Cu2+-Loaded Polydopamine Nanoparticles for Magnetic Resonance Imaging-Guided pH- and Near-Infrared-Light-Stimulated Thermochemotherapy

Redox Responsive Metal Organic Framework Nanoparticles Induces Ferroptosis for Cancer Therapy

Ferroptosis is attracting significant attention due to its effectiveness in tumor treatment. The efficiency to produce toxic lipid peroxides (LPOs) at the tumor site plays a key role in ferroptosis. A hybrid PFP@Fe/Cu-SS metal organic framework (MOF) is synthesized and shown to increase intratumoral LPO content through redox reactions generating ·OH. In addition, glutathione (GSH) depletion through disulfide-thiol exchange leads to the inactivation of glutathione peroxide 4 (GPX4), which results in a further increase in LPO content. This MOF exhibits high inhibitory effect on the growth of xenografted Huh-7 tumors in mice. The coadministration of a ferroptosis inhibitor reduces the antitumor effect of the MOF, leading to a restoration of GPX4 activity and an increase in tumor growth. Moreover, the construction of Cu into mesoporous PFP@Fe/Cu-SS not only allows the MOF to be used as a contrast agent for T1 -weighted magnetic resonance imaging, but also renders its photothermal conversion capacity. Thus, near-infrared irradiation is able to induce photothermal therapy and transform the encapsulated liquid perfluoropentane into microbubbles for ultrasound imaging.

PDA/Cu Bioactive Hydrogel with "Hot Ions Effect" for Inhibition of Drug-Resistant Bacteria and Enhancement of Infectious Skin Wound Healing

Quick and effective sterilization of drug-resistant bacteria inevitably became an ever-growing global challenge. In this study, a multifunctional composite (PDA/Cu-CS) hydrogel mainly composed of polydopamine (PDA) and copper-doped calcium silicate ceramic (Cu-CS) was prepared. It was confirmed that PDA/copper (PDA/Cu) complexing in the composite hydrogel played a key role in enhancing the photothermal performance and antibacterial activity. Through a unique "hot ions effect", created by the heating of Cu ions through the photothermal effect of the composite hydrogel, the hydrogel showed high-efficiency, quick, and long-term inhibition of methicillin-resistant Staphylococcus aureus and Escherichia coli. In addition, the hydrogel possessed remarkable bioactivity to stimulate angiogenesis. The in vivo results confirmed that the "hot ions effect" of the composite hydrogel removed existing infection in the wound area efficiently and significantly promoted angiogenesis and collagen deposition during infectious skin wound healing. Our results suggested that the design of multifunctional hydrogels with "hot ions effect" may be an effective therapeutic approach for the treatment of infectious wounds.

Metal-Containing Polydopamine Nanomaterials: Catalysis, Energy, and Theranostics

Polydopamine (PDA) is a major type of artificial melanin material with many interesting properties such as antioxidant activity, free-radical scavenging, high photothermal conversion efficiency, and strong metal-ion chelation. The high affinity of PDA to a wide range of metals/metal ions has offered a new class of functional metal-containing polydopamine (MPDA) nanomaterials with promising functions and extensive applications. Understanding and controlling the metal coordination environment is vital to achieve desirable functions for which such materials can be exploited. MPDA nanomaterials with metal/metal ions as the active functions are reviewed, including their synthesis and metal coordination environment and their applications in catalysis, batteries, solar cells, capacitors, medical imaging, cancer therapy, antifouling, and antibacterial coating. The current trends, limitations, and future directions of this area are also explored.

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.

Transition Metal-Mediated DNA Adsorption on Polydopamine Nanoparticles

Polydopamine (PDA) is a widely used universal coating for a broad range of materials. Interfacing PDA with various biomolecules, such as DNA, is critical for applications such as sensing, intracellular delivery, and material fabrication. Because of the negative surface charge of PDA at neutral pH, electrostatic repulsion exists between PDA and DNA. In previous studies, modified DNA or low pH was used to overcome this repulsion for DNA adsorption. More recently, divalent Ca²⁺ was found to bridge DNA and PDA. Herein, we studied four transition metals (Mn²⁺, Co²⁺, Zn²⁺, and Ni²⁺) and compared their efficiencies with Ca²⁺ for promoting DNA adsorption. These transition metals induced a more efficient and tighter DNA binding compared to Ca²⁺. In all these cases, the DNA phosphate backbone played a dominant role in adsorption, although DNA bases might also interact with strong binding metals such as Ni²⁺. Moreover, when the adsorption affinity was stronger, sensing was more selective to complementary DNA. Finally, aging of PDA appeared to be detrimental for DNA adsorption, which could be due to further oxidation of PDA. We showed that using Zn²⁺ or Ni²⁺ could considerably relieve the aging effect, while storing PDA at 4 °C could slow down aging.

