Determining the factors affecting dynamic insertion of microneedles into skin
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Determining the factors affecting dynamic insertion of microneedles into skin Sahan A. Ranamukhaarachchi 1 & Boris Stoeber 1,2
# Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract Microneedles are extremely small and minimally-invasive intradermal drug delivery devices that require controlled, accurate, and repeatable insertions into human skin to perform their functions. Due to high variability and elasticity of human skin, dynamic insertion methods are being sought to ensure success in microneedle insertions into the skin passed the tough stratum corneum layer. Dynamic microneedle insertions have not been thoroughly studied to identify and assess the key parameters influencing the skin fracture to date. Here, we have utilized a previously validated artificial mechanical human skin model to identify and evaluate the factors affecting microneedle insertion. It was determined that a microneedle’s velocity at impact against the skin played the most crucial role in successfully inserting microneedle devices of different geometrical features (i.e., tip area) and array size (i.e., number of projections). The findings presented herein will facilitate the development of automated microneedle insertion devices that will enable user-friendly and error-free applications of microneedle technologies for medicine delivery. Keywords Microneedle . Dynamic insertion . Artificial skin . Skin crack propagation
1 Introduction Microneedles (MNs) are projections with typically submillimeter heights that can overcome the stratum corneum (SC) layer of skin to provide mechanical pathways for intradermal drug delivery. MN-mediated drug delivery methods are minimally invasive, pain-free, and potentially self-administrable. Several studies have focused on characterizing MN insertions into skin to understand the factors affecting successful MN performance, in particular geometrical features of MNs (Davis et al., 2004; Yang & Zahn, 2004; Park et al., 2005; Khanna et al., 2010; Olatunji et al., 2013). However, due to the large variability in the mechanical properties of skin (Geerligs, 2006; Ranamukhaarachchi et al., 2016a), the results reported for MN insertion in different studies in the literature are difficult to compare and show inconsistencies (i.e., insertion force per MN ranged between 0.1–3.0 N (Davis et al., 2004; Yang & Zahn, 2004; Khanna et al., 2010)).
* Boris Stoeber [email protected] 1
Department of Electrical and Computer Engineering, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada
2
Department of Mechanical Engineering, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada
To overcome the variability of skin mechanics during the assessments of MN insertions, we developed and validated an artificial mechanical skin model to simulate the mechanical properties of human skin at low and high relative humidity conditions (Ranamukhaarachchi et al., 2016a). The artificial skin model consisted of three layers representing the stratum corneum, viable epidermis, and dermis;
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