketable multifunctional nanoplatforms in biomedicine.

Synergistic Release of Crop Nutrients and Stimulants from Hydroxyapatite Nanoparticles Functionalized with Humic Substances: Toward a Multifunctional Nanofertilizer

The use of salt- or macro-sized NPK fertilizers is typically associated with low nutrient use efficiency and water eutrophication. Nanotechnology can overcome such drawbacks, but its practical application on a large scale is limited by (i) high costs and difficult scale-up of nanoparticle synthesis, (ii) questionable advantages over traditional methods, and (iii) health hazards related to nanomaterial introduction in the food stream and the environment. Here, we report on a novel biocompatible and multifunctional P nanofertilizer obtained by self-assembling natural or synthetic humic substances and hydroxyapatite nanoparticles using a simple and straightforward dipping process, exploiting the interaction between the polyphenolic groups of humic substances and the surface of nanohydroxyapatite. Pot tests using the as-prepared materials were performed on Zea mays as a model crop, and the results were compared to those obtained using commercial fused superphosphate and bare nanohydroxyapatites. A significant improvement, in terms of early plant growth, corn productivity, rhizosphere bacteria, and the resistance to NaCl-induced abiotic stresses, was achieved using hydroxyapatite nanoparticles assembled with humic substances. These effects were ascribed to the synergistic co-release of phosphate ions and humic substances, which are two types of plant-beneficial agents for crop nutrition and stimulation, respectively. The release patterns were proven to be tunable with the amount of humic substances adsorbed on the nanoparticles, inducing competition between humic-substance-driven phosphorous dissolution and block of water contact. Such positive effects on plant growth in association with its intrinsic biocompatibility, simple synthesis, and multifunctionality qualify this novel nanofertilizer as a promising material for large-scale use in the agronomic field.

Melanin nanoparticles as a promising tool for biomedical applications - a review

Melanin is a biopolymer of easy and cheap availability that can be found among the living organisms and excels for its biocompatibility and biodegradability properties, along with scavenging abilities, metal chelation and electronic conductance. This biomaterial can act as a nanocarrier or agent itself to be used in diverse biomedical applications, such as imaging, controlled drug release, bioengineering and bioelectronics, antioxidant applications and theranostics. In this review, the melanin source and structure, its physicochemical properties, melanin-like polymers as well as the differences among those will be elucidated. The focus will be the discussion of the current approaches that apply melanin nanoparticles (MNPs) and melanin-like nanoparticles (MLNPs) in the biomedical field, to which promising capabilities have been attributed, regarding optoelectronic, photoconductivity and photoacoustic. The use of these nanoparticles, in the last 10 years, in topics as drug delivery or theranostics will be detailed and the major achievements will be discussed. Overall, we anticipate that melanin can drive us toward a new paradigm in medical diagnostics and treatments, since applying melanin features possibly its use as a theranostics nanocarrier agent, not only for diagnostics, but also for photothermal therapy and controlled drug release through chemotherapy. STATEMENT OF SIGNIFICANCE: We present here a timely and opportune review article focusing the significant potential of melanin nanoparticles in biomedical applications, which will be discussed thoroughly. This biomaterial presents multiple capabilities that may be taken into consideration towards cancer theranostics, expecting a high future impact in the nanosized-platforms design and performance.

Multi-responsive drug delivery nanoplatform for tumor-targeted synergistic photothermal/dynamic therapy and chemotherapy

“From one to all” multi-mode therapy using an integrated nanoplatform of multi-responsive GFCDH nanoparticles for tumor-targeted synergistic photothermal, photodynamic and chemotherapy.

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.

Nanobiomaterials: from 0D to 3D for tumor therapy and tissue regeneration

Nanobiomaterials have attracted tremendous attention in the biomedical field. Especially in the past few years, a large number of low dimensional nanobiomaterials, including 0D nanostructures, 1D nanotubes and 2D nanosheets, were employed for tumor therapy due to their optically triggered tumor therapy effects and drug loading capacities. However, these low dimensional nanobiomaterials cannot support cell adhesion and possess poor tissue regeneration ability, thus they are not suitable for application in regenerative medicine. Three dimensional (3D) nanofiber scaffolds have attracted extensive attention in tissue regeneration, including bone, skin, nerve and cardiac tissues, due to their similar extracellular matrix structures. Additionally, many 3D scaffolds displayed bone and cartilage regeneration abilities. Therefore, to obtain materials with both tumor therapy and tissue regeneration abilities, it is meaningful and necessary to develop 3D nanobiomaterials with multifunctions. In this review, we systematically review the research progress of nanobiomaterials with varied dimensional structures including 0D, 1D, 2D and 3D, as well as evolutional functions from single tumor therapy to simultaneous tumor therapy and tissue regeneration. This review may pave the way for developing an interdisciplinary research of nanobiomaterials in combination of tumor therapy and regenerative medicine.

