Method to obtain only targeted substances from an artificial circulatory system

Transcription

1 The 14th IFToMM World Congress, Taipei, Taiwan, October 25-30, 2015 DOI Number: /IFToMM.14TH.WC.OS1.019 Method to obtain only targeted substances from an artificial circulatory system Shunsuke Nagahama Shotaro Iida Hiroki Yoneyama Shigeki Sugano Waseda University Tokyo, Japan Abstract In this paper, we propose a filter system that can selectively obtain the required substances from an artificial circulatory system. The blood circulatory system of the human body keeps us healthy. We consider this system to be useful for a robot system to maintain its condition. To realize an artificial circulatory system like a human body, it is important to deliver various substances with only a single vessel and extract only the required substances from them. We propose a method to deliver encapsulated substances. By using this method, each substance can be delivered without mixing for easy separation. We developed a filter system that can trap only the required substances without clogging based on differences in the capsule size. We conducted experiments to evaluate the separation performance of the system. We were able to obtain only the targeted substances with this system. We developed an impurity filtration system as an application of our system. Keywords: Artificial circulatory system, encapsulation, filtration system I. Introduction In the human body, the blood circulatory system serves an important role for homeostasis. The system has four main functions: (1) transferring nutrients, oxygen, waste products, and so on; (2) sustaining normal bodily functions; and (3) protecting the living organism from outside factors. For robots, these functions can be replaced with the following analogous functions: (1) supplying electricity and fuel for the actuators, sensors, computers, and so on; (2) regulating the temperature of the components (e.g., motor) and lubricating joints and removing waste oil and byproducts that negatively affect the performance of the system; and (3) repairing the damaged components on its own. To realize the functions of the robot system, we previously developed an artificial circulatory system in earlier research [1]. The system has three functions: (1) supplying energy for the fuel cell, (2) cooling the motor, and (3) sealing defects that occur in a tube by clotting the mixed liquid. In terms of other work related to an artificial circulatory system, we developed the magnetic powdery wire (MPW) [2] and magnetic powdery sensor (MPS) [3]. The MPW is a wire with a self-repairing function. The wire consists s nagahama@sugano.mech.waseda.ac.jp s iida@sugano.mech.waseda.ac.jp h yoneyama@sugano.mech.waseda.ac.jp sugano@waseda.jp of iron powder and magnetic field. The iron powder lines up along the magnetic field and becomes a wire that can transfer electrical signals. When the wire is broken, the wire is repaired by the transfer of iron powder to the broken area. The MPS is a contact displacement sensor with a self-repairing function of sensing area. The sensor consists of iron powder and magnetic field. The iron powder lines up along the magnetic field and becomes a sensing area whose resistance value changes corresponding to the displacement. When the sensor is broken, the sensor is repaired by the transfer of iron powder to the broken area. Various functions have been realized for the artificial circulatory system. However, different materials are needed to realize these various functions. For example, lubricant is needed for sliding portions, and repairing agents are needed to repair worn members. When various substances exist in the same vessel of a circulatory system, some problems will appear. One is that the substances will become mixed and difficult to separate. In addition, the substances may react with each other. On the other hand, if many vessels are prepared for each substance to avoid the problem of mixing, the occupying space of the vessels will increase, and the system will need many pumps. We propose a method to deliver various substances with a single vessel. We solved the above problems by using encapsulated substances. Various encapsulated substances are separated easily and do not need many vessels and pumps. This method can be used to deliver materials not only in the solid state but also in the liquid state without mixing. To separate the various encapsulated substances, we developed filters to separate them based on differences in the capsule size. II. Artificial circulatory system for the robot Fig. 1 shows our proposed system. First, the robot takes in substances (e.g., lubricants and repairing agents) from outside. These substances are processed in the reactor. The process includes encapsulation, chemical conversion, and breakdown. The processed substances flow through the vessel and are delivered and supplied to the components of the robots (e.g., sliding portion). By supplying the substances to the components, the maintenance of a robot can be performed automatically. We focused on the filter, which extracts only the required substance. Human cells obtain only the required nutrients from blood. Similarly, it is important to supply only the

2 Fig. 1. Overview of artificial circulatory system required substances to the components of a robot. A. Filtering system We propose a filtering system so that components only obtain the required substances (Fig. 2). In this system, substances are separated according to size. At the first filter, substances that are larger than the target capsules cannot enter the acquisition area because the pore size of the filter is too small than the substances. At the second filter, capsules that are smaller than the target capsules leave the acquisition area because the pore size of the filter is larger than the substances. The fluid flows in a circle at the second filter. The target capsules move circularly and stay at the area without clogging the filter. By using this filter, only required substances are taken at the acquisition area (Fig. 3). Fig. 3. Circulatory system with first and second filters B. Encapsulation We developed an alginate capsule that includes an substance(fig. 4). The capsules are classified into two structures (Fig. 5). Mononclear type is used to transfer the liquid substance. Multinuclear type is used to transfer the solid substance. In this paper, we developed multinuclear type capsule. Fig. 2. Filtering system: Red area shows an acquisition area that stores medium-sized capsule (acquisition target). Large capsules (substances) cannot enter the acquisition area. Small capsules (substances) can enter the acquisition area but exit the area through the second filter. Fig. 4. Overview of encapsulation

