Dae-weon Lee

Highly efficient phosphorescent polymer OLEDs fabricated by screen printing

We demonstrate the use of screen printing in the fabrication of highly efficient phosphorescent polymer organic light-emitting devices (OLEDs) based on a green-emitting Ir(ppy)3 and a host polymer PVK. We incorporate PBD in the polymer host as an electron-transporting dopant and a-NPD as a hole-transporting dopant. The best screen-printed single-layer device exhibits very high peak luminous efficiency of 63 cd/A at a relatively high operating voltage of 17.1 V at the luminance of 650 cd/m 2 . We observed the highest luminance of 21,000 cd/m 2 at 35 V. Due to the high operating voltage, despite of the high peak luminous efficiency the peak power efficiency was found to be 12.2 lm/W at the luminance of 470 cd/m 2

Mechanically reinforced cell-laden scaffolds formed using alginate-based bioink printed onto the surface of a PCL/alginate mesh structure for regeneration of hard tissue

Cell-printing technology has provided a new paradigm for biofabrication, with potential to overcome several shortcomings of conventional scaffold-based tissue regeneration strategies via controlled delivery of various cell types in well-defined target regions. Here we describe a cell-printing method to obtain mechanically reinforced multi-layered cell-embedded scaffolds, formed of micron-scale poly(ε-caprolactone) (PCL)/alginate struts coated with alginate-based bioink. To compare the physical and cellular activities, we used a scaffold composed of pure alginate (without cells) coated PCL/alginate struts as a control. We systematically varied the ratio of alginate cross-linking agent, and determined the optimal cell-coating conditions to form the PCL/alginate struts. Following fabrication of the cell (MG63)-laden PCL/alginate scaffold, the bioactivity was evaluated in vitro. The laden cells exhibited a substantially more developed cytoskeleton compared with those on a control scaffold consisting of the same material composition. Based on these results, the printed cells exhibited a significantly more homogenous distribution within the scaffold compared with the control. Cell proliferation was determined via MTT assays at 1, 3, 7, and 14 days of culture, and the proliferation of the cell-printed scaffold was substantially in excess (∼2.4-fold) of that on the control. Furthermore, the osteogenic activity such as ALP was measured, and the cell-laden scaffold exhibited significantly greater activity (∼3.2-fold) compared with the control scaffold.

The Detection of Esophagitis by Using Back Propagation Network Algorithm

The results of this study suggest the use of a Back Propagation Network (BPN) algorithm for the detection of esophageal erosions or abnormalities—which are the important signs of esophagitis—in the analysis of the color and textural aspects of clinical images obtained by endoscopy. The authors have investigated the optimization of the learning condition by the number of neurons in the hidden layer within the structure of the neural network. By optimizing learning parameters, we learned and have validated esophageal erosion images and/or ulcers functioning as the critical diagnostic criteria for esophagitis and associated abnormalities. Validation was established by using twenty clinical images. The success rates for detection of esophagitis during calibration and during validation were 97.91% and 96.83%, respectively.

Three-Dimensional Contact Dynamic Model of the Human Knee Joint During Walking

It is well known that the geometry of the articular surface has a major role in determining the position of articular contact and the lines of action for the contact forces. The contact force calculation of the knee joint under the effect of sliding and rolling is one of the most challenging issues in this field. We present a 3-D human knee joint model including sliding and rolling motions and major ligaments to calculate the lateral and medial condyle contact forces from the recovered total internal reaction force using inverse dynamic contact modeling and the Least-Square method. As results, it is believed that the patella, muscles and tendon affect a lot for the internal reaction forces at the initial heel contact stage. With increasing flexion angles during gait, the decreasing contact area is progressively shifted to the posterior direction on the tibia plateau. In addition, the medial side contact force is larger than the lateral side contact force in the knee joint during normal human walking. The total internal forces of the knee joint are reasonabe compared to previous studies.

Multi-class biological tissue classification based on a multi-classifier

Ultrasonic surgical units (USUs) have the advantage of minimizing tissue damage during surgeries that require tissue dissection by reducing problems such as coagulation and unwanted carbonization, but the disadvantage of requiring manual adjustment of power output according to the target tissue. In order to overcome this limitation, it is necessary to determine the properties of in vivo tissues automatically. We propose a multi-classifier that can accurately classify tissues based on the unique impedance of each tissue. For this purpose, a multi-classifier was built based on single classifiers with high classification rates, and the classification accuracy of the proposed model was compared with that of single classifiers for various electrode types (Type-I: 6 mm invasive; Type-II: 3 mm invasive; Type-III: surface). The sensitivity and positive predictive value (PPV) of the multi-classifier by cross checks were determined. According to the 10-fold cross validation results, the classification accuracy of the proposed model was significantly higher (p<0.05 or <0.01) than that of existing single classifiers for all electrode types. In particular, the classification accuracy of the proposed model was highest when the 3mm invasive electrode (Type-II) was used (sensitivity=97.33-100.00%; PPV=96.71-100.00%). The results of this study are an important contribution to achieving automatic optimal output power adjustment of USUs according to the properties of individual tissues.