CuS@PDA-FA nanocomposites: a dual stimuli-responsive DOX delivery vehicle with ultrahigh loading level for synergistic photothermal-chemotherapies on breast cancer

In this study, CuS@PDA nanoparticles were synthesized and used to create a novel tumor-targeting nanocomposite platform composed of copper sulfide@polydopamine-folic acid/doxorubicin (CuS@PDA-FA/DOX) for performing both photothermal and chemotherapeutic cancer treatment. The nanocomposite platform has ultrahigh loading levels (4.2 ± 0.2 mg mg-1) and a greater photothermal conversion efficiency (η = 42.7%) than CuS/PDA alone. The uptake of CuS@PDA-FA/DOX nanocomposites is much higher in MCF-7 cells than in A549 cells because MCF-7 cells have much higher folic acid receptors than A549. Under near infrared (NIR) irradiation, the CuS@PDA-FA/DOX system using a synergistic combination of photothermal therapy and chemotherapy yields a better therapeutic effect than either photothermal therapy or chemotherapy alone. The treatment is very effective with the cell viability is only 5.6 ± 1.4%.

Targeted multifunctional nanomaterials with MRI, chemotherapy and photothermal therapy for the diagnosis and treatment of bladder cancer

Folate-modified vincristine-loaded polydopamine-coated Fe₃O₄ superparticles are designed as multifunctional nanomaterials for the imaging and treatment of bladder cancer.

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.

Calligraphy/Painting Based on a Bioinspired Light-Driven Micromotor with Concentration-Dependent Motion Direction Reversal and Dynamic Swarming Behavior

Inspired by the collective behavior of natural living systems, the collective behavior of micromotors has become the research highlight. Although great progress has been made, it is still challenging to control the collective behavior of micromotors. In this paper, we demonstrate a novel near-infrared (NIR) light-powered micromotor consisting of a polystyrene microsphere and a polydopamine core-shell structure (PS@PDA) with concentration-dependent motion direction reversal and dynamic swarming behavior. Among others, a single micromotor exhibits negative phototaxis, whereas a group of micromotors shows positive phototaxis, which can be attributed to the competition between the thermophoretic force and hydrodynamic drag caused by the thermal buoyancy. In addition, because of the reversible hydrogen bonding and π-π stacking interactions between the adjacent PS@PDA micromotors, they form aggregation as a result of the positive phototaxis with dynamically controllable shapes tuned by the irradiation position, which makes them potentially attractive for in-solution calligraphy and painting. It is anticipated that the current study may not only provide a new strategy to control the collective behavior of the micromotors, but also promote their application in the practical field.

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.

Tumor-targeting photodynamic therapy based on folate-modified polydopamine nanoparticles

BACKGROUND

Photodynamic therapy (PDT), a clinical anticancer therapeutic modality, has a long history in clinical cancer treatments since the 1970s. However, PDT has not been widely used largely because of metabolic problems and off-target phototoxicities of the current clinical photosensitizers.

PURPOSE

The objective of the study is to develop a high-efficiency and high-specificity carrier to precisely deliver photosensitizers to tumor sites, aiming at addressing metabolic problems, as well as the systemic damages current clinical photosensitizers are known to cause.

METHODS

We synthesized a polydopamine (PDA)-based carrier with the modification of folic acid (FA), which is to target the overexpressed folate receptors on tumor surfaces. We used this carrier to load a cationic phthalocyanine-type photosensitizer (Pc) and generated a PDA-FA-Pc nanomedicine. We determined the antitumor effects and the specificity to tumor cell lines in vitro. In addition, we established human cancer-xenografted mice models to evaluate the tumor-targeting property and anticancer efficacies in vivo.

