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S. Gittard, B. Chen, H. Xu, A. Ovsianikov, B. Chichkov, N. Monteiro-Riviere, R. Narayan:
"The effects of geometry on skin penetration and failure of polymer microneedles";
Journal of Adhesion Science and Technology, 27 (2013), 3; 227 - 243.

Microneedles are small-scale devices that may be used for drug delivery and biosensing. In
this study, the forces required for mechanical failure, the modes of mechanical failure, as
well as the mechanisms for microneedle penetration into porcine skin were examined.
Microneedles produced from the acrylate-based polymer e-Shell 200 using an indirect rapid
prototyping approach involving two-photon polymerization and poly(dimethylsiloxane)
micromolding were found to possess sufficient strength for penetration of porcine skin. The
failure forces were an order of magnitude greater than the forces necessary for full insertion
into the skin. Bending was the most common form of failure; an increasing aspect ratio
and a decreasing tip diameter were associated with lower failure forces. Video captured
during skin penetration revealed that microneedle penetration into the skin occurred by
means of a series of insertions and not by means of a single insertion event. Images
obtained during and after skin penetration confirmed microneedle penetration of skin as
well as transdermal delivery of lucifer yellow dye. These findings shed insight into the
mechanisms of microneedle penetration and failure, facilitating design improvements for
polymer microneedles.

microneedle; micromolding; acrylate-based polymer; porcine skin