A 3-D Information Acquisition Algorithm for Close Range Endoscopy

The imaging system most widely used to obtain 3-D position information for an object is a stereo vision system using two cameras. The purpose of this research is to calculate 3-D distance information using the image differences acquired by making angle changes with one small-sized endoscopy camera. As a result of measuring increments of 1 mm while adding changes of 1°–7° in angle revolution for the distal tip for close range endoscopy (10–25 mm is the working distance for an endoscope) there was 0.25–0.18 mm of error on average. When the test section was 15–20 mm, which is the optimal working distance, it showed 0.15–0.05 mm of error on average. Therefore, the error ratio according to the measured distance is proven to be within 1 %. Also, it is estimated that 3-D short distance information shown on this research will be applicable to medical and industrial automation.

Versatile design of hydrogel-based scaffolds with manipulated pore structure for hard-tissue regeneration.

In recent years, a variety of biomimetic hydrogel scaffolds have been used in tissue engineering because hydrogels can provide reasonable soft-tissue-like environmental conditions for various cell responses. However, although hydrogels can provide an outstanding biofunctional platform, their poor mechanical stability and low processability have been obstacles for their usage as biomedical scaffolds. To overcome this limitation, we propose a simple and versatile method using 3D printing supplemented with a low-temperature working plate and coating process to reinforce the mechanical properties and various cellular activities by accommodating the poly(ε-caprolactone) (PCL). To determine the efficiency of the method, we used two typical hydrogels (alginate and collagen), which were deposited in a multi-layer configuration, and PCL as a coating agent. The scaffolds were evaluated in terms of various physical and cellular activities (metabolic activity and osteogenic activity). Throughout the experiments, significant increases in the tensile modulus (>6-fold), cell proliferation (>1.2-fold), and calcium deposition (>1.3-fold) were observed for the hydrogel/PCL scaffolds compared to those for pure hydrogel. Based on the experimental results, we can confirm that the proposed hydrogel scaffold can be a highly promising biomedical scaffold for application in tissue regeneration.

Image Processing Algorithm for Weight Estimation of Dairy Cattle

The computer vision system was designed and constructed to measure the weight of a dairy cattle. Its development involved the functions of image capture, image preprocessing, image algorithm, and control integrated into one program. The experiments were conducted with the model dairy cattle and the real dairy cattle by two ways. First experiment with the model dairy cattle was conducted by using the indoor vision experimental system, which was built to measure the model dairy cattle in the laboratory. Second experiment with real dairy cattle was conducted by using the outdoor vision experimental system, which was built for measuring 229 heads of cows in the cattle facilities. This vision system proved to a reliable system by conducting their performance test with 15 heads of real cow in the cattle facilities. Indirect weight measuring with four methods were conducted by using the image processing system, which was the same system for measuring of body parameters. Error value of transform equation using chest girth was 30%. This error was seen as the cause of accumulated error by manually measurement. So it was not appropriate to estimate cow weight by using the transform equation, which was calculated from pixel values of the chest girth. Measurement of cow weight by multiple regression equation from top and side view images has relatively less error value, 5%. When cow weight was measured indirectly by image surface area from the pixel of top and side view images, maximum error value was 11.7%. When measured cow weight by image volume, maximum error weight was 57 kg. Generally, weight error was within 30 kg but maximum error 10.7%. Volume transform method, out of 4 measuring weight methods, was minimum error weight 21.8 kg.

Discrimination between Cancer and Normal Tissue using Near Infrared Spectroscopy

NIR (near infrared) spectroscopic analysis was used to distinguish between cancer tissue and normal tissue. Pure cancer tissue versus normal tissue and cancer tissue surrounded by skin versus normal tissue were taken from 14 nude mice. The tissue samples were measured using spectroscopy at wavelengths between 400 and 2500 nm. In addition, principle component analysis (PCA) was carried out and difference between the sample groups was verified using regression analysis. According to the PCA results, there were two types of components. The greatest loading values were seen around 1250–350 nm, 1550–1650 nm, 1850–1950 nm, and 2100–2200 nm. These values are largely in accordance with the known absorption and oscillation area of methyl. Regression analysis of pure cancer tissue versus normal tissue, resulted in a correlation (R2) of 0.94, with a standard error of 0.18. In the case of cancer tissue surrounded by skin versus normal tissue, the correlation was 0.85 with an error of 0.31. These results confirm that it is possible to detect cancer tissue using a NIR spectroscopy due to anomalous methylation patterns.