A biodegradable poly-lactic acid (PLA) microneedle array composed of needles with a maximum length of 3 mm and an aspect ratio of up to approximately 18 was fabricated by drawing lithography. In the proposed fabrication method, the melted polymer is stretched twice. The approximate length is set in the first stretch, and the tip is sharpened in the second stretch. In the first stretch, by changing the thickness of the PLA sheet, PLA pillars with various lengths are fabricated. By defining the initial length of the needle, it is possible to set a wide range of aspect ratios and lengths. In the second stretch, it is possible to control the final aspect ratio and length of the needle, as well as the shape of its tip by changing the temperature and stretch speed of the PLA pillars. Finally, it was confirmed that the needle can pierce the surface of artificial skin and porcine skin.

A hollow microneedles array using biodegradable hyaluronic acid as the material for the microneedle array was fabricated. We proposed a method in which gelatinous hyaluronic acid was affixed to a core and then released after drying. A polylactic acid which has high tensile strength and high affinity for hyaluronic acid was used as the core material. Using this method, we succeeded at fabricating a highly safe hollow microneedle array. An opening was formed in the needle tip by coating the tip of the core with a hydrophobic UV curable resin. The diameter of the needle tip could be reduced by using a conical core, and the needle tip was sharpened by cutting it with a femtosecond laser. The mechanical strength of hyaluronic acid hollow microneedle was evaluated using the surface of artificial skin. (C) 2020 The Japan Society of Applied Physics

A biodegradable PLA (poly-lactic acid) microneedle having high aspect ratio of over 10, e.g., 100 pm in diameter and 1,000 pm (1 mm) in length, was successfully fabricated using thermal nanoimprint method first in the world. First, optimal conditions for fabricating a conical shape, which is assuming a microneedle tip, were preliminarily investigated. Both in vacuum and under atmospheric pressure, pressure of 20 MPa and temperature of 160 degrees C were necessary. Next, fabrication of a long microneedle was investigated. As compared to the conical shape, higher pressure of 25 MPa and higher temperature of 166 degrees C were required. By adjusting the releasing temperature around 98 degrees C, fabrication of a long microneedle having a smooth surface and no deformation, e.g., no bending, was successfully achieved. It was confirmed that the needle surely can puncture the skin and blood vessel of a mouse.

The new sustainable power generation technique which can convert the salinity gradient energy to the hydroelectric energy is expected. This technique is called Pressure Retarded Osmosis (PRO). Clarification of the relationship between the performance of the PRO module and permeation characteristics is important. It's already known that increase of salt concentration can increase the permeation flux through the membrane. As the conventional researches, the effects of increase of fresh water concentration and concentration polarization have evaluated. In this research, relationship between the salt concentration and membrane module is focused. The effects of fresh water dissipation and flow state of salt water in hollow fiber membrane module as new factors are researched with experiment and numerical simulation. As result, in the case of low salt concentration, permeation is not caused sufficiently in module. On the other hand, in the case of high salt concentration, very low permeation flux area exists extensively, and the effects of concentration polarization and fresh water dissipation are relatively large. Therefore salt water flow rate and module shape should be changed for each salt concentration.

Pressure Retarded Osmosis (PRO) is expected to the new power generation system. The performance of the PRO module is closely relating to the permeation characteristics. In this paper, when fresh water flow rate is changed, 4 factors related to the reduction of permeation flow rate are researched with experiment. These 4 factors are concentration of solute in fresh water, salt leakage, concentration polarization, and dissipation of fresh water. The characteristics of the fresh water flow and permeation are studied for the hollow fiber membrane module used in PRO system. It is cleared that the dissipation of fresh water and the concentration polarization in hollow fiber largely influence to the reduction of permeation flow rate in the case of the low fresh water flow rate. Concentration of solute in fresh water, salt leakage influence to the reduction of permeation flow rate in the case of high fresh water flow rate.

Forward Osmosis (FO) is recently paied attention to preprocessing of the Reverse Osmosis (RO). It can reduce the input power of RO plant. It is required to reduce the salt concentration at outlet and increase the permeation flow rate. In this paper, the characteristics of the fresh water flow and permeation are studied for the hollow fiber membrane module used in FO system. It is cleared that the disappearance of fresh water and the concentration polarization in hollow fiber largely influence to the reduction of permeation flow rate in the case of the low fresh water flow rate. Concentration of fresh water and the leakage of salt influence to the reduction of permeation flow rate in the case of high fresh water flow rate.