RESULTS

Our PDA-FA-Pc nanomedicine demonstrated a high stability in normal physiological conditions, however, could specifically release photosensitizers in acidic conditions, eg, tumor microenvironment and lysosomes in cancer cells. Additionally, PDA-FA-Pc nanomedicine demonstrated a much higher cellular uptake and phototoxicity in cancer cell lines than in healthy cell lines. Moreover, the in vivo imaging data indicated excellent tumor-targeting properties of PDA-FA-Pc nanomedicine in human cancer-xenografted mice. Lastly, PDA-FA-Pc nanomedicine was found to significantly suppress tumor growth within two human cancer-xenografted mice models.

CONCLUSION

Our current study not only demonstrates PDA-FA-Pc nanomedicine as a highly potent and specific anticancer agent, but also suggests a strategy to address the metabolic and specificity problems of clinical photosensitizers.

Tuning the ultrasonic and photoacoustic response of polydopamine-stabilized perfluorocarbon contrast agents

Contrast-enhanced ultrasound (CEUS) offers the exciting prospect of retaining the ease of ultrasound imaging while enhancing imaging clarity, diagnostic specificity, and theranostic capability. To advance the capabilities of CEUS, the synthesis and understanding of new ultrasound contrast agents (UCAs) is a necessity. Many UCAs are nano- or micro-scale materials composed of a perfluorocarbon (PFC) and stabilizer that synergistically induce an ultrasound response that is both information-rich and easily differentiated from natural tissue. In this work, we probe the extent to which CEUS is modulated through variation in a PFC stabilized with fluorine-modified polydopamine nanoparticles (PDA NPs). The high level of synthetic tunability in this system allows us to study signal as a function of particle aggregation and PFC volatility in a systematic manner. Separation of aggregated and non-aggregated nanoparticles lead to a fundamentally different signal response, and for this system, PFC volatility has little effect on CEUS intensity despite a range of over 50 °C in boiling point. To further explore the imaging tunability and multimodality, Fe3+-chelation was employed to generate an enhanced photoacoustic (PA) signal in addition to the US signal. In vitro and in vivo results demonstrate that PFC-loaded PDA NPs show stronger PA signal than the non-PFC ones, indicating that the PA signal can be used for in situ differentiation between PFC-loading levels. In sum, these data evince the rich role synthetic chemistry can play in guiding new directions of development for UCAs.

Functionalized theranostic nanocarriers with bio-inspired polydopamine for tumor imaging and chemo-photothermal therapy

Nanocarriers sensitive to near infrared light (NIR) are useful templates for chemo-photothermal therapy (PTT) and imaging of tumors due to the ability to change the absorbed NIR energy to heat. The conventional photo-absorbing reagents lack the efficient loading and release of drug before reaching the target site leading to insufficient therapeutic outcomes. To overcome these limitations, the surface of nanocarriers can be modified with different polymers with wide functionalities to provide systems with diagnostic, therapeutic, and theranostic capabilities. Among various polymers, polydopamine (PDA) has been more interested due to complex structure with various chemical moieties, and the capacity to be used through different coating mechanism. In this review, we describe the complex structure, chemical properties, and coating mechanisms of PDA. Moreover, the advantage and surface modification of some relevant nanosystems based on carbon materials, gold, iron oxide, manganese, and upconverting nanomaterials by using PDA will be discussed, in detail.

Smart nanomedicine agents for cancer, triggered by pH, glutathione, H2O2, or H2S

Effective tumor diagnosis and therapy have always been a significant but challenging issue. Although nanomedicine has shown great potential for improving the outcomes of tumor diagnosis and therapy, the nonspecial targeted distribution of nanomedicine agents in the whole body causes a low diagnosis signal-to-noise ratio and a potential risk of systemic toxicity. Recently, the development of smart nanomedicine agents with diagnosis and therapy functions that can only be activated by the tumor microenvironment (TME) is regarded as an effective strategy to improve the theranostic sensitivity and selectivity, as well as reduce the potential side effects during treatment. This article will introduce and summarize the latest achievements in the design and fabrication of TME-responsive smart nanomedicine agents, and highlight their prospects for enhancing tumor diagnosis and therapy.

