Photocatalytic Synthesis of a Polydopamine-Coated Acellular Mega-Hemoglobin as a Potential Oxygen Therapeutic with Antioxidant Properties

Hemoglobin-based oxygen carriers (HBOCs) are being developed to overcome limitations associated with transfusion of donated red blood cells (RBCs) such as potential transmission of blood-borne pathogens and limited ex vivo storage shelf-life. Annelid erythrocruorin (Ec) derived from the worm Lumbricus terrestris (Lt) is an acellular mega-hemoglobin that has shown promise as a potential HBOC due to the large size of its oligomeric structure, thus overcoming limitations of unmodified circulating cell-free hemoglobin (Hb). With a large molecular weight of 3.6 MDa compared to 64.5 kDa for human Hb (hHb) and 144 oxygen-binding globin subunits compared to the 4 globin subunits of hHb, LtEc does not extravasate from the circulation to the same extent as hHb. LtEc is stable in the circulation without RBC membrane encapsulation and has a lower rate of auto-oxidation compared to acellular hHb, which allows the protein to remain functional for longer periods of time in the circulation compared to HBOCs derived from mammalian Hbs. Surface coatings, such as poly(ethylene glycol) (PEG) and oxidized dextran (Odex), have been investigated to potentially reduce the immune response and improve the circulation time of LtEc in vivo. Polydopamine (PDA) is a hydrophilic, biocompatible, bioinspired polymer coating used for biomedical nanoparticle assemblies and coatings and has previously been investigated for the surface coating of hHb. PDA is typically synthesized via the self-polymerization of dopamine (DA) under alkaline (pH > 8.0) conditions. However, at pH > 8.0, the oligomeric structure of LtEc begins to dissociate. Therefore, in this study, we investigated a photocatalytic method of PDA polymerization on the surface of LtEc using 9-mesityl-10-methylacridinium tetrafluoroborate (Acr-Mes) to drive PDA polymerization under physiological conditions (pH 7.4, 25 °C) over 2, 5, and 16 h in order to preserve the size and structure of LtEc. The resulting structural, biophysical, and antioxidant properties of PDA surface-coated LtEc (PDA-LtEc) was characterized using various techniques. PDA-LtEc showed an increase in measured particle size, molecular weight, and surface ζ-potential with increasing reaction time from t = 2 to 16 h compared to unmodified LtEc. PDA-LtEc reacted for 16 h was found to have reduced oxygen-binding cooperativity and slower deoxygenation kinetics compared to PDA-LtEc with lower levels of polymerization (t = 2 h), but there was no statistically significant difference in oxygen affinity. The thickness of the PDA coating can be controlled and in turn the biophysical properties can be tuned by changing various reaction conditions. PDA-LtEc was shown to demonstrate an increased level of antioxidant capacity (ferric iron reduction and free-radical scavenging) when synthesized at a reaction time of t = 16 h compared to LtEc. These antioxidant properties may prove beneficial for oxidative protection of PDA-LtEc during its time in the circulation. Hence, we believe that PDA-LtEc is a promising oxygen therapeutic for potential use in transfusion medicine applications.

Melanin-like nanoparticles: advances in surface modification and tumour photothermal therapy

Currently, tumor treatments are characterized by intelligence, diversity and personalization, but the therapeutic reagents used are often limited in clinical efficacy due to problems with water solubility, targeting, stability and multidrug resistance. To remedy these shortcomings, the application of multifunctional nanotechnology in the biomedical field has been widely studied. Synthetic melanin nanoparticles (MNPs) surfaces which contain highly reactive chemical groups such as carboxyl, hydroxyl and amine groups, can be used as a reaction platform on which to graft different functional components. In addition, MNPs easily adhere to substrate surface, and serve as a secondary reaction platform to modify it. The multifunctionality and intrinsic biocompatibility make melanin-like nanoparticles promising as a multifunctional and powerful nanoplatform for oncological applications. This paper first reviews the preparation methods, polymerization mechanisms and physicochemical properties of melanin including natural melanin and chemically synthesized melanin to guide scholars in MNP-based design. Then, recent advances in MNPs especially synthetic polydopamine (PDA) melanin for various medical oncological applications are systematically and thoroughly described, mainly focusing on bioimaging, photothermal therapy (PTT), and drug delivery for tumor therapy. Finally, based on the investigated literature, the current challenges and future directions for clinical translation are reasonably discussed, focusing on the innovative design of MNPs and further elucidation of pharmacokinetics. This paper is a timely and comprehensive and detailed study of the progress of MNPs in tumor therapy, especially PTT, and provides ideas for the design of personalized and customizable oncology nanomedicines to address the heterogeneity of the tumor microenvironment.

High-Precision Micropatterning of Polydopamine by Multiphoton Lithography

Mussel-inspired polydopamine (PDA) initiates a multifunctional modification route that leads to the generation of novel advanced materials and their applications. However, existing PDA deposition techniques still exhibit poor spatial control, have a very limited capability of micropatterning, and do not allow local tuning of the PDA topography. Herein, PDA deposition based on multiphoton lithography (MPL) is demonstrated, which enables full spatial and temporal control with nearly total freedom of patterning design. Using MPL, 2D microstructures of complex design are achieved with pattern precision of 0.8 µm without the need of a photomask or stamp. Moreover, this approach permits adjusting the morphology and thickness of the fabricated microstructure within one deposition step, resulting in a unique tunability of material properties. The chemical composition of PDA is confirmed and its ability for protein enzyme immobilization is demonstrated. This work presents a new methodology for high-precision and complete control of PDA deposition, enabling PDA incorporation in applications where fine and precise local surface functionalization is required. Possible applications include multicomponent functional elements and devices in microfluidics or lab-on-a-chip systems.

Site-specific halloysite functionalization by polydopamine: A new synthetic route for potential near infrared-activated delivery system

Halloysite nanotubes (HNTs) represent a versatile core structure for the design of functional nanosystems of biomedical interest. However, the development of selective methodologies for the site-controlled functionalization of the nanotubes at specific sites is not an easy task. This study aims to accomplish a procedure for the site-selective/specific, "pin-point", functionalization of HNTs with polydopamine (HNTs@PDA). This goal was achieved, at pH 6.5, by exploiting the basicity of ZnO nanoparticles anchored on the HNTs external surface (HNTs@ZnO) to induce a punctual polydopamine polymerization and coating. The morphology and the chemical composition of the nanomaterial was demonstrated by several techniques. Turbidimetric analysis showed that PDA coating affected the aqueous stability of HNTs@PDA compared to both HNTs@ZnO and HNTs. Notably, hyperthermia studies revealed that the nanomaterial induced a local thermic rise, up to 50 °C, under near-infrared (NIR) irradiation. Furthermore, secondary functionalization of HNTs@PDA by selective grafting of biotin onto the PDA coating followed by avidin binding was also accomplished.

Ultrasound-assisted dopamine polymerization: rapid and oxidizing agent-free polydopamine coatings on membrane surfaces

Herein, we report a controllable pathway to accelerate the polymerization kinetics of dopamine using ultrasound as a trigger. The use of ultrasound was demonstrated to dramatically accelerate the slow liquid phase reaction kinetics and increase the deposition rate of the polydopamine coating on the surface of polymeric membranes.