Radical Scavenging Activities of Biomimetic Catechol-Chitosan Films

Catechol-derived Mannich bases: radical regulatory properties, cytotoxicity and interaction with biomolecules

Free radicals are ubiquitous in biological systems, being responsible for pathogenesis of degenerative diseases and participating in vitally important biochemical processes, which are mediated by radical regulatory agents. The effects of the aliphatic amine substituents in the catechol-derived Mannich bases on their antioxidant and pro-oxidant activity were investigated. It has been found that the presence of catechol moiety in the structure of Mannich bases allows them to act as Cu(II) reductants, efficient Fe(II) chelators and potent DPPH radical scavengers. It has been found that the plausible mechanism of the DPPH radical scavenging proceeds via quinone formation, followed by their interaction with ethanol via the Michael addition reaction. In the neutrophil respiratory burst assay, several compounds have demonstrated a weak antioxidant activity at the micromolar level (0.1-10 µM), whereas at the millimolar level (0.1 mМ) a strong pro-oxidant effect has been observed. Additionally, at the highest used concentrations a pronounced cytotoxicity against dermal fibroblasts DF-2 and an immunosuppressive effect against T-lymphocytes have been observed for all the synthesized compounds. It has been demonstrated that the oxidation of catechols in the presence of low-molecular thiols results in the formation of covalent adducts, which provides an insight into their cytotoxicity and detoxification pathways.

A dry double-sided tape post-treated with tannic acid for long-term adhesion in a wet environment

Medical adhesives have been used for wound closure with many advantages over sutures, but the wet environment in the human body poses a big challenge for its application. The currently used dry double-sided tape (DST) can remove the water barrier by water absorption, but its over-swelling makes it difficult to achieve long-term adhesion. In this study, a dry double-sided tape post-treated with tannic acid (DST-TA) was developed. A double network adhesive composed of polyacrylic acid and gelatin was first prepared by free radical photocrosslinking, and was post-treated in acidic (pH = 2) tannic acid solution. Tannic acid was immobilized in the DST through the catecholyl group, which could form hydrogen bonds with the DST, or react with the amino group on the gelatin by oxidizing to quinone. In vivo and in vitro studies demonstrated that DST-TA had significantly higher swelling resistance and tensile strength than DST. The introduced catecholyl group could reduce over-swelling of the DST, and improve short-term and long-term adhesion in a wet environment. We also demonstrated that the DST-TA had good hemocompatibility, biodegradability, and no cytotoxicity, offering a potential option for long-term medical adhesive in a wet environment.

Melanin-Inspired Composite Materials: From Nanoarchitectonics to Applications

Synthetic melanin is a mimic of natural melanin analogue with intriguing properties such as metal-ion chelation, redox activity, adhesion, and broadband absorption. Melanin-inspired composite materials are formulated by assembly of melanin with other types of inorganic and organic components to target, combine, and build up the functionality, far beyond their natural capabilities. Developing efficient and universal methodologies to prepare melanin-based composite materials with unique functionality is vital for their further applications. In this review, we summarize three types of synthetic approaches, predoping, surface engineering, and physical blending, to access various melanin-inspired composite materials with distinctive structure and properties. The applications of melanin-inspired composite materials in free radical scavenging, bioimaging, antifouling, and catalytic applications are also reviewed. This review also concludes current challenges that must be addressed and research opportunities in future studies.

Revealing Redox Behavior of Molybdenum Disulfide and Its Application as Rechargeable Antioxidant Reservoir

Molybdenum disulfide (MoS2) is a representative two-dimensional transition metal dichalcogenide and has a unique electronic structure and associated physicochemical properties. The redox property of MoS2 has recently attracted significant attention from various fields, such as biomedical applications. Intriguingly, MoS2 functions as an antioxidant in certain applications and as a pro-oxidant in others. We use the mediated electrochemical probing method to understand the redox behavior of MoS2. This method reveals that MoS2 (i) has a reversible and fast redox activity at a mild potential (between -0.20 and +0.25 V vs Ag/AgCl), (ii) functions as an antioxidant for molecules that have different redox mechanisms (electron or hydrogen atom transfer), and (iii) is electrochemically or molecularly rechargeable. Finally, we show that MoS2 reduces oxidized molecules more efficiently than the potent natural antioxidant, curcumin. This study enhances our understanding of MoS2 and shows its potential as an advanced antioxidant reservoir.

