Kyo-in Koo

Adipose-Derived Stem Cells for Tissue Engineering and Regenerative Medicine Applications

Adipose-derived stem cells (ASCs) are a mesenchymal stem cell source with properties of self-renewal and multipotential differentiation. Compared to bone marrow-derived stem cells (BMSCs), ASCs can be derived from more sources and are harvested more easily. Three-dimensional (3D) tissue engineering scaffolds are better able to mimic the in vivo cellular microenvironment, which benefits the localization, attachment, proliferation, and differentiation of ASCs. Therefore, tissue-engineered ASCs are recognized as an attractive substitute for tissue and organ transplantation. In this paper, we review the characteristics of ASCs, as well as the biomaterials and tissue engineering methods used to proliferate and differentiate ASCs in a 3D environment. Clinical applications of tissue-engineered ASCs are also discussed to reveal the potential and feasibility of using tissue-engineered ASCs in regenerative medicine.

A novel microactuator for microbiopsy in capsular endoscopes

This paper presents a LiGA (a German acronym for lithographie, galvanoformung, abformung) process based microactuator to be used for microbiopsy in capsular endoscopes. This microactuator is designed to be integrated into a capsular endoscope and to extract tissue samples inside the small gastrointestine which a conventional endoscope cannot reach. The proposed microactuator was fabricated as a cylindrical shape of diameter 10 mm and length 1.8 mm. This actuator consists of three parts: a microbiopsy part with a microspike, an actuating part with a torsion spring and a triggering part with a shape memory alloy (SMA) heating wire and polymer string. In order to extract sample tissue, a microspike in the developed actuator moves forward and backward using the slider-crank mechanism. For low power consumption triggering, a polymer-melting scheme was applied. The SMA heating wire consumed approximately 1.5 V × 160 mA × 1 second (66.67 µWH) for triggering. The precise components of the microactuator were fabricated using the LiGA process in order to overcome the limitations in accuracy of conventional precision machining. The developed microactuator was evaluated by extracting tissue samples from the small intestine of a pig ex vivo, and examining the tissue with hematoxylin and eosin (H&E) staining protocol. The experimental tests demonstrated that the developed microactuator with microspike successfully extracted tissue samples from the pigs small intestines.

In Vitro Biocompatibility of Various Polymer-Based Microelectrode Arrays for Retinal Prosthesis

PURPOSE The purpose of our study is to evaluate the biocompatibility of various polymers used as microelectrode arrays (MEAs) in retinal prostheses through in vitro cytotoxicity testing following a standardized METHOD METHODS Three types of polymer-based MEAs were examined: silicone-based platinum, polyimide-based gold and liquid crystal polymer (LCP)-based gold MEAs. The silicone/platinum MEAs were fabricated by a Nd:YAG laser, polyimide/gold MEAs by a semiconductor manufacturing technique, and LCP/gold MEAs by laser micromachining and thermal-bonding process. All experimental procedures followed the International Organization for Standardization (ISO) 10993-5. To obtain the extracts of specimens, 4 g of each type of MEA were eluted by culture media, MEM, for 24 hours. Then, several diluents of extracts, including the original extracts, were applied to a cultured-cell monolayer, L929 fibroblasts. The morphologic changes of cells were analyzed by microscope after 24 and 48 hours of incubation. The quantitative evaluations of cell viability were performed by MTT assay after 24 hours of incubation. RESULTS The microscopic evaluations revealed that extracts from polymer-based MEAs did not induce morphologic changes or reduction of cells compared with control irrespective of concentrations of extracts. The MTT assay showed high viability values of approximately 80 to 130% regardless of diluted ratio of extracts from polymer-based MEAs. None of the polymers demonstrated a significant reduction of cell viability when compared with control. CONCLUSIONS All types of polymer-based MEAs, including silicone/platinum, polyimide/gold, and LCP/gold MEAs, meet the criteria of biocompatibility guided by international standards, ISO 10993-5.

Arrowhead-Shaped Microelectrodes Fabricated on a Flexible Substrate for Enhancing the Spherical Conformity of Retinal Prostheses

In this paper, a novel microelectrode array (MEA), with varying arrowhead shapes, is fabricated and evaluated for retinal prostheses. The proposed MEA has a total of 199 arrowhead-shaped microelectrodes, with heights ranging from 42 to 123.5 μm. This height variation allows each microelectrode to contact the spherical eyeball conformably and to approach the stimulation target retinal cells very closely. The fabricated MEAs are implanted in rabbit eyes. The physical contact of the MEA is evaluated using optical coherent tomography (OCT) images, which show that the implanted MEA makes an excellent conformal contact with the spherically shaped retinal layers. These OCT images also exhibit good biocompatibility of the implanted MEA. The evaluation results show that the proposed MEA has a high potential for clinical applications. Our ongoing project is aimed at clinical application in three years. [2010-0037].

Nanowire-Based Sensors for Biological and Medical Applications

Nanomaterials such as nanowires, carbon nanotubes, and nanoparticles have already led to breakthroughs in the field of biological and medical sensors. The quantum size effects of the nanomaterials and their similarity in size to natural and synthetic nanomaterials are anticipated to improve sensor sensitivity dramatically. Nanowires are considered as key nanomaterials because of their electrical controllability for accurate measurement, and chemical-friendly surface for various sensing applications. This review covers the working principles and fabrication of silicon nanowire sensors. Furthermore, we review their applications for the detection of viruses, biomarkers, and DNA, as well as for drug discovery. Advances in the performance and functionality of nanowire sensors are also surveyed to highlight recent progress in this area. These advances include the improvements in reusability, sensitivity in high ionic strength solvent, long-term stability, and self-powering. Overall, with the advantages of ultra-sensitivity and the ease of fabrication, it is expected that nanowires will contribute significantly to the development of biological and medical sensors in the immediate future.

