Fig. 8: Hollow microneedles for microfluidic drug delivery.

a The first hollow microneedles were developed in silicon for in vivo neural recordings. Adapted with permission from ref. ¹⁸⁵. b The first transdermal hollow microneedles, also developed in silicon. Adapted with permission from ref. ¹⁹³. c–i Various hollow silicon microneedles. c Adapted with permission from ref. ¹⁹⁴. d Adapted with permission from ref. ¹⁹⁶. e Adapted with permission from ref. ¹⁹⁸. f Figure contributed by J.G.E. Gardeniers and A. van der Berg. g Adapted with permission from ref. ²⁰⁰. h Adapted with permission from ref. ²⁰¹. i Adapted with permission from ref. ²⁰². j PMMA hollow microneedles fabricated by the LIGA process. Adapted with permission from ref. ²⁰³. k Polymer hollow microneedles by 3M. The material and fabrication process are proprietary. Adapted with permission from ref. ²⁰⁵