Reaction-Environment-Dependent Photoaddition Reactions of N-Phenyl Amino Acid Esters Possessing a Silyl Group with Fullerene C60: Selective Formation of Aminomethyl-1,2-dihydrofullerenes vs Fulleropyrrolidines

The current study investigates SET-promoted photoaddition reactions of the silyl-group-containing N-phenylglycinates and N-phenylalaninates, N-((trimethylsilyl)methyl)-N-phenyl-substituted glycinates and alaninates, respectively, with fullerene C60 to explore how the types of amino acid esters (AAEs) and molecular oxygen affect the photoaddition reaction efficiencies and chemoselectivity of in situ formed radical cations of AAEs. The results showed that under deoxygenated (N2-purged) conditions, photoreactions of N-phenylglycinates with C60 produced aminomethyl-1,2-dihydrofullerenes through the addition of α-amino radicals arising by sequential SET and desilylation processes from initially formed secondary anilines to C60. In oxygenated conditions, photoreactions of N-phenylglycinates with C60, albeit less efficient, took place to form fulleropyrrolidines through a pathway involving 1,3-dipolar cycloaddition of azomethine ylides to C60 assisted by in situ formed 1O2. The same types of photoproducts were observed with N-phenylalaninates, though the reactions were less efficient. The use of methylene blue (MB) as a photosensitizer in the photoreactions under oxygenated conditions was especially effective in enhancing the efficiency of fulleropyrrolidine formation. These results demonstrate that photoaddition reactions of silyl-tether-containing N-phenyl AAEs with C60 can be governed by the reaction conditions and the presence or absence of a photosensitizer employed.

Programmable Physical Properties of Freestanding Chitosan Membranes Electrofabricated in Microfluidics

Microfluidic-integrated freestanding membranes with suitable biocompatibility and tunable physicochemical properties are in high demand for a wide range of life science and biological studies. However, there is a lack of facile and rapid methods to integrate such versatile membranes into microfluidics. A recently invented interfacial electrofabrication of chitosan membranes offers an in-situ membrane integration strategy that is flexible, controllable, simple, and biologically friendly. In this follow-up study, we explored the ability to program the physical properties of these chitosan membranes by varying the electrofabrication conditions (e.g., applied voltage and pH of alginate). We found a strong association between membrane growth rate, properties, and fabrication parameters: high electrical stimuli and pH of alginate resulted in high optical retardance and low permeability, and vice versa. This suggests that the molecular alignment and density of electrofabricated chitosan membranes could be actively tailored according to application needs. Lastly, we demonstrated that this interfacial electrofabrication could easily be expanded to produce chitosan membrane arrays with higher uniformity than the previously well-established flow assembly method. This study demonstrates the tunability of the electrofabricated membranes' properties and functionality, thus expanding the utility of such membranes for broader applications in the future.

Ti3C2 nanosheets with broad-spectrum antioxidant activity for cytoprotection against oxidative stress

Redox regulation in biological systems represents a fascinating method for treatment and prevention of oxidative stress induced diseases. The key and difficult point is to find ideal materials with excellent antioxidant capability and good biocompatibility. To this end, ultra-thin two-dimensional MXene (Ti3C2) nanosheets (NSs) were investigated for their antioxidant capability. It is found that Ti3C2 NSs can scavenge efficiently reactive oxygen and nitrogen species (˙OH, H2O2, and ˙NO), ABTS+˙ and DPPH˙ free radicals in a concentration dependent manner, showing broad-spectrum antioxidant activities. Ti3C2 NSs exhibit higher antioxidant activity and broader antioxidant capability than natural antioxidant molecules. The significant role of PEG modified Ti3C2 with good stability in preventing cell damage against oxidative stress was demonstrated. Upon treatment of H2O2 induced oxidative stress with Ti3C2, the intracellular ROS level decreases and the cell survival rate increases significantly. An antioxidant mechanism based on gradient oxidation was proposed to account for the superior antioxidant activity of Ti3C2. Our result proves that ultra-thin MXenes as antioxidants have great potential in preventing oxidative stress caused biological damage.

