fig2

Figure 2. Historical timeline of microneedle development. Chambers R introduced the microdissection needle in 1921^[13]. Gerstel and Place first proposed the concept of “Microneedle drug loading” in 1971-1976^[14]. Hashmi et al. fabricated microneedle arrays in 1995^[15]. Henry et al. applied solid microneedles for transdermal drug delivery in 1998^[16]. Matriano et al. reported the first coated microneedle in 2002^[17]. McAllister et al. developed the first hollow microneedle in 2003^[18]. Miyano et al. created the first dissolving microneedle in 2005^[19]. Kim et al. first introduced the gel microneedle in 2012^[20]. Wang et al. proposed the concept of core-shell microneedles in 2018^[21]. Chang et al. developed cryoMNs for delivering living cells in 2021^[22]. Zheng et al. applied microneedles to hair regeneration in 2023^[23]. MN: Microneedle; cryoMNs: cryo-microneedles.