Chi Bum Ahn

Sodium Alginate Hydrogel‐Based Bioprinting Using a Novel Multinozzle Bioprinting System

Bioprinting is a technology for constructing bioartificial tissue or organs of complex three-dimensional (3-D) structure with high-precision spatial shape forming ability in larger scale than conventional tissue engineering methods and simultaneous multiple components composition ability. It utilizes computer-controlled 3-D printer mechanism or solid free-form fabrication technologies. In this study, sodium alginate hydrogel that can be utilized for large-dimension tissue fabrication with its fast gelation property was studied regarding material-specific printing technique and printing parameters using a multinozzle bioprinting system developed by the authors. A sodium alginate solution was prepared with a concentration of 1% (wt/vol), and 1% CaCl(2) solution was used as cross-linker for the gelation. The two materials were loaded in each of two nozzles in the multinozzle bioprinting system that has a total of four nozzles of which the injection speed can be independently controlled. A 3-D alginate structure was fabricated through layer-by-layer printing. Each layer was formed through two phases of printing, the first phase with the sodium alginate solution and the second phase with the calcium chloride solution, in identical printing pattern and speed condition. The target patterns were lattice shaped with 2-mm spacing and two different line widths. The nozzle moving speed was 6.67 mm/s, and the injection head speed was 10 µm/s. For the two different line widths, two injection needles with inner diameters of 260 and 410 µm were used. The number of layers accumulated was five in this experiment. By varying the nozzle moving speed and the injection speed, various pattern widths could be achieved. The feasibility of sodium alginate hydrogel free-form formation by alternate printing of alginate solution and sodium chloride solution was confirmed in the developed multinozzle bioprinting system.

Optimization of the circuit configuration of a pulsatile ECLS: An in vivo experimental study

An extracorporeal life support system (ECLS) with a conventional membrane oxygenator requires a driving force for the blood to pass through hollow fiber membranes. We hypothesized that if a gravity-flow hollow fiber membrane oxygenator is installed in the circuit, the twin blood sacs of a pulsatile ECLS (the Twin-Pulse Life Support, T-PLS) can be placed downstream of the membrane oxygenator. This would increase pump output by doubling pulse rate at a given pump-setting rate while maintaining effective pulsatility. The purpose of this study was to determine the optimal circuit configuration for T-PLS with respect to energy and pump output. Animals were randomly assigned to 2 groups in a total cardiopulmonary bypass model. In the serial group, a conventional membrane oxygenator was located between the twin blood sacs of the T-PLS. In the parallel group, the twin blood sacs were placed downstream of the gravity-flow membrane oxygenator. Energy equivalent pressure (EEP), surplus hemodynamic energy (SHE) and pump output were collected at the different pump-setting rates of 30, 40, and 50 beats per minute (BPM). At a given pump-setting rate the pulse rate doubled in the parallel group. Percent changes of mean arterial pressure to EEP were 13.0 ± 1.7, 12.0 ± 1.9, and 7.6 ± 0.9% in the parallel group, while 22.5 ± 2.4, 23.2 ± 1.9, and 21.8 ± 1.4 in the serial group at 30, 40, and 50 BPM of pump-setting rates. SHE at each pump setting rate was 20,131 ± 1,408, 21,739 ± 2,470, and 15,048 ± 2,108 erg/cm3 in the parallel group, while 33,968 ± 3,001, 38,232 ± 3,281, 37,964 ± 2,693 erg/cm3 in the serial group. Pump output was higher in the parallel circuit at 40, and 50 BPM pump-setting rates (3.1 ± 0.2, 3.7 ± 0.2 L/min vs. 2.2 ± 0.1 and 2.5 ± 0.1 L/min, respectively, p =0.01). Either parallel or serial circuit configuration of T-PLS generates effective pulsatility. As for the pump out, the parallel circuit configuration provides higher flow than the serial circuit configuration by doubling the pulse rate at a given pump-setting rate.

