A Simulated Body Fluid Evaluation of TiO2 Barrier Oxide Layer Formed by Electrochemical Reaction.

The modified surface during implantation is considered to be an effective strategy to improve high adhesion of bone cell and osseointegration activity. In this paper, the TiO2 barrier oxide Layer has been fabricated by using the ion characteristic of an electrolytic solution, the surface characteristics have been investigated by EDS, XPS, and FE-SEM. From the analysis of the chemical states, phosphorus and calcium were observed in the TiO2 barrier layer, which were penetrated from the electrolyte into the oxide layer during deposit process. In addition, Ca 2p spectrum was identified into two peaks for Ca 2p3/2 and 2p1/2 at 347.4 and 351.3 eV, which are related to hydroxyapatite. Also, P spectrum was confirmed into two peaks for P1/2 and P3/2 levels with binding energy 134.2 and 133.4 eV, respectively. Thus, the incorporated phosphate species were found mostly in the forms of HPO-4, PO-3. From the result of biological evaluation in simulated body fluid (SBF), the apatite morphologies were effective for bioactive property on the modified surface.

Electrodeposition of hydroxyapatite nanoparticles onto ultra-fine TiO2 nanotube layer by electrochemical reaction in mixed electrolyte.

Electrochemical depositions of HAp nanoparticles onto Ultra-fine TiO2 nanotube layer were carried out by the electrochemical reaction in mixed electrolyte of 1.6 M (NH4)H2PO4 + 0.8 M NH4F containing 0.15 and 0.25 wt% HAp. The Ca/P ratios of the HAp nanoparticles were evaluated by EDS analysis and their values were 1.53 and 1.66 respectively. The distribution quantity of Ca and P were remained at the middle region of TiO2 nanotube, but the Ti element was mainly stayed at the bottom of barrier layer from the result of line scanning diagram. Especially, adsorbed phosphate ions facilitated nucleation of nanophase calcium phosphate material inside the TiO2 nanotubu layer that resulted in vertical growth of HAp nanoparticles. These surfaces and structures were all effective for biocompatibility from the SBF tests.

Reliable autapse formation using the single-cell patterning method.

Auto neuronal synapses, or autapses, are aberrant structures where the synaptic contact of a neuron forms onto its own branch. The functions of autapses, however, remain unknown. Here, we introduce a simple patterning method for capturing a single-cell, in which we maintained the isolated cell until it reached maturity, and developed arrays of autapses for electrophysiological analysis using multi-electrode arrays (MEA). The pattern arrays were formed by selective patterning of poly-L-lysine and various cell repellent materials. We tested the efficiency of single neuron pattern formed according to materials and pattern dimensions. Autapse formation was verified by immunostaining synaptic markers and physiological measurements via recordings from MEA. The results demonstrated that our multiscale patterning method increased the number of autapses consisting of a single neuron, which matured to connect onto themselves. The proposed patterning method (4.06 ± 0.33 isolated single-cells mm-2) is at least twelve times more efficient and productive than the spray method (0.31 ± 0.10 isolated single-cells mm-2). The spontaneous activity of a single neuron on the patterned MEA occured after 11 d in vitro. The single neuron activity consisted of bursts followed by spike trains (the burst rate was 2.56 min-1). This indicates that our method could be used for electrophysiological analysis, including MEA.

One-photon and two-photon stimulation of neurons in a microfluidic culture system.

In this study, we demonstrate a novel platform for optical stimulation of neural circuits combined with a microfluidic culture method and microelectrode array measurements. Neuron-on-a-chip was designed and fabricated to isolate axons without a soma or dendrite. Thus, it is readily able to manipulate the neuronal alignment and to investigate the neuronal activity at the locations we want to observe. We adapted the optical stimulation technique to the arranged neurons to generate the neuronal signals in a non-invasive fashion. A blue light-emitting diode and a femtosecond laser with 780 nm center wavelength were used for neuronal activation and the corresponding neuronal signals were measured by MEAs at the same time. We found that one-photon light via caged glutamate provoked periodic spiking. In contrast, the femtosecond pulse irradiation generated repetitive firing at constant rates. Response times of one-photon and two-photon stimulation were around 200 ms and 50 ms, respectively. We also quantified neural responses, by varying optical parameters such as exposure time and irradiation power.

Engineering-Aligned 3D Neural Circuit in Microfluidic Device.

The brain is one of the most important and complex organs in the human body. Although various neural network models have been proposed for in vitro 3D neuronal networks, it has been difficult to mimic functional and structural complexity of the in vitro neural circuit. Here, a microfluidic model of a simplified 3D neural circuit is reported. First, the microfluidic device is filled with Matrigel and continuous flow is delivered across the device during gelation. The fluidic flow aligns the extracellular matrix (ECM) components along the flow direction. Following the alignment of ECM fibers, neurites of primary rat cortical neurons are grown into the Matrigel at the average speed of 250 µm d(-1) and form axon bundles approximately 1500 µm in length at 6 days in vitro (DIV). Additionally, neural networks are developed from presynaptic to postsynaptic neurons at 14 DIV. The establishment of aligned 3D neural circuits is confirmed with the immunostaining of PSD-95 and synaptophysin and the observation of calcium signal transmission.

Engineering controllable architecture in matrigel for 3D cell alignment.

We report a microfluidic approach to impart alignment in ECM components in 3D hydrogels by continuously applying fluid flow across the bulk gel during the gelation process. The microfluidic device where each channel can be independently filled was tilted at 90° to generate continuous flow across the Matrigel as it gelled. The presence of flow helped that more than 70% of ECM components were oriented along the direction of flow, compared with randomly cross-linked Matrigel. Following the oriented ECM components, primary rat cortical neurons and mouse neural stem cells showed oriented outgrowth of neuronal processes within the 3D Matrigel matrix.