Achieving traceless ablation of solid tumors without recurrence by mild photothermal-chemotherapy of triple stimuli-responsive polymer–drug conjugate nanoparticles

We put forward an innovative strategy to leverage hyperthermia and a high drug-loading capacity for mild PT-CT, which achieved traceless ablation of solid MCF-7 tumors without recurrence within 50 days.

Facile fabrication of polydopamine nanotubes for combined chemo-photothermal therapy

Polydopamine nanoparticles with higher drug loading capacity and enhanced photothermal behavior.

Application of polydopamine in tumor targeted drug delivery system and its drug release behavior

Inspired by the bionics of marine mussels, polydopamine (PDA), a new polymer with unique physicochemical properties was discovered. Due to its simple preparation, good biocompatibility, unique drug-loading methods, PDA has attracted tremendous attentions in field of drug delivery and imaging, and the combination of chemotherapy and other therapies or diagnostic methods, such as photothermotherapy (PTT), photoacoustic imaging (PAI), magnetic resonance imaging (MRI), etc. As an excellent drug carrier in tumor targeted drug delivery system, the drug release behavior of drug-loaded PDA-based nanoparticles is also an important factor to be considered in the establishment of drug delivery systems. Therefore, the purpose of this review is to provide a comprehensive overview of the various applications of PDA in tumor targeted drug delivery systems and to gain insight into the release behavior of the drug-loaded PDA-based nanocarriers. A sufficient understanding and discussion of these aspects is expected to provide a better way to design more rational and effective PDA-based tumor nano-targeted delivery systems. Apart from this, the prospects for the future application of PDA in this field and some unique insights are listed at the end of the article.

Multistimuli-responsive drug vehicles based on gold nanoflowers for chemophotothermal synergistic cancer therapy

AIM

To design and synthesize a novel multistimuli-responsive drug vehicle based on gold nanoflowers (AuNFs) for chemophotothermal synergistic cancer therapy.

MATERIALS & METHODS

Multistimuli-responsive drug-delivery system based on doxorubicin (DOX)/polydopamine (PDA)-functionalized AuNFs (Lan-AuNFs@PDA/DOX) was prepared. The structural characteristics, photothermal properties and stimuli-responsive drug release properties of Lan-AuNFs@PDA/DOX were evaluated. Antitumor studies in vivo and in vitro were performed.

RESULTS

Lan-AuNFs@PDA/DOX exhibited uniform morphology, excellent biocompatibility and photothermal conversion efficiency, which could also respond to stimulus including near infrared light and pH to trigger on demand drug release. The excellent synergistic therapeutic efficacy was confirmed both in vitro and in vivo.

CONCLUSION

Lan-AuNFs@PDA/DOX would be a promising drug carrier, endowing a great potential for multistimuli-responsive chemophotothermal synergistic cancer therapy.

Noninvasive photothermal cancer therapy nanoplatforms via integrating nanomaterials and functional polymers

In the cutting-edge field of cancer therapy, noninvasive photothermal therapy (PTT) has received great attention because it is considered to overcome the drawbacks of conventional surgery, radiotherapy and chemotherapy of severe body injuries and side effects on the immune system. The construction of PTT therapeutic and theranostic nanoplatforms is the key issue in achieving tumor targeting, imaging and therapy in a synergetic manner. In this review, we focus on the recent advances in constructing PTT therapeutic and theranostic nanoplatforms by integrating nanomaterials and functional polymers. The noninvasive photothermal cancer therapy mechanism and achievement strategies of PTT therapeutic and theranostic nanoplatforms are presented as well as the innovative construction strategies and perspectives for the future. Owing to their high tumor ablation efficiency, biological availability and low- or non-toxicity, PTT therapeutic and theranostic nanoplatforms are promising and emerging in medicine and clinical applications.