Engineering a naturally derived hemostatic sealant for sealing internal organs

Controlling bleeding from a raptured tissue, especially during the surgeries, is essentially important. Particularly for soft and dynamic internal organs where use of sutures, staples, or wires is limited, treatments with hemostatic adhesives have proven to be beneficial. However, major drawbacks with clinically used hemostats include lack of adhesion to wet tissue and poor mechanics. In view of these, herein, we engineered a double-crosslinked sealant which showed excellent hemostasis (comparable to existing commercial hemostat) without compromising its wet tissue adhesion. Mechanistically, the engineered hydrogel controlled the bleeding through its wound-sealing capability and inherent chemical activity. This mussel-inspired hemostatic adhesive hydrogel, named gelatin methacryloyl-catechol (GelMAC), contained covalently functionalized catechol and methacrylate moieties and showed excellent biocompatibility both in vitro and in vivo. Hemostatic property of GelMAC hydrogel was initially demonstrated with an in vitro blood clotting assay, which showed significantly reduced clotting time compared to the clinically used hemostat, Surgicel®. This was further assessed with an in vivo liver bleeding test in rats where GelMAC hydrogel closed the incision rapidly and initiated blood coagulation even faster than Surgicel®. The engineered GelMAC hydrogel-based seaalant with excellent hemostatic property and tissue adhesion can be utilized for controlling bleeding and sealing of soft internal organs.

Facile ultrasonic preparation of a polypyrrole membrane as an absorbent for efficient oil-water separation and as an antimicrobial agent

Polypyrrole (PPY) spherical particles synthesized using carbon dots as an efficient catalyst were strongly embedded on fluorinated nonwoven fabric by ultrasonication to form a membrane with high hydrophilicity. An optimal amount of PPY adhered to the membrane after 30 min of sonication enhanced the overall membrane area with high hydrophilicity. Oil with high hydrophobicity was repelled by the resulting membrane, whereas water was freely penetrated and diffused from the membrane. The membrane exhibited good reusability and efficiency for the recovery of oil from a cooking oil-water mixture within 30 s. The incorporation of PPY in the fluorinated fabric imparts significant antibacterial properties against two common pathogens, Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). The anti-biofouling membrane could pave the way for its potential application to separate spilled oil from contaminated waters, comprising different microorganisms and living species. The novelty of this manuscript is described in a new system, the fabrication of PPY membranes with two important properties: biocidal and oil/water separation.

Real-Time NMR Monitoring of Spatially Segregated Enzymatic Reactions in Multilayered Hydrogel Assemblies*

Compartmentalized chemical reactions at the microscale are important in biotechnology, yet monitoring the molecular content at these small scales is challenging. To address this challenge, we integrate a compact, reconfigurable reaction cell featuring electrochemical functionality with high‐resolution NMR spectroscopy. We demonstrate the operation of this system by monitoring the activity of enzymes immobilized in chemically distinct layers within a multi‐layered chitosan hydrogel assembly. As a benchmark, we observed the parallel activities of urease (Urs), catalase (Cat), and glucose oxidase (GOx) by monitoring reagent and product concentrations in real‐time. Simultaneous monitoring of an independent enzymatic process (Urs) together with a cooperative process (GOx + Cat) was achieved, with chemical conversion modulation of the GOx + Cat process demonstrated by varying the order in which the hydrogel was assembled.

Pro- and Anti-oxidant Properties of Redox-Active Catechol-Chitosan Films

Catechols are abundant in nature and are believed to perform diverse biological functions that include photoprotection (e.g., melanins), molecular signaling (e.g., catecholamine neurotransmitters), and mechanical adhesion (e.g., mussel glue). Currently, the structure-property-function relationships for catechols remain poorly resolved, and this is especially true for redox-based properties (e.g., antioxidant, pro-oxidant, and radical scavenging activities). Importantly, there are few characterization methods available to probe the redox properties of materials. In this review, we focus on recent studies with redox-active catechol-chitosan films. First, we describe film fabrication methods to oxidatively-graft catechols to chitosan through chemical, enzymatic, or electrochemical methods. Second, we discuss a new experimental characterization method to probe the redox properties of catechol-functionalized materials. This mediated electrochemical probing (MEP) method probes the redox-activities of catechol-chitosan films by: (i) employing diffusible mediators to shuttle electrons between the electrode and grafted catechols; (ii) imposing tailored sequences of input voltages to “tune” redox probing; and (iii) analyzing the output current response characteristics to infer properties. Finally, we demonstrate that the redox properties of catechol-chitosan films enable them to perform antioxidant radical scavenging functions, as well as a pro-oxidant (reactive oxygen-generation) antimicrobial functions. In summary, our increasing knowledge of catechol-chitosan films is enabling us to better-understand the functions of catechols in biology as well as enhancing our capabilities to create advanced functional materials.

