Gyumin Kang

Surface-modified microelectrode array with flake nanostructure for neural recording and stimulation.

A novel microelectrode modification method is reported for neural electrode engineering with a flake nanostructure (nanoflake). The nanoflake-modified electrodes are fabricated by combining conventional lithography and electrochemical deposition to implement a microelectrode array (MEA) on a glass substrate. The unique geometrical properties of nanoflake sharp tips and valleys are studied by optical, electrochemical and electrical methods in order to verify the advantages of using nanoflakes for neural recording devices. The in vitro recording and stimulation of cultured hippocampal neurons are demonstrated on the nanoflake-modified MEA and the clear action potentials are observed due to the nanoflake impedance reduction effect.

Pitch‐Dependent Acceleration of Neurite Outgrowth on Nanostructured Anodized Aluminum Oxide Substrates

Nervous systems are composed of microstructured scaffolds with three-dimensional nanofeatured textures. These textures enable the systems to give nanometer-scaled physical cues to the overlying cells, along with biochemical cues. However, the topographical effects on the neurons are still an unexplored territory, although there have been many reports on the biochemical cues for neuronal behavior. It is practically very difficult to investigate the topographical environments in vivo in the biological systems and/or to mimic them precisely in vitro. There is much recent evidence that the cellular response is affected by the physical properties of artificial materials. Studies with such materials could therefore provide us with new insight into the developmental processes of the brain and enable elucidation of the unexplored nanotopographical effects on neuronal behavior. The responses of nerve cells to surface roughness have been studied on various substrates, such as porous silicon, thin titanium nitride films, carbon nanotubes, topographically molded poly(dimethylsiloxane), silicon pillar arrays, gallium phosphide nanowires, aligned nanofiber arrays, and silicon nanowires. Previous studies showed that nerve cells exhibit enhanced attachment and viability as well as the axonal guidance effect on rough surfaces, as opposed to topographically flat surfaces. However, there have been few reports on how nanometer-scaled features regulate neuronal behavior in terms of neurite development. To generate nanotopographical stimuli to neurons in a controllable and systematic manner, it is necessary to make reproducible, rigid structures with variable topographical features. Among the methods for creating topographies on surfaces at the nanometer scale, the fabrication of anodized aluminum oxide (AAO) is highly effective, straightforward,

Generation of Patterned Neuronal Networks on Cell-Repellant Poly(oligo(ethylene glycol) Methacrylate) Films

The utilization of non-biofouling poly(oligo(ethylene glycol) methacrylate) (pOEGMA) films as a background material for the generation of neuronal patterns is reported here. Our previously reported method, which was surface-initiated, atom transfer radical polymerization of OEGMA, and subsequent activation of terminal hydroxyl groups of pOEGMA with disuccinimidyl carbonate, was employed for the generation of activated pOEGMA films on glass. Poly-L-lysine was then microcontact-printed onto the activated polymer films, followed by backfilling with poly(ethylene glycol) moieties. E18 hippocampal neurons were cultured on the chemically patterned substrate, and the resulting neuronal networks were analyzed by phase-contrast microscopy and whole-cell patch clamp method. The results indicated that the pOEGMA films played an important role in the generation of good-quality neuronal patterns for up to two weeks without any negative effects to neurons.

Metal‐Free, Visible‐Light‐Induced Remote C(sp3)–H Pyridylation via Radical Translocation of N‐Alkoxypyridinium Salts

Metal-free, visible-light-induced site-selective heteroarylation of remote C(sp3 )-H bonds has been accomplished through the design of N-alkoxyheteroarenium salts serving as both alkoxy radical precursors and heteroaryl sources. The transient alkoxy radical can be generated by the single-electron reduction of an N-alkoxypyridinium substrate by a photoexcited quinolinone catalyst. Subsequent radical translocation of the alkoxy radical forms a nucleophilic alkyl radical intermediate, which undergoes addition to the substrate to achieve remote C(sp3 )-H heteroarylation. This cascade strategy provides a powerful platform for remote C(sp3 )-H heteroarylation in a controllable and selective manner and is well suited for late-stage functionalization of complex bioactive molecules.