Mechanical characterization and insertion performance of hollow microneedle array for cell surgery

In order to implement cell surgery on a chip-based system, we have been developing microneedle arrays capable of introducing desired biomolecules (nucleic acids, proteins, etc.) into living cells and the parallel extracting biomolecules expressed in the cells. An array of hollow silicon dioxide (SiO2) microneedles with a sharp tip radius of less than 0.5 mu m was successfully fabricated by using a micromachining technique. In order to investigate the mechanical stability of fabricated microneedle arrays, insertion tests with a gelatin as an artificial cell were performed. The results indicated that the microneedles are expected to be sufficiently stiff to insert into living cells without fracture. In addition, bending behavior was characterized by both finite element method (FEM) analysis and experimental fracture test. Needle insertion performance into gelatin was also evaluated. The displacement required for needle insertion increased linearly with an increase in surface area at the needle tip, resulting in the relative value of estimated insertion stresses being approximately constant. Moreover, the results showed that the mechanical oscillation with an amplitude of 0.6 mu m was effective and that increasing oscillation frequency decreased remarkably the displacement probably due to an increase in the viscous resistance of a viscoelastic material. (C) 2009 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3206971]