Biodegradable polymer needle with various tip angles and consideration on insertion mechanism of mosquito's proboscis

The present paper proposes a fabrication method of microneedles with various tip angles made of biodegradable polymer (polylactic acid, referred to herein as PLA). It was confirmed by the finite element method (FEM) simulation that the stress concentration occurs more severely at the tip area, as the needle becomes thin, and the tip angle becomes sharp. Photomasks for silicon cavities (negative dies for micromolding) with various tip angles are designed. The fabrication process involves etching a groove on the surface of a silicon die, molding the polymer into this groove, and then releasing it. The resistance force during inserting a fabricated needle to an artificial skin of silicone rubber was investigated. Effectiveness of sharp tip angle and thin shank for easy insertion is confirmed. Imitating the mosquito's proboscis, the effectiveness of vibrating needle, and giving surface tension to the object surface was also confirmed. The combined needles like the mosquito's proboscis, which are composed of a central straight needle and two outer jagged ones, are assumed. The effectiveness of these needles for easy insertion is three dimensionally investigated by the FEM simulation. Based on the result, the insertion mechanism of the mosquito's proboscis is discussed.