Carrier-free nanodrug by co-assembly of chemotherapeutic agent and photosensitizer for cancer imaging and chemo-photo combination therapy

Nanosized drug delivery systems (NDDS) with photothermal therapy (PTT) and photodynamic therapy (PDT) have been extensively exploited to improve the therapeutic performance and bio-safety of chemotherapeutic drugs in cancer. In this work, a carrier-free nanodrug was developed by co-assembly of the anti-cancer agent ursolic acid (UA), an asialoglycoprotein receptor (ASGPR), which can recognize the target molecule lactobionic acid (LA), and the near-infrared (NIR) probe dye indocyanine green (ICG) to form UA-LA-ICG NPs by a simple and green self-assembly approach. The UA-LA-ICG NPs had suitable stability, showed controlled release profile of UA drugs, and exhibited preferable temperature response (∼59.4 °C) under laser irradiation (808 nm, 1 W/cm2). Compared with free ICG, the UA-LA-ICG NPs significantly enhanced the intracellular ICG uptake. Upon irradiation of the NIR laser, co-assembled nanodrugs demonstrated great performance as a reactive oxygen species (ROS) producer and exhibited more anti-proliferative activities on ASGPR-overexpressing HepG2 cells than ASGPR low-expressing HeLa cells. Meanwhile, in vivo NIR fluorescence imaging exhibited that the co-assembled nanodrugs were specifically targeted to the tumor by the active targeting property of LA, and its circulation time was much longer than that of free ICG. In addition, UA-LA-ICG NPs + NIR irradiation treatment displayed enhanced inhibitory effect on tumor growth in H22 tumor-bearing mice. Overall, the co-assembly of chemotherapeutic agent and photosensitizer by the self-assembly approach might open an alternative avenue and give inspiration to fabricate new carrier-free nanodrugs for cancer imaging and chemo-photo combination therapy.

STATEMENT OF SIGNIFICANCE

The present study for the first time reported carrier-free nanoparticles (NPs) by co-assembly of a natural product ursolic acid (UA), an asialoglycoprotein receptor (ASGPR)-recognized sugar molecule lactobionic acid (LA), and the near-infrared dye indocyanine green (ICG) through a simple and green approach. The preparation process of nanodrugs is simple, rapid, effective, and labor-saving. The co-assembled nanodrugs were capable of stabilizing the ICG molecules and specifically targeting to the tumor, which could increase the tumor accumulation in cancer imaging and also enhance the efficacy of chemo-phototherapy.

Recent progress in the biomedical applications of polydopamine nanostructures

Polydopamine is a dark brown-black insoluble biopolymer produced by autoxidation of dopamine. Although its structure and polymerization mechanism have not been fully understood, there has been a rapid growth in the synthesis and applications of polydopamine nanostructures in biomedical fields such as drug delivery, photothermal therapy, bone and tissue engineering, and cell adhesion and patterning, as well as antimicrobial applications. This article is dedicated to reviewing some of the recent polydopamine developments in these biomedical fields. Firstly, the polymerization mechanism is introduced with a discussion of the factors that influence the polymerization process. The discussion is followed by the introduction of various forms of polydopamine nanostructures and their recent applications in biomedical fields, especially in drug delivery. Finally, the review is summarized followed by brief comments on the future prospects of polydopamine.

Combining photothermal therapy and immunotherapy against melanoma by polydopamine-coated Al2O3 nanoparticles

Photothermal therapy (PTT) can be an effective antitumor therapy, but it may not completely eliminate tumor cells, leading to the risk of recurrence or metastasis. Here we describe nanocarriers that allow combination therapy involving PTT and immunotherapy. Nanocarriers are prepared by coating Al₂O₃ nanoparticles with non-toxic, biodegradable polydopamine, which shows high photothermal efficiency. A near-infrared laser irradiation can kill the majority of tumor tissues, resulting in the release of tumor-associated antigens. The Al₂O₃ within the nanoparticles, together with CpG, acts as an adjuvant to trigger robust cell-mediated immune responses that can help eliminate the residual tumor cells and reduce the risk of tumor recurrence.

Methods: The characteristics and photothermal performance of polydopamine-coated Al₂O₃ nanoparticles were examined after one-step preparation. Then we studied their internalization, photothermal toxicity and immunostimulatory activity in vitro. For in vivo experiments, these nanocarriers were injected directly into B16F10 melanoma allografts in mice to ensure specific localization. After photothermal irradiation on day 0, mice were subcutaneously injected with CpG adjuvant on day 1, 3 and 5. Tumor volumes and number of living mice were recorded every two days. Moreover, various immune responses induced by our combined therapy were tested for mechanism research.

