Material-Independent Surface Chemistry beyond Polydopamine Coating.

Various methods have been developed in surface chemistry to control interface properties of a solid material. A selection rule among surface chemistries is compatibility between a surface functionalization tool and a target material. For example, alkanethiol deposition on noble metal surfaces, widely known as the formation of a self-assembled monolayer (SAM), cannot be performed on oxide material surfaces. One must choose organosilane molecules to functionalize oxide surfaces. Thus, the surface chemistry strictly depends on the properties of the surface. Polydopamine coating is now generally accepted as the first toolbox for functionalization of virtually any material surface. Layer-by-layer (LbL) assembly is a widely used method to modify properties of versatile surfaces, including organic materials, metal oxides, and noble metals, along with polydopamine coating. On flat solid substrates, the two chemistries of polydopamine coating and LbL assembly provide similar levels of surface modifications. However, there are additional distinct features in polydopamine. First, polydopamine coating is effective for two- or three-dimensional porous materials such as metal-organic frameworks (MOFs), synthetic polyolefin membranes, and others because small-sized dopamine (MW = 153.18 u) and its oxidized oligomers are readily attached onto narrow-spaced surfaces without exhibiting steric hindrance. In contrast, polymers used in LbL assembly are slow in diffusion because of steric hindrance due to their high molecular weight. Second, it is applicable to structurally nonflat surfaces showing special wettability such as superhydrophobicity or superoleophobicity. Third, a nonconducting, insulating polydopamine layer can be converted to be a conducting layer by pyrolysis. The product after pyrolysis is a N-doped graphene-like material that is useful for graphene or carbon nanotube-containing composites. Fourth, it is a suitable method for engineering the surface properties of various composite materials. The surface properties of participating components in composite materials can be unified by polydopamine coating with a simple one-step process. Fifth, a polydopamine layer exhibits intrinsic chemical reactivity by the presence of catecholquinone moieties and catechol radical species on surfaces. Nucleophiles such as amine and thiolate spontaneously react with the functionalized layer. Applications of polydopamine coating are exponentially growing and include cell culture/patterning, microfluidics, antimicrobial surfaces, tissue engineering, drug delivery systems, photothermal therapy, immobilization of photocatalysts, Li-ion battery membranes, Li-sulfur battery cathode materials, oil/water separation, water detoxification, organocatalysts, membrane separation technologies, carbonization, and others. In this Account, we describe various polydopamine coating methods and then introduce a number of chemical derivatives of dopamine that will open further development of material-independent surface chemistry.

Addressing the Shortcomings of Polyphenol-Derived Adhesives: Achievement of Long Shelf Life for Effective Hemostasis.

For rapid and effective hemostasis of uncontrollable bleeding, versatile hemostatic agents have been emerging. Among them, polyphenol-derived adhesives have attracted those hemostatic materials due to instantaneous formation of sticky barriers by robust interactions between the material and the serum proteins from wound. However, a critical challenge in such phenolic materials lies in long-term storage due to spontaneous oxidation under humid environments, leading to changes in hemostatic capability and adhesive strength. Here, we report a transparent hemostatic film consisting of gallol-conjugated chitosan (CHI-G) for minimizing the phenolic oxidation even for 3 months and maintaining strong tissue adhesiveness and its hemostatic ability. The film undergoes a phase transition from solid to injectable hydrogels at physiological pH for efficiently stopping internal and external hemorrhage. Interestingly, the hemostatic capability of the CHI-G hydrogels after 3 month storage depends on (i) the folded microstructure of the polymer with optimal gallol modification and (ii) an initial phase of either a solution state or a solid film. When the hydrogels are originated from the dehydrated film, their successful hemostasis is observed in a liver bleeding model. Our finding would provide an insight for design rationale of hemostatic formulations with long shelf-life.

Designing Adaptive Binders for Microenvironment Settings of Silicon Anode Particles.

This study reports the concept of an "adaptive binder" to address the silicon anode challenge in Li-ion batteries. Binders exhibit adaptable capabilities upon gradual changes in the microenvironments surrounding silicon particles during anodic expansion-shrinkage cycles. Long, flexible binder chains are repositioned and reoriented upon the gradual formation of Si-micro-environments (Si-µ-env) during the early battery cycles. At this stage, the chemical interactions between the polymeric binders are reversible hydrogen bonds. As the Si-µ-env become stably set by repeated battery cycles, the chemical interactions exhibit reversible-to-irreversible transitions by the formation of covalent linkages between the binder polymers at the later stage of cycles. The binder polymer showing the aforementioned adaptive properties is hyaluronic acid, which has never been explored as a silicon-anode binder material, onto which the plant-inspired adhesive phenolic moiety, gallol (1,2,3-trihydroxybenzene), is conjugated (HA-GA) for stable adhesion to the surfaces of silicon particles. It is confirmed that the HA-GA binder can maintain a charge capacity that is approximately 3.3 times higher (1153 mAh g-1 ) than that of the nonconjugated HA binder (347 mAh g-1 ) after 600 cycles even at a rapid charge/discharge rate of 1 C (3500 mA g-1 ), indicating that adaptive properties are an important factor to consider in designing silicon-anode binders.