3 One hundred balls was added into the vessel of the circulatory system, and a pump was driven. We counted the number of balls that passed through the acquisition line. The flow ratio was varied (0.2, 0.4, 0.6,0.8), and the capsule acquisition ratio under each condition was observed. The capsule acquisition ratio is the number of balls that passed through the acquisition line against the number of all balls added into the vessel. The pore size of the filter was 5.5 mm. The average ball size was 4.7 mm. Fig. 5. Types of capsule III. Experiments We conducted two experiments. In the separation experiment, we confirmed that the filter was able to separate various capsule sizes properly and that only target capsules were obtained at the acquisition area. In the amount adjustment experiment, we confirmed that the amounts of capsules acquired at the acquisition area can be adjusted. In this experiment, we evaluated the separation performance of the filter. We also confirmed that the system can prevent clogging of the filter. Three sizes of polyethylene balls were prepared. Each size had 10 balls. Table I gives the sizes. They were added into the vessel of the circulatory system, which is shown in Fig. 3. Table II presents the pore sizes of the first and second filters. We drove a pump (PSK-540X, KOSHIN) and confirmed that the system could obtain only the targeted substances (i.e., the medium-sized ball) in this experiment. The flow rate of the pump was 7 L/min. The inner diameter of the vessel was 15 mm. We counted the change in the number of balls obtained at the acquisition area for 5 min. TABLE I. Size of polyethylene ball Ball diameter [mm] Small ball Middle ball Large ball IV. Results As shown in Fig. 6, the number of targeted balls in the acquisition area increased over time. On the other hand, the large balls did not go into the acquisition area. The small balls moved out of the area after going into the area. Fig. 6. Change in number of trapped balls in relation to time As shown in Fig. 7, the number of balls that passed the acquisition line increased with the flow at the acquisition line. TABLE II. Filter pore size Filter pore size [mm] 1st-filter 2nd-filter It is necessary to supply only the needed amount to robot components. In this experiment, we adjusted the numbers of balls that passed through the acquisition line by changing the flow ratio (Fig. 2). The flow ratio is the flow at the acquisition line against the full flow. The ratio was adjusted by changing the heights of the acquisition and transfer line. Fig. 7. Change in number of balls that passed acquisition line in relation to flow ratio

4 V. Discussion The targeted balls were trapped. However, a few of the small balls remained in the acquisition area. It was difficult to remove all of the small balls from the acquisition area, but we were able to solve the problem by increasing the flow rate at the acquisition area and the number of pores of the second filter. For the filter design, it is important to consider the tradeoff with clogging. If the flow rate and number of balls are too great, the target balls will be drawn toward the second filter, and the filter will be clogged. It was possible to adjust the number of balls trapped in the acquisition area by adjusting the flow ratio. However, in this experiment, we adjusted the height of the lines to adjust the flow ratio. Another method would be better. Using valves is a simple method, but they will become clogged with various things such as balls or capsules. We consider changing the inner diameter of the vessels to be better. By using this method, it will be possible to adjust the flow ratio without clogging. VI. Application A. Impurity filtration system We made an alginate capsule that included activated carbon as an adsorbent (Fig. 8). Activated carbon can mainly adsorb to non-polar substances. By encapsulating an adsorbent into the alginate capsules, we could obtain capsules that adsorb to various substances. First, sodium alginate (0.56 g) was added into pure water (51 g), and the liquid was stirred until the substance dissolved in the water. Next, activated carbon (2.0 g, TAIKO S-type, FUTAMURA) was added. The solution was dropped into a 2 wt% CaCl 2 solution, and they were dipped for 30 min. After they were picked out, they were dipped into a 10 wt% CaCl 2 solution. Thus, encapsulated activated carbon was obtained. The process of removing impurities was divided into two parts: (1) adsorbing impurities into the capsule and (2) separating the capsule from the flow of the circulatory system. After the capsule adsorbs the impurities, we can easily exchange capsules. We conducted adsorption experiments. Only the second filter was used in this experiment. The circulatory system was filled with water (about 1200 ml), and a food coloring agent (0.16 g) was added as an impurity (Fig. 9). The above encapsulated activated carbon (11.7 g) was added into the system from the input port, and a pump was driven. The solution was sampled every 24 h, and the ultraviolet visible absorption spectrum of the solution was measured (V-630, JASCO). The capsules were trapped without clogging (Fig. 10) As shown in Fig. 11, we confirmed that the proposed system can remove impurities from a liquid. Fig. 8. Alginate capsule including activated carbon Fig. 9. Circulatory system: system containing impurities (left) and overview of system (Right) Fig. 10. Trapped capsules at second filter; the capsules were trapped without clogging Fig. 11. Change in impurity concentration over time

5 VII. Conclusion & Future works We propose an artificial circulatory system that can supply various substances to robot components as capsules. In addition, we propose an impurity filtration system as an application to remove impurities with encapsulated adsorbents. In future work, we will apply our system to other uses (e.g., lubrication of robot joints). References [1] C. H. Kim, Y. Nishi, S. Nagahama, and S. Sugano, Finding and utilizing self-preserving functions in blood pulsation development for ethanol based artificial circulation system, Proceedings of the IEEE International Conference on Robotics and Biomimetics, pp , [2] S. Nagahama, S.Iida, C.H.Kim, S.Sugano, Signal transmission with magnetic powdery wire in a pipeline, Proceedings of the IEEE International Conference on Robotics and Biomimetics, pp , [3] S. Nagahama, Y.Kimura, C.H.Kim, S.Sugano, The development of magnetic powdery sensor, Proceedings of the IEEE SENSORS 2014, pp , 2014.