To design microneedles that minimize pain, this study tested the hypothesis that microneedles cause significantly less pain than a 26-gauge hypodermic needle, and that decreasing microneedle length and the number of microneedles reduces pain in normal human volunteers.
Single microneedles with lengths ranging from 480 to 1450 μm, widths from 160 to 465 μm, thicknesses from 30 to 100 μm, and tip angles from 20 to 90 degrees; and arrays containing 5 or 50 microneedles were inserted into the volar forearms of 10 healthy, human volunteers in a double-blinded, randomized study. Visual analog scale pain scores were recorded and compared with each other and to the pain from a 26-gauge hypodermic needle.
All microneedles investigated were significantly less painful than the hypodermic needle with microneedle pain scores varying from 5% to 40% of the hypodermic needle. Microneedle length had the strongest effect on pain, where a 3-fold increase in length increased the pain score by 7-fold. The number of microneedles also affected the pain score, where a 10-fold increase in the number of microneedles increased pain just over 2-fold. Microneedle tip angle, thickness, and width did not significantly influence pain.
Microneedles are significantly less painful than a 26-gauge hypodermic needle over the range of dimensions investigated. Decreasing microneedle length and number of microneedles reduces pain.
*Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University
‡School of Chemical and Biomolecular Engineering, Georgia Institute of Technology
†Department of Anesthesiology, Center for Pain Medicine, Emory University, Atlanta, GA. Mark R. Prausnitz is the Emerson-Lewis Faculty Fellow
Conflict of Interest: Harvinder S. Gill and Mark R. Prausnitz are coinventors on a microneedle-based patent that has been licensed to a company. In addition, Mark R. Prausnitz is a coinventor on other patents and is a consultant and advisor to companies working on microneedles. Although there are currently no products based on microneedles, and this study does not involve any commercial products, the results of this research could indirectly influence the success of possible future commercial activities in which these 2 authors have an interest.
Supported in part by the National Institutes of Health. NIH grants 1U01AI074579-01 and 1R01EB006369-01A1.
Reprints: Mark R. Prausnitz, PhD, School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0100 (e-mail: email@example.com).
Received for publication August 15, 2007; revised January 2, 2008; accepted January 6, 2008
This work took place in the Center for Drug Design, Development and Delivery and the Institute for Bioengineering and Bioscience at the Georgia Institute of Technology.