Material considerations for <i>in vitro</i> neural interface technology

Cambridge University Press (Materials Research Soc 2012 MRS bulletin Vol.37 No.6

<▼1><B>Abstract</B><P/></▼1><▼2><P>As biological science advances, there is a need for new technical tools to study biological matters. In neuroscience, new knowledge on the nervous system is discovered through biological experiments carried out under <I>in vitro</I> conditions. As experiments become more delicate, the technical requirements also increase. Recent advances in nano- and microscale technologies have increased the applicability of new emerging technology to neurobiology and neural engineering. As a result, many materials that were not originally developed for neural interfaces have become attractive candidates to sense neural signals, stimulate neurons, and grow nerve cells for tissue engineering. This article focuses on the material requirements for <I>in vitro</I> neural interfaces and introduces materials that are used to design various neural interface platforms <I>in vitro</I>.</P></▼2>

In Vitro Assays of Neurite Outgrowth and Synapse Formation Using Thermoplasmonic Ablation Technique

Hong Nari,Nam Yoonkey 한국바이오칩학회 2023 BioChip Journal Vol.17 No.4

A variety of in vitro assays have been designed based on optical imaging to study essential processes for nervous system development, such as neurogenesis and synaptogenesis. However, it is still diffi cult to assess the developmental processes under culture conditions where uncontrolled neurite growths and numerous neuronal connections occur all at the same time. Moreover, present techniques for in vitro assays lack the ability to induce and evaluate these processes at a specifi c time point. In this study, we applied a nanoparticle-assisted thermoplasmonic ablation of a cell-repulsive hydrogel to realize assays for two developmental processes: neurite outgrowth and synapse formation. We successfully demonstrated that this technique could guide neurites or make connections at diff erent cultivation times, and the length of growing neurites and the number of forming synapses could be quantified. Our developed method for in vitro assays is expected to be helpful in studying various neurodevelopment processes occurring at different developmental stages.

Neurons on Parafilm: Versatile elastic substrates for neuronal cell cultures

Yoo, Sang Jin,Nam, Yoonkey Elsevier 2012 Journal of neuroscience methods Vol.204 No.1

<P><B>Abstract</B></P> <P>A variety of materials has been applied to neuronal cell culture substrates to improve the efficiency of the culture and to provide pertinent cell growth environment. Here we report the application of Parafilm<SUP>®</SUP> M (‘Parafilm’) as a novel substrate for neuronal culture and patterning. Cell culture results show that elastic Parafilm had effects on cell viability, length and number of neurites, and soma spreading. Parafilm was also an effective substrate to obtain patterned neuronal cultures using a conventional micro-contract printing (μCP) technique. Polylysine micropatterns in line or grid forms were readily transferred from PDMS stamp to bare Parafilm surfaces and spatially confined neuronal cultures were successfully maintained for over three weeks. We also demonstrate that batch-processing cell culture substrates can be easily fabricated using a piece of Parafilm. The softness, plasticity, and hydrophobicity were main features that made it attractive for Parafilm to be considered as a practical cell culture platform. The results can be extended to develop an inexpensive and practical neuronal culture substrates in tissue engineering and biochip applications.</P> <P><B>Highlights</B></P> <P>► We apply the Parafilm as a neuronal culture, patterning and biochip substrate. ► Parafilm surfaces were readily modifiable with cell adhesion molecule or polymer. ► Elastic properties of the Parafilm improve neuron viability and development. ► Hydrophobicity of bare-Parafilm surfaces makes the high quality of neural patterning. ► A simple biochip platform can be fabricated by simple processing.</P>

Gold nanograin microelectrodes for neuroelectronic interfaces

Kim, Raeyoung,Hong, Nari,Nam, Yoonkey Wiley (John WileySons) 2013 Biotechnology journal Vol.8 No.2

<P>Neuroelectronic interfaces are imperative in investigating neural tissues as electrical signals are the main information carriers in the nervous system and metal microelectrodes have been widely used for recording and stimulation of nerve cells. For high performance microelectrodes, low tissue-electrode interfacial impedance and high charge injection limits are essential and nanoscale surface engineering has been utilized to meet the requirements for microelectrodes. We report a single-cell sized microelectrode, which has unique gold nanograin structures, using a simple electrochemical deposition method. The fabricated microelectrode had a sunflower shape with 1-5 mu m of micropetals along the circumference of the microelectrode and 500 nm nanograins at the center. The nanograin electrodes had 69-fold decrease of impedance and 10-fold increase in electrical stimulation capability compared to unmodified flat gold microelectrodes. The recording and stimulation performance of nanograin electrodes was tested using dissociated rat hippocampal neuronal cultures. Noise levels were extremely low (2.89 mu V-rms) resulting in high signal-to-noise ratio for low-amplitude action potentials (18.6-315 mu V). Small biphasic current pulses (20-60 mu A) could evoke action potentials from neurons nearby electrodes. This new nanostructured neural electrode may be applicable for the development of cell-based biosensors or clinical neural prosthetic devices.</P>

Characterization of Axonal Spikes in Cultured Neuronal Networks Using Microelectrode Arrays and Microchannel Devices

Hong, Nari,Joo, Sunghoon,Nam, Yoonkey IEEE 2017 IEEE Transactions on Biomedical Engineering Vol.64 No.2

