Design and Evaluation of In-Plane Silicon Microneedles Fabricated with Post-CMOS Compatible Processes

In this paper, a comprehensive study was carried out on in-plane silicon (Si) microneedles, a useful tool for transdermal drug delivery and sample collection. Microneedles with eleven designs were investigated by post-complementary metal-oxide-semiconductor (CMOS) compatible microfabrication processes and characterized via pricking tests by insertion in chicken breast flesh. Mechanical strength of all designs were also evaluated by theoretical calculation and finite element modeling (FEM) for bending and buckling analysis. To efficiently improve the sharpness and insertion, the wedge-shaped needle tips with thickness determined by Si wafer thickness were sharpened by a wet chemical etching process. Insertion forces recorded from pricking tests and bending and buckling from theoretical calculation and FEM analysis before and after etching were compared. The results showed that the insertion force, free bending force and the maximum buckling force were all reduced and the maximum bending stress were improved after tip sharpening. Furthermore, the buckling safety factor of all eleven designs was great than 1 and the maximum bending stress was less than the fracture strength of Si, indicating that our in-plane Si microneedles are robust enough for insertion into human skin.