The unique combination of mechanical, optical and electrical properties offered by carbon nanotubes has fostered research for their use in many kinds of applications, including the biomedical field. However, due to persisting outstanding questions regarding their potential toxicity when considered as free particles, the research is now focusing on their immobilization on substrates for interface tuning or as biosensors, as load in nanocomposite materials where they improve both mechanical and electrical properties or even for direct use as scaffolds for tissue engineering. After a brief introduction to carbon nanotubes in general and their proposed applications in the biomedical field, this review will focus on nanocomposite materials with hydrogel-based matrices and especially their potential future use for diagnostics, tissue engineering or targeted drug delivery. The toxicity issue will also be briefly described in order to justify the safe(r)-by-design approach offered by carbon nanotubes-based hydrogels.

/pdf/overview-of-carbon-nanotubes-for-biomedical-applications-3hnnh7594y.pdf

Overview of Carbon Nanotubes for Biomedical Applications

Nanoparticles modified by polydopamine: Working as "drug" carriers.

Polyphenols are a class of ubiquitous compounds distributed in nature, with fascinating inherent biocompatible, bioadhesive, antioxidant, and antibacterial properties. The unique polyphenolic structures based on catechol or pyrogallol moieties allow for strong non-covalent interactions (e.g., multiple hydrogen bonding, electrostatic, and cation–π interactions) as well as covalent interactions (e.g., Michael addition/Schiff-base reaction, radical coupling reaction, and dynamic coordination interactions with boronate or metal ions). This review article provides an overview of the polyphenol-based scaffolds including the hydrogels, films, and nanofibers that have emerged from chemical and functional signatures during the past years. A full description of the structure–function relationships in terms of their utilization in wound healing, bone regeneration, and electroactive tissue engineering is also carefully discussed, which may pave the path towards the rational design and facile preparation of next-generation polyphenol scaffolds for tissue engineering applications.

Polyphenol scaffolds in tissue engineering

Polydopamine (PDA) is the most typical kind of synthetic melanin, which possesses interesting properties such as antioxidation, photoprotection, metal chelation, and energy dissipation. Over the past few years, PDA has been successfully synthesized via polymerization methods and has demonstrated excellent free radical scavenging ability. The related applications have been rapidly expanded to include sunscreens, anti-inflammatory treatment, and composite material fabrication. Despite great progress, the comprehensive mechanisms of its free radical scavenging behaviors are not fully understood. This article strives to summarize the possible mechanisms, established antioxidant regulation methods and the related biomedical applications of PDA free radical scavengers. We believe this paper can provide insight into the current PDA scavenging systems and offer inspiration towards the design of new melanin-inspired scavengers with a broad range of biomedical applications.

https://pubs.rsc.org/en/content/articlepdf/2020/bm/d0bm01070g

Polydopamine free radical scavengers

Polyphenols, the phenolic hydroxyl group-containing organic molecules, are widely found in natural plants and have shown beneficial effects on human health. Recently, polyphenol-containing nanoparticles have attracted extensive research attention due to their antioxidation property, anticancer activity, and universal adherent affinity, and thus have shown great promise in the preparation, stabilization, and modification of multifunctional nanoassemblies for bioimaging, therapeutic delivery, and other biomedical applications. Additionally, the metal-polyphenol networks, formed by the coordination interactions between polyphenols and metal ions, have been used to prepare an important class of polyphenol-containing nanoparticles for surface modification, bioimaging, drug delivery, and disease treatments. By focusing on the interactions between polyphenols and different materials (e.g., metal ions, inorganic materials, polymers, proteins, and nucleic acids), a comprehensive review on the synthesis and properties of the polyphenol-containing nanoparticles is provided. Moreover, the remarkable versatility of polyphenol-containing nanoparticles in different biomedical applications, including biodetection, multimodal bioimaging, protein and gene delivery, bone repair, antibiosis, and cancer theranostics is also demonstrated. Finally, the challenges faced by future research regarding the polyphenol-containing nanoparticles are discussed.

Polyphenol-Containing Nanoparticles: Synthesis, Properties, and Therapeutic Delivery

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.

Polyphenol-Based Particles for Theranostics.