Comparison of coronary artery blood flow and hemodynamic energy in a pulsatile pump versus a combined nonpulsatile pump and an intra-aortic balloon pump.

We compared the coronary artery blood flow and hemodynamic energy between pulsatile extracorporeal life support (ECLS) and a centrifugal pump (CP)/intra-aortic balloon pump (IABP) combination in cardiac arrest. A total cardiopulmonary bypass circuit was constructed for six Yorkshire swine weighing 30 to 40 kg. The outflow cannula of the CP or a pulsatile ECLS (T-PLS) was inserted into the ascending aorta, and the inflow cannula of the CP or T-PLS was placed into the right atrium. A 30-ml IABP was subsequently placed in the descending aorta. Extracorporeal circulation was maintained for 30 minutes with a pump flow of 75 ml/kg per minute by a CP with an IABP or T-PLS. Pressure and flow were measured in the right internal carotid artery. The energy equivalent pressure (EEP) and surplus plus hemodynamic energy (SHE) were recorded. The left anterior descending coronary artery flow was measured with an ultrasonic coronary artery flow measurement system. The percent change of the mean arterial pressure to EEP was effective in both groups (23.3 ± 6.1 in CP plus IABP vs. 19.8 ± 6.2% in T-PLS, p = NS). The SHE was high enough in the CP/IABP and the T-PLS (20,219.8 ± 5824.7 vs. 13,160.2 ± 4028.2 erg/cm3, respectively, p = NS). The difference in the coronary artery flow was not statistically significant at 30 minutes after bypass was initiated (28.2 ± 9.79 ml/min in CP plus IABP vs. 27.7 ± 9.35 ml/min in T-PLS, p = NS).

Development of a closed air loop electropneumatic actuator for driving a pneumatic blood pump.

In this study, we developed a small pneumatic actuator that can be used as an extracorporeal biventricular assist device. It incorporated a bellows-transforming mechanism to generate blood-pumping pressure. The cylindrical unit is 88 +/- 0.1 mm high, has a diameter of 150 +/- 0.1 mm, and weighs 2.4 +/- 0.01 kg. In vitro, maximal outflow at the highest pumping rate (PR) exceeded 8 L/min when two 55 mL blood sacs were used under an afterload pressure of 100 mm Hg. At a pumping rate of 100 beats per minute (bpm), maximal hydraulic efficiency was 9.34% when the unit supported a single ventricle and 13.8% when it supported both ventricles. Moreover, pneumatic efficiencies of the actuator were 17.3% and 33.1% for LVAD and BVAD applications, respectively. The energy equivalent pressure was 62.78 approximately 208.10 mm Hg at a PR of 60 approximately 100 bpm, and the maximal value of dP/dt during systole was 1269 mm Hg/s at a PR of 60 bpm and 979 mm Hg/s at a PR of 100 bpm. When the unit was applied to 15 calves, it stably pumped 3 approximately 4 L/min of blood at 60 bpm, and no mechanical malfunction was experienced over 125 days of operation. We conclude that the presently developed pneumatic actuator can be utilized as an extracorporeal biventricular assist device.

