Puncture performance of sharpen microneedles by using inclined contact UV lithography
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Microneedles is one of important future dispensing device for vaccination and diabetes. Solid microneedles is of wide application as it have also been designed to be coated with a drug for releasing into the skin by dissolution. Hard biodegradable polylactic acid (PLA) microneedles is suitable for solid microneedles because PLA provides safety in case microneedles accidentally break in the skin. The puncture performance of more sharpen microneedles have been demonstrated in this study. To make small tip radius and sharp tip angle to penetrate the skin from the viewpoints of ease of needling is key point on design of master mold. SU-8 mold manufactured by inclined contact UV lithography have been used for fabricating microneedles. To make designed small tip and shape tip angle on master mold, liquid impregnation method was introduced. Exposure value and developing time were optimized. Microneedles patch was replicated by molding PLA from dimethylpolysiloxane mold. The tip radius of pyramid microneedle was 3 μm and the tip angle of sold polymer microneedle was 18°, and these data were smallest tip radius and angle that have seen in all references. On imprint lithography process, thermoforming process was performed in the vacuum temperature chamber. As duration under decompressing in the vacuum temperature chamber was longer, the defects ratio of PLA microneedles became smaller. Microneedles patch was punctured into a mouse and human skins in high probability that is more than 80% after pressing the patch into the skin.
The authors thank Mr. Uemura and Inoguchi of Toppan Technical research institute for partly experimental assistant and support.
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