We report a facile inking strategy for visual information storage (e.g., writing, printing, and beyond) via surface modification of substrates with polyphenols and subsequent in situ formation of metal-phenolic networks (MPNs) on the substrates. The reported technique has several advantages compared with current printing techniques. Diverse substrates can be used to fulfill the requirements for different applications (e.g., printing, writing, painting, and stamping). A range of colors (e.g., yellow, blue, and green) can be realized using different polyphenols (e.g., tannic acid, gallic acid, and pyrogallol) and metal ions (e.g., CuII, FeIII, and TiIV). The disadvantages (e.g., ink precipitation, color fading) associated with writing or printing using traditional ink can be overcome. The obtained paintings can be easily removed by acids enabling the recycling of substrates. The reported strategy provides a new avenue for the development of portable, nontoxic, and green technologies for writing, printing, and beyond, which expands the applications of MPN-based materials.

/pdf/advancing-metal-phenolic-networks-for-visual-information-25me1wywup.pdf

Advancing Metal-Phenolic Networks for Visual Information Storage.

Poly(ethylene glycol)-mediated mineralization of metal-organic frameworks

Inspired by the unique biological microenvironments of eukaryotic cells, hollow capsules are promising to immobilize enzymes due to their advantages for physical protection and improved activity of enzymes. Herein, we report a facile method to fabricate silica (SiO2) capsules using zeolitic imidazole framework-8 nanoparticles (ZIF-8 NPs) as templates for enzyme immobilization and catalysis. Enzyme-encapsulated SiO2 capsules are obtained by encapsulation of enzymes in ZIF-8 NPs and subsequent coating of silica layers, followed by the removal of templates in a mild condition (i.e., ethylenediaminetetraacetic acid (EDTA) solution). The enzyme (i.e., horseradish peroxidase, HRP) activity in SiO2 capsules is improved more than 15 times compared to that of enzyme-loaded ZIF-8 NPs. Enzymes in SiO2 capsules maintain a high relative activity after being subjected to high temperature, enzymolysis, and recycling compared to free enzymes. In addition, multienzymes (e.g., glucose oxidase and HRP) can also be coencapsulated within SiO2 capsules to show a reaction with a high cascade catalytic efficacy. This work provides a versatile strategy for enzyme immobilization and protection with potential applications in biocatalysis.

Silica Capsules Templated from Metal–Organic Frameworks for Enzyme Immobilization and Catalysis

Nanocarriers with responsibility and surface functionality of targeting molecules have been widely used to improve therapeutic efficiency. Hence, we report the assembly of pH-responsive and targeted polymer nanoparticles (NPs) composed of poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) as the core and poly(carboxybetaine methacrylate) (PCBMA) as the shell, functionalized with cyclic peptides containing Arginine-Glycine-Aspartic acid-D-Phenylalanine-Lysine (RGD). The resulting polymer NPs (PDPA@PCBMA-RGD NPs) can maintain the pH-responsivity of PDPA (pKa ~6.5) and low-fouling property of PCBMA that significantly resist non-specific interactions with RAW 264.7 and HeLa cells. Meanwhile, PDPA@PCBMA-RGD NPs could specifically target αvβ3 integrin-expressed human glioblastoma (U87) cells. The pH-responsiveness and low-fouling properties of PDPA@PCBMA NPs are comparable to PDPA@poly(ethylene glycol) (PDPA@PEG) NPs, which indicates that PCBMA is an alternative to PEG for low-fouling coatings. The advantage of PDPA@PCBMA NPs lies in the presence of carboxyl groups on their surfaces for further modification (e.g., RGD functionalization for cell targeting). The reported polymer NPs represent a new carrier that have the potential for targeted therapeutic delivery.

Qun Yu

Papers

Polyphenol-Based Particles for Theranostics.

Advancing Metal-Phenolic Networks for Visual Information Storage.

Poly(ethylene glycol)-mediated mineralization of metal-organic frameworks

Silica Capsules Templated from Metal–Organic Frameworks for Enzyme Immobilization and Catalysis

Antifouling and pH-responsive poly(carboxybetaine)-based nanoparticles for tumor cell targeting