Development of Magnetic Bearing System for a New Third-Generation Blood Pump

A magnetic bearing system is a crucial component in a third-generation blood pump, particularly when we consider aspects such as system durability and blood compatibility. Many factors such as efficiency, occupying volume, hemodynamic stability in the flow path, mechanical stability, and stiffness need to be considered for the use of a magnetic bearing system in a third-generation blood pump, and a number of studies have been conducted to develop novel magnetic bearing design for better handling of these factors. In this study, we developed and evaluated a new magnetic bearing system having a motor for a new third-generation blood pump. This magnetic bearing system consists of a magnetic levitation compartment and a brushless direct current (BLDC) motor compartment. The active-control degree of freedom is one; this control is used for controlling the levitation in the axial direction. The levitation in the radial direction has a passive magnetic levitation structure. In order to improve the system efficiency, we separated the magnetic circuit for axial levitation by using a magnetic circuit for motor drive. Each magnetic circuit in the bearing system was designed to have a minimum gap by placing mechanical parts, such as the impeller blades, outside the circuit. A custom-designed noncontact gap sensor was used for minimizing the system volume. We fabricated an experimental prototype of the proposed magnetic bearing system and evaluated its performance by a control system using the Matlab xPC Target system. The noncontact gap sensor was an eddy current gap sensor with an outer diameter of 2.38 mm, thickness of 0.88 mm, and resolution of 5 µm. The BLDC motor compartment was designed to have an outer diameter of 20 mm, length of 28.75 mm, and power of 4.5 W. It exhibited a torque of 8.6 mNm at 5000 rpm. The entire bearing system, including the motor and the sensor, had an outer diameter of 22 mm and a length of 97 mm. The prototype exhibited sufficient levitation performance in the stop state and the rotation state with a gap of 0.2 mm between the rotor and the stator. The system had a steady position error of 0.01 µm in the stop state and a position error of 0.02 µm at a rotational speed of 5000 rpm; the current consumption rates were 0.15 A and 0.17 A in the stop state and the rotation state, respectively. In summary, we developed and evaluated a unique magnetic bearing system with an integrated motor. We believe that our design will be an important basis for the further development of the design of an entire third-generation blood pump system.

Vessel Boundary Detection for its 3D Reconstruction by Using a Deformable Model (GVF Snake)

Vessel boundary detection and 3D modeling is a difficult but necessary task in analyzing the mechanics of inflammation and the structure of the microvasculature. We present in this paper a method of analyzing this structure by the means of the deformable model (using GVF Snake) for vessel boundary detection and three-dimensional reconstruction. For this purpose, we used a virtual vessel model and produced synthetic images. From these images, we obtained contours of vessels by the GVF Snake and then reconstructed a three-dimensional structure by using the coordinates of the Snakes

Evaluation of the Performance and Safety of a Newly Developed Intravenous Fluid Warmer

To evaluate the performance and safety of a newly developed blood warmer (ThermoSens), we tested its heating capability under various conditions using isotonic saline and hemolysis analysis with swine blood. The following two in vitro tests were performed: (i) To investigate the performance of the device, the inflow and outflow temperatures were measured at various flow rates (30, 50, and 100 mL/min) using cold (5°C) and room temperature (20°C) isotonic saline (0.9%). Several parameters were measured including the highest temperature of the outlet, the time required to reach the highest temperature, and the temperature of the intravenous line. (ii) To investigate the safety of the device, a hemolysis test was performed using swine blood. We obtained 320 mL of whole blood from swine and refrigerated the blood for 35 days at 3°C. In order to replicate the clinical situation, blood flow by gravity and pressure (300 mm Hg) was used. Before and after the heating test, blood samples were obtained and a comparison was made between these samples. Hemoglobin, hematocrit, lactate dehydrogenase, and plasma hemoglobin were used for red blood cell (RBC) damage analysis. The highest outlet temperatures obtained using flow rates of 30, 50, and 100 mL/min were 39.10 ± 0.59, 39.25 ± 0.69, and 37.63 ± 1.03°C, respectively, with cold saline, and 39.40 ± 0.40, 39.66 ± 0.36, and 39.49 ± 0.49°C, respectively, with room temperature saline. Hemolysis tests showed no significant changes in hemoglobin, hematocrit, lactate dehydrogenase, or plasma hemoglobin (P > 0.05) between before and after heating for both gravity and pressure blood flow. The ThermoSens blood warmer warms isotonic saline effectively, reaching temperatures up to 36°C under various conditions. Hemolysis tests showed no RBC damage. Therefore, the newly developed ThermoSens has good heating performance and is safe for RBC products.