Polyphenol-Based Particles for Theranostics

Polyphenols, due to their high biocompatibility and wide occurrence in nature, have attracted increasing attention in the engineering of functional materials ranging from films, particles, to bulk hydrogels. Colloidal particles, such as nanogels, hollow capsules, mesoporous particles and core-shell structures, have been fabricated from polyphenols or their derivatives with a series of polymeric or biomolecular compounds through various covalent and non-covalent interactions. These particles can be designed with specific properties or functionalities, including multi-responsiveness, radical scavenging capabilities, and targeting abilities. Moreover, a range of cargos (e.g., imaging agents, anticancer drugs, therapeutic peptides or proteins, and nucleic acid fragments) can be incorporated into these particles. These cargo-loaded carriers have shown their advantages in the diagnosis and treatment of diseases, especially of cancer. In this review, we summarize the assembly of polyphenol-based particles, including polydopamine (PDA) particles, metal-phenolic network (MPN)-based particles, and polymer-phenol particles, and their potential biomedical applications in various diagnostic and therapeutic applications.

Mesoporous Polydopamine Carrying Manganese Carbonyl Responds to Tumor Microenvironment for Multimodal Imaging‐Guided Cancer Therapy

Multifunctional nanodrugs integrating multiple therapeutic and imaging functions may find tremendous biomedical applications. However, the development of a simple yet potent theranostic nanosystem with a high payload and microenvironment responsiveness enhancing imaging‐guided cancer therapy is still a great challenge. Herein, a kind of MnCO‐entrapped mesoporous polydopamine nanoparticles are developed, which reach a 1.5 mg payload per gram carrier and exhibit marked theranostic capability through effective CO/Mn2+ generation and photothermal conversion inside the H+ and H2O2‐enriched tumor microenvironment, for a magnetic resonance/photoacoustic bimodal imaging‐guided tumor therapy. The multifunctional nanosystem exhibits a biocompatibility highly desirable for in vivo application and superior performance in inhibiting tumor growth and recurrence via combination CO and photothermal therapy.

Oncogenic MSH6-CXCR4-TGFB1 Feedback Loop: A Novel Therapeutic Target of Photothermal Therapy in Glioblastoma Multiforme

Glioblastoma multiforme (GBM) has been considered the most aggressive glioma type. Temozolomide (TMZ) is the main first-line chemotherapeutic agent for GBM. Decreased mutS homolog 6 (MSH6) expression is clinically recognized as one of the principal reasons for GBM resistance to TMZ. However, the specific functions of MSH6 in GBM, in addition to its role in mismatch repair, remain unknown.

Methods: Bioinformatics were employed to analyze MSH6 mRNA and protein levels in GBM clinical samples and to predict the potential cancer-promoting functions and mechanisms of MSH6. MSH6 levels were silenced or overexpressed in GBM cells to assess its functional effects in vitro and in vivo. Western blot, qRT-PCR, and immunofluorescence assays were used to explore the relevant molecular mechanisms. Cu₂(OH)PO₄@PAA nanoparticles were fabricated through a hydrothermal method. Their MRI and photothermal effects as well as their effect on restraining the MSH6-CXCR4-TGFB1 feedback loop were investigated in vitro and in vivo.

Results: We demonstrated that MSH6 is an overexpressed oncogene in human GBM tissues. MSH6, CXCR4 and TGFB1 formed a triangular MSH6-CXCR4-TGFB1 feedback loop that accelerated gliomagenesis, proliferation (G1 phase), migration and invasion (epithelial-to-mesenchymal transition; EMT), stemness, angiogenesis and antiapoptotic effects by regulating the p-STAT3/Slug and p-Smad2/3/ZEB2 signaling pathways in GBM. In addition, the MSH6-CXCR4-TGFB1 feedback loop was a vital marker of GBM, making it a promising therapeutic target. Notably, photothermal therapy (PTT) mediated by Cu₂(OH)PO₄@PAA + near infrared (NIR) irradiation showed outstanding therapeutic effects, which might be associated with a repressed MSH6-CXCR4-TGFB1 feedback loop and its downstream factors in GBM. Simultaneously, the prominent MR imaging (T1WI) ability of Cu₂(OH)PO₄@PAA could provide visual guidance for PTT.

Conclusions: Our findings indicate that the oncogenic MSH6-CXCR4-TGFB1 feedback loop is a novel therapeutic target for GBM and that PTT is associated with the inhibition of the MSH6-CXCR4-TGFB1 loop.

