Editors' ChoiceBiomedical Engineering

Inspired by Porcupines

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Science Translational Medicine  09 Jan 2013:
Vol. 5, Issue 167, pp. 167ec6
DOI: 10.1126/scitranslmed.3005596

Hypodermic needles are a staple of medical practice, so one might conclude that their design has reached a pinnacle of evolution. After all, they go into skin quite easily with little applied force. But a close look at nature has now revealed subtle design tricks that allow for insertion with even less force (and less damage to the skin). Most surprising is the inspiration of these new tricks: the lowly porcupine.

Most of us have not tangled with a porcupine directly, but we still appreciate that barbed porcupine quills are difficult to remove. Cho and colleagues report that the microstructure of the North American porcupine quills also allows for easy tissue penetration—even easier than a hypodermic needle of the same diameter. Using a combination of finite element modeling and experimentation with real porcupine quills, the authors found that the barbs produced localized stress concentrations during insertion, allowing the quill to penetrate pig skin and chicken muscle tissue with very small forces and reduced damage as compared with barbless controls. They replicated the findings with synthetic polyurethane quills created by replica molding and also fabricated quill-mimetic hypodermic needles. Cho et al. also identified different zones of the porcupine quills that contributed either to easy penetration or to resistance to removal, suggesting a complex mechanism of tissue adhesion.

These new design concepts may now inspire the production of transdermal devices that can penetrate skin with even less force than required by conventional needles—a major consideration for products such as microneedle arrays, which must be able to penetrate skin without buckling. As an added benefit, patches of microneedles could also be designed to stay put, thanks to porcupine quills’ clever coupling of easy penetration and strong adhesion.

W. K. Cho et al., Microstructured barbs on the North American porcupine quill enable easy tissue penetration and difficult removal. Proc. Natl. Acad. Sci. U.S.A. 109, 21289–21294 (2012). [Abstract]

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