title: Monitoring the penetration process of single microneedles with varying tip diameters.
abstract: Microneedles represent promising tools for delivery of drugs to the skin. However, before these microneedles can be used in clinical practice, it is essential to understand the process of skin penetration by these microneedles. The present study was designed to monitor both penetration depth and force of single solid microneedles with various tip diameters ranging from 5 to 37µm to provide insight into the penetration process into the skin of these sharp microneedles. To determine the microneedle penetration depth, single microneedles were inserted in human ex vivo skin while monitoring the surface of the skin. Simultaneously, the force on the microneedles was measured. The average penetration depth at 1.5mm displacement was similar for all tip diameters. However, the process of penetration depth was significantly different for the various microneedles. Microneedles with a tip diameter of 5µm were smoothly inserted into the skin, while the penetration depth of microneedles with a larger tip diameter suddenly increased after initial superficial penetration. In addition, the force at insertion (defined as the force at a sudden decrease in measured force) linearly increased with tip diameter ranging from 20 to 167mN. The force drop at insertion was associated with a measured penetration depth of approximately 160μm for all tip diameters, suggesting that the drop in force was due to the penetration of a deeper skin layer. This study showed that sharp microneedles are essential to insert microneedles in a well-controlled way to a desired depth.
authors.affiliation: Soft Tissue Biomechanics and Engineering, Department of Biomedical Engineering, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands. Electronic address: a.m.romgens@tue.nl.
authors.forename: A M
authors.initials: AM
authors.lastname: Römgens
authors.affiliation: Soft Tissue Biomechanics and Engineering, Department of Biomedical Engineering, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands; Faculty of Health Sciences, University of Southampton, Southampton, UK.
authors.forename: D L
authors.initials: DL
authors.lastname: Bader
authors.affiliation: Division of Drug Delivery Technology, Leiden Academic Centre for Drug Research, Leiden University, Leiden, The Netherlands.
authors.forename: J A
authors.initials: JA
authors.lastname: Bouwstra
authors.affiliation: Soft Tissue Biomechanics and Engineering, Department of Biomedical Engineering, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: F P T
authors.initials: FPT
authors.lastname: Baaijens
authors.affiliation: Soft Tissue Biomechanics and Engineering, Department of Biomedical Engineering, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: C W J
authors.initials: CWJ
authors.lastname: Oomens
mesh_terms: D000328:Adult; D016503:Drug Delivery Systems; D004867:Equipment Design; D005260:Female; D006801:Humans; D008845:Microinjections / Q000295:instrumentation*; D008875:Middle Aged; D009339:Needles; D012867:Skin
keywords: Microneedle; Penetration depth; Penetration force; Skin mechanics