Optimal pressure regulation of the pneumatic ventricular assist device with bellows-type driver

The bellows-type pneumatic ventricular assist device (VAD) generates pneumatic pressure with compression of bellows instead of using an air compressor. This VAD driver has a small volume that is suitable for portable devices. However, improper pneumatic pressure setup can not only cause a lack of adequate flow generation, but also cause durability problems. In this study, a pneumatic pressure regulation system for optimal operation of the bellows-type VAD has been developed. The optimal pneumatic pressure conditions according to various afterload conditions aiming for optimal flow rates were investigated, and an afterload estimation algorithm was developed. The developed regulation system, which consists of a pressure sensor and a two-way solenoid valve, estimates the current afterload and regulates the pneumatic pressure to the optimal point for the current afterload condition. Experiments were performed in a mock circulation system. The afterload estimation algorithm showed sufficient performance with the standard deviation of error, 8.8 mm Hg. The flow rate could be stably regulated with a developed system under various afterload conditions. The shortcoming of a bellows-type VAD could be handled with this simple pressure regulation system.

Simulated Microgravity Effects on Nonsmall Cell Lung Cancer Cell Proliferation and Migration

BACKGROUND Despite improvements in medical technology, lung cancer metastasis remains a global health problem. The effects of microgravity on cell morphology, structure, functions, and their mechanisms have been widely studied; however, the biological effects of simulated microgravity on the interaction between cells and its eventual influence on the characteristics of cancer cells are yet to be discovered. We examined the effects of simulated microgravity on the metastatic ability of different lung cancer cells using a random positioning machine. METHODS Human lung cancer cell lines of adenocarcinoma (A549) and squamous cell carcinoma (H1703) were cultured in a 3D clinostat system which was continuously rotated at 5 rpm for 36 h. The experimental and control group were cultured under identical conditions with the exception of clinorotation. RESULTS Simulated microgravity had different effects on each lung cancer cell line. In A549 cells, the proliferation rate of the clinostat group (2.267 ± 0.010) after exposure to microgravity did not differ from that of the control group (2.271 ± 0.020). However, in H1703 cells, the proliferation rates of the clinostat group (0.534 ± 0.021) was lower than that of the control group (1.082 ± 0.021). The migratory ability of both A549 [remnant cell-free area: 33% (clinostat) vs. 78% (control)] and H1703 cells [40% (clinostat) vs. 68% (control)] were increased after exposure to microgravity. The results of the molecular changes in biomarkers after exposure to microgravity are preliminary. DISCUSSION Simulated microgravity had different effects on the proliferation and migration of different lung cancer cell lines.Chung JH, Ahn CB, Son KH, Yi E, Son HS, Kim H-S, Lee SH. Simulated microgravity effects on nonsmall cell lung cancer cell proliferation and migration. Aerosp Med Hum Perform. 2017; 88(2):82-89.

The Effect of Fluid Viscosity on the Hemodynamic Energy Changes During Operation of the Pulsatile Ventricular Assist Device

Blood viscosity during operation of ventricular assist device (VAD) can be changed by various conditions such as anemia. It is known generally that the blood viscosity can affect vascular resistance and lead to change of blood flow. In this study, the effect of fluid viscosity variation on hemodynamic energy was evaluated with a pulsatile blood pump in a mock system. Six solutions were used for experiments, which were composed of water and glycerin and had different viscosities of 2, 2.5, 3, 3.5, 4, and 4.5 cP. The hemodynamic energy at the outlet cannula was measured. Experimental results showed that mean pressure was increased in accordance with the viscosity increase. When the viscosity increased, the mean pressure was also increased. However, the flow was decreased according to the viscosity increase. Energy equivalent pressure value was increased according to the viscosity-induced pressure rise; however, surplus hemodynamic energy value did not show any apparent changing trend. The hemodynamic energy made by the pulsatile VAD was affected by the viscosity of the circulating fluid.