Iron-Chelated Polydopamine Decorated Doxorubicin-Loaded Nanodevices for Reactive Oxygen Species Enhanced Cancer Combination Therapy

Combination therapy which enhances efficacy and reduces toxicity, has been increasingly applied as a promising strategy for cancer therapy. Here, a reactive oxygen species (ROS) that enhanced combination chemotherapy nanodevices was fabricated based on the Fe-chelated polydopamine (PDA) nanoparticles (NPs). The structure was characterized by dynamic light scattering-autosizer, transmission electron microscopy, energy dispersive spectroscopy, and Fourier-transform infrared (FT-IR) spectrophotometer. The in vitro drug release profile triggered by low intracellular pH indicated that the system demonstrated controlled therapeutic activity. In vitro cell uptake studies showed that doxorubicin (DOX)-loaded Fe-PDA/ folic acid (FA)- polyethylene glycol (DOX@Fe-PDA/FA-PEG) had a strong uptake capacity and can be rapidly internalized by MCF-7 cells. The in vitro experiments demonstrated that DOX@Fe-PDA/FA-PEG triggered the intracellular ROS overproduction, thereby enhancing its therapeutic effect on breast cancer. In summary, this experiment demonstrated the novel DOX-loaded composite NPs used as a potential targeted nanocarrier for breast cancer treatment, which could be a promising therapeutic strategy against breast cancer.

Gadolinium Doping Enhances the Photoacoustic Signal of Synthetic Melanin Nanoparticles: A Dual Modality Contrast Agent for Stem Cell Imaging

In this paper, we show that gadolinium-loaded synthetic melanin nanoparticles (Gd(III)-SMNPs) exhibit up to a 40-fold enhanced photoacoustic signal intensity relative to synthetic melanin alone and higher than other metal-chelated SMNPs. This property makes these materials useful as dual labeling agents because Gd(III)-SMNPs also behave as magnetic resonance imaging (MRI) contrast agents. As a proof-of-concept, we used these nanoparticles to label human mesenchymal stem cells. Cellular uptake was confirmed with bright-field optical and transmission electron microscopy. The Gd(III)-SMNP-labeled stem cells continued to express the stem cell surface markers CD73, CD90, and CD105 and proliferate. The labeled stem cells were subsequently injected intramyocardially in mice, and the tissue was observed by photoacoustic and MR imaging. We found that the photoacoustic signal increased as the cell number increased (R 2 = 0.96), indicating that such an approach could be employed to discriminate between stem cell populations with a limit of detection of 2.3 × 104 cells in in vitro tests. This multimodal photoacoustic/MRI approach combines the excellent temporal resolution of photoacoustics with the anatomic resolution of MRI.

Paramagnetic CuS hollow nanoflowers for T2-FLAIR magnetic resonance imaging-guided thermochemotherapy of cancer

Green synthesized 3D CuS hollow nanoflowers are for the first time proved to be a T₁ positive MRI contrast agent for imaging-guided thermochemotherapy.

Calcium-carbonate packaging magnetic polydopamine nanoparticles loaded with indocyanine green for near-infrared induced photothermal/photodynamic therapy

Indocyanine green (ICG) is an efficient photosensitizer that can facilitate producing cytotoxic reactive oxygen species (ROS). At the same time, ICG also has characteristic absorption of near-infrared light and thus can induce a strong photothermal effect. Both of these important features of ICG may be applied for noninvasive light-induced tumor ablation. On the other hand, ICG is lack of stability in blood circulation and susceptible to aggregation or premature clearance from the body. These issues need to be effectively addressed before antitumor application of ICG becomes possible. Herein, a nanocomposite consisting of calcium carbonate modified magnetic polydopamine (PDA) nanoparticles and loaded with ICG, namely Fe₃O₄@PDA@CaCO₃/ICG (FPCI) NPs, was developed to integrate the photothermal capability of PDA with the photodynamic capability of ICG. Particularly, calcium carbonate not only entrapped ICG in the form of stable aggregate to evade blood clearance, but also facilitated controlled release of ICG in response to acidic tumor microenvironment via self-decomposition. With the aid of magnetic guidance, this multifunctional therapeutic agent makes it possible to achieve the combination of photothermal (PTT) and photodynamic therapies (PDT) against tumors, which was demonstrated by this proof-of-concept study based on in vitro and in vivo tumor models. STATEMENT OF SIGNIFICANCE: Currently, there is an ongoing trend of realizing precise and targeted tumor therapy using functional nanocomplexes. Magnetic particles, which can be manipulated by a magnetic field, have attracted increasing attention for tumor therapy. This submitted work demonstrated that calcium carbonate nanoshell was precipitated onto magnetic nanocores mediated by polydopamine. Moreover, indocyanine green (ICG), as a potent photosensitizer, was embedded in this nanocomplex and protected by the calcium carbonate nanoshell, resulting in high drug loading efficiency and enhanced drug stability on the carrier. This new nanocomposite was demonstrated to achieve controlled and pH-responsive release of ICG in tumor environment. This work explored the relationship between the physiochemical properties of the nanocomplex and their potential biomedical applications, aiming to inspire the development of analogous nanoplatforms featured with calcium carbonate blocks.