Pastable, Adhesive, Injectable, Nanofibrous, and Tunable (PAINT) Biphasic Hybrid Matrices as Versatile Therapeutic Carriers.

A critical challenge in many pharmaceutical fields is developing versatile adjuvant devices that can reduce the off-target delivery of therapeutic materials to target lesions. Herein, a biphasic hybrid fibrous system that can manipulate the spatial and temporal delivery of various therapeutic agents to target lesions by integrating multiple distinct systems and technologies such as fluffy coaxial electrospun polycaprolactone (PCL)/polystyrene (PS) fibers, cyclohexane-mediated leaching to remove PS layers selectively, amine display on PCL fibers, conjugation of naturally occurring adhesive gallol molecules onto hyaluronic acid (HA-g), and electrostatically complexing the aminated PCL fibers with the gallol-conjugated HA. In the context of "paintable" systems on target lesions, the resulting system is called a PAINT matrix (abbreviated according to the initial letter of its features: pastable, adhesive, injectable, nanofibrous, and tunable). Its viscoelastic property, which was attributed by coalescing aminated PCL fibers with viscous HA-g, enabled it to be noninvasively injected and fit into any cavity in the body with various morphologies, manually pasted on tissue surfaces, and adhered onto moisture-rich surfaces to ensure the secure delivery of therapeutics toward the target lesions. The PAINT matrix efficiently supplied immunomodulatory human neural stem cells (hNSCs) at rat hemisectioned spinal cord injury (SCI) sites and promoted both locomotive and sensory recovery in SCI models, presumably by protecting hNSCs against host immunosurveillance. The PAINT matrix will be broadly utilized for efficiently delivering therapeutics to difficult-to-reach target lesions by direct infusion or conventional biomaterial-mediated approaches due to their locations, wet surfaces, or complicated ambient environments.

Polydopamine and Its Derivative Surface Chemistry in Material Science: A Focused Review for Studies at KAIST.

Polydopamine coating, the first material-independent surface chemistry, and its related methods significantly influence virtually all areas of material science and engineering. Functionalized surfaces of metal oxides, synthetic polymers, noble metals, and carbon materials by polydopamine and its related derivatives exhibit a variety of properties for cell culture, microfluidics, energy storage devices, superwettability, artificial photosynthesis, encapsulation, drug delivery, and numerous others. Unlike other articles, this review particularly focuses on the development of material science utilizing polydopamine and its derivatives coatings at the Korea Advanced Institute of Science and Technology for a decade. Herein, it is demonstrated how material-independent coating methods provide solutions for challenging problems existed in many interdisciplinary areas in bio-, energy-, and nanomaterial science by collaborations and independent research.

Diatom Frustule Silica Exhibits Superhydrophilicity and Superhemophilicity.

Special surface wettability attracts significant attention. In this study, dramatic differences in wettability are demonstrated for microparticles with the same chemical composition, SiO2. One is natural silica prepared from the diatom, Melosira nummuloides, and the other is synthetic silica. We found that surface properties of synthetic silica are hydro- and hemophobic. However, diatom frustule silica exhibits superhydrophilicity and even superhemophilicity. Interestingly, such superhydrophilicity of natural silica is not solely originated from nanoporous structures of diatoms but from the synergy of high-density silanol anions and the nanoarchitecture. Furthermore, the observation of superhemophilicity of natural silica is also an interesting finding, because not all superhydrophilic surfaces show superhemophilicity. We demonstrate that superhemowettability is a fundamental principle for developing micropowder-based hemostatic materials despite existing hemorrhaging studies using diatoms.

Phenolic condensation and facilitation of fluorescent carbon dot formation: a mechanism study.

Fluorescent carbon dots have received considerable attention as a result of their accessibility and potential applications. Although several prior studies have demonstrated that nearly any organic compound can be converted into carbon dots by chemical carbonization processes, mechanisms explaining the formation of carbon dots still remain unclear. Herein, we propose a seed-growth mechanism of carbon dot formation facilitated by ferulic acid, a widespread and naturally occurring phenolic compound in the seeds of Ocimum basilicum (basil). Ferulic acid triggers the local condensation of polysaccharide chains and forms catalytic core regions resulting in nanoscale carbonization. Our study indicates that carbon dots generated from natural sources might share the similar mechanism of phenolic compound mediated nanoscale condensation followed by core carbonization.