A novel fabrication process for ultra-sharp, high-aspect ratio nano tips using (111) single crystalline silicon

This paper presents a novel fabrication process for ultra-sharp nano tips on cantilevers with the radius of curvature of less than 10 nm using an (111) single crystalline silicon wafer. The nano tip height 15 /spl mu/m, and the aspect ratio is greater than 3:1. The cone angle of the tip is 19.5/spl deg/. Fabrication process is based on newly obtained etch characteristic data on silicon (111) and the sacrificial bulk micromachining (SBM) technology. The developed fabrication process is simple and robust, and well suited for ultra-sharp, high-aspect ratio nano tips on cantilevers.

A Novel In Vitro Sensing Configuration for Retinal Physiology Analysis of a Sub-Retinal Prosthesis

This paper presents a novel sensing configuration for retinal physiology analysis, using two microelectrode arrays (MEAs). In order to investigate an optimized stimulation protocol for a sub-retinal prosthesis, retinal photoreceptor cells are stimulated, and the response of retinal ganglion cells is recorded in an in vitro environment. For photoreceptor cell stimulation, a polyimide-substrate MEA is developed, using the microelectromechanical systems (MEMS) technology. For ganglion cell response recording, a conventional glass-substrate MEA is utilized. This new sensing configuration is used to record the response of retinal ganglion cells with respect to three different stimulation methods (monopolar, bipolar, and dual-monopolar stimulation methods). Results show that the geometrical relation between the stimulation microelectrode locations and the response locations seems very low. The threshold charges of the bipolar stimulation and the monopolar stimulation are in the range of 10∼20 nC. The threshold charge of the dual-monopolar stimulation is not obvious. These results provide useful guidelines for developing a sub-retinal prosthesis.

Novel Valveless Micro Suction Pump Using a Solid Chemical Propellant

Recently, various micro injection pumps with different driving forces have been reported. However, attributed to the poor performance and reliability of valves in the micro scale, no micro suction pump has found a successful application thus far. In this paper, a valveless micro suction pump, using a solid chemical propellant, azobisisobutyronitrile (AIBN), is developed for the first time. This novel pump is designed based on the Bernoulli Principle applied to a Venturi tube. That is, for an incompressible fluid, a negative pressure is generated as the fluid is accelerated through a vena contracta section. In the designed pump, the width of the vena contracta section is 350 µm, and the width ratio of the input fluid inlet and the vena contracta section is approximately 8.5:1. The core of this pump is a propellant chamber with an AIBN matrix, which generates biologically inert N2 gas as it is heated by an underlying micro heater. The generated gas passes through the Venturi tube producing a negative pressure at the front section of the vena contracta in the Venturi tube. The pump and channels are fabricated by curing polydimethylsiloxane (PDMS) on a silicon mold which was patterned using the deep RIE process. The micro pump is tested for sampling porcine gastric juice. Heating the AIBN core for 3 seconds successfully pumped approximately 20 µl of gastric juice, showing the pump’s potential applicability to various lab-on-a-chip devices and systems.

Effect of Stimulus Waveform of Biphasic Current Pulse on Retinal Ganglion Cell Responses in Retinal Degeneration (rd1) mice

A retinal prosthesis is being developed for the restoration of vision in patients with retinitis pigmentosa (RP) and age-related macular degeneration (AMD). Determining optimal electrical stimulation parameters for the prosthesis is one of the most important elements for the development of a viable retinal prosthesis. Here, we investigated the effects of different charge-balanced biphasic pulses with regard to their effectiveness in evoking retinal ganglion cell (RGC) responses. Retinal degeneration (rd1) mice were used (n=17). From the ex-vivo retinal preparation, retinal patches were placed ganglion cell layer down onto an 8×8 multielectrode array (MEA) and RGC responses were recorded while applying electrical stimuli. For asymmetric pulses, 1st phase of the pulse is the same with symmetric pulse but the amplitude of 2nd phase of the pulse is less than 10 µA and charge balanced condition is satisfied by lengthening the duration of the pulse. For intensities (or duration) modulation, duration (or amplitude) of the pulse was fixed to 500 µs (30 µA), changing the intensities (or duration) from 2 to 60 µA (60 to 1000 µs). RGCs were classified as response-positive when PSTH showed multiple (3~4) peaks within 400 ms post stimulus and the number of spikes was at least 30% more than that for the immediate pre-stimulus 400 ms period. RGC responses were well modulated both with anodic and cathodic phase-1st biphasic pulses. Cathodic phase-1st pulses produced significantly better modulation of RGC activity than anodic phase-1st pulses regardless of symmetry of the pulse.

A Retinal Implant System Based on Flexible Polymer Microelectrode Array for Electrical Stimulation

Photoreceptor loss as a result of retinal degenerative diseases, such as age-related macular degeneration and retinitis pigmentosa is a leading cause of blindness in adult (1). Despite a near-total loss of the photoreceptors, the inner nuclear and ganglion cell layers survive at fairly high rates in the patients with retinitis pigmentosa (2) and age-related macular degeneration (3). Retinal prostheses have great potential in alleviating the problems and disabilities produced by these diseases. The feasibility of the electrical stimulation of the remaining retinal neurons is supported by clinical studies which showed that controlled electrical signals applied to a small area of the retina of a blind volunteer through a microelectrode resulted in the perception of a small spot of light (4).