Bioorthogonal DNA Adsorption on Polydopamine Nanoparticles Mediated by Metal Coordination for Highly Robust Sensing in Serum and Living Cells

DNA-functionalized nanomaterials, such as various 2D materials, metal oxides, and gold nanoparticles, have been extensively explored as biosensors. However, their practical applications for selective sensing and imaging in biological samples remain challenging due to interference from the sample matrix. Bioorthogonal chemistry has allowed specific reactions in cells, and we want to employ this concept to design nanomaterials that can selectively adsorb DNA but not proteins or other abundant biomolecules. In this work, DNA oligonucleotides were found to be adsorbed on polydopamine nanoparticles (PDANs) via polyvalent metal-mediated coordination, and such adsorption bioorthogonally resisted DNA displacement by various biological ligands, showing better performance compared to graphene oxide and metal oxide nanoparticles for DNA detection. Using DNA/PDANs as biosensors, a detection limit of <1 nM target DNA was achieved in serum and other biological samples, and imaging of cancer-related microRNA in cells was demonstrated. The DNA binding mechanism on PDAN was further studied by ligand displacement experiments and X-ray photoelectron spectroscopy characterization, which demonstrated the critical role of polyvalent metal ions to bridge DNA with PDANs. This work provides fundamental insights into the biointerface science of PDANs with DNA, which can benefit applications in biosensor design, directed assembly of nanomaterials, bioimaging, and drug delivery.

Recent advancements in biocompatible inorganic nanoparticles towards biomedical applications

Due to their intrinsic physical properties potentially useful for imaging and therapy as well as their highly engineerable surface, biocompatible inorganic nanoparticles offer novel platforms to develop advanced diagnostic and therapeutic agents for improved detection and more efficacious treatment of major diseases. The in vivo application of inorganic nanoparticles was demonstrated more than two decades ago, however it turns out to be very complicated as nanomaterials exhibit much more sophisticated pharmacokinetic properties than conventional drugs. In this review, we first discuss the in vivo behavior of inorganic nanoparticles after systematic administration, including the basic requirements for nanoparticles to be used in vivo, the impact of the particles' physicochemical properties on their pharmacokinetics, and the effects of the protein corona formed across the nano-bio interface. Next, we summarize the state-of-the-art of the preparation of biocompatible inorganic nanoparticles and bioconjugation strategies for obtaining target-specific nanoprobes. Then, the advancements in sensitive tumor imaging towards diagnosis and visualization of the abnormal signatures in the tumor microenvironment, together with recent studies on atherosclerosis imaging are highlighted. Finally, the future challenges and the potential for inorganic nanoparticles to be translated into clinical applications are discussed.

Laser-Activated Bioprobes with High Photothermal Conversion Efficiency for Sensitive Photoacoustic/Ultrasound Imaging and Photothermal Sensing

Laser-activated bioprobes with high photothermal conversion efficiency (IRPDA@PFH NDs) based on biocompatible IR-780 doped polydopamine perfluorocarbon nanodroplets (NDs) were developed. When protected by gelatin microspheres, their near-spherical morphologies can be easily observed with transmission electron microscope. Doping IR-780 (3 w/w % of added dopamine hydrochloride) can significantly enhance near-infrared (NIR) absorption and photothermal conversion efficiency to 57.7%. The enhanced NIR absorption and nonradiative relaxation are preferred to stronger photoacoustic (PA) signals and higher PA imaging definition; ultrasound (US) signals also increase more than 2.5 times because of easier phase change of NDs. These bioprobes had sensitive PA/US imaging capability with highly effective substitute utilizations, in which polydopamine was used either as a PA contrast or a photothermal agent. Perfluorocarbon can be used as an US contrast agent and temperature indicator. More importantly, the gray value increments of US increase with temperature in a general range from 35 to 55 °C. Especially, an approximate linear increasing of gray value in the optimized photothermal therapy (PTT) range from 35 °C to 50 °C could be used for the temperature monitoring and control of PTT. During PTT, the heated regions and the extent of photothermal heating can be visualized by US imaging. These findings indicate their great potential for biosensing and PTT monitoring.