<P>Objective: Axonal propagation has a pivotal role in information processing in the brain. However, there has been little experimental study due to the difficulty of isolation of axons and recording their signals. Here, we developed dual chamber neuronal network interconnected with axons by integrating microchannel devices with microelectrode arrays (MEAs) to investigate axonal signals in developmental stage. Methods: The device was composed of two chambers and microchannels between them, and hippocampal neurons were cultured in both chambers. Neuronal activity was recorded for four weeks. Results: Large axonal signal was detected in microchannels, which were 137.0 ± 8.5 μV at 14 days in vitro (DIV). It was significantly larger than those in chambers with a similar range of signal-to-noise ratio. Detection efficiency of axonal spikes was analyzed by calculating the number of active electrodes over time. We found that active electrodes were detected earlier and their number increased faster in microchannels than those in chambers. Finally, we estimated the axonal conduction velocity and 73% of axons had the velocity in range of 0.2-0.5 m/s at 14 DIV. By estimating the velocity over the cultivation period, we observed that axonal conduction velocity increased linearly over time. Conclusion: Using MEAs and microchannel devices, we successfully detected large axonal signals and analyzed their detection efficiency and conduction velocity. We first showed the gradual increase in conduction velocity depending on cultivation days. Significance: The developed microchannel device integrated MEA may be applicable for the studies of axonal conduction in cultured neuronal networks.</P>

NeuroCa: integrated framework for systematic analysis of spatiotemporal neuronal activity patterns from large-scale optical recording data

Jang, Min Jee,Nam, Yoonkey SPIE - International Society for Optical Engineeri 2015 Neurophotonics Vol.2 No.3

Recovery of early neural spikes from stimulation electrodes using a DC-coupled low gain high resolution data acquisition system

Jung, Hyunjun,Kim, Jintae,Nam, Yoonkey Elsevier 2018 Journal of neuroscience methods Vol.304 No.-

<P><B>Abstract</B></P> <P><B>Background</B></P> <P>Neural responses to electrical stimulation provide valuable information to probe and study the network function. Especially, recording neural responses from the stimulated site provides improved neural interfacing method. However, it is difficult to measure short-delayed responses at the stimulated electrode due to the saturation of the amplifier after stimulation which is called “stimulus artifact”. Despite the advances in handling stimulation artifacts, it is still very challenging to deal with the artifacts if one tries to stimulate and record from the same electrode.</P> <P><B>New method</B></P> <P>In this paper, we developed a system consisting of 24 bit ADC and low gain DC-amplifier which allows us to record the entire responses including saturation-free stimulus artifact and neural responses with excellent resolution.</P> <P><B>Results</B></P> <P>Our approach showed saturation-free recording after stimulation, which makes it possible to recover neural spike as early as in 2 ms at the stimulating electrode with digital elimination methods.</P> <P><B>Comparison with Existing methods</B></P> <P>With our system we could record neural signals after stimulation that was difficult with high gain and high pass filtered recording system due to amplifier saturation.</P> <P><B>Conclusions</B></P> <P>Our new system can enhance interface performance with its higher robustness and with simple system configuration.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A low gain (10x) DC neural recording with 24-bit ADC was proposed for wide-input dynamic range. </LI> <LI> Immediate artifact recovery as early as 2 ms after the stimulation from the stimulating electrode. </LI> <LI> Successful demonstration with planar-type microelectrode arrays and primary hippocampal neurons. </LI> </UL> </P>

Directional neurite growth using carbon nanotube patterned substrates as a biomimetic cue

Jang, Min Jee,Namgung, Seon,Hong, Seunghun,Nam, Yoonkey IOP Pub 2010 Nanotechnology Vol.21 No.23

<P>Researchers have made extensive efforts to mimic or reverse-engineer <I>in vivo</I> neural circuits using micropatterning technology. Various surface chemical cues or topographical structures have been proposed to design neuronal networks <I>in vitro</I>. In this paper, we propose a carbon nanotube (CNT)-based network engineering method which naturally mimics the structure of extracellular matrix (ECM). On CNT patterned substrates, poly-L-lysine (PLL) was coated, and E18 rat hippocampal neurons were cultured. In the early developmental stage, soma adhesion and neurite extension occurred in disregard of the surface CNT patterns. However, later the majority of neurites selectively grew along CNT patterns and extended further than other neurites that originally did not follow the patterns. Long-term cultured neuronal networks had a strong resemblance to the <I>in vivo</I> neural circuit structures. The selective guidance is possibly attributed to higher PLL adsorption on CNT patterns and the nanomesh structure of the CNT patterns. The results showed that CNT patterned substrates can be used as novel neuronal patterning substrates for <I>in vitro</I> neural engineering. </P>

Identification of feedback loops in neural networks based on multi-step Granger causality.

Dong, Chao-Yi,Shin, Dongkwan,Joo, Sunghoon,Nam, Yoonkey,Cho, Kwang-Hyun Oxford University Press 2012 Bioinformatics Vol.28 No.16

<P>Feedback circuits are crucial network motifs, ubiquitously found in many intra- and inter-cellular regulatory networks, and also act as basic building blocks for inducing synchronized bursting behaviors in neural network dynamics. Therefore, the system-level identification of feedback circuits using time-series measurements is critical to understand the underlying regulatory mechanism of synchronized bursting behaviors.</P>

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

Kim, Ju-Hyun,Kang, Gyumin,Nam, Yoonkey,Choi, Yang-Kyu IOP Pub 2010 Nanotechnology Vol.21 No.8

<P>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 <I>in vitro</I> 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. </P>