Results: 50% of mice after our combined treatment successfully achieved the goal of tumor eradication, and survived for 120 days, which was the end point of the experiment. Mechanism studies demonstrated the combined therapy efficiently led to dendritic cell maturation, resulting in the secretion of antibodies and cytokines as well as the proliferation of splenocytes and lymphocytes for anti-tumor immunotherapy.

Conclusion: Taken together, these results demonstrated the promise of our combined photothermal therapy and immunotherapy for tumor shrinkage, which merited further research.

Recent developments in dopamine-based materials for cancer diagnosis and therapy

Dopamine-based materials are emerging as novel biomaterials and have attracted considerable interests in the fields of biosensing, bioimaging and cancer therapy due to their unique physicochemical properties, such as versatile adhesion property, high chemical reactivity, excellent biocompatibility and biodegradability, strong photothermal conversion capacity, etc. In this review, we present an overview of recent research progress on dopamine-based materials for diagnosis and therapy of cancer. The review starts with a summary of the physicochemical properties of dopamine-based materials in general. Then detailed description is followed on their applications in the fields of diagnosis and treatment of cancers. The review concludes with an outline of some remaining challenges for dopamine-based materials to be used for clinical applications.

Multifunctional Cu-Ag2S nanoparticles with high photothermal conversion efficiency for photoacoustic imaging-guided photothermal therapy in vivo

Photothermal therapy (PTT) has attracted increasing interest and become widely used in cancer therapy owing to its noninvasiveness and low level of systemic adverse effects. However, there is an urgent need to develop biocompatible and multifunctional PTT agents with high photothermal conversion efficiency. Herein, biocompatible Cu-Ag₂S/PVP nanoparticles (NPs) with strong near-infrared absorption and high photothermal conversion efficiency were successfully synthesized for high-performance photoacoustic (PA) imaging-guided PTT in vivo. The novel Cu-Ag₂S/PVP NPs feature high photothermal conversion efficiency (58.2%) under 808 nm light irradiation, noticeably higher than those of most reported PTT agents. Because of their good dispersibility, Cu-Ag₂S/PVP NPs passively accumulate within tumors via the enhanced permeability and retention effect, which can be confirmed by PA imaging, photothermal performance, and biodistribution in vivo. Furthermore, Cu-Ag₂S/PVP NPs are thoroughly cleared through feces and urine within seven days, indicating a high level of biosafety for further potential clinical translation.

Biopolymer-Drug Conjugate Nanotheranostics for Multimodal Imaging-Guided Synergistic Cancer Photothermal-Chemotherapy

Some of the biomedical polymer-drug conjugates are being translated into clinical trials; however, they intrinsically lack photothermal and multi-imaging capabilities, hindering them from imaging-guided precision cancer therapy and complete tumor regression. We introduce a new concept of all-in-one biopolymer-drug conjugate nanotheranostics and prepare a kind of intracellular pH-sensitive polydopamine-doxorubicin (DOX) conjugate nanoparticles (PDCNs) under mild conditions. Significantly, this strategy integrates polymeric prodrug-induced chemotherapy (CT), near-infrared (NIR) light-mediated photothermal therapy (PT), and triple modalities including DOX self-fluorescence, photothermal, and photoacoustic (PA) imaging into one conjugate nanoparticle. The PDCNs present excellent photothermal property, dual stimuli-triggered drug release behavior, and about 12.4-fold blood circulation time compared to free DOX. Small animal fluorescent imaging technique confirms that PDCNs have preferential tumor accumulation effect in vivo, giving a 12.8-fold DOX higher than the control at 12 h postinjection. Upon NIR laser irradiation (5 min, 808 nm, and 2 W·cm^-2), the PDCN-mediated photothermal effect can quickly elevate the tumor over 50 °C, exhibiting good photothermal and PA imaging functions, of which the PA amplitude is 3.6-fold greater than the control. In vitro and in vivo assays persuasively verify that intravenous photothermal-CT of PDCNs produces synergistic antitumor activity compared to single PT or CT, achieving complete tumor ablation during the evaluation period.

Recent progress and development on polymeric nanomaterials for photothermal therapy: a brief overview

This review article summarizes the recent development and progress of polymeric photothermal agents for photothermal therapy and imaging-guided photothermal therapy applications.