Electrobiofabrication: electrically based fabrication with biologically derived materials

While conventional material fabrication methods focus on form and strength to achieve function, the fabrication of material systems for emerging life science applications will need to satisfy a more subtle set of requirements. A common goal for biofabrication is to recapitulate complex biological contexts (e.g. tissue) for applications that range from animal-on-a-chip to regenerative medicine. In these cases, the material systems will need to: (i) present appropriate surface functionalities over a hierarchy of length scales (e.g. molecular features that enable cell adhesion and topographical features that guide differentiation); (ii) provide a suite of mechanobiological cues that promote the emergence of native-like tissue form and function; and (iii) organize structure to control cellular ingress and molecular transport, to enable the development of an interconnected cellular community that is engaged in cell signaling. And these requirements are not likely to be static but will vary over time and space, which will require capabilities of the material systems to dynamically respond, adapt, heal and reconfigure. Here, we review recent advances in the use of electrically based fabrication methods to build material systems from biological macromolecules (e.g. chitosan, alginate, collagen and silk). Electrical signals are especially convenient for fabrication because they can be controllably imposed to promote the electrophoresis, alignment, self-assembly and functionalization of macromolecules to generate hierarchically organized material systems. Importantly, this electrically based fabrication with biologically derived materials (i.e. electrobiofabrication) is complementary to existing methods (photolithographic and printing), and enables access to the biotechnology toolbox (e.g. enzymatic-assembly and protein engineering, and gene expression) to offer exquisite control of structure and function. We envision that electrobiofabrication will emerge as an important platform technology for organizing soft matter into dynamic material systems that mimic biology's complexity of structure and versatility of function.

Role of polydopamine's redox-activity on its pro-oxidant, radical-scavenging, and antimicrobial activities

Polydopamine (PDA) is a bioinspired material and coating that offers diverse functional activities (e.g., photothermal, antioxidant, and antimicrobial) for a broad range of applications. Although PDA is reported to be redox active, the association between PDA's redox state and its functional performance has been difficult to discern because of PDA's complex structure and limitations in methods to characterize redox-based functions. Here, we use an electrochemical reverse engineering approach to confirm that PDA is redox-active and can repeatedly accept and donate electrons. We observed that the electron-donating ability of PDA offers the detrimental pro-oxidant effect of donating electrons to O₂ to generate reactive oxygen species (ROS) or, alternatively, the beneficial antioxidant effect of quenching oxidative free radicals. Importantly, PDA's electron-donating ability depends on its redox state and is strongly influenced by external factors including metal ion binding as well as near-infrared (NIR) irradiation. Furthermore, we demonstrated that PDA possesses redox state-dependent antimicrobial properties in vitro and in vivo. We envision that clarification of PDA's redox activity will enable better understanding of PDA's context-dependent properties (e.g., antioxidant and pro-oxidant) and provide new insights for further applications of PDA. STATEMENT OF SIGNIFICANCE: We believe this is the first report to characterize the redox activities of polydopamine (PDA) and to relate these redox activities to functional properties important for various proposed applications of PDA. We observed that polydopamine nanoparticles 1) are redox-active; 2) can repeatedly donate and accept electrons; 3) can accept electrons from reducing agents (e.g., ascorbate), donate electrons to O₂ to generate ROS, and donate electrons to free radicals to quench them; 4) have redox state-dependent electron-donating abilities that are strongly influenced by metal ion binding as well as NIR irradiation; and 5) have redox state-dependent antimicrobial activities.

Coupling Self-Assembly Mechanisms to Fabricate Molecularly and Electrically Responsive Films

Biomacromolecules often possess information to self-assemble through low energy competing interactions which can make self-assembly responsive to environmental cues and can also confer dynamic properties. Here, we coupled self-assembling systems to create biofunctional multilayer films that can be cued to disassemble through either molecular or electrical signals. To create functional multilayers, we: (i) electrodeposited the pH-responsive self-assembling aminopolysaccharide chitosan, (ii) allowed the lectin Concanavalin A (ConA) to bind to the chitosan-coated electrode (presumably through electrostatic interactions), (iii) performed layer-by-layer self-assembly by sequential contacting with glycogen and ConA, and (iv) conferred biological (i.e., enzymatic) function by assembling glycoprotein (i.e., enzymes) to the ConA-terminated multilayer. Because the ConA tetramer dissociates at low pH, this multilayer can be triggered to disassemble by acidification. We demonstrate two approaches to induce acidification: (i) glucose oxidase can induce multilayer disassembly in response to molecular cues, and (ii) anodic reactions can induce multilayer disassembly in response to electrical cues.

Self curing and voltage activated catechol adhesives

Catechol adhesives are designed for curing with a low voltage signal—no oxidants or metal chelators are required.