Perfluorocarbon-loaded polydopamine nanoparticles as ultrasound contrast agents

A versatile platform for the development of new ultrasound contrast agents is demonstrated through a one-pot synthesis and fluorination of submicron polydopamine (PDA-F) nanoparticles. The fluorophilicity of these particles allows loading with perfluoropentane (PFP) droplets that display strong and persistent ultrasound contrast in aqueous suspension and ex vivo tissue samples. Contrast under continuous imaging by color Doppler persists for 1 h in 135 nm PDA-F samples, even at maximum clinical imaging power (MI = 1.9). Additionally, use of a Cadence Contrast Pulse Sequence (CPS) results in a non-linear response suitable for imaging at 0.5 mg mL-1. Despite the PFP volatility and the lack of a hollow core, PDA-F particles display minimal signal loss after storage for over a week. The ability to tune size, metal-chelation, and add covalently-bound organic functionality offers myriad possibilities for extending this work to multimodal imaging, targeted delivery, and therapeutic functionality.

Cytotoxicity of paramagnetic cations-Loaded polydopamine nanoparticles

Polydopamine (PD) is a synthetic melanin pigment of great importance in biomedicine, where its affinity for metallic cations, especially paramagnetic ions, has sparked interest in its use in the development of magnetic resonance imaging (MRI) contrast agents. In this work, we report the cytotoxicity of metal-enriched PD nanoparticles on NIH3T3, a healthy cell line and BT474, a breast cancer cell line. Remarkably, it was found that the metal- enriched PD particles (Mⁿ⁺ = Fe³⁺, Fe²⁺ and Cu²⁺) were highly cytotoxic to the breast cancer cells, even after 24 h of treatment. Although, this effect was not selective systems, since an acute cytotoxic effect was also observed on the healthy cell line, this system can be considered as starting point for designing advanced antineoplastic agents.

Surface impact on nanoparticle-based magnetic resonance imaging contrast agents

Magnetic resonance imaging (MRI) is one of the most widely used diagnostic tools in the clinic. To improve imaging quality, MRI contrast agents, which can modulate local T1 and T2 relaxation times, are often injected prior to or during MRI scans. However, clinically used contrast agents, including Gd3+-based chelates and iron oxide nanoparticles (IONPs), afford mediocre contrast abilities. To address this issue, there has been extensive research on developing alternative MRI contrast agents with superior r1 and r2 relaxivities. These efforts are facilitated by the fast progress in nanotechnology, which allows for preparation of magnetic nanoparticles (NPs) with varied size, shape, crystallinity, and composition. Studies suggest that surface coatings can also largely affect T1 and T2 relaxations and can be tailored in favor of a high r1 or r2. However, the surface impact of NPs has been less emphasized. Herein, we review recent progress on developing NP-based T1 and T2 contrast agents, with a focus on the surface impact.

Bioinspired, Manganese-Chelated Alginate-Polydopamine Nanomaterials for Efficient in Vivo T1-Weighted Magnetic Resonance Imaging

Manganese-based nanomaterials are an emerging new class of magnetic resonance imaging (MRI) contrast agents (CAs) that provide impressive contrast abilities. MRI CAs that can respond to pathophysiological parameters such as pH or redox potential are also highly in demand for MRI-guided tumor diagnosis. Until now, synthesizing nanomaterials with good biocompatibility, physiochemical stability, and good contrast effects remains a challenge. This study investigated two new systems of calcium/manganese cations complexed with either alginate-polydopamine or alginate-dopamine nanogels [AlgPDA(Ca/Mn) NG or AlgDA(Ca/Mn) NG]. Under such systems, Ca cations form ionic interactions via carboxylic acids of the Alg backbone to enhance the stability of the synthetic nanogels (NGs). Likewise, complexation of Mn cations also increased the colloidal stability of the synthetic NGs. The magnetic property of the prepared CAs was confirmed with superconducting quantum interference device measurements, proving the potential paramagnetic property. Hence, the T₁ relaxivity measurement showed that PDA-complexed synthetic NGs reveal a strong positive contrast enhancement with r₁ = 12.54 mM^-1·s^-1 in 7.0 T MRI images, whereas DA-complexed synthetic NGs showed a relatively lower T₁ relaxivity effect with r₁ = 10.13 mM^-1·s^-1. In addition, both the synthetic NGs exhibit negligible cytotoxicity with >92% cell viability up to 0.25 mM concentration, when incubated with the mouse macrophage (RAW 264.7) and HeLa cells, and high biocompatibility under in vivo analysis. The in vivo MRI test indicates that the synthetic NG exhibits a high signal-to-noise ratio for longer hours, which provides a longer image acquisition time for tumor and anatomical imaging. Furthermore, T₁-weighted MRI results revealed that PEGylated AlgPDA(Ca/Mn) NGs significantly enhanced the signals from liver and tumor tissues. Therefore, owing to the enhanced permeability and retention effect, significantly enhanced in vitro and in vivo imagings, low cost, and one-pot synthesis method, the Mn-based biomimetic approach used in this study provides a promising and competitive alternative for noninvasive tumor detection and comprehensive anatomical diagnosis.

Polydopamine-based nanoparticles with excellent biocompatibility for photothermally enhanced gene delivery

Polyethylenimine-modified polydopamine-based nanoparticles (PPNPs) were constructed for photothermally enhanced gene delivery.

Polydopamine nanoparticles kill cancer cells

Polydopamine (PD) is a synthetic melanin analogue of growing importance in the field of biomedicine, especially with respect to cancer research, due, in part, to its biocompatibility.

Cu(II)-Doped Polydopamine-Coated Gold Nanorods for Tumor Theranostics

Gold nanorods (AuNRs) are potentially useful in tumor theranostics, but the poor stability, high toxicity, and rapid removal by the immune system seriously limit their theranostic applications. In our study, we demonstrate the fabrication of Cu(II)-doped polydopamine-coated AuNR (AuNR@CuPDA), which significantly improves the potentials in tumor theranostics. Besides the improvement of physiological stability and biocompatibility, the PDA shell increases the photothermal performance and prolongs the blood circulation time of AuNRs. The half-life of AuNRs during blood circulation increases from 0.7 to 4.5 h after PDA coating, and the injected dose per gram of tumor tissue is 4.6% ID g^-1 for AuNR@CuPDA. In addition to computer tomography imaging, the loading of Cu(II) in PDA shell endows AuNR@CuPDA with magnetic resonance imaging function. Cu(II) doped in PDA shell also exhibits chemotherapeutic behavior, and the tumor inhibitor rate is 31.2%. Further combining 808 nm laser-driven photothermal therapy, tumors were completely ablated, and no recurrence was observed. Liver and renal functions tests and histological analysis of major organs confirm that AuNR@CuPDA is in good safety.

Polydopamine Based Colloidal Materials: Synthesis and Applications

Polydopamine is a synthetic analogue of natural melanin (eumelanin) produced from oxidative polymerization of dopamine. Owing to its strong adhesion ability, versatile chemical reactivity, biocompatibility and biodegradation, polydopamine is commonly applied as a versatile linker to synthesize colloidal materials with diverse structures, unique physicochemical properties and tunable functions, which allow for a broad scope of applications including biomedicine, sensing, catalysis, environment and energy. In this personal account, we discuss first about the different synthetic approaches of polydopamine, as well as its polymerization mechanism, and then with a comprehensive overview of recent progress in the synthesis and applications of polydopamine-based colloidal materials. Finally, we summarize this personal account with future perspectives.

High Relaxivity Gadolinium-Polydopamine Nanoparticles

This study reports the preparation of a series of gadolinium-polydopamine nanoparticles (GdPD-NPs) with tunable metal loadings. GdPD-NPs are analyzed by nuclear magnetic relaxation dispersion and with a 7-tesla (T) magnetic resonance imaging (MRI) scanner. A relaxivity of 75 and 10.3 mM^-1 s^-1 at 1.4 and 7 T is observed, respectively. Furthermore, superconducting quantum interference device magnetometry is used to study intraparticle magnetic interactions and determine the GdPD-NPs consist of isolated metal ions even at maximum metal loadings. From these data, it is concluded that the observed high relaxivities arise from a high hydration state of the Gd(III) at the particle surface, fast rate of water exchange, and negligible antiferromagnetic coupling between Gd(III) centers throughout the particles. This study highlights design parameters and a robust synthetic approach that aid in the development of this scaffold for T₁ -weighted, high relaxivity MRI contrast agents.